Nanomaterials Characterisation using Transmission Electron Microscopy and Associated Techniques

Understanding how nanostructures assemble and what their properties are (electronic structure and chemical composition), requires imaging and analysis on the nanoscale, beyond the surface of the material. Electron microscopy in transmission is the only technique capable of achieving this with sub-nanometre resolution; when coupled with energy-loss spectroscopy it can also provide information about the electronic structure, chemical composition and chemical bonding with the same sub-nanometre resolution. This information is essential for a wide variety of nanomaterials, as it provides a fundamental understanding of processes on the small scale, such as the way carbon nanotubes grow from catalysts, the way small particles can enhance optical signals through surface plasmon excitation, or how quantum confinement affects the electronic structure in tunnelling devices used in every day devices, such as mobile phones.
This project centres on using a Hitachi Scanning TEM HD2300A, a UK first, to analyse, interpret and understand nanoscale phenomena. The instrument delivers a ~2Å diameter electron probe which is scanned across samples to provide morphology, chemical and electronic structure information. A typical result is shown in the images of a multi-walled WS2 nanotube, with the left panel showing the lattice structure through interference fringes and the right panel showing an atomic-number contrast image of the same region, revealing the position of the W shells. This mode of imaging can only be performed with a focused probe, simultaneous with the acquisition of energy-loss or x-ray spectra.
Thus far, we have shown that carbon nanotubes grow from catalysts via a surface-driven route (and not just volume), explaining the success at the ATI in growing carbon nanotubes at low temperatures. We have also shown that amorphous carbon superlattices are feasible materials for tunnelling devices and proved that coatings have to be a minimum of 4 monolayers thick in order to have properties closer to bulk materials (e.g. 4 monolayers are required for an insulating material to create a barrier).
External collaborators include Hitachi High-Technologies UK, Gatan UK, Varian, National Physics Laboratory, BAE and Rolls-Royce.