Misao Nishino

Nucleus interaction and fine structures of colloidal gold particles

Abstract Typical gold sol particles were examined by high-resolution electron microscopy to study the nucleation and growth mechanism. The samples of colloidal gold were Faraday sol, Weimarn sol and sodium citrate sol, whose average particle diameters were estimated to be 55.2 ± 10.6 A, 131 ± 13 A and 154 ± 70 A, respectively. The shape of particles is mostly spherical excepting some of the Weimarn sol which includes pentagons with some round apices. The high resolution electron micrographs taken at a magnification of 125,000 times clearly show that the majority of the particles consist of smaller elementary crystallites with sharp boundaries which appear as parallel or radial lines defined by distinct diffraction contrasts. Moire fringes of 5–8 A spacings as well as crossed lattice images of 2.03 and 2.35 A due to (200) and (111) reflections were also observed. Systematic analyses of these contrasts indicated that the particles are formed by parallel or radial twins with definite mutual orientations. The origin of the fine structure can be attibuted to the nucleus interactions which precedes the actual growth in the early stage of sol formation. The possibility of the formation of metastable nuclei with icosahedral configuration which grow into the multiple twins and the successive transition to the natural cube-octahedral nuclei which after mutual interactions lead to the parallel twins was also discussed.