Topological Stone–Wales Defects Enhance Bonding and Electronic Coupling at the Graphene/Metal Interface – Publication by A4 (Gottfried) and A6 (Tonner) in ACS Nano

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Benedikt Klein and coworkers of SFB 1083, together with external collaborators, have gained new insight into interfacial interactions of Stone-Wales graphene defects by using molecular models.

Graphene is an astonishing two-dimensional material with diverse and technologically important properties. However, these properties are heavily dependent on topological defects, which have a direct impact on the graphene/metal interface. A common defect is the Stone-Wales (SW) defect, consisting of two five- and two seven-membered rings resulting in a non-alternating bonding situation.  Researchers of the SFB 1083 projects A4 (Gottfried) and A6 (Tonner) investigated the interface between a SW defect and a metal by mimicking the defect with the molecule azupyrene. Pyrene was used as a model for defect-free graphene of the same size as azupyrene. The experiments were complemented by extensive modelling of the graphene-embedded defects.

Figure: Graphene/metal interface with typical topological defect. The local interaction of a topological S–W graphene defect with a metal surface is mimicked by azupyrene, which allow the application of a wide range of experimental techniques. Copyright 2022 American Chemical Society.

In the present work, it was shown by a multi-technique approach (XPS/UPS, NIXSW, NEXAFS, TPD, LT-AFM, DFT) that the embedded defects, modelled by azupyrene, undergo enhanced bonding and electron transfer with a Cu(111) surface. This indicated by increased bond energies of 68 kJ/mol, by 0.9 Å reduced bond distances and enhanced charge transfer. The consistent experimental results were corroborated by DFT calculations.

The defect-induced enhanced electronic coupling at the graphene/metal interface is expected to have significant impact on the performance of (opto-)electronics, e.g., by increasing charge injection rates. Tailoring the topological structure of graphene layer may result in the development of new or imprived devices.

Publication

B.P. Klein, A. Ihle, S.R. Kachel, L. Ruppenthal, S.J. Hall, L. Sattler, S.M. Weber, J. Herritsch, A. Jaegermann, D. Ebeling, R.J. Maurer, G. Hilt, R. Tonner-Zech, A. Schirmeisen, J.M. Gottfried
Topological Stone–Wales Defects Enhance Bonding and Electronic Coupling at the Graphene/Metal Interface
ACS Nano (2022) DOI:10.1021/acsnano.2c01952

Contact

Prof. Dr. J. Michael Gottfried
Philipps-Universität Marburg
SFB 1083 project A4
Tel.: 06421 28-22541
EMAIL

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 – Publication by A2 (Witte) and A8 (Koert)

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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 FxDNTT 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

German Science and Humanities Council recommends research building for materials sciences

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A research building together with a modern transmission electron microscope will be established on the Lahnberge campus of Philipps-University Marburg

Dr. Andreas Beyer, a researcher in SFB 1083, operates a Transmission Electron Microscope, which provides important insights in the development of new materials.

On the Lahnberge Campus, a new research building for a transmission electron microscope for the investigation of novel materials will be established. The German Science and Humanities Council gave its recommendation for the project, which is called ATEMMA (Advanced Transmission Electron Microscopy, Marburg). ATEMMA comprises a volume of 10 Mio €. This is divided into 4 Mio € for the building itself as well as 6 Mio € for the new (S)TEM.

ATEMMA strengthens the focus on material sciences and especially on interfaces at the Philipps-University Marburg and paves the way for high-quality research, e.g., on new materials used for communication and energy technologies, as these represent extremely important topics in our today’s society. The new research lab combines structural characterization with the development of new methods. This combination will boost the research on novel materials also with respect to device applications.

ATEMMA will be used jointly by different groups from physics, chemistry and material sciences distributed over the Philipps-University Marburg as well as Justus-Liebig-University Giessen and the Forschungscampus Mittelhessen. Several of the groups are also part of the SFB 1083, highlighting the importance of interface-related research for ATEMMA.

For further information, please see the press release by the Philipps-Universität Marburg (in German).

Update (12.07.2022): ATEMMA was now officially granted and is scheduled to go into operation in 2026. Again, please see the press release by the Philipps-Universität Marburg for further infromation (in German).

Contact

Prof. Dr. Kerstin Volz
Department of Physics and Materials Science Center
Philipps-Universität Marburg
Tel.: 06421 28-22297
EMAIL