Abstract

The properties of nano-structured materials differ substantially from those of larger sizes. For example, metallic nano-particles often present structural properties that vary dramatically with size. Transition metal nano-particles of 1-20 nm in sizes are also used as synthetic catalysts with high turnover and selectivity, e.g. as catalysts in petroleum-based industries. Gold too, which is chemically inert at macroscopic sizes, is catalytically active when its size is reduced to a few nanometres in diameter.

Characterising the structure of these nano-particles, in three-dimensions, is one of the greatest challenges at present and there is no one, definitive probe that can provide both atomic resolution and single particle discrimination simultaneously. As a consequence, the structure of nano-particles, including surface relaxation and defects, is poorly understood and rarely studied.

This talk will present our group efforts to develop electron diffraction-based techniques for the structure determination of nano-particles. Two approaches have been developed for this: Coherent nano-area electron diffraction, which yields structural information from individual nano-crystals; and in-situ reflection high-energy electron diffraction (RHEED) which monitors the size dependence of structural transitions. Examples will be given for the study of surface structure in gold nano-crystals and structural transition of silver nano-particles.