Ultra-thin Transition Metal Telluride Films: Growth and Structure

• Applicant: Professor Dr. M. Alexander Schneider
• Subject Area: Experimental Condensed Matter Physics ; Solid State and Surface Chemistry, Material Synthesis ; Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 497265814

Transition metal chalcogenides are fascinating materials, not only of interest to fundamental research in condensed matter physics due to the occurrence of a non-trivial topological nature of their band structures, but furthermore, they find application as thermoelectrics, phase-change materials, sensors, and thin-film solar cell. Especially new phenomena arising in single or few layers thick crystalline materials are at the focus of current research.This projects aims to grow by physical vapor deposition (PVD) single-layer transition metal telluride films on metal substrates and graphene and to determine their crystallographic structure. Unlike exfoliation techniques by which single layers of a crystal are mechanically transferred to a substrate, PVD growth allows large area coverage as required for device production. However, very fundamental questions have still to be addressed: upon Te deposition the substrate very often reacts with structural modifications that define not only the interface to the growing film but may also lead to new telluride phases that have no counterpart in bulk. In the project we want to reveal the crystallographic structure and the basic electronic properties of telluride films at the single-layer limit grown in ultra-high vacuum on a range of metallic substrates and on graphene. Further, we want to explore the dependence on process parameters like growth and annealing temperature, etc. which is needed for an atomic scale control of the growth process. We will finally transfer and apply this insight obtained to the PVD growth of telluride heterostructures. Finally, the basic electronic properties like whether the material is metallic or semiconducting and the work function will be determined. In the proposed project we concentrate on group-4 (Ti and Hf) and group-10 (Ni, Pd and Pt) tellurides. Apart from representing substances with a range of topological properties, some of these tellurides have more than one known bulk phase and hence, they offer a possibility for structural tuning by PVD growth parameters. Growth on a range of noble metal surfaces and on graphene on Ni(111) is investigated. As analytical tools quantitative low-energy electron diffraction intensity analysis (LEED-IV), Auger and X-ray electron spectroscopy, scanning tunneling microscopy and spectroscopy (STM/STS), and density functional theory (DFT) are employed. The combination of experimental and theoretical tools will result in a reliable data base concerning growth, crystallographic structure, and properties of single-layer telluride films and their interface to different substrates. Based on the obtained data, experimental and theoretical analyses going beyond those of this project, e.g. the tunability of structures and interfaces, doping and intercalation, may be carried out.

• DFG Programme: Research Grants