1St Berlin Photon School at Bessy II

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1st Berlin Photon

School at Bessy II 14th - 24th of March, 2017 Berlin-Adlershof

WELCOME

It’s our pleasure to welcome you to the first International Photon School held at Helmholtz- Zentrum Berlin (HZB). HZB stands for research with and for new materials in energy-related systems, as well as the on-going operation and continued development of the BESSY II photon source. The Photon School encompasses all these aspects. It will provide you with a unique opportunity to get first-hand training covering a wide range of experimental and theoretical methods for probing the molecular structure, function, and dynamics of complex material systems. Leading experts from all fields of spectroscopy will give lectures, share their latest results, and present future research strategies. More specifically, the school will focus on the study of condensed-phase systems via numerous spectroscopic techniques and present the principles of operation of different light sources, from infrared to soft X-ray wavelengths. The generation of ultrashort light pulses, in particular by means of modern laser technologies will be presented, as well as the use of these ultrashort light pulses for time-resolved experiments in order to track the dynamics of molecular systems on ultrafast time scales. The lectures will emphasize the complementary aspects of the different methods, and a full section is dedicated to the theoretical modelling of spectra. In addition to the intensive programme of the Photon School, we hope that you take the opportunity to enjoy some social and cultural events in Berlin.

We wish you a pleasant and productive time.

Prof. Dr.-Ing. Anke Kaysser-Pyzalla Prof. Dr. Emad Flear Aziz

Contents

Welcome 3 Program Overview 7 Detailed Program 8 CVs and Abstracts – Lecture Week 13 CVs and Abstracts – Training Week 119 Venue - How to find us 140 Accommodation 144 Emergency Numbers 147

6 Program of the Photon School Overview

13.03.2017: Welcome Reception

Theory Days

14.03.2017: Day 1 - X-ray Absorption and Emission Spectroscopy HZB, Berlin-Adlershof

15.03.2017: Day 2 - Photoelectron Spectroscopies and Resonant Process HZB, Berlin-Adlershof

16.03.2017: Day 3 – Laser Light Sources & Time-Resolved Spectroscopy HZB, Berlin-Adlershof

17.03.2017: Day 4 – Infrared Spectroscopy and Microscopy HZB, Berlin-Adlershof

18.03.2017: Day 5 – Theoretical Modelling HZB, Berlin-Adlershof

19.03.2017: Social Event

Practical Training Days

20.03.2017: Day 6 - Computational Training HZB, Berlin-Wannsee

21.03.2017: Day 7 - Practical Training in Small Groups HZB, Berlin-Adlershof and Freie Universität, Berlin-Dahlem

22.03.2017: Day 8 - Practical Training in Small Groups HZB, Berlin-Adlershof and Freie Universität, Berlin-Dahlem

23.03.2017: Day 9 - Practical Training in Small Groups HZB, Berlin-Adlershof and Freie Universität, Berlin-Dahlem

24.03.2017: Day 10 - Practical Training in Small Groups HZB, Berlin-Adlershof and Freie Universität, Berlin-Dahlem

7 Program of the Photon School 14 – 24 of March

Monday, Foyer, Welcome Reception in Berlin-Adlershof March 13th Adlershof 18.30 - 20.00 Welcome Reception: Snack and get together

Tuesday, X-ray Absorption and Emission Spectroscopy Lecture Hall, th March 14 Chair: Emad Aziz (HZB) Adlershof Opening 08.45 - 09.00 Emad Aziz (HZB) Introduction to soft X-ray emission spectroscopy and resonant inelastic soft 09.00 - 10.45 X-ray scattering Jan-Erik Rubensson (Uppsala University) 10.45 - 11.15 Coffee Break XAS for the investigation of adsorbed molecules 11.15 - 13.00 Wolfgang Kuch (Freie University Berlin) 13.00 - 14.00 Lunch Application of micro/nano EXAFS/XANES in environmental and energy 14.00 - 15.30 material research Alexei Erko (HZB) 15.30 - 16.00 Coffee Break Application of XAS/XES and RIXS – Transition metal complexes in solution: 16.00 - 17.30 Interpretation of experimental spectra and theoretical simulation Philippe Wernet (HZB)

Photoelectron Spectroscopies and Resonant Wednesday, Lecture Hall, Process March 15th Adlershof Chair: Robert Seidel (HZB) Introduction to photoelectron and Auger-electron spectroscopy 09.00 - 10.45 Uwe Hergenhahn (HZB-IOM Leipzig) 10.45 - 11.15 Coffee Break Photoelectron spectroscopy of liquids 11.15 - 13.00 Bernd Winter (FHI) 13.00 - 14.00 Lunch Spin- and angle-resolved photoemission and its application to topological 14.00 - 15.30 insulators Jaime Sánchez-Barriga (HZB) 15.30 - 16.00 Coffee Break Applications of photoelectron spectroscopy for atmospheric studies 16.00 - 17.30 Olle Björneholm (Uppsala University)

8 Program of the Photon School 14 – 24 of March

Thursday, Laser Light Sources & Time-Resolved Spectroscopy Lecture Hall, March 16th Chair: Iain Wilkinson (HZB) Adlershof Introduction to lasers, non-linear optics and ultrashort laser pulses 09.00 - 10.45 Mojtaba Hajialamdari (HZB) 10.45 - 11.15 Coffee Break Introduction to strong-field light-matter interactions and HHG 11.15 - 13.00 Igor Kiyan (HZB) 13.00 - 14.00 Lunch Introduction to time-resolved spectroscopies 14.00 - 15.30 Iain Wilkinson (HZB) 15.30 - 16.00 Coffee Break Applications of ultrashort soft X-ray pulses 16.00 - 17.30 Marc Vrakking (MBI)

Friday, Infrared Spectroscopy and Microscopy Lecture Hall, March 17th Chair: Ljiljana Puskar (HZB) Adlershof Introduction to infrared spectroscopy 09.00 - 10.00 Ulrich Schade (HZB) Infrared/THz synchrotron radiation, infrared beamlines and infrared 10.00 - 10.45 spectrometers Ulrich Schade (HZB) 10.45 - 11.15 Coffee Break Advances and applications of infrared synchrotron radiation in 11.15 - 13.00 microspectroscopy Ljiljana Puskar (HZB) 13.00 - 14.00 Lunch Time-resolved infrared spectroscopy and its application in life and material 14.00 - 15.00 sciences Eglof Ritter (Humboldt-University Berlin) Applications of infrared/THz synchrotron radiation in material sciences 15.00 - 16.00 Jihaan Ebad-Allah (Universität Augsburg) 16.00 - 16.15 Coffee Break New trends in IR synchrotron spectroscopy 16.15 - 17.30 Augusto Marcelli (INFN, Frascati)

9 Program of the Photon School 14 – 24 of March

Saturday, Theoretical Modelling Lecture Hall, th March 18 Chair: Matthias Berg, (FU / HZB) Adlershof Introduction to electronic-structure theory for spectroscopy 09.00 - 10.45 Sergey Bokarev (Universität Rostock) 10.45 - 11.15 Coffee Break Practical calculations with density functional theory 11.15 - 13.00 Hilke Bahmann (TU Berlin) 13.00 - 14.00 Lunch Electron dynamics for ionization, high-harmonic generation, or electron 14.00 - 15.30 transfer Jean Christophe Tremblay (FU Berlin) 15.30 - 16.00 Coffee Break Molecular Dynamics: A Computational Microscope 16.00 - 17.30 Matej Kanduc (HZB)

Sunday, Social Event March 19th

Monday, Theoretical Modelling Training March 20th ORCA Tutorial – Computational Spectroscopy 10:00 - 13:00 Kaan Atak (HZB), Fabian Weber (HZB) Groups A, B, C and D 13.00 - 14.00 Lunch MCTDH Tutorial – Electron Dynamics Simulations of Schulungsraum, 14:00 - 17:00 the Interatomic Coulombic Decay in Quantum Dots Wannsee Matthias Berg (FU/HZB), Anika Haller (HZB)

10 Program of the Photon School 14 – 24 of March

Tuesday, Training in Groups March 21st

10:00 - 12:00 Liquid Jet PES Training Group A 13:00 - 16:00 Robert Seidel (HZB), Marvin Pohl (HZB) BESSY II - Adlershof

Group D 10:00 - 12:00 Time-Resolved Spectroscopy Training Freie Universität 13:00 - 16:00 Igor Kiyan (HZB), Martin Wilke (HZB), Iain Wilkinson (HZB) Berlin - Dahlem

10:00 - 12:00 XAS, XES and RIXS Training Group C 13:00 - 16:00 Ronny Golnak (HZB), Jie Xiao (HZB), Marc Tesch (HZB) BESSY II - Adlershof

10:00 - 12:00 Infrared Spectroscopy Training Group B 13:00 - 16:00 Ljiljana Puskar (HZB), Ulrich Schade (HZB) BESSY II - Adlershof

Wednesday, Training in Groups March 22nd

10:00 - 12:00 Liquid Jet PES Training Group B 13:00 - 16:00 Robert Seidel (HZB), Marvin Pohl (HZB) BESSY II - Adlershof

Group A 10:00 - 12:00 Time-Resolved Spectroscopy Training Freie Universität 13:00 - 16:00 Igor Kiyan (HZB), Martin Wilke (HZB), Iain Wilkinson (HZB) Berlin - Dahlem

10:00 - 12:00 XAS, XES and RIXS Training Group D 13:00 - 16:00 Ronny Golnak (HZB), Jie Xiao (HZB), Marc Tesch (HZB) BESSY II - Adlershof

10:00 - 12:00 Infrared Spectroscopy Training Group C 13:00 - 16:00 Ljiljana Puskar (HZB), Ulrich Schade (HZB) BESSY II - Adlershof

Thursday, Training in Groups March 23rd

10:00 - 12:00 Liquid Jet PES Training Group C 13:00 - 16:00 Robert Seidel (HZB), Marvin Pohl (HZB) BESSY II - Adlershof

Group B 10:00 - 12:00 Time-Resolved Spectroscopy Training Freie Universität 13:00 - 16:00 Igor Kiyan (HZB), Martin Wilke (HZB), Iain Wilkinson (HZB) Berlin - Dahlem

10:00 - 12:00 XAS, XES and RIXS Training Group A 13:00 - 16:00 Ronny Golnak (HZB), Jie Xiao (HZB), Marc Tesch (HZB) BESSY II - Adlershof

10:00 - 12:00 Infrared Spectroscopy Training Group D 13:00 - 16:00 Ljiljana Puskar (HZB), Ulrich Schade (HZB) BESSY II - Adlershof

11 Program of the Photon School 14 – 24 of March

Friday, Training in Groups March 24th

10:00 - 12:00 Liquid Jet PES Training Group D 13:00 - 16:00 Robert Seidel (HZB), Marvin Pohl (HZB) BESSY II - Adlershof

Group C 09:00 - 11:00 Time-Resolved Spectroscopy Training Freie Universität 12:00 - 15:00 Igor Kiyan (HZB), Martin Wilke (HZB), Iain Wilkinson (HZB) Berlin - Dahlem

10:00 - 12:00 XAS, XES and RIXS Training Group B 13:00 - 16:00 Ronny Golnak (HZB), Jie Xiao (HZB), Marc Tesch (HZB) BESSY II - Adlershof

10:00 - 12:00 Infrared Spectroscopy Training Group A 13:00 - 16:00 Ljiljana Puskar (HZB), Ulrich Schade (HZB) BESSY II - Adlershof

16:00 – 16:30 Coffee Break 16:30 – 17:00 Exam for all participants Foyer, 17:00 – 17:30 Evaluation / Feedback Round Adlershof 17:45 End of the school

Practical Training Session (in groups of 5 participants):

 Liquid Jet PES Training at BESSY II Adlershof: Photoelectron spectroscopy measurements from a liquid micro-jet at BESSY II.

 Time-Resolved Spectroscopy Training at the Freie Universität Berlin: Time-resolved photoelectron spectroscopy measurements with ionic liquid solutions and ultrashort laser pulses at the Joint Ultrafast Dynamics in Solutions and Interfaces Laboratory at the Freie Universität Berlin.

 XAS, XES and RIXS Training at BESSY II Adlershof: XAS, XES and RIXS measurements from a liquid micro-jet at BESSY II.

 Infrared Spectroscopy Training at BESSY II Adlershof: Hands on the infrared beamline IRIS.

CVs and Abstracts – Lecture Week

13 Theory Days 14.03.2017: Day 1 ‐ X‐ray Absorption and Emission Spectroscopy Chair: Emad Aziz

HZB, Berlin‐Adlershof

Brief CV – Prof. Dr. Emad Aziz

Current positions: Institute director “Methods for Material Development” (since 2014), Helmholtz-Zentrum Berlin für Materialien und Energie; W3 full/chair professor “Structure and Dynamics of Functional Materials in Solution” (since 2015) at Freie Universität Berlin; Distinct (Honour) professor at in the School of Chemistry, Monash University, Australia; Head of “Joint Ultrafast Dynamics Lab in Solutions and at Interfaces (JULiq)” (since 2011) at Freie Universität Berlin and Helmholtz-Zentrum Berlin für Materialien und Energie

Previous positions: 2014 Guest professor Institute of Molecular Science, National Institutes of Natural Sciences, Inter-University Research Institute Corporation, Myodaiji, Okazaki, Japan 2009 – 2014 Helmholtz Young Investigator Group Leader: “Structure and dynamics of functional materials in solution and at interfaces”, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH (HZB), Berlin, Germany 2009 – 2014 Junior professor (W1) “Structure and dynamics of functional materials in solution and at interfaces”, Freie Universität Berlin, Germany 2008 Post Doctor EPFL - École polytechnique fédérale de Lausanne, Lausanne, Switzerland

Awards (selection): 2014 Nernst-Haber-Bodenstein-Preis 2013 Einstein international Postdoctoral fellows 2011 European Research Council (ERC-Starting) 2011 Karl-Scheel-Preis der Physikalischen Gesellschaft zu Berlin (PGzB) 2009 Dale-Sayers Prize: Young Scientist Award 2009 Dissertationspreis Adlershof Humboldt Universität Berlin & IGAFA e.V. 2008 Ernst-Eckhard-Koch-Preis

Publications (selected): [1] Unger et al., Observation of Electron-Transfer-Mediated Decay in Aqueous Solution, Nature Chemistry 2017 DOI: 10.1038/nchem.2727 [2] Moguilevski et al., Ultrafast spin crossover in [FeII(bpy)3]2+: revealing two competing mechanisms by means of XUV photoemission spectroscopy, ChemPhysChem, 2017 DOI: 10.1002/cphc.201601396 [3] Borgwardt et al., Charge Transfer Dynamics at Dye-Sensitized ZnO and TiO2 Interfaces Studied by Ultrafast XUV Photoelectron Spectroscopy, Scientific Reports 2016 doi: 10.1038/srep24422

14 Theory Days 14.03.2017: Day 1 ‐ X‐ray Absorption and Emission Spectroscopy Chair: Emad Aziz HZB, Berlin‐Adlershof

[4] Golnak et al., Joint Analysis of Radiative and Non-Radiative Electronic Relaxation upon X-ray Irradiation of Transition Metal Aqueous Solutions, Scientific Reports 2016 doi: 10.1038/srep24659 [5] Petit et al., Valence holes observed in nanodiamonds dispersed in water. Nanoscale 2015 http://dx.doi.org/10.1039/C4NR06639A [6] Xiao et al., Enhancing the catalytic activity by narrowing the local energy gap – X-Ray studies of a Mn water oxidation catalyst. ChemSusChem. 2015 http://dx.doi.org/10.1002/cssc.201403219 [7] Khan et al., Electronic Structural Insights into Efficient MnOx Catalysts J. Mater. Chem. A 2014 DOI:10.1039/C4TA04185B. [8] Metje et al., Monochromatization of femtosecond XUV light pulses with the use of reflection zone plates Op. Ex. 2014, DOI:10.1364/OE.22.010747. [9] Bokarev, et al., State-Dependent Electron Delocalization Dynamics at the Solute-Solvent Interface: Soft X-ray Absorption Spectroscopy and Ab Initio Calculations, Phys. Rev. Let. 2013, DOI:10.1103/PhysRevLett.111.083002 [10] Suljoti, et al., Direct Observation of Molecular Orbital Mixing in a Solvated Organometallic Complex, Angew. Chem. Int. Ed. 2013, DOI:10.1002/anie.201303310 [11] Lange, Aziz, Electronic Structure of Ions and Molecules in Solution: A View from Modern Soft X- Ray Spectroscopies, Chem. Soc. Rev. 2013, Doi: dx.doi.org/10.1039/C3CS00008G [12] Seidel, et al, Origin of Dark-Channel X-ray Fluorescence from Transition-Metal Ions in Water, J. Am. Chem. Soc 2012,134 (3), 1600–1605 [13] Lange, et al., On the Origin of the Hydrogen Bond Network Nature of Water: X-Ray Absorption and Emission Spectra of Water-Acetonitrile Mixtures, Angew. Chem. Int. Ed. 2011, 123 (45), 10809– 10813 [14] Aziz, et al., Probing the electronic structure of the Hemoglobin active centre in physiological solutions, Phys. Rev. Let. 2009, 102, 68103 [15] Aziz, et al., Interaction between Liquid Water and Hydroxide Revealed by Core-Hole De-Excitation, Nature 2008, 455, 89

15 Theory Days 14.03.2017: Day 1 ‐ X‐ray Absorption and Emission Spectroscopy Chair: Emad Aziz HZB, Berlin‐Adlershof

Brief CV – Prof. Dr. Jan-Erik Rubensson Jan-Erik Rubensson is since 2002 professor at Uppsala University, where he made his PhD in 1988. He has been post-doc at Brookhaven National Laboratory, and scientist at Forschungszentrum Jülich in the 90ies. After the pioneering RIXS work he has continued to work with the refinement of this and methods, and the focus has been primarily on small molecules. He is presently the spokesperson of the VERITAS beamline, and is developing a novel imaging spectrometer for the SQS station of the European XFEL.

16 Theory Days 14.03.2017: Day 1 ‐ X‐ray Absorption and Emission Spectroscopy Chair: Emad Aziz HZB, Berlin‐Adlershof

X-ray emission and resonant inelastic X-ray scattering

Jan-Erik Rubensson Uppsala University jan‐[email protected] I will present a short history and the basic ideas of soft X-ray emission spectroscopy (XES) and resonant inelastic soft X-ray scattering (RIXS). Simplistic interpretation schemes in terms of local partial density of states and site selectivity will be introduced, and the versatility due to the relatively large attenuation length. Why RIXS in general must be described as one-step process will be explained, and the implications of energy and momentum conservation described. Dynamics in terms of lifetime-vibrational and lifetime-electronic interference, and in terms of the core hole clock will be discussed. Application to free molecules, liquids and molecular materials, as well as to materials with large electron correlation and spin-orbit coupling will be discussed. The new opportunities associated with time-resolved and nonlinear inelastic X-ray scattering at free-electron lasers will be briefly described.

17 Theory Days 14.03.2017: Day 1 ‐ X‐ray Absorption and Emission Spectroscopy Chair: Emad Aziz HZB, Berlin‐Adlershof

Brief CV – Prof. Dr. Wolfgang Kuch

Current position: Full professor at Freie Universität Berlin, Institut für Experimentalphysik Research expertise/activities in research: Research focuses on the study of magnetic ultrathin films and multilayer systems, surfaces, nanostructures, and adsorbed molecules. The aim is to perform fundamental investigations into innovative functional properties that are relevant to applications in data transport or storage, for sensors, or for magnetoelectronic devices. Topics include the interaction of antiferromagnetic films with magnetic layers, interaction mechanisms in magnetic multilayer systems, the interaction between magnetic molecules and ferromagnetic substrates, the adsorption properties of molecular switches on surfaces, as well as the intermolecular interactions within ensembles of adsorbed magnetic molecules or within metal–organic monolayers. The use of synchrotron radiation for x-ray absorption experiments is a major component of the research program. Besides, also surface science techniques, magneto–optical Kerr effect, scanning tunneling microscopy, and magnetic resonance techniques are employed. The emphasis is on well-characterized systems, wherever possible single-crystalline, to clearly reveal and capture the underlying physics and to pursue new effects at a fundamental level rather than to actually create prototype devices.

Keywords: x-ray absorption spectroscopy; antiferromagnetic films; magnetic properties of adsorbed molecules; magnetic multilayers

Selected 10 most important articles related to the lecture: [1] H. Wende, M. Bernien, J. Luo, C. Sorg, N. Ponpandian, J. Kurde, J. Miguel, M. Piantek, X. Xu, Ph. Eckhold, W. Kuch, K. Baberschke, P. M. Panchmatia, B. Sanyal, P. M. Oppeneer, and O. Eriksson: Substrate-induced magnetic ordering and switching of iron porphyrin molecules, Nat. Mater. 6, 516 (2007). [2] M. Bernien, J. Miguel, C. Weis, Md. E. Ali, J. Kurde, B. Krumme, P. M. Panchmatia, B. Sanyal, M. Piantek, P. Srivastava, K. Baberschke, P. M. Oppeneer, O. Eriksson, W. Kuch, and H. Wende: Tailoring the Nature of Magnetic Coupling of Fe-Porphyrin Molecules to Ferromagnetic Substrates, Phys. Rev. Lett. 102, 047202 (2009). [3] M. Piantek, G. Schulze, M. Koch, K. J. Franke, F. Leyssner, A. Krüger, C. Navío, J. Miguel, M. Bernien, M. Wolf, W. Kuch, P. Tegeder, and J. I. Pascual: Reversing the Thermal Stability of a Molecular Switch on a Gold Surface: Ring-Opening Reaction of Nitrospiropyran, J. Am. Chem. Soc. 131, 12729 (2009). [4] M. Bernien, D. Wiedemann, C. F. Hermanns, A. Krüger, D. Rolf, W. Kroener, P. Müller, A. Grohmann, and W. Kuch: Spin Crossover in a Vacuum-Deposited Submonolayer of a Molecular Iron(II) Complex, J. Phys. Chem. Lett. 3, 3431–3434 (2012).

18 Theory Days 14.03.2017: Day 1 ‐ X‐ray Absorption and Emission Spectroscopy Chair: Emad Aziz HZB, Berlin‐Adlershof

[5] T. R. Umbach, M. Bernien, C. F. Hermanns, A. Krüger, I. Fernández-Torrente, P. Stoll, J. I. Pascual, K. J. Franke, and W. Kuch: Ferromagnetic Coupling of Mononuclear Fe Centers in a Self- Assembled Metal Organic Network on Au(111), Phys. Rev. Lett. 109, 267207 (2012). [6] C. F. Hermanns, K. Tarafder, M. Bernien, A. Krüger, Y.-M. Chang, P. M. Oppeneer, and W. Kuch: Magnetic Coupling of Porphyrin Molecules Through Graphene, Adv. Mater. 25, 3473 (2013). [7] C. F. Hermanns, M. Bernien, A. Krüger, C. Schmidt, S. T. Waßerroth, G. Ahmadi, B. W. Heinrich, M. Schneider, P. W. Brouwer, K. J. Franke, E. Weschke, and W. Kuch: Magnetic Coupling of Gd3N@C80 Endohedral Fullerenes to a Substrate, Phys. Rev. Lett. 111, 167203 (2013). [8] A. Krüger, M. Bernien, C. F. Hermanns, and W. Kuch: X-Ray-Induced Reversible Switching of an Azobenzene Derivative Adsorbed on Bi(111), J. Phys. Chem. C 118, 12916 (2014). [9] M. Bernien, H. Naggert, L. M. Arruda, L. Kipgen, F. Nickel, J. Miguel, C. F. Hermanns, A. Krüger, D. Krüger, E. Schierle, E. Weschke, F. Tuczek, and W. Kuch: Highly Efficient Thermal and Light- Induced Spin-State Switching of an Fe(II) Complex in Direct Contact with a Solid Surface, ACS Nano 9, 8960 (2015). [10] W. Kuch and M. Bernien: Controlling the magnetism of adsorbed metal-organic molecules, J. Phys.: Condens. Matter 29, 023001 (2017).

19 Theory Days 14.03.2017: Day 1 ‐ X‐ray Absorption and Emission Spectroscopy Chair: Emad Aziz HZB, Berlin‐Adlershof

X-ray absorption spectroscopy for the investigation of adsorbed molecules

Wolfgang Kuch Institut für Experimentalphysik, Freie Universität Berlin, 14195 Berlin, Germany [email protected] Organic molecules have a great potential for the continuing miniaturization of all kind of electronic devices. They can be considered as the smallest building blocks for organic electronics, data storage devices, or sensor applications. Molecules can be produced in large numbers with fully identical properties, which can be tailored by synthetic chemists via certain specific modifications to the molecules’ chemical structure.[1] To take advantage of molecules in such devices, they need to be immobilized and contacted. This involves the interaction with a solid surface and may alter significantly all of their properties. It is thus vital to study the molecule–surface interaction. X-ray absorption spectroscopy (XAS) is a powerful method to do so.[2] It offers a very high sensitivity towards dilute submonolayer coverages required to study molecules in direct contact with a surface. It further offers, by virtue of exciting electronic transitions from core levels, elemental selectivity via the distinctly different binding energies of core levels of different elements. Different chemical environments, characterized by the local charge density, can be separated with the help of the so-called chemical shifts, i.e., the dependence of the binding energy as well as the interaction energy of the photoexcited electron with the resulting core hole on the local surrounding, in particular the charge density. The orientation of unoccupied molecular orbitals can be accessed from the angle dependence of the absorption signal for excitation with polarized x rays. Last, but definitely not least, taking advantage of magnetic dichroisms in x-ray absorption allows to access magnetic properties of adsorbed molecules in an element- resolved way. The word „dichroism“ is of Greek origin and means „bicolored“. “Magnetic dichroism” in general refers to the dependence of spectroscopic properties of a sample on the orientation of its magnetization. The most straightforward way of obtaining magnetic dichroism is by absorption of circularly polarized photons. The circular polarization, which can be regarded as the spin of photons, directly interacts with the angular momentum of the electrons in the sample, thus probing the magnetic moment. Polarized x rays are nowadays abundantly available at synchrotron radiation laboratories. When circularly polarized x rays are absorbed in systems exhibiting a magnetization, which could be ferromagnets or paramagnets in an external field, the cross section of x-ray absorption depends on the orientation of magnetization direction with respect to the helicity of the circularly polarized x rays. This effect is called x-ray magnetic circular dichroism (XMCD) and was first experimentally observed in 1987.[3] It can be understood from considering dipole selection rules for circular polarization in the electronic excitation, leading to a spin polarization of the transition, and the imbalance of density of unoccupied states available for these transitions for majority and minority spins in a magnetic sample.[4] The spin- and orbital-polarized photoelectrons created in the absorption process by a circularly polarized photon can thus be seen as a

20 Theory Days 14.03.2017: Day 1 ‐ X‐ray Absorption and Emission Spectroscopy Chair: Emad Aziz HZB, Berlin‐Adlershof

probe for the final-state’s spin and orbital polarization projected onto the photon k vector. If the absorption of a spin–orbit-split pair of initial states is considered, the different relative orientation of spin and orbital polarization can be used to disentangle their contributions to the XMCD and to separately determine effective spin and orbital moment of the probed atoms in the sample by sum rules.[5], [6] After explaining in detail the basics of x-ray absorption spectroscopy, I will show representative examples in which it has contributed significantly to the experimental study of adsorbed molecules on solids. The first is azobenzene molecules, conformal molecular switches, adsorbed on a Bi(111) single crystal surface. In solution, these molecules undergo a conformational change from a trans to a cis conformation by illumination with UV light, while the reverse switching can be initiated by visible light.[7] When in direct contact with a metal surface, this switching is typically suppressed by the molecule–substrate interaction.[8] On the Bi(111) surface, however, a new switching mechanism is in place: Resonant excitation with soft x rays at the nitrogen K edge leads to a conversion of the adsorbed molecules from the trans to the cis conformation, as can be clearly followed from the angle dependence of the XAS signal. This change is reversible and the back reaction achieved by thermal excitation.[9] Spin-crossover molecules, the second example, are magnetic molecules that can switch reversibly between two states of different magnetic moments.[10] Most common are spin- crossover molecules containing a d6 Fe ion, which switch between a diamagnetic state at low temperatures and a paramagnetic one at room temperature.[11] Such a spin switching, if achieved in contact with a solid, makes the molecules highly interesting for the use as logic elements in a future molecule-based spin electronics. XAS is the method of choice to determine and monitor the spin state of such molecules in adsorbed submonolayers. The different occupancy of the d orbitals responsible for the magnetism is directly mirrored in the spectra.[12],[13] I will present an example of such a molecule that allows to switch its spin state reversibly in contact with a highly oriented pyrolytic graphite (HOPG) surface, not only by temperature variation, but also by light.[14] The possibility offered by the element selectivity of XMCD to detect the relatively tiny magnetic moment of adsorbed molecules independently from the much larger one of a magnetic substrate underneath allows to study the magnetic coupling between molecules and substrate. This coupling could be used to stabilize the molecular magnetic moments against thermal fluctuations in future applications. I will present examples of planar metalloporphyrin molecules, either adsorbed directly [15] or via oxygen [16] or graphene [17] to ferromagnetic substrates, and discuss the information about the coupling obtained from XMCD data. The field of surface magneto-chemistry is rapidly evolving, [18] and it is not possible to give a comprehensive overview in a short lecture. Due to the advantages I hope to clearly demonstrate by this lecture, x-ray absorption spectroscopy will remain the main investigation technique in this vividly growing field and will possibly lead to many exciting discoveries in the future.

21 Theory Days 14.03.2017: Day 1 ‐ X‐ray Absorption and Emission Spectroscopy Chair: Emad Aziz HZB, Berlin‐Adlershof

References: [1] W. Auwärter, D. Écija, F. Klappenberger, J. V. Barth, Porphyrins at interfaces, Nature Chemistry 7, 105-120 (2015). [2] J. Stöhr, NEXAFS Spectroscopy. (Springer, Berlin, Heidelberg, 1992). [3] G. Schütz, W. Wagner, W. Wilhelm, P. Kienle, R. Zeller, R. Frahm, G. Materlik, Absorption of circularly polarized x rays in iron, Phys. Rev. Lett. 58, 737 (1987). [4] J. Stöhr, X-ray magnetic circular dichroism spectroscopy of transition metal thin films, J. Electron Spectrosc. Relat. Phenom. 75, 253 (1995). [5] B. T. Thole, P. Carra, F. Sette, G. van der Laan, X-ray circular dichroism as a probe of orbital magnetization, Phys. Rev. Lett. 68, 1943 (1992). [6] P. Carra, B. T. Thole, M. Altarelli, X. Wang, X-ray circular dichroism and local magnetic fields, Phys. Rev. Lett. 70, 694 (1993). [7] H. Dürr and H. Bouas-Laurent, Photochromism: Molecules and Systems. (Elsevier B.V., Amsterdam, The Netherlands, 2003). [8] F. Leyssner, S. Hagen, L. Ovari, J. Dokic, P. Saalfrank, Peters, M. V., S. Hecht, T. Klamroth, P. Tegeder, Photoisomerization Ability of Molecular Switches Adsorbed on Au(111): Comparison Between Azobenzene and Stilbene Derivatives, J. Phys. Chem. C 114, 1231-1239 (2010). [9] A. Krüger, M. Bernien, C. F. Hermanns, W. Kuch, X-ray-induced reversible switching of an azobenzene derivative adsorbed on Bi(111), J. Phys. Chem. C 118, 12916-12922 (2014). [10] M. A. Halcrow, Ed., Spin-Crossover Materials: Properties and Applications (John Wiley & Sons, Ltd., New York, 2013). [11] P. Gütlich, A. B. Gaspar, Y. Garcia, Spin State Switching in Iron Coordination Compounds, Beilstein J. Org. Chem. 9, 342-391 (2013). [12] C. Cartier dit Moulin, P. Rudolf, A.-M. Flank, C.-T. Chen, Spin transition evidenced by soft x-ray absorption spectroscopy, J. Phys. Chem. 96, 6196-6198 (1992). [13] M. Bernien, D. Wiedemann, C. F. Hermanns, A. Krüger, D. Rolf, W. Kroener, P. Müller, A. Grohmann, W. Kuch, Spin crossover in a vacuum-deposited submonolayer of a molecular iron(II) complex, J. Phys. Chem. Lett. 3, 3431-3434 (2012). [14] M. Bernien, H. Naggert, L. M. Arruda, L. Kipgen, F. Nickel, J. Miguel, C. F. Hermanns, A. Krüger, D. Krüger, E. Schierle, E. Weschke, F. Tuczek, W. Kuch, Highly efficient thermal and light-induced spin-state switching of an Fe(II) complex in direct contact with a solid surface, ACS Nano 9, 8960- 8966 (2015). [15] H. Wende, M. Bernien, J. Luo, C. Sorg, N. Ponpandian, J. Kurde, J. Miguel, M. Piantek, X. Xu, P. Eckhold, W. Kuch, K. Baberschke, P. M. Panchmatia, B. Sanyal, P. M. Oppeneer, O. Eriksson, Substrate-induced magnetic ordering and switching of iron porphyrin molecules, Nature Materials 6, 516-520 (2007). [16] M. Bernien, J. Miguel, C. Weis, M. E. Ali, J. Kurde, B. Krumme, P. M. Panchmatia, B. Sanyal, M. Piantek, P. Srivastava, K. Baberschke, P. M. Oppeneer, O. Eriksson, W. Kuch, H. Wende, Tailoring the nature of magnetic coupling of Fe-porphyrin molecules to ferromagnetic substrates, Phys. Rev. Lett. 102, 047202 (2009). [17] C. F. Hermanns, K. Tarafder, M. Bernien, A. Krüger, Y.-M. Chang, P. M. Oppeneer, W. Kuch, Magnetic coupling of porphyrin molecules through graphene, Advanced Materials 25, 3473-3477 (2013). [18] N. Ballav, C. Wäckerlin, D. Siewert, P. M. Oppeneer, T. A. Jung, Emergence of on-surface magnetochemistry, J. Phys. Chem. Lett. 4, 2303-2311 (2013).

22 Theory Days 14.03.2017: Day 1 ‐ X‐ray Absorption and Emission Spectroscopy Chair: Emad Aziz HZB, Berlin‐Adlershof

Brief CV – Prof. Dr. Alexei Erko

Current position: Head of the Department for Nanometre Optics and Technology, Helmholtz Centre Berlin for Materials und Energy GmbH (HZB) Research expertise/activities in research: Prof. Dr. Erko received his PhD degree in experimental physics at the Moscow Physical Engineering Institute in 1981 and his habilitation in physics (Doctor of Science) in 1991. He became Professor of Experimental Physics in 1993. From 1978 to 1994, he was employed at the Institute of Solid State Physics and the Institute of Microelectronics Technology of the Russian Academy of Sciences in Chernogolovka, Moscow district, initially as Senior Scientist and then later as Head of the “X-ray Optics and Technology Laboratory”. In 1994, he came to Berlin to do research at the storage ring BESSY II, where he worked for the BESSY GmbH Berlin as Senior Scientist from 1994 to 2009, and then from 2009 to 2010 as Senior Scientist for the Helmholtz Centre Berlin for Materials und Energy GmbH (HZB). In 2010, he became Head of the Institute for Nanometre Optics and Technology and since 2017 Head of the Department for Nanometre Optics and Technology. In 2011, he was appointed Honorary Professor for Experimental Physics by the president of the Freie Universität Berlin. His research interests focus especially on x-ray optics, x-ray holography and synchrotron radiation beamline design. He is co-author of two monographs and co-editor of two books on x-ray optics and x-ray microscopy. Professor Erko successfully organized the lecture series for master students on the topic “Modern X-ray and Neutron Methods for Science and Technology” at the Free University Berlin since winter semester 2009/2010.

Keywords: µEXAFS, µXBIC, X-ray Optics.

Selected 10 most important articles related to the lecture: [1] X-ray absorption spectroscopy using a self-seeded soft X-ray free-electron laser, Th. Kroll, J. Kern, M. Kubin, D. Ratner, S. Gul, F. D. Fuller, H. Löchel, J. Krzywinski, A. Lutman, Y. Ding, G. L. Dakovski, S. Moeller, J. J. Turner, R. Alonso-Mori, D. L. Nordlund, J. Rehanek, C. Weniger, A. Firsov, M. Brzhezinskaya, R. Chatterjee, B. Lassalle-Kaiser, R. G. Sierra, H. Laksmono, E. Hill, A. Borovik, A. Erko, A. Föhlisch, R. Mitzner, V. K. Yachandra, J. Yano, P. Wernet, U. Bergmann, Optics Express, (2016), 24(20), 22469-22480 [2] Reflection zone plate wavelength-dispersive spectrometer for ultra-light elements measurements, A. Hafner, L. Anklamm, A. Firsov, A. Firsov, H. Löchel, A. Sokolov, R. Gubzhokov, A. Erko, Optics Express, 23, (23), (2015), 29476 [3] FemtoSpeX: a versatile optical pump-soft X-ray probe facility with 100 fs X-ray pulses of variable polarization, K. Holldack, J. Bahrdt, A. Balzer, U. Bovensiepen, M. Brzhezinskaya, A. Erko, A. Eschenlohr, R. Follath, A. Firsov, W. Frentrup, L. Le Guyader, T. Kachel, P. Kuske, R. Mitzner, R.

23 Theory Days 14.03.2017: Day 1 ‐ X‐ray Absorption and Emission Spectroscopy Chair: Emad Aziz HZB, Berlin‐Adlershof

Müller, N. Pontius, T. Quast, I. Radu, J.-S. Schmidt, C. Schüßler-Langeheine, M. Sperling, C. Stamm, C. Trabant and A. Föhlisch, J. Synchrotron Rad. (2014). 21, 1090-1104 [4] Methods development for diffraction and spectroscopy studies of metalloenzymes at X-ray free- electron lasers, J Kern, J Hattne, R Tran, R Alonso-Mori, H Laksmono, S Gul, RG Sierra, J. Rehanek, A. Erko, R. Mitzner, Ph. Wernet, U. Bergmann, N. K. Sauter, V. Yachandra, J. Yano, Philosophical Transactions of the Royal Society B: Biological Sciences (2014), 369, 1647, 20130590. [5] L‑Edge X‑ray Absorption Spectroscopy of Dilute Systems Relevant to Metalloproteins Using an X ‑ray Free-Electron Laser R. Mitzner, J. Rehanek, J. Kern, S. Gul, J. Hattne, T. Taguchi, R. Alonso- Mori, R. Tran, Ch. Weniger, H. Schroder,̈ W. Quevedo, H. Laksmono, R. G. Sierra, G. Han, B. Lassalle-Kaiser, S. Koroidov, K. Kubicek, S. Schreck, K. Kunnus, M. Brzhezinskaya, A. Firsov, M. P. Minitti, J. J. Turner, S. Moeller, N. K. Sauter, M. J. Bogan, D. Nordlund, W. F. Schlotter, J. Messinger, A. Borovik, S. Techert, F. M. F. de Groot, A. Föhlisch, A. Erko, U. Bergmann, V. K. Yachandra, Ph. Wernet, J. Yano, J. Phys. Chem. Lett. (2013), 4, 3641−3647 [6] Application of Conventional and Microbeam Synchrotron Radiation X-Ray Fluorescence and Absorption for the Characterization of Human Nails, M. Katsikini, A. Mavromati, F. Pinakidou, E. C. Paloura, D. Gioulekas, D. Ioannides, A. Erko, I. Zizak, Journal of Nanoscience and Nanotechnology, 10, 2010, 6266–6275 [7] Review Article Hard X-ray Micro-spectroscopy at Berliner Elektronenspeicherring für Synchrotronstrahlung II, A. Erko, I. Zizak, Spectrochimica Acta, Part B, 64, (2009) 833–848 [8] X-ray standing wave studies of metal ions incorporation in Langmuir-Blodgett films N.N. Novikova, S. I. Zheludeva, N. D. Stepina, A. L. Tolstikhina, R. V. Gainutdinov, W. Haase, A. I. Erko, A.A. Knyasev, Yu. G. Galyametdinov, Applied Physics A 94, (2009), 461-466, DOI 10.1007/s00339- 008-4971-7 [9] Synchrotron microscopy and spectroscopy for analysis of crystal defects in silicon, W. Seifert, O. F. Vyvenko, T. Arguirov, A. Erko, M. Kittler, C. Rudolf, M. Salome, M. Trushin, I. Zizak, Phys. Status Solidi C 6, No. 3, 765– 771 (2009) / DOI 10.1002/pssc. 200880717 [10] Combined XBIC/μ-XRF/μ-XAS/DLTS, investigation of chemical character and electrical properties of Cu and Ni precipitates in silicon, M. Trushin, O. Vyvenko, W. Seifert, M. Kittler, I. Zizak, A. Erko, M. Seibt, C. Rudolf, Phys. Status Solidi C 6, No. 8, (2009), 1868– 1873

24 Theory Days 14.03.2017: Day 1 ‐ X‐ray Absorption and Emission Spectroscopy Chair: Emad Aziz HZB, Berlin‐Adlershof

Application of micro/nano EXAFS/XANES in environmental and energy material research

Alexei Erko HZB – Helmholtz Zentrum Berlin, Albert Einstein Str. 15, 12489 Berlin, Germany [email protected] The use of X-rays as a tool for microscopy and nanometer technology is developing very rapidly. This can be attributed to the development of synchrotron radiation sources and to the progress in optical elements and methods for the X-ray beam control such as focusing. X-ray microprobes are widely used in combination with the most modern experimental techniques such as micro-fluorescence analysis XRF, imaging X-ray microscopy, micro-spectroscopy, micro-tomography, etc. [1]. These methods are established at several Synchrotron Radiation facilities and have been used for investigations of a great number of samples including environmental and energy material objects [2]. These methods are in strong competition with electron microscopy methods which have already resolutions in the order of few nanometers. Such resolution cannot be achieved currently by X-ray microscopy methods. However, there is a rapid evolution in the X-ray regime towards resolution levels of a few tens of nanometers. On the other hand, there are several X-ray methods such as Extended X-ray Absorption Fine Structure spectroscopy (EXAFS) and X-ray beam induced current (XBIC) in combination with X-ray fluorescence spectroscopy (XRF), which can be not explored with an electron beam. Therefore X-rays have an important advantage in structural investigations and high-accuracy fluorescence analysis. Unfortunately the last methods are not so easy in real applications. They demand extraordinary beam direction and beam position stability during the energy scan over a very large (more than 1000 eV) range. The optics applied has to be polychromatic to provide a large energy range. Usually an energy scan is provided by a monochromator. A beam position and direction is slightly varied from step to step which causes to a variation in beam intensity and position on a sample. Recording of an EXAFS spectrum requires extremely stable local intensity with variations less than of 0.1%. Such stability is available to the very short focus optical system, which has a low sensitivity to the beam variation in previous monochromator and mirror optics. In this lecture we describe two optical systems: capillary optical systems with very short focal distances below 1 mm and a waveguide optics / standing waves technique with ultra-short focal distance below 0.1 µm. Both optical systems allow one to collect good quality EXAFS spectra with micrometer, or in the case of standing wave technique nanometer, resolution. Among the others a capillary x-ray optical system with a lateral resolution down to 1 µm has been used at BESSY II beamlines for investigations such as:

 Microfocus XAS measurements on volcano-shaped manganese deposits at the cell- wall of the green alga Chara coralline. The evolutionary origin of the manganese complex of oxygenic photosynthesis and possible formation of a bicarbonate precursor complex has been investigated [3].

25 Theory Days 14.03.2017: Day 1 ‐ X‐ray Absorption and Emission Spectroscopy Chair: Emad Aziz HZB, Berlin‐Adlershof

 the investigation of oxidation and migration processes of inorganic compounds in ink corroded manuscripts. A model of the ink corrosion mechanism has been suggested based on the experimental results of a combination of micro-XRF and micro-XANES methods. The influence of restoration treatment on ink corroded manuscripts was carefully investigated [4].

 the study of glasses containing industrial waste by means of micro-XRF mapping and micro-XANES. An inhomogeneous distribution of Fe was observed in the samples. An alteration of the local environment around the Fe atom, which tends to occupy tetrahedral sites in the glass matrix for the regions with low Fe concentration was also found using micro-XAS [5].

 the 3D micro-fluorescence analysis, depth-resolved investigation using a confocal polycapillary set-up [6].

 the study by the methods of XBIC/RFA and XANES electrical activity of defects and precipitations of transition metals in poly-silicon material. [7]. X-rays are highly penetrative and therefore any information obtained through x-ray based measurements is averaged over a depth of several microns. However, x-ray based techniques can be made depth selective by generating standing waves inside the nanostructure of interest by making use of the phenomenon of total reflection. X-ray intensity is localized in the anti-nodal regions, the position of which inside the nanostructure can be varied by varying the angle of incidence. Use of such x-ray standing waves in elemental depth profiling or XANES measurements with nanometer depth resolution has been demonstrated [8,9]. The angular dependence of the fluorescence yield from a single organic monolayer on a solid substrate modulated by a standing wave in total external reflection conditions has been measured experimentally. The scanning by standing wave field of a single organic molecule has been done and the depth positions of particular ions in the molecule structure have been determined [10]. In this experiment a depth resolution on the order of 1 nm has been achieved. Depth selectivity can further be enhanced by making use of wave-guide structures. For the first time at BESSY II, depth selective EXAFS studies have been performed [11]. The absorption spectra of Fe and W nano-layers were recorded with depth resolution on the order of 0.1 nm. This method combines total external reflection standing waveguide mode and EXAFS measurements. Furthermore, the method was used to study first stages of interface diffusion in Co/Si system [12]. Absorption spectra of Co were measured in different positions at the interface verifying the existence of the Co-Si alloy. Recently the micro-spectroscopy methods have been developed also for the ultra-fast measurements with fs time resolution. [13,14]

26 Theory Days 14.03.2017: Day 1 ‐ X‐ray Absorption and Emission Spectroscopy Chair: Emad Aziz HZB, Berlin‐Adlershof

References: [1] A. Erko in Handbook of Practical X-Ray Fluorescence Analysis, Eds. B. Beckhoff, B. Kanngiesser, N. Langhoff, R. Wedell, H. Wolff, Springer-Verlag, Berlin, (2006) [2] A. Marceau, N. Tamura, M. A. Marcus, A. A. Macdowell, R. S. Celestre, R. E. Sublett, G. Sposito, H. A. Padmore, Deciphering Ni sequestration in soil ferromanganese nodules by combining X-ray fluorescence, absorption, and diffraction at micrometer scales of resolution, American Mineralogist, 87, (2002) 1494–1499 [3] A. Schöler, "Strukturanalyse manganhaltiger Ablagerungen auf der Süßwasseralge Chara corallina", Diplomarbeit, Freie Universität zu Berlin, Fachbereich Physik, 2004 [4] B. Kanngießer, O. Hahn, M. Wilke, B. Nekat, W. Malzer, A. Erko, Investigation of oxidation and migration processes of inorganic compounds in ink corroded manuscripts, Spectrochimica Acta A, Part B59, (2004), 1511-1516 [5] F. Pinakidou, M. Katsikini, E. C. Paloura, P. Kavouras, Ph. Komninou, Th. Karakostas, A. Erko, Study of annealing induced devitrification of stabilized industrial waste glasses by means of micro X-ray fluorescence mapping and absorption fine structure spectroscopy, Journal of Non-Crystalline Solids 351, (2005), 2474–2480 [6] B. Kanngiesser, W. Malzer, I. Reiche, A new 3D micro X-ray fluorescence analysis set-up – first archaeometric applications, Nuclear Instruments and Methods in Physics Research, B211(2), (2003), 259-264 [7] A. Gupta, N. Darowski, I. Zizak, C. Meneghini, G. Schumacher, A. Erko, X-ray measurements with micro- and nano-resolution at BESSY, Spectrochimica Acta Part B, 62, (2007), 622-625 [8] A. Gupta, N. Darowski, I. Zizak, C. Meneghini, G. Schumacher, A. Erko, X-ray measurements with micro- and nano-resolution at BESSY, Spectrochimica Acta Part B, 62, (2007), 622-625 [9] N.N. Novikova, S. I. Zheludeva, N. D. Stepina, A. L. Tolstikhina, R. V. Gainutdinov, W. Haase, A. I. Erko, A.A. Knyasev, Yu. G. Galyametdinov, X-ray standing wave studies of metal ions incorporation in Langmuir-Blodgett films Applied Physics A 94, (2009), 461-466 [10] N. N. Novikova, E. A. Yurieva, S. I. Zheludeva, M. V. Kovalchuk, N. D. Stepina, A. L. Tolstikhina, R. V. Gaynutdinov, D. V. Urusova, T.A. Matkovskaya, A. M. Rubtsov, O. D. Lopina, A. Erko and O.V. Konovalov, X-ray fluorescence methods for investigations of lipid/protein membrane models, Journal of Synchrotron Radiation, 12, (2005), 511–516 [11] A. Gupta, N. Darowski, I. Zizak, C. Meneghini, A. Erko, G. Schumaher, X-ray standing wave/EXAFS measurements with nano-resolution, BESSY Annual Report, (2005), 332-334 [12] Z. Erdélyi, C. Cserháti, A. Csik, L. Daróczi, G. A. Langer, Z. Balogh, M. Varga, D. L. Beke, I. Zizak, A. Erko, Nanoresolution interface studies in thin films by synchrotron x-ray diffraction and by using x-ray waveguide structure, X-Ray Spectrometry, (2009), 338–342 [13] J Kern, J Hattne, R Tran, R Alonso-Mori, H Laksmono, S Gul, RG Sierra, J. Rehanek, A. Erko, R. Mitzner, Ph. Wernet, U. Bergmann, N. K. Sauter, V. Yachandra, J. Yano, Methods development for diffraction and spectroscopy studies of metalloenzymes at X-ray free-electron lasers, Philosophical Transactions of the Royal Society B: Biological Sciences (2014), 369, 1647, 20130590. [14] K. Holldack, J. Bahrdt, A. Balzer, U. Bovensiepen, M. Brzhezinskaya, A. Erko, A. Eschenlohr, R. Follath, A. Firsov, W. Frentrup, L. Le Guyader, T. Kachel, P. Kuske, R. Mitzner, R. Müller, N. Pontius, T. Quast, I. Radu, J.-S. Schmidt, C. Schüßler-Langeheine, M. Sperling, C. Stamm, C. Trabant and A. Föhlisch, FemtoSpeX: a versatile optical pump-soft X-ray probe facility with 100 fs X-ray pulses of variable polarization, J. Synchrotron Rad. (2014). 21, 1090-1104

27 Theory Days 14.03.2017: Day 1 ‐ X‐ray Absorption and Emission Spectroscopy Chair: Emad Aziz HZB, Berlin‐Adlershof

Brief CV – PD Dr. Philippe Wernet

Current positions: Scientist at Helmholtz-Zentrum Berlin and Privatdozent (private lecturer in physics) at Technische Universität Berlin Research expertise/activities in research: The goal of our research is to find simple rules to explain and predict the relationship between structure and function in molecules and bio-molecular systems. This is aimed at helping to develop new concepts and systems for the efficient transformation of photon energy into chemical energy. Ultimately we want to contribute to optimizing photocatalytic systems. We develop and apply innovative x-ray spectroscopic methods, novel short-pulse x-ray sources and theoretical electronic-structure tools to map the electronic structure and its temporal evolution. We start from a fundamental understanding of the local atomic and intermolecular interactions to establish the chemical bonding on atomic length and time scales of Ångströms and femtoseconds. For this we map the local chemical interactions in molecules and metalloproteins in physiological environments to establish a mechanistic understanding of their properties and their bio-molecular function. Furthermore we aim at mapping the electronic structure in real time to understand the excited-state behavior of molecules. We are developing and applying novel x-ray spectroscopic tools with wavelengths from the vacuum-ultraviolet to the x-ray range and including time-resolved x-ray spectroscopy with a time resolution in the femtosecond range. We combine methods and instrumentation for the generation, manipulation and application of femtosecond x-ray pulses in the laboratory with x- ray spectroscopic methods and instrumentation at large-scale facilities such as the x-ray free- electron lasers FLASH in Hamburg (Germany), the Linac Coherent Light Source (LCLS) in Stanford (USA) and the synchrotron radiation source BESSYII in Berlin (Germany). One of the main goals is to improve the instrumentation for x-ray absorption spectroscopy (XAS) and for the x-ray analog of resonant Raman spectroscopy (namely resonant inelastic x- ray scattering, RIXS) for chemical, biochemical and photocatalytic applications as well as new theoretical approaches to the interpretation of x-ray spectra.

Keywords: Molecular dynamics, photochemical dynamics, metalloproteins, x-ray spectroscopy, x-ray absorption spectroscopy, resonant inelastic x-ray scattering, x-ray photoelectron spectroscopy, time-resolved x-ray spectroscopy, femtochemistry, x-ray free- electron lasers, synchrotron radiation.

28 Theory Days 14.03.2017: Day 1 ‐ X‐ray Absorption and Emission Spectroscopy Chair: Emad Aziz HZB, Berlin‐Adlershof

Selected 10 most important articles related to the lecture: [1] K. Kunnus, I. Josefsson, S. Schreck, W. Quevedo, P. S. Miedema, S. Techert, Frank M. F. de Groot, A. Föhlisch, M. Odelius, Ph. Wernet, Quantifying covalent interactions with resonant inelastic soft x-ray scattering: Case Study of Ni2+aqua complex Chem. Phys. Lett. 669, 196-201 (2017) [2] S. Schreck, Ph. Wernet, Isotope effects in liquid water probed by transmission mode x-ray absorption spectroscopy at the oxygen K-edge, J. Chem. Phys. 145, 104502, p. 1-9 (2016) [3] K. Kunnus, W. Zhang, M. G. Delcey, R. V. Pinjari, P. S. Miedema, S. Schreck, W. Quevedo, H. Schröder, A. Föhlisch, K. J. Gaffney, M. Lundberg, M. Odelius, Ph. Wernet, Viewing the valence electronic structure of ferric and ferrous hexacyanide in solution from the Fe and cyanide perspectives, J. Phys. Chem. B 120, 7182-7194 (2016) [4] Ph. Wernet, K. Kunnus, I. Josefsson et al., Orbital-specific mapping of the ligand exchange dynamics of Fe(CO)5 in solution, Nature 520, 78-81 (2015) [5] M. Prémont-Schwarz, S. Schreck, M. Iannuzzi, E. T. J. Nibbering, M. Odelius, Ph. Wernet, Correlating Infrared and X-ray Absorption Energies for Molecular-Level Insight into Hydrogen Bond Making and Breaking in Solution, J. Phys. Chem. B 119, 8115-8124 (2015) [6] R. Mitzner, J. Rehanek, J. Kern, et al., L-edge X-ray Absorption Spectroscopy of Dilute Systems Relevant to Metalloproteins Using a X-ray Free-Electron Laser, J. Phys. Chem. Lett. 4, 3641 (2013) [7] I. Josefsson, K. Kunnus, S. Schreck, et al., Ab Initio Calculations of X‑ray Spectra: Atomic Multiplet and Molecular Orbital Effects in a Multiconfigurational SCF Approach to the L‑Edge Spectra of Transition Metal Complexes, J. Phys. Chem. Lett. 3, 3565 (2012) [8] Ph. Wernet, Electronic structure in real time: Mapping valence electron rearrangements during chemical reactions, Phys. Chem. Chem. Phys. 13, 16941 (2011) [9] Ph. Wernet, M. Odelius, K. Godehusen, et al., Real-time evolution of the valence electronic structure in a dissociating molecule, Phys. Rev. Lett. 103, 013001 (2009) [10] Ph. Wernet, D. Nordlund, U. Bergmann, et al., The structure of the first coordination shell in liquid water, Science 304, 995 (2004)

29 Theory Days 14.03.2017: Day 1 ‐ X‐ray Absorption and Emission Spectroscopy Chair: Emad Aziz HZB, Berlin‐Adlershof

Application of XAS/XES and RIXS – Transition metal complexes in solution: Interpretation of experimental spectra and theoretical simulation

Philippe Wernet Institute for Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz- Zentrum Berlin für Materialien und Energie GmbH, 12489 Berlin, Germany [email protected] Charge and spin density changes at the metal sites of transition-metal complexes and in metalloproteins determine reactivity and selectivity. To understand their function and to optimize complexes for photocatalytic applications the changes of charge and spin densities need to be mapped and ultimately controlled. X-ray spectroscopy offers unique opportunities for mapping charge and spin densities and their ultrafast dynamics in transition-metal complexes and in metalloproteins [1]. The aim of this lecture is to discuss the opportunities provided by x-ray spectroscopy for mapping chemical dynamics in general and for studying transition-metal atoms in coordination complexes and in metalloproteins in particular. The new capabilities offered by time-resolved x-ray spectroscopy to reveal the coupling of nuclear dynamics and transient electronic structure in the electronic excited states of molecular systems will be highlighted (Fig. 1).

Figure1: Conceptual depiction of time-resolved x-ray spectroscopy for mapping the electronic structure evolution of the system while a nuclear wavepacket propagates in the potential energy landscape.

30 Theory Days 14.03.2017: Day 1 ‐ X‐ray Absorption and Emission Spectroscopy Chair: Emad Aziz HZB, Berlin‐Adlershof

Time-resolved x-ray spectroscopy enables a novel way for characterizing chemical interactions on atomic length and time scales of Ångströms and femtoseconds. The question about “Where are the electrons?” during a chemical reaction can be answered by directly addressing the valence electrons and their evolution as the reaction proceeds. I will discuss exemplary cases selected from recent examples [2-7] for how we study chemical interactions and their ultrafast dynamics with soft x-ray spectroscopy [8]. A special emphasize will be given to the investigation of molecules in solution and biomolecular systems under physiological conditions [9]. We use time-resolved and steady-state soft x-ray spectroscopy at synchrotron radiation sources, at x-ray free-electron lasers and in the laboratory [10-12]. The importance of applying short x-ray pulses to the systems under investigation will be highlighted. I will discuss how we extract information on chemical properties based on the experimental observables [13], emphasize the importance of effective and efficient theoretical approaches for this [14] and highlight the importance of choosing suitable sample preparation techniques and experimental procedures in general [15-18] for avoiding x-ray beam damage of the samples.

References: [1] Ph. Wernet, Book chapter on “Orbital-specific Mapping of Chemical Interactions and Dynamics with Femtosecond Soft X-ray Pulses” in „X-Ray Free Electron Lasers“ by J. Yano, V. Yachandra, U. Bergmann (Eds.), Royal Society of Chemistry Energy and Environment Series (2016). [2] Ph. Wernet, K. Kunnus, I. Josefsson, I. Rajkovic, W. Quevedo, M. Beye, S. Schreck, S. Grübel, M. Scholz, D. Nordlund, W. Zhang, R. W. Hartsock, W. F. Schlotter, J. J. Turner, B. Kennedy, F. Hennies, F. M. F. de Groot, K. J. Gaffney, S. Techert, M. Odelius, and A. Föhlisch. Nature 520, 78- 81 (2015). [3] K. Kunnus, I. Josefsson, S. Schreck, W. Quevedo, P. S. Miedema, S. Techert, Frank M. F. de Groot, A. Föhlisch, M. Odelius, Ph. Wernet, Chem. Phys. Lett. 669, 196-201 (2017). [4] K. Kunnus, W. Zhang, M. G. Delcey, R. V. Pinjari, P. S. Miedema, S. Schreck, W. Quevedo, H. Schröder, A. Föhlisch, K. J. Gaffney, M. Lundberg, M. Odelius, Ph. Wernet, J. Phys. Chem. B 120, 7182-7194 (2016). [5] K. Kunnus, I. Josefsson, I. Rajkovic, S. Schreck, W. Quevedo, M. Beye, C. Weniger, S. Grübel, M. Scholz, D. Nordlund, W. Zhang, R. W. Hartsock, K. J. Gaffney, W. F. Schlotter, J. J. Turner, B. Kennedy, F. Hennies, F. M. F. de Groot, S. Techert, M. Odelius, Ph. Wernet, A. Föhlisch, Structural Dynamics 3, 043204 (2016). [6] M. Prémont-Schwarz, S. Schreck, M. Iannuzzi, E. T. J. Nibbering, M. Odelius, Ph. Wernet, J. Phys. Chem. B 119, 8115-8124 (2015). [7] S. Schreck, Ph. Wernet, J. Chem. Phys. 145, 104502 (2016). [8] Ph. Wernet. Phys. Chem. Chem. Phys. 13, 16941 (2011). [9] R. Mitzner, J. Rehanek, J. Kern, S. Gul, J. Hattne, T. Taguchi, R. Alonso-Mori, R. Tran, C. Weniger, H. Schröder, W. Quevedo, H. Laksmono, R. G. Sierra, G. Han, B. Lassalle-Kaiser, S. Koroidov, K. Kubicek, S. Schreck, K. Kunnus, M. Brzhezinskaya, A. Firsov, M. P. Minitti, J. J. Turner, S. Moeller, N. K. Sauter, M. J. Bogan, D. Nordlund, W. F. Schlotter, J. Messinger, A. Borovik, S. Techert, F. M.

31 Theory Days 14.03.2017: Day 1 ‐ X‐ray Absorption and Emission Spectroscopy Chair: Emad Aziz HZB, Berlin‐Adlershof

F. de Groot, A. Föhlisch, A. Erko, U. Bergmann, V. K. Yachandra, Ph. Wernet, and J. Yano. J. Phys. Chem. Lett. 4, 3641 (2013). [10] M. Ibek, T. Leitner, A. Erko, A. Firsov, Ph. Wernet, Rev. Sci. Instrum. 84, 103102, p. 1-9 (2013). [11] Ph. Wernet, J. Gaudin, K. Godehusen, O. Schwarzkopf, W. Eberhardt, Rev. Sci. Instrum. 82, 063114 (2011). [12] Ph. Wernet, M. Odelius, K. Godehusen, et al., Phys. Rev. Lett. 103, 013001 (2009). [13] Ph. Wernet, K. Kunnus, S. Schreck, W. Quevedo, R. Kurian, S. Techert, F. M. F. de Groot, M. Odelius, A. Föhlisch, J. Phys. Chem. Lett. 3, 3448 (2012). [14] I. Josefsson, K. Kunnus, S. Schreck, A. Föhlisch, F.M.F. de Groot, Ph. Wernet, and M. Odelius. J. Phys. Chem. Lett. 3, 3565 (2012). [15] J. Meibohm, S. Schreck, Ph. Wernet, Rev. Sci. Instrum. 85, 103102 (2014). [16] S. Schreck, G. Gavrila, C. Weniger, Ph. Wernet, Rev. Sci. Instrum. 82, 103101 (2011). [17] M. Ekimova, W. Quevedo, M. Faubel, Ph. Wernet, E. T. J. Nibbering, Structural Dynamics 2, 054301 (2015). [18] K. Kunnus, I. Rajkovic, S. Schreck, W. Quevedo, S. Eckert, M. Beye, E. Suljoti, C. Weniger, C. Kalus, S. Grübel, M. Scholz, D. Nordlund, W. Zhang, R. W. Hartsock, K. J. Gaffney, W. F. Schlotter, J. J. Turner, B. Kennedy, F. Hennies, S. Techert, Ph. Wernet, A. Föhlisch, Rev. Sci. Instrum. 83, 123109 (2012).

32 Theory Days 15.03.2017: Day 2 ‐ Photoelectron Spectroscopies and Resonant Process Chair: Robert Seidel HZB, Berlin‐Adlershof

Brief CV – Dr. Uwe Hergenhahn

Current positions: Staff Scientist Leibniz Institute of Surface Modification (HZB-IOM Joint-Photonic Lab) c/o Helmholtz-Zentrum Berlin, Albert-Einstein-Str. 15, 12489 Berlin, Germany also at: Max- Planck-Institute for Plasma Physics, 17489 Greifswald, Germany Research expertise/activities in research: Our group is active in photoionization experiments for research on electron dynamics. Its roots are in high energy resolution photoelectron spectroscopy (XPS) on molecules. In recent years, the focus has been on loosely bonded aggregates, e.g. hydrogen or van-der-Waals bonded systems. These can be investigated in the form of clusters or liquids; for the latter we have adopted the liquid jet technique invented in the last two decades to bridge the vapor pressure afforded by the liquid to the vacuum requirements of electron spectroscopy. A topic we have intensively investigated are decay modes of electronically excited ionized states. It has been found, that an important mode of relaxation proceeds by energy and/or charge transfer to neighboring atoms or molecules (even in the absence of chemical bonding), thus ionizing one of these systems. These decay modes, best known of them being Intermolecular Coulombic Decay (ICD), are probably of great importance for radiation chemistry. Moreover, we hope to make them a spectroscopic tool to investigate e.g. solvation in liquids. Although our experiments are in the energy domain, often conclusions on the ultrafast (fs) temporal dynamics of ICD can be drawn. The group always had a strong activity in new technical developments for electron spectroscopy. An area in which we were particularly active are electron-electron coincidence detection techniques. These allow to draw much deeper conclusions on radiationless decay modes, such as Auger decay and ICD, than conventional electron spectroscopy. Recent developments used both hemispherical and time-of-flight spectrometers for electron spectroscopy, the latter also with a superimposed magnetic field (‘magnetic bottle spectrometer’) to enhance electron acceptance angle.

Keywords: Photoelectron spectroscopy, PES, XPS, Auger decay, ICD

Selected 10 most important articles related to the lecture: [1] S. Marburger, O. Kugeler, U. Hergenhahn, and T. Möller, Phys. Rev. Lett. 90, 203401 (2003), doi: 10.1103/PhysRevLett.90.203401 [2] U. Hergenhahn, Vibrational structure in inner-shell ionization of molecules, J. Phys. B 37, R89 (2004): doi:10.1088/0953-4075/37/12/R01 [3] M. Mucke, M. Braune, S. Barth, M. Förstel, T. Lischke, V. Ulrich, T. Arion, U. Becker, A. Bradshaw, and U. Hergenhahn, A hitherto unrecognized source of low-energy electrons in water, Nat. Phys. 6, 143 (2010), doi: 10.1038/nphys1500

33 Theory Days 15.03.2017: Day 2 ‐ Photoelectron Spectroscopies and Resonant Process Chair: Robert Seidel HZB, Berlin‐Adlershof

[4] V. Ulrich, S. Barth, T. Lischke, S. Joshi, T. Arion, M. Mucke, M. Förstel, A.M. Bradshaw, and U. Hergenhahn, Photoelectron-Auger electron coincidence spectroscopy of free molecules: New experiments, J. Electron Spectrosc. Relat. Phenom. 183, 70 (2011), doi: 10.1016/j.elspec.2010.03.001 [5] U. Hergenhahn, Interatomic and intermolecular coulombic decay: The early years, J. Electron Spectrosc. Relat. Phenom. 184, 78 (2011), doi: 10.1016/j.elspec.2010.12.020 [6] M. Mucke, T. Lischke, T. Arion, A.M. Bradshaw, and U. Hergenhahn, Performance of a Short “magnetic Bottle” electron Spectrometer, Rev. Sci. Instrum. 83, 63106 (2012), doi: 10.1063/1.4729256 [7] M. Förstel, T. Arion, and U. Hergenhahn, Measuring the efficiency of interatomic coulombic decay in Ne clusters, J. Electron Spectrosc. Relat. Phenom. 191, 16 (2013), doi: 10.1016/j.elspec.2013.11.002 [8] T. Arion, O. Takahashi, R. Püttner, V. Ulrich, S. Barth, T. Lischke, A.M. Bradshaw, M. Förstel, and U. Hergenhahn, Conformational and nuclear dynamics effects in molecular Auger spectra: fluorine core-hole decay in CF4, J. Phys. B 47, 124033 (2014), doi: 10.1088/0953-4075/47/12/124033

34 Theory Days 15.03.2017: Day 2 ‐ Photoelectron Spectroscopies and Resonant Process Chair: Robert Seidel HZB, Berlin‐Adlershof

Introduction to photoelectron and Auger electron spectroscopy

Uwe Hergenhahn 1IOM – Leibniz Institute of Surface Modification, HZB-IOM Joint Virtual Lab, 12489 Berlin, 2IPP, Max-Planck-Institute for Plasma Physics, 17491 Greifswald, Germany [email protected] The chemical state of matter is determined by the energies of electrons, in particular those that mediate chemical bonds, or make up valence and conduction bands in bulk condensed matter. By having an electromagnetic field interact with the electrons of a material, it is possible to release single electrons into vacuum and study their energies isolated from other interactions. This technique, 'photoelectron spectroscopy' (PES), is of invaluable importance for studying electronic structure. Photoelectron spectroscopy is a single photon technique: One photon of wavelength n interacts with one electron at a time, reflected in Einstein's equation: Ekin = hn - Eb. The electron kinetic energies in vacuum, Ekin, are the quantities observed in PES. The binding energy Eb is a property specific for the material, and the orbital or band from which the electron was ionized. Its interpretation is the key to the use of PES as a probe for electronic properties. Eb is the energy required to separate the photoelectron (e-ph) to infinite distance from the sample A, which becomes ionized in the process: hn + A → A++ eph-. Strictly speaking, Eb therefore is a property of the orbitals of the ionized final state, not of the neutral ground state. However, photoelectron energies in most situations are a good measure also for orbital energies in the ground state before the photoionization. Within the Hartree-Fock approximation, identifying ground state single particle energies εi of orbital i with those measured by photoionizing this orbital is known as Koopmans' theorem.[1] Thus, in PES on an atomic gas we can expect to detect photoelectrons with a ladder of energies, according to the orbitals of the species. In practice, even for very simple atoms (starting with He) additional photoelectron lines are observed, that have been termed 'satellites'. Satellites can occur due to the multi-electron nature of the electronic state before ionization ('correlation', the ground state is described by more than one electron configuration), or can be produced by the change of electronic orbitals due to the ionization process ('relaxation', ground state orbitals might have some overlap with excited orbitals of the ionized state).[2] Photoelectron spectroscopy of molecules often reveals the bonding or non-bonding character of valence orbitals. Ionization from a bonding orbital may strongly change the molecular geometry. In its ionized state, the molecule feels like a pre-loaded spring: Production of a photoelectron spectrum with a progression of vibrational lines, pertaining to one or several quanta of vibrational energy deposited in the final state, is the consequence.[3] On the timescale of molecular vibrations, the photoionization process itself can be considered instantaneous. This is known as the Franck-Condon principle.[4] Ionization of the inner shell electrons of molecules (and materials in general) leads to element-specific information, as the binding energies of inner shell orbitals are grossly

35 Theory Days 15.03.2017: Day 2 ‐ Photoelectron Spectroscopies and Resonant Process Chair: Robert Seidel HZB, Berlin‐Adlershof

different from element to element. An early finding of utmost importance for PES was the discovery of small, but measurable energy differences for inner shell photoelectrons from the same element in different chemical states (e.g. oxidized vs. non-oxidized, partially vs. fully hydrated etc.). Discovery of this electron spectroscopy for chemical analysis (ESCA) was rewarded with the noble prize for Kai Siegbahn, and still is one of the most important applications of PES. Most intuitively the energy differences in ESCA can be explained as a final state effect: Chemical differences in the valence charge density around the ionized site A+ lead to more or less shielding of the positive charge in the inner shell, thus leading to energy differences of the photoelectron.[5] Interestingly, for molecules even ionization of inner shell orbitals also leads to vibrational excitation, which can reveal the geometries of the (very short-lived, see below) ionizes states.[6] Photoelectrons are emitted with a directional preference. For unordered samples, e.g. for photoionization of gases, or amorphous samples and for the most common case of photoionization by linearly polarized light, typically photoelectrons have a propensity for emission along the direction of the electric field vector of the light. The angular dependence of the emission pattern is then given by a cos2-function of the angle between polarization and emission direction.[7] Things get much more complicated for photoionization of bulk condensed matter having crystalline order, and will be covered in a separate lecture. From a quantum-mechanical viewpoint, photoionization is mediated by a matrix element of the electric dipole operator, applied between ground state and ionized final state.[8] (Higher multipole orders of interaction with the e.m. field do not play a role for spectroscopic application.) The square of this matrix element models the strength with which a certain orbital can be seen in the photoelectron spectrum, and is a non-trivial quantity. With respect to variation of the ionizing wavelength, typically photoelectron lines are strong at the respective ionization threshold (that is at low kinetic energy), and become weaker when the ionization energy is increased. [7] Notable exceptions are possible due to interference in the electron continuum.[9] Tabulated photoionization cross sections over a wide range of photon energies (calculated within a fairly simple, yet useful model) are available for all elements.[10] From a technical viewpoint, electron spectroscopy requires working in a vacuum as otherwise propagation of free electrons will be stopped by collisions with gas molecules. A typical pressure level is 10-6 mbar. For the actual measurement of the electron kinetic energies, most often the deflection of the electron trajectories in an electric field is used. Most widespread, due to some advantages in practical use, is the hemispherical electron analyser, in which electrons are bent onto Kepler trajectories between two electrodes shaped as concentric half-spheres.[11] A competing principle uses a time-of-flight measurement along a linear drift tube, and can have a much higher detection efficiency,[12] in particular when combined with magnetic fields.[13] Recent developments have made it possible to relax the vacuum requirements imposed on the sample, to e.g. study catalysis under realistic conditions by PES. This 'near ambient pressure PES' is one of the most exciting directions of development in this field.[14] Photoelectron spectroscopy requires a monochromatic light source in the ultra-violet or soft X-Ray range of wavelength. When PES was invented, discharge lamps or X-Ray tubes were

36 Theory Days 15.03.2017: Day 2 ‐ Photoelectron Spectroscopies and Resonant Process Chair: Robert Seidel HZB, Berlin‐Adlershof

used, but PES profited enormously when electron storage for production of synchrotron radiation became available as a light source. [7] The quasi-continuous, highly collimated, tuneable nature of SR makes it the ideal excitation source for PES, at least when the sample under investigation can be transported to a or fabricated at a suitable facility. Inner shell vacancies created by photoionization are highly unstable. They can be filled either by relaxation under X-ray emission, or in a radiationless process, which is the likely case for single vacancies of light and medium-Z elements. In this so-called Auger decay one valence electron fills the inner shell vacancy, while another one is emitted into the continuum.[15] The energy of Auger electrons is given by the energies of the inner shell vacancy and of the two final state vacancies alone, and is therefore element specific and independent of the excitation process. Auger spectra can be measured with any type of excitation source, e.g. also electron bombardment or broad band radiation. Auger electron spectroscopy amongst other purposes therefore is a popular method to check for surface contaminants in an in- vacuum experiment. Radiationless processes involving not a single atom, but two or three atoms or molecules in a weakly bonded aggregate, have recently become a subject of research and are now known as Intermolecular Coulombic Decay and Electron Transfer Mediated Decay.[16] These decay channels can be important for inner valence and for inner shell ionized states.[17]

References: [1] A. Szabo and N. Ostlund, Modern Quantum Chemistry; Dover: New York, 1996. [2] U. Becker, R. Hölzel, H.G. Kerkhoff, B. Langer, D. Szostak, R. Wehlitz, and Abstract, Near Threshold Resonance Enhancement of Neon Valence Satellites Studied with Synchrotron Radiation, Phys. Rev. Lett. 56, 1120 (1986) [3] L. Karlsson, L. Mattson, R. Jadrny, R.G. Albridge, S. Pinchas, T. Bergmark, and K. Siegbahn, Isotopic and Vibronic Coupling Effects in the Valence Electron Spectra of H216O, H218O, and D216O, J. Chem. Phys. 62, 4745 (1975). [4] P. W. Atkins and R. S. Friedman, Molecular Quantum Mechanics, Oxford University Press [5] K. Siegbahn, C. Nordling, G. Johansson, J. Hedman, P.F. Héden, K. Hamrin, U. Gelius, T. Bergmark, L.O. Werme, R. Manne, and Y. Baer, ESCA Applied to Free Molecules (North-Holland, Amsterdam, 1969); S. Svensson, Soft X-Ray Photoionization of Atoms and Molecules, J. Phys. B 38, 821 (2005) [6] U. Hergenhahn, Vibrational Structure in Inner Shell Photoionization of Molecules, J. Phys. B 37, R89 (2004) [7] V. Schmidt, Photoionization of atoms using synchrotron radiation, Rep. Prog. Phys. 55, 1483 (1992). [8] R. Santra, Concepts in X-Ray Physics, J. Phys. B 42, 023001 (2009). [9] U. Becker and D.A. Shirley, in VUV- Soft X-Ray Photoionization, edited by U. Becker and D.A. Shirley (Plenum Press, New York, 1996), pp. 13–180. [10] J.-J. Yeh and I. Lindau, Atomic Subshell Photoionization Cross Sections and Asymmetry Parameters: 1 <= Z <= 103, At. Data Nucl. Data Tables 32, 1 (1985) [11] E.H.A. Granneman and M.J. van der Wiel, in Handb. Synchrotron Radiat., edited by E.E. Koch (North-Holland, Amsterdam, 1983), pp. 367–462.

37 Theory Days 15.03.2017: Day 2 ‐ Photoelectron Spectroscopies and Resonant Process Chair: Robert Seidel HZB, Berlin‐Adlershof

[12] G. Öhrwall, P. Karlsson, M. Wirde, M. Lundqvist, P. Andersson, D. Ceolin, B. Wannberg, T. Kachel, H. Dürr, W. Eberhardt, and S. Svensson, A New Energy and Angle Resolving Electron Spectrometer - First Results, J. Electron Spectrosc. Relat. Phenomena Electron Spectrosc. 183, 125 (2011) [13] M. Mucke, T. Lischke, T. Arion, A.M. Bradshaw, and U. Hergenhahn, Performance of a Short “magnetic Bottle” electron Spectrometer, Rev. Sci. Instrum. 83, 63106 (2012). [14] A. Kolmakov, L. Gregoratti, M. Kiskinova, and S. Günther, Recent Approaches for Bridging the Pressure Gap in Photoelectron Microspectroscopy Top. Catal. 59, 448 (2016). [15] T. Åberg and G. Howat, in Corpuscles Radiat. Matter I, Handbuch d. Physik XXXI, edited by W. Mehlhorn (Springer-Verlag, Berlin, 1982), pp. 469–619. [16] U. Hergenhahn, Interatomic and Intermolecular Coulombic Decay: The Early Years, J. Electron Spectrosc. Relat. Phenom. 184, 78 (2011). [17] P. Slavíček, B. Winter, L.S. Cederbaum, and N. V Kryzhevoi, Proton-Transfer Mediated Enhancement of Nonlocal Electronic Relaxation Processes in X-Ray Irradiated Liquid Water. J. Am. Chem. Soc. 136, 18170 (2014).

38 Theory Days 15.03.2017: Day 2 ‐ Photoelectron Spectroscopies and Resonant Process Chair: Robert Seidel HZB, Berlin‐Adlershof

Brief CV – Dr. Bernd Winter Bernd Winter received his Ph.D. in physics from the Freie Universität Berlin and the Fritz- Haber-Institut der Max-Planck-Gesellschaft, Germany, and did postdoctoral studies at Argonne National Laboratory, USA, and at the Institut für Plasmaphysik in Garching, Germany. In the mid-1990s he joined the Max-Born-Institut, Berlin, where he was a staff researcher until 2009, when he moved to BESSY, now Helmholtz-Zentrum Berlin. Since January 2017 BW leads a research group at the Fritz-Haber-Institut. His current research interests include synchrotron radiation and laser spectroscopy, structure of water and aqueous solutions, and fundamental ionization, excitation, and ultrafast relaxation processes in solution.

Selected publications: [1] X-ray and Electron Spectroscopy of Water. T. Fransson, Y. Harada, N. Kosugi, N. Besley, B. Winter, J. Rehr, L. Pettersson, and A. Nilsson; Chem Rev 116: 7551-7569 (2016) [2] Relaxation Processes in Aqueous Systems upon X-ray Ionization: Entanglement of Electronic and Nuclear Dynamics. P. Slavicek, N. V. Kryzhevoi, E. F. Aziz, and B. Winter; J Phys Chem Lett 7:234- 243 (2016) [3] Valence Electronic Structure of Aqueous Solutions: Insights from Photoelectron Spectroscopy. R. Seidel, B. Winter, and S. E. Bradforth; Ann Rev Phys Chem 67: 13.1-13.23 (2016) [4] Oxidation Half-Reaction of Aqueous Nucleosides and Nucleotides via Photoelectron Spectroscopy Augmented by ab Initio Calculations. Ch. A. Schroeder, E. Pluharovǎ ,́ R. Seidel, W. P. Schroeder, M. Faubel, P. Slavícek,̌ B. Winter, P. Jungwirth, and S. E. Bradforth; J Am Chem Soc 137: 201–209 (2015) [5] On the nature and origin of dicationic, charge-separated species formed in liquid water on X-ray irradiation. S. Thürmer, M. Ončák, N. Ottosson, R. Seidel, U. Hergenhahn, S. E. Bradforth, P. Slavíček, B. Winter; Nature Chemistry 5: 590-596 (2013) [6] Photoelectron angular distributions from liquid water: Effects of electron scattering. S. Thürmer, R. Seidel, M. Faubel, W. Eberhardt, J. C. Hemminger, S. E. Bradforth, B. Winter; Phys Rev Lett 111: 173005 (2013) [7] Bond-Breaking, Electron-Pushing and Proton-Pulling: Active and Passive Roles in the Interaction between Aqueous Ions and Water as Manifested in the O 1s Auger Decay. W. Pokapanich, N. Ottosson, S. Svensson, G. Öhrwall, B. Winter, and O. Björneholm; J Phys Chem B 116 (1): 3-8 (2012) [8] Ultrafast hybridization screening in Fe3+ aqueous solution. S. Thürmer, R. Seidel, W. Eberhardt, S.E. Bradforth, and B. Winter; J Am Chem Soc 133 (32): 12528-12535 (2011) [9] Dissociation of Strong Acid Revisited: X-ray Photoelectron Spectroscopy and Molecular Dynamics Simulations of HNO3 in Water. T. Lewis, B. Winter, A.C. Stern, M.D. Baer, C.J. Mundy, D.J. Tobias, and J.C. Hemminger; J Phys Chem B 115 (30): 9445-9451 (2011) [10] Interaction between liquid water and hydroxide revealed by core-hole de-excitation. E. F. Aziz, N. Ottosson, M. Faubel, I. V. Hertel, and B. Winter; Nature 455 (7209): 89-91 (2008) [11] Photoemission from liquid aqueous solutions. B. Winter and M. Faubel; Chem Rev 106 (4): 1176- 1211 (2006) [12] Full valence band photoemission from liquid water using EUV synchrotron radiation. B. Winter, R. Weber, W. Widdra, M. Dittmar, M. Faubel, and I. V. Hertel; J Phys Chem A 108 (14): 2625-2632 (2004)

39 Theory Days 15.03.2017: Day 2 ‐ Photoelectron Spectroscopies and Resonant Process Chair: Robert Seidel HZB, Berlin‐Adlershof

[13] D(H) Atom Impact-Induced Eley-Rideal Hydrogen Abstraction Reaction Towards HD at Fully Hydrogenated C:H(D) Film Surfaces Lutterloh, C.; Schenk, A.; Biener, J.; Winter, B.; Küppers, J. Surf Sci 316, L1039-L1043 (1994) [14] Magic Numbers through Chemistry - Evidence for Icosahedral Structure of Hydrogenated Cobalt Clusters Klots,T.D.; Winter, B.J.; Parks, E.K.; Riley, S.J. J Chem Phys 92, 2110 (1990)

40 Theory Days 15.03.2017: Day 2 ‐ Photoelectron Spectroscopies and Resonant Process Chair: Robert Seidel HZB, Berlin‐Adlershof

Photoelectron spectroscopy of liquids

Bernd Winter Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin [email protected] We review soft-X-ray photoelectron spectroscopy from liquids, mostly aqueous solutions, with the main focus on liquid microjets.[1-3] Starting with an overview of the history, we summarize how this technique has advanced our understanding of the electronic structure of solutions. Also so-called ambient-pressure photoelectron-spectroscopy studies will be discussed.[4, 5] The detection of electrons emitted from an aqueous volatile solution has not been possible

Figure 1 Figure 2 Figure 3 Figure 4

before the development of techniques that allow electrons to travel sufficiently long distance to reach a detector that. In using a liquid microjet in vacuum (see Figure 1) the so-called electron inelastic mean free path is considerably increased, and enables the use of electron spectrometers as applied in surface and gas-phase studies.[6] With the application of photoelectron spectroscopy to liquid solutions, and particularly to liquid water and aqueous solutions, the important electronic structure properties can be accessed that govern solution chemistry, and that are at the heart of understanding how solutes and solvent molecules interact. Here, multiple aspects are to be explored, including solute and solvent ionization energies,[7-9] the nature of hydration structure,[10] hybridization between solute and solvent,[11] intermolecular charge and energy transfer, nuclear dynamics and reactive transient species occurring upon core-level ionization.[12] Some of these properties can be directly inferred from the direct emission of a photoelectron – the technique is then referred to as photoelectron spectroscopy [13] –, and this process is to be distinguished from electronic relaxation processes, giving rise to the emission of second-order electrons, in so- called autoionization processes. [13, 14] When referring to all processes the technique is often called photoemission. In this lecture several liquid-jet photoemission studies from a variety of solutions, characterized by very different interactions and properties will be discussed. Such differences are for instance the strength of solute – solvent interaction, the propensity a given solute may have to exist at the solution surface (see Figure 3),[15] the tendency for forming ion pairs. Results will be presented for simple electrolyte aqueous

41 Theory Days 15.03.2017: Day 2 ‐ Photoelectron Spectroscopies and Resonant Process Chair: Robert Seidel HZB, Berlin‐Adlershof

solutions, for hydrogen-bonded molecular solutes, water complexes with transition metal ions, nanoparticles, and biological relevant molecules (see Figures 2, 4) in aqueous solution. Typically, the electronic structure characterization involves the application of valence- and core-level photoelectron spectroscopy, as well as some kind of electronic relaxation processes. We first present electron binding energies of organic and inorganic atomic and small (also biologically relevant) molecular solvents, and discuss the relevance particularly of the lowest- ionization (electron detachment) energies for solution chemistry. This is followed by application of core-level photoelectron spectroscopy for investigating solute charge state and the interfacial solution structure. Here, one chief research interest is whether solutes can reside at the very top solution surface, which is of considerable relevance for atmospheric chemistry. Experimentally such information can be accessed by exploiting the electron travel length in solution through the variation of electron kinetic energy. We will address the current limitations of such experiments, and also briefly address related topics, e.g., the angular distribution of photoelectrons, and why they are important.[16, 17] The remaining part of the presentation is on the relaxation processes following core-level ionization or excitation of aqueous solutions. In these experiments one detects Auger or some other autoionization electrons, and from the spectral shapes detailed information on orbital mixing between solute and solvent orbitals can be inferred. In addition, for hydrogen-bonding systems processes can be described by an electronic relaxation that involves neighboring weakly interacting atoms or molecules, via charge or energy transfer.[14, 18-20] Future directions and challenges will be discussed.

References: [1] Winter, B. and M. Faubel, Photoemission from liquid aqueous solutions. Chemical Reviews, 2006. 106(4): p. 1176-1211. [2] Winter, B., Liquid microjet for photoelectron spectroscopy. Nucl. Intrum. Meth. A, 2009. 601(1- 2): p. 139-150. [3] Seidel, R., S. Thürmer, and B. Winter, Photoelectron spectroscopy meets aqueous solution: Studies from a vacuum liquid microjet. Phys. Chem. Lett., 2011. 2: p. 633-641. [4] Liu, Z. and H. Bluhm, Liquid/solid interfaces studied by ambient pressure HAXPES. Springer (submitted), 2015. [5] Wu, C.H., R.S. Weatherup, and M.B. Salmeron, Probing electrode/electrolyte interfaces in situ by X-ray spectroscopies: old methods, new tricks. Phys. Chem. Chem. Phys., 2015. 17: p. 30229- 30239. [6] Winter, B. and M. Faubel, Photoemission from liquid aqueous solutions. Chem. Rev., 2006. 106(4): p. 1176-1211. [7] Pluhařová, E., et al., Transforming Anion Instability into Stability: Contrasting Photoionization of Three Protonation Forms of the Phosphate Ion upon Moving into Water. J. Phys. Chem. B, 2012. 116(44): p. 13254-13264. [8] Pluhařová, E., et al., Unexpectedly Small Effect of the DNA Environment on Vertical Ionization Energies of Aqueous Nucleobases. J. Phys. Chem. Lett., 2013. 4(21): p. 3766-3769.

42 Theory Days 15.03.2017: Day 2 ‐ Photoelectron Spectroscopies and Resonant Process Chair: Robert Seidel HZB, Berlin‐Adlershof

[9] Yepes, D., et al., Photoemission Spectra and Density Functional Theory Calculations of 3d Transition Metal-Aqua Complexes (Ti-Cu) in Aqueous Solution. J. Phys. Chem. B, 2014. 118(24): p. 6850-6863. [10] Aziz, E.F., et al., Interaction between liquid water and hydroxide revealed by core-hole de- excitation. Nature, 2008. 455(7209): p. 89-91. [11] Thürmer, S., et al., Ultrafast Hybridization Screening in Fe3+ Aqueous Solution. J. Am. Chem. Soc., 2011. 133(32): p. 12528-12535. [12] Thürmer, S., et al., On the nature and origin of dicationic, charge-separated species formed in liquid water upon X-ray irradiation. Nat. Chem., 2013. 5: p. 590–596. [13] Hüfner, S., Photoelectron Spectroscopy: Principles and Applications. Solid-State Sciences 8, ed. M. Cardona, et al. 1995, Berlin, Heidelberg, New York, London, Paris, Tokyo, Hong Kong, Barcelona, Budapest: Springer-Verlag. [14] Slavíček, P., et al., Relaxation Processes in Aqueous Systems upon X-ray Ionization: Entanglement of Electronic and Nuclear Dynamics. J. Phys. Chem. Lett., 2016. 7: p. 234-243. [15] Jungwirth, P. and D.J. Tobias, Specific ion effects at the air/water interface. Chem. Rev., 2006. 106(4): p. 1259-1281. [16] Thürmer, S., et al., Photoelectron Angular Distributions from Liquid Water: Effects of Electron Scattering. Phys. Rev. Lett., 2013. 111(17): p. 173005. [17] Suzuki, Y.-I., et al., Effective attenuation length of an electron in liquid water between 10 and 600 eV. Phys. Rev. E, 2014. 90(1): p. 010302. [18] Cederbaum, L.S., J. Zobeley, and F. Tarantelli, Giant intermolecular decay and fragmentation of clusters. Phys. Rev. Lett., 1997. 79(24): p. 4778-4781. [19] Öhrwall, G., et al., Charge Dependence of Solvent-Mediated Intermolecular Coster-Kronig Decay Dynamics of Aqueous Ions. J. Phys. Chem. B, 2010. 114(51): p. 17057-17061. [20] Pokapanich, W., et al., Auger Electron Spectroscopy as a Probe of the Solution of Aqueous Ions. Journal of the American Chemical Society, 2009. 131(21): p. 7264-7271.

43 Theory Days 15.03.2017: Day 2 ‐ Photoelectron Spectroscopies and Resonant Process Chair: Robert Seidel HZB, Berlin‐Adlershof

Brief CV – Dr. Jaime Sánchez-Barriga

Current position: Staff research scientist at the synchrotron BESSY II, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin, Germany Research expertise/activities in research: My research is mainly focused on the investigation of spin-dependent, electronic and dynamical properties of topological phases of matter using laser-based and synchrotron radiation spectroscopy techniques. A topological phase in a solid is fundamentally different from any other conventional state of matter in that it is characterized by robust electronic states that are spin-polarized and protected by distinct symmetries. Therefore, my activity primarily concerns the use of spin- and angle-resolved photoemission to investigate the unprecedented properties of these symmetry-protected states, which are very promising for the exploitation of spin-dependent transport in future information technology. One of my major research interests concerns the modification of topological properties via light-matter interaction, which is not only of fundamental significance but also important in the context of novel opto-spintronic applications. Hence, part of my research is focused on controlling and coherently manipulating topological phases of matter and their excitations. To this end, I utilize time-, spin- and angle-resolved photoemission spectroscopy to investigate the out-of- equilibrium response of topological states of matter to femtosecond-laser excitation. Other areas of my research activities run along the fundamental electronic properties of ferromagnetic 3d metals, quantum-well states, and graphene. In the latter, of primary focus in my research is control of the Rashba effect in graphene grown on metals via spin-orbit interaction.

Keywords: Topological phases of matter, electronic structure, spintronics, opto-spintronics, ultrafast electron dynamics, femtosecond spin dynamics, spin currents, topological quantum- phase transitions, graphene, Rashba effect

Selected 10 most important articles related to the lecture: [1] Nonmagnetic band gap at the Dirac point of the magnetic topological insulator (Bi1-xMnx)2Se3, J. Sánchez-Barriga, A. Varykhalov, G. Springholz, H. Steiner, R. Kirchschlager, G. Bauer, O. Caha, E. Schierle, E. Weschke, A.A. Ünal, S. Valencia, M. Dunst, J. Braun, H. Ebert, J. Minár, E. Golias, L.V. Yashina, A. Ney, V. Holy, V and O. Rader, Nature Communications 7, 10559 (2016) [2] Ultrafast spin-polarization control of Dirac fermions in topological insulators, J. Sánchez-Barriga, E. Golias, A. Varykhalov, J. Braun, L.V. Yashina, R. Schumann, J. Minár, H. Ebert, O. Kornilov and O. Rader, Phyiscal Review B 93, 155426 (2016); Editor’s suggestion [3] Tunable Fermi level and hedgehog spin texture in gapped graphene, A. Varykhalov, J. Sánchez- Barriga, D. Marchenko, P. Hlawenka, P. S. Mandal and O. Rader, Nature Communications 6, 7610 (2015) [4] Observation of quantum-tunneling-modulated spin texture in ultrathin topological insulator films, M. Neupane, A. Richardella, J. Sánchez-Barriga, S.-Y. Xu, N. Alidoust, I. Belopolski, C. Liu, G. Bian,

44 Theory Days 15.03.2017: Day 2 ‐ Photoelectron Spectroscopies and Resonant Process Chair: Robert Seidel HZB, Berlin‐Adlershof

D. Zhang, D. Marchenko, A. Varykhalov, O. Rader, M. Leandersson, T. Balasubramanian, T.-R. Chang, H.-T. Jeng, S. Basak, H. Lin, A. Bansil, N. Samarth, and M. Z. Hasan, Nature Communications 5, 3841 (2014) [5] Photoemission of Bi2Se3 with Circularly Polarized Light: Probe of Spin Polarization or Means for Spin Manipulation? J. Sánchez-Barriga, A. Varykhalov, J. Braun, S.-Y. Xu, N. Alidoust, O. Kornilov, J. Minár, K. Hummer, G. Springholz, G. Bauer, R. Schumann, L. V. Yashina, H. Ebert, M. Z. Hasan, and O. Rader, Physical Review X 4, 011046 (2014) [6] Reversal of the Circular Dichroism in Angle-Resolved Photoemission from Bi2Te3, M.R. Scholz, J. Sánchez-Barriga, J. Braun, D. Marchenko, A. Varykhalov, M. Lindroos, Y.J. Wang, H. Lin, A. Bansil, J. Minár, H. Ebert, A. Volykhov, L.V. Yashina and O. Rader, Physical Review Letters 110, 216801 (2013) [7] Tolerance of topological surface states towards magnetic moments: Fe on Bi2Se3, M.R. Scholz, J. Sánchez-Barriga, D. Marchenko, A. Varykhalov, A. Volykhov, L.V. Yashina and O. Rader, Physical Review Letters 108, 256810 (2012) [8] Strength of Correlation Effects in the Electronic Structure of Iron, J. Sánchez-Barriga, J. Fink, V. Boni, I. Di Marco, J. Braun, J. Minár, A. Varykhalov, O. Rader, V. Bellini, F. Manghi, H. Ebert, M. I. Katsnelson, A. I. Lichtenstein, O. Eriksson, W. Eberhardt, and H. A. Dürr, Physical Review Letters 103, 267203 (2009) [9] Is there a Rashba effect in graphene on 3d ferromagnets?, O. Rader, A. Varykhalov, J. Sánchez- Barriga, D. Marchenko, A. Rybkin and A.M. Shikin, Physical Review Letters 102, 057602 (2009); [10] Electronic and Magnetic Properties of Quasifreestanding Graphene on Ni, A. Varykhalov, J. Sánchez-Barriga, A.M. Shikin, C. Biswas, E. Vescovo, A. Rybkin, D. Marchenko and O. Rader, Physical Review Letters 101, 157601 (2008)

45 Theory Days 15.03.2017: Day 2 ‐ Photoelectron Spectroscopies and Resonant Process Chair: Robert Seidel HZB, Berlin‐Adlershof

Spin- and angle-resolved photoemission and its application to topological insulators

Jaime Sánchez-Barriga and Oliver Rader Helmholtz-Zentrum Berlin [email protected], [email protected] This talk combines an introduction to spin- and angle-resolved photoemission with the investigation of basic properties of the novel material class of topological insulators. Photoelectron spectroscopy is the prime method to probe the electronic band structure of occupied states. At first, the three-step model of photoemission is introduced starting with Albert Einstein’s explanation of the photoelectric effect. This model leads naturally to the importance of the energy dependence of the inelastic mean free path of electrons and its consequences for the probing depth of the method [1,2]. The basis for angle-resolved photoemission is laid in the conservation rules for electron momentum in the third step of the model [3,4]. The differences in the measurement of two- and three-dimensional band structures and the role of the inner potential are discussed. To this end, the concept of band structure is related to orbital symmetry [5] and it is demonstrated how the linear light polarization is used to distinguish electronic states of different symmetries [6]. With the example of copper, the application of these rules to the measurement of the Fermi surface is demonstrated which becomes possible due to the introduction of modern types of electrostatic analyzers [7]. Low-dimensional systems play a major role as subjects for photoemission investigations, and the method of Cooper minimum spectroscopy [8] can be used to further enhance the signal from diluted systems such as impurities. We will demonstrate its use for monoatomic chains at stepped crystal surfaces [9]. The concept of surface states and resonances is introduced along with bulk band projections. A famous surface state of tungsten is discussed [10]. The identification of surface states is often supported by adsorption measurements, and an example of its effect is shown for iron [11]. With the knowledge that bulk band gaps can effectively confine electronic states in metals, the foundations are laid for creating two- and one-dimensional states at surfaces, and examples involving noble metals are given. We will discuss the importance of broadening effects of the electron as well as the photoemission hole. Spin-orbit interaction plays a fundamental role for topological insulators. It is also the governing principle of spin polarimetry in spin-resolved photoemission [13-15]. We will show the principle and a typical setup. As an important effect, the excitation of spin-polarized photoelectrons by circularly polarized light is described for the example of GaAs which is an important photocathode [16]. This method is also used for the generation of spin-polarized electrons in the complementary method of inverse photoemission which probes unoccupied

46 Theory Days 15.03.2017: Day 2 ‐ Photoelectron Spectroscopies and Resonant Process Chair: Robert Seidel HZB, Berlin‐Adlershof

states. For the two principle sources of polarized electrons in solids, spin orbit interaction and ferromagnetism, examples involving quantum well states are given. Topological insulators have an either 2D or 3D insulating bulk and 1D or 2D surface states protected by time-reversal symmetry [17-20]. Strong spin orbit interaction lifts the spin degeneracy of the surface states which form a Dirac-like linear dispersion with a peculiar spin texture. With these properties, the topological surface state are a highly interesting subject for ultrafast spin dynamics, and in the end of the presentation, time-, spin-, and angle- resolved photoemission data will be discussed for a typical topological insulator with the focus on spin manipulation and spin-current generation.

References: [1] C. D. Wagner, W. M. Riggs, L. E. Davis, J. F. Moulder, G. E. Muilenberg: Handbook of X-Ray Photoelectron Spectroscopy, Physical Electronics Division, Perkin-Elmer Corporation, Eden Prairie (Minnesota), 1979 [2] Briggs, D. und Seah, M. P. (Hrsg.); Practical Surface Analysis Volume I, John Wiley & Sons, Chichester, 1990 [3] S. D. Kevan (ed.), Angle-Resolved Photoemission, Elsevier, Amsterdam, 1992 [4] S. Hüfner, Photoelectron spectroscopy - Pinciples and applications, Springer, Berlin, 2003 [5] R. Hoffmann, Solids and Surfaces: A Chemist's View of Bonding in Extended Structures, Wiley, 1989 [6] P. Thiry, Ph. D. Thesis, Université Pièrre et Marie Curie, Paris, 1981 [7] F. Matsui et al. Phys. Rev. B (2005) [8] J. W. Cooper, Phys. Rev. 128, 681 (1962) [9] A. Dallmeyer et al., Phys. Rev. B 61, 2254 (2000) [10] A. Feydt et al., Phys. Rev. B (1998) [11] Turner and Erskine, Phys. Rev. B (1984) [12] C. Pampuch et al., Phys. Rev. Lett. (2000) [13] J. Kessler, Polarized Electrons, Springer, Berlin, 1976 [14] G. C. Burnett, T. J. Monroe, and F. B. Dunning, Rev. Sci. Instrum. 65, 1893 (1994) [15] C. Tusche et al., Ultramicroscopy 159, 520 (2015) [16] Pierce, Meier, Phys. Rev. B (1978) [17] B. A. Bernevig and T. L. Hughes, Topological Insulators and Topological Superconductors, Princeton University Press, Princeton (2013). [18] M. Franz and L. Molenkamp (eds.), Topological Insulators, Elsevier, Amsterdam (2013). [19] M. Z. Hasan and C. L. Kane, Colloquium: Topological insulators, Rev. Mod. Phys. 82, 3045 (2010). [20] X.-L. Qi and S.-Ch. Zhang, Topological insulators and superconductors, Rev. Mod. Phys. 83 , 1057 (2011).

47 Theory Days 15.03.2017: Day 2 ‐ Photoelectron Spectroscopies and Resonant Process Chair: Robert Seidel HZB, Berlin‐Adlershof

Brief CV – Prof. Dr. Olle Björneholm

Current positions: Professor in physics at Division of Molecular and Condensed Matter Physics, Department of Physics and Astronomy, Uppsala University, Sweden. Director of the Center for Photon Science at Uppsala University. Research expertise/activities in research: My present research interest is primarily concerned with phenomena and processes in liquids studied by synchrotron radiation-based spectroscopic techniques, mainly XPS. I study how the composition of aqueous solutions differs between surface and bulk. This is connected to atmospheric aerosols, which affect the global radiative balance, directly by scattering of sunlight and thus increasing Earth’s albedo, and indirectly by being a major source of condensation nuclei for the formation of clouds. It is estimated that the aerosols counteract the green house effect by ≈1/3, but the effects of aerosols are identified by IPCC as a key uncertainty in predicting climate change. The surface is important for aerosols due to their small size, but surface effects are not generally taken into account in current climate models. To include surface effects in climate models, it is paramount to improve our molecular level understanding of atmospheric surface phenomena and processes.

Keywords: synchrotron radiation, XPS, x-ray photoelectron spectroscopy, surface, aerosol, atmosphere

Selected 10 most important articles related to the lecture: [1] Large variations in the propensity of aqueous oxychlorine anions for the solution/vapor interface, N. Ottosson, R. Vácha, E. F. Aziz, W. Pokapanich, W. Eberhardt, S. Svensson, G. Öhrwall, P. Jungwirth, O. Björneholm and B. Winter, J. Chem. Phys 131, 124706 (2009) [2] The influence of concentration on the molecular surface structure of simple and mixed aqueous electrolytes, N Ottosson, J Heyda, E Wernersson, W Pokapanich, S Svensson, B Winter, G Öhrwall, P Jungwirth and O Björneholm, Physical Chemistry Chemical Physics 12, 10693 (2010) [3] The Protonation State of Small Carboxylic Acids at the Water Surface from Photoelectron Spectroscopy, N. Ottosson, E. Wernersson, J. Söderström, W. Pokapanich, S. Kaufmann, S. Svensson, I. Persson, G. Öhrwall, and O. Björneholm, Phys. Chem. Chem. Phys. 13, 12261 (2011) [4] Surface/bulk partitioning and acid/base speciation of aqueous decanoate: direct observations and atmospheric implications, NL Prisle, N Ottosson, G Öhrwall, J Söderström, M Dal Maso and O Björneholm, Atmos. Chem. Phys. Discuss. 12, 12227 (2012) [5] The Surface Behavior of Hydrated Guanidinium and Ammonium Ions: A Comparative Study by Photoelectron Spectroscopy and Molecular Dynamics, Josephina Werner, Erik Wernersson, Victor Ekholm, Niklas Ottosson, Gunnar Öhrwall, Jan Heyda, Ingmar Persson, Johan Söderström, Pavel Jungwirth and Olle Björneholm, J. Phys. Chem. B 118, 7119 (2014) [6] Succinic acid in aqueous solutions: Connecting microscopic surface composition and macroscopic surface tension, Josephina Werner, Jan Julin, Maryam Dalirian, Nønne L. Prisle, Gunnar Öhrwall, Ingmar Persson, Olle Björneholm, and Ilona Riipinen, Phys. Chem. Chem. Phys.16, 21486 (2014)

48 Theory Days 15.03.2017: Day 2 ‐ Photoelectron Spectroscopies and Resonant Process Chair: Robert Seidel HZB, Berlin‐Adlershof

[7] Acid-base Speciation of Carboxylate Ions in the Surface Region of Aqueous Solutions in the Presence of Ammonium and Aminium Ions, Gunnar Öhrwall, Nønne L. Prisle, Niklas Ottosson, Josephina Werner, Victor Ekholm, Marie-Madeleine Walz, and Olle Björneholm, J. Phys. Chem. B 119, 4033 (2015) [8] Surface behavior of amphiphiles in aqueous solution: a comparison between different pentanol isomers, M-M Walz, C Caleman, J Werner, V Ekholm, D Lundberg, NL Prisle, G Öhrwall and O Björneholm, Phys. Chem. Chem. Phys. 17, 14036 (2015) [9] Alcohols at the aqueous surface: chain length and isomer eﬀects, M.-M. Walz, J. Werner, V. Ekholm, N. L. Prisle, G. Öhrwall and O. Björneholm, Phys. Chem. Chem. Phys. 18, 6648 (2016) [10] Surface partitioning in organic-inorganic mixtures contributes to the size-dependency of the phase-state of atmospheric nanoparticles, J Werner, M Dalirian, M-M Walz, V Ekholm, U Wideqvist, S Lowe, G Öhrwall, I Persson, I Riipinen, and O Björneholm, Environmental Science & Technology 50, 7434 (2016)

49 Theory Days 15.03.2017: Day 2 ‐ Photoelectron Spectroscopies and Resonant Process Chair: Robert Seidel HZB, Berlin‐Adlershof

Applications of Photoelectron Spectroscopy for Atmospheric Studies

Olle Björneholm Division of Molecular and Condensed Matter Physics, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden [email protected] Atmospheric aerosols partially counteract the green-house effect by cooling the Earth via reflection of solar radiation (the direct effect), and promoting cloud formation (the indirect effect), see fig. 1. According to the UN climate change panel IPCC, the magnitude of these effects is the major uncertainty in climate change prediction (1), and it is crucial to constrain these better to improve climate modeling. Aerosols are microscopic particles with a large surface-to-volume ratio, which makes the surface important for the properties. As the chemical composition differs between surface and bulk, it has become evident that a description using the average composition of an aerosol particle is insufficient to describe its climatologically relevant properties. I will discuss how to use advanced synchrotron-radiation- based spectroscopy to study atmospherically relevant aqueous surfaces and aerosols. In the atmosphere there are species of both natural and anthropogenic origin incorporated

Figure 1: Aerosols origin and effects (left), schematic of an organic molecule at an aqueous aerosol surface (right)

50 Theory Days 15.03.2017: Day 2 ‐ Photoelectron Spectroscopies and Resonant Process Chair: Robert Seidel HZB, Berlin‐Adlershof

into aqueous aerosols. This includes salt ions from the sea, organic molecules from both direct emissions and decomposition of biomaterial, soot from combustion, pollutants and mineral particles, see fig. 1. Organic compounds represent a significant fraction (20-90%, depending on the environment) of the submicron aerosol mass (2). Many atmospheric organic compounds are formed by oxidation of primary organics (3). The products are further influenced by other chemical reactions and ionizing radiation, resulting in a broad range of complex compositions, denoted Secondary Organic Aerosols (SOA) (2-6). The chemical composition and structure of aerosols determine their climate effects, both their efficiency as cloud condensation nuclei (CCN), and how much they scatter solar radiation. Due to the small size of aerosols, surface phenomena and processes become important. First, surface-active species affect the surface tension, which is a key parameter in Köhler theory of water condensation into liquid droplets. Second, enrichment of organics into a hydrophobic surface layer may strongly influence condensation and evaporation rates (7), and thus aerosol growth and CCN activity. Third, the surface composition strongly affects aerosol chemical activity. Fourth, for small aerosols, which are microscopic systems, surface enrichment of a species will lead to bulk depletion, affecting macroscopic properties. These examples illustrate that important properties of aerosols affecting climate are influenced by the composition and microscopic internal spatial distribution of chemical species. Surface effects are, however, not generally taken into account in current climate models. The atmospheric science community is now beginning to recognize the need to include surface effects in climate models (8), making it crucial to improve our molecular level understanding of atmospheric surface phenomena and processes. The liquid-vapor interface of water, henceforth denoted the water surface, is of tremendous importance in the atmosphere. For solutions of inorganic salts, the classic model with a surface depleted of ions is now being replaced by a model in which ions may be present, and even enriched, at the surface (9-13). There are both enthalpic and entropic factors contributing to the surface propensity ranging from depletion to enrichment (14), but there is considerable uncertainty of the magnitude of these factors, and the amount of ions at the surface. I will discuss examples of the surface propensity of ionic electrolyte systems, for example the oxidation-state-dependent surface propensity of oxychloro ions (15), and the surface enrichment of bromide due to the collective effect competitive solvation (16), a possible mechanism for the higher-than-expected importance of bromine in atmospheric chemistry. It has recently been suggested that also another collective effect, ion-pairing, may influence the surface propensity of otherwise surface-depleted ions (17). Similarly, molecular solutions are found to exhibit pronounced differences in composition and concentration between surface and bulk (18, 19). This includes both enrichment and depletion at the surface, the enhanced surface propensity of organics by inorganic ions due to competition for solvation, known as “salting out”, and effects of temperature and pH. I will describe studies of selected representatives of important types of molecules (alcohols, aromatics, amines, carboxylic acids and amino acids,), obtaining detailed information about the surface in term of speciation (e.g. protonated/deprotonated acids/bases) (20), molecular orientation (21), quantitative measures of the surface concentration and/or enrichment

51 Theory Days 15.03.2017: Day 2 ‐ Photoelectron Spectroscopies and Resonant Process Chair: Robert Seidel HZB, Berlin‐Adlershof

factors from “Langmuir curves” or comparison to bulk (21-23), as well as surface-specific acid-base reactions (24, 25). The acid/base characteristics of the aqueous surface is a current hot topic, with mutually contradictory results in the literature (20, 26-28). The pure water surface may be different from the bulk in terms of concentration of H3O+ and OH- ions, and there are considerable discrepancies between various experimental and theoretical results, spanning from the surface being basic to the surface being acidic (14, 26-28). Connected to this is the behavior of an acid or base at the aqueous surface (20, 28). X-ray Photoelectron Spectroscopy (XPS) results for aqueous acetic acid show the surface to be different from the bulk in terms of both the solute amount and speciation due to the different surface propensity of the protonated or deprotonated species (20). To what extent there are also differences due to changes in water pH or acid pKa, is an open question. From these and other studies a new picture of aqueous surfaces is emerging, in which the surfaces are seen to differ from the bulk in terms of fundamental chemical properties. I will discuss how we can learn about atmospherically relevant aqueous interfaces using XPS and synchrotron radiation (SR). XPS is one of the main techniques for surface characterization of solids as it offers a unique combination of chemical selectivity and surface sensitivity. Aqueous systems were for long not possible to study with XPS due to the high vapor pressure of water, but this obstacle was solved by the development of the liquid micro jet by Manfred Faubel (29).

References: [1] Intergovernmental Panel on Climate Change, Climate Change 2013: The Physical Basis (2013). [2] J. L. Jimenez et al., Evolution of organic aerosols in the atmosphere. Science. 326, 1525 (2009). [3] J. H. Kroll et al., Carbon oxidation state as a metric for describing the chemistry of atmospheric organic aerosol. Nat. Chem. 3, 133 (2011). [4] M. Kanakidou et al., Organic aerosol and global climate modelling: a review. Atmos. Chem. Phys. 5, 1053–1123 (2005). [5] A. L. Robinson et al., Rethinking organic aerosols: semivolatile emissions and photochemical aging. Science. 315, 1259 (2007). [6] A. H. Goldstein, I. E. Galbally, Known and unexplored organic consistuents in the Earth’s atmosphere. Environ. Sci. Technol. 41, 1514 (2007). [7] J. F. Davies, R. E. H. Miles, A. E. Haddrell, J. P. Reid, Influence of organic films on the evaporation and condensation of water in aerosol. PNAS 110, 8807 (2013). [8] C. R. Ruehl, D. F. James, K. R. Wilson, Droplet Formation on Organic Aerosols. Science. 351, 1447 (2016). [9] P. B. Petersen, R. J. Saykally, On the nature of ions at the liquid water surface. Annu. Rev. Phys. Chem. 57, 333 (2006). [10] P. Jungwirth, B. Winter, Ions at aqueous interfaces: from water surface to hydrated proteins. Annu. Rev. Phys. Chem. 59, 343 (2008). [11] R. R. Netz, D. Horinek, Progress in modeling of ion effects at the vapor/water interface. Annu. Rev. Phys. Chem. 63, 401 (2012).

52 Theory Days 15.03.2017: Day 2 ‐ Photoelectron Spectroscopies and Resonant Process Chair: Robert Seidel HZB, Berlin‐Adlershof

[12] P. Jungwirth, D. J. Tobias, Molecular Structure of Salt Solutions: A New View of the Interface with Implications for Heterogeneous Atmospheric Chemistry. J. Phys. Chem. B. 105, 10468 (2001). [13] D. Liu, G. Ma, L. M. Levering, H. C. Allen, Vibrational Spectroscopy of Aqueous Sodium Halide Solutions and Air - Liquid Interfaces : Observation of Increased Interfacial Depth. J. Phys. Chem. B. 108, 2252 (2004). [14] J. S. Hub et al., Thermodynamics of hydronium and hydroxide surface solvation. Chem. Sci. 5, 1745 (2014). [15] N. Ottosson et al., Large variations in the propensity of aqueous oxychlorine anions for the solution/vapor interface. J. Chem. Phys. 131, 124706 (2009). [16] N. Ottosson et al., The influence of concentration on the molecular surface structure of simple and mixed aqueous electrolytes. Phys. Chem. Chem. Phys. 12, 10693 (2010). [17] V. Venkateshwaran, S. Vembanur, S. Garde, Water-mediated ion – ion interactions are enhanced at the water vapor – liquid interface. PNAS. 111, 8729 (2014). [18] G. L. Richmond, Structure and bonding of molecules at aqueous surfaces. Annu. Rev. Phys. Chem. 52, 357 (2001). [19] M. Mucha et al., Unified molecular picture of the surfaces of aqueous acid, base, and salt solutions. J. Phys. Chem. B. 109, 7617 (2005). [20] N. Ottosson et al., The protonation state of small carboxylic acids at the water surface from photoelectron spectroscopy. Phys. Chem. Chem. Phys. 13, 12261 (2011). [21] M. Walz et al., Surface behavior of amphiphiles in aqueous solution : a comparison between different. Phys. Chem. Chem. Phys. 17, 14036 (2015). [22] M.-M. Walz et al., Alcohols at the aqueous surface: chain length and isomer effects. Phys. Chem. Chem. Phys. 18, 6648 (2016). [23] J. Werner et al., Surface Behavior of Hydrated Guanidinium and Ammonium Ions: A Comparative Study by Photoelectron Spectroscopy and Molecular Dynamics. J. Phys. Chem B. 118, 7119 (2014). [24] N. L. Prisle et al., Surface/bulk partitioning and acid/base speciation of aqueous decanoate: direct observations and atmospheric implications. Atmos. Chem. Phys. 12, 12227 (2012). [25] G. Öhrwall et al., Acid–Base Speciation of Carboxylate Ions in the Surface Region of Aqueous Solutions in the Presence of Ammonium and Aminium Ions. J. Phys. Chem. B. 119, 4033 (2015). [26] R. J. Saykally, Air/water interface: Two sides of the acid-base story. Nat. Chem. 5, 82 (2013). [27] H. Mishra et al., Brønsted basicity of the air-water interface. PNAS 109, 18679 (2012). [28] Y. Tabe, N. Kikkawa, H. Takahashi, A. Morita, Surface acidity of water probed by free energy calculation for trimethylamine protonation. J. Phys. Chem. C. 118, 977 (2014). [29] M. Faubel, B. Steiner, J. P. Toennies, Photoelectron spectroscopy of liquid water, some alcohols, and pure nonane in free micro jets. J. Chem. Phys. 106, 9013 (1997).

53 Theory Days 16.03.2017: Day 3 – Laser Light Sources & Time‐Resolved Spectroscopy Chair: Iain Wilkinson HZB, Berlin‐Adlershof

Brief CV – Dr. Mojtaba Hajialamdari

Current position: Postdoctoral Researcher, Institute of Methods for Material Development, Helmholtz Zentrum Berlin, 2016-present. Research expertise/activities in research: My field of research is ultrashort pulse lasers specifically the development of these systems for unique applications. I deal with lasers, generation and measurement of ultrashort pulses, nonlinear optics, fiber optics, and interaction of ultrashort pulses with matter. I obtained my PhD in Atomic/Molecular/Optical Physics from the University of Waterloo, Canada in 2013 during which I worked on the development of a tunable two-color ultrafast Yb:fiber chirped pulse amplifier system and a tunable ultrafast mid-infrared radiation source. Since January 2016 and as a postdoctoral researcher I am part of a team at the Institute of Helmholtz Zentrum Berlin working on the design and construction of an infrared optical parametric chirped pulse amplifier (IR-OPCPA) system with the output of 15 fs laser pulses, 250 µJ pulse energy and 50 kHz repetition rate at the center wavelength 2.1 µm. The IR- OPCPA is pumped by a commercial Yb:YAG disk laser with the output of 1 ps laser pulses, 8mJ pulse energy and 50 kHz repetition rate at the center wavelength 1.03 µm. The IR-OPCPA output will be used for the generation of ultrashort pulse radiation in the water window x-ray range (280-530 eV) by high harmonic generation (HHG). The ultrashort x-ray pulses will be used in time-resolved pump-probe experiments to study the atomic/molecular dynamics within temporal and spatial atomic resolution scales. HHG is produced by focusing an intense ultrashort laser pulse into a solid or gas target. In HHG, considerable effort has been devoted to increasing the highest harmonic energy called cut-off frequency with an increased photon flux. OPCPA has been proven to be an excellent laser diver for HHG due to its generosity with bandwidth and energy/power as well as the wavelength tunability. Although Ti:sapphire laser is excellent in terms of its femtosecond pulse output, it is limited to a few watts output power at room temperature due to the thermal lensing that deteriorates the laser pulse or damages the Ti:sapphire crystal. Thus, one has to sacrifice the output power for an increased pulse energy. On the contrary to a laser amplifier that is an energy storage, OPCPA is energy/power scalable due to the parametric amplification in which energy is exchanged between pump and signal in a nonlinear optical crystal without the necessity of storing the pump energy in the nonlinear medium. Thus, thermal effects can be minimized to a great extent. In addition, a large bandwidth supporting optical pulses with a few femtosecond duration at a desired center wavelength can be achieved by carefully designing the OPCPA system. This has flourished the research on developing best performance OPCPA laser systems as the laser driver for HHG. The research objectives are to optimize wavelength, increase bandwidth/decrease pulse duration and scale up the pulse energy and output power of the OPCPA systems that are tailored to the needs of a specific HHG system.

54 Theory Days 16.03.2017: Day 3 – Laser Light Sources & Time‐Resolved Spectroscopy Chair: Iain Wilkinson HZB, Berlin‐Adlershof

Keywords: Ultrashort pulse lasers, nonlinear optics, optical parametric chirped pulse amplifiers, laser matter/plasma interaction.

Selected important articles related to the lecture: [1] M. Hajialamdari, D. Strickland, Tunable Mid-Infrared Source From an Ultrafast Two-Color Yb:Fiber Chirped Pulse Amplifier, Opt. Lett., 37, 3570, 2012. [2] M. Hajialamdari, A.M. Al-Kadry, and D. Strickland, Modeling of a Two-Color, Two-Stage, Ultrafast Yb-Doped Fiber Amplifier, Opt. Comm., 284, 2843, 2011.

55 Theory Days 16.03.2017: Day 3 – Laser Light Sources & Time‐Resolved Spectroscopy Chair: Iain Wilkinson HZB, Berlin‐Adlershof

Introduction to lasers, non-linear optics and ultrashort laser pulses

Mojtaba Hajialamdari Institute of Methods for Material Development, Helmholtz Zentrum Berlin, Germany [email protected] Lasers, nonlinear optics and ultrafast lasers emitting ultrashort pulses have become immensely broad multidisciplinary fields. Hence, there is too much material to fit in a two- hour lecture. I will present some general topics and explain the ultrafast Ti:sapphire laser that we are using as well as an optical parametric chirped pulse amplifier (OPCPA) system that we will be constructing at the Helmholtz Zentrum Berlin institute to study ultrafast electronic dynamics.

Part 1- Introduction to lasers Laser is an acronym for light amplification by stimulated emission of radiation. Lasers are devices that generate (laser oscillator) or amplify (laser amplifier) coherent radiation. In 1960, T. H. Maiman demonstrated the first working optical laser from synthesized ruby crystal. Typically, a laser consists of 1- a gain medium to amplify the radiation, 2- an optical resonator to provide feedback, and 3- a mechanism to pump the gain medium. In ruby laser, the gain medium is chromium ions doped in the Al2O3 crystal. A simple laser resonator consists of a pair of mirrors located on each end of the laser gain medium and perpendicular to the optical axis. In the first ruby laser, the optical resonator was constructed by silver coating on two parallel faces of the ruby crystal. A high-power flash lamp surrounding the ruby rod was used to pump it optically. After the invention of the ruby laser, other materials as well as novel laser resonators and pumping schemes have been intensively researched. In addition, a wide variety of liquid solutions, gases, vapours and solid state media (including crystals and semiconductors) have been used as the gain materials in lasers. The free electron laser is another type of laser without a gain medium which is not covered in this lecture. Some of the invented lasers have not been commercialized for technical reasons, high costs, a lack of application and so on. Some were used for research, medical and industrial applications but have been replaced by novel laser systems. For example, researchers relied on dye lasers for its high energy and short pulse output before the widespread use of Ti:sapphire lasers. The laser theory has remained unchanged for over fifty years. General textbooks on lasers published in the past decades will continue to be used for many years to come. In this part, I will explain the performance of typical lasers from Ref. [1]. The following topics will be presented:

1. Some important concepts in lasers; sections 1.1, 1.2, 1.3, 1.4.

2. Saturation and gain coefficient; section 2.8.

3. Threshold pump power; sections 6.3.3, 6.3.4.

56 Theory Days 16.03.2017: Day 3 – Laser Light Sources & Time‐Resolved Spectroscopy Chair: Iain Wilkinson HZB, Berlin‐Adlershof

4. Fabry-Perot resonator, resonant longitudinal modes and fineness; section 4.5.

5. Schawlow-Townes linewidth limit; section 7.9.

6. Spatial modes and Gaussian mode; Sections 4.6, 4.7.

7. Laser resonators; section 5.1.

8. Photon life time and Q factor; section 5.3.

9. Resonator stability condition; section 5.4.

10. Continuous wave laser behaviour in four-level system; sections 7.2.1, 7.3.1.

11. Multimode oscillation; section 7.7.

12. Single-mode oscillation; section 7.9. Interested students can also see Chapter 11 ‘Lasers and Coherent Light Sources’ in the ‘Handbook of Lasers and Optics’ Ref. [2].

Part 2- Nonlinear optics Nonlinear optics deals with the interaction of intense laser with matter. Second harmonic generation can be considered as the first observation of nonlinear optics. The interaction of light with matter can be conveniently understood by the polarization of a material system that is induced by an optical electric field. Nonlinear optical phenomena occur when the polarization has a nonlinear response to the strength of the optical electric field. Depending on the characteristic nonlinear response of a material system, one may need tens of MW/cm2 to GW/cm2 light intensity to observe a significant nonlinear optical response from the material. Nonlinear optics has found many applications in science and technology. For example, nonlinear optical mechanisms such as second harmonic generation, sum- and difference- frequency generation, optical parametric amplification and self-phase modulation have been used for generating optical frequencies that are not available from laser materials. The green light from a green laser pointer is generated by frequency doubling of the output of a diode pumped solid state laser in such a way that the 808nm emission from an AlGaAs semiconductor laser optically pumps a neodymium-doped laser crystal lasing at the 1064nm which is then frequency doubled by a KTP crystal to the 532nm green light. At the Institute of Helmholtz Zentrum Berlin, an infrared optical parametric chirped pulse amplifier (IR-OPCPA) system that emits ultrashort infrared pulses is currently under development. The output of the system will be used to generate ultrashort pulse XUV/X-ray radiations by high harmonic generation. The ultrashort XUV/X-ray pulses will be used in time- resolved pump-probe experiments to study the atomic/molecular dynamics within temporal and spatial atomic resolution scales. In the IR-OPCPA system, ultrashort laser pulses are amplified by means of nonlinear optical crystals. The scalability of the energy/power output of the laser amplifier is due to its energy storage characteristics. However, the energy/power output of the OPCPA system is scalable without

57 Theory Days 16.03.2017: Day 3 – Laser Light Sources & Time‐Resolved Spectroscopy Chair: Iain Wilkinson HZB, Berlin‐Adlershof

the necessity of storing the pump energy in the nonlinear medium. This is because of the parametric amplification process by which energy is exchanged between pump and signal fields in the nonlinear optical crystal. Thus, thermal effects can be minimized to a great extent. In addition, optical pulses with a few femtosecond duration at a desired center wavelength as well as a broad wavelength tunability range can be achieved from OPCPA systems. Hence, OPCPA systems are indispensable tools in modern spectroscopy. In this part, I will give an introduction to nonlinear optics and an overview on some selected nonlinear optical phenomena from Ref. [3]. Then I will present the ultrafast IR-OPCPA system which is under development at the institute of HZB. The following topics will be presented.

1. Introduction to nonlinear optics; section 1.1

2. Second harmonic, sum- and difference-frequency generation; section 1.2.1 to 1.2.4.

3. Optical parametric oscillation; section 1.2.5.

4. Third order nonlinear optical processes; section 1.2.6.

5. Intensity-dependent refractive index (Kerr effect); section 1.2.8.

6. Self-focusing, self-trapping and multi-filamentation of light; section 7.1.

7. Wave-equation description of nonlinear optical interactions; section 2.1.

8. Difference-frequency generation and parametric amplification; section 2.8.

9. Phase matching; section 2.3.

10. Optical parametric chirped pulse amplifier; Ref. [4], [5]

Part 3- Ultrashort laser pulses An ultrashort laser pulse has a time duration less than a few picoseconds. Lasers that emit ultrashort pulses are called ultrafast lasers or ultrashort pulse lasers. Ultrashort laser pulses have found numerous applications in science and technology. For example, in femtochemistry with the help of unique temporal and spectral properties of ultrashort pulses, chemical reactions can be traced down to the time scale of femtosecond where the charge transfer occurs. Routinely, ultrashort pulses are generated by mode-locked lasers. From Fourier transform theory, pulse duration and spectral bandwidth are inversely proportional. Therefore, broadband laser gain media are used in mode-locked lasers as well as in laser amplifiers to provide a sufficient gain bandwidth for ultrashort pulses. The mode-locking mechanism is based on constructive interference of the laser cavity frequency modes in the time domain. This will happen when the phase difference between each two adjacent oscillating modes is locked either actively or passively. Ti:sapphire crystal as a laser gain medium offers a broad gain bandwidth between 670 nm and 1070 nm. From this broad bandwidth, Ti:sapphire oscillators with pulse durations <6 fs are commercially available now. No laser material has been found yet to support a bandwidth sufficient for pulse durations less than the

58 Theory Days 16.03.2017: Day 3 – Laser Light Sources & Time‐Resolved Spectroscopy Chair: Iain Wilkinson HZB, Berlin‐Adlershof

Ti:sapphire’s limit. However, high harmonic generation (HHG) has been found to be successful for generating femtosecond/attosecond pulses. The temporal/spectral phase of the pulse plays an important role in characterizing and controlling ultrashort pulses. The knowledge of the Fourier transform limited pulse and linearly chirped pulse is essential to understand ultrashort laser pulses. The Fourier-transform limited pulse has the minimum pulse duration whereas a chirped pulse has an increased pulse duration, thus, the latter has a decreased peak power. The chirped pulse amplification technique was invented to amplify high peak power pulses to prevent the laser materials from damaging. We will discuss the temporal/spectral phase for the two types of pulses. The following topics will be presented:

1. Ultrashort pulses, chirped pulses, and pulse shaping; section 12.1 of Ref. [2]

2. Measurement techniques for ultrashort pulses; section 12.3 of Ref. [2].

3. Mode locking and mode-locked Ti:sapphire oscillator; section 8.6 of Ref. [1], Ref. [6].

4. Chirped pulse amplification and ultrafast Ti:sapphire amplifier; Ref. [7]. A comprehensive reference on ultrashort laser pulses is [8].

References: [1] O. Svelto, "Principle of Lasers," no. 5th, 2010. [2] K. Asakawa et al, "Handbook of Lasers and Optics," Springer, 2012. [3] R. W. Boyd, "Nonlinear Optics," Elsevier, 2008. [4] S. Witte and K. S. E. Eikema, "Ultrafast optical parametric chirped-pulse amplification," IEEE J. Sel. Topics Quantum Electron, vol. 18, pp. 296-307, 2011. [5] Y. Deng et al, "Carrier-envelope-phase-stable, 1.2 mJ, 1.5 cycle laser pulses at 2.1 μm," Optics Letters, vol. 37, pp. 4973-4975, 2012. [6] S. Yefet and A. Pe'er, "A Review of Cavity Design for Kerr Lens Mode-Locked Solid State Lasers," Applied Science, vol. 3, pp. 694-724, 2013. [7] S. Backus, C. G. Durfee III, M. M. Murnane and H. C. Kapteyn, "High Power Ultrafast Lasers," Review of Scientific Instruments, vol. 69, no. 3, pp. 1207-1223, 1998. [8] J.-C. Diels and W. Rudolph, "Ultrashort Laser Pulse Phenomena," Elsevier, 2006.

59 Theory Days 16.03.2017: Day 3 – Laser Light Sources & Time‐Resolved Spectroscopy Chair: Iain Wilkinson HZB, Berlin‐Adlershof

Brief CV – Dr. Igor Kiyan

Current position: Helmholtz Zentrum Berlin, Group leader Research expertise/activities in research: A major part of previous research activities includes studies on photodetachment of atomic negative ions in strong laser fields. The quantum interference effect in the process of electron emission was revealed for the first time and analyzed in terms of a theory based on the strong-field approximation. The speaker has extended this theory to describe photodetachment in a circularly polarized laser field. The choice of gauge in the description of interaction with the external field was tested experimentally, providing an answer to a long- standing question of many debates. The effect of electron rescattering on the parent core, leading to the emission of energetic electrons, was demonstrated for the first time for quantum systems of short-range binding potential. Coherence in the electron dynamics of the ground state of the residual atom generated in the process of photodetachment was experimentally demonstrated. The mechanism of double photo-detachment in a strong laser field was investigated. Some aspects of photodetachment of molecular anions were considered. More recently, strong-field ionization of dense media was investigated, revealing the role of laser-assisted scattering of photoelectrons on the neighboring particles. Another part of previous research involves investigation of the electronic structure of atomic negative ions, including doubly excited states and the continuum spectrum. The polynomial convergence of energies of a series of doubly excited states on the photodetachment threshold was predicted and experimentally verified. The autodetachment mechanism of doubly excited states was described, revealing the oscillatory behavior of their widths as a function of the binding energy. The threshold law of photodetachment from a repulsive potential was predicted and experimentally verified. The current research activities include the study of ultrafast electron dynamics induced by light in transition-metal coordination complexes. The method of transient XUV photoemission spectroscopy, employing laser-induced high-order harmonic generation to produce XUV light, was developed and applied to investigate photoreactions in a number of materials in solutions and at solid interfaces. The studies include: revealing the photoinduced spin crossover mechanism in the iron tris-bipyridine complex, tracking the charge injection kinetics in dye- sensitized mesoporous semiconductor films, and identifying the electron relaxation pathway in photoexcited ferricyanide. The role of the space charge effect arising from multiphoton ionization of the sample by the optical pump laser beam was characterized in details.

Keywords: lasers, non-linear optics, multiphoton processes, photoemission, wave packet dynamics, transient spectroscopy, strong-field—matter interaction.

60 Theory Days 16.03.2017: Day 3 – Laser Light Sources & Time‐Resolved Spectroscopy Chair: Iain Wilkinson HZB, Berlin‐Adlershof

Selected 10 most important articles related to the lecture: [1] I. Yu. Kiyan and H. Helm, “Production of energetic electrons in the process of photodetachment of F-“, Phys. Rev. Lett. 90, 183001 (2003). [2] S. Beiser, M. Kleiber, and I. Yu. Kiyan, “Photodetachment in a strong circularly polarized laser field”, Phys. Rev. A 70, 011402(R) (2004). [3] B. Bergues, Z. Ansari, D. Hanstorp, and I. Yu. Kiyan, “Photodetachment in a strong laser field: An experimental test of Keldysh-like theories”, Phys. Rev. A 75, 063415 (2007). [4] B. Bergues and I. Yu. Kiyan, “Two-electron photodetachment of negative ions in a strong laser field”, Phys. Rev. Lett. 100, 143004 (2008). [5] A. Gazibegovic-Busuladzic, D. B. Milosevic, W. Becker, B. Bergues, H. Hultgren, and I. Yu. Kiyan, “Electron rescattering in above-threshold photodetachment of negative ions”, Phys. Rev. Lett. 104, 103004 (2010). [6] H. Hultgren, M. Eklund, D. Hanstorp, and I. Yu. Kiyan, “Electron dynamics in the ground state of a laser-generated carbon atom”, Phys. Rev. A 87, 031404(R) (2013). [7] M. Eklund, H. Hultgren, D. Hanstorp, and I. Yu. Kiyan, “Orbital alignment in atoms generated by photodetachment in a strong laser field”, Phys. Rev. A 88, 023423 (2013). [8] J. Metje, M. Borgwardt, A. Moguilevski, A. Kothe, N. Engel, M. Wilke, R. Al-Obaidi, D. Tolksdorf, A. Firsov, M. Brzhezinskaya, A. Erko, I. Yu. Kiyan, and E. F. Aziz, “Monochromatization of femtosecond XUV light pulses with the use of reflection zone plates”, Opt. Express 22, 10747 (2014). [9] M. Wilke, R. Al-Obaidi, A. Moguilevski, A. Kothe, N. Engel, J. Metje, I. Yu. Kiyan, and E. F. Aziz, “Laser-assisted electron scattering in strong-field ionization of dense water vapour by ultrashort laser pulses”, New J. Phys. 16, 063032 (2014). [10] M. Wilke, R. Al-Obaidi, I. Yu. Kiyan, and E. F. Aziz, “Maltiplateau structure in photoemission spectra of strong-field ionization of dense media”, Phys. Rev. A 94, 033423 (2016).

61 Theory Days 16.03.2017: Day 3 – Laser Light Sources & Time‐Resolved Spectroscopy Chair: Iain Wilkinson HZB, Berlin‐Adlershof

Interaction of strong laser radiation with matter

Igor Yu. Kiyan Helmholtz-Zentrum Berlin (HZB), Albert-Einstein-Str. 15, 12489 Berlin, Germany [email protected] The recent development of femtosecond laser technologies enables to reach ultrahigh peak intensities of radiation, giving rise an AC electric field with a strength that exceeds the atomic value. In the talk, laser intensities in the range up to 1016 W/cm2 will be considered, which can be achieved nowadays with the use of a tabletop commercial laser system. Interaction of such a strong laser field with diluted media (atomic and molecular gases) gives rise to various interesting elementary processes which have been widely studied during the past decades. These processes include electron emission at high kinetic energies, multiple ionization of atoms and molecules, and high-order harmonic generation of incident light. Their basic mechanisms and the accompanied effects will be considered in the talk. The phenomena that arise with the increase of the medium density will be briefly described as well. In a strong laser field, the photoelectron can absorb more photons than needed to overcome the ionization threshold. This process is called “above-threshold ionization” (ATI) and it involves free-free transitions in the continuum spectrum. The kinetic energy spectrum of emitted electrons is affected by the ponderomotive effect, originating from the quiver motion of a free electron in the presence of an external AC laser field. This effect leads to the increase of the ionization threshold, which is proportional to the laser intensity. In a sufficiently strong laser field, the lower ionization channels can be closed due to the ponderomotive shift of the ionization threshold. On the other hand, the ionized electron appears in the laser beam of non-uniform intensity distribution and is accelerated by the ponderomotive force that pushes the electron from high- to low-intensity region. If the laser pulse duration is sufficiently long, the ponderomotive acceleration exactly compensates the energy loss due to the threshold shift. The pulse duration regime will be considered in the talk. The description of the strong field interaction with atoms and molecules requires application of methods beyond the perturbation theory. One of these methods, based on the strong-field approximation (SFA), received great attention. In the SFA theory, the binding potential of the atomic system is neglected in the final state. Thus, the final state is represented by the Volkov function that describes a free electron in the presence of an AC electromagnetic field. The analytical character of this approach allows to reveal interesting effects of the ionization process, such as the effect of quantum interference. The electron emission in a linearly polarized laser field can be described in terms of double-slit interference, giving rise to an interference pattern in the angular distribution of photoelectrons. In a circularly polarized field, however, such interference is absent. The basic aspects of the SFA theory and its capability to describe the experimental photoemission spectra will be presented in the talk. Apart from the interference effect in the continuum spectrum of emitted electrons, coherence is also preserved in the ground state of the residual atomic core. The electron density of the core acquires a periodic motion, associated with a coherent superposition of the spin-orbit

62 Theory Days 16.03.2017: Day 3 – Laser Light Sources & Time‐Resolved Spectroscopy Chair: Iain Wilkinson HZB, Berlin‐Adlershof

states of the core populated in the process of ionization. The motion period is defined by the frequency beat of the spin-orbit energy levels. The periodic motion of the electron density can be probed by applying a second strong laser pulse, as will be demonstrated in the talk. The interaction of atoms and molecules with a strong linearly polarized laser field also gives rise to high-order above-threshold ionization (HATI). This process yields a characteristic plateau in the kinetic energy spectrum of photoelectrons, which extends far beyond the kinetic energies of direct electrons produced by ATI. The HATI process can be well understood in terms of classical electron trajectories in the laser field. After the ionization event, the released electron is driven by the external AC field and can revisit the parent core, where it acquired additional energy via elastic scattering on the core in the presence of the external field. The analysis of electron trajectories predicts the energy cutoff of rescattered electrons to be 10Up, where Up is the quiver (ponderomotive) energy of a free electron in the laser field. The rescattering model was successfully used to describe also other processes such as non-sequential multiple ionization and high-order harmonic generation. High-order harmonic generation finds various applications nowadays as a source of coherent light in the XUV – soft X-ray photon energy range. According to the rescattering model, this process can be represented by a sequence of three steps: (1) release of the photoelectron, (2) acceleration of the free electron by the external field and its return to the core, and (3) recombination of the returned electron with the parent core leading to the emission of a high- energy photon. The analysis of classical trajectories shows that the maximum kinetic energy of the returned electron is 3.17Up and, thus, the energy cutoff of emitted harmonics is 3.17Up +I0, where I0 is the ionization potential of the atom. Some quantum-mechanical aspects of harmonic generation and the phase-matching conditions, required for efficient energy transfer from the pump laser beam to the harmonic beam, will also be discussed in the talk. With the increase of the medium density, the released and accelerated by the external field photoelectron can scatter on a neighbouring particle instead of the parent core. This process, called “laser-assisted electron scattering” (LAES), results in the increase of the electron kinetic energy. The analysis of classical electron trajectories can be applied, revealing a multiplateau structure in the kinetic energy spectra of photoelectrons produced in this incoherent HATI process. The highest energy cutoff is shown to be 18Up, thus, exceeding the HATI cutoff value. Results of recent experimental studies with the use of a liquid micro-jet technique, enabling to vary the target gas pressure in the interaction region, will be presented in the talk.

63 Theory Days 16.03.2017: Day 3 – Laser Light Sources & Time‐Resolved Spectroscopy Chair: Iain Wilkinson HZB, Berlin‐Adlershof

References: [1] I. Yu. Kiyan and H. Helm, “Production of energetic electrons in the process of photodetachment of F“, Phys. Rev. Lett. 90, 183001 (2003). [2] S. Beiser, M. Kleiber, and I. Yu. Kiyan, “Photodetachment in a strong circularly polarized laser field”, Phys. Rev. A 70, 011402(R) (2004). [3] B. Bergues, Z. Ansari, D. Hanstorp, and I. Yu. Kiyan, “Photodetachment in a strong laser field: An experimental test of Keldysh-like theories”, Phys. Rev. A 75, 063415 (2007). [4] B. Bergues and I. Yu. Kiyan, “Two-electron photodetachment of negative ions in a strong laser field”, Phys. Rev. Lett. 100, 143004 (2008). [5] A. Gazibegovic-Busuladzic, D. B. Milosevic, W. Becker, B. Bergues, H. Hultgren, and I. Yu. Kiyan, “Electron rescattering in above-threshold photodetachment of negative ions”, Phys. Rev. Lett. 104, 103004 (2010). [6] H. Hultgren, M. Eklund, D. Hanstorp, and I. Yu. Kiyan, “Electron dynamics in the ground state of a laser-generated carbon atom”, Phys. Rev. A 87, 031404(R) (2013). [7] M. Eklund, H. Hultgren, D. Hanstorp, and I. Yu. Kiyan, “Orbital alignment in atoms generated by photodetachment in a strong laser field”, Phys. Rev. A 88, 023423 (2013). [8] J. Metje, M. Borgwardt, A. Moguilevski, A. Kothe, N. Engel, M. Wilke, R. Al-Obaidi, D. Tolksdorf, A. Firsov, M. Brzhezinskaya, A. Erko, I. Yu. Kiyan, and E. F. Aziz, “Monochromatization of femtosecond XUV light pulses with the use of reflection zone plates”, Opt. Express 22, 10747 (2014). [9] M. Wilke, R. Al-Obaidi, A. Moguilevski, A. Kothe, N. Engel, J. Metje, I. Yu. Kiyan, and E. F. Aziz, “Laser-assisted electron scattering in strong-field ionization of dense water vapour by ultrashort laser pulses”, New J. Phys. 16, 063032 (2014). [10] . M. Wilke, R. Al-Obaidi, I. Yu. Kiyan, and E. F. Aziz, “Maltiplateau structure in photoemission spectra of strong-field ionization of dense media”, Phys. Rev. A 94, 033423 (2016).

64 Theory Days 16.03.2017: Day 3 – Laser Light Sources & Time‐Resolved Spectroscopy Chair: Iain Wilkinson HZB, Berlin‐Adlershof

Brief CV – Dr. Iain Wilkinson

Current positions: Liquid & Interfacial Dynamics with Ultrafast X-rays (LIDUX) laboratory group leader and deputy institute director of EM-IMM at HZB Research Activities: The main focus of my research group is to understand and exploit the fundamental dynamic molecular processes that occur in a range of photoexcited condensed phase and interfacial systems. Such dynamic processes occur on ultrafast timescales and produce transient, often highly reactive, intermediate species that are the driving agents behind efficient chemical transformations. Using time-resolved spectroscopies, we aim to characterise these intermediates, measuring their time-varying energetics and condition dependent production, reaction, and/or relaxation kinetics. In combination with the multi-dimensional x-ray spectroscopic probes that we are currently developing, such studies will allow us to probe increasingly complex chemical transformations in detail. Ongoing projects within my research group include the development of high-flux few-optical- cycle infrared optical parametric chirped pulsed amplification (OPCPA) laser sources and associated characterisation devices, high-harmonic generation chambers for the efficient production of ultrashort soft x-ray supercontinua, high-throughput and time-preserving soft x- ray monochromator systems, few-optical-cycle tunable light sources, and high collection and detection efficiency spectrometers for time-resolved EUV/soft x-ray spectroscopies. These developments will allow us to probe chemical processes with few-femtosecond time- resolution and atomic- and chemical state-selectively, facilitating spectroscopic measurements at the spatial and temporal limits of chemistry itself. In addition, my research group performs a range of condensed phase femtosecond time-resolved EUV spectroscopy experiments at the JULiq laboratory of the Freie Universität Berlin and HZB as well as time- averaged liquid microjet soft x-ray spectroscopy experiments with the SOL3 end-station at BESSY II. In the future, we aim to combine the infrastructure that we are developing with our experience in high-photon-energy time-resolved spectroscopies to probe and understand the mechanisms of operation of condensed-phase functional materials in unprecedented detail. Through internal and external collaborations, such experiments will aid in the development of increasingly efficient functional materials and photochemical processes. Research Experience: Iain Wilkinson obtained his PhD from the University of Leeds, UK, in 2010 with his doctoral research focusing on the construction of a high-energy-resolution charged particle imaging spectrometer and its application to study charge and energy transfer pathways in a range of gas-phase molecules. A short fellowship period, focusing on the development of infrastructure to generate and characterise transient radical species, followed at the University of Leeds. Later in 2010, he relocated to the Steacie Institute for Molecular Sciences of the National Research Council of Canada, Canada. There he performed a variety of gas-phase femtosecond time-resolved photoelectron and photoion spectroscopy studies in

65 Theory Days 16.03.2017: Day 3 – Laser Light Sources & Time‐Resolved Spectroscopy Chair: Iain Wilkinson HZB, Berlin‐Adlershof

the perturbative and non-perturbative regimes. In parallel, he developed laser sources and spectrometers to facilitate high-collection-efficiency, time-resolved photoelectron imaging experiments with improved energetic observation ranges. In 2015, he joined the energy materials – methods for material development institute (EM-IMM) at HZB as a research group leader where he has developed the complete concept for a state-of-the-art time-resolved x- ray spectroscopy laboratory (the LIDUX laboratory) that is currently under construction. In parallel, with his research group, he is developing novel infrastructure for time-resolved soft x-ray spectroscopy experiments and performing time- and energy-resolved liquid jet photoelectron spectroscopy experiments with high photon energy light sources. He was appointed deputy institute director of EM-IMM in 2016.

Keywords: Molecular Dynamics, Time-Resolved Spectroscopy, Ultrashort Laser Pulses, Non- Linear Optics, Strong-Field Light-Matter Interactions, Liquid Microjets, Charged Particle Detection

Selected Publications: [1] Ferré et al., Nature Communications, 6 (2015) 5952, Multi-Channel Electronic & Vibrational Dynamics in Polyatomic Resonant High-Order Harmonic Generation [2] Wilkinson et al., J. Chem. Phys., 140 (2014) 204301, Excited State Dynamics in SO2. I. Bound State Relaxation Studied by Time-Resolved Photoelectron-Photoion Coincidence Spectroscopy [3] Mikosch et al., Phys. Rev. Lett., 110 (2013) 023004, Channel- and Angle-Resolved Above Threshold Ionization in the Molecular Frame [4] Mikosch et al., J. Chem. Phys., 139 (2013) 024304, The Quantitative Determination of Laser Induced Molecular Axis Alignment [5] Wilkinson et al., Phys. Chem. Chem. Phys., 12 (2010) 15766, The Photodissociation of NO2 by Visible and Ultraviolet Light [6] Wilkinson & Whitaker, Annu. Rep. Prog. Chem., Sect. C: Phys. Chem., 106 (2010) 274, Some Remarks on the Photodynamics of NO2 [7] Wilkinson et al., J. Chem. Phys., 131 (2009) 054308, Photodissociation of NO2 in the (2)2B2 State: the O(1D2) Dissociation Channel [8] Wilkinson et al., J. Chem. Phys., 129 (2008) 154312, Photodissociation of NO2 in the (2)2B2 State: A Slice Imaging Study and Reinterpretation of Previous Results [9] Raffael et al., Chem. Phys. Lett., 460 (2008) 59, Time-dependent Photionization of Azulene: Optically Induced Anisotropy on the Femtosecond Timescale [10] Blanchet et al., J. Chem. Phys., 128 (2008) 164318, Time-Dependent Photoionization of Azulene: Competition Between Ionization and Relaxation in Highly Excited States'

66 Theory Days 16.03.2017: Day 3 – Laser Light Sources & Time‐Resolved Spectroscopy Chair: Iain Wilkinson HZB, Berlin‐Adlershof

Introduction to Time-Resolved Spectroscopy

Iain Wilkinson 1EM-IMM – Helmholtz-Zentrum Berlin, 14109 Berlin, Germany [email protected] Nature, functional devices and chemistry itself are dynamic. Time-resolved spectroscopies allow us to interrogate such dynamics, offering unique insights into the mechanisms of chemical transformations and the behaviours of functional devices. The quantum efficiencies of all molecular processes are governed by the time-varying energetics of a system and the kinetic competition that occurs between accessible reaction channels. Such kinetic competition is exploited in nature, the primary process in vision(1,2) and DNA base photoprotection mechanisms(3) being notable examples where ultrafast kinetics is used to efficiently direct charge and energy flow. Similar principles underlie the performance of all man-made energy conversion and charge-based functional devices (4). For example, ultrafast charge carrier dynamics at interfaces govern the efficiencies of fuel cells, batteries, electrocatalysts, photocatalysts, and photovoltaic devices. In this lecture the utility of time-resolved spectroscopies for the elucidation of chemical mechanisms and the characterisation and development of such functional devices will be demonstrated. The lecture will primarily focus on spectroscopic probes of the ultrafast dynamic processes that occur in molecular and material systems following photoexcitation. Principles that are often used to consider dynamic molecular processes will be reviewed; including the time- dependent Schrödinger equation, the Born-Oppenheimer approximation, potential energy surfaces and nonadiabatic interactions. Based on this review, a brief overview of photoinduced chemical reaction dynamics will be presented. The necessary steps to perform time-resolved measurements will be introduced as will the pump-probe methodology. The characteristic timescales of different dynamic molecular processes and the technical developments that allowed the temporal resolutions of time-resolved measurements to improve from the millisecond to attosecond (10-18 s) timescales will also be described. Furthermore, the ways in which short laser pulses interact with matter to generate coherent wavepackets and initiate dynamic behaviours will be discussed (5-8). Wavepacket probing, the choice of the spectroscopic probe pulse, and the effect of the probe pulse on what is measured in time-resolved experiments will also be considered (8, 9). Using a variety of example systems, ranging from isolated gas-phase diatomic molecules to more complex multi-phase functional devices, practical ultrafast time-resolved spectroscopy studies will be described. Perturbative and non-perturbative time-resolved spectroscopic probes will be considered as will the potentially differing sensitivities of associated probe techniques to underlying dynamic processes. Some theoretical approaches that can be used to interpret the time-resolved data recorded in such experiments will also be referred to. Finally, a brief perspective on emerging time-resolved spectroscopic techniques will be presented.

67 Theory Days 16.03.2017: Day 3 – Laser Light Sources & Time‐Resolved Spectroscopy Chair: Iain Wilkinson HZB, Berlin‐Adlershof

References: [1] Schoenlein et al., Science, 254 (1991) 412, The first step in vision: femtosecond isomerisation of Rhodopsin [2] Wang et al., Science, 266 (1994) 422, Vibrationally coherent photochemistry in the femtosecond primary event of vision [3] Pecourt et al., J. Am. Chem. Soc., 123 (2001) 10370, DNA excited-state dynamics: ultrafast internal conversion & vibrational cooling in a series of nucleosides [4] Adams et al., J. Phys. Chem. B, 107 (2003) 6668, Charge transfer on the nanoscale, current status [5] Heller, J. Chem. Phys., 62 (1975) 1544, Time-dependent approach to semiclassical dynamics [6] Garraway & Suominnen, Contemporary Physics, 43 (2002) 97, Wavepacket dynamics in molecules [7] Stolow, Farad. Disc., 163 (2013) 9, The three pillars of photo-initiated molecular dynamics [8] Stolow, Phil. Trans. R. Soc. Lond. A, 356 (1998) 345, Application of wavepacket methodology [9] Wu et al., Phys. Chem. Chem. Phys., 13 (2011) 18447, Time-resolved photoelectron spectroscopy: from wavepackets to observables

68 Theory Days 16.03.2017: Day 3 – Laser Light Sources & Time‐Resolved Spectroscopy Chair: Iain Wilkinson HZB, Berlin‐Adlershof

Brief CV – Prof. Dr. Marc J.J. Vrakking

Master's (‘Doctoraal’): University: Eindhoven University of Technology, 8/1987 (cum laude) 9/1985 – 5/1986: Visiting scientist at Institute for Molecular Science, Okazaki, Japan Doctorate: University/College of Higher Education: University of California at Berkeley (USA), 11/1992; Supervisor (‘Promotor’): Prof. Yuan T. Lee (1986 Chemistry Nobel laureate); Title of thesis: Towards rotationally state-resolved differential cross sections for the hydrogen exchange reaction

Work experience since Ph.D. degree: 11/1992 – 08/1994: Postdoctoral researcher, University of California at Berkeley, USA 09/1994 – 08/1995: Postdoctoral researcher, National Research Council, Ottawa, Canada 09/1995 – 12/1996: Fellowship from the Royal Dutch Academy of Sciences, Vrije Universiteit Amsterdam, the Netherlands 01/1997 – 12/1999: Project leader AMOLF, Amsterdam, the Netherlands 01/2000 – 06/2011: Tenured group leader position at AMOLF 09/2004 – 2012: Adjunct Professor Radboud University Nijmegen, the Netherlands 03/2010 – present: Professor at the Freie Universität Berlin 03/2010 – present: Director of the Max-Born Institut in Berlin 05/2015 – present: Chairman of the Board of the Forschungsverbund Berlin

International activities: Chairman of the Scientific Advisory Committee of the Amsterdam Research Center for NanoLithography – ARNCL (2013-present) Chairman of the EUCALL Scientific Advisory Committee (2016-present) Chairman of Physics Faculty Evaluation Panel, Eindhoven University of Technology (2017) President of Scientific Advisory Board of CILEX-APOLLON (2013-present) Chairman of Artemis Access Board (2009-present) Member of the proposal review panel for the LCLS x-ray FEL facility (2015-present). Member of the project review panel for the FLASH FEL facility (2014-present) Member of Management Board of Laserlab Europe-III & IV (2012-present) Member of two ERC evaluation panels (2014-present) Member of Marie Curie evaluation panel (2016-present) Permanent member of the CEA Visiting Committee advising the CEA High Commissioner (2014- present)

69 Theory Days 16.03.2017: Day 3 – Laser Light Sources & Time‐Resolved Spectroscopy Chair: Iain Wilkinson HZB, Berlin‐Adlershof

Member of ELI-HU Scientific Advisory Committee (2011-2014) Coordinator FP7 Marie Curie Initial Training Network ‘JMAP’ (Joint Max Born Institute - Amplitude Phd Program), (2012-present) Coordinator FP7 Marie Curie Initial Training Network ‘ATTOFEL’ (Ultrafast Dynamics using Attosecond and XUV Free Electron Laser sources), (2009-2013) Coordinator of FP7 Marie Curie Industry-Academia Partnership Program ‘FLUX’ (Femtosecond Lasers for the Generation of Ultrashort XUV Pulses), (2008-2012). Coordinator of FP6 Marie Curie Research Training Network ‘XTRA’ (Ultrashort XUV Pulses for Time- Resolved and Non-Linear Applications), (2004-2008) Faculty opponent at thesis defenses in Denmark (2x), Sweden (1x), Spain (1x) and France (3x) Reviewer for Science, Nature, Nature Physics, Nature Photonics, Physical Review Letters, FOM, DFG, NSF, EU, DOE, ANR, etc.

Recent Grants: Leibniz SAW Scheme “Electron dynamics and charge correlations studied by ultrafast soft x-ray absorption spectroscopy” (2015). FP7 ETN ASPIRE “Angular studies in innovative research environments” (2015) FP7 Research for SMEs project FLAME “Femtosecond Light Amplifiers in the Megahertz regime” (2012). FP7 European Industrial Doctorate program JMAP “Joint Max Born Institute - Amplitude Phd Program” (2 partners, 2012). ERA Chemistry “Time-resolved molecular dynamics using XUV ionization of aligned molecules” (2012). Einstein Foundation “Attosecond Electron Dynamics” (4 partners, 2011). Leibniz SAW Scheme “High average power ultrashort laser pulses in the near and mid-infrared by chirped optical parametric amplification (2011).

10 Selected Publications related to the lecture: [1] Weisshaupt, J., et al., Ultrafast modulation of electronic structure by coherent phonon excitations. Physical Review B, 2017. 95(8): p. 081101. [2] Schutte, B., et al., Ionization Avalanching in Clusters Ignited by Extreme-Ultraviolet Driven Seed Electrons. Physical Review Letters, 2016. 116(3). [3] Eckstein, M., et al., Direct Imaging of Transient Fano Resonances in N-2 Using Time-, Energy-, and Angular-Resolved Photoelectron Spectroscopy. Physical Review Letters, 2016. 116(16). [4] Drescher, L., et al., Communication: XUV transient absorption spectroscopy of iodomethane and iodobenzene photodissociation. The Journal of Chemical Physics, 2016. 145(1): p. 011101. [5] Willems, F., et al., Probing ultrafast spin dynamics with high-harmonic magnetic circular dichroism spectroscopy. Physical Review B, 2015. 92(22). [6] Marciniak, A., et al., XUV excitation followed by ultrafast non-adiabatic relaxation in PAH molecules as a femto-astrochemistry experiment. Nature Communications, 2015. 6: p. 8909.

70 Theory Days 16.03.2017: Day 3 – Laser Light Sources & Time‐Resolved Spectroscopy Chair: Iain Wilkinson HZB, Berlin‐Adlershof

[7] Schütte, B., et al., Rare-Gas Clusters in Intense Extreme-Ultraviolet Pulses from a High-Order Harmonic Source. Physical Review Letters, 2014. 112(7): p. 073003. [8] Lepine, F., M.Y. Ivanov, and M.J.J. Vrakking, Attosecond molecular dynamics: fact or fiction? Nat Photon, 2014. 8(3): p. 195-204. [9] Leone, S.R., et al., What will it take to observe processes in 'real time'? Nat Photon, 2014. 8(3): p. 162-166. [10] Vrakking, M.J.J., Attosecond imaging. Physical Chemistry Chemical Physics, 2014. 16(7): p. 2775- 2789.

71 Theory Days 16.03.2017: Day 3 – Laser Light Sources & Time‐Resolved Spectroscopy Chair: Iain Wilkinson HZB, Berlin‐Adlershof

Applications of ultrashort soft X-ray pulses

Marc J.J. Vrakking Max-Born Institute (MBI), Max-Born Strasse 2a, 12489 Berlin [email protected] Presently, the emergence of novel XUV/X-ray sources such as HHG sources and free electron lasers like the LCLS, is causing a revolution in the ultrafast laser sciences. Using ultrafast XUV/X-ray sources, structural changes can be observed with spatial resolutions down to Angström-scales, with time-resolutions down to the femtosecond, or – in some cases – attosecond scale, and, using the dependence of XUV/X-ray core-level transitions on the atomic mass, often times with atomic specificity. It is against this background that in the last few years, we have shifted a large part of our research efforts at the Max-Born Institute towards the further development of labscale XUV/X-ray sources, and towards the exploitation of ultrashort XUV/X-ray pulses in a range of novel spectroscopies. In my tutorial, I will present an overview of these research activities, and in doing so, will present an overview of the various ways that HHG techniques can be used to great advantage to study attosecond electronic and femtosecond structural dynamics. I will moreover sketch an outlook of further improvements in labscale XUV/X-ray sources that we may envision in the next few years, and the novel research opportunities that this will bring. High-harmonic generation (HHG) was discovered in the late 80´s of the last century, in the course of experiments targeting a better understanding of the role of intermediate state resonances in multi-photon ionization [1]. After a while, it was understood that many of the characteristic features of HHG, in particular the occurrence of a high energy cut-off in the XUV spectrum, could be understood by a simple semi-classical three-step picture, where (tunnel) ionization by an intense laser sets an electron free in the continuum, subsequent acceleration of the electron by the oscillatory laser field increases the kinetic energy of the electron and drives a re-collision process, and recombination leads to the production of XUV photons [2]. In the years that followed, it was soon realized that HHG not only produces coherent XUV radiation over a wide range of photon energies, but moreover produces this XUV radiation in a phase-locked manner that almost unavoidably leads to the production of attosecond laser pulses. Given that the ionization that is the initial step in the three-step picture depends highly non-linearly on the laser electric field amplitude, the ionization produces bunches of electrons with a duration much shorter than the duration of the laser optical cycle (2.7 fs for a Ti:Sa laser), and hence, after acceleration, the recombination that produces the XUV light also only occurs during a small fraction of the optical cycle. Hence, the production of attosecond pulses is inherent to the process of HHG. Since their first demonstration in 2001 [3, 4], attosecond pulses have been used in an ever- growing number of applications. First applications focused on electron dynamics in atomic systems, and revealed, among other things, the lifetime of Auger processes [5], the sub-cycle time dependence of strong field ionization by an IR field [6] and the existence of minute time delays between ionization events starting from different orbitals within an atom [7]. In my tutorial I will in particular discuss some first applications in molecular systems. I will discuss

72 Theory Days 16.03.2017: Day 3 – Laser Light Sources & Time‐Resolved Spectroscopy Chair: Iain Wilkinson HZB, Berlin‐Adlershof

experiments where dissociative ionization of nature´s simplest molecule, the hydrogen molecule, is initiated by an attosecond pulse, and where the outcome of the dissociative ionization process is influenced (probed) on attosecond timescales using a co-propagating IR laser field. I will explain that measurements of an asymmetry in the direction of ejection of protons are related in this experiment to coupling of the electronic and nuclear degrees of freedom in the molecule on attosecond to few-femtosecond timescales, as well as quantum- mechanical entanglement between a produced photoelectron and the molecular ion it leaves behind [8]. I will moreover discuss experiments that have been performed since (by other groups) on attosecond to few-femtosecond time-scale dynamics in bio-molecules [9], as well as experiments that are currently going on at MBI on attosecond time-scale electron dynamics in methyl-iodide molecules that are subjected to a moderately intense IR pulse. The development of attosecond science in the last decade-and-a-half has attracted numerous research groups to this emerging research field. Accordingly, the development of HHG- technology has received a major boost, and it has become much easier to implement HHG- sources in the lab. According, a number of additional properties of HHG-radiation – in addition to the ability to produce attosecond pulses – are now actively being exploited in many labs around the world.

 HHG can produce XUV continua up to very high photon energies. Scaling of – in particular – the wavelength of the driver laser used in the HHG process has allowed to increase the high energy cut-off of HHG spectra, and these days an increasing number of research groups are pushing the generation of XUV continue that extend into the water window, i.e. the wavelength region where light elements like C, N and O have their absorption edges. This allows putting together experiments, where XUV absorption of selected atoms is used as a site-specific “detector” for particular processes of interest. In my talk, I will present several examples of this concept. I will show how time-resolved absorption around an Iodine edge can be used to study the photodissocation of small Iodine-containing molecules [10], how absorption around a Co edge can be used to study laser-induced demagnetization in magnetic films [11], and how time-resolved absorption around the Li K-edge can be used to study coupled electronic and nuclear dynamics in ionic LiBH4 crystals [12].

 HHG can be used as a tool for time-resolved photoelectron spectroscopy. While the full XUV bandwidth in the HHG process supports attosecond pulses, the duration of single, selected harmonics is in the femtosecond domain (typ. about half of the duration of the HHG driver laser). In my talk I will present the combination of an HHG source and a time-compensating monochromator that allows the selection of a single harmonic without noticeable changes to the XUV pulse duration. I will illustrate the opportunities offered by this instrument by discussing an experiment on Fano resonances in the N2 molecule [13].

 HHG pulses can be intense enough to drive nonlinear processes and permit coherent diffractive imaging (CDI). While early HHG sources typically allowed the generation of focused XUV intensities <1011 W/cm2, significant progress in the laser few years has allowed the production of intensities beyond 1012 W/cm2. This has permitted the

73 Theory Days 16.03.2017: Day 3 – Laser Light Sources & Time‐Resolved Spectroscopy Chair: Iain Wilkinson HZB, Berlin‐Adlershof

emergence of two significant and novel capabilities, namely (1) the ability to drive nonlinear ionization/excitation processes (i.e. laser-matter interactions where the sample absorbs more than one photon), and (2) the ability to use the HHG pulses for single-shot CDI measurements. As an example of (1), I will discuss experiments where large Ar and Xe clusters are ionized by intense HHG pulses [14, 15], as well as an experiment where Rabi oscillations are induced in an Ar+ ion [16], whereas as an example of (2), I will discuss experiments where CDI measurements were performed on sub-micron size Helium droplets. All the work mentioned above, is possible using relatively standard, commercially available femtosecond laser amplifiers. However, yet more will become possible in the near future, when – increasingly – OPCPA drivers will become available that are superior to commercially available laser amplifiers in just about every parameter (average power, reprate, pulse duration, etc.). I will finish my tutorial with a brief overview on ongoing developments at MBI and the prospects that these developments will bring.

References: [1] Ferray, M., et al., Multiple-harmonic conversion of 1064 nm radiation in rare gases. Journal of Physics B: Atomic, Molecular and Optical Physics, 1988. 21(3): p. L31. [2] Corkum, P.B., Plasma Perspective on Strong-Field Multiphoton Ionization. Physical Review Letters, 1993. 71(13): p. 1994-1997. [3] Hentschel, M., et al., Attosecond metrology. Nature, 2001. 414(6863): p. 509-513. [4] Paul, P.M., et al., Observation of a train of attosecond pulses from high harmonic generation. Science, 2001. 292(5522): p. 1689-1692. [5] Drescher, M., et al., Time-resolved atomic inner-shell spectroscopy. Nature, 2002. 419(6909): p. 803-807. [6] Uiberacker, M., et al., Attosecond real-time observation of electron tunnelling in atoms. Nature, 2007. 446(7136): p. 627-632. [7] Schultze, M., et al., Delay in Photoemission. Science, 2010. 328(5986): p. 1658-1662. [8] Sansone, G., et al., Electron localization following attosecond molecular photoionization. Nature, 2010. 465(7299): p. 763-U3. [9] Calegari, F., et al., Ultrafast electron dynamics in phenylalanine initiated by attosecond pulses. Science, 2014. 346(6207): p. 336-339. [10] Drescher, L., et al., Communication: XUV transient absorption spectroscopy of iodomethane and iodobenzene photodissociation. The Journal of Chemical Physics, 2016. 145(1): p. 011101. [11] Willems, F., et al., Probing ultrafast spin dynamics with high-harmonic magnetic circular dichroism spectroscopy. Physical Review B, 2015. 92(22). [12] Weisshaupt, J., et al., Ultrafast modulation of electronic structure by coherent phonon excitations. Physical Review B, 2017. 95(8): p. 081101. [13] Eckstein, M., et al., Direct Imaging of Transient Fano Resonances in N-2 Using Time-, Energy-, and Angular-Resolved Photoelectron Spectroscopy. Physical Review Letters, 2016. 116(16). [14] Schütte, B., et al., Rare-Gas Clusters in Intense Extreme-Ultraviolet Pulses from a High-Order Harmonic Source. Physical Review Letters, 2014. 112(7): p. 073003.

74 Theory Days 16.03.2017: Day 3 – Laser Light Sources & Time‐Resolved Spectroscopy Chair: Iain Wilkinson HZB, Berlin‐Adlershof

[15] Schütte, B., et al., Tracing Electron-Ion Recombination in Nanoplasmas Produced by Extreme- Ultraviolet Irradiation of Rare-Gas Clusters. Physical Review Letters, 2014. 112(25): p. 253401. [16] Flögel, M., et al., Rabi oscillations in extreme ultraviolet ionization of atomic argon. Physical Review A, 2017. 95(2): p. 021401.

75 Theory Days 17.03.2017: Day 4 – Infrared Spectroscopy and Microscopy Chair: Ljiljana Puskar HZB, Berlin‐Adlershof

Brief CV–Dr. Ulrich Schade

Current position: Group Leader Infrared at Helmholtz-Zentrum Berlin. Research expertise/activities in research: Ulrich Schade graduated from the Humboldt-Universität zu Berlin and received his doctorate degree in physics in 1990. He was postdoc at the Tohoku Daigaku, Japan, doing research in the field of semiconductor science and technology. Later, he managed an infrared instrumentation in the frame of the cometary mission ROSETTA at the DLR in Berlin and was involved in several infrared studies on planetary surfaces. Since 2000 he has been with the electron storage ring BESSY II where he designed the infrared beamline IRIS. At present he is Senior Scientist at the Helmholtz-Zentrum Berlin with a focus on the application of infrared and THz synchrotron radiation to material and energy sciences. Ulrich Schade authored or co-authored over 130 papers in peer-review journals.

76 Theory Days 17.03.2017: Day 4 – Infrared Spectroscopy and Microscopy Chair: Ljiljana Puskar HZB, Berlin‐Adlershof

Abstract: Introduction to infrared spectroscopy, infrared/THz synchrotron radiation and infrared spectrometers

Ulrich Schade HZB – Helmholtz Zentrum Berlin, Albert Einstein Str. 15, Berlin, Germany [email protected] The lecture deals with the basic concept and the application of infrared Fourier transform spectroscopy with synchrotron radiation. The first part of the lecture provides a short introduction to vibrational spectroscopy and discusses how this well established analytical method can benefit from the unique properties of the synchrotron radiation in order to address questions in modern life and material sciences. The second part of the lecture is dedicated to the infrared synchrotron radiation source and gives an overview on the instrumentations. A series of exemplary experiments which were conducted at the BESSY II spectromicroscopy/THz beamline will be presented. This includes time-resolved experiments, con-focal microscopy, ellipsometry and linear THz spectroscopy. Infrared radiation from synchrotron radiation sources has found increasing use in research over the last decade. At synchrotron light sources of third generation like BESSY II the emitted radiation in the infrared wavelength region is some orders of magnitude brighter than standard thermal broadband sources (e.g., globar). In addition, infrared synchrotron radiation is an absolute source being polarized and pulsed in the picosecond timescale. As a particular specialty, BESSY II provides a new technique (low-a) to generate high power, stabile and low- noise coherent terahertz (THz) radiation (Abo-Bakr et al. 2003). The beamline was inaugurated in December 2001 (Schade et al. 2002) and is now used by a multi-disciplinary community. The beamline uses radiation from the homogenous magnetic field (Schade et al. 2000) of the dipole D11 and its optical layout (Peatman and Schade 2001) is shown in Fig. 1. A plane extraction mirror is be placed at about 900 mm from the dipole source in the plane of the storage ring allowing a horizontal and vertical collecting angles of about 60 x 30 mrad2, respectively. The mirror is split into two water-cooled halves which are positioned above and below the narrow high energy radiation fan in the ring plane, permitting most of the heat to pass through to an absorber. The extraction mirror deflects the beam upwards to a combination of two cylindrical mirrors. These mirrors focus the beam outside the radiation shielding of the ceiling of the storage ring tunnel just behind a CVD diamond window. The diamond window separates the UHV of the storage ring from the vacuum system of the remainder of the beam line. The subsequent optical elements direct the light to the different experiments. The ellipsometer (Gensch et al. 2006) is attached to a vacuum FT IR spectrometer. Samples can be investigated with different polarization states of the light under several geometries (e.g., transmittance, grazing and normal incidence reflectance, diffuse reflectance, ATR) and for different environmental conditions, like pressure and temperature.

77 Theory Days 17.03.2017: Day 4 – Infrared Spectroscopy and Microscopy Chair: Ljiljana Puskar HZB, Berlin‐Adlershof

Figure1: Schematic of the optical layout of the Infrared Beamline IRIS.

References: [1] Abo-Bakr, M., Feikes, J., Holldack, K., Kuske, P., Peatman, W. B., Schade, U., Wüstefeld, G., Hübers, H.-W. (2003): Brilliant, Coherent Far-Infrared (THz) Synchrotron Radiation. Physical Review Letter, 90, 094801. http://dx.doi.org/10.1103/PhysRevLett.90.094801 [2] Gensch, M., Korte, E.H., Esser, N., Schade, U. , Hinrichs, K. (2006). Microfocus-infrared synchrotron ellipsometer for mapping of ultra thin films. Infrared Physics & Technology,49, 74–77. http://dx.doi.org/10.1016/j.infrared.2006.01.007 [3] Schade, U., Ortolani, M., Lee, J. (2007). THz Experiments with Coherent Synchrotron Radiation from BESSY II. Synchrotron Radiation News, 20, 17-24. http://dx.doi.org/10.1080/08940880701631351 [4] Schade, U., Röseler, A., Korte, E. H., Scheer, M., Peatman, W. B. (2000). Measured characteristics of infrared edge radiation from BESSY II, Nuclear Instruments and Methods in Physics Research A, 455, 476-486. http://dx.doi.org/10.1016/S0168-9002(00)00507-6 [5] Schade, U., Röseler, A., Korte, E. H., Bartl, F., Hofmann, K. P., Noll, T., Peatman, W. B. (2002). New infrared spectroscopic beamline at BESSY II. Review of Scientific Instruments, 73, 1568- 1570. http://dx.doi.org/10.1063/1.1423781 [6] Peatman, W. B., Schade, U. (2001). A brilliant infrared light source at BESSY. Review of Scientific Instruments, 72, 1620-1624. http://dx.doi.org/10.1063/1.1347976

78 Theory Days 17.03.2017: Day 4 – Infrared Spectroscopy and Microscopy Chair: Ljiljana Puskar HZB, Berlin‐Adlershof

Brief CV –Dr. Ljiljana Puskar

Current position: Senior Scientist, Infrared Beamline, Institute of Methods for Material Development Helmholtz- Zentrum Berlin für Materialien und Energie, HZB, Berlin Research expertise/activities in research: Ljiljana Puskar is a Senior Scientist at the IRIS beamline at BESSY II within the institute of Methods of Material Developments Helmholtz-Zentrum Berlin für Materialien und Energie, HZB (EM-IMM), Berlin with research focus on energy and materials. One of her interests is the investigation of water retention efficiency and stability of ionomeric proton exchange membranes (PEMs) used in fuel cells. She employs in situ infrared techniques available at the infrared beamline using both infrared and THz synchrotron radiation. Prior to joining the EM- IMM group she had held a positon of an Infrared Beamline Scientist at the Australian Synchrotron with 7 years of experience of Infrared Microspectroscopy. She was involved in diverse fields of science, in particular biological and biomedical research and led the development and support of the cultural heritage community on the IR beamline. She has undertaken experiments at IR beamlines at several international synchrotron facilities including Soleil in Paris, SRC Wisconsin, NSLS Brookhaven, ALS Berkeley and the CLIO Free Electron laser facility in Paris.

Keywords: Infrared microspectroscopy, synchrotron sources, infrared beamline, spatial resolution beyond diffraction limit, advanced IR imaging and enhanced spatial resolution techniques.

Selected 10 most important articles related to the lecture: [1] Chemically Imaging the Spatial Distribution of Acetylated Nanocrystalline Cellulose (NCC) in a Polylactic Acid (PLA) polymer matrix for Improved Dispersion, T. Mukherjee, M.J. Tobin, L. Puskar, M.A. Sani, N. Kao, R. K. Gupta, M. Pannirselvam, N. Quazi, S. Bhattacharya, Cellulose, 2017. doi:10.1007/s10570-017-1217-x [2] Infrared dynamics study of thermally treated perfluoroimide acid proton exchange membranes. L. Puskar, E. Ritter, U. Schade, M. Yandrasits, S. Hamrock, M. Schaberg, E.F. Aziz, Physical Chemistry Chemical Physics, 19, 2017, 626-635. doi:10.1039/C6CP06627E [3] Advances in Fourier transform infrared spectroscopy of natural glasses: From sample preparation to data analysis. F. von Aulock, B. M. Kennedy, C. I. Schipper, J. M. Castro, D. Martin, C. Oze, A. R. Nichols, J. M. Watkins, P. J. Wallace, L. Puskar, F. Bégué, H. Tuffen, Lithos, 206(1), 2014, 52-64. [4] Synchrotron FTIR microscopy of synthetic and natural CO2-H2O fluid inclusions. M.K. Nieuwoudt, M.P. Simpson, J.L. Mauk, M. Tobin, L. Puskar. Vibrational Spectroscopy, 75, 2014, 136-148. [5] Investigation of Historical Dart Poisons Using Synchrotron Based Infrared Microscopy and Spectroscopy. R. A. Goodall, L. Puskar, K. Fisher, E. Mccartney, H. Privett, Vibrational Spectroscopy, 78, 2014, 66-74 [6] Qualitative spectroscopic characterization of the matrix – silane coupling agent interface across metal fibre reinforced ion exchange resin composite membranes. L. Dumée, F.-M. Allioux, R. Reis,

79 Theory Days 17.03.2017: Day 4 – Infrared Spectroscopy and Microscopy Chair: Ljiljana Puskar HZB, Berlin‐Adlershof

M. Duke, S. Gray, M.Tobin, L. Puskar, L. He, P. Hodgson, L. Kong, Vibrational Spectroscopy, 75, 2014, 203 - 212. [7] Deuterated polymers for probing phase separation using Infrared microspectroscopy. R.A. Russell, T. A. Darwish, L. Puskar, D. E. Martin, P.J. Holden, L. John, R. Foster, Biomacromolecules., 15(2), 2014, 644-649. [8] High Spatial Resolution Infrared Micro-Spectroscopy Reveals the Mechanism of Leaf Lignin Decomposition by Aquatic Fungi. J.L. Kerr, D.S. Baldwin, M.J. Tobin, L. Puskar, P. Kappen, G.N. Rees, E. Silvester, PloS one, 8(4), 2013: e60857 [9] High spatial resolution mapping of superhydrophobic cicada wing surface chemistry using infrared microspectroscopy and infrared imaging at two synchrotron beamlines. M.J. Tobin, L. Puskar, J. Hasan, H.K. Webb, C.J. Hirschmugl, M.J. Nasse, G. Gervinskas, S. Juodkazis, G.S. Watson, J.A. Watson, R.J. Crawford and E.P. Ivanova, J. Synchrotron Rad. 20, 2013, 482-489. [10] Synchrotron FTIR Microscopy of Langmuir-Blodgett Monolayers and Polyelectrolyte Multilayers at the Solid-Solid Interface. D.A. Beattie, A. Beaussart, A. Mierczynska-Vasilev, S.L. Harmer, B. Thierry, L. Puskar, M. Tobin, Langmuir, 28, 2012, 1683-1688

80 Theory Days 17.03.2017: Day 4 – Infrared Spectroscopy and Microscopy Chair: Ljiljana Puskar HZB, Berlin‐Adlershof

Advances and applications of infrared synchrotron radiation in microspectroscopy

Ljiljana Puskar Methods for Material Development, Helmholtz-Zentrum für Materialien und Energie GmbH, 12489 Berlin, Germany. [email protected] Fourier transform infrared (FTIR) spectroscopy is an absorbance based technique that provides information on molecular vibrations and rotations.[1]–[3] It allows for specific identification of molecular groups and chemical composition of matter. Both organic and inorganic samples can be analysed ranging from identification of small molecules to complex systems such as biological cells and tissues. It is a non-destructive technique that requires only a small amount of sample for analysis without the use of any staining or tagging. FTIR spectroscopy can provide a biochemical snapshot of complicated biological samples and is often used both diagnostically and as a research tool. FTIR in conjunction with microscopes enables very precise spatial selection of the regions of interest. Many commercially available systems are now capable of fast analysis of large sample areas, as they comprise sophisticated multi-array detectors providing high quality spectra. [4] In this lecture the advantages of infrared radiation from synchrotron sources, instead of the conventional globar sources as available in laboratory based instrumentation, will be highlighted. In order to understand the superior spatial resolution (only limited by diffraction) achieved when synchrotron sources are used, the synchrotron advantages such as the small source size, high beam collimation and focusing capability and high brightness will be discussed.[5] The important factors contributing to the microscope resolution (Fraunhofer diffraction, Point-Spread function and Numerical Aperture) will also be covered. The diffraction limited spatial resolution achievable with synchrotron source microspectroscopy (3 to 5 microns in the Mid-infrared region) allows for the identification of features that are otherwise too small to detect with sufficient signal-to-noise ratio when using conventional instrumentation. Specific examples highlighting this superior lateral resolution, covering diverse fields of scientific research, will be presented. This includes examples from materials science research such as polymer materials used in fuel cells, biological and biomedical research looking at effect of chemotherapeutic drugs for example and also the advantage to the study of cultural heritage materials. [6]–[9] The presentation will describe different methods of measurements and relevant sample preparation and mounting on the microscope stage to achieve the best results. Dispersion artefacts in microscopy such as Mie scattering for example are sometimes a problem and data treatments such as RMieS correction algorithms based on extended multiplicative signal correction (EMSC) have been developed to remove the baseline distortion in FTIR spectra, in particular in biological spectra.[10,][11]

81 Theory Days 17.03.2017: Day 4 – Infrared Spectroscopy and Microscopy Chair: Ljiljana Puskar HZB, Berlin‐Adlershof

Most synchrotron infrared beamlines operate in a point scanning mode using a high sensitivity single element detector and a Fourier transform infrared spectrometer to record IR absorbance spectra sequentially as the sample is scanned through the focused synchrotron beam. Commercial infrared microscopes with multi element focal plane array (FPA) imaging detectors trade a reduction in signal-to-noise performance for high sample throughput. Several synchrotron beamlines have now been coupled to FPA instruments which allows large samples areas to be imaged with a spatial resolution not achievable using conventional IR sources.[12][13] Further developments to extent infrared microspectroscopy beyond the far field diffraction limit are being undertaken at several synchrotron facilities worldwide.[14]–[16] Two alternative techniques based on photothermal expansion and on near-field scattering from an AFM probes are used. These latest developments will be outlined in the talk.

References: [1] Chalmers John M. and Griffiths Peter R., Handbook of Vibrational Spectroscopy. Chichester, UK: John Wiley & Sons, Ltd, 2001. [2] P. R. Griffiths and J. A. de Haseth, Fourier Transform Infrared Spectrometry. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2007. [3] B. H. Stuart, Infrared Spectroscopy: Fundamentals and Applications, vol. 8. 2004. [4] T. G. Rochow and P. A. Tucker, “Fourier Transform Infrared Microscopy,” in Introduction to Microscopy by Means of Light, Electrons, X Rays, or Acoustics, Boston, MA: Springer US, 1994, pp. 257–264. [5] P. Dumas and L. Miller, “The use of synchrotron infrared microspectroscopy in biological and biomedical investigations,” vol. 32, pp. 3–21, 2003. [6] K. L. Munro, K. R. Bambery, E. A. Carter, L. Puskar, M. J. Tobin, B. R. Wood, and C. T. Dillon, “Synchrotron radiation infrared microspectroscopy of arsenic-induced changes to intracellular biomolecules in live leukemia cells,” Vib. Spectrosc., vol. 53, no. 1, pp. 39–44, May 2010. [7] J. L. Kerr, D. S. Baldwin, M. J. Tobin, L. Puskar, P. Kappen, G. N. Rees, and E. Silvester, “High Spatial Resolution Infrared Micro-Spectroscopy Reveals the Mechanism of Leaf Lignin Decomposition by Aquatic Fungi,” PLoS One, vol. 8, no. 4, 2013. [8] T. Mukherjee, M. J. Tobin, L. Puskar, M.-A. Sani, N. Kao, R. K. Gupta, M. Pannirselvam, N. Quazi, and S. Bhattacharya, “Chemically imaging the interaction of acetylated nanocrystalline cellulose (NCC) with a polylactic acid (PLA) polymer matrix,” Cellulose, Feb. 2017. [9] N. Salvadó, S. Butí, M. a. G. Aranda, and T. Pradell, “New insights on blue pigments used in 15th century paintings by synchrotron radiation-based micro-FTIR and XRD,” Anal. Methods, vol. 6, p. 3610, 2014. [10] P. Bassan, H. J. Byrne, F. Bonnier, J. Lee, and P. Gardner, “Resonant Mie scattering in infrared spectroscopy of biological materials – understanding the ‘ dispersion artefact ,’” vol. 2009, no. 1, pp. 1586–1593, 2009. [11] J. Filik, M. D. Frogley, J. K. Pijanka, K. Wehbe, and G. Cinque, “Electric field standing wave artefacts in FTIR micro-spectroscopy of biological materials.,” Analyst, vol. 137, no. 4, pp. 853– 61, 2012.

82 Theory Days 17.03.2017: Day 4 – Infrared Spectroscopy and Microscopy Chair: Ljiljana Puskar HZB, Berlin‐Adlershof

[12] E. C. Mattson, M. Unger, B. Manandhar, Z. Alavi, and C. J. Hirschmugl, “Multi-beam Synchrotron FTIR Chemical Imaging: Impacts of Schwarzschild Objective and Spatial Oversampling on Spatial Resolution,” J. Phys. Conf. Ser., vol. 425, no. 14, p. 142001, Mar. 2013. [13] C. J. Hirschmugl and K. M. Gough, “Fourier transform infrared spectrochemical imaging: Review of design and applications with a focal plane array and multiple beam synchrotron radiation source,” Appl. Spectrosc., vol. 66, no. 5, pp. 475–491, 2012. [14] H. a Bechtel, E. a Muller, R. L. Olmon, M. C. Martin, and M. B. Raschke, “Ultrabroadband infrared nanospectroscopic imaging,” Proc. Natl. Acad. Sci. U. S. A., vol. 111, no. 20, pp. 7191–6, 2014. [15] P. Hermann, A. Hoehl, P. Patoka, F. Huth, E. Ruehl, and G. Ulm, “Near-field imaging and nano- Fourier-transform infrared spectroscopy using broadband synchrotron radiation.,” Opt. Express, vol. 21, no. 3, pp. 2913–9, 2013. [16] P. M. Donaldson, C. S. Kelley, M. D. Frogley, J. Filik, K. Wehbe, and G. Cinque, “Broadband near- field infrared spectromicroscopy using photothermal probes and synchrotron radiation,” Opt. Express, vol. 24, no. 3, pp. 1852–1864, 2016.

83 Theory Days 17.03.2017: Day 4 – Infrared Spectroscopy and Microscopy Chair: Ljiljana Puskar HZB, Berlin‐Adlershof

BRIEF CV – Dr. Eglof Ritter

Current position: Eglof Ritter is a scientist at the Insititute for Biology, Experimental Biophysics, Institute of Biophysics (BPI) at the Humboldt-Universität zu Berlin. His focus is on the application of time- resolved infrared and UV/Vis spectroscopy for the investigation of structure/ function relationships of proteins, especially photoreceptors. He is a visiting scientist at the Helmholtz- Zentrum Berlin and at the Charité-Universitätsmedizin Berlin. Research expertise/activities in research: His research activities comprise spectroscopical techniques (with focus on time-resolved infrared, UV/Vis and fluorescence spectroscopy) and other biophysical methods (reconstitution of proteins in lipid membranes, HPLC, site-directed mutagenesis) for the investigation of biological systems involved in signal transduction, the visual system and physiology of vision, chromophore-protein interactions, membrane proteins. A special focus lies also on the function of proton channels and proton pumps. Currently, he is setting up a new time-resolved mid-infrared/UV/Vis spectrometer for single-shot processes at the infrared beamline IRIS at BESSY II.

Keywords: infrared spectroscopy, UV/Vis spectroscopy, flash photolysis, single-shot reactions; photoreceptor, protein conformational changes, ion channels, ion pumps, protein- cofactor interactions, rhodopsin, channelrhodopsin

Selected 10 most important articles related to the lecture: [1] Ritter E, Puskar L, Bartl FJ, Aziz EF, Hegemann P, Schade U. Time-resolved infrared spectroscopic techniques as applied to channelrhodopsin. Front Mol Biosci. 2015;2:38. [2] Schade U, Ritter E, Hegemann P, Aziz EF, Hofmann KP. Concept for a single-shot mid-infrared spectrometer using synchrotron radiation. Vib Spectrosc. Elsevier B.V.; 2014;75:190–5. [3] Kuhne J, Eisenhauer K, Ritter E, Hegemann P, Gerwert K, Bartl F. Early formation of the ion- conducting pore in channelrhodopsin-2. Angew Chemie - Int Ed. 2015;54(16):4953–7. [4] Puskar L, Ritter E, Schade U, Yandrasits M, Hamrock SJ, Schaberg M, et al. Infrared dynamics study of thermally treated perfluoroimide acid proton exchange membranes. Phys Chem Chem Phys. Royal Society of Chemistry; 2017; [5] Ritter E, Piwowarski P, Hegemann P, Bartl FJ. Light-dark adaptation of channelrhodopsin C128T mutant. J Biol Chem. 2013;288(15):10451–8. [6] Beyrière F, Sommer ME, Szczepek M, Bartl FJ, Hofmann KP, Heck M, Ritter E. Formation and Decay of the Arrestin·Rhodopsin Complex in Native Disc Membranes. J Biol Chem. 2015 May 15;290(20):12919–28. [7] Ritter E, Piwowarski P, Hegemann P, Bartl FJ. Light-dark adaptation of channelrhodopsin C128T mutant. J Biol Chem. 2013;288(15):10451–8. [8] Ritter E, Stehfest K, Berndt A, Hegemann P, Bartl FJ. Monitoring light-induced structural changes of Channelrhodopsin-2 by UV-visible and Fourier transform infrared spectroscopy. J Biol Chem. 2008 Dec;283(50):35033–41.

84 Theory Days 17.03.2017: Day 4 – Infrared Spectroscopy and Microscopy Chair: Ljiljana Puskar HZB, Berlin‐Adlershof

[9] Ritter E, Elgeti M, Hofmann KP, Bartl FJ. Deactivation and proton transfer in light-induced metarhodopsin II/metarhodopsin III conversion: A time-resolved fourier transform infrared spectroscopic study. J Biol Chem. 2007;282(14):10720–30. [10] Ritter E, Zimmermann K, Heck M, Hofmann KP, Bartl FJ. Transition of rhodopsin into the active metarhodopsin II state opens a new light-induced pathway linked to schiff base isomerization. J Biol Chem. 2004;279(46):48102–11.

85 Theory Days 17.03.2017: Day 4 – Infrared Spectroscopy and Microscopy Chair: Ljiljana Puskar HZB, Berlin‐Adlershof

Time-resolved infrared spectroscopy and its application in life and material sciences

Eglof Ritter Institut für Biophysik (BPI), Experimentelle Biophysik Humboldt-Universität zu Berlin, 10115 Berlin, Germany [email protected] Infrared (IR) spectroscopy is an important and widely used tool in physics, chemistry and biology (1). By probing vibrational and rotational modes of bonds it provides information about matter on a molecular level. Due to its relatively low energy it allows to study the molecules in their native or nearly native environments. This is of high importance, for example, when structure/ function relationships in proteins or other functional systems are to be investigated. The infrared spectral range spans from ~800 nm to ~1 mm and can be divided into near infrared (NIR), 0.8 – 2.5 μm, mid-infrared (MIR), 2.5 – 25 μm and far-infrared (FIR), 25 – 1000 μm. Due to the variety of vibrational modes showing up in MIR, this spectral range is usually of highest scientific interest. An overview of the applications of MIR spectroscopy in biophysics is given in ref. (2). Proteins are one of the key-players in living organisms. They perform a huge variety of functions in the cell, for example in the process of signaling, transport or energy conversion. They consist of amino acids linked by peptide bonds. The sequence of the amino acids determines the three-dimensional structure, and thus, together with the amino acid side chains and covalently attached other residues – so-called prosthetic groups or cofactors – the protein’s function. This function can be achieved through a conformational change of the protein, initiated by signals like the binding of a molecule or absorption of light. Even slight changes in the amino acid sequence can lead to tremendous alterations in function. One example are the microbial rhodopsins whose prototype bacteriorhodopsin (bR) has been extensively studied by IR spectroscopy. It is a light-driven proton (H+) pump in the purple membranes of Halobacterium salinarum. Absorption of light in this protein causes a trans-cis isomerization of its cofactor retinal. This triggers in turn conformational changes in the protein resulting in the transport of a proton across the membrane against the electrochemical gradient. However, the exchange of a single amino acids converts the protein into a chloride (Cl-) pump (3). Other closely related proteins are the channelrhodopsins, first discovered in the eye spot of green algae (4). Although of high sequence homology with bR, instead of pumping protons through the membrane these proteins constitute light-switching ion channels. Due to these properties, their discovery and application has founded the new field of optogenetics (5). Infrared spectroscopy has been among the first techniques to study the molecular basis of their photocycles (6). Conventional IR spectroscopy provides information on the static structure of matter such as water (7), amino acids, protonation of groups, and composition of lipids (8), and protein secondary structures (9). For the study of dynamical systems, changes of these properties on timescales usually much faster than seconds are of interest. To obtain these changes is a huge challenge, since extinction coefficients in the infrared are usually low and in the order of

86 Theory Days 17.03.2017: Day 4 – Infrared Spectroscopy and Microscopy Chair: Ljiljana Puskar HZB, Berlin‐Adlershof

~ 200 - 300 M-1 cm-1. Therefore, difference spectroscopy is applied, where the spectrum of an active, “working” state is subtracted from a spectrum of the inactive, “resting” state (10). The most commonly used type of infrared spectrometer, the Fourier Transform (FT) spectrometer, is well suited for the acquisition of time-resolved difference spectra. It is based on an interferometer that allows recording of spectra down to the millisecond time regime. Starting from this type of spectrometer, the lecture gives an overview of current time- resolved infrared techniques and their applications, including the FTIR rapid- and Step-Scan methods (1,11–13), dispersive techniques (14), methods based on quantum cascade lasers (15,16) or pump-probe techniques (17).

References: [1] Griffiths PR, Haseth JA De. Fourier Transform Infrared Spectrometry. Vol. 222, Transform. 2007. 704 p. [2] Friedrich Siebert; Peter Hildebrandt. Vibrational Spectroscopy in life science. Vol. 286, Wiley VCH. 2008. 321 p. [3] Brown LS, Chon Y, Kandori H, Maeda A, Needleman R, Lanyi JK. Conversion of Bacteriorhodopsin into a. 1995;269(July):73–5. [4] Nagel G, Ollig D, Fuhrmann M, Kateriya S, Musti AM, Bamberg E, et al. Channelrhodopsin-1: a light-gated proton channel in green algae. Science. Max-Planck-Institut fur Biophysik, Kennedyallee 70, 60596 Frankfurt am Main, Germany. [email protected]; 2002 Jun;296(5577):2395–8. [5] Hegemann P, Nagel G. From channelrhodopsins to optogenetics. EMBO Mol Med. 2013;5(2):173–6. [6] Ritter E, Stehfest K, Berndt A, Hegemann P, Bartl FJ. Monitoring light-induced structural changes of Channelrhodopsin-2 by UV-visible and Fourier transform infrared spectroscopy. J Biol Chem. 2008 Dec;283(50):35033–41. [7] Garczarek F, Gerwert K. Functional waters in intraprotein proton transfer monitored by FTIR difference spectroscopy. Nature. Lehrstuhl für Biophysik, Ruhr-Universität Bochum, D-44780 Bochum, Germany.; 2006 Jan;439(7072):109–12. [8] Barth A. Infrared spectroscopy of proteins. Biochim Biophys Acta - Bioenerg. 2007 Sep;1767(9):1073–101. [9] Goormaghtigh E, Cabiaux V, Ruysschaert J-M. Secondary Structure and Dosage of Soluble and Membrane Proteins by Attenuated Total Reflection Fourier Transform Infrared Spectroscopy. Eur Journal Biochem. 1990;193:409–20. [10] Rothschild KJ, Zagaeski M, Cantore WA. Conformational changes of bacteriorhodopsin detected by Fourier transform infrared difference spectroscopy. Biochem Biophys Res Commun. 1981;103(2):483–9. [11] Griffiths PR, Hirsche BL, Manning CJ. Ultra-rapid-scanning Fourier transform infrared spectrometry. Vib Spectrosc. 1999;19:165–76. [12] Murphy RE, Cook FH, Sakai H. Time-resolved Fourier spectroscopy. J Opt Soc Am. 1975;65(5):600–4. [13] Uhmann W, Becker A, Taran C, Siebert F. Time-resolved FT-IR absorption spectroscopy using a step-scan interferometer. Appl Spectrosc. 1991;45:390–7.

87 Theory Days 17.03.2017: Day 4 – Infrared Spectroscopy and Microscopy Chair: Ljiljana Puskar HZB, Berlin‐Adlershof

[14] Schade U, Ritter E, Hegemann P, Aziz EF, Hofmann KP. Concept for a single-shot mid-infrared spectrometer using synchrotron radiation. Vib Spectrosc [Internet]. Elsevier B.V.; 2014;75:190–5. Available from: http://dx.doi.org/10.1016/j.vibspec.2014.07.004 [15] Zhang L, Tian G, Li J, Yu B. Applications of Absorption Spectroscopy Using Quantum Cascade Lasers. Appl Spectrosc. 2014;68(10):1095–107. [16] Lórenz-Fonfría VA, Schultz B-J, Resler T, Schlesinger R, Bamann C, Bamberg E, et al. Pre-Gating Conformational Changes in the ChETA Variant of Channelrhodopsin-2 Monitored by Nanosecond IR Spectroscopy. J Am Chem Soc. 2015;137(5):1850–61. [17] van Wilderen LJGW, van der Horst M a., van Stokkum IHM, Hellingwerf KJ, van Grondelle R, Groot ML. Ultrafast infrared spectroscopy reveals a key step for successful entry into the photocycle for photoactive yellow protein. Proc Natl Acad Sci U S A. 2006; 103(41):15050–5.

88 Theory Days 17.03.2017: Day 4 – Infrared Spectroscopy and Microscopy Chair: Ljiljana Puskar HZB, Berlin‐Adlershof

Brief CV –Dr. Jihaan Ebad-Allah

Current position: Postdoctoral of experimental physics at the University Augsburg, Germany Research expertise/activities in research: The research activities of Dr. Ebad-Allah focus on the study of the vibrational, electronic, and structural properties of the transition-metal oxide compounds (e. g., magnetite and Iridates), low-dimensional oxychloride compounds, super hard nitrides, square-planar d8-ML4 complexes, and nanocrystal compounds such as spider Silk of Nephila pilipes. These compounds may exhibit several interesting physical phenomena such as insulator-to-metal transition, topological order, charge ordering, and structural phase transition. The main aim of her research is concentrating on characterization of the physical phenomena of these compounds using IR microspectroscopy and x-ray diffraction techniques under external pressures up to 25 GPa and\or low temperatures down to 10 K. Infrared spectroscopy technique, together with high pressure and low temperature, forms a powerful tool to probe the dynamics of the charge carriers and provides important information on the fundamental energy scales involved in the various physical phenomena. Moreover, it allows to study both electronic and vibrational low-energy excitations, providing useful information on the microscopic mechanism that develops the electronic ground states. Keywords: infrared spectroscopy, x-ray diffraction, high pressure, low temperature, transition-metal compounds

Selected 8 most important articles related to the lecture: [1] J. Ebad-Allah, B. Kugelmann, F. Rivadulla, and C. A. Kuntscher, Infrared study of the magnetostructural phase transition in correlated CrN, Phys. Rev. B 94, 195118 (2016). [2] W. Scherer, A. C. Dunbar, J. E. Barquera-Lozada, D. Schmitz, G. Eickerling, D. Kratzert, D. Stalke, A. Lanza, P. Macchi, N. P. M. Casati, J. Ebad-Allah, and C. A. Kuntscher, Anagostic Interactions under Pressure: Attractive or Repulsive?, Angew. Chem. 127, 2553 (2015). [3] A. M. Anton, W. Kossack, C. Gutsche, R. Figuli, P. Papadopoulos, J. Ebad-Allah, C. A. Kuntscher and F. Kremer, Pressure-Dependent FTIR-Spectroscopy on the Counterbalance between External and Internal Constraints in Spider Silk of Nephila pilipes, Macromolecules 46, 4919-4923 (2013). [4] J. Ebad-Allah, L. Baldassarre, M. Sing, R. Claessen, V.A.M. Brabers, and C.A. Kuntscher, Polaron physics and crossover transition in magnetite probed by pressure-dependent infrared spectroscopy under pressure, J. Phys.: Condens. Matter 25, 035602 (2013). [5] J. Ebad-Allah, L. Baldassarre, R. Claessen, M. Sing, V.A.M. Brabers, and C.A. Kuntscher, Pressure dependence of the Verwey transition in magnetite: an infrared spectroscopic point of view, J. Appl. Phys. 112, 073524 (2012). [6] J. Ebad-Allah, A. Schoenleber, S. van Smaalen, M. Hanfland, M. Klemm, S. Horn, S. Glawion, M. Sing, R. Claessen, and C.A. Kuntscher, Two pressure-induced structural phase transitions in TiOCl, Phys. Rev. B 82, 134117 (2010). [7] C. A. Kuntscher, J. Ebad-Allah, A. Pashkin, S. Frank, M. Klemm, S. Horn, A. Schoenleber, S. van Smaalen, M. Hanfland, S. Glawion, M. Sing, and R. Claessen, Filling of the Mott-Hubbard gap in

89 Theory Days 17.03.2017: Day 4 – Infrared Spectroscopy and Microscopy Chair: Ljiljana Puskar HZB, Berlin‐Adlershof

the oxyhalides TiOCl and TiOBr induced by external pressure, High Pressure Research 29, 509 (2009). [8] J. Ebad-Allah, L. Baldassarre, M. Sing, R. Claessen, V.A.M. Brabers, and C.A. Kuntscher, Infrared studies of magnetite under high pressure, High Pressure Research 29, 500 (2009).

Brief CV – Prof. Dr. Christine Kuntscher

Current position: Professor of experimental physics at the University Augsburg, Germany Research expertise/activities in research: The research activities of Prof. Kuntscher focus on the study of the electronic, lattice dynamical, and structural properties of materials with strong electronic correlations, materials with strong spin-orbit coupling, materials with novel topological phases, low- dimensional materials, as well as molecular nanostructures. The materials are characterized by optical spectroscopy and x-ray diffraction under extreme conditions (low temperature, high pressure). Her research group in particular focuses on IR microspectroscopy studies on materials at high pressure. By reflection and transmission measurements from the infrared up to the visible frequency range, the charge and lattice dynamics can be studied as a function of pressure up to ~25 GPa. The pressure-dependent spectroscopic experiments are routinely conducted at room temperature. Studied materials include transition-metal compounds, organic charge-transfer salts, and carbon nanotubes. The scientific questions addressed are, e.g., charge transport mechanism, pressure-induced superconductivity, structural phase transitions, insulator-metal transition, and pressure-induced changes of the dimensionality of low-dimensional systems.

Keywords: infrared microspectroscopy, high pressure, functional transition-metal compounds, molecular nanostructures

Selected 10 most important articles related to the lecture: [1] F. Burkert, J. Kreisel, and C. A. Kuntscher, Optical spectroscopy study on the photo-response in multiferroic BiFeO3, Appl. Phys. Lett. 109, 182903 (2016). [2] B. Anis, K. Yanagi, and C. A. Kuntscher, Optical microspectroscopy study on enriched (11,10) SWCNTs encapsulating C60 fullerene molecules, Carbon 107, 593 (2016). [3] J. Ebad-Allah, B. Kugelmann, F. Rivadulla, and C. A. Kuntscher, Infrared study of the magnetostructural phase transition in correlated CrN, Phys. Rev. B 94, 195118 (2016). [4] E. Uykur, T. Kobayashi, W. Hirata, S. Miyasaka, S. Tajima, and C. A. Kuntscher, Optical Study of BaFe2As2 under pressure: Coexistence of spin-density-wave gap and superconductivity, Phys. Rev. B 92, 245133 (2015). [5] C. A. Kuntscher, A. Huber und M. Hücker, Suppression of the Charge-Density-Wave State in Sr10Ca4Cu24O41 by External Pressure, Phys. Rev. B 89, 134510 (2014).

90 Theory Days 17.03.2017: Day 4 – Infrared Spectroscopy and Microscopy Chair: Ljiljana Puskar HZB, Berlin‐Adlershof

[6] C. A. Kuntscher, K. Rabia, M. K. Forthaus, M. M. Abd-Elmeguid, F. Rivadulla, Y. Kato, and C. D. Batista, Nonmonotonic evolution of the charge gap in ZnV2O4 under pressure, Phys. Rev. B 86, 020405(R) (2012). [7] S. Bordacs, D. Varjas, I. Kezsmarki, G. Mihaly, L. Baldassarre, A. Abouelsayed, C.A. Kuntscher, K. Ohgushi, and Y. Tokura, Magnetic-Order-Induced Crystal Symmetry Lowering in ACr2O4 Ferrimagnetic Spinels, Phys. Rev. Lett. 103, 077205 (2009). [8] R. Haumont, P. Bouvier, A. Pashkin, K. Rabia, S. Frank, B. Dkhil, W. A. Crichton, C. A. Kuntscher, and J. Kreisel, Effect of high pressure on multiferroic BiFeO3, Phys. Rev. B 79,184110 (2009). [9] C. A. Kuntscher, S. Frank, A. Pashkin, M. Hoinkis, M. Klemm, M. Sing, S. Horn und R. Claessen, Possible pressure-induced insulator-to-metal transition in low-dimensional TiOCl, Phys. Rev. B 74, 184402 (2006). [10] C. A. Kuntscher, S. Schuppler, P. Haas, G. Gorshunov, M. Dressel, F. Lichtenberg, A. Herrnberger, F. Mayr, and J. Mannhart, Extremely small energy gap in the quasi-one dimensional linear chain compound SrNbO3.41, Phys. Rev. Lett. 89, 236403 (2002).

91 Theory Days 17.03.2017: Day 4 – Infrared Spectroscopy and Microscopy Chair: Ljiljana Puskar HZB, Berlin‐Adlershof

Application of infrared/THz synchrotron radiation in material sciences

Christine Kuntscher, Jihaan Ebad-Allah Experimentalphysik 2, Universität Augsburg, D-86159 Augsburg, Germany [email protected], [email protected] Infrared spectroscopy is a well-established technique to determine the charge dynamics, lattice dynamics and various excitations, like intraband transitions, interband transitions, and excitons, in materials by measuring the optical response in transmission or reflection mode.1 The combination of infrared spectroscopy with a lateral resolution in the m range – so-called microspectroscopy – enables the mapping of inhomogeneous samples and the study of small, micrometer sized samples. The latter is in particular interesting for the characterization of materials under high external pressure, which is generally generated in diamond anvil cells on samples with lateral dimensions of a few hundred m.2 In situ investigations of the phenomena induced or tuned by external pressure are of great interest and importance for both fundamental and applied sciences. This has just recently been demonstrated by the metallization of hydrogen under a pressure of several hundred 100 GPa – a phenomenon predicted already 80 years ago.3 Pressure provides a unique possibility to modify the crystal structure and the properties of materials, like the electronic band structure, the chemical bonding, and also enables the formation of new compounds. The application of pressure can induce structural phase transitions, insulator-metal-transitions or a dimensional crossover in materials, and exotic new topological phases or superconductivity can emerge. Studies of the materials’ properties under high pressure are of high importance of many fields of research in physics, materials science, chemistry, geoscience, and mineralogy. I will give recent examples of interesting phenomena, which can be induced in materials by applying high external pressure. An introduction of the technical aspects of pressure studies, the acquisition and analysis of optical data in a diamond anvil cell, as well as the microscopic setups will be given.4, 5 As a demonstration of the capability of this experimental technique, the results of pressure- dependent infrared microspectroscopy studies on magnetite Fe3O4 will be discussed in detail. Magnetite is the oldest know magnetic material and the prototype material for the Verwey 6-9 transition, which leads to charge ordering below the transition temperature TV~120 K. The behaviour of the Verwey transition at high pressure will be discussed based on the temperature- and pressure-dependent optical response.10, 11 The optical results will be compared to the controversial results found in the literature.

References: [1] M. Dressel and G. Grüner, Electrodynamics in Solids (Cambridge University Press, 2002). [2] M. Eremets, High pressure experimental methods (Oxford University Press, 1996). [3] R. P. Dias and I. F. Silvera, Science (2017).

92 Theory Days 17.03.2017: Day 4 – Infrared Spectroscopy and Microscopy Chair: Ljiljana Puskar HZB, Berlin‐Adlershof

[4] E. Uykur, T. Kobayashi, W. Hirata, S. Miyasake, S. Tajima, and C. A. Kuntscher, Optical study of BaFe2As2 under pressure: Coexistence of spin-density-wave gap and superconductivity, Phys. Rev. B 92, 245133 (2015). [5] C. A. Kuntscher, A. Huber, and M. Hücker, Suppression of the charge-density-wave state in Sr10Ca4Cu24O41 by external pressure, Phys. Rev. B 89, 134510 (2014). [6] P. A. Miles, W. B. Westphal, and A. von Hippel, Dielectric spectroscopy of ferromagnetic semiconductors, Rev. Mod. Phys. 29 279 (1957). [7] L.V. Gasparov, D. B. Tanner, D. B. Romero, H. Berger, G. Margaritondo, and L. Forro, Infrared and Raman studies of the Verwey transition in magnetite, Phys. Rev. B, Vol.62, 7939 (2000).

[8] S. Todo, N. Takeshita, T. Kanehara, T. Mori, and N. Mori, Metallization of magnetite (Fe3O4) under high pressure, J. Appl. Phys. 89, 7347(2001). [9] G. Kh. Rozenberg, M. P. Pasternak, W. M. Xu, Y. Amiel, M. Hanfland, M. Amboage, R. D. Taylor, and R. Jeanloz, Origin of the Verwey transition in magnetite, Phys. Rev. Lett. 96, 045705 (2006). [10] J. Ebad-Allah, L. Baldassarre, M. Sing, R. Claessen, V. A. M. Brabers, and C. A. Kuntscher, Polaron physics and crossover transition in magnetite probed by pressure-dependent infrared spectroscopy, J. Phys.: Condens. Matter 25, 035602 (2013). [11] J. Ebad-Allah, L. Baldassarre, M. Sing, R. Claessen, V. A. M. Brabers, and C. A. Kuntscher, Pressure dependence of the Verwey transition in magnetite: An infrared spectroscopic point of view, J. Appl. Phys. 112, 073524 (2012).

93 Theory Days 17.03.2017: Day 4 – Infrared Spectroscopy and Microscopy Chair: Ljiljana Puskar HZB, Berlin‐Adlershof

Brief CV – Dr. Augusto Marcelli

Current positions: INFN - Laboratori Nazionali di Frascati, Frascati, 00044, Italy; also at RICMASS, Rome International Center for Materials Science Superstripes, 00185 Rome, Italy; also at CNR - Instituto Struttura della Materia and Elettra-Sincrotrone Trieste, I-34149 Trieste, Italy Research expertise/activities in research: Augusto Marcelli was involved in synchrotron radiation (SR) researches since his degree in Physics in 1984. He was appointed to a permanent position as a staff scientist at the INFN in 1985 and in the 90’s was leader of one of the first European teams working in the Japanese SR facilities of Tristan and PF at Tsukuba. In Japan he realized some of the early SR x-ray circular polarized experiments. In particular, he performed the first x-ray circular dichroism experiments able to monitor the dynamics of magnetic transitions. From 1990 to 1996 he was a Contract Professor of Physics at Camerino University, but lectured also in the Universities of Roma I, Roma III and Salerno. He proposed and built in the DAΦNE-Light laboratory the first Italian Infrared SR beamline and was the scientist responsible for its operation till 2006. From 2005 to 2006 he was also responsible of the UV beamline at DAΦNE. He opened new frontiers in mineralogical analysis of extremely small amount of dust, gathering unique information by applying SR spectroscopic methods such as Total-Reflection X-Ray Fluorescence (TXRF) and X-ray Absorption Near Edge Structure (XANES) techniques. He demonstrated that the characterization of airborne particle components trapped inside deep ice cores, precious proxy for assessing environmental and atmospheric circulation variability and regional-to- global climate change at different time scales, is possible also at concentration down to the ppb range. For the INFN he was responsible of projects approved within the framework of the X Protocol of Scientific and Technological Cooperation between Italy and China devoted to SR applications. In the framework of International Cooperation Agreements of the Foreign Minister he was coordinator of a bilateral program between Italy and Argentina for biomedical researches (Non conventional analysis with synchrotron radiation of biological samples for biomedical applications - 2006-08) and coordinator of the project Imaging and spectromicroscopy with synchrotron radiation within the framework of the XII Protocol of Scientific and Technological Cooperation between Italy and China (2007-09). From 2001 he is consultant of the IHEP (Institute of High Energy Physics - China) for synchrotron radiation activities and in 2011 has been the first Italian Visiting Physics Professor of the Chinese Academy of Science. Since 1984, he proposed and run in cooperation with national and international teams several experiments approved by the Scientific Panels of many SR facilities operational in the world: BESSY, BSRF, Diamond, NSRL, KEK, LURE, SSRL, SRS, UVSOR and ESRF.

94 Theory Days 17.03.2017: Day 4 – Infrared Spectroscopy and Microscopy Chair: Ljiljana Puskar HZB, Berlin‐Adlershof

In the European framework he has been the principal investigator for INFN of two networks and coordinators of the DASIM (Diagnostic Applications of Synchrotron Infrared Micro- spectroscopy) initiative involving all European SR IR microscopy facilities. With a H-index = 37, since 2013 Marcelli is present in the list of the Top Italian Scientists (TIS) of the Via-academy.org (http://www.topitalianscientists.org).

Keywords: correlation phenomena in x-ray absorption spectroscopy, multiple scattering theory applied to core level x-ray absorption spectra of solid and liquid systems, circular magnetic x-ray dichroism in intermetallic rare earth compounds, soft x-ray absorption of light elements of geophysical interest and under extreme conditions, FTIR micro-spectroscopy and IR imaging applied to proteins, cells and tissues, time resolved experiments in the IR domain and synchrotron radiation instrumentation, IR and x-ray optics, fast infrared detectors and RF accelerator components.

Selected 10 most important articles related to the lecture: [1] N. Poccia, A. Ricci, G. Campi, M. Fratini, A. Puri, D. Di Gioacchino, A. Marcelli, M. Reynolds, M. Burghammer, N.L. Saini, G. Aeppli and A. Bianconi, Optimum inhomogeneity of local lattice distortions in La2CuO4+y, PNAS 109, 15685-15690 (2012) [2] C. Petibois, M. Piccinini, M.A. Cestelli-Guidi, G. Déléris and A. Marcelli, A bright future for synchrotron imaging, Nature Photonics 3, 177 (2009) [3] E.M. Sheregii, J. Cebulski, A. Marcelli, and M. Piccinini, Temperature Dependence Discontinuity of the Phonon Mode Frequencies Caused by a Zero-Gap State in HgCdTe Alloys, Phys. Rev. Lett. 102, 045504 (2009) [4] P. Innocenzi, L. Malfatti, M. Piccinini, D. Grosso and A. Marcelli, Stain Effects Studied by Time- Resolved Infrared Imaging, Anal. Chem 81, 551-556 (2008) [5] Jun Zhong, Li Song, Jie Meng, Bin Gao, Wangsheng Chu, Haiyan Xu, Yi Luo, Jinghua Guo, Augusto Marcelli, Sishen Xie and Ziyu Wu, Bio-nano interaction of proteins adsorbed on single-walled carbon nanotubes, Carbon 47, 967-973 (2009) [6] P. Falcaro, S. Costacurta, L. Malfatti, M. Takahashi, T. Kidchob, M.F. Casula, M. Piccinini, A. Marcelli, B. Marmiroli, H. Amenitsch, P. Schiavuta and P. Innocenzi, Fabrication of Mesoporous Functionalized Arrays by Integrating Deep X-Ray Lithography with Dip-Pen Writing, Adv. Mat. 20, 1864-1869 (2008) [7] M. Takahashi, T. Maeda, K. Uemura, J. Yao, Y. Tokuda, T. Yoko, H. Kaji, A. Marcelli and P. Innocenzi, Photoinduced Formation of Wrinkled Microstructures with Long-Range Order in Thin Oxide Films, Adv. Mater. 19, 4343–4346 (2007) [8] A. Sacchetti, M. Cestelli Guidi, E. Arcangeletti, A. Nucara, P. Calvani, M. Piccinini, A. Marcelli and P. Postorino, Far-infrared absorption of La(1-x)CaxMnO(3-y) at high pressure, Phys. Rev. Lett. 96, 035503 (2006) [9] P. Falcaro, S. Costacurta, G. Mattei, H. Amenitsch, A. Marcelli, M. Cestelli Guidi, M. Piccinini, A. Nucara, L. Malfatti, T. Kidchob and P. Innocenzi, Highly ordered “defect-free” self-assembled hybrid films with a tetragonal mesostructure, J. Amer. Chem. Soc. 127, 3838 (2005)

95 Theory Days 17.03.2017: Day 4 – Infrared Spectroscopy and Microscopy Chair: Ljiljana Puskar HZB, Berlin‐Adlershof

[10] P. Innocenzi, L. Malfatti, T. Kidchob, P. Falcaro, M. Cestelli Guidi, M. Piccinini and A. Marcelli, Kinetics of polycondensation reactions during self-assembly of mesostructured films studied by in situ synchrotron infrared spectroscopy, Chem. Comm. 18, 2384 (2005)

96 Theory Days 17.03.2017: Day 4 – Infrared Spectroscopy and Microscopy Chair: Ljiljana Puskar HZB, Berlin‐Adlershof

SR IR micro-spectroscopy, a unique powerful molecular probe for time resolved imaging experiments at high spatial resolution. Perspectives for combinatorial experiments to characterize materials and dynamical phenomena

Augusto Marcelli 1INFN - Laboratori Nazionali di Frascati, Frascati, 00044, Italy 2RICMASS, Rome International Center for Materials Science Superstripes, 00185 Rome, Italy [email protected] Fourier-transform infrared (FTIR) synchrotron radiation (SR) micro-spectroscopy is a powerful molecular probe at relatively high temporal (~msec) and spatial resolution (~μm) that probes rotations and vibrations of molecules, low-energy excitations of solids and many other phenomena occurring in condensed matter physics, chemistry, biophysics and materials science.[1] Not only at long wavelengths, the role of spatial resolution is widely recognized and advances in microscopy correlate well with advances in materials science, biology, and medicine. Toraldo di Francia is credited with the introduction of the concept of super-resolution of images and in one of his manuscripts he introduced this concept as “detail finer” than the Abbe resolution limit using a series of concentric apertures.[2, 3] Actually, no matter is the wavelength, a focal spot has to satisfy a general relation and may represent an analogous of the Heisenberg uncertainty principle applied to classical fields.[4] We will discuss this issue that is particularly relevant for IR imaging. IR micro-spectroscopy is a non-destructive method that can be applied to metallic, semiconductor or insulator systems but also to biological samples returning accurate information on vibrational and phonon spectra also as a function of external parameters such as temperature or pressure. The incredible performances of non-thermal synchrotron radiation (SR) sources are witnessed by the results obtained in different research areas and the continuously increasing number of users in the existing facilities all around the world. [5,6] Since in the IR region the brilliance of a SR source is between two and three orders of magnitude higher than conventional sources, we observed in the last three decades a continuous increase of IR beamlines and users. The high brilliance of SR (defined as the photon flux or power emitted per source area and solid angle) enables FTIR microscopy and imaging to be performed within a few minutes at the resolution of few microns providing much better performances than any conventional source. Moreover, because of the lack of thermal noise the high signal-to-noise ratio guarantees the achievement of spatial resolution down to the diffraction limit. I will show representative experiments that may experience a great advantage by using IR SR sources and unique applications such as imaging and time-resolved spectroscopy. Indeed SR has a time structure that ranges from hundreds of ps to ns, e.g., comparable with the time of molecular vibrations and several times faster than conformational changes or protein folding phenomena.[5] With the new Focal Plane Array (FPA) detectors now available, the possibility

97 Theory Days 17.03.2017: Day 4 – Infrared Spectroscopy and Microscopy Chair: Ljiljana Puskar HZB, Berlin‐Adlershof

to investigate many processes in real time is now feasible. I will show how with the use of a high circulating current, a dedicated detector set up and a slight defocusing of the source, it is now possible to collect IR images of individual cells at high sensitivity and high spatial resolution within a few minutes. Actually, an optimal coupling between a SR IR source and a FTIR imaging instrumentation equipped with array detectors may really push the existing limits towards a “real time” imaging of many chemical-physical phenomena.[7] Several storage rings are going to be built or upgraded to become ultimate facilities working with high currents and as brilliant and ultra-brilliant radiation sources. [8] Many experiments at high spatial resolution, such as spectro-microscopy at the nanometer scale and with high temporal resolution to investigate kinetics down to the picosecond regime, are now possible. FEL source are going to open also unimaginable time domains and many pump probe experiments are already now feasible combining a SR beam and a laser. Actually, the availability of ultrabright, ultrashort pulses may allow exploring regimes down to the femtosecond where the behavior of a wide variety of samples and materials are fully unknown. Pump-probe experiments where the sample is excited with coherent radiation and the resulting state is measured after a time delay with an ultrabrilliant radiation source can be only one of the main applications of many of the next generation radiation sources. However, one of the next frontiers of SR sources is certainly the combination of different methods in a unique set-up with the ultimate available spatial and temporal resolutions. In the last decade many synchrotron-based researches have exploited the advantage of complementary information provided by time-resolved X-ray techniques and optical methods in the UV/Vis and IR domains. Indeed, new time-resolved and concurrent approaches are necessary to characterize complex systems where physico–chemical phenomena occur under the same experimental conditions, for example to detect kinetic intermediates via complementary but independent observations. I will discuss the possibility to perform combinatorial experiments using IR and other damaging and non-damaging radiation. After the first attempt in 1995 at Daresbury, where a simultaneous IR and x-ray small angle scattering analysis was performed, [9] other SR radiation experiments have been later performed. They probed systems at different wavelengths using X-ray techniques and optical methods in UV/Vis and THz domains, providing unique complementary information. In 2006, a real concurrent approach has been used at Elettra (Trieste) to investigate non-equilibrium processes in mesostructured systems. [10] The scientific case to support an IR/X-ray simultaneous approach with both probes exploiting synchrotron radiation sources is very large going from catalysis, biological systems and materials science phenomena such as molecular structure dynamics, spin crossover dynamics, etc. Reasonable experimental layouts that take advantage of the high brilliance and the wide spectral distribution of the synchrotron radiation emission exist. Some proposals have been already presented and discussed by the scientific panels or are under review. Such conceptually new instruments will be optimized for specific researches or applications devoted to the investigation of dynamic processes and non-equilibrium

98 Theory Days 17.03.2017: Day 4 – Infrared Spectroscopy and Microscopy Chair: Ljiljana Puskar HZB, Berlin‐Adlershof

phenomena, widely occurring in many condensed matter and biological systems and of great interest for both fundamental research and technological applications. I will show experimental results that show the great advantage of IR SR sources and unique applications such as imaging and time-resolved spectroscopy. Indeed combining SR with new Focal Plane Array (FPA) detectors the possibility to investigate many processes in real time becomes feasible. Many other opportunities are around the corner. The first IR-laser source enabled IR microscope covering the 7-12 µm spectral range was released in early 2014 using a series of quantum cascade laser (QCL) sources11 and the operation of the first mid-IR supercontinuum spanning from ~1 μm to more then 13 μm has been experimentally demonstrated. [12] After more than a century, the mid-IR molecular ‘fingerprint region’, which is of key importance for many applications still offer extraordinary research opportunities.

References: [1] A. Marcelli and G. Cinque, Infrared synchrotron radiation beamlines: high brilliance tools for IR spectromicroscopy. A practical guide to the characteristics of the broadband and brilliant non- thermal sources, in: Biomedical Applications of Synchrotron Infrared Microspectroscopy, Ed. D. Moss (Royal Society of Chemistry, 2011) Chapt. 3 pag. 67-104 [2] G. Toraldo di Francia, Super-gain antennas and optical resolving power, Suppl. Nuovo Cimento 9,426–438 (1952). [3] G. Toraldo di Francia, Resolving power and information, J. Opt. Soc. Am. 45: 497-501 (1955) [4] Tasso R. M. Sales, Smallest Focal Spot, Phys. Rev. Lett. 81, 3844-8347 (1988) [5] A. Marcelli, A. Cricenti, W.M. Kwiatek, C. Petibois, Biological applications of synchrotron radiation infrared spectromicroscopy, Biotech. Adv. 30, 1390-1404 (2012) [6] G. Della Ventura, A. Marcelli, F. Bellatreccia, SR-FTIR microscopy and FTIR imaging in the Earth Sciences, Rev. Miner. Geochem. 78, 447-479 (2014) [7] E. Ritter, L. Puskar, F.J. Bartl, E.F. Aziz, P. Hegemann and U. Schade, Time-resolved infrared spectroscopic techniques as applied to channel rhodopsin, Frontiers in Molecular Biosciences 2, 1-7 (2015) doi: 10.3389/fmolb.2015.00038 [8] H. Oyanagi, M. Katoh, R. Bartolini and A. Marcelli, Synchrotron Radiation with New Storage Rings and Upgrades - Our Promised Land, IXAS Research Review 14, 2015 (February 2015) [9] W. Bras, G.E. Derbyshire, D. Bogg, J. Cooke, M.J. Elwell, B.U. Komanschek, S. Naylor and A. Ryan, Simultaneous Studies of Reaction-Kinetics and Structure Development in Polymer Processing, Science 267, 996 (1995). [10] P. Innocenzi, L. Malfatti, T. Kidchob, S. Costacurta, P. Falcaro, M. Piccinini, A. Marcelli, P. Morini, D. Sali and H. Amenitsch, Time-Resolved Simultaneous Detection of Structural and Chemical Changes during Self-Assembly of Mesostructured Films, J. Phys. Chem. C 111, 5345 (2007) [11] G. Clemens, B. Bird, M. Weida, J. Rowlette, M.J. Baker, Quantum cascade laser-based mid-infrared spectrochemical imaging of tissues and biofluids, Spectrosc Eur 26, 14-19 (2014) [12] C. Rosenberg Petersen, U. Møller, I. Kubat, B. Zhou, S. Dupont, J. Ramsay, T. Benson, S. Sujecki, N. Abdel-Moneim, Z. Tang, D. Furniss, A. Seddon and O. Bang, Mid-infrared supercontinuum covering the 1.4–13.3 μm molecular fingerprint region using ultra-high NA chalcogenide step- index fibre, Nature Photonics 8, 830-834 (2014)

99 Theory Days 18.03.2017: Day 5 – Theoretical Modeling Chair: Matthias Berg HZB, Berlin‐Adlershof

Brief CV – Dr. Sergey Bokarev

Sergey Bokarev received his Ph.D. in physical and computational chemistry at the Lomonosov Moscow State University, Russia in 2009 and proceeded with postdoctoral research at Institute of Physics, University of Rostock, Germany. Since 2013 he is a subgroup leader in the same institution. His current research interests include development and application theoretical tools for interpretation of various kinds of spectroscopic experiments in different photon energy ranges as applied to photocatalysis and material science.

Selected publications: [1] H. Wang, S.I. Bokarev, S.G. Aziz, O. Kühn Ultrafast spin-flip dynamics in transition metal complexes triggered by soft X-ray light Phys. Rev. Lett. 118 (2017) 023001. [2] S. Karsten, S.D. Ivanov, S.G. Aziz, S.I. Bokarev, O. Kühn Nuclear dynamical correlation effects in X-ray spectroscopy from a time-domain perspective J. Phys. Chem. Lett. 8 (2017) 992. [3] A. Moguilevski, M. Wilke, G. Grell, S.I. Bokarev, S.G. Aziz, N. Engel, A. Raheem, O. Kühn, I.Y. Kiyan, E.F. Aziz, Ultrafast spin crossover in [FeII(bpy)3]2+: revealing two competing mechanisms by means of XUV photoemission spectroscopy, ChemPhysChem (2017), 10.1002/cphc.201601396. [4] R. Golnak, S.I. Bokarev, R. Seidel, J. Xiao, G. Grell, K. Atak, I. Unger, S. Thürmer, S.G. Aziz, O. Kühn, B. Winter, E.F. Aziz, Joint Analysis of Radiative and Non-radiative Electronic Relaxation Upon X-ray Irradiation of Transition Metal Aqueous Solutions, Sci. Rep. 6 (2016) 24659. [5] S.I. Bokarev, O.S. Bokareva, O. Kühn, A theoretical perspective on charge transfer in photocatalysis. The example of Ir-based systems, Coord. Chem. Rev. 304-305 (2015) 133. [6] G. Grell, S.I. Bokarev, B. Winter, R. Seidel, E.F. Aziz, S.G. Aziz, O. Kühn, Multi-reference approach to the calculation of photoelectron spectra including spin-orbit coupling, J. Chem. Phys. 143 (2015) 074104. [7] O.S. Bokareva, G. Grell, S.I. Bokarev, O. Kühn, Tuning Range-Separated Density Functional Theory for Photocatalytic Water Splitting Systems, J. Chem. Theory Comput. 11 (2015) 1700. [8] S.I. Bokarev, M. Khan, M.K. Abdel-Latif, J. Xiao, R. Hilal, S.G. Aziz, E.F. Aziz, O. Kühn, Unraveling the Electronic Structure of Photocatalytic Manganese Complexes by L-Edge X-ray Spectroscopy, J. Phys. Chem. C 119 (2015) 19192. [9] N. Engel, S.I. Bokarev, E. Suljoti, R. Garcia-Diez, K.M. Lange, K. Atak, R. Golnak, A. Kothe, M. Dantz, O. Kühn, E.F. Aziz, Chemical Bonding in Aqueous Ferrocyanide: Experimental and Theoretical X-ray Spectroscopic Study, J. Phys. Chem. B 118 (2014) 1555. [10] A. Neubauer, G. Grell, A. Friedrich, S.I. Bokarev, P. Schwarzbach, F. Gärtner, A.-E. Surkus, H. Junge, M. Beller, O. Kühn, S. Lochbrunner, Electron- and Energy-Transfer Processes in a Photocatalytic System Based on an Ir(III)-Photosensitizer and an Iron Catalyst, J. Phys. Chem. Lett. 5 (2014) 1355. [11] E. Suljoti, R. Garcia-Diez, S.I. Bokarev, K.M. Lange, R. Schoch, B. Dierker, M. Dantz, K. Yamamoto, N. Engel, K. Atak, O. Kühn, M. Bauer, J.-E. Rubensson, E.F. Aziz, Direct Observation of Molecular Orbital Mixing in a Solvated Organometallic Complex, Angew. Chem. Int. Ed. 52 (2013) 9841. [12] S.I. Bokarev, M. Dantz, E. Suljoti, O. Kühn, E.F. Aziz, State-Dependent Electron Delocalization Dynamics at the Solute-Solvent Interface: Soft X-ray Absorption Spectroscopy and Ab Initio Calculations, Phys. Rev. Lett. 111 (2013) 83002.

100 Theory Days 18.03.2017: Day 5 – Theoretical Modeling Chair: Matthias Berg HZB, Berlin‐Adlershof

Introduction to electronic structure theory for spectroscopy

Sergey I. Bokarev Institut für Physik, Universität Rostock, Albert-Einstein-Str. 23-24, 18059 Rostock [email protected] Due to the rapid growth of the computational capabilities and intensive development of the computer facilities, modeling of different effects and processes for atomic, molecular, and extended systems up to nanoscale becomes a routine instrument of the modern material scientist. Nowadays the cutting edge research providing insights into the structure of matter and light-matter interactions necessarily includes theoretical modeling to guide and support the interpretation of the involved experiments and entangled data. The logic of the development of experimental-theoretical collaborations implies that even experimentalists face with a need to understand or even to conduct computations themselves. Although many

Figure 1. Selected examples of joint experimental/theoretical work on transition metal complexes in solution.

101 Theory Days 18.03.2017: Day 5 – Theoretical Modeling Chair: Matthias Berg HZB, Berlin‐Adlershof

theory developers aim at the black-box methods, where the dependence of the reliability of the results on the choice of approximations and parameters is not pronounced, the profound understanding of the underlying principles is important to avoid hidden pitfalls. In this lecture, the way from the postulates of quantum mechanics to the advice for practitioners dealing with various kinds of problems will be sketched. The hierarchy of the frequency- and time-domain methods will be explained step by step pointing out critical issues for the choice of the theoretical tool on the problem-based basis. The basics of the self-consistent field theory, configuration interaction, perturbation theory, and coupled- clusters techniques [1, 2] lying in the basement of the modern quantum chemistry will be explained. The particular focus will be put onto the description of systems with pronounced electron correlation and to the reliable prediction of the properties of the excited states which are relevant for the interpretation of various spectroscopic experiments from the UV/Vis up to hard X-ray regime. In particular, the non-adiabatic and spin crossover dynamics as well as the interaction of the system of interest with the environment, which are crucial for understanding photochemistry in gas and solution phases, will be addressed. As a practical illustration, the results of joint work of Helmholtz-Zentrum and the University of Rostock for the photochemistry and electronic structure of transition metal complexes in solution will be presented. The approaches to the XUV and X-ray absorption, photoelectron, resonant inelastic scattering, and Auger spectra of highly correlated systems will be discussed [3-9]. At the end of the lecture, the listener will be armed with basic knowledge allowing orienting him/herself on the market of the electronic structure tools and building up an effective collaboration between experiment and theory.

References: [1] F. Jensen Introduction to Computational Chemistry (John Wiley & Sons, Chichester, 1999). [2] T. Helgaker, P. Jorgensen, J. Olsen Molecular Electronic-Structure Theory (John Wiley & Sons, Chichester, 2000). [3] R. Golnak, S.I. Bokarev, R. Seidel, J. Xiao, G. Grell, K. Atak, I. Unger, S. Thürmer, S.G. Aziz, O. Kühn, B. Winter, E.F. Aziz, Joint Analysis of Radiative and Non-radiative Electronic Relaxation Upon X-ray Irradiation of Transition Metal Aqueous Solutions, Sci. Rep. 6 (2016) 24659. [4] A. Moguilevski, M. Wilke, G. Grell, S.I. Bokarev, S.G. Aziz, N. Engel, A. Raheem, O. Kühn, I.Y. Kiyan, E.F. Aziz, Ultrafast spin crossover in [FeII(bpy)3]2+: revealing two competing mechanisms by means of XUV photoemission spectroscopy, ChemPhysChem (2017), 10.1002/cphc.201601396. [5] G. Grell, S.I. Bokarev, B. Winter, R. Seidel, E.F. Aziz, S.G. Aziz, O. Kühn, Multi-reference approach to the calculation of photoelectron spectra including spin-orbit coupling, J. Chem. Phys. 143 (2015) 074104. [6] S.I. Bokarev*, M. Khan, M.K. Abdel-Latif, J. Xiao, R. Hilal, S.G. Aziz, E.F. Aziz, O. Kühn, Unraveling the Electronic Structure of Photocatalytic Manganese Complexes by L-Edge X-ray Spectroscopy, J. Phys. Chem. C 119 (2015) 19192.

102 Theory Days 18.03.2017: Day 5 – Theoretical Modeling Chair: Matthias Berg HZB, Berlin‐Adlershof

[7] N. Engel, S.I. Bokarev, E. Suljoti, R. Garcia-Diez, K.M. Lange, K. Atak, R. Golnak, A. Kothe, M. Dantz, O. Kühn, E.F. Aziz, Chemical Bonding in Aqueous Ferrocyanide: Experimental and Theoretical X-ray Spectroscopic Study, J. Phys. Chem. B 118 (2014) 1555. [8] E. Suljoti, R. Garcia-Diez, S.I. Bokarev, K.M. Lange, R. Schoch, B. Dierker, M. Dantz, K. Yamamoto, N. Engel, K. Atak, O. Kühn, M. Bauer, J.-E. Rubensson, E.F. Aziz, Direct Observation of Molecular Orbital Mixing in a Solvated Organometallic Complex, Angew. Chem. Int. Ed. 52 (2013) 9841. [9] S.I. Bokarev, M. Dantz, E. Suljoti, O. Kühn, E.F. Aziz, State-Dependent Electron Delocalization Dynamics at the Solute-Solvent Interface: Soft X-ray Absorption Spectroscopy and Ab Initio Calculations, Phys. Rev. Lett. 111 (2013) 83002.

103 Theory Days 18.03.2017: Day 5 – Theoretical Modeling Chair: Matthias Berg HZB, Berlin‐Adlershof

Brief CV – Dr. Hilke Bahmann

Current position: Postdoc with Prof. Dr. Martin Kaupp, Department of Chemistry, Theoretical Chemistry – Quantum Chemistry, Technische Universität Berlin Research expertise/activities in research: Hilke Bahmann studied chemistry at the University of Würzburg, where she completed, in 2005, her Diploma with specialization in theoretical chemistry. She did her PhD in the group of Prof. Martin Kaupp, with whom she developed a new type of exchange-correlation functionals based on the local hybrid ansatz. These exhibit a particularly well balanced performance for thermochemical and kinetic properties as well as different types of excitation energies including core-valence and Rydberg excitations. Local hybrids have also shown early promises for hybrid organic/inorganic materials and adsorbate/surface systems. The efficient implementation of these local hybrid functionals in the commercially available quantum chemistry program Turbomole was central to her research activities during her postdoctoral stay at the Technical University Berlin. Several research visits at the Université de Montréal (Canada) laid the foundations for a collaboration with Prof. Matthias Ernzerhof and Dr. Jana Pavlíková Prěcechtělová (now in Brno). Their derivation of novel correlation factors lead to the development of a new family of functionals, which are compatible with exact exchange. This new paradigm facilitates the inclusion of exact constraints and full removal of the self-interaction error. It is expected to rival existing hybrid functionals both in terms of accuracy and efficiency. Her current research interests extend from local interpolations along the adiabatic connection, and density functional approximations for strong correlation. The latter is also the subject of a new collaboration with Prof. Paola Gori- Giorgi at the Vrije Universiteit Amsterdam.

Keywords: Density functional theory, exact exchange, efficient implementation, exchange- correlation hole

Selected 10 most important articles related to the lecture: [1] “The shell model for the exchange-correlation hole in the strong-correlation limit”, H. Bahmann, Y. Zhou, M. Ernzerhof, J. Chem. Phys. 145, 124104 (2016) [2] “Implementation of Molecular Gradients for Local Hybrid Density Functionals Using Seminumerical Integration Techniques”, S. Klawohn, H. Bahmann, M. Kaupp, J. Chem. Theory Comput. 12, 4254 (2016) [3] “Validation of local hybrid functionals for TDDFT calculations of electronic excitation energies”, T. M. Maier, H. Bahmann, A. V. Arbuznikov, M. Kaupp, J. Chem. Phys. 144, 074106 (2016) [4] “Construction of exchange-correlation functionals through interpolation between the noninteracting and the strong-correlation limit”, Y. Zhou, H. Bahmann, M. Ernzerhof, J. Chem. Phys. 143, 124103 (2015).

104 Theory Days 18.03.2017: Day 5 – Theoretical Modeling Chair: Matthias Berg HZB, Berlin‐Adlershof

[5] “Efficient semi-numerical implementation of global and local hybrid functionals for time- dependent density functional theory”, T. Maier, H. Bahmann, M. Kaupp, J. Chem. Theory Comput. 11, 4226 (2015) [6] “Design of exchange-correlation functionals through the correlation factor approach”, J. Pavlíková Prěcechtělová, H. Bahmann, M. Kaupp, M. Ernzerhof, J. Chem. Phys. 143, 144102 (2015) [7] “Efficient self-consistent implementation of local hybrid functionals”, H. Bahmann, M. Kaupp, J. Chem. Theory Comput. 11, 1540 (2015) [8] “A non-empirical correlation factor model for the exchange-correlation energy”, J. Prěcechtělová, H. Bahmann, M. Kaupp, M. Ernzerhof, J. Chem. Phys. 141, 111102 (2014) [9] "Generalized-gradient exchange-correlation hole obtained from a correlation factor ansatz", H. Bahmann, M. Ernzerhof, J. Chem. Phys. 128, 2341041 - 2341049 (2008) [10] "A thermochemically competitive local hybrid functional without gradient corrections", H. Bahmann, A. Rodenberg, A. V. Arbuznikov, M. Kaupp, J. Chem. Phys. 126, 0111031 - 0111034 (2007)

105 Theory Days 18.03.2017: Day 5 – Theoretical Modeling Chair: Matthias Berg HZB, Berlin‐Adlershof

Fundamental Concepts and Practical Aspects of Density Functional Theory

Hilke Bahmann Technische Universität Berlin, Straße des 17. Juni, 135, 10623 Berlin, Deutschland [email protected] Electronic structure calculations have become an indispensable tool to analyze and support experimental data and to understand chemical mechanisms. They are used as a starting point for other theoretical models of physical and chemical concepts. Due to a combination of efficiency and accuracy density functional theory (DFT) is the most popular method to characterize the electronic structure of molecules and solids. In Kohn-Sham DFT [1] a noninteracting reference system is introduced to be able to calculate the largest part of the kinetic energy as a functional of the Kohn-Sham orbitals. The remaining kinetic energy stemming from nonclassical interactions is added to the exchange-correlation functional that constitutes the key quantity in Kohn-Sham DFT. It is crucial part in the computational setup and a large number of approximations to the exchange-correlation functional is available. Their predictive power and accuracy often depends on the system and property under investigation. A good understanding of the underlying concepts and the ability to identify and classify popular approximations to the XC functional is therefore paramount. A classification based on the ingredients has been proposed by Perdew et al. [2] According to Jacob’s ladder of exchange-correlation functionals, purely local, semi-local, non-local and functionals depending on the virtual orbital space are distinguished. The local density approximation constitutes the first rung. It is derived from the homogeneous electron gas, a fictitious system of constant density which resembles however real systems such as bulk metals. This model is also one of the cornerstones of approximations to the exchange- correlation functionals and is usually included in the limit of homogeneous electron densities. [3]. There are several strategies for the development of exchange-correlation functionals: [4] exact constraints such as upper and lower bounds on the energy density or the high- and low- density limit, empirical fits like the well-known Minnesota functionals, [5] or models to the underlying exchange-correlation hole. [6]- [8] This hole describes the reduction in the electron density around a reference electron due to nonclassical interactions with the other electrons. Many of its properties are known exactly and functionals have been derived using either explicit model holes or implicitly considering its properties. Semi-local functionals that depend only on the density and its gradient exhibit the well-known one-electron self-interaction error (SIE) unless this interaction is explicitly removed using e.g. the Perdew-Zunger approximation. [9] The SIE is the unphysical Coulomb interaction of one electron with itself. It is e.g. responsible for too delocalized states, overbinding, or too small band gaps in extended systems and thus overstabilization of metals. The exchange energy as defined in the Hartree-Fock approximation (referred to as exact exchange) fully removes the unphysical self-interaction. This motivates replacing a fix part of DFT exchange by the exact-

106 Theory Days 18.03.2017: Day 5 – Theoretical Modeling Chair: Matthias Berg HZB, Berlin‐Adlershof

exchange energy leading to global hybrid functionals. They offer a good comprise between partial removal of SIE and error cancellation inherent to approximate DFT exchange and correlation functional.[10] Popular representatives are B3LYP [11]-[13] or PBE0.[14] An established generalization of global hybrid functionals are range-separated hybrid functionals.[15] They are obtained by dividing the electron-electron interaction into a short- range and a long-range part. For molecules long-range corrected functionals such as CAM- B3LYP [16] have been applied successfully while the HSE functional [17] with short-range exact exchange is used widely for periodic systems. [18] A formal physical basis for such a hybrid scheme is the adiabatic connection (AC). It describes the transition of the noninteracting reference system to the fully interacting system through a coupling constant. Several properties of the AC are known, making it a powerful tool in the derivation of exchange-correlation functionals. It is a convex function of the coupling constant. At zero coupling strength the electron interaction is described by the exact exchange energy from the Hartree-Fock approximation. The initial slope is given through the Görling-Levy second order perturbation theory [19] and motivates double hybrid functionals such as B2PLYP. [20] Taking the coupling constant to infinity leads to strictly correlated electrons. In this limit of strong correlation the Coulomb repulsion between electrons prevails their kinetic energy and the electrons become strictly localized. Integration over the coupling strength parameter yields the usual exchange-correlation functional including the kinetic energy contribution. For periodic system some flaws of semi-local functionals are also remedied by the DFT+U method. [21] It is motivated through the Hubbard model that can describe systems with strongly localized electrons e.g. Mott insulators. This method explicitly correlates only localized valence electrons (mostly d- and f) with an exact-exchange like term. The U- parameter can be adjusted to experimental data or determined from other calculations. [22] Strong correlation in the sense that the Coulomb repulsion between electrons dominates over their kinetic energy has also been studied as an exact limit of the adiabatic connection (with infinite coupling strength). [23] The exact functionals [24] in this limit localizes electrons in delta functions and has shown to cure several notorious problems of semi-local functionals such as the linearity condition of the energy or bond dissociation. [25] Another challenge for Kohn-Sham DFT are systems with two or more antiferromagnetically coupled spin centers. A correct description would require multi-determinant wave function methods that are not feasible for large systems. Therefore one usually resorts to broken- symmetry DFT. [26] the spin symmetry and spatial symmetry is broken by generating orbitals from an unrestricted calculation and placing the electrons in alpha and beta orbitals localized at the different spin centers. The orbitals are subsequently relaxed to obtain the broken- symmetry energy and orbitals. This scheme also allows for a better albeit unphysical description of stretched bonds. Additionally to ground state properties, excitation energies are accessible via linear-response time-dependent DFT (LR-TDDFT). [27] It is usually used within the adiabatic approximation, i.e. the exchange-correlation potential is considered to be static. [28] Thus any ground state exchange-correlation functional can be used for LR-TDDFT calculations. Regarding the

107 Theory Days 18.03.2017: Day 5 – Theoretical Modeling Chair: Matthias Berg HZB, Berlin‐Adlershof

performance, semi-local functionals have a tendency to underestimate excitation energies. This holds particularly for charge-transfer and Rydberg excitations. While the latter have been discussed to suffer predominantly from the wrong asymptotic decay of semi-local potentials, [29] charge-transfer excitation require a certain amount of exact exchange due to missing overlap between the two orbitals. [30] Range-separated functionals with exact exchange at large interelectronic distances have thus been shown to overcome both problems largely. [31]

References: [1] W. Kohn and L. J. Sham Phys. Rev. 140, A1133 (1965) [2] J. P. Perdew, K. Schmidt, AIP Conf. Proc. 577, 1 (2001) [3] R. G. Parr and W. Yang, Density-Functional Theory of Atoms and Molecules, Oxford University Press, Oxford, 1989 [4] G E. Scuseria and V. N. Staroverov, Progress in the development of exchange-correlation Functionals in Theory and Applications of Computational Chemistry: The First 40 Years, edited by C. E. Dykstra, G. Frenking, K. S. Kim, and G. E. Scuseria, Elsevier, Amsterdam, 2005 [5] Y. Zhao, D. G. Truhlar, Theor. Chem. Account 120, 215 (2008) [6] A.D. Becke, M.R. Roussel, Phys. Rev. A 39, 3761 (1989) [7] M. Ernzerhof, J. P. Perdew, J. Chem. Phys. 109, 3313 (1998) [8] J. P. Perdew, K. Burke, Y. Wang, Phys. Rev. B 54, 16533 (1996) [9] J. P. Perdew, A. Zunger, Phys. Rev. B 23, 5048 (1981) [10] E. J. Baerends, O. V. Gritsenko, J. Phys. Chem. A 101, 5383, 1997 [11] A. D. Becke, Phys. Rev. A 38, 3098 (1988) [12] C. Lee, W. Yang, and R. G. Parr, Phys. Rev. B 37, 785 (1988) [13] A. D. Becke, J.Chem.Phys. 98, 5648 (1993) [14] J. P. Perdew; M. Ernzerhof; K. Burke, J. Chem. Phys. 105, 9982 (1996) [15] J. Toulouse, F. Colonna, A. Savin Phys. Rev. A 70, 062505 (2004) [16] T. Yanai, D. P. Tew, N. C. Handy, Chemical Physics Letters 393, 51 (2004) [17] J. Heyd, G. E. Scuseria, M. Ernzerhof, J. Chem. Phys. 118, 8207 (2003) [18] J. Paier, M. Marsman, K. Hummer, G. Kresse, I. C. Gerber, J. G. Ángyán, J. Chem. Phys. 124, 154709 (2006) [19] A. Görling, M. Levy, Phys. Rev. A 50, 196 (1994) [20] S. Grimme, J. Chem. Phys. 124, 034108 (2006) [21] V. I. Anisimov, J. Zaanen, O. K. Andersen, Phys. Rev. B 44, 943 (1991) [22] V. I Anisimovy, F. Aryasetiawanz and A. I. Lichtenstein J. Phys.: Condens. Matter 9, 767 (1997) [23] M. Seidl, J. P. Perdew, M. Levy, Phys. Rev. A 59, 51 (1999) [24] F. Malet, A. Mirtschink, K. J. H. Giesbertz, L. O. Wagner, P. Gori-Giorgi, Phys.Chem.Chem.Phys. 16, 1455 (2014)

108 Theory Days 18.03.2017: Day 5 – Theoretical Modeling Chair: Matthias Berg HZB, Berlin‐Adlershof

[25] S. Vuckovic, L. O. Wagner, A. Mirtschink, P. Gori-Giorgi, J. Chem. Theory Comput., 11, 3153 (2015) [26] F. Neese, Coordination Chem. Rev. 253, 526 (2009) [27] E. Runge and E.K.U. Gross, Phys. Rev. Lett. 52, 997 (1984) [28] P. Elliott, F. Furche, K. Burke, Excited States from Time-Dependent Density Functional Theory, in Reviews in Computational Chemistry, Volume 26 (eds K. B. Lipkowitz and T. R. Cundari), John Wiley & Sons, Inc., Hoboken, NJ, USA, 2008 [29] Y. Tawada, T. Tsuneda, S. Yanagisawa, J. Chem. Phys. 120, 8425 (2004) [30] A. Dreuw, M. Head-Gordon, Chem. Rev. 105, 4009 (2005) [31] M. J. G. Peach, D. J. Tozer, J. Phys. Chem. A 116, 9783 (2012)

109 Theory Days 18.03.2017: Day 5 – Theoretical Modeling Chair: Matthias Berg HZB, Berlin‐Adlershof

Brief CV – Jean Christophe Tremblay, Ph.D.

Current position: Emmy-Noether Group Leader Research expertise/activities in research: After completing his college degree in music, Jean Christophe Tremblay studied chemistry at the University of Montreal (Canada), where he obtained in 2007 his PhD in theoretical spectroscopy under the guidance of Prof. Tucker Carrington Jr. During his postdoctoral stay in the group of Prof. Dr. Peter Saalfrank at the University of Potsdam, he was introduced to the methods of quantum dynamics in the condensed phase. He is since November 2012 Emmy- Noether group leader at the Freie Universität Berlin. His current research activities focus on the development of fully quantum mechanical, bottom-up models to characterize the dynamics in nanostructures and at metallic surfaces. A central aspect of the latter topic is the role played by energy transfer between a reaction center and its environment. For the systems at hand, energy relaxation is either due to non- adiabatic coupling with metal electrons of the surroundings or intramolecular vibrational energy redistribution, for which quantum mechanical expressions can be derived. Energy relaxation has profound repercussions on the dynamics happening on the picosecond to nanosecond timescales, which are involved, e.g., in reactions induced by scanning tunnelling microscopy or in scattering from surfaces. Processes of interest related to electron dynamics include laser control of charge migration and of charge transfer in highly symmetric molecules, as well as in semiconductor quantum dots and hybrid interfaces. Further, great effort is devoted to developing numerical tools to analyze N-electron dynamics. In recent work, the current flux density has been promoted as a general tool to reveal the evolution of dynamical correlation and yield mechanistic information about ultrafast electron transfer reactions.

Keywords: Quantum dynamics, electron migration, energy exchange, laser control, nanoelectronics, scanning tunneling microscopy, surface reactions

Selected 10 most important articles related to the lecture: [1] D. Jia, J. Manz, B. Paulus, V. Pohl, J.C. Tremblay, and Y. Yang “Quantum control of electronic fluxes during adiabatic attosecond charge migration in degenerate superposition states of benzene”, Chem. Phys. DOI : 10.1016/j.chemphys.2016.09.021. [2] G. Hermann, C. Liu, J. Manz, B. Paulus, J.F. Pérez-Torres, V. Pohl, and J.C. Tremblay “Multi- directional Angular Electron Flux During Adiabatic Attosecond Charge Migration in Excited Benzene”, J. Phys. Chem. A 120, 5360 (2016). [3] G. Hermann and J.C. Tremblay “Ultrafast photoelectron migration in dye-sensitized solar cells: influence of the binding mode and many-body interactions”, J. Chem. Phys. 145, 174704 (2016). [4] S. Klinkusch and J.C. Tremblay “Resolution-of-identity stochastic time-dependent configuration interaction for dissipative electron dynamics in strong fields”, J. Chem. Phys. 144, 184108 (2016).

110 Theory Days 18.03.2017: Day 5 – Theoretical Modeling Chair: Matthias Berg HZB, Berlin‐Adlershof

[5] G. Hermann, V. Pohl, J.C. Tremblay, B. Paulus, H.-C. Hege, and A. Schild “ORBKIT - A Modular Python Toolbox for Cross-Platform Post-Processing of Quantum Chemical Wavefunction Data”, J. Comput. Chem. 37, 1511 (2016). [6] G. Hermann and J.C. Tremblay “Laser-driven hole trapping in a Ge/Si core-shell nanocrystal: an atomistic configuration interaction perspective”, J. Phys. Chem. C119, 25606 (2015). [7] T. Gómez, G. Hermann, X. Zárate, J.F. Pérez-Torres, and J.C. Tremblay “Imaging the ultrafast electron transfer in alizarine-TiO2”, Molecules 20, 13830 (2015). [8] J.C. Tremblay, S. Klinkusch, T. Klamroth, and P. Saalfrank “Dissipative many-electron dynamics of ionizing systems”, J. Chem. Phys. 134, 044311 (2011) [9] J.C. Tremblay, P. Krause, T. Klamroth, and P. Saalfrank “The effect of energy and phase relaxation on dynamic polarizability calculations”, Phys. Rev. A 81, 063420 (2010). [10] J.C. Tremblay, T. Klamroth, and P. Saalfrank “Time-dependent configuration-interaction calculations of laser-driven dynamics in presence of dissipation”, J. Chem. Phys. 129, 084302 (2008)

111 Theory Days 18.03.2017: Day 5 – Theoretical Modeling Chair: Matthias Berg HZB, Berlin‐Adlershof

Ultrafast Electron Dynamics in Strong Laser Fields: Insights from Wave Function Methods

Jean Christophe Tremblay Institut für Chemie und Biochemie, Freie Universität Berlin, Germany [email protected] Understanding the behavior of electrons out of equilibrium is central to predicting the reactivity of molecules as well as their spectroscopic properties. With the advent of intense femto- and attosecond laser sources, it has now become possible to manipulate and to probe electrons on the natural timescale associated with their dynamics. A spectacular example that comes to mind is that of the charge migration observed in HCCI+ following sudden ionization, which was recently achieved in the group of H.J. Wörner in Zürich1. This new wealth of experimental information requires careful theoretical analysis of the underlying electron dynamics, which can be simulated using a variety of methods. This presents the practitioner with a difficult choice, and one purpose of this lecture is to help guide the novice user through the myriad of available theoretical approaches to tackle such problems. Since it has now established itself as the most popular solution for studying electron dynamics in real-time, I will succinctly describe the basic equations of explicitly time- dependent density functional theory (TDDFT). From the Runge-Gross theorem2, which states that the N-electron dynamics of a system can be mapped onto the evolution of the one- electron density under the influence of a time-dependent external potential, the main advantages and limitations of TDDFT will be presented. The implications for the simulation of ultrafast electron dynamics in strong laser fields will be discussed using examples from the literature3-4, e.g., for the optimal control of selective excitations. Following this discussion, an introduction to systematically improvable methods based on wave function expansions will be given. The common denominator of these approaches is that a transient wave packet is represented using a basis of N-electron wave functions at a desired level of theory. These include traditional configuration interaction5-6 and multi- configuration7-9 methodologies, where different types of electron correlation effects can be included explicitly in the wave packet. I will give a brief introduction to the advantage and disadvantages of each method, as well as pointing out their realm of applicability. Throughout the lecture, a number of examples will be given where wave function methods were useful to investigate ultrafast, field-induced N-electron dynamics. These include charge trapping in self-assembled Germanium/Silicon core-shell heterostructures10, electron injection in dye-sensitized solar cells11, charge migration in benzene and in HCCI+, and the simulation of high-harmonic spectra12. I will also introduce a suite of tools based on the current density and derived quantities to reveal the mechanisms of these processes and give an intuitive interpretation to the dynamical evolution of correlated N-electron wave packets13.

112 Theory Days 18.03.2017: Day 5 – Theoretical Modeling Chair: Matthias Berg HZB, Berlin‐Adlershof

References: [1] P.M. Kraus, B. Mignolet, D. Baykusheva, A. Rupenyan, L. Horny, E.F. Penka, G. Grassi, O.I. Tolstikhin, J. Schneider, F. Jensen, L.B. Madsen, A.D. Bandrauk, F. Remacle, H.J. Worner,̈ Science 350 (2015) 790 [2] E. Runge and E. K. U. Gross, Phys. Rev. Lett. 52, 997 (1984). [3] S. Raghunathan and M. Nest, J. Chem. Theory Comput. 8, 806 (2012). [4] S. Raghunathan and M. Nest, J. Chem. Phys. 136, 064104 (2012). [5] T. Klamroth, Phys. Rev. B 68, 245421 (2003). [6] N. Rohringer, A. Gordon, and R. Santra, Phys. Rev. A 74, 043420 (2006). [7] J. Zanghellini, M. Kitzler, C. Fabian, T. Brabec, and A. Scrinzi, Laser Phys. 13, 1064 (2003). [8] T. Kato and H. Kono, Chem. Phys. Lett. 392, 533 (2004). [9] M. Nest, T. Klamroth, and P. Saalfrank, J. Chem. Phys. 122, 124102 (2005). [10] G. Hermann and J. C. Tremblay, J. Phys. Chem. C 119, 25606–25614 (2015). [11] G. Hermann and J. C. Tremblay, J. Chem. Phys. 145, 174704 (2016) [12] A. White, C. Heide, P. Saalfrank, M. Head-Gordon, and E. Luppi, Mol. Phys. 114, 947 (2016). [13] G. Hermann, V. Pohl, J.C. Tremblay, B. Paulus, H.-C. Hege, A. Schild, J. Comput. Chem. 37 (2016) 1511.

113 Theory Days 18.03.2017: Day 5 – Theoretical Modeling Chair: Matthias Berg HZB, Berlin‐Adlershof

Brief CV –Dr. Matej Kanduč

Current position: Institut für Weiche Materie und Funktionale Materialien, Helmholtz-Zentrum Berlin, 14109 Berlin, Germany Research expertise/activities in research: One of the research interests of Dr. Kanduč are electrostatic interactions in soft and biological matter. In particular, how multivalent ions can give rise to strong correlation effects that lead to several counter-intuitive phenomena, such as charge inversion and like-charge attraction. Theoretical understanding of these phenomena has only started unraveling in the last two decades with upgrading the traditional Poisson–Boltzmann theory, utilizing field- theoretical approaches, and Monte Carlo (MC) simulations. Within this still relatively simple theory it is possible to qualitatively explain the overcharging effects of charged surfaces in multivalent salt solution and the adhesion of similarly charged surfaces. The theoretical predictions were also confirmed by MC simulations. Another research interests are hydration and hydrophobic interactions in aqueous environments. These interactions dominate at the nanometer scale and are thus vital for the structural organization of cells and organelles. They govern biomolecular assemblies and ultimately prevent the collapse of biological matter, and at the same time promote the diffusion of biomolecules through resulting interlamellar water layers. The nature of these interactions is highly sensitive on atomic and structural details of surfaces and solvent. Consequently, the method of choice for such kind of research is atomistically-detailed Molecular Dynamics simulations. The state of the art for these problems are related to open- ensemble techniques at prescribed water chemical potential, which is even nowadays a challenging task. He studied the nanoscopic mechanisms that lead to hydration repulsive and hydrophobic attractive forces, their relation to surface structure, surface chemistry, and hydrogen bonding network among water and surface molecules. The third larger research field of Dr. Kanduč is the catalysis by metal nanoparticles, which is one of the fastest growing areas in nanoscience. He collaborates in a project that pursuits a theoretical understanding and design of nanoparticle catalysis by means of thermosensitive carrier systems. Here, the research is based on multiscale computer simulations of solvated polymers with the statistical and continuum mechanics of soft matter structures and dynamics. The key challenge is to integrate the molecular solvation effects and the growing knowledge of hydrogel mechanics and thermodynamics into advanced mathematical equations for a quantitative rate prediction.

Keywords: – Electrostatic interactions in soft matter – Charge correlations effects – Polyelectrolytes

114 Theory Days 18.03.2017: Day 5 – Theoretical Modeling Chair: Matthias Berg HZB, Berlin‐Adlershof

– Colloid clustering and aggregation – Hydration and hydrophobic forces – Biological membranes – Wetting phenomena and liquid films – Polymer physics, polymer gels, networks

Selected 10 most important articles related to the lecture: [1] C. Yigit, M. Kanduc,̌ M. Ballauff, and J. Dzubiella, “Interaction of Charged Patchy Protein Models with Like-Charged Polyelectrolyte Brushes”, Langmuir 33, 417 (2017). [2] M. Kanduc,̌ A. Schlaich, E. Schneck, and R. R. Netz, “Water-Mediated Interactions between Hydrophilic and Hydrophobic Surfaces”, Langmuir 32, 8767 (2016). [3] X. Xu, M. Kanduc,̌ J. Wu, and J. Dzubiella, “Potential of mean force and transient states in polyelectrolyte pair complexation”, J. Chem. Phys. 145, 034901 (2016). [4] E. Ioannidou, M. Kanduc,̌ L. Li, D. Frenkel, J. Dobnikar, and E. Del Gado, “The crucial effect of early-stage gelation on the mechanical properties of cement hydrates”, Nat. Commun. 7, 12106 (2016). [5] M. Kanduc ̌ and R. R. Netz, “Hydration force fluctuations in hydrophilic planar systems”, Biointerphases 11, 019004 (2016). [6] A. Botan, F. Fernando, P. Fuchs, M. Javanainen, M. Kanduc,̌ W. Kulig, A. Lamberg, C. Loison, A. Lyubartsev, M. Miettinen, L. Monticelli, J. Määttä, S. Ollila, M. Retegan, T. Róg, H. Santuz, and J. Tynkkynen, “Towards Atomistic Resolution Structure of Phosphatidylcholine Headgroup and Glycerol Backbone at Different Ambient Conditions”, J. Phys. Chem. B 119, 15075 (2015). [7] M. Kanduc ̌ and R. R. Netz, “From hydration repulsion to dry adhesion between asymmetric hydrophilic and hydrophobic surfaces”, Proc. Natl. Acad. Sci. USA 112, 12338 (2015). [8] M. Kanduc,̌ E. Schneck, and R. R. Netz, “Attraction between hydrated hydrophilic surfaces”, Chem. Phys. Lett. 610, 375 (2014). [9] M. Kanduc,̌ A. Schlaich, E. Schneck, and R. R. Netz, “Hydration repulsion between membranes and polar surfaces: Simulation approaches versus continuum theories”, Adv. Colloid Inter- face Sci. 208, 142 (2014). [10] M. Kanduc,̌ E. Schneck, and R. R. Netz, “Hydration Interaction between Phospholipid Membranes: Insight into Different Measurement Ensembles from Atomistic Molecular Dynamics Simulations”, Langmuir 29, 9126 (2013).

115 Theory Days 18.03.2017: Day 5 – Theoretical Modeling Chair: Matthias Berg HZB, Berlin‐Adlershof

Molecular Dynamics: A Computational Microscope

Matej Kanduč Institut für Weiche Materie und Funktionale Materialien, Helmholtz-Zentrum Berlin, 14109 Berlin, Germany [email protected] Some problems in physics are exactly soluble. By this, we mean that a specification of the microscopic properties of a system (such as the prescription of the interaction acting between particles) leads directly to a set of interesting results of the behavior of the system. But even ‘simple physics’ becomes very difficult when more bodies are involved, and we speak of a ‘many-body problem’. There are only a handful of non- trivial, exactly soluble many- body problems in physics. Some problems in statistical mechanics, while not being exactly soluble, succumb readily to analysis based on approximation schemes. The problem is that, many ‘straightforward’ approximation schemes simply do not work when applied to more complex systems. The more difficult and interesting the problem, the more desirable it becomes to have exact results available, both to test existing approximation methods and to point the way towards new approaches [1, 2]. Nowadays, computer simulations play a valuable role in providing essentially exact results for problems in statistical mechanics. We carry out computer simulations in the hope to understand the properties of assemblies of molecules in terms of their structure and the microscopic interactions between them. This serves as a complement to conventional experiments, enabling us to learn something new, something that cannot be found out in other ways. The two main families of simulation technique are molecular dynamics (MD) and Monte Carlo (MC); additionally, there is a whole range of hybrid techniques that combine features from both. In this lecture, we will predominantly concentrate on MD. An obvious advantage of MD over MC is that it gives a route to dynamical properties of the system: transport coefficients, time-dependent responses to perturbations, rheological properties and spectra [3]. Computer simulations act as a bridge between microscopic length and time scales and the macroscopic world of the laboratory: we provide a guess at the interactions between molecules, and obtain ‘exact’ predictions of bulk properties. The predictions are exact in the sense that they can be made as accurate as we like, subject to the limitations imposed by our computer budget. At the same time, the hidden detail behind bulk measurements can be revealed. An example is the link between the diffusion coefficient and velocity autocorrelation function (the former easy to measure experimentally, the latter much harder). Simulations act as a bridge in another sense: between theory and experiment. We may test a theory by conducting a simulation using the same model. We may test the model by comparing with experimental results. We may also carry out simulations on the computer that are difficult or impossible in the laboratory (for example, working at extremes of temperature or pressure) [3]. In its basics, a molecular dynamics simulation solves the equations of motion for a system of atoms. The solution for the Newton’s equations of motion of a molecule represents the time

116 Theory Days 18.03.2017: Day 5 – Theoretical Modeling Chair: Matthias Berg HZB, Berlin‐Adlershof

evolution of the molecular motions, the trajectory. The temperature is defined by the average kinetic energy of the system according to the kinetic theory of gases. By averaging over the velocities of all of the atoms in the system, the temperature can be estimated. It is assumed that once an initial set of velocities has been generated, the Maxwell–Boltzmann distribution will be maintained throughout the simulation. Depending on the temperature at which a simulation is performed, MD allows barrier crossing and exploration of multiple configurations of a phase space [1, 2]. A crucial component for a reliable MD simulation, yet also its biggest challenge, is the definition of potential functions, or a description of the terms by which the particles in the simulation will interact. In chemistry and biology this is usually referred to as a ‘force field’ and in materials physics as an ‘interatomic potential’. Potentials may be defined at many levels of physical accuracy; those most commonly used in chemistry are based on molecular mechanics and embody a classical mechanics treatment of particle–particle interactions that can reproduce structural and conformational changes but usually cannot reproduce chemical reactions [4]. There are dozens of different force fields on the ‘market’, all designed for different purposes. When finer levels of detail are needed, potentials based on quantum mechanics are used; some methods attempt to create hybrid classical/quantum potentials where the bulk of the system is treated classically but a small region is treated as a quantum system, usually undergoing a chemical transformation [5]. Others incorporate explicit polarizability, in which a particle’s charge is influenced by electrostatic interactions with its neighbors, especially important when simulating molecules near metallic particles [6]. Accurate force fields are essential for the success of molecular dynamics simulations. For over a half century, interatomic potentials have served us well, providing useful insights into and interpretation of biomolecular structure and function. Undoubtedly, it will continue to be widely used, thanks to its computational efficiency, while its reliability will continue to be improved. The largest increase in the number of studies using molecular dynamics is in the field of biological macromolecules. There, the number of publications using molecular dynamics is now in the thousands per year. The early view of proteins as relatively rigid structures has been replaced by a dynamic model in which the internal motions and resulting conformational changes play an essential role in their function [7]. With continuing advances in the methodology and the speed of computers, molecular dynamics studies are being extended to larger systems and longer time scales. This makes possible the investigation of motions that have particular functional implications and to obtain information that is not accessible from experiment. The results available today make clear that the applications of molecular dynamics will play an even more important role for our understanding of biology in the future [7]. A comprehensive listing of scientific achievements using molecular dynamics in a short lecture is not possible. Therefore, we will take a look at a small number of specific and interesting examples that illustrate particularly clearly the uses of molecular dynamics simulations to obtain functionally relevant information that complements experimental data.

117 Theory Days 18.03.2017: Day 5 – Theoretical Modeling Chair: Matthias Berg HZB, Berlin‐Adlershof

References: [1] M. P. Allen and D. J. Tildesley, Computer Simulation of Liquids (Oxford University Press, 1991). [2] D. Frenkel and B. Smit, Understanding Molecular Simulation: From Algorithms to Applications (Academic Press, 2001). [3] N. Attig, K. Binder, H. Grubmuller, and K. Kremer, John von Neumann Institute for Computing (NIC), Juelich (2004). [4] J. W. Ponder and D. A. Case, Advances in protein chemistry 66, 27 (2003). [5] H. M. Senn and W. Thiel, Angewandte Chemie International Edition 48, 1198 (2009). [6] I. V. Leontyev and A. A. Stuchebrukhov, The Journal of chemical physics 141, 06B621 1 (2014). [7] M. Karplus and J. A. McCammon, Nature Structural & Molecular Biology 9, 646 (2002).

118

CVs and Abstracts – Training Week

119 Practical Training Days 20.03.2017: Day 6 ‐ Computational Training Training Session Leader: Kaan Atak, Matthias Berg HZB, Berlin‐Wannsee

Monday, March 20th Theoretical Modelling Training ORCA Tutorial – Computational Spectroscopy Kaan Atak (HZB), Fabian Weber (HZB)

Brief CV – Dr. Kaan Atak

Staff Scientist at Helmholtz Zentrum Berlin, Institute of Methods and Material Development Experience: Postdoctoral Fellow for Einstein Foundation, Berlin Research and Teaching Assistant at Bogazici University, Istanbul Expertise: XANES, RIXS, PES, RPES spectroscopies (experimental), Quantum chemical computation (theoretical) Education: PhD from Bogazici University Department of Physics, 2009

Brief CV – Fabian Weber

Fabian Weber achieved his BSc. and MSc. at the Freie Universität Berlin from 2010-2015. His Master Thesis, entitled „Applications of Range-Separated DFT Functionals to Metal-Graphene Interactions“ was part of a collaboration with Priv. Doz. Peter Reinhardt of the Université Marie et Pierre Curie (UPMC) in Paris and Prof. Beate Paulus of the Freie Universität Berlin. At the moment he is a PhD student of the workgroup of Annika Bande, where he studies the interatomic Coulombic decay (ICD) in paired quantum dots and electron transfer processes from graphene oxide quantum dots to small molecules.

120 Practical Training Days 20.03.2017: Day 6 ‐ Computational Training Training Session Leader: Kaan Atak, Matthias Berg HZB, Berlin‐Wannsee

ORCA Tutorial - Computational Spectroscopy

Fabian Weber, Kaan Atak Institute of Methods for Material Development, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Str. 15, 12489 Berlin, Germany [email protected], [email protected] ORCA [1] is a widely used quantum chemical software developed by F. Neese and his coworkers. In the application of X-ray spectroscopic methods such as X-ray absorption near- edge structure (XANES) or X-ray emission spectroscopy (XES), ORCA offers suitable computational schemes for interpretation of the spectral outcomes. ORCA hosts standard density functional theory (DFT) methods for structure optimization and single point energy calculation (including molecular orbital visualization), time-dependent DFT for K-edge XANES and UV-Vis spectroscopy, a restricted open-shell configuration interaction singles (ROCIS) DFT hybrid (DFT/ROCIS) method to calculate L-edge XANES. In this tutorial, students will be introduced to this palette of quantum computational techniques, from building molecular structures up to simulating their spectral responses.

References: [1] 1. Neese, F. The ORCA program system. Wiley Interdiscip. Rev. Comput. Mol. Sci. 2, 73–78 (2012).

121 Practical Training Days 20.03.2017: Day 6 ‐ Computational Training Training Session Leader: Kaan Atak, Matthias Berg HZB, Berlin‐Wannsee

MCTDH Tutorial – Electron Dynamics Simulations of the Interatomic Coulombic Decay in Quantum Dots Matthias Berg (FU/HZB), Anika Haller (HZB)

Brief CV – Dr. Annika Bande

Annika Bande is leading the interdisciplinary Theory Group in the Institute of Methods for Materials Development at the Helmholtz-Zentrum Berlin since 2014, for which she acquired the prestigious Freigeist Fellowship of the Volkswagen Foundation. In 2000 she initiated her chemistry studies at RWTH Aachen University, where she also obtained her PhD degree in 2007 in the field of Quantum Monte Carlo simulations. After two postdoctoral stays with a focus on electronic structure methods at the University of Colorado in Boulder, U.S. and at the Quantum Chemistry Research Institute in Kyoto, Japan, she opened up the field of electron dynamics of energy-transfer processes in quantum dot systems at the University of Heidelberg. Lately, her group also focuses on theoretical spectroscopy in the gas, liquid, and solid phase and at interfaces in close cooperation with the experimental teams of the institute.

Brief CV – Matthias Berg

Matthias Berg studied chemistry (BSc. and MSc.) at Freie Universität Berlin form 2005-2012. He pursued his PhD work in Theoretical Chemistry with Prof. Beate Paulus at Freie Universität Berlin from 2012-2017, where he investigated dihydrogen-dihalogen van der Waals dimers and the folding of partially fluorinated n-alkane molecules. In 2017, he joined the group of Dr. Annika Bande at the Helmholtz-Zentrum Berlin. In his postdoctoral research, he focuses on the description of ultrafast energy transfer processes in connected quantum-dot metal-nanoparticle systems.

Brief CV – Anika Haller

Anika Haller did her Bachelor and Master studies in physics at Freie Universität Berlin from 2008-2014. There, she focused on theoretical solid state physics and did her master thesis project on quantum transport in superconductor-quantum dot junctions as guest in the condensed matter theory group at the Niels Bohr Institute/University of Copenhagen. In 2015 she started her PhD studies at Helmholtz-Zentrum Berlin within the field of theoretical chemistry as the first PhD student in the group led by Dr. Annika Bande. Her research topic is the laser control and electron dynamics of ultrafast energy transfer processes in quantum dots.

122 Practical Training Days 20.03.2017: Day 6 ‐ Computational Training Training Session Leader: Kaan Atak, Matthias Berg HZB, Berlin‐Wannsee

MCTDH Tutorial -Electron Dynamics Simulations of the Interatomic Coulombic Decay in Quantum Dots

Anika Haller, Matthias Berg, and Annika Bande Freigeist Young Investigator Group for Theoretical Chemistry, Institute of Methods for Material Development, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Str. 15, 12489 Berlin, Germany [email protected], [email protected], [email protected] The interatomic Coulombic decay (ICD) is an ultrafast long-range energy transfer process. ICD can be understood as a delocalized Auger decay over two or more atomic species which is mediated by the Coulomb interaction among electrons residing on the different sites: on one site a high-energy electron relaxes into a lower-energy state and transfers its energy to another electron on one of the neighboring sites which is then ionized. ICD has originally been predicted for molecules and atoms [5] and soon also shown experimentally [6-8]. However, recent studies show that ICD also takes place between electrons confined in quantum dots [9-12]. Quantum dots (QDs) are nano-structured semiconductor systems, which show a discrete set of electronic energy levels due the quantum confinement effect. Hence, QDs are often referred to as 'artificial atoms'. The electronic structure of QDs and thus their optical properties are highly tunable by variation of the QD geometry or the material. Paired QD (PQD) systems are potential candidates for a device application of ICD in form of next generation infrared photo detectors or solar cells [11]. In this hands-on tutorial, you will perform electron dynamic simulations of the ICD process for a two-electron system, where each of the electrons is initially located in a QD. The time-independent (TISE) and time-dependent Schrödinger equations (TDSE) that describe the states and the dynamics of this system are solved numerically within the framework of the multi-configuration time-dependent Hartree (MCTDH) method [1-3], as implemented in the Heidelberg MCTDH package [4]. First, you will investigate the bound states of the two-electron PQD system. Second, you will propagate an electron wave-packet and follow the real-time dynamics during ICD. Third, you will initiate electron dynamics, including ICD, using a laser pulse.

References: MCTHD [1] H.-D. Meyer, U. Manthe, L.S. Cederbaum., Chem.Phys.Lett. 165, 1990, 73. [2] Multidimensional Quantum Dynamics: MCTDH Theory and Applications, (Eds.: H.-D. Meyer, F. Gatti, G. A. Worth), Wiley-VCH, Weinheim, 2009 [3] M. H. Beck, A. Jäckle, G. A. Worth, H.-D. Meyer, Phys. Rep. 324, 2000, 1.

123 Practical Training Days 20.03.2017: Day 6 ‐ Computational Training Training Session Leader: Kaan Atak, Matthias Berg HZB, Berlin‐Wannsee

[4] G. A. Worth, M. H. Beck, A. Jäckle, H.-D. Meyer, The MCTDH Package, Version 8.2, (2000). H.-D. Meyer, Version 8.3 (2002), Version 8.4 (2007). Current version: 8.4.12 (2016). See http://mctdh.uni-hd.de, University of Heidelberg, Germany.

ICD [5] L. S. Cederbaum, J. Zobeley, F. Tarantelli, Phys. Rev. Lett. 79, 1997, 4778. [6] Marburger et al, Phys. Rev. Lett. 90, 2003, 203401. [7] Y. Morishita et al, Phys. Rev. Lett. 96, 2006, 243402. [8] T. Jahnke, J. Phys. B. 48, 2015, 082001.

ICD in QDs [9] A. Bande, K. Gokhberg, L. S. Cederbaum, J. Chem. Phys. 135, 2011, 144112. [10] A. Bande, J. Chem. Phys. 2013, 138, 214104. [11] P. Dolbundalchok, D. Peláez, E. F. Aziz, A. Bande, J. Comput. Chem. 37, 2016, 2249–2259. [12] A. Haller, Y.-C. Chiang, M. Menger, E. F. Aziz, A. Bande, Chem. Phys. 482, 2017, 135-145

124 Practical Training Days 21. – 24.03.2017: Day 7 ‐10 ‐ Training in Groups Training Session Leader

Liquid Jet PES Training Robert Seidel (HZB), Marvin Pohl (HZB)

Brief CV – Dr. Robert Seidel

Current position: Emmy-Noether young investigator group leader at HZB (Operando Interfacial Photochemistry, EE-NOGP) Research expertise/activities in research: I work since 2008 (Ph.D. + postdoc) in the field of (resonant) photoelectron spectroscopy on liquids, especially on aqueous solutions. I studied in the groups of Bernd Winter, HZB/BESSY II, Berlin, and Stephen E. Bradforth, USC Los Angeles, the electronic structure interactions between water and solutes, mostly 3d-transition metal complexes, by synchrotron-based X- ray photoemission and lab-based optical/UV pump-probes photoelectron spectroscopy techniques. Within the last five years we expanded our interest on the angular dependence of outgoing photoelectrons from aqueous solutions, enabling us to answer key questions regarding the electron scattering in the water interface and the related (elastic/inelastic) mean free path, which are crucial for depth-probing measurements. Since January 2017 I am leader of the newly formed young investigator group ‘Operando Interfacial Photochemistry’ at HZB, where we will spectroscopically investigate the water-splitting mechanism(s) at the interface of photoanodes in contact with water in photoelectrochemical cells.

Keywords: Angular-resolved X-ray photoelectron spectroscopy, resonant photoelectron spectroscopy, liquid-microjet, electronic-structure

Selected articles related to the training session: [1] S. Thürmer et al., Physical Review Letters 111, 173005 (2013) [2] N. Ottosson et al., Journal of Electron Spectroscopy and Related Phenomena 177, 60 (2010) [3] R. Seidel et al., Annual Review of Physical Chemistry 67, 283 (2016) [4] R. Seidel et al., Journal of Physical Chemistry Letters 2, 633 (2011) [5] B. Winter et al., Chemical Review, 106, 1176 (2006) [6] Y. Suzuki et al., Physical Review E 90, 010302 (2014)

125 Practical Training Days 21. – 24.03.2017: Day 7 ‐10 ‐ Training in Groups Training Session Leader

Angular-resolved X-ray photoelectron spectroscopy on liquids

Dr. Robert Seidel, M. Sc. Marvin N. Pohl Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Str. 15, 12489 Berlin, Germany [email protected], [email protected] In this training session we will perform angular-resolved photoelectron spectroscopy measurements on neat liquid water. This will be a follow-up study on previous works on neat liquid water [1-3] where we found that the photoelectron angular distribution, PAD, from oxygen 1s ionization (i.e., of water’s core level) is not isotropic even for electron kinetic energies smaller than 100 eV, where elastic scattering within the liquid has been assumed to wash out the initial anisotropy of the outgoing p-wave. In other words, molecular angular anisotropy (typically detected for isolated species), which contains detailed information on orbital symmetry and even on the ionization process [2], is partially accessible from molecules even in an aqueous environment. This is of fundamental importance for characterizing the effect of hydrogen bonds on solute electronic structure, and we expect that this feature can also reveal information on molecular orientation at the (aqueous) solution surface. Another important implication from ref [1] is that the electron inelastic mean free path (IMFP) in water may not exhibit the same strong increase for low kinetic energies (<100 eV) typical for most condensed-phase systems, as reflected in the universal IMFP curve. Such a different behavior in water would imply that in typical laser studies (producing electron energies with kinetic energies far below 100 eV), unlike usually assumed, the experiment essentially probes the solution interface rather than the bulk aqueous solution. All these issues are crucial when attempting to use photoelectron spectroscopy (i.e., experimental photoelectron intensities) for instance for probing-depth measurements that aim to identify molecular species that exist at the surface at atmospheric aerosols or at an electrode-water surface, e.g., in a photo-catalytic or electro-chemical cell. Furthermore, knowledge of IMFP as well as elastic scattering is one of the key ingredients for modeling radiation tracks through water, aqueous electrolytes and other liquid solutions.

References: [1] S. Thürmer et al., Physical Review Letters 111, 173005 (2013) [2] N. Ottosson et al., Journal of Electron Spectroscopy and Related Phenomena 177, 60 (2010) [3] R. Seidel et al., Annual Review of Physical Chemistry 67, 283 (2016)

126 Practical Training Days 21. – 24.03.2017: Day 7 ‐10 ‐ Training in Groups Training Session Leader

Time-Resolved Spectroscopy Training Igor Kiyan (HZB), Martin Wilke (HZB), Iain Wilkinson (HZB)

Time-resolved spectroscopy training

Igor Yu. Kiyan, Iain Wilkinson, and Martin Wilke Helmholtz-Zentrum Berlin (HZB), Albert-Einstein-Str. 15, 12489 Berlin, Germany [email protected], [email protected], [email protected] Pump-probe experiments will be performed with an apparatus designed to study photoinduced, ultrafast electron dynamics in catalytic materials. The transient XUV photoemission spectroscopy method will be applied to track such dynamics. A femtosecond laser system will be used to generate pump laser pulses in the visible spectral region (400 nm wavelength). High-order harmonic generation will be used to generate an XUV frequency comb through phase-matched up-conversion. The 21st harmonic of the driving laser will be selected with the use of a reflective zone-plate monochromator and will be applied as ultrashort probe pulses in the experiments. Following photoexcitation of the sample with an ultrashort pump pulse, the delayed probe pulse will be applied to project the transient electron density distribution among the excited states onto the ionisation continuum. The associated photoelectron spectra will be recorded using a time-of-flight electron spectrometer. Using an optical delay stage, multiple measurements will be performed at different pump-probe delay times, allowing time- dependent electron dynamics to be interrogated. A computer program will be used to control the delay stage position, the voltage settings of the spectrometer, convert the time-of flight spectra of the photoelectrons to kinetic energy spectra, and to save the recorded data. Initially, the participants will be introduced to the principles of operation of the experimental setup; including the laser system, optical parametric amplification and tunable pump pulse generation, high-order harmonic generation, XUV optics, ultrahigh vacuum technology, and the photoelectron spectrometer. This introduction will be followed by a test measurement, where a steady-state XUV emission spectrum of argon gas will be recorded. This test will reveal the purity of the selected 21st harmonic and the energy resolution of the experiment. 3- Eventually, a sample droplet of ionic liquid containing ferricyanide, [Fe(CN)6] , will be introduced into the experimental vacuum chamber. The primary task will be to find and optimize the spatial overlap of the pump and probe beams on the sample and in front of the input aperture of the electron spectrometer. Subsequently, the temporal overlap of the visible and XUV pulses will be predefined. Following this optimization step, a series of pump-probe scans will be performed to interrogate the time-evolving electronic structure of electronically 3- excited [Fe(CN)6] . A separate program will be used to analyse the recorded data and to find the spectral region that correlates with transient electronically excited states.

127 Practical Training Days 21. – 24.03.2017: Day 7 ‐10 ‐ Training in Groups Training Session Leader

XAS, XES and RIXS Training Ronny Golnak (HZB), Jie Xiao (HZB), Marc Tesch (HZB)

Brief-CV of Dr. Jie Xiao

2012-present, Beamline Scientist, Helmholtz-Zentrum Berlin (BESSY II), Germany 2010-2012, Postdoc, Chair of Physical Chemistry II, University of Erlangen-Nuremberg, Germany 2004-2009, PhD, Department of Physics, University of Nebraska-Lincoln, USA 2000-2003, Master, Department of Physics, Nanjing University, China 1996-2000, Bachelor, Department of Physics, Suzhou University, China

128 Practical Training Days 21. – 24.03.2017: Day 7 ‐10 ‐ Training in Groups Training Session Leader

Study of electronic structure of liquid water in vacuum by soft X-ray spectroscopy

Jie Xiao, Marc F. Tesch, Ronny Golnak Institute of Methods for Material Development, Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Strasse 15, 12489 Berlin, Germany [email protected], [email protected], ronny.golnak@helmholtz- berlin.de Water is the most essential element for life on earth. Despite its simple molecular structure, there are still many intriguing phenomena about water that remains unsolved, which arouses extensive scientific investigations to probe its property. Soft X-ray spectroscopy, among various probing techniques, possesses a unique advantage because it can uncover local electronic structure of active sites where interesting reactions occur. Vacuum condition is necessary for soft X-ray propagation, which makes the study of liquid water in vacuum very challenging. We will demonstrate the application of liquid jet technique that introduces liquid water into vacuum chamber while suppressing its vapor pressure significantly. A high-flux, micro-focus beamline and an advanced X-ray spectrometer will be adopted to provide an intense X-ray source and detect X-ray photons emitted from the liquid jet, respectively. The detected X-ray signals give rise to X-ray emission and absorption (XE/XA) spectra of certain targeted chemical element. The detailed detection scheme is shown in the figure.

The water XA and XE spectra reveal valuable information about molecular orbitals and hydrogen bonding. Characteristic features of water spectra will be introduced and discussed.

129 Practical Training Days 21. – 24.03.2017: Day 7 ‐10 ‐ Training in Groups Training Session Leader

Even though the water spectra appear to be not much complicated, they are still not fully understood, and the origin of some intriguing spectral features is currently under debate in scientific society.

130 Practical Training Days 21. – 24.03.2017: Day 7 ‐10 ‐ Training in Groups Training Session Leader

Infrared Spectroscopy Training Ljiljana Puskar (HZB), Ulrich Schade (HZB)

Abstract: Infrared Spectroscopy Training:

Ulrich Schade, Ljiljana Puskar HZB – Helmholtz Zentrum Berlin, Albert Einstein Str. 15, Berlin, Germany [email protected], [email protected] The participants will have the possibility to perform experiments using the infrared microscope at the IRIS beamline attached to the electron storage ring BESSY II of HZB. After a short introduction the participants will independently discover the concept of diffraction limited spatial resolution using samples of defined geometry. From these results they will derive the high brightness of infrared synchrotron radiation and will compare it with the brightness of conventional broadband infrared sources. With that understanding chemical imaging experiments will be conducted on selected samples spanning from energy materials, cultural heritage and life sciences.

131 Practical Training Days 21.03.2017: Day 7 ‐ Training in Groups Training Session Leader HZB, Berlin‐Adlershof Groups A, B, C Freie Universität, Berlin‐Dahlem Group: D

Tuesday, Training in Groups March 21st

Liquid Jet PES Training 10:00 - 12:00 Robert Seidel (HZB), Marvin Pohl (HZB) Group A

12.00 – 13.00 Lunch BESSY II - Liquid Jet PES Training Adlershof 13:00 - 16:00 Robert Seidel (HZB), Marvin Pohl (HZB)

Time-Resolved Spectroscopy Training 10:00 - 12:00 Group D Igor Kiyan (HZB), Martin Wilke (HZB), Iain Wilkinson (HZB) Freie 12.00 – 13.00 Lunch Universität Time-Resolved Spectroscopy Training Berlin - 13:00 - 16:00 Igor Kiyan (HZB), Martin Wilke (HZB), Iain Wilkinson (HZB) Dahlem

XAS, XES and RIXS Training 10:00 - 12:00 Ronny Golnak (HZB), Jie Xiao (HZB), Marc Tesch (HZB) Group C

12.00 – 13.00 Lunch BESSY II - XAS, XES and RIXS Training Adlershof 13:00 - 16:00 Ronny Golnak (HZB), Jie Xiao (HZB), Marc Tesch (HZB)

Infrared Spectroscopy Training 10:00 - 12:00 Ljiljana Puskar (HZB), Ulrich Schade (HZB) Group B

12.00 – 13.00 Lunch BESSY II - Infrared Spectroscopy Training Adlershof 13:00 - 16:00 Ljiljana Puskar (HZB), Ulrich Schade (HZB)

132 Practical Training Days 21.03.2017: Day 7 ‐ Training in Groups Training Session Leader HZB, Berlin‐Adlershof Groups A, B, C Freie Universität, Berlin‐Dahlem Group: D

133 Practical Training Days 22.03.2017: Day 8 ‐ Training in Groups Training Session Leader HZB, Berlin‐Adlershof Groups B, C, D Freie Universität, Berlin‐Dahlem Group: A

Wednesday, Training in Groups March 22nd

Liquid Jet PES Training 10:00 - 12:00 Robert Seidel (HZB), Marvin Pohl (HZB) Group B

12.00 – 13.00 Lunch BESSY II - Liquid Jet PES Training Adlershof 13:00 - 16:00 Robert Seidel (HZB), Marvin Pohl (HZB)

Time-Resolved Spectroscopy Training 10:00 - 12:00 Group A Igor Kiyan (HZB), Martin Wilke (HZB), Iain Wilkinson (HZB) Freie 12.00 – 13.00 Lunch Universität Time-Resolved Spectroscopy Training Berlin - 13:00 - 16:00 Igor Kiyan (HZB), Martin Wilke (HZB), Iain Wilkinson (HZB) Dahlem

XAS, XES and RIXS Training 10:00 - 12:00 Ronny Golnak (HZB), Jie Xiao (HZB), Marc Tesch (HZB) Group D

12.00 – 13.00 Lunch BESSY II - XAS, XES and RIXS Training Adlershof 13:00 - 16:00 Ronny Golnak (HZB), Jie Xiao (HZB), Marc Tesch (HZB)

Infrared Spectroscopy Training 10:00 - 12:00 Ljiljana Puskar (HZB), Ulrich Schade (HZB) Group C

12.00 – 13.00 Lunch BESSY II - Infrared Spectroscopy Training Adlershof 13:00 - 16:00 Ljiljana Puskar (HZB), Ulrich Schade (HZB)

134 Practical Training Days 22.03.2017: Day 8 ‐ Training in Groups Training Session Leader HZB, Berlin‐Adlershof Groups B, C, D Freie Universität, Berlin‐Dahlem Group: A

135 Practical Training Days 23.03.2017: Day 9 ‐ Training in Groups Training Session Leader HZB, Berlin‐Adlershof Groups A, C, D Freie Universität, Berlin‐Dahlem Group: B

Thursday, Training in Groups March 23rd

Liquid Jet PES Training 10:00 - 12:00 Robert Seidel (HZB), Marvin Pohl (HZB) Group C

12.00 – 13.00 Lunch BESSY II - Liquid Jet PES Training Adlershof 13:00 - 16:00 Robert Seidel (HZB), Marvin Pohl (HZB)

Time-Resolved Spectroscopy Training 10:00 - 12:00 Group B Igor Kiyan (HZB), Martin Wilke (HZB), Iain Wilkinson (HZB) Freie 12.00 – 13.00 Lunch Universität Time-Resolved Spectroscopy Training Berlin - 13:00 - 16:00 Igor Kiyan (HZB), Martin Wilke (HZB), Iain Wilkinson (HZB) Dahlem

XAS, XES and RIXS Training 10:00 - 12:00 Ronny Golnak (HZB), Jie Xiao (HZB), Marc Tesch (HZB) Group A

12.00 – 13.00 Lunch BESSY II - XAS, XES and RIXS Training Adlershof 13:00 - 16:00 Ronny Golnak (HZB), Jie Xiao (HZB), Marc Tesch (HZB)

Infrared Spectroscopy Training 10:00 - 12:00 Ljiljana Puskar (HZB), Ulrich Schade (HZB) Group D

12.00 – 13.00 Lunch BESSY II - Infrared Spectroscopy Training Adlershof 13:00 - 16:00 Ljiljana Puskar (HZB), Ulrich Schade (HZB)

136 Practical Training Days 23.03.2017: Day 9 ‐ Training in Groups Training Session Leader HZB, Berlin‐Adlershof Groups A, C, D Freie Universität, Berlin‐Dahlem Group: B

137 Practical Training Days 24.03.2017: Day 10 ‐ Training in Groups Training Session Leader HZB, Berlin‐Adlershof Groups A, B, D Freie Universität, Berlin‐Dahlem Group: C

Friday, Training in Groups March 24th

Liquid Jet PES Training 10:00 - 12:00 Robert Seidel (HZB), Marvin Pohl (HZB) Group D

12.00 – 13.00 Lunch BESSY II - Liquid Jet PES Training Adlershof 13:00 - 16:00 Robert Seidel (HZB), Marvin Pohl (HZB)

Time-Resolved Spectroscopy Training 09:00 - 11:00 Group C Igor Kiyan (HZB), Martin Wilke (HZB), Iain Wilkinson (HZB) Freie 11.00 – 12.00 Lunch Universität Time-Resolved Spectroscopy Training Berlin - 12:00 - 15:00 Igor Kiyan (HZB), Martin Wilke (HZB), Iain Wilkinson (HZB) Dahlem

XAS, XES and RIXS Training 10:00 - 12:00 Ronny Golnak (HZB), Jie Xiao (HZB), Marc Tesch (HZB) Group B

12.00 – 13.00 Lunch BESSY II - XAS, XES and RIXS Training Adlershof 13:00 - 16:00 Ronny Golnak (HZB), Jie Xiao (HZB), Marc Tesch (HZB)

Infrared Spectroscopy Training 10:00 - 12:00 Ljiljana Puskar (HZB), Ulrich Schade (HZB) Group A

12.00 – 13.00 Lunch BESSY II - Infrared Spectroscopy Training Adlershof 13:00 - 16:00 Ljiljana Puskar (HZB), Ulrich Schade (HZB)

138 Practical Training Days 24.03.2017: Day 10 ‐ Training in Groups Training Session Leader HZB, Berlin‐Adlershof Groups A, B, D Freie Universität, Berlin‐Dahlem Group: C

139 Venue HZB/ ADLERSHOF Helmholtz‐ Zentrum Berlin 12489 Berlin

Venue - How to find us at ADLERSHOF

The Helmholtz-Zentrum Berlin für Materialien und Energie has two campuses, one in Berlin Wannsee and the other in Berlin Adlershof. The photon school will mainly take place at the Wilhelm-Conrad-Röntgen-Campus in Berlin Adlershof (which is in the south east of Berlin). Helmholtz-Zentrum Berlin für Materialien und Energie GmbH Wilhelm-Conrad-Röntgen-Campus Albert-Einstein-Strasse 15 12487 Berlin (Adlershof) Fon +49 30 8062 – 0 Fax +49 30 8062 - 12990 How to get to the Helmholtz-Zentrum in Berlin-Adlershof

140 Venue HZB/ Wannsee Helmholtz‐ Zentrum Berlin 14109 Berlin

Venue - How to find us at WANNSEE

One training day will take place at the Lise-Meitner-Campus in Berlin Wannsee (which is in the south west of Berlin). Helmholtz-Zentrum Berlin für Materialien und Energie GmbH Hahn-Meitner-Platz 1 (formerly: Glienicker Str. 100) 14109 Berlin (Wannsee) Fon +49 30 8062 – 0 Fax +49 30 8062 - 42181

How to get to the Helmholtz-Zentrum in Berlin-Wannsee

141 Venue FUB / JULiq Freie Universität Berlin 14195 Berlin

Venue - How to find us at FREIE UNIVERSITÄT

The practical training in “Time-resolved Spectroscopy“ takes place at JULiq, the Joint Ultrafast Dynamics Lab in Solutions and at Interfaces at Freie Universität Berlin (in the south west of Berlin).

Freie Universität Berlin Physic Department Arnimallee 14 14195 Berlin (Dahlem)

How to get to the Freie Universität in Berlin-Dahlem.

142 Venue FUB / JULiq Freie Universität Berlin 14195 Berlin

Please note that the Physic Department is located in a large building that is divided into four parts (called Trakt 1 – 4). Coming from U Dahlem Dorf walk down Takustraße and enter Trakt 2. The Laser Lab JULiq can be found at Trakt 2. The meeting point is the office, room -1.2.06.

143 Accommodation Berlin ‐ Köpenick Hotel Pension Flussbad 12557 Berlin

Accommodation

A room has been pre-reserved for most of the participant at the guesthouse “Hostel am Flussbad” near the Altstadt Köpenick from 13 to 24 March 2017 (11 nights). The organisers are pleased to cover the costs for max. 11 nights in this guesthouse. Please note that additional nights and extras are not covered by the organisers and need to be paid directly by the participant.

The accommodation is located in the south east of Berlin. Der Cöpenicker e.V. Gartenstraße 46-48 12557 Berlin (Köpenick)

144 Accommodation Berlin ‐ Köpenick Hotel Pension Flussbad 12557 Berlin

Guesthouse “Hostel am Flussbad”

145

146 Emergency Numbers

Emergency Numbers

HZB-MOBILE PHONE 1 0175/ 185 6887 HZB-MOBILE PHONE 2 0160/ 893 0845

General Emergency Numbers

Police (Polizei) 110

Fire Department and Emergency Rescue (Feuerwehr und Notfall-Rettung) 112

Emergency Information Advice Center for Poison Symptoms and Embryo 192 40 Toxicology/(Emergency Phone Line Berlin (Giftnotruf Berlin)

Standby Services

Medical on-call Service (Ärztlicher Bereitschaftsdienst) 030 – 31 0031

Pharmaca Emergency Service (Apotheken-Notdienst) www.akberlin.de

Hospital near Hostel am Flussbad: 030 30353000 DRK Kliniken Berlin | Köpenick Salvador-Allende-Straße 2–8, 12559 Berlin drk-kliniken-koepenick.de

Health Centre (Ärztehaus) near HZB in Adlershof: Apotheke Ärztehaus Adlershof Albert-Einstein-Straße 2, 12489 Berlin

147 We are researching new energy materials that will convert and store energy more efficiently and with a smaller ecological footprint than ever before, for example solar cells, thermoelectrics and solar fuels. The photon source BESSY II is an ideal place for studying thin film systems and our CoreLabs an excellent place for producing and analysing them. We make these Photo: M Fernahl infrastructures available to researchers from everywhere in the world. Industrial companies are also very welcome. Our in- ternationality, creativity and pursuit of new solutions are what set us apart.

When are you coming to visit? helmholtz-berlin.de

1st Berlin Photon School at Bessy II

CONTACT [email protected]

Further information hz-b.de/photonschool