Last News Items
- Probing electron-hole Coulomb correlations in the exciton landscape of a twisted semiconductor heterostructure – Publication by B9 (Malic) in Science Advances7. February 2024 - 12:00
- Heteroepitaxy in Organic/TMD Hybrids and Challenge to Achieve it for TMD Monolayers: The Case of Pentacene on WS2 and WSe2 – Publication by A2 and B58. January 2024 - 10:06
- Layer-by-layer deposition of organic molecules controlled by selective click reactions – Publication by A8 (Koert/Dürr) in Chemistry of Materials 23. December 2023 - 14:48
- Enhanced Circular Dichroism and Polarized Emission in an Achiral, Low Band Gap Bismuth Iodide Perovskite Derivative5. October 2023 - 11:25
- 34. Erfinderlabor: Scientific curiosity of the next Generation1. August 2023 - 14:34
- Measuring spatially-resolved potential drops at semiconductor hetero-interfaces using 4D-STEM– Publication by A5 (Volz) in Small Methods28. May 2023 - 14:07
- Interface engineering of charge-transfer excitons in 2D lateral heterostructures – Publication by B9 (Malic) in Nature Communications9. May 2023 - 09:27
- Electrical control of hybrid exciton transport in a van-der-Waals heterostructure – Publication by B9 (Malic) in Nature Photonics20. April 2023 - 09:46
- When electrons dress up in light – Publication by B11 (Güdde/Höfer) in Nature12. April 2023 - 16:21
- 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
Search news items
In a joint study including the experimental group of Stefan Mathias from the University of Göttingen and the theoretical group of Ermin Malic the ultrafast charge transfer in twisted van der Waals heterostructures was studied.
In two-dimensional semiconductors, cooperative and correlated interactions determine the material’s excitonic properties and can even lead to the creation of correlated states of matter.
In a joint experiment theory study, the research groups of Stefan Mathias (Göttingen) and Ermin Malic (Marburg) have studied the ultrafast charge transfer in twisted van der Waals heterostructures. The researchers found that the transfer of an excitons hole across a type II band-aligned heterostructure leads to an unexpected sub-200-femtosecond upshift of the single-particle energy of the electron being photoemitted from the two-particle exciton state. While energy relaxation usually leads to an energetic downshift of the spectroscopic signature, is was shown that this upshift is a clear fingerprint of the correlated interaction of the electron and hole parts of the exciton.
In this way, time-resolved photoelectron spectroscopy is straightforwardly established as a powerful method to access electron-hole correlations and cooperative behavior in quantum materials. The joint work highlights this capability and motivates the future study of optically inaccessible correlated excitonic and electronic states of matter.
J.P. Bange, D. Schmitt, W. Bennecke, G. Meneghini, A.A. Al Mutairi, K. Watanabe, T. Taniguchi, D. Steil, S. Steil, R.T. Weitz, G.S.M. Jansen, S. Hofmann, S. Brem, E. Malic, M. Reutzel, S. Mathias
Probing electron-hole Coulomb correlations in the exciton landscape of a twisted semiconductor heterostructure
Sci. Adv. 10 (2024) eadi1323 DOI:10.1126/sciadv.adi1323
Prof. Dr. Ermin Malic
SFB 1083 project B9
Tel.: 06421 28-22640
In their study published in ACS Applied Materials & Interfaces, Darius Günder, Marleen Axt and Gregor Witte reveal an epitaxial alignment of organic films on crystalline TMD substrates and demonstrate strategies for achieving this intrinsic van der Waals epitaxy, which is very sensitive to surface defects of the underlying 2D material, also for exfoliated monolayers.
The intriguing photophysical properties of monolayer stacks of different transition-metal dichalcogenides (TMDs) have recently prompted an extension of similar investigations on the interfacial excitonic coupling to hybrid systems of TMDs and organic films, as the latter combine large photoabsorption cross-section with the ability to tailor energy levels by targeted synthesis. In order to achieve such an excitonic coupling in momentum space a defined azimuthal alignment of the molecular adsorbate is crucial, which occurs on highly defined 2D material surfaces. However, this intrinsic van der Waals epitaxy of crystalline organic films cannot be automatically transferred to every 2D material surface because surface defects caused by exfoliation and transfer can result in significantly different film structures without any epitaxial order.
In this combined study of projects A2 and B5, Darius Günder et al. used X-ray diffraction, optical polarization, and atomic force microscopy to resolve the epitaxial alignment of crystalline pentacene (PEN) films grown at the basal plane of WS2 and WSe2 samples. While (022)-oriented PEN films with recumbent molecular orientation are formed on both studied TMDs, the azimuthal orientation of the long molecular axis is quite different. Moreover, it is shown that this intrinsic epitaxial growth of PEN films depends sensitively on the TMD surface quality. While it occurs on exfoliated TMD single crystals and multilayer flakes, it is hardly found on exfoliated and transferred monolayers, which often exhibit bubbles and wrinkles. This enhances the surface roughness and results in (001)-oriented PEN films with upright molecular orientation but without any azimuthal alignment. However, monolayer flakes can be smoothed by AFM operated in contact mode or by transferring TMD monolayers to ultrasmooth substrates such as hBN, which again yields epitaxial PEN films, but with significantly smaller domains than on TMD single crystals.
The presently demonstrated existence of epitaxial crystalline organic adlayers on TMDs paves the way for future investigations of interface or moiré excitons in such hybrid systems and also highlights the challenges in fabricating organic/TMD hybrid systems with well-defined interfaces.
D. Günder, M. Axt, G. Witte
Heteroepitaxy in Organic/TMD Hybrids and Challenge to Achieve it for TMD Monolayers: The Case of Pentacene on WS2 and WSe2
ACS Appl. Mater. Interfaces (2023) DOI:doi.org/10.1021/acsami.3c15829
Prof. Dr. Gregor Witte
SFB 1083 project A2
Tel.: 06421 28-21384
In a joint effort, the research groups led by Ulrich Koert and Michael Dürr realized the controlled layer-by-layer synthesis of organic molecular structures on silicon.
The application of molecular layer deposition on silicon surfaces may open the route to directly synthesizing organic molecular architectures with tailored physical and/or physicochemical properties on the technologically most relevant silicon substrates (“more than Moore”).
In their most recent publication, the researchers from A8 show how to use a combination of two selective and orthogonal click reactions (Cu-mediated and strain promoted azide-alkyne couplings) for such a controlled layer-by-layer growth of organic architectures on Si(001). Starting point was the Si(001) substrate, which was selectively functionalized with a substituted cyclooctyne under ultrahigh-vacuum (UHV) conditions. The subsequent layer-by-layer synthesis using the two orthogonal click chemistry reaction steps was then performed in solution in an alternating fashion. The product of each reaction step was analyzed in UHV by means of X-ray photoelectron spectroscopy; controlled layer-by-layer growth up to 11 molecular layers was realized and monitored in this way.
Together with previous studies of the researchers from A8 (Koert/Dürr), B5 (Höfer/Mette) and A6 (Tonner) on selective functionalization of the Si(001) surface and the combination of UHV-based surface chemistry with solution-based click chemistry, a complete toolbox for the well-controlled growth of molecular structures on silicon is now available.
T. Glaser, J.A. Peters, D. Scharf, U. Koert, M. Dürr
Layer-by-Layer Deposition of Organic Molecules Controlled by Selective Click Reactions
Chem. Mater. 36 (2024) 561 DOI:10.1021/acs.chemmater.3c02707
Prof. Dr. Ulrich Koert
SFB 1083 project A8
Tel.: 06421 28-26970
Prof. Dr. Michael Dürr
SFB 1083 project A8
Tel.: 0641 99-33490
Johanna Heine (A15) and Sangam Chatterjee (B2) successfully prepared a novel iodido bismuthate that shows strong optical activity despite being achiral
Lead halide perovskites and related main group halogenido metalates offer unique semiconductor properties and diverse applications in photovoltaics, solid-state lighting, and photocatalysis. Recent advances in incorporating chiral organic cations have led to the emergence of chiral metal-halide semiconductors with intriguing properties such as chiroptical activity and chirality-induced spin selectivity. This enables the generation and detection of circularly polarized light and spin-polarized electrons for applications in spintronics and quantum information, fields that use the spin of electrons or photons to store and process data.
However, understanding the structural origin of chiroptical activity remains challenging due to macroscopic factors and experimental limitations. In general, chiroptical activity originates in the crystal symmetry of the solid state. However, the compound does not need to be chiral to exhibit chiroptical activity. Some non-centrosymmetric crystal classes are sufficient as well – a fact that is often overlooked in current research.
The groups of Dr. Heine (A15) and Prof. Chatterjee (B2) present a novel achiral perovskite derivative [Cu2(pyz)3(MeCN)2][Bi3I11] (pyz = pyrazine; MeCN = acetonitrile), that exhibits remarkable circular dichroism. Notably, single crystals display linear and circular optical activity as well as a significant degree of circularly polarized photoluminescence. The magnitude of these effects on par or even larger than what can be achieved by incorporating chiral organic molecules into perovskites. These findings provide insights into the macroscopic origin of circular dichroism and offer design guidelines for developing materials with high chiroptical activity without expensive chiral building blocks.
J. Möbs, P. Klement, G. Stuhrmann, L. Gümbel, M. Müller, S. Chatterjee, J. Heine
Enhanced Circular Dichroism and Polarized Emission in an Achiral, Low Band Gap Bismuth Iodide Perovskite Derivative
J. Am. Chem. Soc. 145 (2023) 23478 DOI:10.1021/jacs.3c06141
Dr. Johanna Heine
SFB 1083 project A15
Tel.: 06421 28-25482
Hessen’s young MINT scientists conduct research on hydrogen and renewable energies within the SFB 1083 and Philipps University Marburg
The 34th Inventors’ Lab (Erfinderlabor) of the Center for Chemistry (Zentrum für Chemie, ZFC) has successfully entered its finale. This year’s event was once again organized by the ZFC in cooperation with the Philipps University of Marburg and Elkamet and supported by other renowned cooperation partners such as the SFB 1083.
The practice-oriented workshop not only offers valuable career orientation on career opportunities in the MINT environment (mathematics, informatics, natural sciences and technology), but also always addresses a current topic of high socio-political and economic relevance. The focus of this years Inventors’ Lab was on renewable energies and hydrogen.
The sixteen students in four teams dealt with different issues in the context of the energy transition in different research groups, which are part of the SFB 1083. The topics were novel crystalline materials for the use of surface structures as energy converters, the functioning of batteries and the basics of laser spectroscopy as well as the self-construction of a spectrometer. Finally, the storage of hydrogen in metal hydrides was investigated.
The experts were impressed by the technical curiosity and quick comprehension, but also by the motivation and team spirit of the young people. “Here, a highly complex topic was explained precisely,” said Prof. Dr. Gregor Witte from the SFB during the virtual closing event.
The local project partner was the Chemikum Marburg represented by Dr. Christof Wegscheid-Gerlach. “The Inventors’ Lab exemplifies how scientific topics of the future can be communicated at the intersection of school and university, and thus how both levels of education can be interlinked.”
Dr. Christof Wegscheid-Gerlach
SFB 1083 project Oe
Tel.: 06421 28-25843
The team of project A5 of the SFB successfully measured the potential drop across a hetero interface using four-dimensional scanning transmission electron microscopy
Characterizing long-range electric fields and built-in potentials in functional materials at nano to micrometer scales is of supreme importance for optimizing devices. For example, the functionality of semiconductor heterostructures or battery materials is determined by the electric fields established at interfaces, which can also vary spatially. In this study, we propose momentum-resolved four-dimensional scanning transmission electron microscopy (4D-STEM) for the quantification of these potentials. So far, dynamic effects have inhibited the quantitative evaluation of fields at heterointerfaces. The scientists in SFB project A5 carefully adopted their experimental setup to overcome these challenges and for the first time quantitatively measured the potential drop across a GaAs/AlAs interface.
In detail, a precession electron diffraction (PED) system was introduced, which rocks the impinging electron beam at a rate of 1 kHz, while scanning across the sample. This significantly reduces the impact of dynamic effects in the 4D data. In turn, an energy filter minimizes the influence of inelastic scattering.
Using the method proposed, allows the quantification of intentional or parasitic electric fields even in the presence of heterointerfaces. Accordingly, the characterization of real-life devices, like solar cells or battery materials, which often involve a multitude of such internal interfaces, becomes feasibly to optimize their performance.
V. Chejarla, S. Ahmed, J. Belz, J. Scheunert, A. Beyer, K. Volz
Measuring spatially-resolved potential drops at semiconductor hetero-interfaces using 4D-STEM
Small Methods (2023) 2300453 DOI:10.1002/smtd.202300453
Prof. Dr. Kerstin Volz
SFB 1083 project A5, A14, B13
Tel.: 06421 28-22297
In a joined publication, the groups of Ermin Malic, Bernhard Urbaszek and Andrey Turchanin explained the behavior of quasiparticles in composite semiconductor nanosheets
The presence of bound charge transfer (CT) excitons at the interface of monolayer lateral heterojunctions has been a topic of debate in the literature. However, unlike interlayer excitons in vertical heterostructures, their confirmation through observation is still pending.
In this work, a microscopic study investigating signatures of bound CT excitons in photoluminescence spectra at the interface of hBN-encapsulated lateral MoSe2-WSe2 heterostructures is presented. The fully microscopic and material-specific theory illustrates the many-particle processes behind the formation of CT excitons and details their potential manipulation through interface- and dielectric engineering. For junction widths smaller than the Coulomb-induced Bohr radius the appearance of a low-energy CT exciton is predicted. This theory is further compared with experimental low-temperature photoluminescence measurements showing emission in the bound CT excitons energy range. It is observed that CT excitons in hBN-encapsulated heterostructures possess small binding energies of just a few tens meV while exhibiting significant dipole moments. These properties make them ideal materials for optoelectronics applications that take advantage of efficient exciton dissociation and fast dipole-driven exciton propagation.
The joint theory-experiment study presents a significant step towards a microscopic understanding of optical properties of technologically promising 2D lateral heterostructures.
– Press release of the university of Marburg (in German).
R. Rosati, I. Paradisanos, L. Huang, Z. Gan, A. George, K. Watanabe, T. Taniguchi, L. Lombez, P. Renucci, A. Turchanin, B. Urbaszek, E. Malic
Interface engineering of charge-transfer excitons in 2D lateral heterostructures
Nat Commun 14 (2023) 2438 DOI:10.1038/s41467-023-37889-9
Prof. Dr. Ermin Malic
SFB 1083 project B9
Tel.: 06421 28-22640
A research team including the experimental group of Andras Kis from the EPFL and the theoretical group of Ermin Malic demonstrated electrical control of the hybrid exciton transport in 2D material heterostructures.
Interactions between out-of-plane dipoles in bosonic gases enable the long-range propagation of excitons. However, the lack of direct control over collective dipolar properties has hitherto limited the degrees of tunability and the microscopic understanding of exciton transport.
In this work, the authors modulated the layer hybridization and interplay between many-body interactions of excitons in a van-der-Waals heterostructure with an applied vertical electric field. By performing spatiotemporally resolved measurements supported by microscopic theory, the dipole-dependent properties and transport of excitons with different degrees of hybridization were characterized. Moreover, it was found that constant emission quantum yields of the transporting species as a function of excitation power with dominating radiative decay mechanisms over nonradiative ones, a fundamental requirement for efficient excitonic devices.
The findings provide a complete picture of the many-body effects in the transport of dilute exciton gases and have crucial implications for the study of emerging states of matter, such as Bose-Einstein condensation, as well as for optoelectronic applications based on exciton propagation.
F. Tagarelli, E. Lopriore, D. Erkensten, R. Perea-Causín, S. Brem, J. Hagel, Z. Sun, G. Pasquale, K. Watanabe, T. Taniguchi, E. Malic, A. Kis
Electrical control of hybrid exciton transport in a van der Waals heterostructure
Nat. Photon. (2023) DOI:10.1038/s41566-023-01198-w
Prof. Dr. Ermin Malic
SFB 1083 project B9
Tel.: 06421 28-22640
Suguru Ito, Jens Güdde and Ulrich Höfer, together with the group of Rupert Huber in Regensburg and physicists from across Europe, observed the ultrafast birth, rise, and collapse of a Floquet-Bloch band structure.
New material properties, at lightning speed and on demand – this vision moves a step closer thanks to the team’s findings. They used time- and angle-resolved photoemission spectroscopy to study the electrons in the Dirac surface state of the topological insulator Bi2Te3 that were previously shown to be effectively protected from scattering [Reimann et al., Nature 562, 396 (2018)]. By employing intense 25 THz light pulses, Ito and coworkers could drive these electrons back and forth periodically and watch how hybrid states between electrons and light, known as Floquet states or Floquet-Bloch bands, form at electric field strengths of ~ 1 MV/cm.
In Floquet states, the electrons don’t have just one fixed energy, but many energy states evenly spaced apart by the driving photon energies. The original eigenstate of the electron surrounds itself as if it was dressed with several envelopes of light. In terms of the dynamics of these exotic states, the team’s measurements went far beyond the limit of what could be achieved to date. They managed to take actual videos of the moving electrons with a time resolution better than a single oscillation cycle of the electromagnetic carrier wave of light. As a result, they made an unforeseen discovery, namely that Floquet-Bloch bands form already after a single optical cycle. This surprising finding paves the way to tailored quantum functionalities and ultrafast electronics. It is supported by theoretical modeling contributed by Michael Schüler of the Paul Scherrer Institute in Villigen, Switzerland, and Michael Sentef of the Max Planck Institute for Structure and Dynamics of Matter in Hamburg.
Having established the fundamental time limit for light-induced material engineering, the breakthrough discovery of Ito and coworkers could lead to a new age of physics, enabling the creation of new functionalities on demand. Following this avenue, Ulrich Höfer, Rupert Huber, Peter Puschnig (Graz), and Stefan Tautz (Jülich) were recently jointly awarded an ERC Synergy Grant from the European Research Council for their “Orbital Cinema” research project. This project aims to take slow-motion videos of electronic motion in quantum mechanical orbitals of adsorbed molecules and to push the research of SFB 1083 on organic/solid interfaces into the high-field regime.
– Joint Press release of the Universities of Marburg and Regensburg (in German).
– Press release of the Max Planck Institute for Structure and Dynamics of Matter in Hamburg (in English).
– Homepage of the Huber Group in Regensburg.
– News & Views Article by David Abergel (Chief Editor, Nature Physics).
S. Ito, M. Schüler, M. Meierhofer, S. Schlauderer, J. Freudenstein, J. Reimann, D. Afanasiev, K.A. Kokh, O.E. Tereshchenko, J. Güdde, M.A. Sentef, U. Höfer, R. Huber
Build-up and dephasing of Floquet–Bloch bands on subcycle timescales
Nature (2023) DOI:10.1038/s41586-023-05850-x
Prof. Dr. Ulrich Höfer
SFB 1083 project B6, B11
Tel.: 06421 28-
In a new publication in Nature Communications, the groups of Gregor Witte (A2) and Ulrich Koert (A8) introduce a new concept that allows to control the mesoscopic shape of 2D molecular islands grown on weakly interacting substrates like MoS2 without affecting their nanoscopic packing motif.
Hybrid heterostructures of transition metal dichalcogenides (TMDCs) and molecular materials combine the excellent charge carrier transport properties of TMDCs with the possibility to tailor optoelectronic properties of organic semiconductors. Since molecular materials often decompose upon exposure to radiation, lithographic patterning techniques established for inorganic materials are usually not applicable for the fabrication of organic nanostructures. Compared to metallic substrates, where molecule-substrate interactions dominate the mutual intermolecular interactions, the latter becomes decisive for adlayers grown on weakly interacting substrates such as TMDCs. This fact can be used to employ electrostatic Coulomb interactions between specifically designed, partially fluorinated pentacene derivatives to tailor the intermolecular interactions.
Using scanning tunneling microscopy, Maximilian Dreher and Pierre Dombrowski found that while the anisotropic attractive Coulomb forces between partially fluorinated pentacenes determine the molecular packing motif, distinctly elongated nanosheets are formed at submonolayer coverage, where the direction of elongation is different between directly grown nanosheets and those prepared by partial desorption of a complete molecular monolayer. Using kinetic Monte Carlo (MC) simulations, it could be shown that the nanosheet formation is not driven by an energy minimization of the intermolecular interactions. Instead, the sheet shape is determined by the evolution of individual molecules either attaching to or detaching from the nanosheets. Further MC simulations demonstrate statistically, that their formation is determined i) by the geometrical anisotropy of the intermolecular interactions and ii) by the kinetics during growth and desorption. By comparison of the behavior of differently fluorinated molecules, both experimentally and computationally, important design rules for molecules could be derived.
M. Dreher, P.M. Dombrowski, M.W. Tripp, N. Münster, U. Koert, G. Witte
Shape control in 2D molecular nanosheets by tuning anisotropic intermolecular interactions and assembly kinetics
Nat. Comm. 14 (2023) 1554 DOI:10.1038/s41467-023-37203-7
Prof. Dr. Gregor Witte
SFB 1083 project A2
Tel.: 06421 28-21384