Growth mechanism and charge transport properties of hybrid Au/ZnO nanoprisms

Abstract

Hybrid Au/ZnO nanoprisms with different Zn:Au atomic ratios are synthesized by a facile co–precipitation method followed by calcination process in which highly monodispersed Au nanocrystals were grown on the tips of ZnO prismatic nanocrystals. It is found that the growth mechanism followed by hindering of {011¯0} ZnO planes during thermal decomposition leading to a prismatic crystal growth. X-ray diffraction reveals that during hybrid Au/ZnO nanoprism formation in the presence of Au, a decrease in the Zn:Au ratio results in a higher amount of Au being incorporated into the ZnO lattice structure. This increase in Au leads to an increase in crystallographic defects such as density of dislocations and dislocation cut-off length. Optical absorption measurements show that by decreasing Zn:Au ratio from 315:1 to 79:1, the bandgap of the hybrid nanoprism structures reduces from 2.77 eV to 2.27 eV. Photoluminescence spectroscopy reveals that the emission from surface defects is the dominant emission. Besides, with increasing Au atomic ratio, luminescence spectra are quenched due to increased dislocation density. The electron/hole pair recombination time is increased due to the diversion which is responsible for the enhancement of photocatalytic activity. Finally, the charge transport mechanism is proposed using photoluminescence and X-ray photoelectron spectroscopy results.