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MM: Fachverband Metall- und Materialphysik

MM 47: Invited Talk (Hauptvortrag) Robinson

MM 47.1: Hauptvortrag

Donnerstag, 3. April 2014, 09:30–10:00, BAR 205

Coherent X-ray Diffraction Imaging of Excitations in Metal Nanoparticles — •Ian Robinson — University College London, UK — Research Complex at Harwell, UK

The physical reason why nanoparticles differ in structure from the bulk is fundamentally crystallographic. As with all surfaces, the missing-neighbour unit cells, which become removed to create a surface, cause a structural response. In a metal this is an inward relaxation, detectable as crystal strain. Where two surfaces meet along the edge of a crystal, the effect is enhanced. Nanocrystals are in precisely the size range which is dominated by these surface and edge properties. This results in a pattern of strain which follow the crystallographic structure of the particle. Certain simple properties of nanoparticles can be explained through these structural differences. Coherent X-ray Diffraction can be used to study these effects within the three dimensional structure of nanocrystals. A key experiment will be discussed that uses this method to study the redistribution of strains on the surface of a Au nanocrystal by adsorption of a chemical layer [1]. Ultrafast imaging with free-electron laser sources allows visualization of the strain patterns in vibrating crystals [2].

[1] Differential stress induced by thiol adsorption on facetted nanocrystals, Moyu Watari, Rachel McKendry, Manuel Voegtli, Gabriel Aeppli, Yeong-Ah Soh, Xiaowen Shi, Gang Xiong, Xiaojing Huang, Ross Harder and Ian Robinson, Nature Materials 10 862-866 (2011) [2] Ultrafast three dimensional imaging of lattice dynamics in gold nanocrystals J. N. Clark et al Science 341 56 (2013)