Lancaster University, UK

International Workshop on “Molecular-Scale Electronics: Concepts, Contacts, and Stability”

15th – 19th May 2017, Lancaster University, UK

Organised within the framework of the EC FP7 Marie Curie ITN "Molecular-Scale Electronics: MOLESCO" http://www.physics.lancs.ac.uk/gollum/index.php/community/molesco-lancaster

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Workshop organizing committee

Prof. Colin Lambert [email protected]

Dr. Hatef Sadeghi [email protected]

Dr. Steven Bailey [email protected]

Dr. Iain Grace [email protected]

Dr. Sara Sangtarash [email protected]

Ms. Deborah Szpunar [email protected]

IMPORTANT INFORMATION

Accommodation check in: CETAD building, location number 13 on campus map (grid E4) Car parking permits: available at check in.

Conference venue, registration, reception, posters, breakfasts, lunches and dinners (except Thursday): County South, location number 18 on campus map (grid D4) Conference dinner, 19.00 Thursday May 18th: Lancaster House hotel, location number 59b on campus map (grid F11) Other useful information including bus and train times, places to eat and visit: download the university app onto your mobile phone: http://m.lancaster.ac.uk/

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Workshop program Monday May 15th 18.30-19.00 Arrival and registration 19.00 Reception and buffet dinner Tuesday May16th 09.00-09.15 Welcome 09.15-10.00 Colin Nuckolls, Silane and Germane molecular electronics Columbia University 10.00-10.45 Harry Anderson, Porphyrin-based molecular wires Oxford University 10.45-11.15 Coffee 11.15-11.45 Hatef Sadeghi, Quantum interference in molecular junctions with Lancaster University graphene electrodes 11.45-12.00 Simon Svatek, Quantum thermopower in thin layers of MoS2 IMDEA Nanoscience 12.00-13.00 Lunch 13.00-14.00 Tour of Lancaster IsoLab 14.00-14.45 Bernd Gotsmann, Heat transport in thermoelectric devices IBM, Zurich 14-45-15.30 Andrew Briggs, Gated single-molecule devices Oxford University 15.30-16.30 Tea 16.30-16.45 Luke O’Driscoll, University A molecular rectifier incorporating tetrathiafulvalene of Southern Denmark 16.45-17.00 Markus Gantenbein, Tuning of quantum interference through asymmetric Duham University single-molecule junctions 17.00-18.00 MOLESCO management meeting 18.00-19.00 Poster session 19.00 Dinner Wednesday May 17th 09.00-09.45 Elke Scheer Atomic and molecular scale functional devices University of Konstanz 09.45-10.30 Richard Nichols STM studies of electrochemical single molecule Liverpool University transistors and molecular wires 10.30-11.00 Coffee 11.00-11.45 András Halbritter, Budapest Temporal correlations and structural memory effects in University of Technology break junction measurements 11.45-12.00 Laerte Patera, Crystallization of a two-dimensional hydrogen-bonded University of Regensburg molecular assembly: evolution of the local structure resolved by atomic force microscopy 12.00-14.00 Lunch 14.00-14.45 Sense van der Molen, Probing electron transmission and reflection in quasi- Leiden University molecular structures 14-45-15.30 Kristian Thygesen, Energy level alignment at the nanoscale: from molecular TU Denmark, Lyngby junctions to 2D materials 15.30-15.45 Ganna Gryn’ova, A long story short: deciphering orbital and length effects EPFL, Lausanne in oligothiophene single molecule junctions 15.45-16.30 Tea 16.30-16.45 Xunshan Liu, Probing Lewis acid-base interactions in single-molecule University of Bern junctions 16.45-17.00 Anna Zieleniewska, Control over electronic communication in meso-meso FAU Erlangen-Nürnberg two-atom-bridged diporphyrins

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

17.00-17.15 Valentina Sacchetti, Wires based on Amidinium-Carboxylate salt-bridge IMDEA Nanoscience interaction: single molecule-junction approach 19.00 Dinner Networking and posters Thursday May 18th 09.00- 09.45 Gemma Solomon, Developing chemical intuition for molecular charge Copenhagen University transport 09.45-10.30 Tim Albrecht, Challenges in probing single-molecule charge transport Imperial College London in complex molecular structures 10.30 Depart for Lathom Visit to NSG Pilkington , Lathom, Ormskirk, L40 5UF 11.45 Arrive Lathom 11.45-13.00 Presentations in the Lecture theatre at Lathom 13.00-14.00 Lunch 14.00 Coach to St Helens 14.30 Group 1 arrives at location A Tour A begins 14.40 Group 2 arrives at location B 14.45 Tour B begins 15.15 Group 1 joins bus and travels to location B 15.25 Group 1 arrives at location B 15.30 Second tour B begins 15.30 Group 2 joins bus and travels to location A 15.40 Group2 arrives at location A 15.45 Second tour A begins 16.15 Group 2 joins bus to join group 1 location B 16.30 Groups 1 and 2 depart for Lancaster 19.00 Conference dinner, Lancaster House Hotel Friday May 19th 09.00-09.45 Simon Higgins, Quantum interference effects from charge transfer Liverpool University complexes in molecular junctions 09.45-10.30 Jan van Ruitenbeek, High current-bias effects in atomic and molecular Leiden University junctions 10.30-11.00 Coffee 11.00-11.30 Víctor Manuel García Suárez, Thermoelectricity in vertical graphene-C60-graphene Oviedo University architectures 11.30-12.00 Benjamin Robinson, Novel scanning probe methods for 2D materials and Lancaster University organic assemblies 12.00-13.00 Lunch Departure Afternoon Optional Excursion: Lake District

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Silane and Germane molecular electronics

Colin Nuckolls

Columbia University, USA [email protected]

This presentation will provide an account of our recent efforts to uncover the fundamental charge transport properties of Si-Si and Ge-Ge single bonds and introduce useful functions into group 14 molecular wires. We utilize the tools of chemical synthesis and a scanning tunneling microscopy- based break-junction technique to study the mechanism of charge transport in these molecular systems. We evaluated the fundamental ability of silicon, germanium, and carbon molecular wires to transport charge by comparing conductances within families of well-defined structures, the members of which differ only in the number of Si (or Ge or C) atoms in the wire. We also studied their breakdown in electric fields. These fundamental studies have guided the design of new functional systems based on the Si- and Ge-based wires. For example, we exploited the principle of strain- induced Lewis acidity from reaction chemistry to design a single molecule switch that can be controllably switched between two conductive states by varying the distance between the tip and substrate electrodes. Furthermore, we demonstrate the first example of a stereoelectronic conductance switch, and we demonstrate that the switching relies crucially on the electronic delocalization in Si-Si and Ge-Ge wire backbones. These studies illustrate the untapped potential in using Si- and Ge-based wires to design and control charge transport at the nanoscale and to allow quantum mechanics to be used as a tool to design ultra-miniaturized switches.

References: 1. Su, T. A.; Li, H.; Klausen, R. S.; Kim, N. T.; Neupane, M.; Leighton, J. L.; Steigerwald, M. L.; Venkataraman, L.; Nuckolls, C. Acc. Chem. Res. 2017. 2. Li, H.; Garner, M. H.; Shangguan, Z.; Zheng, Q.; Su, T. A.; Neupane, M.; Li, P.; Velian, A.; Steigerwald, M. L.; Xiao, S.; Nuckolls, C.; Solomon, G. C.; Venkataraman, L. Chem. Sci. 2016. 3. Su, T. A.; Neupane, M.; Steigerwald, M. L.; Venkataraman, L.; Nuckolls, C. Nat. Rev. Mater. 2016, 1, 16002. 4. Su, T. A.; Li, H.; Klausen, R. S.; Widawsky, J. R.; Batra, A.; Steigerwald, M. L.; Venkataraman, L.; Nuckolls, C. J. Am. Chem. Soc. 2016, 138, 7791. 5. Su, T. A.; Neupane, M.; Steigerwald, M. L.; Venkataraman, L.; Nuckolls, C. Nat. Rev. Mater. 2016, 1, 16002. 6. Su, T. A.; Li, H.; Steigerwald, M. L.; Venkataraman, L.; Nuckolls, C. Nat Chem 2015, 7, 215.

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Porphyrin-based molecular wires

Harry L. Anderson

University of Oxford, Department of Chemistry, UK [email protected]

Porphyrins are large redox-active pi-systems which makes them interesting components for the construction of molecular wires. This talk will summarize recent work on transport and charge delocalization through porphyrin monomers and large porphyrin arrays, such as the butadiyne-linked 12-porphyrin nanoring shown below.

References: 1. “Constructive quantum interference in a bis-copper six-porphyrin nanoring”, S. Richert, J. Cremers, I. Kuprov, M. D. Peeks, H. L. Anderson, C. R. Timmel, Nat. Commun. 2017, 8, 14842. 2. “Aromatic and antiaromatic ring currents in a molecular nanoring”, M. D. Peeks, T. D. W. Claridge, H. L. Anderson, Nature 2017, 541, 200–203. 3. “Hopping versus tunneling mechanism for long-range electron transfer in porphyrin oligomer bridged donor–acceptor systems”, M. Gilbert Gatty, A. Kahnt, L. J. Esdaile, M. Hutin, H. L. Anderson, B. Albinsson, J. Phys. Chem. B 2015, 119, 7598–7611. 4. “Comparison of the conductance of three types of porphyrin-based molecular wires: β,meso,β-fused tapes, meso-butadiyne-linked and twisted meso-meso linked oligomers”, G. Sedghi, L. J. Esdaile, H. L. Anderson, S. Martin, D. Bethell, S. J. Higgins, R. J. Nichols, Adv. Mater., 2012, 24, 653–657. 5. “Long-range electron tunnelling in oligo-porphyrin molecular wires”, G. Sedghi, V. M. García-Suárez, L. J. Esdaile, H. L. Anderson, C. J. Lambert, S. Martin, D. Bethell, S. J. Higgins, M. Elliott, N. Bennett, J. E. Macdonald, R. J. Nichols, Nat. Nanotech. 2011, 6, 517–523.

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Quantum interference in molecular junctions with graphene electrodes

Hatef Sadeghi

Lancaster University, UK [email protected]

Provided the electrical properties of electroburnt graphene junctions can be understood and controlled, they have the potential to underpin the development of a wide range of future sub-10-nm electrical devices. In this talk, I will discuss signatures of quantum interference (QI) in the electroburnt graphene junctions. Room temperature QI in the electroburnt graphene junctions leads to a counterintuitive increase in electrical conductance just before the gap forms. This arises from a cross- over from electrodes with multiple-path connectivity to single-path connectivity just before breaking. Furthermore, sharp antiresonance features with a Fano line shape could be observed in graphene nanojunctions formed by electroburning due to localized states inside the constriction, which couple to the delocalized states. Electroburnt graphene electrodes can also be used to probe transport through molecules, although optimization of this technology requires control of sample-to-sample fluctuations and junction stability. The former can be reduced by magnetic field averaging and the latter can be addressed by exploring anchoring modalities to graphene electrodes.

References: 1. Sadeghi, H.; Mol, J. a.; Lau, C. S.; Briggs, G. A. D.; Warner, J.; Lambert, C. J. Proc. Natl. Acad. Sci. U. S. A. 2015, 112, 2658−2663. 2. Gehring, P.; Sadeghi, H.; Sangtarash, S.; Lau, C. S.; Liu, J.; Ardavan, A.; Warner, J. H.; Lambert, C. J.; Briggs, G. A. D.; Mol, J. A. Nano Lett. 2016, 16, 4210−4216. 3. Lau, C. S.; Sadeghi, H.; Rogers, G.; Sangtarash, S.; Dallas, P.; Porfyrakis, K.; Warner, J.; Lambert, C. J.; Briggs, G. A. D.; Mol, J. A. Nano Lett. 2016, 16, 170−176. 4. Sadeghi, H.; Sangtarash, S.; Lambert, C.J. Nano Lett. 2016, 15(11), 7467-7472. 5. Sadeghi, H.; Algaragholy, L.; Pope, T.; Bailey, S.; Visontai, D.; Manrique, D.; Ferrer, J.; Garcia-Suarez, V.; Sangtarash, S.; Lambert, C. J. .J. Phys. Chem. B, 2014, 118, 6908−6914. 6. Sadeghi, H.; Sangtarash, S.; Lambert, C.J. 2D Materials. 2017, 4, 1, 015012. 7. Gehring, P.; Sowa, J. K.; Cremers, J.; Wu, Q.; Sadeghi, H,; Sheng, Y.; Warner, J. H.; Lambert, C. J.; Briggs, G. A. D.; Mol, J. A. ACS Nano. 2017, DOI: 10.1021/acsnano.7b00570.

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Quantum thermopower in thin layers of MoS2

Simon A. Svatek1,2, Hatef Sadeghi3, Sara Sangtarash3, Laura Rincón-García2, Riccardo Frisenda1, Patricia Gant1, David Pérez de Lara1, Gabino Rubio-Bollinger2, Andres Castellanos-Gomez1,4, Colin J Lambert3, Nicolás Agraït1,2

1 Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia), Faraday 9, Ciudad Universitaria de Cantoblanco, 28049, Madrid, Spain 2 Departamento de Física de la Materia Condensada and Condensed Matter Physics Center (IFIMAC), Facultad de Ciencias, C/ Francisco Tomás y Valiente 7, Universidad Autónoma de Madrid, 28049, Madrid, Spain 3 Department of Physics, Lancaster University, Lancaster LA1 4YW, UK 4 Instituto de Ciencia de Materiales de Madrid (ICMM), CSIC, c. Sor Juan Inés de la Cruz 3, E-28049 Madrid, Spain [email protected]

The thermoelectric effect and applications have been investigated intensively. Of great interest are thermoelectric properties linked to quantum phenomena that enhance efficiencies in heat conversion and heat flux. So far, quantum thermoelectricity has only been observed in bulk samples containing nanoscale constituents (1), single-molecule junctions (2) and atomic chains (3). Here, we report the observation of quantum thermoelectricity in the cross-plane direction of a 2D material. The effect is observed in the thin layers of MoS2 which generate a thickness-dependent thermopower ranging from -22 ± 1 for a monolayer to -330 ± 70 µV/K at 6 layers. This layer number dependence stems from an increase in the differential transmission through the MoS2 with the thickness and indicates the quantum nature of the effect. We furthermore find an exceptionally high value in the heat flux for a bilayer of 440 W/cm². Our results provide an example for quantum thermoelectricity in a 2D material, demonstrate that the thermopower may be modified by appropriately selecting the sample thickness, and show that a high heat flux can be achieved in ultrathin semiconducting layers, which is of relevance to nano-thermoelectrical systems, electronics and hot-spot cooling.

References: 1. Dresselhaus, M. S., Chen, G., Tang, M. Y., Yang, R. G., Lee, H., Wang, D. Z., Ren, Z. F., Fleurial, J.-P., and Gogna, P., 2007, “New Directions for Low-Dimensional Thermoelectric Materials,” Adv. Mater., 19(8), pp. 1043–1053. 2. Reddy, P., Jang, S.-Y. S.-Y., Segalman, R. A., and Majumdar, A., 2007, “Thermoelectricity in molecular junctions.,” Science, 315(5818), pp. 1568–1571. 3. Evangeli, C., Matt, M., Rincón-García, L., Pauly, F., Nielaba, P., Rubio-Bollinger, G., Cuevas, J. C., and Agraït, N., 2015, “Quantum Thermopower of Metallic Atomic-Size Contacts at Room Temperature,” Nano Lett., 15(2), pp. 1006–1011.

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Heat transport in thermoelectric devices

Bernd Gotsmann

IBM Research, Zurich, Switzerland bgo@zurich.ibm.com

This is a tutorial-style, relaxed, and opinionated discussion on issues related to thermal transport in thermoelectric devices and materials. The goal is to review some technological constraints, give a layman's overview of some phonon-physics relevant to the problem, and address some arguments used in funding decisions. The first part of the talk discusses "an inconvenient truth about thermoelectrics" [1] in view of some of the application areas of thermoelectric energy conversion, including automotive, internet of things and waste-heat recovery. We will use back-of-the-envelope calculations to get a feeling for orders of magnitude of some relevant key metrics. The second part is a micro-review of some popular approaches to increase thermoelectric efficiency by phonon engineering.

80 Heat engines: Carnot limit best practice (Vining 2009) state of the art (Xie and Gruen 2010) 60

Solar Coal Nuclear 40

Nuclear Solar Solar

Efficiency (%) Solar 20 Solar Cement Geothermal TECs available today Geothermal

0 0 200 400 600 800 1000 1200 Heat source temperature (oC)

References: 1. C. B. Vining, An inconvenient truth about thermoelectrics, Nature Materials 8, 83 - 85 (2009)

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Gated single-molecule devices

Andrew Briggs

Department of Materials, University of Oxford, Oxford OX1 3PH, UK [email protected]

How does electricity flow through a single molecule? How does the arrival of an electron make a molecule move? How stiff is one electron in a nanotube? Advances in nanotechnology make it possible to answer such questions.1,2 The results have implications for quantum foundations and for practical technologies. In the past molecular electronics has promised much, but what it can deliver has been limited by instability and irreproducibility. The ability to make nanogaps in graphene3 has opened up new possibilities for making and studying transistors consisting of a gated single molecule.4 Significant effects can occur when the charge couples to vibrational modes,5 and when there is quantum interference.6,7

a b c HOMO

LUMO

a zinc porfphyrin molecule; b single-molecule transistor; c local density of states.

References: 1. Redox-dependent Franck-Condon blockade and avalanche transport in a graphene-fullerene nanoelectromechanical oscillator. Nano Lett. 16, 170-176 (2015). C.S. Lau, H. Sadeghi, G. Rogers, S. Sangtarash, P. Dallas, K. Porfyrakis, J.H. Warner, C.J. Lambert, G.A.D. Briggs and J.A. Mol. 2. Resonant optomechanics with a vibrating carbon nanotube and a radio-frequency cavity. Phys. Rev. Lett. 117, 170801 (2016). N. Ares, T. Pei, A. Mavalankar, M. Mergenthaler, J.H. Warner, G.A.D. Briggs and E.A. Laird. Selected as a PRL Editors’ Suggestion. 3. Conductance enhancement in pico-scale electro-burnt graphene nano junctions. Proc. Natl. Acad. Sci. USA 112, 2658–2663 (2015). H. Sadeghi, J.A. Mol, C.S. Lau, G.A.D. Briggs and C.J. Lambert. 4. Graphene-porphyrin single-molecule transistors. Nanoscale 7, 13181-13185 (2015). J.A. Mol, C.S. Lau, W.J.M. Lewis, H. Sadeghi, C. Roche, A. Cnossen, J.H. Warner, C.J. Lambert, H.L. Anderson and G.A.D. Briggs. 5. Vibrational effects in charge transport through a molecular double quantum dot. Phys. Rev. B 95, 085423 (2017). J.K. Sowa, J.A. Mol, G.A.D. Briggs and E.M. Gauger. 6. Quantum interference in graphene nanoconstrictions. Nano Lett. 16, 4210-4216 (2016). P. Gehring, H. Sadeghi, S. Sangtarash, C.S. Lau, J. Liu, A. Ardavan, J.H. Warner, C.J. Lambert, G.A.D. Briggs and J.A. Mol. 7. Distinguishing lead and molecule states in graphene-based single-electron transistors. ACS Nano DOI: 10.1021/acsnano.7b00570 (2017, in press). P. Gehring, J.K. Sowa, J. Cremers, Q. Wu, H. Sadeghi, Y. Sheng, J.H. Warner, C.J. Lambert, G.A.D. Briggs and J.A. Mol.

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

A molecular rectifier incorporating

tetrathiafulvalene

Luke O’Driscoll

University of Southern Denmark [email protected]

Molecular rectifiers, which conduct only when a voltage of a given bias is applied, were first proposed by Aviram and Ratner in 1974 [1], at the very beginning of the field of molecular electronics. Suitable molecules are composed of a donor (D) and an acceptor (A) group linked in a non-conjugated fashion by a bridging unit (σ), in so-called D-σ-A systems. Many examples of this type of molecule have since been shown to exhibit rectification [2]. In this work we set out to extend an existing study of D-σ-A systems where 'A' is perylene bisimide (PBI) [3,4] by replacing previously investigated 'D' units with the strong electron donor monopyrrolotetrathiafulvalene (MPTTF).

References: 1. Aviram, A.; Ratner, M. A. Chem. Phys. Lett. 1974, 29, 277-283. 2. Metzger, R. M. Chem. Rev. 2015, 115, 5056-5115. 3. Kota, R.; Samudrala, R.; Mattern, D. L. J. Org. Chem. 2012, 77, 9641-9651. 4. Johnson, M. S.; Kota, R.; Mattern, D. L.; Metzger, R. M. Langmuir 2016, 32, 6851-6859.

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Tuning of quantum interference through

asymmetric single-molecule junctions

Yang Yang†, Markus Gantenbein§, Afaf Alqorashi‡, Sara Sangtarash‡, Duan Hu†, Hatef Sadeghi‡, Junying Wei†, Guogang Yang†, Rui Zhang†, Junyang Liu†, Jia Shi†, Wenjing Hong†, Colin Lambert‡, Martin R. Bryce§

† State Key Laboratory of Physical Chemistry of Solid Surfaces/Collaborative Innovation Center of Chemistry for Energy Materials (iChEM)/Pen-Tung Sah Institute of Micro-Nano Science and Technology, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China. § Department of Chemistry, Durham University, Durham DH1 3LE, United Kingdom. ‡Department of Physics, Lancaster University, Lancaster LA1 4YB, United Kingdom. [email protected]

We have characterized the single-molecule conductances of molecules with five-membered ring core units. Eight compounds of the type X-Y-X, where X is a pyridyl anchor and Y represents the central ring (thiophene, N-ethylpyrrole, furan or 1,1-dimethylcyclopentadiene) with symmetric or asymmetric functionalization at the core, were synthesized, then wired between two dynamic electrodes to form single-molecule junctions during the mechanically controllable break junction (MCBJ) operation. The single-molecule conductances of the asymmetric series were consistently lower than that of the symmetric isomers, implying the existence of quantum interference. More importantly, from a comparison of the symmetric and asymmetric cores it was found that for charge transport through single-molecule junction there is an interaction between molecular symmetry and quantum interference.

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Atomic and molecular scale functional devices

E. Scheer1, C. Schirm 1, M. Matt1, F. Pauly1, J.-C. Cuevas2, P. Nielaba1, F. Strigl1, C. Espy1, M. Bückle1, M. Keller1, D. Weber1, T. Pietsch1, R. Hayakawa1,3, A. Karimi1, J. Wolf 4, T. Huhn4, M. S. Zöllner5, C. Herrmann5

1 Department of Physics, University of Konstanz, D-78457 Konstanz, Germany 2 Departamento de Física Teórica de la Materia Condensada and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain 3 International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan 4 Department of Chemistry, University of Konstanz, D-78457 Konstanz, Germany 5 Institute for Inorganic and Applied Chemistry, University of Hamburg, Martin-Luther-King-Platz 6, 20146 Hamburg, Germany [email protected]

The possibility to fabricate electronic devices with functional building blocks of atomic size is a major driving force of nanotechnology [1]. Key elements in microelectronics are reliable switches and memories as well as devices showing spin-dependent transport phenomena. Switches are usually realized by transistors and these components have been miniaturized all the way down close to the atomic scale. However, at such scales three terminals, as required for transistors, are technically challenging to implement. Here I will first present an experiment in which a metallic atomic-size contact has been operated as a reliable and fatigue-resistant two-terminal switch. Current pulses are used to toggle the conductance between two well-defined values in the range of a few conductance quanta [2]. I will then address the question of the emergence of magnetism in atomic contacts and wires and how it can be revealed by magnetoconductance measurements [3]. Finally, will discuss recent observations of magnetic-field tunable transport in organic radical molecules [4].

References: 1. R. Waser, Nanoelectronics and Information Technology, (Wiley-VCH, Weinheim, 2nd edition 2012) 2. C. Schirm et al., Nature Nano. 8, 645 (2013) 3. F. Strigl et al., Nature Comm. 6, 7172 (2015), F. Strigl et al., Phys. Rev. B 94, 144431 (2016) 4. R. Hayakawa et al., Nano Letters 16, 4960 (2016)

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

STM studies of electrochemical single molecule

transistors and molecular Wires

Richard J. Nichols; Osorio, H. M.; Cea, P.; Gluyas, J. B. G.; Hartl, F.; Higgins, S. J.; Leary, E.; Low, P. J.; Martín, S.; Tory, J.; Ulstrup, J.; Vezzoli, A.; Milan, D. C.; Zeng, Q.; Catarelli, S. R.; Schwarzacher, W.; Mao, B.-W.; Yan, J.-W.; Jeppesen, J. O.; Lycoops, J; Kay, N. J.; Haiss, W. and Sedghi, G.

The University of Liverpool, UK [email protected]

We have exploited STM based methods for making single molecule measurements under electrochemical potential control in ionic liquid electrolytes.1-4 The electrochemical potential can be used to control the redox state of single molecule bridges and switch the electrical conductance from low to higher values. This has been referred to as the “single molecule electrochemical transistor” configuration, with the electrochemical potential “gating” the molecular conductance in the STM nano-gap configuration. Recent results from our group on gating the conductance of single molecules in ionic liquid electrolytes will be discussed including studies of viologens, redox active metal terpyridine molecular wires and pyrrolo-tetrathiafulvalene (pTTF) molecular bridges. Mechanisms of charge transport in the STM nano-gap setup are discussed alongside the advantages of undertaking such single molecule electrochemical measurements in ionic liquids.

References: 1. Osorio, H. M.; Catarelli, S.; Cea, P.; Gluyas, J. B. G.; Hartl, F.; Higgins, S. J.; Leary, E.; Low, P. J.; Martín, S.; Nichols, R. J.; Tory, J.; Ulstrup, J.; Vezzoli, A.; Milan, D. C.; Zeng, Q. Electrochemical Single-Molecule Transistors with Optimized Gate Coupling. Journal of the American Chemical Society 2015, 137, 14319- 14328. 2. Catarelli, S. R.; Higgins, S. J.; Schwarzacher, W.; Mao, B.-W.; Yan, J.-W.; Nichols, R. J. Ionic Liquid Based Approach for Single-Molecule Electronics with Cobalt Contacts. Langmuir 2014, 30, 14329-14336. 3. Kay, N. J.; Higgins, S. J.; Jeppesen, J. O.; Leary, E.; Lycoops, J.; Ulstrup, J.; Nichols, R. J. Single-Molecule Electrochemical Gating in Ionic Liquids. Journal of the American Chemical Society 2012, 134, 16817- 16826. 4. Kay, N. J.; Nichols, R. J.; Higgins, S. J.; Haiss, W.; Sedghi, G.; Schwarzacher, W.; Mao, B.-W. Ionic Liquids As a Medium for STM-Based Single Molecule Conductance Determination: An Exploration Employing Alkanedithiols. Journal of Physical Chemistry C 2011, 115, 21402-21408.

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Temporal correlations and structural memory

effects in break junction measurements

András Magyarkuti1, Kasper Primdal Lauritzen2, Zoltán Balogh1, Gábor Mészáros3, Péter Makk1, Gemma C. Solomon2 and András Halbritter1

1 Department of Physics, Budapest University of Technology and Economics, MTA-BME Condensed Matter Research Group, Hungary 2 Nano-Science Center and Department of Chemistry, University of Copenhagen, Denmark 3 Research Centre for Natural Sciences, Hungarian Academy of Sciences, Hungary [email protected]

Data analysis techniques are reviewed that can be used to study temporal correlations among conductance traces in break junction measurements [1]. We show that temporal histograms are a simple but efficient tool to check the temporal homogeneity of the conductance traces, or to follow spontaneous or triggered temporal variations, like structural modifications in trained contacts, or the emergence of single-molecule signatures after molecule dosing. To statistically analyze the presence and the decay time of temporal correlations, we introduce shifted correlation plots. Finally, we demonstrate that correlations between opening and subsequent closing traces may indicate structural memory effects in atomic-sized metallic and molecular junctions. Applying opening-closing correlation analysis on Au-4,4'-bipyridine-Au single-molecule junctions, we demonstrate that after rupture the molecule does not rearrange significantly, rather it remains protruding from one electrode.

References: 1. A. Magyarkuti, K.P. Lauritzen, Z. Balogh, A. Nyáry, G. Mészáros, P. Makk, G.C. Solomon, A. Halbritter, Temporal correlations and structural memory effects in break junction measurements, The Journal of Chemical Physics 146, 092319 (2017, Special Topic: Frontiers in Molecular Electronics)

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Crystallization of a two-dimensional hydrogen- bonded molecular assembly: evolution of the local

structure resolved by atomic force microscopy

Laerte L. Patera1, Xunshan Liu2, Nico Mosso3, Silvio Decurtins2, Shi-Xia Liu2, Jascha Repp1

1 Department of Physics, University of Regensburg, Universitatsstrasse 31, D-93053 Regensburg, Germany 2 Departement für Chemie und Biochemie, University of Bern, Freiestrasse 3, CH-3012 Bern, Switzerland 3 IBM Research - Zurich, Säumerstrasse 4, CH-8803 Rüschlikon, Switzerland [email protected]

Noncontact Atomic Force Microscopy (nc-AFM) provides detailed insights into the structure of surface-supported molecular self-assemblies, overcoming restrictions given by scanning tunneling microscopy (STM) [1]. Here we show how this approach can be extended to two-dimensional amorphous organic films, presenting a higher degree of complexity. Surface-assisted self-assembly patterns of the aromatic N-heterocyclic hexaazatriphenylene (HAT) molecular synthon were determined with sub-Å resolution, either in the kinetically trapped amorphous state or in the thermodynamically stable structure. These results reveal how, for non-flexible molecular species, the crystallization governs the length-scale of the network order, without affecting the local bonding schemes.

References: 1. L. Gross, F. Mohn, N. Moll, P. Liljeroth, G. Meyer, Science 2009, 325, 1110–1114.

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Probing electron transmission and reflection in

quasi-molecular structures

Sense Jan van der Molen

Huygens-Kamerlingh Onnes Laboratory, Leiden University, Netherlands [email protected]

Strictly speaking, this talk is not about molecular electronics. Still, I hope to convey the message that our latest research has everything to do with the field and may be seen as an extension of it to other energy scales and boundary conditions. In our lab, we work with a low-energy electron microscope (LEEM). With this rather unique instrument, we can probe the reflection of electrons with tunable energies 0-30 eV, where 0 eV energy refers to the vacuum level. Not only does this allow for microscopy, with a resolution of 1.5 nm, it also enables us to do local spectroscopy in electron reflection. Recently, we have extended our instrument such that we can also probe electron transmission. This technique can be seen as an extension of transmission electron microscopy (TEM) to extremely low electron energies (eV-range). Hence, we have coined it eV-TEM. We apply both LEEM and eV-TEM to graphene layers of varying thickness. In the normal or z- direction, it turns out that unoccupied states exist between the graphene layers, in the energy range that we probe at. With every additional layer of graphene, an interlayer state is added to the system, which can hybridize with the other interlayer states. In this way, a quasi-molecular set of orbitals is formed in the z-direction, which nicely follows tight binding. In electron reflection, these eigenstates appear as minima in the spectrum R(E).[1,2] In an electron transmission spectrum, however, they show up as maxima, just as one expects in a Landauer transmission function at resonance. I will discuss the differences and the similarities between Landauer's T(E) in charge transport and the T(E) that we determine in our electron microscope, which clearly have different boundary conditions. Remarkably, the method also allows us to determine a scattering function S(E) = 1-T(E)-R(E), which includes all scattering processes (e.g. phonon and plasmon scattering). I will discuss that function in the light of the IETS (inelastic electron transmission spectroscopy) spectra determined in charge transport measurements.

References: 1. J. Jobst, J. Kautz, D. Geelen, R.M. Tromp, S.J. van der Molen Nanoscale measurements of unoccupied band dispersion in few-layer graphene Nature Communications 6, 8926 (2015) 2. J. Jobst, A.J.H. van der Torren, E.E. Krasovskii, J. Balgley, C.R. Dean, R.M. Tromp, S.J. van der Molen Quantifying electronic band interactions in van der Waals materials using angle-resolved reflected- electron spectroscopy, Nature Communications 7, 13621 (2016)

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Energy level alignment at the nanoscale: from

molecular junctions to 2D materials

Kristian Thygesen

Computational Atomic-scale Materials Design (CAMD), Technical University of Denmark (DTU), Denmark [email protected]

Energy level alignment at interfaces are decisive for the functionality and performance of almost any nanoscale device. In molecular electronics, the distance between the Fermi level of the metal electrode and the frontier molecular orbitals are crucial for the transport properties. In (opto)- electronic devices like transistors, solar cells or light emitting diodes, the band alignment at metal- semiconductor (SC) or SC-SC interfaces determine Schottky barrier heights and charge separation efficiencies. In the first part of the talk I will describe different methods for predicting energy levels and transport in single-molecule junctions from first-principles calculations. Compared to standard density functional theory (DFT) based approaches, the many-body GW method is shown to yield a much improved agreement with experimental data for single-molecule conductance thanks to a much improved prediction of the molecular energy levels [1]. In the second part of the talk I will focus on two-dimensional (2D) materials and their potential as building blocks for opto-electronic devices [2,3]. After a brief review of the basic electronic properties that distinguishes the 2D materials from their 3D counterparts, I will describe the idea of “dielectric engineering” as a means for controlling the optical and electronic properties of 2D heterostructures. Specifically, I will show how the excitons binding energy and band gap of a 2D semiconductor can be tuned via the support or encapsulation of the 2D material [4]. Again, the use of many-body methods, like the GW approximation and Bethe- Salpeter equation, is found to be essential for obtaining quantitative agreement with experimental data.

References: 1. Energy level alignment and quantum conductance of functionalized metal-molecule junctions: Density functional theory versus GW calculations, C. Jin, M. Strange, T. Markussen, G. C. Solomon, and K. S. Thygesen, J. Chem. Phys. 139, 184307 (2013) 2. Calculating excitons, plasmons and quasiparticles in 2D materials and van der Waals heterostructures, Kristian S. Thygesen, 2D Materials (in print) 3. Computational 2D Materials Database: Electronic Structure of Transition-Metal Dichalcogenides and Oxides, F. A. Rasmussen and K. S. Thygesen, J. Phys. Chem. C 119, 13169 (2015) 4. Dielectric Genome of van der Waals Heterostructures, K. Andersen, S. Latini, and K. S. Thygesen Nano Letters 15, 4616 (2015)

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

A long story short: deciphering orbital and length effects in oligothiophene single molecule junctions

G. Gryn’ova, P. Ollitrault, C. Corminboeuf*

Institute of Chemical Sciences and Engineering, École polytechnique fédérale de Lausanne *[email protected]

Single molecule junctions represent a powerful tool for studying the intimate details of molecular charge transport. The latter can be either p-type (hole transport, through HOMO) or n-type (electron transport, through LUMO). It is trivially assumed that the type of the linker group connecting the central π-conjugated molecular fragment to the conducting electrodes dictates the conductance channel [1]. However, recent studies on oxidised oligothiophene junctions revealed that the nature of the charge carriers can be tuned by molecular length [2] and substituents in the thiophene ring [3]. In this work we employ the standard NEGF+DFT approach [4] to identify the factors governing conductance in these fascinating junctions and determine the design guidelines for molecular wires with targeted transport characteristics [5]. We establish how the nature and position of the substituents influence the frontier orbitals of the thiophene ring (Fig. 1) and that increasing the number of units in a wire leads to more molecular resonances entering the transport window. We also observe a number of interesting trends, including the odd/even n alteration in the conductance due to contact geometry and a very characteristic relationship between the charge distribution within the junction and the nature of charge transport (Fig. 2).

References: 1. L. A. Zotti, T. Kirchner, J.-C. Cuevas, F. Pauly, T. Huhn, E. Scheer, A. Erbe, small 2010, 6, 1529. 2. E. J. Dell, B. Capozzi, J. Xia, L. Venkataraman, L. M. Campos, Nature Chem. 2015, 7, 209. 3. J. Z. Low, B. Capozzi, J. Cui, S. Wei, L. Venkataraman, L. M. Campos, Chem. Sci. 2017,8, 3254. 4. (a) J. S. Seldenthuis, PhD thesis 2011, TU Delft. (b) J. Maassen, M. Harb, V. Michaud-Rioux, Y. Zhu, H. Guo, Proc. IEEE 2013, 101, 518. 5. G. Gryn’ova, P.J. Ollitrault, C. Corminboeuf, in preparation.

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Probing Lewis acid-base interactions in single-

molecule junctions

Xunshan Liu,§ Xiaohui Li,† Sara Sangtarash,|| Hatef Sadeghi,|| Silvio Decurtins,§ Wenjing Hong,† Colin J. Lambert,|| and Shi-Xia Liu§

§Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, CH-3012 Bern, Switzerland †Department of Chemical and Biochemical Engineering, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China ||Quantum Technology Centre, Physics Department, Lancaster University, Lancaster LA1 4YB, UK [email protected]

It still remains a challenge to deliberately manipulate and control charge transport in molecular assemblies. Herein we present a novel strategy to regulate the tunneling mechanism of an organoborane wire via Lewis acid-base interactions. We demonstrate that fluoride binding leads to a decrease in the molecular junction conductance by ca. 4 fold. This finding is also verified by ab-initio transport calculations, indicative of a switching from LUMO- to HOMO-dominated charge transport upon the addition of the fluoride. It is believed, that the ability to control transport resonances at a molecular scale has potential applications in the design of new thermoelectric materials and chemical sensors.

References: 1. Jing C.; Oliver S. W. Chem. Sci. 2015, 6, 3582-3592

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Control over electronic communication in meso-

meso two-atom-bridged diporphyrins

Anna Zieleniewska

FAU Erlangen-Nürnberg, Germany [email protected]

At the focal point of this work was photophysical characterization of three meso-meso two-atom- bridged diporphyrins (1-3). Detailed investigations by means of cyclic voltammetry, absorption, fluorescence, and femto-/nano-second transient absorption spectroscopy enabled the evaluation of the electronic communication between two porphyrins connected by azo-, imine-, or ethene-bridges. In the ground state, the azo-bridge facilitates the strongest electronic communication between the two porphyrins. In the excited state, however, the ethene-bridge induces the strongest coupling, followed by the imine- and azo-bridges.

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Wires based on Amidinium-Carboxylate salt-bridge interaction: single molecule-junction approach

Valentina Sacchetti

IMDEA Nanoscience, Spain [email protected]

Little is known about molecular wires with non-covalent interactions in their structure. In this regard, hydrogen bonds emerge as a promising connection for molecular wires as they allow strong electronic communication through the coupled units, comparable to σ or  bonds.1 Moreover, the conductance and junction formation of these molecular-scale devices can be tuned varying the strength of hydrogen bonds with external stimuli.2 A series of simple linear supramolecular hydrogen-bonded wires modified with two different aurophilic anchoring groups were synthesized. Their electron transport properties through the amidinium-carboxylate salt-bridge interaction was probed employing the scanning tunneling microscopy break junction (STM-BJ) technique.

References: 1. L. Sánchez, M. Sierra, N. Martín, A. J. Myles, T. J. Dale, J. Rebek, Jr., W. Seitz, D. Guldi, Angew. Chem. Int. Ed., 2006, 45, 4637-4641. 2. M. Kotiuga, P. Darancet, C. R. Arroyo, L. Venkataraman, J. B. Neaton, ArXiv e-prints, 2014, 1410.1439.

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Developing chemical intuition for molecular

charge transport

Gemma C. Solomon

University of Copenhagen, Denmark [email protected]

As our computational methods for modeling transport properties become increasingly sophisticated, we run the risk of falling into the trap of simply conducting “computational experiments”. That is, we can compute the observables (current, conductance etc) but aside from agreement, or lack-thereof, with experiment, we have no deeper insight into why the system behaves as it does. In this talk, I will outline our efforts using and developing tools to provide chemical insight/intuition for molecular charge transport. In particular, I will discuss diagrams for back-of-the-envelope predictions, partitioning into σ and π contributions in non-planar molecules, extracting Hückel model parameters from density functional theory calculations and complex band structure.

References: 1. A. Borges, and G. C. Solomon J. Chem. Phys 2016, 144, 194111 2. A. Borges, and G. C. Solomon J. Phys. Chem. C 2017, 121, 8272.

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Challenges in probing single-molecule charge

transport in complex molecular structures

Tim Albrecht

Imperial College, London, UK [email protected]

While the charge transport properties of relatively simple, linear molecules have been studied in some detail both theoretically and experimentally, complex molecular structures such branched and ring- shaped systems, perhaps with multiple redox-active centres, have received less attention to date.[1,2] Nevertheless, these are interesting targets for scientific study, since such molecules are more akin to small "molecular" circuits and could display exciting quantum mechanical phenomena, such as quantum interference and local gating. On the other hand, such structures can be very difficult to synthesize, may be less stable, more difficult to probe in a well-defined way (multiple contact points with the electrodes), and often have low conductance. Due to their sheer size, they are also much more difficult to treat in electronic structure and charge transport calculations. However, in recent years we have been fortunate to collaborate with leading synthesis and theory groups in the field and my group has developed the important tools to study such structures in detail, including automated data acquisition/STM imaging methodologies and analysis techniques based on Machine Learning.[3,4] First results are beginning to emerge and we have come some way towards a more complete understanding of the data. Our work highlights new opportunities as well as some significant fundamental limitations, which I will discuss during my talk.

References: 1. M.S. Inkpen et al., "Oligomeric Ferrocene Rings", Nature Chemistry 2016, 8, 825-830. 2. L.E. Wilson et al., "A tri-ferrocene macrocyclic system", Angewandte Chemie 2016 (accepted) 3. M.S. Inkpen et al., "New Insights into Single-Molecule Junctions Using a Robust, Unsupervised Approach to Data Collection and Analysis", J. Amer. Chem. Soc. 2015, 137, 9971-9981. 4. M. Lemmer et al., "Unsupervised vector-based classification of single-molecule charge transport data", Nat. Comm. 2016, 7, art. no. 12922.

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Quantum interference effects from charge transfer

complexes in molecular junctions

Simon Higgins

University of Liverpool, UK [email protected]

Some charge transfer materials (e.g. the well-known tetrathiafulvalene:tetracyanoquinodimethane, TTF:TCNQ) have high electrical conductivity in the solid state as a result of the formation of delocalised charge carriers along the stacks of partially-oxidised TTF molecules and partially-reduced TCNQ molecules. We have shown that even at the single molecule level, for donor molecules with the appropriate structure (e.g. 1 and 2 below), the formation of a charge transfer complex with the acceptor tetracyanoethene (TCNE) can significantly boost the electrical conductance of metal | molecule | metal junctions. However, in contrast to the collective nature of the charge carriers in materials like TTF:TCNQ, this conductance boost arises as a result of a new resonance in the transmission function, close to the metal contact Fermi energy, that is a signal of room-temperature quantum interference [1]. Since this publication we have gone on to examine the effects of varying the alkyl chain length (n in structure 1 below), the strength of the acceptor (e.g. TCNE, TCNQ, dichlorodicyanoquinone DDQ and others) and the strength of the donor (e.g. 1 vs. 2), on the size of the conductance boost observed, and these results will form the main subject of this presentation.

HS S S SH n S n n = 1-8 1

HS SH 2

References: 1. A. Vezzoli, I. Grace, C. Brooke, K. Wang, C.J. Lambert, B.Q. Xu, R.J. Nichols and S.J. Higgins, Nanoscale, 2015, 7, 18949-18955.

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

High current-bias effects in atomic and molecular

junctions

Sumit Tewari, Manohar Kumar, Carlos Sabater, Jan van Ruitenbeek

Leiden University, Netherlands [email protected]

Single-atom and single-molecule junctions survive surprisingly high currents [1]. This fact is understood as being due to the ballistic character of the electron transport. The major part of the dissipation of energy takes place inside the leads, at a large distance from the junction. This permits the study of atomic and molecular wires under extreme non-equilibrium conditions. Under such conditions the fundamental processes of electron-electron and electron-ion scattering can be revealed and studied. For this study we employ break junction techniques and scanning tunneling microscopy. One of the tools revealing the statistics of electron scattering effects is the measurement of shot noise. We have extended the range of shot noise spectroscopy up to 10MHz, which opens a new window on the scattering phenomena [2]. The observations demonstate dramatic deviations from the linear low-bias behaviour, to such a degree that it is even possible to observe shot noise decrease for increasing bias. We offer an explation by connecting the information from differential conductance and shot noise into a unified picture.

References: 1. Quantum properties of atomic-sized conductors. N. Agraït, A. Levy Yeyati and J.M. van Ruitenbeek, Phys. Rep. 377 (2003) 81-380. 2. Fast and accurate shot noise measurements on atomic-size junctions in the MHz regime, S. Tewari, C. Sabater, M. Kumar, S. Stahl, B. Crama, J.M. van Ruitenbeek, Rev. Sci. Instrum. (2017), sumitted

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Thermoelectricity in vertical graphene-C60-

graphene architectures

Qingqing Wu1, Hatef Sadeghi1, Víctor Manuel García Suárez2,3, Jaime Ferrer2,3, and Colin Lambert1

1 Quantum Technology Centre, Lancaster University, LA1 4YB Lancaster, United Kingdom 2 Departamento de Física, Universidad de Oviedo, 33007 Oviedo, Spain 3 Nanomaterials and Nanotechnology Research Center (CSIC-Universidad de Oviedo) [email protected]

The electrical and thermoelectric properties of two C60 molecules in parallel, sandwiched between top and bottom graphene electrodes are presented in this talk. Recent studies have identified families of molecules with relatively high thermoelectric performance [1][2] but there is still a need for an understanding of the fundamental issues arising when such molecules are placed in parallel, which is relevant for controlled scalability. We find that, in contrast with classical conductors, increasing the number of C60 molecules in parallel from one to two can cause the electrical conductance to increase by more than the factor of 2. Furthermore, the Seebeck coefficient is sensitive to the number of parallel molecules sandwiched between the electrodes, whereas classically it should be unchanged. This non-classical behaviour of the electrical conductance and Seebeck coefficient are due to inter- molecular quantum interference, mediated by the electrodes, which leads to an enhanced thermoelectric response in these vertical molecular devices.

References: 1. S. V Aradhya and L. Venkataraman, “Single-molecule junctions beyond electronic transport,” Nat. Nanotechnol., vol. 8, no. 6, p. 399, 2013. 2. C. Evangeli, K. Gillemot, E. Leary, M. T. Gonza, G. Rubio-bollinger, and C. J. Lambert, “Engineering the Thermopower of C 60 Molecular Junctions,” pp. 2141–2145, 2013.

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Novel scanning probe methods for 2D materials

and organic assemblies

Benjamin Robinson

Lancaster University, UK [email protected]

Here I will present an overview of the novel scanning probe methods we employ at Lancaster to characterise organic self-assembled structures [1] and polymers, semiconductors, and 2D materials [2, 3]. Work reported here is from the groups of Robinson, Kolosov and Jarvis in collaborations with Lambert and Bryce. Combining 2D materials, such as graphene, MoS2, BN, either as active components or as electrodes with organic self-assembled films is highly promising for applications including thermoelectrics, photovoltaics and smart windows. However, whilst the composite electrical, thermal, and mechanical properties 2D material-based heterostructures are widely studied, the nanoscale exploration of subsurface and interfacial properties is significantly challenging. Here I will show how we can probe these interfaces (figure) using multi-parametric characterisation techniques based upon contact scanning probe methods [4]. These techniques include ultrasonic force microscopy, scanning thermal microscopy and electrically conductive probe microscopy. Further I will show how we can extend the study of such systems beyond ‘ideal’ conditions to range of application-specific environments such as liquid [5].

References: 1. Robinson B.J.; Bailey, S.; O’Driscoll, L.J; et al, ACS Nano, 11 (3), 3404–3412 (2017) 2. Kay N.D.; Robinson B.J.; Fal’ko V.; Novoselov K; et al, Nano Letters, 14 (6), 3400-3404, (2014) 3. Sercombe, D.; Schwarz, S.; Del Pozo-Zamudio, O.; et al, Scientific Reports 3, 3489, (2013) 4. Robinson, B.J.; Giusca, C.E.; Gonzalez, Y.T.; et al, 2D Materials 2, 015005 (2015) 5. Robinson, B.J. and Kolosov, O.V., Nanoscale, 6 (18), 10806-10816, (2014)

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Poster

Mid-gap theory for single molecule electronics

Sara Sangtarash

Lancaster University, UK [email protected]

If quantum interference patterns in the hearts of polycyclic aromatic hydrocarbons could be isolated and manipulated, then a significant step toward realizing the potential of single-molecule electronics would be achieved. In this poster, we demonstrate that connectivity is a useful starting point for designing single-molecule junctions with desirable electrical properties. As an example of such design considerations, for the purpose of connecting molecules to source-drain electrodes, a high conductance is desirable. On the other hand for the purpose of connecting to an electrostatic gate, a low conductance is needed to avoid leakage currents. M-functions provide new design strategies for identifying molecules with phase-coherent logic functions and enhancing the sensitivity of molecular- scale interferometers.

References: 1. Sara Sangtarash, Cancan Huang, Hatef Sadeghi, Gleb Sorohhov, Jürg Hauser, Thomas Wandlowski, Wenjing Hong, Silvio Decurtins, Shi-Xia Liu, Colin J Lambert, Searching the hearts of graphene-like molecules for simplicity, sensitivity, and logic, 2015, JACS, 137 (35), 11425-11431 2. Yan Geng, Sara Sangtarash, Cancan Huang, Hatef Sadeghi, Yongchun Fu, Wenjing Hong, Thomas Wandlowski, Silvio Decurtins, Colin J Lambert, Shi-Xia Liu, Magic ratios for connectivity-driven electrical conductance of graphene-like molecules, 2015, JACS, 137 (13), 4469-4476 3. Sara Sangtarash, Hatef Sadeghi, Colin J. Lambert, Exploring quantum interference in heteroatom-substituted graphene-like molecules, 2016, Nanoscale 6, 13199-13205 4. Xunshan Liu, Sara Sangtarash, David Reber, Dan Zhang, Hatef Sadeghi, Jia Shi, Zong‐Yuan Xiao, Wenjing Hong, Colin J Lambert, Shi‐Xia Liu, Gating of quantum interference in molecular junctions by heteroatom substitution, 2017, Angewandte Chemie International Edition 56 (1), 173-176

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Poster

A chiral ferrocene derivative for spin-dependent electrochemistry

Kevin Weiland§, Francesco Tassinari†, Ron Naaman†, Marcel Mayor§

§ Department of Chemistry, University of Basel, St. Johanns-Ring 19, 4056 Basel, Switzerland † Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel [email protected]

For the past two decades, self-assembled monolayers (SAMs) were investigated for their ability to change the charge transfer rates in electrochemical experiments, when deposited on electrodes.1,2 Recent studies have shown that the electron transmission through chiral molecules depends on the electrons’ spin orientation. This is referred to as the Chiral Induced Spin Selectivity effect.3 We propose a novel, chiral ferrocene derivative, which obtains it’s chirality from pseudo-meta substituted [2.2]paracyclophane. The poster will discuss the synthesis, chiral resolution and investigation of the properties of the two enantiomeric compounds displayed above in spin-dependent electrochemistry experiments when deposited as SAMs on metal surfaces.

O O

S S

Fe Fe

Figure 1: Enantiomeric target compounds for Spin-Dependent Electrochemistry.

References: 1. Langmuir, 1990, 6, 682-691. 2. Langmuir, 1991, 7, 1510-1514. 3. J. Phys. Chem. Lett., 2012, 3, 2178-2187.

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Poster

TTF analogues for electrochemically-switched

single molecular conductance

Luke J. O’Driscoll,† Joseph M. Hamill,*‡ Iain Grace,§ Bodil W. Nielsen,† Eman Almutib,§ Yongchun Fu,‡ Wenjing Hong,‡‖ Colin J. Lambert,*§ and Jan O. Jeppesen*†

†U. Southern Denmark, ‡University of Bern, §Lancaster U. [email protected]

Electrochemically-controlled single molecular conductance switching among different TTF redox states is discussed. Comparisons to other conjugated TTF analogues are made. Break junctions were measured using electrochemically-controlled scanning tunneling microscope [1].

References: 1. Electrochemical control of the single molecule conductance of a conjugated bis(pyrrolo)tetrathiafulvalene based molecular switch. (submitted)

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Poster

Electrical breakdown of monolayer graphene: substrate and environment effects

M. El Abbassi1, L. Posa2, P. Makk1,2, A. Halbritter2 , M. Calame3

1 University of Basel - BASEL, Switzerland 2 Budapest University of Technology and Economics and Condensed Matter Research Group of the Hungarian Academy of Sciences, Department of Physics - Budapest, Hungary 3 EMPA, Transport at Nanoscale interfaces - Dubendorf, Switzerland [email protected]

Graphene offers a flat and gateable platform for single molecule measurements, with new binding possibilities, and is operable at room temperature [1]. First measurements of graphene based single molecule nanojunctions have already appeared [2,3]. To form nanogaps in the graphene, EB process is the main used technique [2, 4, 5]. It consists of increasing the current density (that induces joule heating [6]) until electrical breakdown. We previously reported [7] on the fabrication of sub-5nm gaps with the EB technique with a yield of 95% . However single molecule features like Coulomb blockade [8] and Fabry Perot interference [9] were also reported, albeit without the presence of molecules. Distinguishing between the signature of a molecule and the one of carbon islands resulting from the EB process is crucial. As such, one needs to be able to create featureless devices. To control the formation of the graphene nanogaps, the breakdown mechanism has to be better understood. We report on the characterization of the Electrical-Breakdown (EB) process for the production of tunneling gaps in single-layer graphene. To investigate the role of oxygen in the EB process, graphene tunneling junction were created under different environmental conditions (vacuum and ambient conditions). Moreover, to exclude the substrate as source of oxygen, the measurements were performed on different substrates (SiNx and SiOx). We show that the density of oxygen molecules in the chamber is a crucial parameter that de nes the physical breakdown process: at low density, the graphene lattice is sublimating, whereas at high density the process involved is oxidation, independent on the substrate material.

References: 1. Jia et al., Acc. Chem. Res., 2015, 48 (9), 2565-2575 2. Prins et al., Nano Lett., 2011, 11 (11), pp 4607-4611 3. C. Jia et al., Science,2016, Vol. 352, Issue 6292, pp.1443-1445 4. Mol et al., Nanoscale, 2015, 7, 13181 5. C. S. Lau et al., Phys. Chem. Chem. Phys., 2014, 16, 20398-20401 6. Grosse et al., Nature Nanotechnology 6, 287-290 (2011) 7. Nef et al., Nanoscale, 2014, 6, 7249 8. Barreiro et al., Nano Lett., 2012, 12 (12), 6096-6100 9. Gehring et al., Nano Lett., 2016, 16 (7), 4210-4216

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Poster

Thermoelectricity in vertical graphene-C60-

graphene architectures

Qingqing Wu1, Hatef Sadeghi1, Victor Garcia-Suarez2,3, Jaime Ferrer2,3, and Colin Lambert1

Recent studies of single-molecule thermoelectricity have identified families of molecules with high thermoelectric performance. In order to translate this performance into practical thin-film energy- harvesting devices, there is a need for an understanding of the fundamental issues arising where such molecules are placed in parallel. Here we investigate the electrical transport and thermoelectric properties of two C60 molecules in parallel sandwiched between graphene electrodes. In contrast with classical conductors, increasing the number of C60 molecules in parallel from one to two causes the electrical conductance to increase by more than a factor of 2. Furthermore, due to quantum interference, the Seebeck coefficient is sensitive to the number of parallel molecules sandwiched between the electrodes, whereas classically it should be unchanged. This non-classical electrical conductance increase conspiring with a higher Seebeck coefficient yields an enhanced thermoelectric response in these vertical molecular devices.

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Poster

Heat transport through atomic contacts

Nico Mosso, Ute Drechsler, Fabian Menges, Peter Nirmalraj, Siegfried Karg, Heike Riel and Bernd Gotsmann

IBM Research – Zurich, Säumerstrasse 4, 8803 Rüschlikon, Switzerland. [email protected]

Heat transport and dissipation in nanoscopic contacts pose severe limitations to the scaling and performances of electronic devices. Scanning thermal microscopy was recently proved as a powerful tool to measure temperature at the nanoscale with a spatial resolution below 10 nm. However, at smaller dimensions heat conduction mechanisms remain to be fully explored because of the lack of characterization techniques. Here we present heat transport measurements through metallic contacts formed by single gold atoms at room temperature and analyse the dependence of the thermal conductance on the contact size. Simultaneous measurements of charge and heat transport reveal the proportionality of electrical and thermal conductance, quantized with the respective conductance quanta. This constitutes a verification of the Wiedemann–Franz law at the atomic scale.

References: 1. Mosso, N., et al. Nat. Nanotech., (February), 23 (2017)

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Poster

Towards high thermoelectric performance of thiophene and ethylenedioxythiophene (EDOT) molecular wires

M.Famili, I. M. Grace, Q. Al-Galiby, C. J. Lambert

Department of Physics, Lancaster, Lancaster University, LA1 4YB, UK [email protected]

The design of efficient thermoelectric materials for the conversion of waste heat into electricity requires simultaneous tuning of their electrical and thermal conductance. The presented theoretical study, compares the electron and phonon transport in thiophene and ethylenedioxythiophene (EDOT) based molecular wires. We show that the proposed modification, enhances the thermoelectric figure of merit for molecules of the same length.

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Poster

Low temperature investigation of 4,4'-bipyridine

molecule

Zoltán Balogh, András Magyarkuti, András Halbritter

Department of Physics, Budapest University of Technology and Economics and MTA-BME Condensed Matter Research Group, 1111 Budapest, Budafoki ut 8., Hungary [email protected]

We have investigated Au-4,4’-bipyridine-Au molecular junctions with the mechanically controllable break junction technique at low temperature (T=4.2K) utilizing an in-situ molecule dosing setup. Due to the frozen surface diffusion of the electrode atoms in cryogenic temperature measurements the molecular junctions stay stable for detailed characterization. Applying opening-closing correlation analysis on the single-molecule junctions, we have demonstrated that after rupture the molecule does not rearrange significantly, rather it remains protruding from one electrode. Investigating the I(V) characteristics of these junctions we could show bistable electrical switching.

References: 1. P. Makk, D. Tomaszewski, J. Martinek, Z. Balogh, S. Csonka, M. Wawrzyniak, M. Frei, L. Venkataraman, A. Halbritter, Correlation Analysis of Atomic and Single-Molecule Junction Conductance ACS Nano 6 (4) pp. 3411-3423. (2012) 2. Z. Balogh, D. Visontai, P. Makk, K. Gillemot, L. Oroszlány, L. Pósa, C. Lambert, A. Halbritter, Precursor configurations and post-rupture evolution of Ag-CO-Ag single-molecule junctions Nanoscale 6 (24) pp. 14784-14791. (2014) 3. A. Magyarkuti, K. P. Lauritzen, Z. Balogh, A. Nyáry, G. Mészáros, P. Makk, G. C. Solomon, A. Halbritter, Temporal correlations and structural memory effects in break junction measurements Journal of chemical physics 146 (9) Paper 092319. (2017)

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Poster

Charge-gating dibenzothiophene-S,S-dioxide bridges in electron donor-bridge-acceptor conjugates

Gilles Yzambart,[a] Anna Zieleniewska,[b] Stefan Bauroth,[b] Timothy Clark,[c] Martin R. Bryce,[a] Dirk M. Guldi,[b]

[a] Department of Chemistry, Durham University, Durham DH1 3LE, United Kingdom. [b] Department of Chemistry and Pharmacy & Interdisciplinary Center for Molecular Materials, Friedrich- Alexander-Universität Erlangen-Nürnberg, Egerlandstr. 3, 91058 Erlangen, Germany. [c] Computer-Chemie-Centrum & Interdisciplinary Center for Molecular Materials, Department of Chemistry and Pharmacy, Friedrich-Alexander-Universität Erlangen-Nürnberg, Nägelsbachstr. 25, 91052 Erlangen, Germany. [email protected]

One-dimensional molecular wires have drawn increasing attention due to their large range of potential applications such as sensors, optoelectronics, photovoltaics and emerging nanoscale technologies[1- 3]. The cases of photoinduced Donor-Bridge-Acceptor type molecules constitute a good example where charge transfers could be useful in the development of photovoltaic devices. Herein, we present the synthesis and the study of the photophysical properties of the first ZnPorphirine/C60 wires connected by π-conjugated co-oligomers built from Fluorene (Fl) and Dibenzothiophene-S,S-dioxide (S) units. In addition, this research was focused on the influence of both the place of the electron withdrawing group (S) and the length of the bridge. Detailed investigations using cyclic voltammetry, absorption, fluorescence, and femto/nanosecond transient absorption spectroscopy in combination with quantum chemical calculations have enabled us to develop a detailed mechanistic view of the charge-transfer processes that follow photoexcitation of either ZnP, the bridge or C60.

References: 1. Jortner, J., Ratner, M., Eds. Molecular Electronics; Blackwell: London, 1997. 2. Joachim, C.; Gimzewski, J. K.; Aviram, A. Electronics Using Hybrid-Molecular and Mono-molecular Devices. Nature, 2000, 408, 541-548. 3. Troisi, A.; Ratner, M. A. Molecular Signatures in the Transport Properties of Molecular Wire

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Poster

Quantum interference and heteroaromaticity of para- and meta-linked bridged biphenyl units in single molecular conductance measurements

Markus Gantenbein, Lin Wang, Alaa A. Al-jobory, Ali K. Ismael, Colin J. Lambert, Wenjing Hong & Martin R. Bryce

Department of Chemistry, Durham University, Durham DH1 3LE, UK. Department of Chemistry, University of Bern, Switzerland. Department of Physics, Lancaster University, Lancaster LA1 4YB, UK. [email protected]

In this poster we are going to answer the fundamental interest question in molecular electronics, is there a correlation between the (hetero X)aromaticity of the core of a molecule and its conductance in a single molecular junction? To address this question, oligo(arylene-ethynylene) (OAE) molecular wires have been synthesized with core units comprising (X= S, N, O and CMe2). A combined experimental and computational study, using mechanically controlled break junction measurements and density functional theory calculations, demonstrates consistently higher conductance in the para series compared to the meta series: this is in agreement with increased conjugation of the π–system in the para series. Within the para series conductance increases in the order of decreasing heteroaromaticity (S < N < O). However, the sequence is very different in the meta series, where S ≈ O < N. Excellent agreement between theoretical and experimental conductance values is obtained. Our study establishes that both quantum interference and heteroaromaticity in the molecular core units play important and inter-related roles in determining the conductance of single molecular junctions.

References: 1. Soler, J. M. et al. The SIESTA method for ab initio order- N materials simulation. J. Phys. Condens. Matter 14, 2745 (2002) 2. Chen, W. et al. Aromaticity Decreases Single-Molecule Junction Conductance. J. Am. Chem. Soc. 136, 918– 920 (2014).

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Poster

Multiple physical timescales and dead time rule in few-nm sized graphene-SiOx-graphene

memristors

László Pósa1, András Halbritter1, Maria El Abbassi2, Péter Makk2, Cornelia Nef2 and Michel Calame2

1 Department of Physics, Budapest University of Technology and Economics and MTA-BME Condensed Matter Research Group 2 Department of Physics, University of Basel [email protected]

Controlled electrical breakdown of graphene nanoribbons allows us to fabricate few nanometers wide gaps between graphene electrodes serving as a promising tool for molecular electronics. In recent years, a high-yield fabrication process was developed [1] to study the breaking mechanism of single- layer graphene under high current density on different substrates and atmospheric conditions. In case of SiOx substrate resistive switching was observed after the nanogap formation which is attributed to the intrinsic switching of SiOx in the gap region. Further investigation of the switching mechanism revealed multiple physical timescales including a peculiar dead time, which plays a crucial role in the device operation. This dead time only holds for the OFF to ON transition and it is found to be independent of the biasing conditions. Depending on the relation between the dead time and the driving frequency a variety of switching curves are observed.

References: 1. C. Nef, L. Pósa, P. Makk, W. Fu, A. Halbritter, C Schönenbergerand M. Calame, High-yield fabrication of nm-size gap in monolayer CVD graphene, Nanoscale, 6, 7249 (2014)

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Poster

Identifying the electronic and mechanical

characteristics of Pi-stacked dimers

András Magyarkuti*, András Halbritter*, Latha Venkataraman+

*Department of Physics, Budapest University of Technology and Economics, Budapest +Department of Applied Physics and Applied Mathematics, Columbia University, New York [email protected]

Break-junction measurements are typically aimed at characterizing electronic properties of single molecules bound between two metal electrodes. Although these measurements have provided structure-function relations for such devices, there is little work that studies the impact of molecule- molecule interaction on junction characteristics. Here, we focus on junctions formed with two amine- terminated conjugated molecules bridging the gap between two electrodes by forming a pi-stacked dimer, using the scanning tunneling microscope and atomic force microscope based break-junction technique. We show that the conductance, force and flicker noise of such pi-stacked dimers differ dramatically when compared with the corresponding monomer junctions. The implications of these results on intra and inter-molecular charge transport are discussed.

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Poster

Effect of substituent and inter-ring in 4,4'-

biypyridine molecular junctions

Mohsin K. Al-Khaykanee1, Andrea Vezzoli2, Richard Brooke3, Ali K. Ismael1, Carly Brooke3, Iain Grace1, Richard J. Nichols2, Walther Schwarzacher3, Simon J. Higgins2, and Colin Lambert1

1Department of Physics, Lancaster University, Lancaster, LA1 4YB, UK 2Department of Chemistry, University of Liverpool, Crown Street, Liverpool L69 7ZD, UK 3H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, UK [email protected]

In this study, We have studied the conductance of a family of 4,4-Bipyridyl molecules with conformationally varied twist angles between the two phenyl rings. These molecules synthesised a series of 3,3'- 3,3, 5,5'-siubstited bipyridyls with functional group ranging from simple methyl units to a number of halogens, and two phosphoryl-biridged planarised analogues. The well-established STM_Break Junction technique was used to characterise such junction. The position of the HOMO and LUMO resonances is studied at different substitutions from molecule to molecule. In addition, the theoretical and experimental results increase linearly dependence on cos2(α). Finally, we have agreement in the low and high values of the conductance with the experimental findings.

References: 1.Shaporenko, A. et al. Self-assembled monolayers from biphenyldithiol derivatives: Optimization of the deprotection procedure and effect of the molecular conformation. J. Phys. Chem. B 110, 4307–4317 (2006). 2.Mishchenko, A. et al. Influence of conformation on conductance of biphenyl-dithiol single-molecule contacts. Nano Lett. 10, 156–63 (2010). 3.Dell, E. J. et al. Impact of molecular symmetry on single-molecule conductance. J. Am. Chem. Soc. 135, 11724–7 (2013). 4.Vezzoli, A. et al. Gating of single molecule junction conductance by charge transfer complex formation. Nanoscale 7, 18949–18955 (2015). 5.Ismael, A. et al. Increasing the thermopower of crown-ether-bridged anthraquinones Nanoscale 7 (41), 17338- 17342 (2015).

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Poster

Switchable rectification of ruthenium-complex molecular junctions

Huseyin Atesci1,†, Veerabhadrarao Kaliginedi1,2,†, Jose A. Celis Gil3, Hiroaki Ozawa4, Joseph M. Thijssen3, Masa-aki Haga4, Sense Jan van der Molen1

1 Kamerlingh Onnes Laboratorium, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands. E- mail: [email protected], [email protected] 2 Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, CH-3012 Bern, Switzerland. E-mail: [email protected] 3 Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands. 4 Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, Bunkyo-ku, Tokyo 112-8551, Japan. † These authors contributed equally to this work. [email protected]

In the quest for ever smaller electronic circuits, functional molecules have been proposed as building blocks for devices. Many molecular diodes rely on asymmetric junction geometries, anchoring groups, or the misalignment of the orbital levels. Here we demonstrate a novel functionality of the junction, namely that by using the conductive AFM technique, Ru-complex self-assembled monolayers on an indium tin oxide surface can show switchable rectification ratios in the same junction, depending on the humidity of the atmosphere. The rectification ratios increase reversibly after changing the atmospheric condition from dry to humid nitrogen by 3 orders of magnitude. Our results show the reversibility of the functionality of Ru-complex junctions as an attractive option for developing nanometer scale humidity sensors. Furthermore, multiple monolayers of Ru-complexes can be stacked on top of each other. This opens up a wealth of possibilities in terms of functionality, yet to be discovered.

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Poster

Scanning thermal microscopy on 2D materials at cryogenic temperatures

Charalambos Evangeli, Jean Spiece, Alex Robson, Nicholas Kay, Benjamin Robinson, Oleg Kolosov

Physics Department, Lancaster University, Lancaster, UK. [email protected]

Thermal transport in Graphene is of great interest due to its high thermal conductivity, for both fundamental research and future applications such as heat dissipation in electronic devices. Although, the thermal conductivity of graphene can reduce depending on the coupling to the substrate [1]. In this work, we report high-resolution imaging of nanoscale thermal transport in single and few layers of Graphene on Silicon Oxide (SiO2) and hexagonal Boron Nitride (hBN), by Scanning Thermal Microscopy (SThM) in high vacuum. SThM is a leading technique for mapping thermal properties with nanoscale resolution [2], consisting of a self-heated probe which acts as a thermosensor during sample scanning. By using doped Si probes and cooling the sample down to 150K, we mapped the thermal resistance of Graphene layers on SiO2 and hBN with sub-10nm resolution. We observed that thermal transport in these layers changes at the elastically deformed areas, which were formed during deposition in the form of bubbles [3]. More specifically, the thermal conductance at the center of the bubbles increases with their surface area. In addition, we study the effect of the sample temperature and the substrate on the thermal conductance of the graphene layers.

Figure. 1. AFM topography and SThM probe Thermal Response of few graphene layers on SiO2, acquired simultaneously.

References: 1. Yong Xu , Zuanyi Li and Wenhui Duan, small,10, (2014), p. 2182–2199 2. Gomès S et al, Phys. Status Solidi A, 212, (2015), p. 477–494. 3. S. J. Haigh et al, Nature Materials, 11, (2012), p. 765-767.

Acknowledgement: The authors acknowledge the support of project EU FP7-NMP-2013-LARGE-7 QuantiHeat.

MOLESCO meeting, Lancaster University, 15th – 19th May 2017

Poster

High-performance thermoelectricity in edge-over- edge zinc-porphyrin molecular wires

Mohammed Noori1,2, Hatef Sadeghi1, and Colin J. Lambert1

1Quantum Technology Centre Department of Physics, Lancaster University, Lancaster LA1 4YB, UK 2Department of Physics, Thi-Qar University, Thi-Qar, IRAQ [email protected]

If high efficiency organic thermoelectric materials could be identified, then these would open the way to a range of energy harvesting technologies and Peltier coolers using flexible and transparent thin- film materials. We have compared the thermoelectric properties of three zinc porphyrin (ZnP) dimers and a ZnP monomer and found that the “edge-over-edge” dimer formed from stacked ZnP rings possesses a high electrical conductance, negligible phonon thermal conductance and a high Seebeck coefficient of the order of 300 μV K−1. These combine to yield a predicted room-temperature figure of merit of ZT ≈ 4, which is the highest room-temperature ZT ever reported for a single organic molecule. This high value of ZT is a consequence of the low phonon thermal conductance arising from the stacked nature of the porphyrin rings, which hinders phonon transport through the edge-over- edge molecule and enhances the Seebeck coefficient.

References: 1. M Noori, H Sadeghi, C Lambert, High-performance thermoelectricity in edge-over-edge zinc-porphyrin molecular wires. Nanoscale, 2017, 9, 5299-5304