Functionalizing nanowires with catalytic nanoparticles for gas sensing application

Metal oxide semiconducting nanowires are among the most promising materials systems for use as conductometric gas sensors. These systems function by converting surface chemical processes, often catalytic processes, into observable conductance variations in the nanowire. The surface properties, and hence the sensing properties of these devices can be altered dramatically improving the sensitivity and selectivity, by the deposition of catalytic metal nanoparticles on the nanowire's surface. This leads not only to promising sensor strategies but to a route for understanding some of the fundamental science occurring on these nanoparticles and at the metal/nanowire junction. In particular studying these systems can lead to a better understanding of the influence of the catalyst particle on the electronic structure of the nanowire and its electron transport. This report surveys results obtained so far in this area. In particular, the comparative sensing performance of single quasi-1D chemiresistors (i.e., nanowires or nanobelts) before and after surface decoration with noble metal catalyst particles show significant improvement in sensitivity toward oxidizing and reducing gases. Moreover, one finds that the sensing mechanism can depend dramatically on the degree of metal coverage of the nanowire.