Christopher Castleton

Christopher Castleton

Lecturer/Senior Lecturer

School of Science & Technology

Staff Group(s)
Physics and Mathematics

Role

Dr Castleton is Year Tutor for Year Two Physics, and Module Leader for the undergraduate modules:

  • Fundamental Forces (PHYS22123), specifically gravity, electromagnetism and particle physics
  • Digital Techniques (PHYS22513) for which he teaches image processing
  • MSc level - Materials and Security Imaging (PHYS42532), where amongst other things he leads case studies on the applications of various advanced imaging techniques.

He also conducts research in computational materials physics and supervises postgraduate students.

Career overview

After completing his undergraduate and doctoral degrees at the Universities of Bristol and Birmingham, Dr Castleton spent time as a Postdoctoral Researcher at University of Sheffield, UK, Universite Paris-Sud, France, the European Synchrotron Radiation Facility (ESRF), France, and at Uppsala and Mid-Sweden Universities, Sweden.

He also delivered lecture courses at University of Sheffield, UK, and Delhi University, India, and spent several further years as a researcher at Linköping and Uppsala Universities, Sweden before coming to NTU in 2008.

Research areas

Dr Castleton's area of interest is computational condensed matter physics, particularly the use of electronic structure calculations to study defects, surfaces, nanoclusters and interfaces involving metal oxides and semiconductors.

A great many of the key properties of semiconductors, oxides and other insulators are due to point defects (mistakes in the ordered structure of atoms within crystalline materials), both native and impurity related. The computational study of these has exploded in recent years, as improvements to algorithms and computer resources have made realistic atomic level quantum mechanical simulations increasingly viable and increasingly accurate. These types of calculations can then provide important insights into the materials needed for new technologies, from solar cells to fuel cells and hydrogen storage, to catalysis and gas sensing, to optoelectronics and data storage.

His own particular activities in recent years have been focused on supercell based Density Functional Theory (DFT) studies of defects in III-V semiconductors, and in various metal / metal oxide systems, particularly involving cerium dioxide.

Opportunities to carry put postgraduate research towards an MPhil / PhD exist in the areas identified above. Further information may be obtained from the NTU Graduate School.

External activity

  • Member of the Institute of Physics
  • Assisted in the examination of PhD students at Uppsala University, Sweeden and at Helsinki University of Technology, Finland.

Sponsors and collaborators

Current External Collaborations

  • Prof. Kersti Hermansson, Uppsala University, Sweden
  • Dr. Susanne Mirbt, Uppsala University, Sweden
  • Dr. Zhansheng Lu, Hennan University, China

Dr Castleton has previously received funding from Richert's Foundation, Sweden.

Current & recent projects

  • Vacancies and Polarons in Cerium Dioxide (aka ceria). This material is a key component of the catalytic converters used to clean up car exhaust gases, and can also be used in other catalytic systems, and as a solid electrolyte in fuel cells and gas sensors. One particularly important defect in ceria is the oxygen vacancy. These are easy to add and remove, allowing the material to be used as a rapid oxygen storage/release material. Together with collaborators, Dr Castleton's recent studies have involved the structure and properties of these vacancies, both in bulk material and on the surface. Another unusual property of ceria is that electrons added for, say, electrical conduction, become localized (self trapped) on individual cerium ions, forming polarons. We are currently examining the behaviour of both polarons and vacancies, in particular their transport properties, and their potential appearance under atomic resolution scanning tunnelling microscopy (STM).
  • Properties of III-V Semiconductors. These are the optoelectronic workhorses of the telecommunications industry, providing, for example, lasers and detectors for fibreoptic cable networks. Recent studies here have examined at the properties of both native defects and dopants in various III-Vs, looking, amongst other things, at the mobility of Zn dopants (which can limit device performance, lifetime and cost), the relative stability of bulk and surface defects, and at the appearance of vacancies and hydrogen contaminants under STM. We have also studies the ways in which the composition of III-V semiconductor alloys influences, and may perhaps be used to tune, defect stabilities, and hence dopant solubilities.
  • Methodology. Several recent studies here have focused on estimating and controlling the errors that may results from the use of DFT with the supercell approximation. This includes looking at the effect of system size and boundary conditions, and analysing the performance of various approximate DFT functionals for the materials under consideration.

Publications

Selected publications

For full list click 'Go to Christopher Castleton's publications' link above.

See all of Christopher WM Castleton's publications...