Gas Sensing With Mats of Gold-Nanoparticle Decorated GaN Nanowires

We report on the use of mats of gold nanoparticle decorated GaN nanowires as gas sensors. The sensing was by the repeated and reversible measurement of changes in the current-voltage characteristics of the mat of nanowires. The nanowires had diameters of about 200 nm and were many microns long. The mat was grown on a 1-cm diameter sapphire disk and was about 10 $\mu\hbox{m}$ thick. The selectivity mechanism is attributed to the details of the surface morphology of the gold nanoparticles decorating the surface of the nanowires. The changes in the currents are attributed to a depletion mechanism in the nanowires due to the formation of a Schottky barrier due to the presence of the gold on the inherently n-type GaN. We were able to detect CO, $\hbox{CH}_{4}$ , $\hbox{CO}_{2}$, $\hbox{H}_{2}$, and observed possible evidence of creation of the by-products of the water-gas shift reaction.