Dr Thomas Walther
CPhys, PhD, Dipl-Phys
School of Electrical and Electronic Engineering
Reader in Advanced Electron Microscopy
Full contact details
School of Electrical and Electronic Engineering
- Profile
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I received my undergraduate degree in physics from RWTH Aachen in 1993 and my PhD in materials science from the University of Cambridge in 1996/97.
I was a postdoc at CEA Grenoble, Université d’Aix-Marseille (both in France) and University of Bonn (in Germany) where I later became assistant professor in the chemistry department.
After a short spell at a new research centre where I sat up an electron microscopy lab in the same city, I joined the University of Sheffield as Senior Lecturer in 2006 and was promoted to a readership in 2010.
My research focuses on electron microscopy as a fundamental tool to measure chemical changes at the interfaces between different materials with atomic resolution. This can produce fantastic images that directly show where the atoms are located!
My research is relevant for understanding epitaxial growth processes as well as degradation and failure of semiconductor devices, such as transistors, light-emitting diodes, lasers and solar cells: atoms can sometimes move to lattice positions where they should not be, their agglomeration producing extended lattice defects called dislocations that can multiply and finally lead to device failure.
These studies bridge the gap from fundamental science to applied engineering.
My research involves aspects of electron optics, solid state physics and inorganic chemistry as it combines different experimental methods of high-resolution analytical electron microscopy, based on inelastic electron scattering and X-ray photon generation, with detailed modelling of atomic movements in solids.
Presently, this methodology is expanded into materials for energy conversion and storage, such as electrodes in batteries.
- Research interests
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- Method development for analytical transmission electron microscopy, including energy-dispersive X-ray and electron energy-loss spectroscopy
- Diffusion and segregation measurements in semiconductor nano-structures
- Lattice defects in quantum dots, nano-wires and quantum wells
- Characterization of doping, surface treatments, metal layers for plasmonics and oxides for energy storage applications
- Microstructural characterization of prototype electronic devices, such as photodiodes, field-effect transistors, quantum well, quantum dot or quantum cascade lasers, photovoltaic cells
- Publications
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Journal articles
- Thermodynamics of stacking faults in GaAs-based system revealed by in-situ heating in TEM. Applied Surface Science, 719, 165072-165072.
- Disorder-induced electron localization and electronic states coupling in nitride semiconductors. Applied Physics Letters, 127(25).
- Recent developments in transmission electron microscopy for crystallographic characterization of strained semiconductor heterostructures. Crystals, 15(2). View this article in WRRO
- Transmission electron microscopy of epitaxial semiconductor materials and devices. Journal of Physics D: Applied Physics, 58(4). View this article in WRRO
- Recent improvements in quantification of energy-dispersive X-ray spectra and maps in electron microscopy of semiconductors. Applied Research, 3(6). View this article in WRRO
- Preface to the special issue on microscopy of semiconducting materials 2023. Journal of Microscopy, 293(3), 135-137. View this article in WRRO
- Towards quantification of doping in gallium arsenide nanostructures by low-energy scanning electron microscopy and conductive atomic force microscopy. Journal of Microscopy, 293(3), 160-168. View this article in WRRO
- The evolution of indium precipitation in gallium focused ion beam prepared samples of InGaAs/InAlAs quantum wells under electron beam irradiation. Journal of Microscopy, 293(3), 169-176. View this article in WRRO
- Clustering in gallium ion beam sputtered compound materials driven by bond strength and interstitial/vacancy reaction. Applied Physics Letters, 123(10). View this article in WRRO
- Chemical structure comparison via scanning electron microscopy of spent commercial nickel–metal hydride batteries. Materials, 16(17). View this article in WRRO
- Determining bismuth content in GaAsBi alloys by energy-dispersive X-ray spectroscopy: a case study with multiple sets of k*-factors for analytical transmission electron microscopy. Journal of Microscopy.
- Characterization of Iron Oxide Nanoparticles Inside the Myxococcus xanthus Encapsulin. Nanomaterials, 15(23), 1793-1793.
- Comparison of different X‐ray‐based scanning electron microscopy methods to detect sub‐nanometre ultra‐thin InAs layers deposited on top of GaAs. Journal of Microscopy.
- Thermodynamics of stacking faults in GaAs-based system revealed by in-situ heating in TEM. Applied Surface Science, 719, 165072-165072.
- Teaching activities
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- EEE345 - Engineering Electromagnetics
- EEE6212 - Semiconductor Materials
- EEE6216 - Energy Efficient Semiconductor Devices
- Professional activities and memberships
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- Fellow - RMS, IoP
- Member EM Section Committee of RMS
- Member of Editorial Board, Journal of Microscopy
- Member of Editorial Board, Journal of Spectroscopy
- Member of Editorial Board, Electronics
- Responsible for installing two aberration corrected electron microscopy facilities, in Bonn (2004-06) and in Sheffield (2009-11).