Gas phase interactions with Au nanoparticles decorated GaN nanowires by X-ray photoelectron spectroscopy

Au nanoparticle coated GaN (Au-GaN) nanowires have been shown to exhibit gas sensing capabilities, yet virtually nothing is known about the interactions of gases at the surface of Au-GaN nanowires. The electronic surface structure and the gas adsorption behavior of the nanoparticles have been examined by X-ray photoelectron spectroscopy (XPS). The interaction of gold nanoparticles as a function of CO, H$_{2}$O and O$_{2}$ exposures was investigated by examining binding energy shifts of the Au 4f, C1s and O1s electron core level states at 298 K, 77 K and 14 K. XPS analysis reveals that for T= 298 K and T=77 K for all gases the interaction with the surface of the Au-GaN nanowires is too weak to be observed on the timescale of XPS. However at T=14K binding energy shifts of the Au 4f, C1s and O1s electron core level states occur, indicative of adsorption onto the Au-GaN nanowire surface. The temperature dependence of the gas adsorption indicates that the interaction of all the gases investigated is physisorption.