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- Shape control in 2D molecular nanosheets by tuning anisotropic intermolecular interactions and assembly kinetics – Publication by A2 (Witte) and A8 (Koert/Dürr)22. March 2023 - 12:58
- LernortLabor awards Chemikum Marburg and Oe with LeLa-Prize 202314. March 2023 - 15:30
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- Poster Presentation Prize at DPT 2022 in Karlsruhe28. November 2022 - 07:47
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SFB 1083’s biannual winter school for its young researchers
More than 50 young staff-members involved in the various physics- and chemistry-based SFB 1083 subprojects have come together in Schloss Rauischholzhausen near Marburg for two days of talks and intensive discussion of their research. Invited speakers from Germany and abroad round of the program by contributing more technical tutorials and presentations of their research.
Invited Speakers: Ellen Backus (Mainz), Alexey Chernikov (Regensburg), Matteo Gatti (Gif-sur-Yvette), Christian Papp (Erlangen-Nürnberg), Katrin Siefermann(Leipzig)
Chemists and physicists of SFB projects A8 (Koert) and B5 (Höfer) demonstrate for the first time the controlled chemoselective attachment of bifunctional organic molecules to silicon.
With these results, which were highlighted on the cover page of The Journal of Physical Chemistry, an interface between silicon and organic multilayers has been created . This interface opens the road for a controlled functionalization of silicon with organic molecules. In this way, it offers new perspectives in semiconductor technology (“More than Moore”).
Chemoselective attachment of multifunctional organic molecules is the first fundamental process step for the controlled organic functionalization of semiconductor surfaces. However, the high reactivity of pristine silicon surfaces, especially of the technologically most relevant Si(001) surface, has prohibited so far such a controlled functionalization: multifunctional molecules do not show chemical selectivity on these surfaces but are found with different functional groups attached.
In a joint effort, chemists and physicists of the SFB 1083 “Structure and Dynamics of Internal Interfaces” developed for the first time a general strategy for solving this problem: Using substituted cyclooctynes, they obtained well-defined inorganic-organic interfaces on Si(001) with the bifunctional molecules attached to the silicon surface solely via a cyclooctyne’s strained triple bond. The second functionality is thus available for further building up of complex molecular architectures, e.g., using organic click chemistry. The strategy for the observed chemoselectivity is based on the distinctly different adsorption dynamics of the separate functional groups and thus widely applicable.
In combination with the results for controlled multilayer synthesis in solution using the same classes of molecules , this work is a promising basis for a multitude of applications combining semiconductor technology and organic chemistry, e.g., the integration of optically active organic layers on silicon devices. The obtained structures are also of high interest for further studies of the electronic properties at organic/semiconductor interfaces within SFB 1083.
 M. Reutzel, N. Münster, M. A. Lipponer, C. Länger, U. Höfer, U. Koert, M. Dürr, Chemoselective Reactivity of Bifunctional Cyclooctynes on Si(001),
J. Phys. Chem. C (2016), DOI: 10.1021/acs.jpcc.6b07501.
 N. Münster, P. Nikodemiak, and U. Koert, Chemoselective Layer-by-Layer Approach Utilizing Click Reactions with Ethynylcyclooctynes and Diazides,
Org. Lett. 18, 4296 (2016), DOI:10.1021/acs.orglett.6b02048.
See also press release in German.
Prof. Dr. Ulrich Koert
Fachbereich Chemie, Philipps-Universität Marburg
Hans-Meerwein-Straße, D-35032 Marburg
Tel.: (+49) 6421 28-26970, Email: firstname.lastname@example.org
Prof. Dr. Michael Dürr
Institut für Angewandte Physik, Justus-Liebig-Universität Gießen
Heinrich-Buff-Ring 16, D-35392 Gießen
Tel: (+49) 641 9933-490, Email: email@example.com
In a new publication in Physics Status Solidi Rapid Research Letters project A2 (Witte) reports on the fabrication of well-defined hybrids of organic semiconductors and transition metal-dichalcogenides (TMDCs).
The two-dimensional material graphene has garnered extreme interest due to its interesting electronic properties in combination with utmost structural stability despite merely nanometer thickness. Motivated by this prominent example, further two-dimensional materials have become the focus of today’s cutting-edge research. One important class of such materials are transition metal dichalcogenides such as MoS2, WS2 or MoSe2. Their interesting electronic properties have not only revealed novel physics but already enabled the fabrication of prototypical devices.
In their recent work, Tobias Breuer and Gregor Witte used such TMDC surfaces, in particular of MoS2, to fabricate crystalline, well-defined hybrid structures with organic semiconductors (OSCs), in themselve up-and-coming technologically relevant materials. Brought together, the characteristic advantages of both material classes can be combined to potentially fabricate novel synthetic materials with superior characteristics. The authors report on the successful fabrication of such hybrids combining MoS2 with the molecular donor and acceptor systems pentacene and perfluoropentacene. In particular, they observe that both materials are structurally compatible despite their strongly different shape symmetry and form
large crystalline islands on highly ordered MoS2 basal planes. Interestingly, the molecules arrange in such a fashion that the contact area at the interface between TMDC and organic semiconductor is maximized, hence allowing for an efficient coupling of both constituents. Surprisingly, the OSCs are even epitaxially aligned on the substrates.
A crucial aspect for the successful fabrication of these heterostructures is the structural quality of TMDC surfaces. In previous work, it has been shown that photoluminescence efficiency is strongly increased for MoS2 surfaces with significant defect density as compared to pristine surfaces. For the hybrid structures, the lateral dimensions of the crystalline OSC islands are reduced and the relative orientation of the molecules on the surface is inverted, hence leading to an upright molecular growth on defective MoS2 surfaces instead of a lying configuration on pristine
MoS2. Since the preparation of ideal, defect-free TMDC surfaces is challenging and commercially available TMDCs frequently have considerable defect densities, this aspect requires appropriate consideration. The achieved expertise on the preparation of such well-defined novel hybrid structures will enable the detailed investigation of their electronic and optical coupling mechanisms within further projects of SFB 1083.
Tobias Breuer, Tobias Massmeyer, Alexander Mänz, Steffen Zoerb, Bernd Harbrecht, Gregor Witte
Structure of van der Waals bound Hybrids of Organic Semiconductors and Transition Metal Dichalcogenides: the Case of Acene Films on MoS2
Physica Status Solidi – Rapid Research Letters (2016).
In a publication in Applied Physics Letters project B6 (Höfer) reports on a new experimental setup for time-resolved two-photon photoemission (2PPE). The method, which combines femtosecond pump-probe techniques with photoelectron spectroscopy, makes it possible to map the dynamics of electron transfer processes at surfaces and interfaces directly in momentum space.
The new experiment combines a high-harmonic generation (HHG) light source, developed and built in Marburg, with a state-of-the-art 3D hemispherical electron analyzer (VG Scienta DA30). The analyzer can measure electron energies as a function of both parallel momentum directions (kx and ky) without movement of the sample. The high-harmonic source gives access to the full 2D Brillouin zone whereas conventional 2PPE setups are restricted to electrons near the ? point.
The large parallel momenta, which become accessible with the new experiment, enable SFB 1083 to study electron dynamics at interfaces of many interesting new materials. Particularly, in the class of two-dimensional transition-metal dichalcogenides (TMDCs), most of the interesting electron dynamics take place at the boundary of the first Brillouin zone. Investigations of the intervalley scattering in the topmost layer of MoS2, a prototypical TMDC, demonstrate this capability. Electrons excited at the K-point are found to scatter to the Σ-point in less than 50 fs by directly mapping the electron population in k-space as a function of time.
The new experiment opens up the possibility to study charge transfer and exciton formation with 2PPE in a variety of systems, most prominently van-der-Waals heterostructures, which are a combination of different single-layer TMDCs. In these systems, upon excitation, charge transfer excitons can form. Their formation and relaxation pathways can now be examined by a direct mapping technique in momentum space.
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.
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.
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.
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. 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.
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.
Published on Apr 1, 2016 by the American Chemical Society. Image reprinted with permission. Copyright 2016, American Chemical Society.
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.
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