Doctoral College TU-D Unravelling advanced 2D materials
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Surface Physics (U. Diebold)

Ulrike Diebold, Institute of Applied Physics

UD is an experimental surface physicist with a research focus on metal oxides.  The main tool is Scanning Probe Microscopy (STM, and Scanning Force Microscopy, SFM). In combination with surface spectroscopic and diffraction techniques SPMs are used to unravel the geometry [1], electronic structure [2], and reactivity of surfaces at the atomic scale [3]. UHV systems in her lab are also equipped with deposition sources for molecular-beam epitaxy (MBE), and a recent extension to electrochemical STM [4].  UD’s research program is mainly focused on metal oxides [5, 6]; an important new addition to her arsenal of surface characterization techniques is Scanning Force Microscopy, which allows a direct inspection of the electron density (hence bond order) between atoms. Since 2D materials are, by their very nature, surfaces, a thorough, research-guided training in the experimental capabilities and expertise available in the Diebold lab is a central component of TU-D.

PhD Project 1: Graphene Nanoribbons on TiO2

Co-supervisor:  Dominik Eder

The interface between graphene and semiconducting metal oxides is very interesting for photocatalysis and other applications that rely on charge-separation.  From a fundamental standpoint, this interface is far from understood.  In this project we will study its atomic-scale electronic and geometric properties using local (LT STM, STS, SFM) and area-averaging probes (XPS, UPS, ELS) using an appropriate model system.  The project rests on our established expertise of working with single-crystalline TiO2 surfaces (rutile and anatase).   We will utilize the a ‘bottom-up’ method to fabricate graphene nano-ribbons, using surface-assisted reactions of halogenated organic precursor molecules.  This technique has been successfully applied to noble metal surfaces that catalyse the de-halogenation and de-hydrogenation processes, here we will utilize the photocatalytic properties of TiO2 to achieve a similar control. Fertile collaborations with the Eder group is envisioned in the synthesis part, and once the preparation procedure is established, investigations will be extended towards prototype devices (Müller).  An extension to other oxide substrates (e.g., Fe3O4, Parkinson) is also envisioned. Dominik Eder, who has has extensive experience with graphene/TiO2 interfaces,  is co-supervisor as for this project.

PhD Project 2: Two-dimensional oxide heterostructures

Co-supervisor:  Florian Libisch

The dream of a materials scientist is to manufacture tailor-made materials with specific properties. This is, in principle, possible with molecular epitaxy techniques (MBE) combined with electron diffraction (RHEED): exquisite control of the film growth with atomic-scale precision can be achieved, and any material can be built up one 2-D layer at a time. To understand the resulting, interface-dominated heterostructures, a tight control of all deposition parameters is a prerequisite. In this PhD project, a variety of complex metal oxides shall be grown and their surface properties shall be investigated in-situ with surface science techniques (STM, LEED, XPS, LEIS, etc. [7]) The emphasis is on energy materials that can be used in, e.g., solid oxide fuel and electrolysis cells, with the goal of obtaining a detailed understanding of growth processes and relating surface structure to fundamental chemical processes that underlie device functioning. Connecting with theory is an important component of this project, and Florian Libisch would be the co-supervisor.


Literature

  1. Bernhard Stöger, et al., “A strong chemical reaction of CO with the surface of Sr3Ru2O7”, Physical Review Letters 113, 116101 (2014) DOI: 10.1103/PhysRevLett.113.116101
  2. M. Setvin, et al., “A direct view of polarons in TiO2 rutile and anatase”, Physical Review Letters 113, 086402 (2014) DOI: 10.1103/PhysRevLett.113.086402
  3. Martin Setvin, et al., “Reaction of O2 with Subsurface Oxygen Vacancies on TiO2 Anatase (101)”, Science 341, 988 (2013) DoI: 10.1126/science.1239879
  4. Giulia Serrano, et al., Molecular Ordering at the Interface Between Liquid Water and TiO2 Rutile (110), Adv. Mater. Interfaces 2, 1500246 (2015) DOI: 10.1002/admi.201500246
  5. U. Diebold, “The Surface Science of Titanium Dioxide”, Surface Science Reports 48, 53 (2003) DOI: 10.1016/S0167-5729(02)00100-0
  6. M. Batzill and U. Diebold, “The Surface and Materials Science of Tin Oxide”, Progress in Surface Science 79, 47 (2005) DOI: 10.1016/j.progsurf.2005.09.002