Department of Materials Science & Metallurgy

Alexander Eggeman

Alex Eggeman

Royal Society University Research Fellow

MEng. (MatSci) University of Oxford
DPhil. University of Oxford

+44 (0)1223 760748
ase25@cam.ac.uk
www-hrem.msm.cam.ac.uk

Electron diffraction, nanoscale structure and dynamics

My research in the electron microscopy group is based on the application of electron diffraction techniques to study the structure materials [1]. Electron diffraction in the TEM offers nanometre spatial resolution and is sensitive to small changes in structure, making it an ideal tool for researching modern materials. My main research interests can be broadly catagorised as:

Electron crystallography of disordered materials

While crystallography typically focuses on the periodic structure of atomic lattices, when this long-range order is disrupted information about the form of the disorder is still encoded in diffraction data. Extracting such information can be more difficult than for ordered crystals, primarily because simulating the scattering from disordered materials requires much larger atomic arrays to be considered. Through parallel-computing techniques based on GPU technologies [2] I have been able to simulate the diffraction from disorder in organic semiconductors (in collaboration with researchers at the Cavendish Laboratory) [3] as well as oxide materials and novel lithium-ion battery materials.

Scanning electron crystallography

Scanning transmission electron microscopy has been used to study the chemical and electron properties of materials by addressing a sample point-by-point. This approach has also been developed for crystallographic analysis, where the diffraction pattern at each point of a scan is analysed for phase and orientation identification. I am working on combining this technique with tomographic approaches and modern statistical analyses to allow the complete 3D microstructure and the 3D atomic arrangement throughout a volume to be determined simultaneously. This work is being applied to aerospace alloys [4], reactor materials and engineering ceramics.

 

Simulated electron diffraction pattern from TIPS-pentacene including (a) a frozen phonon model and (b) molecular dynamics modelling. (c) Indicates the molecular displacements determined from molecular dynamics (black) and the frozen phonon refinement (blue) while (d) shows the change in hole transport between adjacent molecules as a function of displacement.
  • [1] A. S.  Eggeman and P. A. Midgley, IUCrJ, 2, available online (2014)
  • [2] A. S. Eggeman, A. London and P. A. Midgley, Ultramicroscopy 134, 44, (2013)
  • [3] A. S. Eggeman, S. Illig, A. Troisi, H. Sirringhaus and P. A. Midgley, Nature Materials 12, 1045, (2013)
  • [4] A. S. Eggeman, R. Krakow and P. A. Midgley Acta Cryst. A70, C368, (2014)