The European Research Council (ERC) awarded two Synergy Grant to the SFB-related projects “Photoemission Orbital Cinematography: An ultrafast wave function lab” (Orbital Cinema) and “Tackling the Cyclacene Challenge” (TACY).

The ERC has awarded two Synergy Grants to Michael Gottfried, Ulrich Höfer, Stefan Tautz, and collaborators, for projects that built on work in SFB 1083.

Foto: Jan Hosan

Michael Gottfried, Vice Speaker of SFB 1083, receives around 4.5 million euros for “Tackling the Cyclacene Challenge” (TACY). Cyclacenes are an elusive class of ring-shaped carbon-based molecules with unique electronic and magnetic properties. They are expected to provide fundamental insight into the chemistry of strained aromatic systems and to find applications in organic electronic and spintronics. The TACY team, which includes Michael Mastalerz from Heidelberg and Holger Bettinger from Tübingen, pursues the goal of generating cyclacenes for the first time. The ERC funds this project with around 11 million euros.

Foto: Jan Hosan

The second Synergy Grant was awarded to Ulrich Höfer and Stefan Tautz, project leaders of SFB 1083, and their collaborators Rupert Huber from Regensburg and Peter Puschnig from Graz. Ulrich Koert and Jens Güdde, two other SFB 1083 project leaders, are associated partners. Their project “Photoemission Orbital Cinematography: An ultrafast wave function lab”, in short “Orbital Cinema”, aims to reach sub-cycle time resolution in orbital videography and to actively shape and functionalize molecular orbitals with lightwaves. This project is funded with up to 11.4 million euros.

For further information about these projects, see the following:

• Press release by European Research Council (in English)
• SFB-News of TACY (in English)
• Press release of TACY by Philipps University Marburg (in German)
• SFB-News of Orbital Cinema (in English)
• Press release of Orbital Cinema of the Forschungszentrum Jülich, the universities of Regensburg and Graz (in German)

In a combined experimental and theoretical study, the groups of Gregor Witte (A2) and Jérôme Cornil from the University Mons present a new approach of patterning organic semiconductor films with simultaneous molecular orientation control based on an electrostatic stabilization at the film/substrate interface in the presence of F-centers in alkali halide substrates created by controlled electron irradiation.

Scheme of the process chain that allows transfer of patterned organic films to any non-water-soluble substrate. Reprinted with permission from ACS Appl. Mater. Interfaces 2022. Copyright 2022 American Chemical Society.

A key problem in organic electronics remains the lateral patterning and structuring of organic films for device applications since photo­lithography is not applicable due to the lack of chemical robustness of the organic materials in the etching process. Therefore, alternative approaches are necessary for the patterning of organic films.

In this study, Darius Günder et al. demonstrate that electron irradiation of KCl(100) substrates induces surface localized F-centers (halide vacancies) that strongly influence the molecular orientation and lateral structure of subsequently grown organic films. By combining AFM, SEM and XRD measurements they show for the case of dinaphto­thieno­thiophene (DNTT) that molecules adopt a recumbent molecular orientation and form elongated fibers while hexagonally shaped islands with upright orientation are present on pristine KCl. Interestingly, both morphologies exhibit epitaxial alignments that are understood by higher-order commensurabilities. A complementary DFT-based theoretical analysis in the group of Jérôme Cornil identified electrostatic interactions between F-centers and interfacial DNTT molecules as origin of the different film morphologies. Furthermore, shadow masks or electron beam lithography techniques also allow spatially selective surface irradiation to generate patterns of F-centers, and thus enable lateral structuring of DNTT films.

Finally, it could be shown that due to the water solubility of the alkali halide growth templates, the patterned organic films can also be transferred to other substrates, including amorphous elastomeric plastic substrates, while the lateral and orientational order remain fully intact, hence underlining the great potential of this new patterning method for device applications.

Publication

D. Günder, V. Diez-Cabanes, A. Huttner, T. Breuer, V. Lemaur, J. Cornil, G. Witte
F-Center-Mediated Growth of Patterned Organic Semiconductor Films on Alkali Halides
ACS Appl. Mater. Interfaces (2022) DOI:10.1021/acsami.2c13934

Contact

Prof. Dr. Gregor Witte
Philipps-Universität Marburg
SFB 1083 project A2
Tel.: 06421 28-21384
EMAIL

A large research team including Ermin Malic and coworkers observed the formation of a “dark” moiré interlayer exciton for the first time

A large number of so-called optically dark excitons form between two twisted layers of tungsten diselenide (top) and molybdenum disulfide (bottom) after optical excitation. (Reprinted with permission from Nature, link see below)

Atomically thin structures made of two-dimensional semiconductor materials are promising candidates for future devices in electronics, optoelectronics and photovoltaics. The properties of these semiconductors can be controlled by stacking atomically thin layers on top of each other. However, the angle of rotation in the structure of the semiconductors can be adjusted as desired, and this angle of rotation is of interest for the production of novel solar cells. Typical experimental approaches have only indirect access to the moiré interlayer excitons and are blind to the ‘dark’ excitons.

An international research team including Ermin Malic and coworkers from the SFB succeeded in directly visualizing so-called dark moiré interlayer excitons by using time-resolved ARPES measurements combined with microscopic many-particle theory. The researchers show how the time-resolved momentum microscopy provides deepest microscopic insights into these technologically relevant questions.

These results not only provide a fundamental insight into the formation of dark moiré interlayer excitons, but also open up a new perspective to study the optoelectronic properties of these new and fascinating materials, e.g., the signature of the moiré potential and the influence of the combined properties of the two twisted semiconductor layers.

For further information, please see the press release by the university of Göttingen (in German).

Publication

D. Schmitt, J.P. Bange, W. Bennecke, A.A. Al Mutairi, G. Meneghini, K. Watanabe, T. Taniguchi, D. Steil, D.R. Luke, R.T. Weitz, S. Steil, G.S.M. Jansen, S. Brem, E. Malic, S. Hofmann, M. Reutzel, S. Mathias
Formation of moiré interlayer excitons in space and time
Nature 608 (2022) 499 DOI:10.1038/s41586-022-04977-7

Contact

Prof. Dr. Ermin Malic
Philipps-Universität Marburg
SFB 1083 project B9
Tel.: 06421 28-22640
EMAIL

In a new publication in Advanced Materials Interfaces, the groups of Gregor Witte (A2), Ulrich Koert (A8) as well as Jérôme Cornil from the University of Mons report on the formation of an internal interface dipole at a metal/2D metal/organic hetero-interface, which can be modified by the outer organic monolayer.

Schematic representation of the outer and internal interface dipoles at the FxDNTT/cesium/copper hetero-interface (Image: Maximilian Dreher, CC BY-NC-ND 4.0).

The use of organic contact layers is a versatile tool to control the work function of metal electrodes. While partial fluorination of robust organic molecules leads to a significant shift of their frontier energy levels in the isolated molecules, this effect can be wiped out for organic films adsorbed on high work function metal substrates leading to an equalization of the corresponding HOMO levels. Consequently, also the work function shift is equalized in the condensed phase, which is often referred to as HOMO (resp. LUMO) level pinning. Especially the LUMO level pinning has been reported only on a theoretical level in literature yet.

By using partially fluorinated DNTTs, which were synthesized by project A8 and exhibit such a HOMO level pinning on high work function noble metals, the group of Jérôme Cornil (Mons, Belgium) demonstrated that a LUMO level pinning also exists on low work function Cs(110) surfaces on a theoretical level. To face low work function surfaces experimentally, Maximilian Dreher and coworkers used atomically thin cesium layers that grow epitaxial on Cu(100) single crystals and provide more inert, low work function surfaces. In contrast to the expectation, this copper/cesium/organic hetero-stack reveals no LUMO pinning effect. Complementary DFT calculations demonstrate, that the contributions prevailing on the work function shift can be separated into (i) an outer interface dipole between the organic layer and the 2D cesium layer and (ii) an inner, buried interface dipole at the metal/cesium interface. While the outer interface dipole is again equalized for the different F_xDNTT species, the buried interface dipole is modulated dependent on the degree of fluorination of the molecules.

Such a sandwich hetero-interface provides new possibilities to effectively tailor contact layers between metal electrodes and active organic layers improving their energy level alignment and emphasizes the importance of internal interfaces.

Publication

M. Dreher, D. Cornil, M. W. Tripp, U. Koert, J. Cornil, G. Witte
On the Role of Collective Electrostatic Effects in Electronic Level Pinning and Work Function Changes by Molecular Adlayers: The Case of Partially Fluorinated DNTTs Adsorbed Flat-Lying on Various Metals and Hetero-Structures
Adv. Mater. Interfaces (2022) DOI:10.1002/admi.202200361

Contact

Prof. Dr. Gregor Witte
Philipps-Universität Marburg
SFB 1083 project A2
Tel.: 06421 28-21384
EMAIL

We congratulate Dr. Gerson Mette, former PI of SFB project B5, on completing his habilitation in experimental physics at the Philipps-University Marburg.

Dr. Gerson Mette studied physics at the Philipps-University Marburg and finished his PhD in the group of Prof. Höfer in 2012. After working as a postdoc at the University of Zurich for two years, he went back to Marburg and became a research associate in 2015 while simultaneously joining the SFB 1083 as a young researcher and co-PI of project B5.

With his broad background in surface science and laser spectroscopy, he has set up new SHG imaging microscopy for pump-probe experiments of van der Waals heterostructures and explored the dynamics of charge-transfer processes across interfaces of 2D materials in well-defined environments. Furthermore, he explored the influence of electronic interface states on the ultrafast charge-transfer at buried GaP/Si interfaces.

In February 2022 he gave his habilitation talk on “How big is the proton? The proton radius puzzle” and completed his habilitation in experimental physics. The members of the SFB thank Dr. Mette for his work and commitment for the SFB 1083 and wish him all the best on his future career path.