Ultrafast charge carrier dynamics and photoelectrochemical properties of ZnO nanowires decorated with Au nanoparticles

Abstract

This study was designed to examine the possible photosensitization effect of zinc oxide (ZnO) nanowires (NWs) by Au nanoparticles (AuNPs) by directly monitoring the charge carrier lifetime in AuNP-decorated ZnO NWs. ZnO-Au nanocomposite structures showed reduced photocurrent compared to pristine ZnO NWs due to the combined effect of ZnO etching during the AuNPs growth and competitive absorption/scattering effects from AuNPs of incident UV photons. Ultrafast transient pump-probe spectroscopy was utilized to characterize the charge carrier dynamics. The bleach recovery of ZnO indicates electron-hole recombination on the 150 ps time scale attributed to shallow donor recombination. The AuNP-decorated ZnO NWs exhibit a fast decay of 3 ps in addition to the decays observed for ZnO NWs. This fast decay is similar to the hot electron relaxation lifetime observed for AuNPs in solution. Overall, the dynamics features for AuNP-decorated ZnO NWs appear as a simple sum of those from AuNPs and ZnO NWs alone. There is no evidence of photosensitization of the ZnO NWs by AuNPs investigated in this study.