83 82 Principal Scientist Profiles Torsten Fritz Torsten Fritz Principal Scientist Profiles PROFESSOR FOR APPLIED PHYSICS / SOLID-STATE PHYSICS INSTITUTE OF SOLID-STATE PHYSICS (IFK) Torsten Fritz studied physics and mathematics at the TU Dresden and is currently professor and chair of Applied Physics / Solid State Physics at the Institute of SolidState Physics (IFK) at the Friedrich Schiller University Jena. Currently, he is appointed as IFK‘s institute director. Since 2019 he is also Visiting Professor at the Department of Chemistry and Biochemistry at the University of Arizona at Tucson, AZ, USA. In 2015 and 2016, he was appointed as Specially Appointed Professor at the Department of Chemistry, Graduate School of Science, Osaka University, Osaka, Japan. TORSTEN FRITZ RESEARCH AREAS The surface science group of Prof. Fritz is involved in the research of organic molecules which in the form of thin films possess semiconducting properties. We specialize in the preparation and characterization of highly ordered (epitaxial) layers on singlecrystalline substrates in ultra-high vacuum, placing emphasis on the structure-property-relations. Further research topics include 2D-materials (epitaxial graphene, hexagonal boron nitride (h-BN), transition metal dichalcogenides) and organic superconductors. The diversity of complementary experimental methods (optical spectroscopy, photoelectron spectroscopy, electron diffraction, scanning probe microscopy at 1.2 K, and many more) is a key aspect of this group. TEACHING FIELDS • Solid-state physics • Advanced solid-state physics and materials science • Organic and inorganic semiconductors • Surface science RESEARCH METHODS • Low-temperature scanning probe methods at 1.2 K (STM, AFM, STS) • In-situ optical spectroscopy (Differential Reflectance Spectroscopy [DRS], PL) • All variants of photoelectron spectroscopy (ARPES, XPS, PMM, AES, XPD) • Quantitative distortion corrected electron diffraction (LEED, RHEED) • Joule-Thomson STM/AFM (specs: T control <20 K [MCPLEED, DRS] or 1.2 K [STM, AFM], H-field ~3 T, 4-probemeasurements, organic molecule crucibles, Ar sputter gun and e-beam heating, doping, QMS,) • Surface analysis system (specs: T control down to 20 K [XPS, UPS, ARUPS], monochromatic UV source, crucibles for organic molecules, Ar sputter gun and e-beam heating, doping with alkali metals and alkaline earth metals, MCP-LEED, AES, DRS, QMS) RECENT RESEARCH RESULTS • In-depth characterization of the potassium doping of PTCDA monolayers, including the direct observation of the K adsorption sites [1-3]. • First direct observation of static distortion waves (SDWs) in flexible 2D crystals of organic molecules, see Research highlight” [4]. • Study of dielectric background effect on optical transition energies of isolated molecular monomers and weakly interacting two-dimensional aggregates [5]. • Development of a full and most comprehensive classification scheme of the epitaxial types in reciprocal and real space, including both, rigid and flexible lattices [6]. • Development of a new consistent model for the interpretation of different spectroscopic results (including ARPES, IPES, 2PPE, and optical spectroscopy) which takes into account the perturbations of the different measurement processes on a molecular system [7]. STATIC DISTORTION WAVES (SDWS) IN FLEXIBLE 2D CRYSTALS OF ORGANIC MOLECULES The epitaxy of many organic films on inorganic substrates can be understood within the framework of rigid lattice epitaxy. However, there are cases where this concept fails, and tiny shifts in molecular positions away from ideal lattice points, so-called static distortion waves (SDWs), are responsible for the observed orientational epitaxy. Using LEED and STM, we were able to directly detect SDWs in organic adsorbate films. They manifest themselves as wave-like sub-Angstrom molecular shifts (on average only 0.5 Å) away from an ideal adsorbate lattice. Using a DFT-based model, we show that due to the flexibility of the adsorbate layer the resulting total energy in the domain is indeed minimal. The left part of the image shows an STM image of the static distortion waves observed for a monolayer of the organic molecule HBC on a graphite single crystal. The inset shows the sub-molecular structure of the layer. On the right, the extracted molecular shifts are shown, exaggerated by a factor of 15. From [4]. [1] Zwick et al., ACS Nano 10, 2365 (2016). [2] Baby et al., ACS Nano 11, 10495 (2017). [3] Zwick et al., Phys. Rev. Materials 3, 085604 (2019). [4] Meissner et al., ACS Nano 10, 6474 (2016). [5] Forker et al., Phys. Rev. B 93, 165426 (2016). [6] Forker et al., Soft Matter 13, 1748 (2017). [7] Kirchhuebel et al., Phys. Chem. Chem. Phys. 21, 12730 (2019). Contact: Phone: + 49 3641 9-47400 Email: torsten.fritz@uni-jena.de
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