Book of Abstracts
3rd International Conference on Ultrafast Structural Dynamics
June 10-12, 2015
ETH Zurich
Conference Chairs: Peter Hamm (University of Zurich) Steven Johnson (ETH Zurich) 3rd International Conference on Ultrafast Structural Dynamics
2 3rd International Conference on Ultrafast Structural Dynamics
Wednesday, June 10
8:30-8:40 Opening remarks (S. Johnson, ETHZ)
Session A: Free-electron lasers and structural dynamics in biology Chair: S. Johnson 8:40-9:10 R. Abela (PSI): “The SwissFEL X-Ray Laser Project” 9:10-9:40 K. Nass (MPI-MR, Heidelberg): “Ultra-Fast Time-Resolved Serial Femtosecond Crystallography on Myoglobin Ligand Dissociation” 9:40-10:00 J. Ihalainen (U. Jyvaskyla): “Light Induced Conformational Changes of Red Light Photosensor Detected by Time-Resolved X-ray Scattering” 10:00-10:20 N. Engel (HZ Berlin & FU Berlin): “Femtosecond Laser-Driven Dynamics of Solvated Ferricyanide”
10:20-10:50 Coffee break
Session B: Multidimensional spectroscopy and applications in biology Chair: K. Nass 10:50-11:20 M. Chergui (EPFL): “Ultrafast Studies of Tryptophan-Mediated Electron Transfer in Proteins” 11:20-11:50 K. Kubarych (U. Michigan): “Structural Dynamics in Solution and Engineered Proteins with 2D-IR and Simulation” 11:50-12:10 I. A. Heisler (U. East Anglia): “Porphorin Dimer: Twisting Dynamics Revealed by 2D Electronic Spectroscopy”
12:10-14:00 Lunch
Session C: Solid-state structural dynamics I Chair: P. Werner 14:00-14:30 H. Dürr (SLAC): “Imaging the Ultrafast Spin-Lattice Motion during All- Optical Switching of Ferromagnets” 14:30-15:00 P. Beaud (PSI): “A Detailed View on the Ultrafast Photo-Induced Phase Transition in Pr0.5Ca0.5MnO3” 15:00-15:20 C. Laulhé (Soleil): “Photo-Induced Phase Transition between Charge Density Wave States in 1T-TaS2” 15:20-15:40 E. Baldini (EPFL): “Evidence for Pre-Formed Cooper Pairs in the Pseudogap Phase of Slightly Underdoped NdBa2Cu3O6+x”
15:40-16:10 Coffee break
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Session D: Electron transfer and dynamics in transition metals Chair: M. Chergui 16:10-16:40 K. Haldrup (TU Denmark): “Electronic and Structural Dynamics in Transition Metal Complexes—Recent Results from Synchrotron and XFEL Experiments” 16:40-17:10 K. Gaffney (Stanford & SLAC): “Tracking the Charge and Spin Dynamics of Electronic Excited States in Inorganic Complexes” 17:10-17:30 C. Milne (PSI): “Revealing Charge Carrier Trapping in ZnO Nanoparticles with Femtosecond Time-Resolved X-ray Spectroscopy”
19:00-21:00 Poster session
Thursday, June 11
8:30-8:40 Presentation of the special issue of Structural Dynamics
Session E: Spectroscopic investigations Chair: K. Gaffney 8:40-9:10 M. Khalil (U. Washington): “Two-Dimensional Fourier Transform Vibrational-Electronic Spectroscopy” 9:10-9:40 T. Brixner (U. Würzburg): “Chirality-Sensitive Ultrafast Spectroscopy”
9:40-10:00 R. Costard (MBI): “Ultrafast Phosphate Hydration Dynamics in Bulk H2O“ 10:00-10:20 M. S. Pshenichnikov (U. Groningen): “Towards Bulk Heterojunction-Free Organic Solar Cells”
10:20-10:50 Coffee break
Session F: Prospects for nonlinear EUV and x-ray spectroscopies Chair: C. Milne 10:50-11:20 S. Mukamel (UC Irvine): “Probing Charge and Energy Transfer in Molecules by Multidimensional Stimulated Raman Spectroscopy” 11:20-11:50 C. Masciovechio (Elettra): “Towards FEL Based Four Wave Mixing” 11:50-12:10 J. Grilj (EPFL): “Heterodyne Transient Grating Signal in the Extreme Ultraviolet”
12:10-14:00 Lunch
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Session G: Solid-state structural dynamics II Chair: P. Beaud 14:00-14:30 P. Werner (U. Fribourg): “Nonequilibrium Dynamical Mean Field Simulation of Electron-Phonon Systems” 14:30-15:00 F. Carbone (EPFL): “The Mott Energy Scale Revealed by Ultrafast Spectroscopy in Transition Metal Oxides” 15:00-15:20 L. Rettig (PSI): “Ultrafast Structural Dynamics of the Fe-Pnictide Parent Compound BaFe2As2”
15:20-16:00 Coffee break
Session H: Scattering-based methods Chair: T. Elsaesser 16:00-16:30 H. Ihee (KASIT): “Femtosecond X-ray Liquidography Captures the Formation of Chemical Bond in the Solution Phase” 16:30-17:00 M. Trigo (SLAC): “Phonon Spectroscopy by Fourier-Transform Inelastic X-ray Scattering” 17:00-17:20 M. Hengsberger (U. Zurich): “Study of Coherent Phonon Excitation by Means of Time-Resolved Photoelectron Diffraction”
19:00 Conference Dinner (Zunfthaus zur Saffran)
Friday, June 12
Session I: Ultrafast structural dynamics with electrons Chair: F. Carbone 8:30-9:00 D. Miller (MPI-SDM & U. Toronto): “Mapping Atomic Motions with Ultrabright Electrons: Developing a Reaction Mode Basis for Chemistry” 9:00-9:30 J. Demsar (U. Mainz): “Cooperative Atomic Motion probed by Femtosecond Electron Diffraction” 9:30-9:50 W. A. Bryan (Swansea University): “Femtosecond Electron Microscopy of Charge Motion Along the Surface of a Nanoscale Object” 9:50-10:10 A. Senftleben (U. Kassel): “Spatial and Temporal Resolution Studies on a Highly Compact Ultrafast Electron Diffractometer”
10:10-10:40 Coffee break
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Session J: Charge and structure in condensed matter Chair: P. Hamm 10:40-11:10 N. Huse (U. Hamburg & MPI-SDM): “Structural Dynamics of Charge- Transfer Excitations in Transition Metal Complexes Probed with X-ray Spectroscopy” 11:10-11:40 E. Collet (U. Rennes): “Watching Coherent Structural Molecular Trapping of Light-Induced Excited Spin-State by Ultrafast X-ray and Optical Absorption Spectroscopies” 11:40-12:00 M. Odelius (Stockholm University): “Core-Level Spectrum Simulations of Ultra-fast Dynamics” 12:00-12:30 T. Elsaesser (MBI): “Transient Charge Density Maps of Ionic Crystals Studied by Femtosecond X-Ray Powder Diffraction”
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Talks Wednesday
7 3rd International Conference on Ultrafast Structural Dynamics
The SwissFEL X-Ray Laser Project
Abela R, Beaud P, Braun HH, Ganter R, Hauri CP, Ingold G, Knopp G, Milne Ch, Loehl F, Patterson BD, Patthey L, Pedrini B, Pedrozzi M, Schmid B, Szlachentko J
Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
X-ray free electron laser facilities are in operation and planning stage producing pulses of coherent x-rays in the femtosecond range (5 to 500 fsec) and a wide wavelength range, with extremely high peak brightness. The brightness, the coherence and the short pulses provide opportunities for performing novel science in chemistry, solid state physics, biochemistry and materials science. The presentation will focus on the characteristics of the SwissFEL facility [1], the proposed experimental stations as well as the so far achieved goals. Challenges in instrumentation, characterization and experimental techniques will be addressed [2].
[1] B.D. Patterson et al., New Journal of Physics, 12, 035012 (2010). [2] B.D. Patterson et. al, Chimia Int. J. Chem. 68, 1 (2014)
8 3rd International Conference on Ultrafast Structural Dynamics
Ultra-fast time-resolved serial femtosecond crystallography on myoglobin ligand dissociation
Karol Nass1, Lutz Foucar1, Thomas R.M. Barends1, Sabine Botha1, R. Bruce Doak1, Aliakbar Jafarpour1, Robert L. Shoeman1, Jason E. Koglin2, Mengning Liang2, Despina Milathianaki2, Andrew Aquila3, Henrik T. Lemke2, Sébastien Boutet2, Ilme Schlichting1
1Max Planck Institute for Medical Research, Heidelberg, Germany 2SLAC National Accelerator Laboratory, Menlo Park, USA 3European XFEL GmbH, Hamburg, Germany
Myoglobin is a well-established model system to study the structural dynamics involved in hemoprotein ligand binding. Photodissociation of the ligand carbon monoxide from the heme cofactor upon absorption of a visible photon initiates a hierarchical reaction involving several intermediates [1] that has been followed by time- resolved Laue crystallography to 150 ps time resolution [2], the lower limit accessible by synchrotron X-ray sources. However, this time resolution is not sufficient to capture the earliest events happening upon photodissociation, which include the motion of the ligand to a binding site above the heme plane, movement of the distal histidine, the heme iron atom recoiling out of the heme plane and a “protein quake”, which is a series of rapid structural changes emanating from the breaking ligand bond towards the surface of the protein. In the earliest snapshots available to date, all these things have already occurred and the protein quake has already spread throughout the protein. With the time resolution attainable at synchrotrons, the time-course of these effects cannot be resolved. However, the recent advent of X-ray free electron lasers has extended the time resolution attainable with time- resolved crystallography into the chemical time scale of femtoseconds, which allows analysis of these early events upon breaking of the heme iron—carbon monoxide bond at high temporal and spatial resolution. We describe our recent time-resolved serial femtosecond crystallography experiments performed at the Linac Coherent Light Source (LCLS), which show the first snapshots of the effects of ligand dissociation in myoglobin at (sub)picosecond time resolution.
[1] Ansari, A., Berendzen, J., Bowne, S. F., Frauenfelder, H., Iben, I. E., Sauke, T. B., Shyamsunder, E., & Young, R. D. (1985). Proc. Natl. Acad. Sci. U. S. A 82, 5000-5004. [2] Schotte, F., Lim, M., Jackson, T. A., Smirnov, A. V., Soman, J., Olson, J. S., Phillips, G. N., Jr., Wulff, M., & Anfinrud, P. A. (2003). Science 300, 1944-1947.
9 3rd International Conference on Ultrafast Structural Dynamics
Light induced conformational changes of red light photosensor detected by time-resolved X-ray scattering
Janne Ihalainen1, Sebastian Westenhoff2, Heikki Takala1,2, Alexander Björling2, Heli Lehtivuori1
1University of Jyvaskyla, Nanoscience Center, Department of Biological and Environmental Sciences, Jyväskylä, Finland 2University of Gothenburg, Department of Chemistry and Molecular Biology, Gothenburg, Sweden
A combination of optical spectroscopy, X-ray scattering and advanced molecular biology are utilized for detecting light-activated structural and chemical changes of phytochrome proteins. Phytochrome superfamily is a large and diverse set of photoreceptors present in plants, fungal and bacterial kingdoms, where light regulation is crucial for their life. Bacterial phytochromes use a linear tetrapyrrole, biliverdin, for “sensing” red and far-red light. The conformational and chemical rearrangement of amino acids around the light activated chromophore leads to conformational changes in protein domains leading finally to a signaling state of the protein.
In our studies we have been able obtain the structures of the dimeric phytochrome protein for the signaling and resting state. Moreover, we were able to establish the time-scales of the key reactions of the process. Our findings reveal an unusual mechanism where atomic scale conformational changes around the chromophore are first amplified into a Ångström scale distance change, and further grow into a nanometer scale conformational signal on the other side of the protein complex. The structural mechanism is a blueprint for understanding how sensor proteins connect to the cellular signaling network [1-3].
[1] H. Takala et al., Nature 509, 245 (2014). [2] A. Björling et al., Submitted (2014). [3] A. Björling and H. Lehtivuori et al., Manuscript (2015).
10 3rd International Conference on Ultrafast Structural Dynamics
Femtosecond Laser-Driven Dynamics of Solvated Ferricyanide
Nicholas Engel, Alexandre Moguilevski, Martin Wilke, Daniel Tolksdorf, Azhr Raheem, Mario Borgwardt, Jan Metje, Ruba Al-Obaidi, Igor Yu. Kiyan, Emad F. Aziz
Institute of Methods for Material Development Helmholtz-Zentrum Berlin, Albert-Einstein-Str. 15, 12489 Berlin, Germany Joint Laboratory for Ultrafast Dynamics in Solutions and at Interfaces Freie Universität Berlin, Department of Physics, Arnimallee 14, 14195 Berlin, Germany
Application of laser pulses to solvated species leads to manifold dynamic system responses. These depend on, e.g., the laser power, pulse length, and energy as well as the concentration of the solute, the selected solvent, and of course the solute itself. In this study, we employ femtosecond UV-laser pulses to electronically excite ferricyanide. XUV probe pulses are created through the process of high harmonics generation and are used to monitor the electron dynamics in the excited complex by XUV photoelectron spectroscopy with a time resolution of ~100 fs. Using XUV light as a probe allows to directly attribute spectral features to electronic states of the complex. While both XUV light and the detection of photoelectrons require high vacuum conditions, we use the liquid micro-jet technique to introduce the sample into the interaction region which allows to maintain high vacuum conditions even when using volatile samples.
Charge transfer mechanisms play important roles throughout many fields of science. In particular, some of the most important charge transfer processes are initiated by photo-absorption, e.g., those occurring in photosynthesis. In this study, the main focus lies on the photo-reduction of the iron complex by metal to ligand charge transfer excitation and on revealing solvent mediated charge transfer processes. The charge transfer excitation was initiated by photons of 3.1 eV energy. We show that the relaxation of the excited state occurs in the time scale of ~1 ps. In a more general scope, the present work aims to better understand the nature of the excitation and relaxation mechanisms.
11 3rd International Conference on Ultrafast Structural Dynamics
Ultrafast studies of tryptophan-mediated electron transfer in proteins
Roberto Monni, Gerald Auböck, Frank van Mourik and Majed Chergui
Laboratoire de spectroscopie ultrarapide, Ecole Polytechnique Fédérale de Lausanne, Faculté des Sciences de Base, ISIC, 1015 Lausanne, Switzerland
Tryptophan (Trp) is an amino-acid residue, which is abundant in all biological systems. Its absorption (< 300 nm) and emission bands are very sensitive to the environment. This is the reason why Trp has emerged as the “molecular ruler” in FRET (fluorescence resonance energy transfer) studies of protein dynamics. FRET is due to dipole-dipole coupling between chromophores and its rate scales as the inverse 6th power of the distance between the two chromophores. Fluorescence lifetime shortening of Trp in the course of biological functions has invariably attributed to FRET. One of the earliest examples of FRET is the case of myoglobins (Mb’s) contains two Trp’s: Trp14 and Trp7, whose fluorescence decay is in the range of ~20 ps and ~120 ps, respectively.
By a combination of ultrafast 2-dimensional UV spectroscopy [1,2], UV pump/visible probe and UV pump/infrared probe, and UV fluorescence up-conversion [3], we have investigated the excited Trp fluorescence decay in the ferric Mb’s: MbCN, MbH2O [4], and ferrous ones: deoxyMb (unligated) [5], MbCO and MbNO [6]. We show that while Trp7 decays indeed by FRET, Trp7 undergoes decay by both FRET and electron transfer in a ratio of ~60:40. This process is independent of ligation and of the oxidation state of the Mb, however, the final reduced species is not the same depending on whether the Mb is ligated or not and if it is in a ferric or ferrous state. We will discuss the mechanism of electron transfer with Trp as donor. These results question the widespread assumption that Trp fluorescence quenching is exclusively due to FRET.
[1] An Ultrabroad Femtosecond 2D Transient Absorption Set-Up in the Ultraviolet. G. Auböck, C. Consani, F. van Mourik and M. Chergui, Optics letters 37 (2012) 2337 [2] Femtosecond pump/supercontinuum-probe setup with 20 kHz repetition rate. G. Auböck, C. Consani, R. Monni, A. Cannizzo, F. van Mourik and M. Chergui, Review of Scientific Instruments 83 (2012) 093105 [3] A femtosecond fluorescence up-conversion set-up with broad-band detection in the Ultraviolet. A. Cannizzo, O. Bräm, G. Zgrablic, A. Tortschanoff, A. Ajdarzadeh Oskouei, F. van Mourik and M. Chergui Optics Letters 32 (2007) 3555 [4] Ultrafast tryptophan-to-haem electron transfer in myoglobins: a two-dimensional UV spectroscopy study C. Consani, G. Auböck, F. van Mourik and M. Chergui, Science 339 (2013) 1586-1589 [5] Tryptophan-to-haem electron transfer in ferrous myoglobins, R. Monni, A. Al Haddad, F. van Mourik, G. Auböck and M. Chergui, Proceedings of the National Academy of Science (doi:10.1038/cr.2015.49) [6] Tryptophan-to-haem electron transfer in ferrous ligated myoglobins: UV pump/IR probe studies. R. Monni, G. Auböck, R. Horwarth, M. Towrie, M. George and M. Chergui, in preparation.
12 3rd International Conference on Ultrafast Structural Dynamics
Structural Dynamics in Solution and Engineered Proteins with 2D-IR and Simulation
Kubarych K1
1Department of Chemistry, University of Michigan, Ann Arbor, USA
Ultrafast spectroscopy is inherently linked to the structural dynamics of the probed transition as well as its surroundings, though the link between structure and spectrum is often a challenge to establish. Nevertheless, one is often able to leverage established computational methods to complement spectral dynamics measurements. In my talk I will highlight our recent investigations using 2D-IR coupled with computational chemistry approaches to address structural dynamics in two new areas. First, I will show how we can use spectral diffusion and other information contained in 2D-IR spectra to characterize solvent shell structural dynamics in mixed-solvents where one species preferentially solvates the vibrational chromophore. We have investigated two different systems, a vibrationally labeled biotin derivative both in solution and bound to streptavidin, and a rhenium bipyridyl photocatalyst, where we are able to measure quasi-equilibrium solvation dynamics on both the ground singlet state and the excited metal-to-ligand charge transfer state. In the case of the photocatalyst, studied in both organic solvents and ionic liquids, we have found clear evidence for preferential solvation, which suggests that the electron transfer step critical to the photocatalytic reduction of CO2 is not likely to be diffusion controlled in solution. Second, I will introduce our newest studies of a de novo enzyme, where we have engineered a copper binding site into a self-assembled, coiled-coil trimeric peptide. Using a bound CO ligand as a vibrational probe, we have observed not only unusual, nonequilibrium spectral dynamics, but through an extensive computational study, have also been able to link the spectroscopic observations directly to structural changes of the ligand launched by vibrational excitation. In dissecting the origin of this dynamical coupling, we have learned how the histidines coordinating the Cu site sense the electric field of the protein, and, through their angular orientations, modulate the Cu-CO bonding potential energy surface. Many of our results may prove of interest to those using direct structural characterization methods, which can test our conclusions more rigorously.
13 3rd International Conference on Ultrafast Structural Dynamics
Porphyrin Dimer: Twisting Dynamics Revealed by 2D Electronic Spectroscopy Franco V. A. Camargo1, Harry L. Anderson2, Stephen R. Meech1 and Ismael A. Heisler1 1School of Chemistry, Norwich Research Park, University of East Anglia, Norwich NR4 7TJ, United Kingdom 2Department of Chemistry, University of Oxford, Chemistry Research Laboratory, Oxford OX1 3TA, United Kingdom
Porphyrins and their derivatives constitute an important group of chromophores.[1] They are part of the broader cyclic tetrapyrroles class of molecules which include hemoglobin, cytochromes and chlorophylls, which perform essential chemical and biological functions. The possible applications envisaged for porphyrin derivatives are varied and include biomimetic structures for light-harvesting, photodynamic therapy in medicine, nanoscale electron wires for use in electronic devices, etc.[1-3] More recently multichromophoric porphyrin arrays have been synthesized with the specific purpose of mimicking the ability of natural light-harvesting pigment-proteins to collect photon energy and transmit it efficiently reaction centers.[2] A thorough understanding of the ground and excited-state dynamics of such new molecular structures will be critical for their use in technological applications. Newly developed techniques like 2D spectroscopy are enabling a more direct and clearer understanding of the coupling, energy transfer, vibronic and excitonic coherence and other effects present in such multichromophoric structures.[3]
In this work the twisting reaction of a porphyrin dimer (Figure 1a) is studied in detail through 2D electronic spectroscopy.[4] In the ground state, due to a low twisting energy barrier, the dimer presents a distribution of twisted conformations ranging from planar to fully twisted (90o). Excitation to the first singlet excited state however drives the system to a mainly planar conformation. This is clearly captured in the rising cross peak in the evolving 2D spectra (Figure 1b). This result is interpreted with a model, which incorporates information obtained by fluorescence, transient absorption and computational results.
[1] H. L. Anderson, Inorganic Chemistry 33, 972 (1994). [2] H. L. Anderson et al., Chemical Science 6, 181(2015). [3] H. L. Anderson et al., Nature Nanotechnology 6, 517 (2011). [4] I. A. Heisler et al., The Review of Scientific Instruments 85, 063103 (2014).
14 3rd International Conference on Ultrafast Structural Dynamics
Imaging the ultrafast spin-lattice motion during all-optical switching of ferromagnets
Hermann A. Dürr
Stanford Institute for Materials & Energy Sciences SLAC National Accelerator Laboratory, Menlo Park CA 94025, USA
Understanding the ultrafast interplay between charge, magnetic and lattice degrees of freedom is central to gaining control of condensed matter phenomena as diverse as insulator-metal transitions and magnetic switching. While generally accepted for strongly correlated oxides, the coupling of spins with other degrees of freedom is not well established for metallic magnetic materials. Magnetism, by symmetry could be expected to couple only weakly to phonons and electrons, however the observed ultrafast demagnetization [1] and all- optical magnetic switching [2,3], indicate just the opposite. Femtosecond x-ray pulses from the Linac Coherent Light Source offer the unique opoertunity to image with soft x-rays in realtime the ultrafast spin dynamics that leads to magnetization reversal [4]. Hard x-rays as well as femtosecond electron pulses enable first glimpses at the laser induced lattice motion. Understanding the evolving spin-lattice motion on time- and lengthscales associated with the exchange interaction opens a new way of engineering spin relaxation pathways in magnetic systems
[1] E. Beaurepaire, et al., Phys. Rev. Lett, 76, 4250 (1996). [2] C.D. Stanciu et al., Phys. Rev. Lett, 99, 047601 (2007). [3] S. Mangin, et al. Nature Materials 13, 286 (2014). [4] C. E. Graves, A. H. Reid et al., Nature Materials, 12, 293 (2013).
15 3rd International Conference on Ultrafast Structural Dynamics
A detailed view on the ultrafast photo-induced phase transition in Pr0.5Ca0.5MnO3
P. Beaud1,2, A. Caviezel1, S. O. Mariager1, L. Rettig1, G. Ingold2, C. Dornes3, S-W. Huang1, J. A. Johnson1, M. Radovic1,2, T. Huber3, T. Kubacka3, A. Ferrer1,3, H. T. Lemke4, M. Chollet4, D. Zhu4, J. M. Glownia4, M. Sikorski4, A. Robert4, H. Wadati5,6, M. Nakamura7, M. Kawasaki5,7, Y. Tokura5,7, S. L. Johnson3, and U. Staub1
1Swiss Light Source, Paul Scherrer Institut, 5232 Villigen, Switzerland 2SwissFEL, Paul Scherrer Institut, 5232 Villigen, Switzerland 3Institute for Quantum Electronics, ETH Zürich, 8093 Zürich, Switzerland 4LCLS, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA 5Department of Applied Physics and Quantum-Phase Electronics Center, University of Tokyo, Hongo, Tokyo 113-8656, Japan 6Institute for Solid State Physics, University of Tokyo, Chiba 277-8581, Japan 7RIKEN Center for Emergent Matter Science, Wako 351-0198, Japan
Perovskite-type manganites are prototypical examples of strongly correlated electron systems which exhibit properties such as colossal magnetoresistance and insulator-to-metal transitions that are intrinsically related to symmetry changes of the atomic lattice and to intriguing ordering patterns of the spins, orbitals and charges. The application of an intense ultrashort optical pulse triggers an insulator-metal transition [1] and launches a structural phase transition [2,3].
Taking advantage of the high flux of the LCLS free electron laser we probed with time-resolved resonant x-ray diffraction, both the long-range order of the electronic and the lattice subsystems during the transition. Although the actual change in crystal symmetry associated with this transition occurs over different time scales characteristic of the many electronic and vibrational coordinates of the system, we find that the dynamics of the phase transformation can be well described using a single time-dependent order parameter that depends exclusively on the electronic excitation and drives the electronic phase transition as well as the coherent motion of the atomic lattice [4].
[1] D. Polli et al., Nature Mater. 6, 643–647 (2007). [2] P. Beaud et al., Phys. Rev. Lett. 103, 155702 (2009). [3] A. Caviezel et al., Phys. Rev. B 86, 174105 (2012). [4] P. Beaud et al., Nature Mater. 13, 923–927 (2014).
16 3rd International Conference on Ultrafast Structural Dynamics
Photo-Induced Phase Transition between Charge Density Wave States in 1T-TaS2
C. Laulhé1,2, T. Huber3, G. Lantz4, L. Cario5, B. Corraze5, E. Janod5, A. Ferrer3,6, S.O. Mariager6, S. Grübel6, J. A. Johnson6, J. Rittmann6, L. Huber3, A. Lübcke6, M. Kubli3, M. Savoini3, V. Esposito6, G. Ingold6, P. Beaud6, S.L. Johnson3, and S. Ravy1
1 SOLEIL, L’Orme des Merisiers, Saint-Aubin BP48, Gif-sur-Yvette 91192, France 2 Université Paris-sud, 91405 Orsay, France 3Institute for Quantum Electronics, Physics Department, ETH Zürich, CH-8093, Switzerland 4LPS, Université Paris-Sud, CNRS, UMR 8502, F-91405 Orsay, France 5IMN - UMR 6502, Université de Nantes, 2 rue de la Houssinière, F-44322 Nantes, France 6 Swiss Light Source, Paul Scherrer Institute, CH-5232, Villigen, Switzerland
1T-TaS2 is a beautiful example of a 2D metal, which undergoes a series of electronically driven phase transitions. It is a lamellar compound formed by sheets of edge-linked TaS6 octahedra. Within each sheet, the Ta-atoms form a hexagonal lattice which presents a series of structural modulations as the temperature decreases. The unmodulated structure observed at highest temperatures undergoes a first transition below 543 K with the formation of an incommensurate (I) Charge Density Wave (CDW), which further evolves into a nearly commensurate (NC) CDW below 353 K, and a commensurate (C) CDW below 183 K. We will report on pump- probe diffraction experiments performed in the NC phase of 1T-TaS2, on timescales ranging from fs to µs:
Figure 1 Figure 2
Figure 1 shows the time-evolution of the diffracted intensity at a NC satellite position of reciprocal space, for laser fluences ranging from 0.25 to 1.70 mJ/cm². The NC satellite peaks were chosen because their intensity is directly proportional to the square of the amplitude of the NC modulation. Coherent oscillations associated with the amplitude mode of the NC-CDW are clearly visible at the lowest laser fluence only (560 µJ/cm²). At all fluences studied, a drop of diffracted intensity is observed, followed by a partial recovery within 3 ps. The higher the fluence, the less intensity recovers at the NC satellite peak position. The average NC modulation amplitude is thus reduced, for at least 250 ps after excitation (not shown). Figure 2 shows diffracted intensity profiles on the line that joins the NC and I satellite peak positions, for various pump-probe delays in the [0 - 100 ps] range at a fluence of 2.2 mJ/cm². The region shown is centered on the I satellite peak position, and only the base of the NC satellite peak is visible. One can observe that the reduction of intensity on the NC satellite peak is accompanied by an increase of diffuse scattering, which progressively condenses into a narrow satellite peak characteristic of a photo-induced I phase. Our measurements thus provide a unique view on the dynamics of a 1st order phase transition on its characteristic timescale. We will expose a tentative scenario of nucleation-growth processes for the presently studied NC → I photo-induced phase transition in 1T-TaS2.
17 3rd International Conference on Ultrafast Structural Dynamics
Evidence for Pre-Formed Cooper Pairs in the Pseudogap Phase of Slightly
Underdoped NdBa2Cu3O6+x
Edoardo Baldini1,2, Andreas Mann1, Benjamin Mallett3, Christopher Arrell2, Frank Van Mourik2, Thomas Wolf4, Christian Bernhard3, Jeff Tallon5, José Lorenzana6, Fabrizio Carbone1
1Laboratory for Ultrafast Microscopy and Electron Scattering, EPFL, Lausanne, Switzerland 2Laboratory of Ultrafast Spectroscopy, EPFL, Switzerland 3Department of Physics, University of Fribourg, Fribourg, Switzerland 4Karlsruhe Institute of Technology, Karlsruhe, Germany 5MacDiarmid Institute, Lower Hutt, New Zealand 6Institute for Complex Systems - CNR, and Physics Department, University of Rome “La Sapienza”, Rome, Italy
In the last years ultrafast experiments have contributed to shed new light on high-temperature superconductivity. In particular, tailored excitation in the mid-infrared spectral range was demonstrated to suppress competing structural and electronic orders and to promote a highly coherent state in several underdoped cuprates [1 - 4]. In
YBa2Cu3O6+x this transient state was found to persist up to room temperature, evidenced by the enhancement of the superfluid strength in the THz response. The question whether the high coherence is the signature of a perfect conducting or of an exotic superconducting state at nonequilibrium still remains open. Here, we address this problem from a spectroscopic point of view, by investigating a slightly underdoped sample of
NdBa2Cu3O6+x through ultrafast spectroscopy in the optical regime. The use of a broadband detection scheme enables us to reveal evidence for quasiparticle (QP) excitation in a wide range of temperatures up to the pseudogap temperature scale T*. The existence of a QP spectral signature in the pseudogap phase, together with its peculiar temporal evolution and temperature dependence, can be directly related to the presence of a pairing gap for QP excitation. This observation leads to the hypothesis that the selective melting of a competing order using intense resonant mid-infrared pulses can establish coherence in pre-formed Cooper pairs underlying the pseudogap phase [5].
[1] D. Fausti et al., Science 331, 189 (2011). [2] W. Hu et al., Nature Materials 13, 705 (2014). [3] S. Kaiser et al., Phys. Rev. B 89, 184516 (2014). [4] M. Först et al., Phys. Rev. B 90, 184514 (2014). [5] E. Baldini et al., to be submitted.
18 3rd International Conference on Ultrafast Structural Dynamics
Electronic and structural dynamics in transition metal complexes – recent results from synchrotron and XFEL experiments
Kristoffer Haldrup1
1Technical University of Denmark, Physics Department, NEXMAP Section, Molecular Movies Group, 2800 Kongens Lyngby, Denmark
This talk will highlight a series of synchrotron and XFEL experiments aimed at characterizing ultrafast dynamics in photoactive transition metal complexes in solution. Emphasis will be on how combined X-ray spectroscopic and scattering-based techniques can be applied to obtain a full-field view of the photochemical processes both in and around the photo-excited solute [1,2], and on recent direct measurements of intramolecular electronic and structural dynamics in mono- and bi-nuclear transition metal complexes. A few of the interesting challenges encountered when utilizing novel X-ray sources and detector systems may also be discussed [3, 4]. The work presented in this talk has been done in the group led by Martin Meedom Nielsen, Technical University of Denmark, and in close collaboration with the groups of V. Sundström, C. Bressler, S. Southworth, G. Vanko and K..Gaffney.
[1] K. Haldrup et al., J. of Phys. Chem. A, 2012 [2] S. Canton et al., Nature Communications, 2015 [3] K. Haldrup, Proc. Roy. Soc. B, 2014 [4] T. van Driel et al., Faraday Disc., 2015
19 3rd International Conference on Ultrafast Structural Dynamics
Tracking the charge and spin dynamics of electronic excited states in inorganic complexes. Kelley Gaffney Stanford University and SLAC National Accelerator Laboratory
Inorganic complexes have many advantageous properties for solar energy applications, including strong visible absorption and photocatalytic activity. Whether used as a photocatalyst or a photosensitizer, the lifetime of electronic excited states and the earth abundance of the molecular components represent a key property for solar energy applications.
These dual needs have undermined the usefulness of many coordination compounds. Isoelectronic iron and ruthenium based complexes represent a clear example. Ru-polypyridal based molecules have been the workhorse of solar energy related research and dye sensitized solar cells for decades, but the replacement of low abundance Ru with Fe leads to million-fold reductions in metal to ligand charge transfer (MLCT) excited state lifetimes.
Understanding the origin of this million-fold reduction in lifetime and how to control excited state relaxation in 3d-metal complexes motivates the work I will discuss. We have used the spin sensitivity of hard x-ray fluorescence spectroscopy and the intense femtosecond duration pulses generated by the LCLS x-ray laser to probe the spin dynamics in a series of electronically excited [Fe(CN)6-2N(2,2’-bipyridine)N]2N-4 complexes, with N = 1-3. These femtosecond resolution measurements demonstrate that modification of the solvent and ligand environment can lengthen the MLCT excited state lifetime by more than two orders of magnitude. They also verify the role of triplet ligand field excited states in the spin crossover dynamics from singlet to quintet spin configurations.
20 3rd International Conference on Ultrafast Structural Dynamics
Revealing Charge Carrier Trapping in ZnO Nanoparticles with Femtosecond Time-Resolved X-ray Spectroscopy
T.J. Penfold1, J. Szlachetko1,10, W. Gawelda2, F.G. Santomauro3, A. Britz2, T.B. van Driel4, L. Sala1, S. Ebner1, S.H. Southworth5, G. Doumy5, A.M. March5, C.S. Lehmann5, T. Katayama6, M. Mucke9, D. Iablonskyi8, Y. Kumagai8, G. Knopp1, K. Motomura8, T. Togashi6, S. Owada7, M. Yabashi7, J. Rittmann3, M.M. Nielsen4, M. Pajek10, K. Ueda8, M. Chergui3, R. Abela1, and C.J. Milne1
1Paul Scherrer Institute, Villigen-PSI, Switzerland, 2European XFEL GmbH, Hamburg, Germany, 3EPFL, Lausanne, Switzerland, 4Technical University Of Denmark, Denmark, 5APS, Argonne, USA, 6JASRI, SPring-8, Japan, 7RIKEN SPring-8 Center, SPring-8, Japan, 8Tohoku University, Sendai, Japan, 9Uppsala University, Uppsala, Sweden, 10Jan Kochanowski University, Kielce, Poland
Understanding the nature of the charge trapping sites within metal oxide nanostructures plays a crucial role in evaluating the intrinsic properties that define their technological potential. Due to its desirable nanoscale material properties, ZnO has attracted significant interest.[1] Understanding the mechanism by which charge carriers become trapped and/or recombine is of significant practical importance. Here we study the electron-hole dynamics within a colloidal solution of 35 nm ZnO nanoparticles[2] photo-excited with above band-gap UV light. Using pump-probe X-ray absorption spectroscopy (XAS) combined with a dispersive X-ray emission spectrometer[3], we perform time-resolved resonant X-ray emission spectroscopy (RXES),[4] which yields detailed information on both the occupied and unoccupied electronic states and geometric structure after photo- excitation.
8.65 SACLA 2 ps Kα1,2 APS 100 ps 1.4 5 8.64 5
1.2 Normalized XAS (a.u.) XAS Normalized
0 1.0 8.63 0
0.8 -5 8.62 0.6 -5
-10 SACLA 2 ps 0.4 X-ray emission energy (keV)
Normalized difference signal (a.u.) Normalized difference signal (a.u.) APS XANES 100 ps 8.61 Ground-state XAS 0.2 -3 -3 -10x10 -15x10 Δt=100 ps 8.60 9.65 9.66 9.67 9.68 9.69 9.70 9.66 9.68 9.70 9.72 9.74 9.76 9.78 9.80 9.65 9.66 9.67 9.68 9.69 9.70 X-ray energy (keV) X-ray incident energy (keV) X-ray energy (keV)
Fig.1 Pump-probe XANES (Left), Kα RXES (Middle), and EXAFS (Right) measured on an aqueous solution of 35 nm diameter ZnO nanoparticles after photoexcitation with 355 nm.
Time-resolved results measured both 100 ps (Advanced Photon Source) and 2 ps (SACLA X-FEL) after photo excitation are shown in Figure 1. The XAS transient signals show clear signatures of structural changes due to the trapped electronic excitation in the nanoparticle. Our simulations of the XAS signals indicate that the primary contribution to our measurement is from a hole trapped at a native oxygen vacancy in the lattice, ++ leading to an inward structural distortion of the neighbouring Zn atoms (VO ). This analysis is confirmed by simulation of the XES signal, which shows a slight charge density change on the Zn atoms, leading to a shift in the XES signal. Our transient XAS measurements from SACLA reveal that this charge trapping occurs on a sub- ps timescale.
[1] U. Özgür et al., J Appl Phys 98, 041301 (2005). [2] T. Rossi et al., J. Phys. Chem. C 118, 19422 (2014). [3] J. Szlachetko et al., Rev Sci Instrum 83, 103105 (2012). [4] C. J. Milne, T. J. Penfold, and M. Chergui, Coordination Chemistry Reviews 277, 44 (2014).
21 3rd International Conference on Ultrafast Structural Dynamics
22 3rd International Conference on Ultrafast Structural Dynamics
Talks Thursday
23 3rd International Conference on Ultrafast Structural Dynamics
Two-Dimensional Fourier Transform Vibrational-Electronic Spectroscopy
Trevor L. Courtney1, Zachary W. Fox1 and Munira Khalil1
1Department of Chemistry, University of Washington, Seattle, WA 98195, USA.
The last two decades have seen enormous progress in the development and application of coherent multidimensional two-dimensional electronic and vibrational spectroscopy for probing structural dynamics in the condensed phase. In this talk, I will discuss the development of Fourier transform (FT) two-dimensional vibrational-electronic (2D VE) spectroscopy utilizing a pulse sequence of femtosecond mid-IR and optical pulses. The selection rules and experimental configurations will be detailed and recent results on the coupling of specific high frequency vibrations to charge transfer transitions in small molecules will be presented. We have recently used 2D VE spectroscopy to help understand the vibrational-electronic couplings in the cyanide- II III - 1 bridged transition metal mixed valence complex [(CN)5Fe CNRu (NH3)5] dissolved in formamide. The talk will highlight how the newly developed vibrational-electronic spectroscopies can be used to measure coupled electronic and vibrational motions in complex systems in the condensed phase.1,2
[1] Courtney, Trevor L.; Fox, Zachary W.; Estergreen, Laura; Khalil, Munira., The Journal of Physical Chemistry Letters 6, 1286 (2015) [2] Oliver, Thomas A. A.; Lewis, Nicholas H. C.; Fleming, Graham R., Proceedings of the National Academy of Sciences 111, 10061 (2014)
24 3rd International Conference on Ultrafast Structural Dynamics
Chirality-Sensitive Ultrafast Spectroscopy
A. Steinbacher1, S. Schott1, F. Kanal1, C. Schwarz1, P. Nuernberger2, T. Brixner1
1Institut für Physikalische und Theoretische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany, [email protected] 2Physikalische Chemie II, Ruhr-Universität Bochum, Universitätsstr. 150, 44780 Bochum, Germany
Ultrafast structural dynamics can be investigated by a variety of methods. For example, we have shown the applicability of coherent multidimensional spectroscopy for photochemical reactions on the example of cis-trans isomerization [1]. A different approach – the topic of this presentation – is to employ chirality as a signature of (time-dependent) structure. In general, chirality arises from symmetry considerations: A chiral object cannot be superimposed with its mirror image. Progress will be shown toward chirally selective time-resolved spectroscopy of molecules in the condensed phase. For this purpose, a variety of fundamental and practical issues have to be addressed. Solutions to some of the problems will be discussed.
As a means to introduce and probe chirality via light in the most flexible fashion, we have developed vector- field shaping with independent ultrafast control over amplitude, phase, and polarization of an ultrashort pulse as a function of time [2]. In a second project, we have developed shot-to-shot detection of full spectra at 100 kHz repetition rate with a synchronized 50 kHz chopper [3]. This is helpful since chiral signals are small and it is thus desirable to increase the signal-to-noise ratio for a given measurement time.
In time-resolved spectroscopy of population dynamics one also has to take care that anisotropic contributions to the signal are avoided. With linearly polarized pump and probe pulses in transient absorption spectroscopy, the “magic angle” configuration is commonly employed. However, for pulses with other polarizations or more than two laser beams the situation is more complicated. We have derived conditions for anisotropy-free measurements with arbitrary polarizations and geometry [4].
Another necessary ingredient for chiral spectroscopy is a detection method that provides chiral sensitivity. We have constructed a highly sensitive polarimeter and combined it with accumulative spectroscopy to measure the optical rotation change upon a chirality-modifying photochemical reaction [5]. With this setup we further achieved all-optical discrimination between racemic and achiral molecular solutions [6].
A second option for chiral detection is to measure photoinduced changes in circular dichroism (CD). Femtosecond time-resolved CD spectroscopy is challenging and prone to artefacts, thus in the literature single- wavelength detection is mostly employed. We have developed broadband time-resolved CD spectroscopy [to be published]. It is based on a “light-pulse enantiomer” setup that can create a copy, as well as its precise polarization-mirrored image, of any (polarization-shaped) input laser pulse. Thus, we can switch between opposite chiralities of the (probing) laser field on a shot-to-shot basis and measure broadband time-resolved CD spectra. As an example, we investigated the ultrafast dynamics of hemoglobin upon oxygen release.
[1] S. Ruetzel, M. Diekmann, P. Nuernberger, C. Walter, B. Engels, T. Brixner, PNAS 111, 4764 (2014). [2] C. Schwarz, O. Hüter, T. Brixner, J. Opt. Soc. Am. B, in press (2015). [3] F. Kanal, S. Keiber, R. Eck, T. Brixner, Opt. Express 22, 16965 (2014). [4] S. Schott, A. Steinbacher, J. Buback, P. Nuernberger, T. Brixner, J. Phys. B 47, 124014 (2014). [5] A. Steinbacher, J. Buback, P. Nuernberger, T. Brixner, Opt. Express 20, 11838 (2012). [6] A. Steinbacher, P. Nuernberger, T. Brixner, Phys. Chem. Chem. Phys. 17, 6340 (2015).
25 3rd International Conference on Ultrafast Structural Dynamics
Ultrafast Phosphate Hydration Dynamics in Bulk H2O
Rene Costard,1 Benjamin P. Fingerhut,1 Tobias Tyborski,1 and Thomas Elsaesser1
1Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, D-12489 Berlin, Germany
Phosphate groups are important hydration sites of biomolecules such as DNA and phospholipids and their vibrations have served as local probes of structural fluctuations of hydration shells [1]. In contrast, there is very limited information on small phosphate ions in water, an important benchmark case. Here, interactions of − H2PO4 ions with bulk H2O are studied combining femtosecond 2D infrared spectroscopy, ab-initio calculations and hybrid quantum-classical molecular dynamics (MD) simulations (Fig. 1). The 2D IR spectra cover the spectral range from 900 cm-1 to 1300 cm-1 and reveal the couplings of the − − asymmetric P-(OH)2 stretch (νAS(P-(OH)2)), the symmetric and asymmetric PO2 stretching vibrations (νS(PO2 ) − and (νAS(PO2 )) and δ(P-(OH)2) bending modes. The spectra display nearly homogeneous lineshapes and are characterized by a frequency-time correlation function with a predominant 50 fs decay and a weak constant component accounting for a residual inhomogeneous broadening. MD simulations show that the fluctuating electric field of the aqueous environment induces strong fluctuations of the − − νS(PO2 ) and νAS(PO2 ) transition frequencies − with larger frequency excursions for νAS(PO2 ). The calculated frequency-time correlation function is in good agreement with the experiment (Fig. 1c). The larger fluctuation − amplitude of νAS(PO2 ) is microscopically assigned to the mode mixing with δ(P-(OH)2) bending modes which act as hydrogen bond (HB) donors. − Ab-initio analysis of H2PO4 /H2O − clusters reveals that the ν(PO2 ) frequencies are mainly determined by polarization contributions induced by electrostatic phosphate-water - interactions. Predicted phosphate-water HB Figure 1: (a) 2D spectra of H2PO4 (b) MD lifetimes have values on the order of 10 ps, snapshot (c) frequency-time correlation function substantially longer than water-water HB (solid: experiment, dashed theory) lifetimes. The ultrafast phosphate-water interactions observed in bulk H2O [2] will be compared to hydration dynamics of phospholipids [1] where a quasi-static inhomogeneous broadening of phosphate vibrations suggests minor structural fluctuations of interfacial water.
[1] R. Costard, I. A. Heisler, and T. Elsaesser. J. Phys. Chem. Lett. 5, 506 (2014). [2] R. Costard, T. Tyborski, B. P. Fingerhut, and T. Elsaesser. J. Chem. Phys. 142, 212406 (2015).
26 3rd International Conference on Ultrafast Structural Dynamics
Towards Bulk Heterojunction-Free Organic Solar Cells
Maxim S. Pshenichnikov1, Oleg V. Kozlov1, Barry P. Rand2, and David Cheyns3
1Zernike Institute for Advanced Materials, University of Groningen, The Netherlands 2 Department of Electrical Engineering and Andlinger Center for Energy and the Environment, Princeton University, Princeton, NJ, USA 3imec, Leuven, Belgium [email protected]
Organic solar cells rely on the ability of relatively fragile Frenkel excitons to migrate to the interface between two organic semiconducting materials (the donor and the acceptor). At their interface, the exciton is split into charges that are whisked away to their respective electrodes, thereby generating a current. Short Frenkel exciton diffusion lengths (<10 nm) in typical organics necessitate the use of the so-called bulk heterojunctions (BHJs), a nanotextured interpenetrating network between the donor and acceptor materials. The BHJ presents a compelling compromise between two contradictory requirements: short-scale exciton diffusion to the interface and long-scale charge migration to the electrodes. The BHJ is notoriously difficult to control and optimize due to its spontaneous formation and self-organization so that tremendous efforts of experimentalists and theoreticians alike are being invested in its better understanding. However, the very need of BHJs may be fully waived if exciton diffusion lengths increase sufficiently to match light penetration depths of ~ 100 nm. Furthermore, a number of current concepts in organic optoelectronics will be reconsidered if the exciton diffusion lengths would match the characteristic spatial scale of the devices. Therefore, there exists a critical need to directly assess the exciton dynamics in organic materials and develop new approaches to their control. Here we demonstrate surprisingly large exciton diffusion distances (>50 nm) in one of the most popular acceptor, C70. For this, we developed a unique time-of-flight approach to follow the exciton dynamics by ultrafast photoinduced absorption spectroscopy. Vacuum-deposited C70 layers with varying thickness are sandwiched between two TPTPA layers that work as the charge (holes) detectors. After spectrally-selective photoexcitation of C70 by the visible pump pulse (Fig. 1b), C70 excitons diffuse to the TPTPA/C70 interface where they split into a pair of charges. Instantaneous distortions of TPTPA conjugated backbone caused by hole polarons are probed with the delayed IR (1.6 µm) pulse (Fig.1c). (paragraph below was shifted) The time-of-flight dynamics of exciton harvesting efficiency from C70 layers of different thicknesses directly yield the exciton diffusion time and distance (Fig. 1d). The initial growth at the timescale of ~1 ps is caused by dissociation of excitons generated at the TPTPA/C70 interface. Next, the signal increases with a timescale that is strongly dependent on the C70 thickness (Fig. 1e) due to diffusion-delayed exciton dissociation. Efficient exciton harvesting of >50% even from a 48 nm C70 layer clearly points towards extremely high exciton diffusion rate. All these suggest high potential of development of simple layered organic solar cells with high light harvesting efficiency also applicable to organic thin-film transistors and light-emitting transistors.
Fig. 1. (a) Schematics of the experiment; (b) Linear absorption spectra of C70 and TPTPA; (c) Polaron absorption of TPTPA at different delays of the IR probe pulse. The wavelengths of pump and probe pulses are shown by the arrows; (d) Photoinduced absorption transients (dots) and Monte-Carlo model simulations (solid lines) for different sandwich samples. Thickness of the C70 layer is indicated next to the transients. Charge separation and diffusion processes are colored in green and blue, respectively; (e) Diffusion time (green) and exciton harvesting efficiency (blue) vs. C70 layer thickness. The solid lines are derived from the model fit.
[1] Cheyns et al., Appl. Phys. Lett., 104 (2014), 093302
27 3rd International Conference on Ultrafast Structural Dynamics
Probing Charge and Energy Transfer in Molecules by Multidimensional Stimulated Raman Spectroscopy
Shaul Mukamel, Kochise Bennett, Konstantin E. Dorfman, and Markus Kowalewski
Department of Chemistry, University of California, Irvine, Irvine, California 92697- 2025, USA
Ultrafast nonlinear x-ray spectroscopy is made possible by newly developed free electron laser sources. We propose how to use stimulated X-ray Raman spectroscopy (SXRS) with broadband attosecond X-ray pulses to probe energy and charge transfer dynamics in biomolecules. In this technique, one X-ray pulse creates localized valence excited state wavepacket around the target atom through a Raman process and its evolution is then probed by another X-ray pulse after some time delay. We study long-range charge transfer in azurin and in cytochrome P450. Simulations show that the ultrafast duration of X-ray pulses and the atomic selectivity of core X-ray excitations offer high spatial and temporal resolution. SXRS offers a complementary observation window to UV and IR techniques. Many important photophysical and photochemical molecular processes take place via conical intersections (COIS). So far the experimental evidence for their existence is only circumstantial. Femtosecond stimulated Raman spectroscopy (FSRS) signals of conical intersections in the excited state dynamics of the acrolein molecule made using an ab initio surface hopping simulation protocol are presented.
We propose a technique TRUE-CARS, Transient Redistribution of Ultrafast Electronic Coherences in Attosecond Raman Signals, that can detect the passage through a COIS. An off-resonant composite attosecond and femtosecond probe pulse directly detects electronic coherences that appear as the system approaches the COI.
[1] “Monitoring Long-Range Electron Transfer Pathways in Proteins by Stimulated Attosecond Broadband X- ray Raman Spectroscopy”, Y. Zhang, J. D. Biggs, N. Govind and S. Mukamel, J. Phys. Chem. Lett. 5, 3656 (2014). [2] "Characterizing the Compound I and II Intermediates in the Cytochrome P450 Catalytic Cycle with Nonlinear X-ray Spectroscopy: A Simulation Study", Yu Zhang, Jason D. Biggs, and Shaul Mukamel. Chem Phys Chem (In Press, 2015) [3] “Monitoring conical intersections in the ring opening of furan by Attosecond Stimulated X-ray Raman Spectroscopy",Weijie Hua , Sven Oesterling , Jason Biggs , Yu Zhang , Hideo Ando , Regina De Vivie- Riedle , Benjamin Fingerhut. Nature Comm. (submitted, 2014)
28 3rd International Conference on Ultrafast Structural Dynamics
Towards FEL based Four Wave Mixing
F. Bencivenga1, R. Cucini1, C. Masciovecchio1
1 Elettra-Sincrotrone Trieste S.C.p.A., I-34012 Basovizza, Trieste, Italy.
Wave mixing processes, based on coherent nonlinear light-matter interactions, can combine time resolution with energy and wavevector selectivity, and enables to explore dynamics inaccessible by linear methods.1 Wave mixing experiments have allowed important advances in physics, chemistry and biology, and led to the development of cutting edge technologies. The extension of this approach to extreme ultraviolet (EUV) and x- ray wavelengths is a revolutionary step towards dynamic studies with elemental selectivity and nano to atomic spatial resolution. Here we show how EUV transient gratings generated by coherent free electron laser (FEL) pulses can be used to stimulate FWM processes at sub-optical wavelengths. Furthermore, we found that the time evolution of the FWM signal encodes the dynamics of coherent excitations, as collective molecular vibrations. In a broader context, the demonstration of FEL-based FWM opens up new perspectives for the application of coherent non-linear optics in the EUV/x-ray range.2
[1] N. Bloembergen Nonlinear optics and spectroscopy, Rev. Mod. Phys. 54, 685-695 (1982). [2] F. Bencivenga, R. Cucini, F. Capotondi, A. Battistoni, R. Mincigrucci, E. Giangrisostomi, A. Gessini, M. Manfredda, I. P. Nikolov, E. Pedersoli, E. Principi, C. Svetina, P. Parisse, F. Casolari, M. B. Danailov, M. Kiskinova & C. Masciovecchio, Nature (in press).
29 3rd International Conference on Ultrafast Structural Dynamics
Heterodyne transient grating signal in the extreme ultraviolet
Jakob Grilj1,2, Emily Sistrunk2,3, Majed Chergui1, Markus Gühr2
1LSU, Ecole Polytechnique Federale de Lausanne, Switzerland 2Stanford PULSE Institute, SLAC National Accelerator Laboratory,USA 3NIF and Photon Sciences, Livermore National Laboratory, USA
Heterodyning by a phase stable reference electric field is a well known technique to amplify weak nonlinear responses by several orders of magnitude and is applied routinely in the infrared and optical domain [1]. Its experimental implementation in the short wavelength region is far from trivial because of the required phase stability between the signal and the local oscillator. In the visible spectral range, this has been achieved through diffractive optics that generate intrinsically phase stabilised pairs of pulses [2,3,4]. In the extreme ultraviolet and x-ray spectral regions, the necessary sub-wavelength accuracy of the optical path length are even harder to achieve.
In this contribution we present heterodyne transient grating signal between 18 and 53 nm (70 to 23 eV). We achieve heterodyning by structuring the sample at the same periodicity as the interference pattern of the two grating pulses and use the 1st diffraction order of the probe pulse as local oscillator. The latter is hence automatically phase locked to the nonlinear transient grating response since it is created at the same spot. We have demonstrated the technique for a transient grating on VO2 and observed constructive as well as destructive interference signals [5].
With our approach, the relative phase between reference and nonlinear signal can be tuned by translating the permanent grating under the transient grating orthogonal to the grating lines. The enormous advantage of this technique is that controlling the phase of a few nanometer wavelength pulses is accomplished by translating a grating by parts of its grating constants, which can be well into the 100 nm to micron range.
[1] S.M. Gallagher et al., J. Opt. Soc. Am. B 15, 2338 (1998). [2] G. Goodno el al., J.Opt. Soc. Am. B 15, 1791 (1998). [3] Maznev et al., Opt. Lett 23, 1319 (1998) [4] Xu et al., Chem. Phys. Lett. 338, 254 (2001) [5] J. Grilj et al. Submitted
30 3rd International Conference on Ultrafast Structural Dynamics
Nonequilibrium Dynamical Mean Field Simulation of Electron-Phonon Systems
Philipp Werner1, Martin Eckstein2 , Denis Golez1
1Department of Physics, University of Fribourg, 1700 Fribourg, Switzerland 2Max Planck Research Department for Structural Dynamics, University of Hamburg-CFEL, Hamburg, Germany
We present a formalism that allows to simulate the time-evolution of strongly interacting electrons coupled to dispersionless phonons [1], and use it to study the effect of strong electric fields in the Holstein-Hubbard model [2]. We show that the electron-phonon coupling opens new relaxation channels and thus qualitatively changes the life-time and fluence dependence of photo-doped carriers. Another interesting effect is that the field-induced localization of electrons in quasi-static electric fields effectively enhances the electron-phonon interactions. With suitable extensions, the same machinery can also be used to study dynamical screening and plasmon emission/absorption in photo-doped Mott insulators [3].
[1] P. Werner and M. Eckstein, Phys. Rev. B 88, 165108 (2013). [2] P. Werner and M. Eckstein, Europhys. Lett. 109, 37002 (2015). [3] D. Golez, M. Eckstein and P. Werner, in preparation.
31 3rd International Conference on Ultrafast Structural Dynamics
The Mott Energy Scale revealed by Ultrafast Spectroscopy in Transition Metal Oxides
F. Carbone1, S. Borroni1, A. Mann1, E. Baldini1, J. Lorenzana2.
1Laboratory for Ultrafast Microscopy and Electron Scattering (LUMES), ICMP EPFL, Lausanne Switzerland 2 Dipartimento di Fisica, Università la Sapienza, Roma, Italy
Strong on-site Coulomb repulsions govern the physics of several complex oxides. In particular, multiferroic materials, high-temperature superconductors, charge and orbitally ordered insulators among others, belong to this family of compounds. Spectroscopically, valuable information comes from the quantification of the coupling parameters between low-energy excitations, such as phonons or spin-waves, and the high energy charge-transfer or Mott-Hubbard electronic states. Here we will present the results of our recent studies on high- temperature superconductors and insulating magnetic oxides in which information on such a coupling is obtained via the Impulsive Stimulated Raman Scattering mechanism. The resonance between the many-body ground state responsible for the electronic properties of these materials, and the Charge-Transfer or Mott gap will be discussed.
32 3rd International Conference on Ultrafast Structural Dynamics
Ultrafast Structural Dynamics of the Fe-Pnictide Parent Compound BaFe2As2
L. Rettig1, S. O. Mariager1, A. Ferrer2,1, S. Grübel1, J. A. Johnson1, J. Rittmann3,1, T. Wolf4, S. L. Johnson2, G. Ingold1,5, P. Beaud1,5, and U. Staub1
1Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland 2Institute for Quantum Electronics, Physics Department, ETH Zürich, CH-8093 Zürich, Switzerland 3Ecole Polytechnique Fédérale de Lausanne, Laboratoire de Spectroscopie Ultrarapide, ISIC, FSB, CH-1015 Lausanne, Switzerland 4Karlsruhe Institute of Technology, Institut für Festkörperphysik, D-76021 Karlsruhe, Germany 5SwissFEL, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
Understanding the interplay of the various degrees of freedom such as the electrons, spins and lattice is essential for many complex materials, including the high-temperature superconductors. In the case of the Fe pnictides, especially the strong sensitivity of the electronic and magnetic properties to the exact shape and size of the Fe- As tetrahedra plays a crucial role for superconductivity and demonstrates a strong magneto-structural coupling [1]. In addition, antiferromagnetic phases are closely linked to structural distortions in these materials.
Here, we use femtosecond time-resolved x-ray diffraction to investigate the structural dynamics in the Fe- pnictide parent compound BaFe2As2 [2]. We observe fluence dependent intensity oscillations of two specific Bragg reflections with a period of ~200 fs. Their distinctly different sensitivity to the pnictogen height in the compound demonstrates the coherent excitation of the A1� phonon mode and allows us to quantify the coherent modifications of the Fe-As tetrahedra. By a comparison with time-resolved photoemission data [3] we derive the electron-phonon deformation potential for this particular mode, which is comparable to theoretical predictions. Our results demonstrate the importance of this structural degree of freedom for the electron-phonon coupling in the Fe pnictides and indicate a transient increase of the Fe magnetic moments on an ultrafast timescale.
In addition, in the spin-density wave ground state we investigate the reduction of the orthorhombic distortion by the laser excitation. The orthorhombic splitting of the Bragg peak reduces on a timescale of several tens of picoseconds, compatible with domain motion. This contrasts with the ultrafast quench of the magnetic ordering in <200 fs [4] and provides further information about the coupling of magnetic and structural degrees of freedom.
[1] I. I. Mazin, Nature 464, 183 (2010). [2] L. Rettig, S. O. Mariager, A. Ferrer, et al., Phys. Rev. Lett. 114, 067402 (2015). [3] L. X. Yang, G. Rohde, T. Rohwer, et al., Phys. Rev. Lett. 112, 207001 (2014). [4] K. W. Kim, A. Pashkin, H. Schäfer, et al., Nat. Mater. 11, 497 (2012).
33 3rd International Conference on Ultrafast Structural Dynamics
Femtosecond X-ray liquidography captures the formation of chemical bond in the solution phase
Hyotcherl Ihee
Center for Nanomaterials and Chemical Reactions, IBS, Daejeon 305-701, South Korea Department of Chemistry, KAIST, Daejeon 305-701, South Korea, [email protected]
The pump-probe X-ray diffraction and scattering techniques have now been fully established as a powerful method to investigate molecular structural dynamics [1-5]. We have employed the techniques to study structural dynamics and spatiotemporal kinetics of many molecular systems including diatomic molecules, haloalkanes, organometallic complexes and protein molecules over timescales from ps to milliseconds. X-ray crystallography, the major structural tool to determine 3D structures of proteins, can be extended to time- resolved X-ray crystallography with a laser-excitation and X-ray-probe scheme, but has been limited to a few model systems due to the stringent prerequisites such as highly-ordered and radiation-resistant single crystals. These problems can be overcome by applying time-resolved X-ray diffraction directly to protein solutions rather than protein single crystals. To emphasize that structural information can be obtained from the liquid phase, this time-resolved X-ray solution scattering technique is named time-resolved X-ray liquidography (TRXL) in analogy to time-resolved X-ray crystallography where the structural information of reaction intermediates is obtained from the crystalline phase. We will present our recent results including the achievement of femtosecond TRXL by using an X-ray free electron laser.
[1] “Direct observation of bond formation in solution with femtosecond X-ray scattering”, K. H. Kim, J. G. Kim, S. Nozawa, T. Sato, K. Y. Oang, T. W. Kim, H. Ki, J. Jo, S. Park, C. Song, T. Sato, K. Ogawa, T. Togashi, K. Tono, M. Yabashi, T. Ishikawa, J. Kim, R. Ryoo, J. Kim, H. Ihee*, S. Adachi, Nature, 2015, 518, 385-389. [2] “Volume-conserving trans-cis isomerization pathways in photoactive yellow protein visualized by picosecond X-ray crystallography”, Y. O. Jung, J. H. Lee, J. Kim, M. Schmidt, K. Moffat, V. Srajer, H. Ihee*, Nat. Chem., 2013, 5, 212-220. [3] “Visualizing Solution-Phase Reaction Dynamics with Time-Resolved X-ray Liquidography”, H. Ihee*, Acc. Chem. Res., 2009, 42, 356-366 (Review Article). [4] “Tracking the structural dynamics of proteins in solution using time-resolved wide-angle X-ray scattering”, M. Cammarata*, M. Levantino, F. Schotte, P. A. Anfinrud, F. Ewald, J. Choi, A. Cupane, M. Wulff, H. Ihee*, Nature Methods, 2008, 5, 881-887. [5] “Ultrafast X-ray diffraction of transient molecular structures in solution”, H. Ihee*, M. Lorenc, T. K. Kim, Q. Y. Kong, M. Cammarata, J. H. Lee, S. Bratos, M. Wulff, Science, 2005, 309, 1223-1227.
34 3rd International Conference on Ultrafast Structural Dynamics
Phonon spectroscopy by Fourier-transform inelastic x-ray scattering
Mariano Trigo
SLAC, [email protected]
In a solid, the elementary excitations of the lattice (phonons) can be obtained by inelastic neutron or x-ray scattering where the energy of the phonon is known from the energy shift of the outgoing particle. In the case of x-ray scattering these require sophisticated monochromators and spectrometers. In this talk, I will present an alternative approach for measuring collective excitations in solids that exploits femtosecond diffuse x-ray scattering using Free Electron Laser pulses. I will show that the ultrafast excitation induces time-dependent coherences in the lattice modes that span multiple wavelengths across the entire reciprocal space. The frequency of the phonon is then recovered by a simple Fourier transform. Using this approach we obtain an extremely high-resolution map (~ 0.3 meV) of the phonon dispersion of germanium over large sections of momentum space. I will discuss the advantages and limitations of this method and present a few examples of potential important impact.
35 3rd International Conference on Ultrafast Structural Dynamics
Study of Coherent Phonon Excitation by Means of Time-Resolved Photoelectron Diffraction
M. Hengsberger1, M. Greif1, L. Kasmi2, L. Castiglioni1, M. Lucchini2, L. Gallmann2, U. Keller2, and J. Osterwalder1
1Department of Physics, University of Zurich, Switzerland 2Department of Physics, ETH Zurich, Switzerland
We present first experiments using time-resolved photoelectron diffraction for the measurement of structural dynamics on surfaces. Photoelectrons excited by absorption of vacuum ultraviolet (VUV) or x-ray light will undergo scattering processes at nearest-neighbors of the emitter atoms. The direct and scattered photoelectron waves generate an interference pattern. Such patterns are recorded by measuring the photoemission intensity as function of emission direction at fixed kinetic energy [1]. Since the kinetic energy at given photon energy is a fingerprint of the emitter atom, the method is sensitive to the chemical nature of the emitter and even to specific chemical shifts in case of narrow linewidth VUV radiation. The pattern carries information about the local environment of the emitter atom and allows bond lengths and bond directions to be retrieved with high precision. Since long-range order is not required the method is well suited to study the structural dynamics in molecules adsorbed on surfaces [2].
Electrons have very high scattering cross-sections, which only weakly depend on the mass of the scatterer. Together with the very short inelastic mean-free path of electrons in condensed matter this renders electrons a suitable tool to study surface atomic structure and the structural dynamics [3]. In photoelectron diffraction, the final temporal resolution in a pump-probe experiment will be determined by the cross correlation of the pump and probe light pulses, only. Photoelectron diffraction can be observed using both x-ray and VUV light for the photoelectron excitation [2,4]. Hence, infrared pump - VUV probe experiments are readily available on a laboratory scale using high-harmonics setups [5,6].
In a first experiment, the displacive excitation of coherent phonons in Bi(111) was studied by time-resolved ultraviolet photoelectron diffraction (UPD): As a function of delay between infrared pump and XUV probe (about 22 eV photon energy), modulations of the electron yield and changes in the intensity distribution are observed for different detection directions. These modulations are due to the excitation of the A1g mode at 2.8 THz, slightly softened due to the high excitation density. The photoemission intensity modulations observed at different angles exhibit different phases with respect to the moment of absorption of the pump pulse. This phase gives first information about the underlying nature of the modulations, which may be of both, structural and electronic origin. By means of this phase shift, the amplitude of the total change, and the modulation depth the electronic and structural effects can be disentangled. This allows in principle the electronic excitations driving the coherent phonons and the phonon mode to be studied simultaneously [5].
[1] J. Osterwalder in Surface Analysis by Auger and X-Ray Photoelectron Spectroscopy, edited by D. Briggs and J. Grant, p. 557 ff., IM Publications and Surface Spectra Limited, 2003. [2] M. Greif et al., Phys. Rev. B 87, 085429 (2013). [3] C. Ruan, F. Vigliotti, V. Lobastov, S. Chen, and A. Zewail, PNAS 101, 1123 (2004). [4] P. Krüger, F. Da Pieve, and J. Osterwalder, Phys. Rev. B 83, 115437 (2011). [5] M. Greif, Ph.D. Thesis, University of Zürich 2014. [6] R. Locher et al., Rev. Sci. Instr. 85, 013113 (2014).
36 3rd International Conference on Ultrafast Structural Dynamics
Talks Friday
37 3rd International Conference on Ultrafast Structural Dynamics
Mapping Atomic Motions with Ultrabright Electrons: Developing a Reaction Mode Basis for Chemistry
R. J. Dwayne Miller
Max Planck Institute for the Structure and Dynamics of Matter/Hamburg The Hamburg Centre for Ultrafast Imaging and Departments of Chemistry and Physics University of Toronto
Electron sources have achieved sufficient brightness to literally light up atomic motions on the primary timescales of chemistry. In this context both rf pulse compression and relativistic regimes will be touched up. However, the most robust e source is the simple compact electron gun concept that has now reached new brightness levels capable of resolving unit cells up to 4 nm (scale of protein systems). These sources provide a direct observation of the far from equilibrium atomic motions central to chemistry for which general reduction principles are emerging. Studies of formally a photoinduced charge transfer process in charge ordered organic systems have directly observed the most strongly coupled modes that stabilize the charge separated state (Gao et al Nature 2013). It was discovered that this nominally 280 dimensional problem distilled down to projections along a few principle reaction coordinates. Similar reduction in dimensionality has also been observed for ring closing reactions in organic systems (Jean-Ruel et al JPC B 2013). Even more dramatic reduction in complexity has been observed for the material, Me4P[Pt(dmit)2]2, which exhibits a photo-induced metal to metal centre charge transfer process. The large-amplitude modes can be identified by eye from the molecular movie and involve a dimer expansion and a librational mode. These studies will be further amplified by recent studies of spin cross over molecular systems and a direct observation of Pauli explosion in alkali halides (Hada et al, Nature Comm, 2014) – the reverse of the classic “electron harpooning” reaction that helped establish transition state concepts. This reduction principle to a few key modes appears to be general, even for very complex systems. The far from equilibrium motions that sample the highly anharmonic barrier region are strongly coupled, which in turn leads to highly localized motions projected onto the reaction coordinate. In this respect, one of the marvels of chemistry, and biology by extension, is that despite the enormous number of possible nuclear configurations for any given construct, chemical processes reduce to a relatively small number of reaction mechanisms. We now are beginning to see the underlying physics for these generalized reaction mechanisms. The “magic of chemistry” is this enormous reduction in dimensionality in the barrier crossing region that ultimately makes chemical concepts transferrable. With a large enough basis, it may be possible to characterize reaction mechanisms in terms of reaction modes, or reaction power spectra, in analogy to the characterization of equilibrium fluctuations in terms of vibrational normal modes.
38 3rd International Conference on Ultrafast Structural Dynamics
Cooperative Atomic Motion probed by Femtosecond Electron Diffraction
Maximilian Eichberger1 and Jure Demsar2
1Department of Physics, University of Konstanz, Germany 2Institute of Physics, Johannes Gutenberg-University Mainz, Germany
In numerous solids exhibiting broken symmetry ground states, changes in electronic (spin) structure are accompanied by structural changes. Femtosecond time-resolved techniques recently contributed many important insights into the origin of their ground states by tracking their dynamics using femtosecond light pulses [1,2]. Moreover, several studies of structural dynamics in systems with periodic lattice modulation (PLD) were performed [3-6]. Since intensities of the super-lattice diffraction peaks are in the first approximation proportional to the square of the PLD amplitude, their temporal dynamics provides access to cooperative atomic motion. This process takes place on a 100 femtosecond timescale, which corresponds to a fraction of a period of the corresponding lattice vibration. However, since energy transfer from the excited electronic system to the lattice takes place on a comparable sub-picosecond timescale, contribution of the incoherent lattice motion on diffraction intensities is not negligible and has to be taken into account, when trying to extract the order parameter trajectory.
Here, we demonstrate an ultrafast transmission electron diffraction apparatus, where relative changes in individual diffraction peaks of less than 1% can be studied. Taking a prototype two-dimensional charge density wave system 1T-TaS2 as an example, we demonstrate, that by simultaneously tracking the dynamics of intensities in super-lattice peaks, lattice peaks and of the incoherent background over multiple diffraction orders the two processes, order parameter dynamics and the incoherent electron-phonon thermalization, can be effectively disentangled [6]. This approach provides direct access to the dynamics of the order parameter.
[1] H. Schaefer et al., Phys. Rev. Lett. 105, 066402 (2010); H. Schaefer et al., Phys. Rev. B 89, 045106 (2014). [2] M. Porer et al., Nature Mat. (2014); K.W. Kim, et al., Nature Mat. 11, 497 (2012). [3] M. Eichberger, et al., Nature 468, 799 (2010). [4] E. Vorobeva, et al., Phys. Rev. Lett. 107, 036403 (2011). [5] N. Erasmus, et al., Phys. Rev. Lett. 109, 167402 (2012). [6] T. Huber et al., Phys. Rev. Lett. 113, 026401 (2014). [7] M. Eichberger, et al., in preparation
39 3rd International Conference on Ultrafast Structural Dynamics
Femtosecond Electron Microscopy of Charge Motion along the Surface of a Nanoscale Object
A. R. Bainbridge, C. Barlow-Myers, W. A. Bryan
Department of Physics, College of Science, Swansea University, Singleton Park, Swansea SA2 8PP, United Kingdom.
The impact of electron microscopy and diffraction is clearly established, facilitating unprecedented imaging of matter on atomic length scales. Major advances in ultrafast electron microscopy and diffraction over the last decade are bringing about a paradigm shift to using electrons as a time-resolved imaging tool. Much as with femtosecond pulses of x-rays generated by XFELs being employed to image processes on chemical and biological time- and length-scales, ultrafast electron microscopy is moving towards being able to image on atomic time- and length-scales. Our recent results to be presented in Zurich are a step in this direction, using sub-picosecond and sub-micron temporal and spatial resolution to directly observe the response of a nanoscale metal conductor to an applied ultrafast laser pulse.
We have developed and demonstrated time-resolved imaging in a novel instrument which makes use of point projection microscopy (PPM), originally developed as a CW technique by Fink and co-workers in 1989 [1,2]. PPM is closely related to the original holographic scheme of Gabor, and the beauty of PPM lies in its simplicity. Typical PPMs [3,4] are composed of a highly coherent electron source (typically a nanoscale metal tip), the target or object to be imaged and an electron detector. In CW mode, other groups have reported a resolution of 2 nm, however very recent results indicate a single-atom source could resolve to 2 Angstroms.
One of our medium-term goals is to directly observe nanoplasmonic responses in the vicinity of nanorods, nanowires and 2D crystalline planes illuminated with femtosecond laser pulses. As a proof-of-principle, we have made use of two nanoscale metal tips (NSMTs) as source and target as they have a well understood response to laser fields. A Light Conversion Pharos (1028nm, 290fs, 50kHz, 4W) pumped an Orpheus-N NOPA producing 800nm, 20 fs, 0.85W at 50kHz which was actively pointing stabilized. These laser pulses were split 1:10, with the lower energy pulse transmission focused on a tungsten NSMT pointing at a distant MCP + phosphor screen. The tight radius of curvature at the apex of such NSMTs caused a field enhancement which, when coupled with the electric field induced by the laser field, caused tunneling of bunches of electrons directly into the continuum.
A second tungsten NSMT perpendicular to the first and illuminated by the remaining split of the laser output is a perfect test object for temporally resolved electron microscopy. By reducing the separation of the NSMTs to around 100 microns formed a low-energy PPM with sub-micron resolution. This configuration allowed the observation of a “wave” of charge along the shank of the second nanotip as the laser pulse delay was varied. This charge wave is initiated by the nanoplasmonic response to the applied laser field, so our observations combine information about how the charge density evolves as a function of space and time. Interestingly, we see the influence of the changing shape of the nanotip taper. Our current efforts are centred on modelling these observations, and novel Monte Carlo results will be presented and discussed, as will future applications of this technique.
[1] Stocker W et al, Ultramicroscopy 31 379 (1989) [2] Fink H W et al, Phys. Rev. Lett. 65 1204 (1990) [3] Gulde et al, Science 345 200 (2014) [4] Muller et al, Nature Comms. 5 5292 (2014)
40 3rd International Conference on Ultrafast Structural Dynamics
Spatial and Temporal Resolution Studies on a Highly Compact Ultrafast Electron Diffractometer
Christian Gerbig, Silvio Morgenstern, Marlene Adrian, Christian Sarpe, Arne Senftleben, Thomas Baumert
University of Kassel, Institute of Physics and Center for Interdisciplinary Nanostructure Science and Technology (CINSaT)
Time-resolved diffraction with femtosecond electron pulses has become a promising technique to directly provide insights into photo induced primary dynamics at the atomic level in molecules and solids. Ultrashort pulse duration as well as extensive spatial coherence are desired, however, space charge effects complicate the bunching of multiple electrons in a single pulse. We experimentally investigate the interplay between spatial and temporal aspects of resolution limits in ultrafast electron diffraction (UED) on our highly compact transmission electron diffractometer. To that end, the initial source size and charge density of electron bunches are systematically manipulated and the resulting bunch properties at the sample position are fully characterized in terms of lateral coherence, temporal width and diffracted intensity. We obtain electron pulse durations down to 120 fs and transversal coherence lengths up to 20 nm. Instrumental impacts on the effective signal yield in diffraction and electron pulse brightness are discussed as well. The performance of our compact UED setup at selected electron pulse conditions is finally demonstrated in a time-resolved study of lattice heating in multilayer graphene after optical excitation. During the heating process, we observe shearing modes and acoustic breathing modes.
41 3rd International Conference on Ultrafast Structural Dynamics
Structural Dynamics of Charge-Transfer Excitations in Transition Metal Complexes Probed with X-ray Spectroscopy
Nils Huse1, Kiryong Hong2, Amy Cordones-Hahn3, Hana Cho2,3, Jae Hyuk Lee3, Komal Garg4, Jeffrey Rack4, Robert W. Schoenlein3, Tae Kyu Kim2
1Department of Physics, University of Hamburg & Max Planck Institute for the Structure and Dynamics of Matter, Center for Free Electron Laser Science, Hamburg, Germany 2Department of Chemistry and Chemistry Institute of Functional Materials, Pusan National University, Busan, South Korea 3Ultrafast X-ray Science Lab, Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA 4Department of Chemistry and Biochemistry, Ohio University, Athens, Ohio, USA
The importance of transition-metal ions to chemistry and biology underscores the need to understand reaction mechanisms of metal-containing molecular systems from a structural and electronic point of view. The surroundings of metal ions in the form of ligands determine the molecular structure and strongly influences the valence charge and spin density of the metal ions. Often, competing structural arrangements and electronic configurations in close energetic vicinity and/or several possible reaction pathways to new chemical species or material phases exist, raising many questions related to fundamental design principles of transition-metal containing systems. Transient 1s and 2p core-level absorption spectra of transitions- light elements [1] and metal ions in molecular systems provide information on structure, electronic configuration and spin-states of the metal centers and the surrounding atoms in the condensed phase [2,3]. Combined temporal and spectral information from metal and ligand atomic species not only reports on structural and electronic/spin degrees of freedom but allows for the identification of complex reaction pathways and the corresponding intermediate states. In particular, ligand-1s and metal-2p absorption spectra of ruthenium(II) complexes will be discussed [4] to demonstrate that the information content from two atomic species greatly facilitates the identification of more complex reaction pathways with multiple bifurcation points and intermediates.
[1] H. Wen et al., J. Chem. Phys. 131, 234505 (2009). [2] N. Huse et al., J. Phys. Chem. Lett. 99, 213 (2011). [3] H. Cho et al, Faraday Discuss. 157, 463 (2012). [4] K. Garg et al, Chem. Eur. J. 19, 11686 (2014)
42 3rd International Conference on Ultrafast Structural Dynamics
Watching coherent structural molecular trapping of light-induced excited spin-state by ultrafast X-ray and optical absorption spectroscopies
Collet E.1, Lemke H.T. 2, Bertoni R.,1 Lorenc M.,1 Cammarata M.1
1 Institut de Physique de Rennes, Université de Rennes, France. 2 Linac Coherent Light Soure, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA, USA
During the last years, we have studied how electronic excitation by light drives ultrafast photoswitching in bistable spin-crossover molecular solids. In the solid state, the photo-induced transformation pathway of the material is complex because in the active medium, which the crystal is, other effects of elastic or thermal nature should be considered [1]. In addition, unusual out-of-equilibrium processes such as the erasing of spin-state concentration waves exist in these prototypes light-active systems [2,3]. It is of fundamental interest to understand the basic mechanisms allowing light to switch the molecular state, here from low spin (LS) to high spin (HS). We combined femtosecond x-ray absorption, performed at LCLS X- FEL, and optical spectroscopy, performed in Rennes, to reveal that the stabilization of the photoinduced HS state results from a structural self-trapping of the electronic excited state. This ultrafast process is driven by the generation of coherent molecular phonons [4,5]. The stabilization of the newly formed electronic state results from a two steps relaxation sequentially involving molecular stretching and torsion. More accurate ultrafast X- ray absorption near edge structure (XANES) measurements were performed on aqueous SCO molecules for measuring structural and electronic changes. The oscillating time resolved XANES signal is directly associated with the activation and damping of the so called breathing vibrational mode of the molecule, which is the main reaction coordinate associated with the change of spin state [6].
[1] R. Bertoni et al., Coord. Chem. Rev. 282-283, 66-76 (2015). [2] A. Maroni et al., Faraday Discuss., DOI: 10.1039/C4FD00164H (2015) [3] E. Collet et al, Phys. Rev. Lett. 109, 257206 (2012). [4] M. Cammarata, Phys. Rev. Lett. 113, 227402 (2014). [5] R. Bertoni et al., Acc. Chem. Res. doi:10.1021/ar500444d (2015). [6] H. T. Lemke et al., In preparation.
43 3rd International Conference on Ultrafast Structural Dynamics
Core-level spectrum simulations of ultra-fast dynamics
Odelius M, Josefsson, I
Department of Physics, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden
Core-level spectroscopy comprises of many rich probes of the electronic structure, and the techniques give unique information about chemical bonding in applications ranging from precise measurements in gas phase to in operando experiments on complex materials. In particular, L-edge X-ray spectroscopy is a valuable probe of the local electronic valence structure in transition metal compounds, due to the strong signals from 2p-to-3d transitions. However, the interpretation of L-edge spectra is complicated and relies on accurate theoretical modeling and spectrum simulations to take into account effects of multiplet effects, spin-orbit coupling, chemical interactions, dynamics in the spectroscopic process [1].
The challenge for a theoretically supported interpretation of core-level spectra both consists in simulating the spectroscopic process and in creating realistic models of the system. Liquid solutions require treatment of finite temperature effects and dynamical sampling, for which classical molecular dynamics simulations and Monte Carlo simulations are well established tools. Today small models can be treated with ab initio molecular dynamics and with inclusion of quantum effects. The simulation trajectories can be used to sample theoretical spectra and determine the relation between structure and spectral signature. In the presentation, I discuss studies of solution dynamics in aqueous tri-iodide [2,3], hydrogen bonding in aqueous glycine [4] and photo- dissociation of ironpentacarbonyl in solution [5]. A range of methods are used for simulation of core-level spectra, but the presentation is focused mainly on quantum chemical methods. Within the framework of density functional theory, spectrum simulations based on the Kohn-Sham eigenstates has been successfully employed for simulations of photo-electron, X-ray absorption and emission spectra in particular of K-edge core-levels. However, measurements at certain core levels and the recently development of time-resolved X-ray spectroscopy call for theoretical methods which can handle (i) relativistic effects, in particular spin-orbit coupling, (ii) spectra of valence-excited molecules, and (iii) distorted and dissociating molecules. From the experience in quantum chemistry, multiconfigurational self- consistent field (SCF) calculations are required for a general accurate description of valence-excited states, and also for core- excited states. Calculations using the restricted active space (RASSCF) method allows us to simulate L-edge resonant inelastic X-ray scattering of transition metal complexes in solution to investigate solvation and ultra-fast excited state dynamics [1,5].
[1] I. Josefsson, K. Kunnus, S. Schreck, A. Föhlisch, F. de Groot, Ph.Wernet, and M. Odelius, J. Phys. Chem. Lett. 3, 3565 (2012). [2] I. Josefsson, S. K. Eriksson, N. Ottosson, G. Öhrwall, H. Siegbahn, A. Hagfeldt, H. Rensmo, O. Björneholm, and M. Odelius, Phys. Chem. Chem. Phys. 15, 20189 (2013). [3] N. K. Jena, I. Josefsson, S. K. Eriksson, A. Hagfeldt, H. Siegbahn, O. Björneholm, H. Rensmo, and M. Odelius, Chem. Eu. J. 21, 4049 (2015). [4] M. Blum, M. Odelius, L. Weinhardt, S. Pookpanratana, M. Bär, Y. Zhang, O. Fuchs, W. Yang, E. Umbach, and C. Heske, J. Phys. Chem. B 116, 13757 (2012). [5] 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 (2015).
44 3rd International Conference on Ultrafast Structural Dynamics
Transient Charge Density Maps of Ionic Crystals Studied by Femtosecond X-Ray Powder Diffraction
Thomas Elsaesser
Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Str. 2a, D-12489 Berlin, Germany
Relocation of electronic charge upon photoexcitation and/or under the action of an external electric field plays a key role in chemical reactions and for functional processes in molecular materials. The extension of x-ray diffraction techniques into the femtosecond time domain has allowed for spatially resolving transient atomic arrangements and charge distributions on the intrinsic length and time scales of molecular motions [1]. In particular, x-ray powder diffraction with laser-driven hard x-ray sources has provided spatial maps of electron density with a 100 fs time resolution for a number of prototype ionic materials. In this talk, recent progress in this research field will be discussed by addressing novel table-top femtosecond hard x-ray sources [2], new results on field-driven charge dynamics in crystals [3,4], and methods for extracting charge density maps from transient diffraction patterns [4]. The results give insight into dynamics of valence electrons in light materials such as LiH, LiBH4, and NaBH4 which in the case of LiH are strongly influenced by many-body effects originating from electron-electron interactions.
[1] T. Elsaesser, M. Woerner, J. Chem. Phys. 140, 020901 (2014). [2] J. Weisshaupt et al., Nature Photonics 8, 927 (2014). [3] V. Juvé et al., Phys. Rev. Lett. 111, 217401 (2013). [4] M. Woerner et al., Faraday Discuss. 171, 373 (2014).
45 3rd International Conference on Ultrafast Structural Dynamics
46 3rd International Conference on Ultrafast Structural Dynamics
Posters
47 3rd International Conference on Ultrafast Structural Dynamics
Lattice dynamics in few-layer Molybdenum disulfide investigated by Ultrafast Electron Diffraction
Marlene Adrian, Christian Gerbig, Silvio Morgenstern, Christian Sarpe, Arne Senftleben, Thomas Baumert
University of Kassel, Institute of Physics and Center for Interdisciplinary Nanostructure Science and Technology (CINSaT)
Molybdenum disulfide (MoS2) is a prototype example for transition metal dichalcogenides (TMDs), which form a group of van-der-Waals bound two-dimensional layered materials [1]. Due to their unique electronic and optical properties such as circular dichroism, a strong spin-orbit coupling and a shift from indirect to direct band-gap semiconductor with decreasing film thickness from bulk to monolayer, TMDs are interesting for both fundamental research and industrial applications such as electronic devices [2, 3]. We study dynamical processes following optical excitation in few-layer MoS2 by means of time-resolved Ultrafast Electron Diffraction (UED), which has become a promising technique to directly provide insights into dynamics in crystalline solids at the microscopic level with a sub-picosecond temporal resolution [4, 5]. Our highly compact UED-setup is fully characterized by experiments and many-body simulations [6].
[1] S. Z. Butler et al., ACS Nano 7, 2898 (2013). [2] G. Berghäuser and E. Malic, Phys. Rev. B 89, 125309 (2014). [3] B. Radisavljevic et al., Nature Nanotech. 6, 147-150 (2011). [4] A. H. Zewail, J. Phys. Chem. 98, 2782-2796 (1994). [5] B. Siwick and D. Miller, Science 302, 1382-1385 (2003). [6] C. Gerbig et al., New J. Phys. accepted (2015).
48 3rd International Conference on Ultrafast Structural Dynamics
Table-top Plasma-driven XUV-photoemission Spectroscopies
Yunieski Arbelo and Davide Bleiner*
Empa - Swiss Federal Laboratories for Materials Science and Technology. Überlandstrasse 129, 8600 Dübendorf – Switzerland. *[email protected]
Photoemission spectroscopies (e.g. PES, XPES, ARPES, PEPICO) can be exploited in the investigation of electronic structures of solids, characterization of dispersions in energy-momentum space, and ion-dissociation rates [1]. The photoemission must be triggered e.g. with short-wavelength radiation produced in large scale facilities like Synchrotron, having state-of-art figures of merit [2] like photon-energy tenability, ultrafast time- resolution and high brightness (1019 ph.s-1mrad-2mm-20.1%BW). Unfortunately, the beam-time limitation and high cost restricts the possibility of measurements-optimization and 24/7 utilization. A lab-scale alternative is thus required to overcome these restrictions, which shall be found in table-top sources based on plasma- emission at XUV wavelengths.
Our XUV photons are generated across a “pseudospark switch” (cold cathode thyratron) on 20Hz-pulsed configuration. Advantages of pseudospark switches include the ability to carry high lifetime and a high current rise of about 1012 A/sec. In fact, since the cathode is not heated prior to switching, the standby power is approximately one order of magnitude lower than in thyratrons. In this source system, narrow linewidths (Δλ/λ<10-4) and high brightness (up to 1025 ph.s-1mrad-2mm-20.1%BW) were demonstrated [2].
A well-established detector, such as the time-of-flight (TOF) for photoelectron spectroscopy is acknowledged for advantages like e.g. simultaneous acquisition of entire photoemission spectrum, thus increasing the collection efficiency in pulsed measurements. The TOF analyzers can be implemented to measure in electron or ion modes; however simultaneous measurements cannot be performed, such as for photoelectron-photoion coincidence (PEPICO) [3] techniques which can allow ion-dissociation rates analysis.
Aim of this work is allowing simultaneous ultrafast measurement of photoelectron-photoions by means of measurement with a high-pass FT detector, coupled to a table-top XUV source. Our self-designed detector is being tested (patent pending), which allows increasing the duty cycle and measuring in the frequency domain of photoemission pulses. For the initial calibration of the FT-TOF spectrometer, the photoemission from Au samples after XUV-irradiation is measured.
[1] J.Omachi et al., Opt. Express. 20, 23542-23552 (2012). [2] D. Bleiner et al., PhyS.T162, 014050. [3] T.Baer, Int. J. Mass Spectrom. 200, 443-457 (2000) [4] O.Trapp et al., Angew. Chem.Int. Ed. Engl. 43, 6541-6544 (2004).
49 3rd International Conference on Ultrafast Structural Dynamics
On the Nature of the Excitonic Quasiparticles in Anatase TiO2
Edoardo Baldini1, 2, Letizia Chiodo3, Simon Moser2, Julien Levallois4, Enrico Pomarico1, Gerald Aubock1, Arnauld Magrez2, Marco Grioni2, Angel Rubio5, 6, 7, Majed Chergui1
1Laboratoire de Spectroscopie Ultrarapide, ISIC, EPFL, Lausanne, Switzerland 2Institute of Condensed Matter Physics, EPFL, Lausanne, Switzerland 3Center for Life Nano Science, Sapienza, IIT, Rome, Italy 4Department of Condensed Matter Physics, University of Geneva, Geneva, Switzerland 5Max Planck Institute for the Structure and Dynamics of Matter, Hamburg, Germany 6Fritz- Haber-Institut der Max-Planck-Gesellschaf, Berlin, Germany 7Departamento Fisica de Materiales, Universidad del Pais Vasco, San Sebastian, Spain
Bound electronic excitations play a major role in the electrodynamics of insulators and are usually described by the concept of Wannier and Frenkel excitons. The former represent hydrogenic electron-hole pairs delocalized over several unit cells of a crystal and they usually occur in uncorrelated materials with high dielectric constant. The latter correspond to a correlated electron-hole pair localized on a single lattice site and mostly prevail in molecular solids. Between these two extremes, an intermediate type of excitons exists, typically referred to as charge-transfer excitons. These species have originally been proposed for alkali halides [1] and subsequently reported in molecular crystals and strongly correlated materials [2-3]. A prototypical system in which charge- transfer excitons have been proposed theoretically [4] but never confirmed experimentally is the anatase polymorph of TiO2, which represents a superior material for a variety of challenging applications.
Here, by combining steady-state angle-resolved photoemission (ARPES), spectroscopic ellipsometry, and ultrafast 2D ultraviolet (UV) spectroscopy, along with many-body theoretical calculations, we demonstrate that the first direct charge excitations in anatase TiO2 are strongly bound charge-transfer excitons rising over the continuum of interband transitions. In particular, we find that the first exciton retains a two-dimensional nature and is characterized by a giant binding energy exceeding 200 meV. Finally, we interrogate the system out-of- equilibrium by means of ultrafast 2D UV spectroscopy in a broad spectral range covering the excitonic resonances, in order to demonstrate the universality of our findings in samples of different nature (single- crystals with various degrees of oxygen vacancies and nanoparticles) and to unravel the many-body dynamics resulting from bandgap excitation. Following this approach, we are able to disentangle the contributions related to the charge and lattice degrees of freedom in the ultrafast dynamics, studying the impact of uncorrelated electron-hole pairs and of coherent phonons on the excitonic resonances. To our knowledge, these results represent the first application of two-dimensional broadband UV spectroscopy to solid systems and demonstrate the potentiality of this technique in offering novel insights into the physics of strongly correlated quantum states of matter [5].
[1] S. Knox, Theory of Excitons, Academic New York (1965). [2] E. Collart et al., Physical Review Letters 96, 157004 (2006). [3] D. S. Ellis, Physical Review B 77, 060501 (2008). [4] L. Chiodo et al., Physical Review B 82, 045207 (2010). [5] E. Baldini et al., to be submitted.
50 3rd International Conference on Ultrafast Structural Dynamics
An Ultrafast Electron Microscope with Integrated Laser Optics
Banhart F1, Bücker K1, Picher M1, Derouet J-P2, Brunetti G2, LaGrange T3, Reed B W4, Masiel D J4
1Institut de Physique et Chimie des Matériaux, Université de Strasbourg, CNRS, 23 rue du Loess, 67034 Strasbourg, France 2JEOL Europe SAS, 1 Allée de Giverny, 78290 Croissy-sur-Seine, France 3Interdisciplinary Center of Electron Microscopy, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne 4Integrated Dynamic Electron Solutions, Pleasanton CA, USA
A new ultrafast transmission electron microscope (UTEM) has recently been installed at the Institut de Physique et Chimie de Matériaux in Strasbourg (France). The microscope is based on a Jeol JEM-2100, operated at 200 kV, with a thermal electron gun that can also be used as a photoelectron emitter. The photocathode is a Ta disc in a Wehnelt assembly with an adjustable bias. A dedicated electron lens is placed above the condenser to increase the number of electrons in the pulses. Two laser ports are integrated into the column. The microscope is also equipped with an electron energy-loss spectrometer. The optical platform is directly attached to the column so that the whole setup is supported by the antivibration damping of the microscope. This leads to an exceptional stability of both the microscope and the laser optics and avoids shifts of the laser beams relative to the microscope.
At present, the microscope is operated in the stroboscopic mode with a femtosecond fibre laser. The infrared laser beam (1030 nm, pulse length 370 fs) is split into two beams. One IR beam is directed onto the specimen whereas the other is frequency-quadruplicated to UV (257 nm) for generating photoelectrons on the cathode. The high repetition rate of the laser (10 kHz – 40 MHz) generates a continuous train of pulses. The IR and UV pulses are synchronized on the sample with sub-picosecond precision using an optical delay line. In the stroboscopic mode, experiments from the pico- to the nanosecond time scale are possible. The microscope will also be fitted with an additional nanosecond laser system for the operation in the single-shot mode.
The first results show comparable image resolution (0.23 nm) in the thermionic and the photoelectron mode. Without laser excitation of the specimen, lattice resolution of metals is obtained with photoelectrons. The energy resolution for EELS in the photoelectron mode is 0.7 eV which is clearly better than in the thermionic mode (1.6 eV). A detailed characterization of the electron pulses (duration and intensity distribution) as a function of the microscope parameters was carried out by using photon-induced near-field electron microscopy (PINEM). This technique makes use of the inelastic electron scattering in the photon near field around the object during laser excitation. With an order of magnitude of 100 electrons per pulse, a pulse length of approximately 3.5 ps was measured.
51 3rd International Conference on Ultrafast Structural Dynamics
Probing Host-Guest Interaction in Cryogenic Solids by IR Photon Echo
Wutharath Chin1, Raphaël Thon2, Didier Chamma3, Jean-Pierre Galaup4 and Claudine Crépin1
1Institut des Sciences Moléculaires d’Orsay, CNRS – Univ. Paris-Sud, F91405 Orsay Cedex, France 2CNRS DR4, F91191 Gif-sur-Yvette, France 3LAMPS, Univ. de Perpignan, F66860 Perpignan, France 4Laboratoire Aimé Cotton, CNRS - Univ. Paris-Sud, F91405 Orsay Cedex, France
Vibrational dynamics provides a fine tool for probing environment effects on the molecular processes at the electronic ground state. With IR photon echo experiments where three femtosecond IR pulses successively interact with the molecule we have access to dephasing and vibrational relaxation processes, which reflect the interactions within the molecule and with its environment [1, 2]. The CO stretching modes of W(CO)6 and Fe(CO)5 complexes trapped in cryogenic solids were used to study the influence of the matrix on the vibrational dynamics of the molecule. [3] These studies show that different processes occurring in the time scale of tens of picoseconds can be well separated and identified by the IR photon echo technique.
In the case of W(CO)6 isolated in a methane matrix, it turned out to be an original tool to follow the transition phase of solid methane (~ 20K). The presence of an additional short component in the relaxation times measured above phase transition evidenced different population relaxation processes in the two phases of methane. On the other hand, the temperature-dependence behavior of the dephasing time was showed to be due to coupling with a rotational mode of methane.
In the case of Fe(CO)5 trapped in nitrogen matrix (Figure 1), two CO modes were coherently excited. Their dynamics revealed the presence of energy transfer between the two modes. The photon echo signals seem to be more complex than in W(CO)6 and their analysis is still under progress. For both complexes, the photon echo signals also enabled a more precise assignment for vibrational bands in terms of trapping sites in the matrix.
Figure 1- Stimulated photon echo signal of Fe(CO)5/N2 à 20K at different Tw waiting times.
[1] M. Broquier, C. Crépin, H. Dubost, J.-P. Galaup, Chem. Phys. 341, 207 (2007). [2] R. Thon, W. Chin, J.-P. Galaup, A. Ouvrard, B. Bourguignon, C. Crépin, J. Phys. Chem. A 117, 8145 (2013). [3] R. Thon, PhD thesis 2013, Univ. Paris-Sud, France.
52 3rd International Conference on Ultrafast Structural Dynamics
Do Ultrafast Demagnetisation and LLG dynamics meet in the far IR?
Christian Dornes1, Jérôme Bonvin1, Steven Johnson1
1 Institute for Quantum Electronics, ETH Zürich, 8093 Zürich, Switzerland
Ultrafast time-resolved magnetisation measurements are powerful methods for understanding effects in magnetic solid state materials, one prominent example being ultrafast demagnetisation in the elemental ferromagnets iron and nickel [1]. One way to achieve femtosecond resolution in such a measurement is combining an optical pump with an ultrafast X-ray-probe – a free-electron laser [2] or at a synchrotron slicing source [3]. More commonly, all-optical tabletop methods are employed, based on the magneto-optical Kerr effect (MOKE). This poster presents a compact MOKE apparatus with a flexible and powerful pump setup (266nm THG / 400nm SHG / 800nm / 1.14-1.6µm OPA / 9-15µm DFG > 2µJ) driven by a kilohertz Ti:Sa laser system. The focus lies on the high-fluence long-wavelength mid-IR beam generated by difference frequency generation in gallium selenide which has been characterised by FTIR [4]. Finally, the simulation and development of iron thin-film structures which will be able to efficiently take advantage of the available pump fluence is presented. The motivation for this long wavelengths pump experiment is reaching a possible crossover regime between classical LLG magnetisation dynamics and ultrafast demagnetisation, in an attempt to elucidate the latter.
[1] Beaurepaire et al., Phys. Rev. Lett. 76, 4250–4253 (1996). [2] von Korff Schmising et al., Phys. Rev. Lett. 112, 217203 (2014). [3] Eschenlohr et al., Nature Materials 12, 332–336 (2013). [4] J. Bonvin, Master’s Thesis, ETH Zürich (2014).
53 3rd International Conference on Ultrafast Structural Dynamics
Interferometric Vibrational Circular Dichroism and Transient Linear Dichroism measurement
Biplab Dutta1& Jan Helbing1
1 Department of Chemistry, University of Zurich, Switzerland
Vibrational Circular Dichorism (VCD) Spectroscopy is an important tool to resolve the configuration and conformation of chiral molecules in solution. The goal of our work is to extend this technique to time resolved measurements [1] with femtosecond resolution of the laser. Despite the high temporal resolution and brilliance achieved in the laser based VCD measurements, it always suffers from different polarization artifacts and large achiral background contributions whereas the changes in chiral signal are 10-5 to 10-6 OD. We will discuss our interferometer based approach to detect and enhance VCD signal [2] as well as artifacts suppression. We use spectral interferometry to acquire the complete signal field (free induction decay) which gives us access to VCD (absorptive part) and Vibrational Optical Rotatory Dispersion (dispersive part) signal [3].
In a transient VCD and transient Vibrational Optical Rotatory Dispersion (VORD) measurement, transient Linear Birefringence (LB) and transient Linear Dichroism (LD) is the predominant artifact respectively. Thus, it is crucial to characterize these artifacts and suppress them during transient VCD measurements. We show that, using same spectral interferometric principle it is possible to extract and enhance transient LB and transient LD signals. These signals can be eliminated completely by using specific polarization scheme of Uv pump and Ir probe pulses. A proof of principle demonstration will be shown for a Rhenium carbonyl complex (Re (bipy)
CO)2 Cl). While we can completely eliminate transient LB and transient LD signal (decay on a 20 ps timescale), a small achiral signal (slowly decaying) still persists, which may originate from a pump-induced phase change between Ir probe and Ir local oscillator in the sample.
[1] M. Bonmarin et al., Optics Letters 33, 2086 (2008). [2] M. Bonmarin et al., J Chem Phys 131, 174507 (2009). [3] H. Rhee et al., J Opt Soc B 26, 1008 (2009).
54 3rd International Conference on Ultrafast Structural Dynamics
A Liquid Flatjet System for Soft X-Ray Spectroscopy in the liquid phase
M. Ekimova1, W. Quevedo 2, M. Faubel3, Ph. Wernet2 and E. T. J. Nibbering1
1 Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie Max-Born-Str. 2A, D-12489 Berlin, Germany 2 Institute for Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz- Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Str. 15, 12489 Berlin, Germany 3 Max-Planck-Institut für Dynamik und Selbstorganisation, Am Fassberg 17, 37077 Göttingen, Germany
We present a liquid flatjet system as a new approach to perform soft X-ray spectroscopy in solution phase. The flatjet set-up is based on the phenomenon of formation of liquid sheets upon collision of two identical laminar jets. [1-3] Colliding single water jets, coming out of the nozzles with 50 µm orifices, under an impact angle of 48o leads to double sheet formation, of which the first sheet is 6 mm long and 1 mm wide. We determine the flatjet thickness under vacuum conditions (<10-3 mbar), measuring the absorbance of liquid water at the oxygen K-edge and comparing them with the tabulated data from the Henke tables. [4] Moreover, the thickness is characterized at atmospheric pressure using the interferometric method and IR transmission. We show that the thickness varies between 1.4 – 3 µm depending on the position along the sheet surface. A catcher unit facilitating the recycling of the solutions allows for measurements on smaller sample volumes (~ 10 ml), making it a clear technological advance compared to previously reported single liquid jet systems [5], where the liquid solution is guided towards cooling traps in the vacuum chamber. We demonstrate the potential of the + flatjet set-up by presenting measurements on the nitrogen K-edge of aqueous NH4 recorded directly in transmission mode. Our results suggest the high potential of using liquid flatjets in steady-state and time- resolved soft X-ray spectroscopy.
[1] G. Taylor, Proceedings of the Royal Society of London Series A 259, 1 (1960). [2] J. W. M. Bush et al., Journal of Fluid Mechanics 511, 285 (2004). [3] N. Bremond et al., Journal of Fluid Mechanics 549, 273 (2006). [4] B. L. Henke et al., Atomic Data and Nuclear Data Tables 54, 181 (1993). [5] B. Winter et al., Journal of Chemical Review 106, 1176 (2006).
55 3rd International Conference on Ultrafast Structural Dynamics
Transient IR Pump-Probe Spectroscopy of Photoactive Molecules using Chirped Pulse Upconversion
Hidefumi Hata1,2, Ryosuke Nakamura1, Norio Hamada1, Tomosumi Kamimura2
1Science & Technology Entrepreneurship Laboratory, Osaka University, Japan 2Graduate School of Engineering, Osaka Institute of Technology, Japan
Transient one- and two-dimensional infrared (IR) spectroscopies have been proven to be a powerful tool to study photo-induced structural dynamics of photoactive molecular species [1]. Photodissociation and photoisomerization are essential steps in biochemical processes. Photoactive yellow protein (PYP) contains p- coumaric acid as a chromophore. Upon photoexcitation, PYP undergoes a photocycle with a number of intermediate states, which involve the trans-cis isomerization of the chromophore, rearrangement of the hydrogen-bonding network surrounding the chromophore, and large structural changes in the protein. In this study, to probe the vibrational structure and its anharmonicity during the photocycle of PYP, transient IR pump- probe spectroscopy was constructed using chirped pulse upconversion detection. At first, we have measured photodissociation dynamics of Mn2(CO)10 in cyclohexane to evaluate our transient IR pump-probe spectroscopic system. Photoexcitation of Mn2(CO)10 at 400 nm results in metal-metal bond dissociation, yielding two Mn(CO)5 products. Mn2(CO)10 has been used as a model system in the field of ultrafast infrared spectroscopy [2].
Transient IR pump-probe spectra with a time resolution of 0.2 ps (a) IR-Pump-Probe (ΔA) were measured after initiating photoreaction with a visible pump Vis-Pump / IR-Pump / IR-Probe ( ΔΔA) pulse. The IR probe pulse after the sample was upconverted into the visible using a chirped pulse at 800 nm with duration of 150 ps. A 0.2-mm thick AgGaGeS4 was used as a nonlinear crystal for upconversion in the frequency range of 1300 – 2500 cm-1 [3]. (b) Difference (ΔΔA - ΔA) The visible pulse was dispersed and detected by a silicon CCD camera. The solid line in Figure 1(a) shows the IR pump-probe spectrum (ΔA) of Mn2(CO)10 in cyclohexane. The broken line indicates the difference spectrum ( A) between the two A Absorbance Change ΔΔ Δ (c) Vis-Pump / IR-Probe spectra measured without and with the visible pump prior to the IR pump. A remarkable difference between ΔA and ΔΔA is recognized in a frequency range of 1960 - 2000 cm-1, which is consistent with the previous report [2]. It is expected that the 2080 2060 2040 2020 2000 1980 1960 Wavenumber (cm -1) vibrational signals originated from both Mn2(CO)10, and its photoproduct, Mn(CO)5, contribute to the ΔΔA spectrum. To extract a contribution from Mn(CO)5, we plot the difference Figure 1: (a) IR pump-probe spectrum (D spectrum between ΔA and ΔΔA in Figure 1(b) and also the (a) IR pump-probe spectrum visible pump / IR probe spectrum in Figure 1(c). The negative (nge induced by visible pump pulse peak at 1986 cm-1 in Figure 1(b) agree well with the transient (DDA, broken). Time delays are 40 ps betw absorption peak of Mn(CO)5 in Figure 1(c). Therefore, the een IR pump and probe, and 100 ps between negative peak is assigned to a bleach signal of the photoproduct, Vis pump and probe. (b) The difference spec while the positive peak at 1973 cm-1 can be attributed to the trum (DDA-DA). (c) Vis pump and IR probe transient absorption of the photoproduct. In addition to these spectrum. The pump- probe delay is 100 ps. results for Mn2(CO)10, transient IR pump-probe spectra of the intermediate states of PYP will be presented and discussed.
[1] P. Hamm et al., Annu. Rev. Phys. Chem. 59, 291 (2008). [2] C. R. Baiz et al., J. Phys. Chem. A 113, 8907 (2009).
56 3rd International Conference on Ultrafast Structural Dynamics
Thermal Denaturation of DNA studied by Ultrafast 2D-IR Spectroscopy Gordon Hithell, a Daniel J. Shaw, a Gregory M. Greetham, b Michael Towrie, b Anthony W. Parker, b Glenn Burley, c Matthew Baker, c Neil T. Hunt a
a) Department of Physics, University of Strathclyde, SUPA, Glasgow, UK b) Central Laser Facility, STFC Rutherford Appleton Laboratory, Research Complex at Harwell, Didcot, UK c) WestCHEM Department of Pure and Applied Chemistry, University of Strathclyde, Glasgow, UK
The thermal denaturation of two double-stranded DNA duplexes has been studied using ultrafast two- dimensional infrared spectroscopy (2D-IR) in the 1600cm-1-1700cm-1 region. These measurements were supported with data obtained using linear FT-IR and UV-visible absorption spectroscopy. The duplex DNA systems studied were a 10mer (sequence GGAAATTTGC plus complementary oligomer) and a 12mer (sequence GGCAAATTTCGC plus complementary oligomer). In the 2D-IR experiments, clear changes in the diagonal and off diagonal regions of the spectra were observed as the sample temperature increased (Fig 1). By obtaining 2D-IR spectra at a range of temperatures between 20 and 80 oC the changes in the vibrational modes and their couplings were correlated with temperature using Principal Component Analysis (PCA) and comparisons to FT-IR and UV-vis measurements demonstrate that they are attributable to duplex melting. Using this approach, the spectral contributions due to inter-base coupling resulting from Watson-Crick base pairing have been separated for both AT and GC components of the duplex for the first time. Duplex melting temperatures were obtained from PCA analysis of the FTIR and 2D-IR spectra and compared o favourably but were both found to be consistently ~15 C higher than the Tm found from UV-experiments. This suggests that the IR data reports on H-bond cleavage processes that show different temperature dependence to base stacking.
Figure 1 - FTIR (top) and corresponding 2D-IR spectra (bottom) of 10mer double-stranded DNA recorded at o o 20 C and 80 C in D2O
57 3rd International Conference on Ultrafast Structural Dynamics
Coherent Acoustic Perturbation of SHG in NiO
L. Huber1, A. Ferrer1,2, T. Kubacka1, T. Huber1, C. Dornes1, T. Sato3, K. Ogawa3, K. Tono3, T. Katayama3, Y. Inubushi3, M. Yabashi3, Y. Tanaka3, P. Beaud2, M. Fiebig4, V. Scagnoli1,5,6, U. Staub2, S. L. Johnson1
1Institute for Quantum Electronics, ETH Zürich, 8093 Zurich, Switzerland 2Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland 3RIKEN SPring-8 Center, Harima Institute, Sayo, Hyogo 679-5148, Japan 4Department of Materials, ETH Zürich, 8093 Zurich, Switzerland 5Lab. for Mesoscopic Systems, Department of Materials, ETH Zürich, 8093 Zurich, Switzerland 6Laboratory for Micro- and Nanotechnology, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
We investigate the structural and magnetic origins of the unusual ultrafast second-harmonic-generation (SHG) response of femtosecond-laser-excited nickel oxide (NiO) previously attributed to oscillatory reorientation dynamics of the magnetic structure induced by d-d excitations [1-3]. Using time-resolved x-ray diffraction from the (3/2 3/2 3/2) magnetic planes, we show that changes in the magnitude of the magnetic structure factor following ultrafast optical excitation are limited to � �� / �� = �. � % in the first 30 ps. Investigation of the spectral dependence of the ultrafast SHG response, together with the observation of characteristic echoes give evidence for an acoustic origin of the dynamics. We therefore propose an alternative mechanism for the SHG response based on perturbations of the nonlinear susceptibility via optically induced strain in a spatially confined medium. In this model, the two observed oscillation periods can be understood as the times required for an acoustic strain wave to traverse one coherence length of the SHG process in either the collinear or anti- collinear geometries.
[1] N. P. Duong, T. Satoh, and M. Fiebig, Phys. Rev. Lett. 93, 117402 (2004) [2] T. Satoh, N. P. Duong, and M. Fiebig, Phys. Rev. B 74, 012404 (2006) [3] A. Rubano, T. Satoh, A. Kimel, A. Kirilyuk, T. Rasing, and M. Fiebig, Phys. Rev. B 82, 174431 (2010)
58 3rd International Conference on Ultrafast Structural Dynamics
Ultrafast Structural Dynamics of a Prototypical Charge-Density-Wave-to- Metal Transition
T. Huber1, S.O. Mariager2, A. Ferrer 1,2, H. Schaefer 3, J.A. Johnson 2, S. Gruebel 2, A. Luebcke2,5, L. Huber 1, T. Kubacka 1, C. Dornes 1, C. Laulhe 6,7 , S. Ravy 6, G. Ingold 2, P. Beaud 2, J. Demsar 3,4, and S.L. Johnson 1
1Institute for Quantum Electronics, Physics Department, ETH Zurich, CH-8093, Switzerland 2Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland 3Physics Department, Universitaet Konstanz, D-78457, Germany 4Institut für Physik, Johannes Gutenberg-Universitaet Mainz, D-55128, Germany 5Laboratoire de Spectroscopie Ultrarapide, EPF Lausanne, CH-1015 Lausanne, Switzerland and 6Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, BP 48, FR-91192 Gif-sur-Yvette Cedex, France 7Universitê Paris-Sud, F-91405 Orsay Cedex, France
We use time-resolved x-ray diffraction to directly monitor the coherent structural dynamics during a photoinduced charge-density-wave (CDW)-to-metal transition in the prototypical CDW compound K0.3MoO3 [1]. For low excitation fluences, we follow the structural dynamics associated with the amplitude mode of the system. Above a critical excitation fluence, we observe the destruction of the periodic lattice distortion and its subsequent transient recovery on a sub-picosecond timescale. The rich structural dynamics can be explained with a simple model of the time-dependent interatomic potential during the nonthermal phase transition. To accurately describe the data, we have to introduce a time-dependent damping factor for the coherent atomic motion after photoexcitation. The results indicate that the dynamics of a structural symmetry-breaking transition are determined by a high-symmetry excited state potential energy surface distinct from that of the initial low- temperature state.
[1] T. Huber et al., Phys. Rev. Lett. 113, 026401 (2014).
59 3rd International Conference on Ultrafast Structural Dynamics
Time-resolved X-ray Diffraction Study of the Phonon Dispersion in InSb Nanowires A. Jurgilaitis1,2, H. Enquist2, B. P. Andreasson1, A. I. H. Persson1, B.M. Borg5, P. Caroff3, K.A. Dick1,4, M. Harb1,2, H. Linke1, R. Nüske1, L. E. Wernersson5 and J. Larsson1
1Department of Physics, Lund University, P.O. Box 118, SE-221 00 Lund, Sweden. 2MAX IV laboratory, Lund University, P.O. Box 118, Lund, Sweden. 3Department of Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University, Canberra, ACT 0200, Australia. 4Division of Polymer and Materials Chemistry, Department of Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden. 5Department of Electrical and Information Technology, Lund University, P.O. Box 118, SE-221 00 Lund, Sweden.
We present a recent experiment at the current time resolved X-ray diffraction (TXRD) beamline, D611 at MAX- lab. Here we show a nondestructive way of measuring the phonon dispersion relation in nanowires using TXRD. By measuring phonon dispersion relation one can extract sound velocity in the material. We find that speed of sound InSb nanowires is lower than in the bulk InSb material, and conclude that the major origin of the reduced sound speed is due to changes in elastic constants compared to the bulk material [1].
Fig. 1 (a) simulated dispersion relation for bulk like InSb nanowire. The slope of the red dashed curve is 3880 m/s, which is the speed of sound in bulk InSb, (b) Simulated dispersion relation for nanowire with elastic constants giving the best fit to the experimental sound speed of 2880 m/s. Green curve represents experimental data.
[1] A. Jurgilaitis, et al., Nano Lett., 14, 2 (2014).
60 3rd International Conference on Ultrafast Structural Dynamics
Quantifying Equilibrium Binding Affinity using 2D IR Spectroscopy and Non-native Amino Acids
Klemens L. Koziol1, Philip J.M. Johnson1 and Peter Hamm1
1Departement of Chemistry, University of Zurich, 8057 Zurich, Switzerland; [email protected], [email protected]
Azidohomoalanine (Aha) is a very versatile label that can be incorporated into proteins. It absorbs in the non- congested part of protein IR spectra and the center frequency is sensitive to the environment [1]. The combination of ultrasensitive 2D IR spectroscopy and Aha labelling of proteins gives rise to new possibilities of investigating biological structures and their dynamics with very low sample demands. With voice coil flexure guided delay stages and automated exchange of buffer and protein samples it is possible to measure Aha labelled proteins down to a concentration of 0.5 mM with good signal to noise ratio. This is demonstrated with equilibrium binding studies of Aha-labelled peptide with its associated wild-type protein binding domain PDZ2. Upon binding, the Aha band redshifts by ~ 15 cm-1a and can clearly be resolved from the unbound fraction. For a fixed ligand concentration of 0.5 mM, analysis of fractional binding recovered from 2D IR spectra collected at various protein concentrations allows for the direct observation of the binding affinity.
Fig 1: 2D IR Spectra of Aha-labelled peptide at 0.5 mM concentration and PDZ2 at 0, 0.5 and 3mM concentrations (from left to right).
[1] R. Bloem, K. Koziol, S. A. Waldauer, B. Buchli, R. Walser, B. Samatanga, I. Jelesarov, P. Hamm, J. Phys. Chem. B, 116 (2012)
61 3rd International Conference on Ultrafast Structural Dynamics
Surface-Enhanced, Multi-Dimensional Attenuated Total Reflectance Spectroscopy
Jan Philip Kraack, Davide Lotti, Peter Hamm
Department of Chemistry, University of Zürich, Winterthurerstrasse 190, CH-8057
Vibrational dynamics of molecules at solid-liquid interfaces attract special attention due to their involvement in heterogeneous catalysis.[1] This includes simple samples like small molecules (e.g., carbon monoxide) and large organic molecules (e.g., self-assembled monolayers) on metallic or semiconducting substrates. It is therefore highly desirable to develop spectroscopic techniques for obtaining surface-sensitive molecular information.
Here, we present a new method which delivers coherent, time-resolved two-dimensional (2D) infrared (IR) spectra from adsorbates on metallic thin films.[2, 3] The technique is based on the acquisition of reflection absorption spectra under total reflection conditions at interfaces of different refractive index materials (solid-gas or solid-liquid interfaces) (Fig. 1). We demonstrate the details of femtosecond 2D ATR IR spectroscopy along with its benefits and challenges. Concerning applications, 2D ATR IR spectroscopy is used to resolve ultrafast interfacial dynamics of molecules on metallic thin films. We characterize surface-enhancement effects due to the presence of the metal. The experiments focus on the impact of different chemical environments on the samples vibrational dynamics. The technique is capable for a surface-sensitive characterization of vibrational lifetimes, dephasing, spectral diffusion and sample inhomogeneity. Finally, we discuss the future scope of 2D ATR IR spectroscopy regarding its applicability on more complex samples such as heterogeneous photocatalysts or transient intermediates in spectro-electrochemistry.
Fig. 1. 2D ATR IR spectroscopy in pump probe geometry. Two collinear, coherent, femtosecond pump (pu/pu’) and a probe pulse (pr) excite and interrogate the dynamics of organic monolayers (MLs) within the penetration depth in the medium of lower refractive index (n2 < n1). MLs are equipped with a local vibrational probe, i.e. the asymmetric stretch vibration of the azide group (N3). Polarization of the pulses is indicated for the probe pulse.
[1] H. Arnolds and M. Bonn, Surf. Sci. Rep. 65, 45 (2010). [2] J.P. Kraack, D. Lotti, and P. Hamm, J. Phys. Chem. Lett. 18, 2325 (2014). [3] J.P. Kraack, D. Lotti, and P. Hamm, J. Chem. Phys. 145, 212413 (2015).
62 3rd International Conference on Ultrafast Structural Dynamics
63 3rd International Conference on Ultrafast Structural Dynamics
Structural Characterization of the Quintet State in Fe NHC-complex by Means of Time-Resolved X-ray Scattering
Leshchev D.1, Harlang T.2, Kjær K.2, Liu Y.3, Fredin L.4, Wulff M.1, Persson P.4, Sundström V.2, Wärnmark K.3
1European Synchrotron Radiation Facility, Grenoble, France 2 Department of Chemical Physics, Lund University, Sweden 3Centre for Analysis and Synthesis, Department of Chemistry, Lund University, Sweden 4Theoretical Chemistry Division, Chemistry Department, Lund University, Sweden
For a long time earth abundant and environmentally friendly iron-based complexes were considered unusable for light harvesting due to their extremely short metal-to-ligand-charge-transfer (MLCT) state lifetimes. A recent investigation by Liu et. al. [1] has shown that the application of N-heterocyclic carbene (NHC) chemistry [2] can prolong the lifetimes of the charge separated states by two orders of magnitude. This is achieved by increasing of the ligand field strength, which leads to destabilization of metal centred (MC) states; this in turn blocks MLCT deactivation via transitions to those MC states. This work aims to elucidate the main deactivation pathway of the tert-butyl substituted Fe NHC-complex reported in [1] by means of time resolved X-ray 2+ scattering. This complex takes a transition place between the methylated Fe NHC-complex and [Fe(terpy)2] (terpy = 2,2’:6’,2’-terpyridine) [1], by having moderate ligand field and, therefore, just slightly perturbed MC states.
Structural rearrangements taking place after laser excitation (λ = 485 nm) in acetonitrile solution were measured with the standard setup for time resolved X-ray scattering at ID09b (ESRF, Grenoble, France). This work covers two scattering experiments. First, high resolution data were collected using high-energy X-rays of 25.2 keV (BW = 1.6 %), which allowed the structure to be refined due to extended Q. Secondly, we used the time-slicing technique [3] with higher flux 18 keV (BW = 1.9 %) X-rays in order to catch the solute dynamics and the hydrodynamics of the bulk solvent.
Figure 1. a) Experimental data and fits for the MC states with different multiplicity; b) Ground state structure of the molecule obtained from 5 DFT calculations (no hydrogen atoms are shown); c) comparison of the ground state and T2 structures which were used to calculate the differential scattering (hydrogen atoms and tBu groups are not shown).
5 One of the results is a clear assignment of the long lived excited state as the quintet T2 MC state (Figure 1). The high-energy data were used to optimise the structural parameters allowing to benchmark the theoretical predictions, which are in a good agreement with the experiment. The time-slicing experiment helped to determine the lifetime of the excited state, 210±15 ps, which agrees with the results from optical spectroscopy.
[1] Y. Liu et. al., Chem. Commun., (2013) 49, 6412-6414. [2] L. Mercsa and M. Albrecht, Chem. Soc. Rev., (2010) 39, 1903. [3] J. H. Lee et. al., J. Am. Chem. Soc., (2013) 135 (8), 3255–3261.
64 3rd International Conference on Ultrafast Structural Dynamics
Ultrafast, Infrared-Spectroelectrochemistry in Attenuated Total Reflectance Geometry
Davide Lotti1, Jan Philip Kraack1, Peter Hamm1
1Department of Chemistry, University of Zürich, Winterthurerstrasse 190, CH-8057
Metal-liquid interfaces are of central importance in various research fields, including heterogeneous catalysis and electrochemistry.[1] To shed light on the microscopic effect of electric fields at the metal -liquid interface, we make use of the surface sensitivity of 2D Attenuated Total Reflectance Infrared Spectroscopy (2D-ATR- IR).[2,3] To this end, we introduce a multilayered working electrode composed of a nanometer thick stack of indium tin oxide and platinum in a homemade electrochemical ATR cell. The used single-reflection ATR cell combines acceptable electrical and spectroscopic properties such as conductivity, electrochemical stability and reflectivity of the intense IR pulses. In order to demonstrate the applicability of the method, Carbon monoxide (CO) was adsorbed from aqueous solution onto platinum-coated ITO electrodes. Here, CO acts as a reporter group of the interfacial electric field in the double layer. The ultrafast dynamics of the adsorbed CO molecules in dependence of the electrode potential is then assessed by vibrational Stark-shift spectroscopy (Fig.1). The contribution will focus on three points of investigation: (i) Disentangling of the ultrafast infrared response from sample and conductive layer (referred to as background subtraction in Fig.1), (ii) occurrence of lineshape distortions in dependence of sample preparation details, and (iii) currently furthergoing investigations regarding the 2D-ATR-IR spectroelectrochemistry of self-assembled monolayers with different local vibrational probes.[4,5]
A B
-7.000 -7.000 2150 -5.000 2150 -5.000 -3.000 -3.000 -1.000 -1.000 2100 2100 -1 -1 1.000 1.000 3.000 3.000 2050 5.000 2050 5.000 7.000 7.000
2000 2000 Wavenumbers/ cm Wavenumbers/ cm
1950 1950 2 4 6 8 2 4 6 8 t/ps t/ ps
Fig.1 Background subtracted IR pump/ IR probe spectra of Pt-CO(ads.) in contact with NaClO4 0.1 M (aq.) at the applied potentials of -1.0 V (Ag/AgCl) (A) and +1.0 V (Ag/AgCl) (B). Fig.1 Background subtracted IR pump/ IR probe spectra of Pt-CO(ads.) in contact with NaClO4 0.1 M (aq.) at the applied potentials of -1.0 V (Ag/AgCl) (A) and +1.0 V (Ag/AgCl) (B).
[1] J.M.Andanson et al., Chem. Soc. Rev., 39, 4571 (2010). [2] J.P. Kraack et al., J.Phys. Chem. Lett., 5, 2325 (2014). [3] J.P. Kraack et al., J.Chem. Phys., 142, 212413 (2015). [4] P. Hildebrandt et al.,Int. J. Mol. Sci., 13, 7466 (2012). [5] T. Bürgi, Phys.Chem.Chem.Phys., 3, 2124 (2001).
65 3rd International Conference on Ultrafast Structural Dynamics
Single-shot femtosecond x-ray streaking method for ultrafast dynamics M.Makita a, M.Buzzi a, I.Vartiainen a, I.Mohacsi a, A.Diaz a, P.Juranic a,M.Marsha, A.Meentsb, C.Milne a, A.Mozzanica a, N.Opara a, C.Padeste,a V.Panneelsa, H.Redlinb, M. Sikorski c, S. Song c, K.Tiedtkeb, P.Willmott a, L.Veraa, F.Nolting a, J.Lueningd and C.David a
a Paul Scherrer Institut, Villigen PSI, CH5232, Switzerland b Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, 22603 Hamburg, Germany c LCLS, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, CA94025, USA d Sorbonne Universites, UPMC Univ Paris 06, LCPMR, 75005 Paris, France
The advent of ultrashort and intense x-ray pulses from free electron lasers has paved the way to new possibilities for sub-picosecond time-resolved studies. Typically these studies are carried out in a pump-probe method where a single probe beam is directed to the sample at a fixed delay time after the pump beam. This requires multiple pump-probe cycles at different delays in order to reconstruct the full dynamics. To circumvent this problem we have developed and demonstrated a single-pump- multiple-probing method – a unique grating-based setup which allows one to record the full dynamics of transient phenomena, with femtosecond time resolution, from a single x-ray pulse [1]. We present two independent implementation of this scheme in the XUV energy range (performed at FLASH, DESY) and in the multi-keV range (recently performed at LCLS, SLAC). The accessible time window is 1.57ps for 60eV at FLASH, and 350fs for 5050eV at LCLS. The measurements of ultrafast demagnetization dynamics of ferromagnetic layers (in the XUV range), and of time resolved Bragg reflectivity of inorganic and macromolecular crystals (in the multi-keV range) will be shown. We will also highlight some of the key features of the setup, including the robustness of the diffraction gratings with respect to beam damage and misalignment, and the absence of timing jitter between each probe beams due to their fixed geometrical arrangement. References [1] C. David, P. Karvinen, M. Sikorski, I. Vartiainen, S. Song, C.J. Milne, A. Mozzanica, Y. Kayser, A. Diaz, I. Mohacsi, G. Carini, S. Herrmann, E. Färm, M. Ritala, D.M. Fritz, A. Robert, Following the dynamics of matter with femtosecond precision using the X-ray streaking method, Scientific Reports 5 (2015) p. 7644
Schematic drawing of the LCLS experiment setup. The multiple probe beams created by the upstream splitter gratings are re-directed with the recombiner gratings such that they follow the direct (transmitted) beam after controlled delay times, all from a single pulse. Only 3 different delay channels are shown for simplicity, the experimental implementation featured more than 10 channels.
66 3rd International Conference on Ultrafast Structural Dynamics
2+ Ultrafast electron dynamics of [Fe(bpy)3] (aq) studied with the use of time- resolved photoelectron spectroscopy
Alexandre Moguilevski, Nicholas Engel, Daniel Toksdorf, Martin Wilke, Azhr Raheem, Mario Borgwardt, Jan Metje, Igor Yu. Kiyan, Emad F. Aziz
Institute of Methods for Material Development at Helmholtz-Zentrum Berlin, Albert-Einstein-Str. 15, 12489, Berlin, Germany and Joint Laboratory for Ultrafast Dynamics in Solutions and at Interfaces at Freie Universität Berlin, Department of Physics, Arnimallee 14, 14195, Berlin, Germany
2+ Iron(II)-trisbypiridine ([Fe(bpy)3] ) is a well-known transition metal complex with a promising perspective to be used in photovoltaics in the future. It is also an attractive quantum system for studying the spin crossover (SCO) phenomenon which plays an important role in biology [1]. The electronic structure and dynamics of this complex in aqueous solution has already attracted much attention in fields of transient fluorescence and absorption spectroscopies [2, 3]. In our work, we extend these studies by using transient XUV photoemission spectroscopy. This method allows us to directly attribute the spectral features to specific electronic states of the complex, which is not possible with the use of other spectroscopic methods.
The liquid-microjet technique is used which allows maintaining high vacuum conditions that are required for the photoelectron measurements. In the experiment, we initiate metal-to-ligand charge transfer (MLCT) and ligand- centered electron transitions with the use of ultrashort pulses in the UV/VIS range from an optical parametric amplifier, and probe the electron population dynamics with XUV pulses produced by high-order harmonic generation [4]. We directly monitor how the electron population undergoes a transition to the singlet MLCT state with subsequent intersystem crossing to the triplet MLCT state. These processes are found to occur on a sub-100 fs time scale, which represents a characteristic lifetime of these states. Somewhat slower relaxation dynamics are observed for exited states populated in the ligand-centered transition with lifetimes of ca. 200 fs. These results provide insight on the ultrafast electron dynamics associated with charge transfer processes in transition metal complexes.
[1] W. Gawelda et al., J. Am. Chem. Soc. 129, 8199-8206 (2007). [2] A. Cannizzo et al., Coord. Chem. Rev. 254, 2677-2686 (2010). [3] H.T. Lemke et al., J. Phys. Chem. A 117, 735-740 (2013). [4] J. Metje et. al., Optics Express 22, 10747-10760 (2014).
67 3rd International Conference on Ultrafast Structural Dynamics
Vibrational Energy Flow of Chromophore in Protein Probed by IR Pump and Visible Probe Spectroscopy
Ryosuke Nakamura1, Norio Hamada1
1Science & Technology Entrepreneurship Laboratory, Osaka University, Japan
Vibrational energy flow in proteins is a fundamental process that is essential to understanding how proteins function in photosensing, enzyme kinetics, and ligand binding and dissociation. In this study, vibrational energy flow in the electronic ground state of the chromophore in a protein is studied by ultrafast infrared (IR) pump and visible probe spectroscopy. Vibrational modes of the chromophore and the surrounding protein are excited with a femtosecond IR-pump pulse, and the subsequent vibrational dynamics in the chromophore are selectively probed with a visible probe pulse through changes in the absorption spectrum of the chromophore. The pump energy dependence of the vibrational energy flow reveals the anharmonic coupling among various vibrational modes.
Here, we have studied vibrational energy flow in photoactive yellow protein (PYP) that contains p-coumaric acid as a chromophore. PYP Wavelength (nm) has a characteristic photoreaction known as a photocycle with a number 500 450 of intermediate states which involve the trans-cis isomerization of the Abs chromophore, rearrangement of the hydrogen-bonding network 0.1 ps surrounding the chromophore, and large structural changes in the 2mOD protein. Figure 1 shows the transient absorption (TA) spectra at delay times from 0.1 to 10 ps after photoexcitation of vibrational states with 0.2 ps an IR pulse centered at 1420 cm-1. The stationary absorption spectrum is also shown in the top panel. A negative signal around 440 nm is 0.3 ps assigned to the ground state bleach of the S0 → S1 transition, whereas the positive signal located at a lower energy than the stationary 1.0 ps absorption spectrum is assigned to TA from the excited vibrational levels in the S0 to the S1 state. The peak energy of TA shifts with time to 3.0 ps
a higher energy as indicated by arrows. And also, the signal intensity of AbsorbanceChange TA decreases with time. By analyzing a data set of these temporal 10 ps(× 2) changes in the TA spectra, we thus obtained the vibrational energy flow with four characteristic time constants. The vibrational excitation with an IR pulse at 1340, 1420, 1500, or 1670 cm-1 results in ultrafast intramolecular vibrational redistribution (IVR) with a time constant of 1.9 2 2.1 2.2 2.3 2.4 [ 104] 0.2 ps. The vibrational modes excited through the IVR process relax to × -1 the initial ground state with a time constant of 5-7 ps in parallel with Wavenumber (cm ) vibrational cooling with a time constant of 14 ps. In addition, upon Figure 1: TA spectra measured with an excitation with an IR pulse at 1670 cm-1, we observed the energy flow IR pulse centered at 1420 cm-1. from the protein backbone to the chromophore that occurs with a time constant of 4.3 ps. These characteristic behaviors of PYP will be compared with other proteins including heme proteins.
68 3rd International Conference on Ultrafast Structural Dynamics
Ultrafast Electron Spectrometry of Liquid Samples
J. Ojeda1, C. Arrell1, J. Grilj1, L. Mewes1, J. Löffler1, F. van Mourik1 and M. Chergui1
1Ecole Polytechnique Fédérale de Lausanne, Laboratoire de Spectroscopie Ultrarapide, Lausanne, Switzerland.
We present a UV-VIS pump tunable EUV probe photoelectron spectroscopy setup for ultrafast photoelectron spectroscopy in liquid samples [1]. The ̴ 27-100 eV EUV is produced by high harmonic generation with photon fluxes ranging from approximately 1011 photons/second at ̴ 36 eV to 108 photons/second at ̴ 100 eV. Choosing from a set of gratings with different geometries in a time-preserving EUV monochromator, the time and energy resolution of the system can be adjusted for a particular experiment. For example, energy resolutions in the order of 0.2 eV for photon energies around 40 eV can be achieved and vibrational progressions of the water monomer have been identified for the first time using high harmonic generation and photoelectron spectroscopy. 2+ As another example, the different spin states of Fe(II) in aqueous Fe[(bpy)3] and FeCl2 are reflected in their photoelectron spectra as a shift in binding energy of the Fe(II) HOMO peak (see Figure 1). Several ultrafast dynamical processes can be studied with our setup, e.g., the light-induced spin cross-over in metal complexes [2].
2+ Figure 1. Aqueous Fe[(bpy)3] and FeCl2 photoelectron spectra. A clear shift in the Fe(II) HOMO peak energy is visible.
[1] J. Ojeda et al., Structural Dynamics, in submission. [2] A. Cannizzo et al., Coordination Chemistry Reviews 254, 2677 (2010).
69 3rd International Conference on Ultrafast Structural Dynamics
Charge Transfer Processes in a Molecular Pentad
M. Orazietti1, M. Kuss-Petermann2, O. S. Wenger2 and P. Hamm1
1Department of Chemistry, University of Zürich, Zürich, Switzerland 2Department of Chemistry, University of Basel, Basel, Switzerland
A better understanding of single and multiple electron transfer (ET) is needed in order to design systems able to mimic natural photosynthesis. Thus, triad systems capable of forming photoinduced charge-separated state with single ET have been extensively studied.
We focused our research on a different system, a new linear pentad (fig.1), formed by two triarylamines, acting as electron donors (D), two ruthenium-trisbipyridine as photosensitizers (PS) and anthraquinone as acceptor (AQ). Due to its design and to the ability of AQ of accommodating two electrons, it has the unique capability of performing a double intramolecular ET, thus forming a long-living charge-separated state where two negative charges are located in the final electron acceptor.
Using VIS-pump IR-probe ultrafast spectroscopy, we are following the formation of the charge-separated state and the charge-recombination processes, discriminating between the different intermediates. Preliminary data show the presence of a band in the transient spectrum corresponding to AQ•- (1483 cm-1). Furthermore, if we compare the spectrum to the one of the reference triad (D-PS-AQ), where the second ET cannot occur, one band (1365 cm-1), corresponding to the AQ=, can be clearly distinguished, confirming the double ET (fig.2). The kinetics of the AQ•- show that both pentad and triad form a photoinduced charge-separated state that lives for hundreds of nanoseconds and that when an acid is present in solution, it stabilizes the charge-separated state, protonating the reduced AQ, leading to shorter kinetics (fig.3).
A double-pulse experiment will be performed to selectively excite both PSs and follow both ETs.
Fig.1: Pentad 6 Triad 1446 cm-1 5 Pentad 1.5 1483 cm-1 4 1680 cm-1 3 1.0 2 0.5 1
0 0.0 -1 Absorbance (mOD) Absorbance (mOD) Absorbance -2 -0.5 -3 -4 -1.0 1200 1300 1400 1500 1600 1700 0.01 0.1 1 10 100 1000 10000 Wavenumbers (cm-1) Time (ns)
Fig.2 – Transient IR spectra of triad and Fig.3 – Kinetics for different AQ species pentad, 0.5 ns after the pump pulse (got rid of white line)
70 3rd International Conference on Ultrafast Structural Dynamics
Early stages of the pH-jump-triggered coil-to-globule transition of poly(methacrylic acid) in water
Pastorczak M1, Skibinski P1,2, Nejbauer M1 and Radzewicz Cz1
1Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Pasteura 5, 02- 093 Warsaw, Poland 2Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
Poly(methacrylic acid), pMAA belongs to the group of pH-responsive polymers whose solubility, diffusivity and chain conformation may be manipulated by changing the pH of the solution [1]. Such change is often abrupt even after a tiny modification of external pH. Therefore, these materials are applied as smart materials e.g. in controlled drug delivery, industrial coatings and membrane science [1,2]. The polymer (pMAA) changes its conformation in water from expanded ionized chain into compact globule below pH 6. [3,4] The peculiar potentiometric titration curve of pMAA with a pronounced plateau suggests nontrivial kinetics of conformational transition and led to speculations on presence of intermediate conformers.[4] The coil-to-globule transition in pMAA has been studied with various indirect methods. In the field of time-resolved spectroscopy Ruiz-Perez et al. studied sub-microsecond kinetics of that transition with use fluorescence lifetime measurements of fluorescent probe copolimerized into pMAA chain.[3]
In presented work we study sub-nanosecond stages of the pH-jumped triggered conformational transition of pMAA in water with use of time-resolved vibrational spectroscopy methods. As a trigger of the pH-jump we use the photoacid pyranine (8-hydroxy-1,3,6-pyrenetrisulfonic acid, HPTS) whose acidity constant increases significantly (pKa deacreases from 6 to 0) upon electronic excitation to S1 state.[5,6] In the aqeous solution of polyacid (pMAA) it leads to dissociation of pyranine into its photobase and a proton and intermolecular transfer of the latter to carboxylate group of pMAA. We use femtosecond visible pump-infrared probe spectroscopy to study kinetics of pyranine dissociation and of the intermolecular proton transfer in the aqeous polymer solution. We perform pH-jump time-resolved experiments for various initial neutralization degrees of pMAA (various initial pH) to study the proton transfer kinetics at different stages of polymer coil-to-globule transition.
It is well evidenced that pH- and temperature-induced polymer coil-to-globule transitions are related to changes of equilibrium between hydrophilic polymer-water and hydrophobic polymer-polymer interactions. They are henceforth manifested in shift in positions of vibrational bands related to polymer C-H bending and stretching modes.[7,8] As Raman cross-sections of these modes are significantly larger then infrared ones, we used newly built in our laboratory femtosecond Raman stimulated spectroscopy setup to follow kinetics of pH-induced folding of pMAA chain in water.
This research has been financed by Polish National Science Centre (NCN) in the frame of „Fuga” grant No. DEC-2013/08/S/ST4/00556. M.P. would like to thank Prof. Piotr Ulanski for fruitful discussion.
[1] Dai, S. et al., Soft Matter 4, 435, (2008). [2] Hoffman, A. S. Advanced Drug Delivery Reviews 65, 10, (2013). [3] Ruiz-Pérez, L. et al. Macromolecules 41, 2203, (2008). [4] Finch, C. A. Synthetic water-soluble polymers in solution E. A. Bekturov and Z. Kh. Bakauova, Huthig & Wepf Verlag, Basel: Heidelberg: New York, 1986. [5] Rini, M. et al.,. Science 301, 349, (2003). [6] Siwick, B. J. et al. JACS 129, 13412, (2007). [7] Maeda, Y. Langmuir 17, 1737,2001). [8] Maeda, Y. et al., Langmuir 23, 11259, (2007)
71 3rd International Conference on Ultrafast Structural Dynamics
Itinerant and localized magnetization dynamics in antiferromagnetic Ho
L. Rettig,1 C. Dornes,2 N. Thielemann-Kühn,3 N. Pontius,3 H. Zabel,4 T. A. Lograsso,5 D. L. Schlagel,5 M. Chollet,6 A. Robert,6 M. Sikorsky,6 S. Song,6 G. James,6 C. Schüssler- Langeheine,3 S. L. Johnson,2 and U. Staub1
1Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland 2Institute for Quantum Electronics, Physics Department, ETH Zürich, 8093 Zürich, Switzerland 3Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Strasse 15, 12489 Berlin, Germany 4Institute for Experimental Physics, Ruhr-Universität Bochum, 44780 Bochum, Germany 5Ames Laboratory - ISU, Ames, Iowa 50011, USA 6The Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
Using time-resolved resonant magnetic hard x-ray diffraction, we investigate the demagnetization dynamics in antiferromagnetically ordered metallic Ho after femtosecond optical excitation via the suppression of the magnetic (2 1 3-τ) satellite peak at the Ho L3 absorption edge. Tuning the x-ray energy to the electric dipole (E1) or quadrupole (E2) transition allows us to selectively study the dynamics of the itinerant 5d and localized 4f electronic subsystems independently. We find demagnetization timescales very similar to ferromagnetic 4f systems, suggesting angular momentum transfer as dominating process also in the demagnetization of 4f antiferromagnets. The simultaneous demagnetization of both subsystems demonstrates strong intra-atomic 4f-5d exchange coupling. In addition, an ultrafast lattice contraction due to the release of magnetostriction leads to a transient shift of the magnetic satellite peak.
72 3rd International Conference on Ultrafast Structural Dynamics
Femtosecond X-ray Absorption Study of Electron Localization in Photoexcited TiO2 Nanoparticles
F. G. Santomauro1, A. Lübcke1, J. Rittmann1, E. Baldini1, A. Ferrer2,4, M. Silatani1, P. Zimmermann1, S. Grübel2,4, J. A. Johnson4, S. O. Mariager3, P. Beaud3,4, D. Grolimund4, C. Borca4, G. Ingold3,4, S.L. Johnson2 and M. Chergui1
1Laboratoire de Spectroscopie Ultrarapide, ISIC-FSB, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland 2Institut für Quantenelektronik, ETH Zürich, Wolfgang-Pauli-Str. 16, CH-8093 Zürich, Switzerland 3SwissFEL, Paul Scherrer Institut, CH-5232 Villigen, Switzerland 4Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen, Switzerland
The anatase form of Titanium dioxide (TiO2) is among the most used in solar energy conversion processes, either into electrical or chemical energy. These are entirely based on the generation of charge carriers (electrons and holes) by absorption of light, their transport and eventually, their localization due to the electron-phonon coupling and/or defects.1 In order to investigate these processes, element and geometry sensitive tools are required at high temporal resolution and at the working conditions of solar devices (i.e. room temperature). To this aim, we implemented picosecond (ps) and femtosecond (fs) X-ray absorption spectroscopy at the K-edge of Ti, on colloidal solutions of anatase and amorphous TiO2 nanoparticles (typically ~20 nm). Fig. 1b shows the transient spectra (excited minus unexcited sample absorption) at 100 ps time delay (green) and 1 ps (time delay) upon band gap excitation of anatase TiO2 NPs at 355 nm. The 100 ps transient was already discussed in ref. 2, which showed that the photogenerated electrons form Ti3+ centres with nearly a full electron charge localizing on them. Because anatase TiO2 NPs are known to have an ordered core with a defect-rich surface shell containing a high degree of Ti under- coordination and since the spectral changes pointed to the reduced centres being in an amorphous-like environment, it was also concluded that these traps are mostly localized at pentacoordinated trapping site located in the shell region. The transient recorded at 1 ps time delay using the slicing scheme at the Swiss Light Source (SLS) basically shows the same features as in the 100 ps transient, suggesting that the traps observed at <1 ps are the same as those at 100 ps.2 The temporal profile of the signal at maximum (4.982 keV), which maps the evolution of the population of reduced Ti sites, shows a prompt rise within 200 fs, reaching a level that remains constant FIG. 1. a) Normalized static Ti K-edge up to the limit of our scan (50 ps). Considering the diffusion XANES spectrum of colloidal constant of the electron in the conduction band of the material, nanoparticles of anatase TiO2 at room this implies that the electron is localized with about 5 Å of where temperature. b) Transient (difference) Ti it was created, i.e. there is no electron migration prior to K-edge XANES spectra upon 355 nm trapping. These results and those of ref. 2, also suggest that upon excitation of colloidal nanoparticles of injection from an adsorbed dye as in dye-sensitized solar cells, anatase TiO2, recorded at time delays of the electron will end up close to the cation on the surface 100 ps (green squares, left vertical axis)2 and 1 ps (this work, blue dots, right [1] C. Di Valentin et al., J Phys Chem Lett 2, 2223 (2011). vertical axis). (this was moved) [2] M. H. Rittmann-Frank et al., Angew Chem Int Edit 53, 5858 (2014).
73 3rd International Conference on Ultrafast Structural Dynamics
2D Raman–THz Spectroscopy of Aqueous Salt Solutions
Andrey Shalit, Saima Ahmed, Janne Savolainen and Peter Hamm
Institut für Chemie , Universitat Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland, [email protected]
Short-lived local structural discontinuities in liquid water are believed to be responsible for non-monotonous behavior of its various thermodynamic and dynamic properties [1]. The novel time-resolved THz-Raman multidimensional spectroscopy recently developed in our group [2] allows direct observation of the dynamics of the collective intermolecular modes in the aqueous solutions, resolving the heterogeneous distribution of hydrogen bond network in liquid water. Unlike common two-dimensional spectroscopies in IR regime [3] this method interrogates the hydrogen-bond stretching and bending modes of liquid water in the low frequency range directly and not through the changes of the hydroxyl stretch absorption frequency. Here we apply 2D THz-Raman spectroscopy to investigate the effect of ions on the structural and dynamical properties of water. We demonstrate that direct comparison of the 2D THz-Raman response of pure water (fig. 1a) to that of the 3M NaCl aqueous solution (fig. 1b) reveals an extended relaxation component along the diagonal (dashed line) of µ µ the Raman-THz-THz pulseSignal sequenceV (fig 1c). Single exponentialSignal V data fit (doted curve in fig. 3c) shows somewhat slower relaxation (85fs vs. 60fs) in aqueous salt solution. Albeit small, such a difference might be a signature of the enhanced inhomogeneity.
-50 0 50 100 0 50 100 1 0.6 a) 0.6 b) c) Water 3M NaCl 0.4 0.4
0.2 0.2
0 0 (THz, ps) (THz, (THz, ps) (THz, 2 2 t t -0.2 -0.2 Normalized Intensity Intensity Normalized -0.4 -0.4
-0.6 Water -0.6 3M NaCl
-0.5 0 0.5 -0.5 0 0.5 0 100 200 300 400 t (Raman, ps) t (Raman, ps) t =t (fs) 1 1 1 2
Fig. 1 a) The experimental 2D Raman-THz signal of water and b) the experimental 2D Raman-THz signal of 3M NaCl. Dotted line indicates the diagonal (t1=t2). c) Cuts along the diagonal (t1=t2), blue for a water and red for a salty solution. Single exponential fit are shown and discussed in the text.
References: [1] H. E. Stanley, P. Kumar, G. Franzese, L. Xu, Z. Yan, M. G. Mazza, S. V. Buldyrev, S. H. Chen, and F. Mallamace, Eur. Phys. J.: Spec. Top. 161, 1 (2008) [2] J.Savolainen, S. Ahmed, and P. Hamm, Proc. Natl. Acad. Sci. U.S.A. 110 20402 (2013) [3] P. Hamm and M. T. Zanni, Concepts and Methods of 2D Infrared Spectroscopy (Cambridge University Press, Cambridge, 2011).
74 3rd International Conference on Ultrafast Structural Dynamics
Applications and some Photophysical Properties of Anthraquinone Derivatives
Ionut Radu Tigoianu1,2, Anton Airinei1, Mirela Zaltariov1, Maria Cazacu1 and Volker Ribitsch3
1Laboratoire De Spectroscopie Ultrarapide, École Polytechnique Fédérale De Lausanne, ISIC, FSB, CH-1015 Lausanne, Switzerland 2”Petru Poni” Institute of Macromolecular Chemistry, Aleea Grigore Ghica Voda, 41A, Iasi- 700487, Romania 3University of Graz, Heinrichstrasse 28A, 8010, Graz, Austria
In the last time a great attention has been paid to fluorescent sensors and many new systems were developed. The development of sensors in solution for metal ions always has been of particular importance for cations with chemical, biological and environmental interest [1]. Absorption and emission are analytical methods that can be used to probe molecular structure and dynamics in a wide variety of ways. Anthraquinone derivatives are some of the most widely used polycyclic compounds in nature and technology. Dyes based on anthraquinones have been among the major compounds used in dye technologies or in dyeing of textiles. These compounds have proven to be useful as functional elements of organic photoelectric structures, optical transducers and oscillators and thin-film structures. An important feature of anthraquinone derivatives is their strong fluorescence that is very useful in order to construct highly sensitive fluorescent chemical sensors for metal ion detection. In this presentation, absorption and emission spectroscopy was used to investigate and characterize the photophysical properties of some anthraquinone derivatives by using polar and nonpolar solvents. This study shown that are predominant non-radiative processes compared with radiative processes. These can be explaining by involving the processes, such: internal conversion, intersystem crossing. As an application, a new sensor for detecting Fe2+ from water was obtained by study the mechanism of the fluorescence quenching.
[1] J. R. Lakowicz, “Principles of Fluorescence Spectroscopy”, (3rd Ed., Springer, New York, 2006).
75 3rd International Conference on Ultrafast Structural Dynamics
The Solvated Carbon-Fluorine Bond in Water Investigated by 2D IR spectroscopy
Halina Tran1, Peter Hamm1
1 University of Zürich
Organic fluorinated molecules are very rare in nature, however 20-25% of current drugs contain at least one fluorine atom [1]. The interactions of the C-F bond with surrounding water molecules play an important role in the functionality of fluorinated drugs.
We investigate this intermolecular coupling utilizing two-dimensional infrared spectroscopy on the femtosecond time scale. The two-dimensional line shape of the C-F band gives information about the dynamics of the surrounding, especially through the decay of the central line slope, which is caused by spectral diffusion of its inhomogeneous frequency distribution [Fig].
Fig.: Sequence of 2D-IR spectra of FACN in D2O for increasing population times. The thick black lines depict the central line slopes.
Fluoroacetonitrile (FACN) was chosen as a model system, because it has a simple infrared absorption spectrum and it exists as a single conformer - however it is a relatively weak absorber (ε ~ 60 M-1 cm-1). We used NMR studies to determine the maximum sample concentration at which the system can still be considered to be dilute (200 mM FACN in D2O). We observe that the tilt of the 2D-IR line-shape as a function of population time decays with a lifetime of τ = 1.7 ps.
In analogy to previous studies [2,3] our results can be used to further test and develop molecular dynamics force fields to better describe the solvation properties of fluorinated molecules. A comparison of the experimental data with semiempirical mixed quantum mechanical/molecular mechanics simulations and force field simulations with multipolar interactions reveals a CF–HOH hydrogen bond (population of 25%) which is found from the radial distribution function g(r) from both simulations [4].
[1] S. Purser, P. R. Moore, S. Swallow, V. Gouverneur, Chemical Society Reviews 37, 320–330 (2008). [2] M. Koziński, S. Garrett-Roe, P. Hamm, Chemical Physics 34, 5–10 (2007). [3] M. W. Lee, J. K. Carr, M. Göllner, P. Hamm, M. Meuwly, The Journal of Chemical Physics 139, 054506 (2013) [4] P.-A. Cazade, H. Tran, T. Bereau, A. K. Das, F. Kläsi, P. Hamm, M. Meuwly, The Journal of Chemical Physics 142, 212415 (2015).
76 3rd International Conference on Ultrafast Structural Dynamics
Probing a Conformational Change of a Photoswitchable Allosteric Protein with Ultrafast IR Spectroscopy
Steven A. Waldauer1, Brigitte Stucki-Buchli1, Peter Hamm1
1 Department of Chemistry, University of Zurich, Winterthurerstr. 190, CH-8057 Zürich, Switzerland
Allostery has long been an intense research topic, and much about the underlying mechanism allowing a signal to propagate across a protein still must be investigated. What properties and characteristics internal and external of the protein are crucial to the signal, and how do they shape the energy landscape? How does internal and external friction modulate the dynamics and kinetics of these transitions, and at what length and timescales does one dominate over the other? To investigate these questions experimentally, we have covalently linked an azobenzene photoswitch across the binding groove of an allosteric protein domain such that a conformational transition can be initiated by a laser pulse (Fig. 1) [1]. This transition mimics the conformational change experienced by the wild type domain upon ligand binding (Fig. 2). We have studied this light induced conformational change by ultrafast IR spectroscopy.
We have found that the binding groove opens on a timescale of 100 ns in a non-exponential manner. Even after the binding groove has equilibrated, the protein conformation still continues to change elsewhere. MD simulations have shown evidence that the solvent plays an integral part in the kinetics. To explore this further, we have investigated the role of the solvent and external friction by observing the transition kinetics as a function of temperature and solvent viscosity [2]. Currently, we are incorporating site-specific IR labels to learn more about the response of the protein to the perturbation of the binding groove.
Figure 1. NMR structures with the photoswitch in cis (left, PDB 2M0Z) and in trans (right, PDB 2M10) 2. Overlay of the unmodified apo (blue, PDB 3LNX) and holo structures (red with green ligand, PDB 3LNY)
[1] B. Buchli et al., Proc Natl Acad Sci USA 110, 11725-30 (2013). [2] S. Waldauer et al., J Chem Phys, 141, 22D514 (2014).
77 3rd International Conference on Ultrafast Structural Dynamics
Overview
78 3rd International Conference on Ultrafast Structural Dynamics
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