Observation of Au nanoparticles on the surface of silicon nanowire grown by rapid thermal chemical vapour deposition

Abstract

The size evolution of gold (Au) nanoparticles (NPs) on the sidewall surface of silicon (Si) nanowires (NWs) has been investigated by thermal treatments, using high-angle annular dark field scanning transmission electron microscopy. The Si NWs grown at 550 degrees C by rapid thermal chemical vapour deposition have been observed to be surrounded by Au NPs with less than 5 nm diameter and similar to 10(12) cm(-2) density on the whole Si NW surface. To explore the size change of Au NPs, the Au NPs on the Si NW were annealed ex situ at the temperature range of 700-900 degrees C for 20 min. The sizes of NPs for samples annealed at 700, 800 and 900 degrees C represent Gaussian distribution with the average size of 4, 6 and 7 nm, respectively, while at high temperatures above 900 degrees C, they change to a bimodal distribution. It is suggested that the surface diffusion rate of Au NPs on Si NW is much lower than that on the Si substrate because of the substitutional diffusion mechanism.