Gas phase interactions with bare and gold nanoparticle decorated gallium nitride nanowires by ultraviolet photoelectron spectroscopy

Ultraviolet photoelectron spectroscopy (UPS) has been used to characterize the interaction of CO and H$_{2}$O with the surface of bare and gold nanoparticle (Au NP) decorated gallium nitride nanowires at 298 K, 77 K and 20 K. The average diameter of the Au NPs is 4.5 $\pm $ 0.5 nm and the average nanowire diameter is 105 $\pm $ 75 nm. CO and H$_{2}$O do not bond to the surface of the bare GaN nanowires at 298K, 77K, or 20K. Temperature dependent UPS analysis reveals that CO and H$_{2}$O weakly physisorbed to the Au NP decorated GaN nanowires with heats of adsorption of 4.37 $\pm $ 0.03 meV and 1.25 $\pm $ 0.04 meV , respectively. The adsorption at 298K of 50 Langmuir of CO followed by 50 Langmuir of H$_{2}$O showed that CO adsorption promotes H$_{2}$O adsorption, while 50 Langmuir of H$_{2}$O followed by 50 Langmuir of CO showed that H$_{2}$O inhibits CO adsorption. The findings of this study that the adsorption of H$_{2}$O inhibits CO adsorption onto the Au NP-GaN nanowires explains previous studies of the gas sensing properties of mats of Au NP- GaN nanowires.