The interplay between interface structure, energy level alignment and chemical bonding strength at organic-metal interfaces
What do energy level alignments at metal-organic interfaces reveal about the metal-molecule bonding strength? Is it permissible to take vertical adsorption heights as indicators of bonding strengths? In this paper we analyse 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) on the three can...
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| Published in | Physical chemistry chemical physics : PCCP Vol. 17; no. 3; pp. 153 - 1548 |
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| Main Authors | , , , , , , , , |
| Format | Journal Article |
| Language | English |
| Published |
England
21.01.2015
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| Subjects | |
| Online Access | Get full text |
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| Summary: | What do energy level alignments at metal-organic interfaces reveal about the metal-molecule bonding strength? Is it permissible to take vertical adsorption heights as indicators of bonding strengths? In this paper we analyse 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) on the three canonical low index Ag surfaces to provide exemplary answers to these questions. Specifically, we employ angular resolved photoemission spectroscopy for a systematic study of the energy level alignments of the two uppermost frontier states in ordered monolayer phases of PTCDA. Data are analysed using the orbital tomography approach. This allows the unambiguous identification of the orbital character of these states, and also the discrimination between inequivalent species. Combining this experimental information with DFT calculations and the generic Newns-Anderson chemisorption model, we analyse the alignments of highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) with respect to the vacuum levels of bare and molecule-covered surfaces. This reveals clear differences between the two frontier states. In particular, on all surfaces the LUMO is subject to considerable bond stabilization through the interaction between the molecular π-electron system and the metal, as a consequence of which it also becomes occupied. Moreover, we observe a larger bond stabilization for the more open surfaces. Most importantly, our analysis shows that both the orbital binding energies of the LUMO and the overall adsorption heights of the molecule are linked to the strength of the chemical interaction between the molecular π-electron system and the metal, in the sense that stronger bonding leads to shorter adsorption heights and larger orbital binding energies.
What do energy level alignments at metal-organic interfaces reveal about the metal-molecule bonding strength? |
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| Bibliography: | Dr Serguei Soubatch obtained his PhD degree in physics at Tomsk State University, Russia, in 2002. After a spell as a postdoctoral fellow at the Max-Planck-Institute for Solid State Research in Stuttgart, Germany, he in 2004 joined the group of Professor Tautz at Jacobs University Bremen, Germany, and since then he has been involved in experimental research on the structural and electronic properties of adsorbed organic molecules. Currently, he is a research scientist at the Peter Grünberg Institute at Forschungszentrum Jülich. Dr Peter Puschnig received his PhD degree from the Physics Department of the University of Graz in 2002, and did his postdoctoral research at Graz University of Technology and at the Chair for Atomistic Modelling and Design of Materials at the University of Leoben, Austria. Since 2012 he has been associate professor at the Institute of Physics of the University of Graz. His expertise is in ab initio electronic structure calculations within the framework of density functional theory and many body perturbation theory. Current research interests include the electronic and optical properties of interfaces of organic molecules with metallic substrates. Martin Willenbockel studied Physics at the Philipps Universität Marburg, Germany, and obtained his Diploma in 2010. He is currently a PhD candidate in physics at RWTH Aachen University under the supervision of Professor Tautz, conducting his research at the Peter Grünberg Institute at Forschungszentrum Jülich. He is investigating the structural and electronic properties of metal-organic interfaces. Professor F. Stefan Tautz obtained his PhD in Experimental Low Temperature Physics at the Cavendish Laboratory, University of Cambridge, in 1994. After a Postdoc at the University of Amsterdam he moved to the University of Technology in Ilmenau, Germany, in 1995, where he started his surface science work, soon focussing on interfaces between metals and π-conjugated organic molecules. In 2001 he became a member of the founding faculty of International University Bremen (Jacobs University Bremen as of 2007). Since 2007 he has been at Forschungszentrum Jülich, as a Director of the Peter Grünberg Institute, and heading the Institute "Functional Nanostructures at Surfaces". His research interest is in exploring and extending the limits of nanoscale engineering. Daniel Lüftner received his master's degree in Material Sciences from the University of Leoben, Austria, in 2011. He is currently a PhD candidate in physics at the University of Graz under the supervision of Dr Puschnig. He is studying the electronic structure of interfaces of metals with organic molecules, relevant for organic semiconducting devices. Professor Michael G Ramsey obtained his PhD in physics at the University of New South Wales, Australia, before moving in 1987 to the Physical Chemistry Institute at the University of Innsbruck, Austria, where he began his work on the surface science of conjugated molecules. He moved to the Institute of Physics at the Karl-Franzens University Graz in 1992 where he helped build up a Surface and Interface Division which focuses on the self-assembly and properties of both oxides and conjugated molecules on surfaces. ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
| ISSN: | 1463-9076 1463-9084 1463-9084 |
| DOI: | 10.1039/c4cp04595e |