Morphology and Structure of Ultrafine Gold Particles

Abstract

Morphology and structure of ultrafine gold particles dispersed over alumina support films have been studied by transmission electron microscopy. It is shown that gold particles generally correspond to f.c.c. structure, but, also assume a distorted cubic phase in some situations. The unit cell becomes smaller on one side by about 5% and thus cubic symmetry is destroyed. The resulting structure is tetragonal with a ~ 0.407 nm or EquationSource% MathType!MTEF!2!1!+- % feaagCart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaSGbaeaaca % WGHbaabaWaaOaaaeaacaaIYaaaleqaaaaaaaa!37C7!]]</EquationSource><EquationSource Format="TEX"><![CDATA[$${a \mathord{\left/{\vphantom {a {\sqrt 2 }}}\right.\kern-\nulldelimiterspace}{\sqrt 2 }}$$ , c ~ 0.387 nm. On exposing the particles to hydrogen at temperatures 200 – 500°C for various lengths of time, an overall increase in particle size is found to occur. No evidence is obtained to support the particle migration, collision and subsequent coalescence for growth. Instead, Ostwald ripening mechanism is operative, whereby, the coarsening results due to transfer of atoms from smaller to larger particles via the substrate and/or by jump process. Gold particles show morphological variations, e.g. from irregular shapes to spherical or well defined such as hexagonal, pentagonal, etc.