Gas phase interactions at the surface of bare and gold nanoparticle decorated gallium nitride nanowires by ultraviolet photoelectron spectroscopy

摘要

Ultraviolet photoelectron spectroscopy (UPS) has been used to characterize the interactions of CO and H_2O with the surface of bare and gold nanoparticle decorated gallium nitride (Au-GaN) nanowires (NWs) at 20, 77, and 298 K at three different dosing pressures: 9 × 10~(-8), 9 × 10~(-7), and 9 × 10~(-6) Torn The average diameter of the Au NPs is 4.5 ± 0.5 nm and the average NW diameter is 105 ± 75 nm. CO and H_2O do not bond to the surface of the bare GaN NWs at 20, 77, or 298 K, even at the highest dosing pressure. Temperature and pressure dependent UPS analysis reveals that CO and H_2O weakly physisorbed to the Au NP decorated GaN NWs. For the exposure up to 200 L (Langmuir), the activation energy of adsorption of CO and H_2O has been found to range from 9.0 ± 1.0 to 45.6 ± 4.3 kj/mol and 2.0 ± 0.1 to 5.0 ± 0.1 kJ/mol, respectively. The adsorption at 298 K of 100 L of CO at all the three dosing pressures, followed by 100 L of H_2O, showed that CO adsorption promotes H_2O adsorption, while 100 L of H_2O followed by 100 L of CO showed that H_2O inhibits CO adsorption. The findings of this study that the adsorption of H_2O inhibits CO adsorption onto the Au-GaN NWs explain previous studies of the gas sensing properties of mats of Au-GaN NWs.