Professor Paul Midgley

My research is based on the development and application of new electron microscopy techniques to study the structural and functional properties of a variety of materials with high spatial resolution in 2 and 3 dimensions.

Electron tomography

By recording a tilt-series of transmission electron micrographs, using a variety of novel imaging modes, electron tomography can be used to reconstruct the 3-dimensional morphology, defect structure and composition of materials systems with nanometre resolution in all 3 dimensions. Materials studied range from cell sections and bacteria to heterogeneous catalysts, semiconductor quantum dots and aerospace alloys. Recently we have started a research programme developing mesoscale tomography using the dual beam SEM-FIB to link the length scales probed by TEM with those investigated by X-ray methods.

Electron holography and phase-sensitive imaging

Quantitative off-axis and in-line (Fresnel) electron holography is being used to study the electrostatic potentials at unbiased and biased device junctions in two and three dimensions. Magnetic fields in ferromagnetic thin films and nanoparticle arrays are also being mapped with electron holography. Low-temperature microscopy is being carried out to investigate the structure and dynamics of flux vortices in high Tc superconductors. Vortex contrast is amplified by energy-filtered Lorentz imaging or by the use of a phase plate.

Electron crystallography

Precession electron diffraction is being developed to determine the atomic structure of sub-micrometre particles. This technique, which minimizes the effects of dynamical interaction, can now be used to determine atomic positions to an accuracy approaching that of X-ray diffraction. Why the technique works, and over what range of sample thickness and precession angle, is being investigated. The technique is being used to determine the structure of inorganic and organic crystals, including metal oxides, metal-organic frameworks and pharmaceutical crystals.

Nanoscale structures

Novel structures, including mesoporous catalysts, organic and inorganic nanotubes, and semiconducting nanowires, are being characterized by high-resolution electron microscopy, electron diffraction and electron tomography. The cellular toxicity of fullerenes and carbon nanotubes is investigated by chemical assay and electron tomography.