News

Prof. Echenique (GP1) receives Honorary Doctorate from Aalto University, Finland

We congratulate Prof. Dr. Pedro M. Echenique, PI of SFB-project GP1, on his honorary doctorate received from Aalto University, Finland.

In a ceremony on Oct.7th, Aalto University conferred an Honorary Doctorate in Technology on Pedro Miguel Echenique, Professor of the University of the Basque Country (UPV/EHU) and President of Donostia  international Physics Center (DIPC), together with another ten eminent persons in the fields of science, technology and society. The award, which is conferred every two years by Aalto University Schools of Technology, can look back on a tradition of more than 80 years, and among the recipients are renowned scientists, technologists and influencers in science and society with outstanding professional careers.
More details under Aalto University or DIPC-press release.

Dr. Tonner (A6) receives Hans G. A. Hellmann-Prize for Theoretical Chemistry

We congratulate Dr. Ralf Tonner, PI of SFB-project A6, on the prestigious prize awarded him by the working group on theoretical chemistry (AGTC) at the 52nd Symposium on Theoretical Chemistry held in Bochum.

Marburg chemist Dr. Ralf Tonner (right), PI of SFB 1083, receives the „Hans G. A. Hellmann-Preis für Theoretische Chemie“ from AGTC-president Prof. Dr. Christian Ochsenfeld. (Picture: Alexander Esser, Ruhr-Universität Bochum. Picture may be used in reporting on the award-process only.)

Dr. Tonner, who completed his habilitation in June, received the “Hans G. A. Hellmann-Prize for Theoretical Chemistry” in recognition of his ground-breaking contributions to a detailed theoretical understanding of the chemical processes at surfaces and interfaces. His research-project in SFB 1083 focuses on the detailed understanding of inorganic/organic interfaces from electronic structure theory.

Since 1999 the Hellmann-Prize has been awarded annually for outstanding scientific contributions in the field of theoretical chemistry. Recipients must be less than 41 years of age and not yet employed on a professorial position. However, all recipients to date succeeded in securing a permanent professorship within a couple of years after receiving the award.

German press release.

Young research delegation from India and Thailand

The German Research Foundation organizes an annual information tour for young researchers from India and Thailand on the days following their participation at the Nobel laureate meeting in Lindau. This is their second visit to the Physics department at the Philipps-Universität Marburg.

21 young researchers (students to postdocs) from India and 5 from Thailand were selected by their national committees (Department of Science & Technology of India and National Science and Technology Development Agency in Thailand) to attend the annual Nobel Laureate meeting in Lindau. This year the focus in Lindau was on Physics and Marburg was happy to host the participants on their information tour which included visits to the Peter Grünberg Institute at Forschungszentrum Jülich and the MPI for Gravitational Physics.

Professor Höfer, spokesperson of SFB 1083, gave a lecture introducing the scientific background before the delegation visited laboratories at the Renthof-location of the Physics department and had opportunity to meet and discuss their research with young research staff from SFB 1083.

New Publication by A6 (Tonner) & A3 (Jakob)

Members from projects A6 and A3 successfully joined forces in the investigation and quantification of electron-vibron coupling at the interface of the organic semiconductor 1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTCDA) and the Ag(111) surface.

This effect, where vibrational modes become infrared active due to electron flow across the interface, has been previously described using theoretical reasoning and heuristic models. However, the new study provides the first proof and quantitative examination thereof based on first-principles calculations. Thus, the findings provide an important insight into a key electronic property of interfaces between organic molecules and coinage metal surfaces.

The effect of electron-vibron coupling has been observed for molecular adsorbates, when a molecular orbital is partially filled upon adsorption (static charge transfer), such that its occupation changes dynamically during certain vibrations with respect to the Fermi level of the surface (dynamical charge transfer). This leads to an electron flow between metal and adsorbate, giving rise to an oscillating dipole moment perpendicular to the surface. This fulfils the selection rule for infrared activity. The effect has thus been named interfacial dynamical charge transfer (IDCT).

1,4,5,8-Naphthalenetetracarboxylic dianhydride (NTCDA), a common model compound for an important class of organic semiconductors, adsorbs on the Ag(111) surface by accepting metal electrons in the lowest unoccupied molecular orbital (LUMO), thus fulfilling the above requirement. Molecular vibrations with a specific symmetry can usually not be observed in infrared spectroscopy in the gas phase. However, strong signals were observed in the experimental spectrum of the
molecule adsorbed on the surface for the very same modes. By theoretical investigations it could be proven that this is due to strong IDCT effects.

By studying the projected density of π-symmetric electronic states, the authors verified the observation with first-principles calculations and quantified the effect with partial charge analysis. An excellent correlation between charge transfer and infrared intensity for the fully symmetric vibrational modes has been found. These findings can be applied to any metal-organic interface with a similar bonding situation and matching of energy levels.

Publication:

P. Rosenow, P. Jakob, and R. Tonner
Electron-Vibron Coupling at Metal-Organic Interfaces from Theory and Experiment
J. Phys. Chem. Lett. 7 (2016) DOI:10.1021/acs.jpclett.6b00299

Published on Apr 1, 2016 by the American Chemical Society. Image reprinted with permission. Copyright 2016, American Chemical Society.

New Publication by A2 (Witte)

In a new publication by members of project A2 of SFB 1083, the authors identify unexpected chemical modifications at interfaces between the organic semiconductors Pentacene and Buckminster-Fullerene.

This finding has a severe impact on the current understanding of organic solar cells, since blends of these two compounds are frequently considered as prototypes for organic solar cells.

En route to the fabrication of reliable and efficient organic photovoltaic cells (OPV), a number of fundamental physical processes remain poorly understood. In many OPV devices polymeric compounds exhibiting rather undefined structures are being used both as donor and acceptor material, which hampers detailed interface-related studies. Therefore, well-defined model systems for OPVs are required to gain a deeper understanding of the charge transfer at the internal interfaces. One such model system is the combination of the organic donor-type semiconductor Pentacene and the acceptor Buckminster-Fullerene (C60).

In previous studies the internal structure and electronic characteristics of this organic multilayer interface were analyzed, both by experiment and theory. In our present study, we identify an unexpected and very important effect: at the interface, the compounds do not remain chemically separated from one another but instead form
supramolecular adducts. This adduct-formation by chemical Diels-Alder reaction leads to severe changes of the electronic characteristics of the internal interface which strongly determines the properties of potential OPV devices. We show that the supramolecular adducts are preferentially formed upon post-deposition heating of the blends and that the dimers exhibit strongly enhanced thermal stability as well as modified spectroscopic characteristics compared to pure Pentacene.

In all hitherto known studies of this model system with a focus on device properties as well as theoretical modeling, the molecular constituents have been considered as chemically inert. Thus, identification of the novel process presented here is of utmost importance for understanding the physical properties of this interface, e.g. regarding charge transfer characteristics. The present findings will influence a number of current studies that are conducted within SFB 1083 and stimulate additional future work in this field.

Publication:

T. Breuer, A. Karthäuser, and G. Witte
Effects of Molecular Orientation in Acceptor-Donor Interfaces between Pentacene and C60 and Diels-Alder Adduct Formation at the Molecular Interface
Adv. Mat. Interfaces (2016) DOI:10.1002/admi.201500452

Prof. Gottfried (A4) is awarded SCS Lectureship 2016

Prof. Michael Gottfried is honored with an SCS Lectureship 2016.

The SCS Lectureship is sponsored by the Swiss Chemical Society and Prof. Gottfried will tour from June 6-10, 2016. His host during this time is Prof. Dr. Karl-Heinz Ernst at EMPA.

Poster Prize at BESSY User Meeting 2015

At the 7th Joint BER II and BESSY II User Meeting in Berlin, Michael Klues, Ph.D. student in SFB-project A2 of Prof. Dr. Gregor Witte, won this year’s poster prize.

In his poster Michael Klues presented results of a combined experimental and theoretical study on the NEXAFS signature of perfluorinated acenes. The detailed understanding of these data will enable the future analysis of more complex spectra, arising from samples containing two or more different molecular specimen for instance in organic/organic interfaces which are in the scope of SFB 1083. The project was realized in cooperation with members of Prof. Dr. Robert Berger’s group in SFB-project B8 from the chemistry department.

7th Joint BER II and BESSY II User Meeting: The conference brings together the international user communities of the two HZB large scale research facilities to enable presentation and discussion of results obtained with neutrons and synchrotron radiation. Especially the latter is of interest for projects within SFB 1083 since many questions can experimentally only be addressed by synchrotron radiation based methods.

Poster “Gaining deeper insight into the electronic structure of extended aromatic molecules by NEXAFS” by M. Klues, T. Breuer, P. Jerabek, M. Oehzelt, R. Berger, and G. Witte (Philipps-Universität Marburg) – The 7th Joint BER II and BESSY II User Meeting Dec 9-11, 2015, Berlin Adlershof, Germany.

See also press release (in German) of the Helmholtz Zentrum Berlin.

New APS-Fellows Mackillo Kira & Daniel Sánchez-Portal

SFB 1083 congratulates its members Prof. Dr. Mackillo Kira, Marburg, and Dr. Daniel Sánchez-Portal from the Donostia International Physics Center (DIPC) in Spain upon their election as Fellows to the American Physical Society (APS).

Prof. Dr. Mackillo Kira (left), Co-PI of project B4 “Microscopic theory of optical excitations in interface- dominated material systems”, has been elected Fellow of the APS in recognition “for contributions to theoretical semiconductor quantum optics”. His nomination came through the Division of Laser Science of the APS. See also: Physics-Homepage.

Dr. Daniel Sánchez-Portal (right), Co-PI of project GP1 “Electron dynamics at organic/inorganic interfaces from first principles” based at the Donostia International Physics Center (DIPC) in San Sebastián Spain, has been elected Fellow of the APS in recognition “for contributions to the development and use of electronic structure methods, especially SIESTA and its time-dependent version, which has enabled the simulation of systems of unprecedented complexity.” His nomination came through the Computational Physics Division of the APS.

New Publication by A2 (Witte)

The authors Tobias Breuer and Gregor Witte working in project A2 of SFB 1083 demonstrate a novel concept for the preparation of organic interfaces and solid heterostructures of tunable molecular orientation in a new publication in ACS Applied Materials & Interfaces.

The controlled preparation of heterostructures of various materials is an important prerequisite for the fabrication of electronic devices and sensors. For example, structural control of heterostructures of conventional, inorganic semiconductors enables electronic band engineering. In contrast with such covalently bound systems, rather little is known on appropriate strategies to facilitate organic heterostructures of precise, controlled structure. This is especially true, as organic materials are typically bound by rather weak van-der-Waals interaction only. Therefore, direct utilization of covalent bonding mechanisms which also direct the structure formation
in inorganic heterostructures is not possible. In the past, a number of strategies were developed to prepare organic films of high structural order and homogeneity. These mostly utilized enhanced adsorption energies at inorganic substrates or lattice match to gain control over film structure and molecular orientation. However, these approaches have been limited to unitary films only. The realization of organic heterostructures also requires consideration of molecular orientation, a peculiarity of molecular materials which is absent in the inorganic counterparts. Due to their anisotropic shape, the orientation of individual molecules in the films constitutes an important parameter, as opto-electronic characteristics of processed molecular solids are strongly determined by their alignment.

The authors developed the idea to employ molecular pattern recognition on the nanoscale. They show that molecules of sufficiently similar structure can transfer their orientation from a bottom layer to the top layer of the second compound and thereby “inherit” their structure. The authors also show that this process reliably takes place for all different mutual configurations (i.e. in standing or recumbent orientation) of the model-type organic donor molecules pentacene (PEN) and acceptor molecules perfluoropentacene (PFP). This has allowed them to facilitate internal interfaces in organic heterostructures in different exclusive orientations. Unlike frequently observed for unitary organic film growth, orientation of the constituents is not only controlled at the interface with the organic bottom layer but also persists for thicker top layers (thicknesses up to 30 nm), proving the stability of this concept.

This novel structuring method for precise molecular interfaces with tunable molecular orientation paves the way for a detailed characterization of the intermolecular
electronic coupling as a function of the mutual alignment which will be addressed in upcoming studies within SFB 1083.

Publication:

T. Breuer and G. Witte: Controlling Nanostructures by Templated Templates: Inheriting Molecular Orientation in Binary Heterostructures,
ACS Applied Materials & Interfaces (2015), DOI: 10.1021/acsami.5b07409

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