**6.5 In2O3-core/ZnO-shell nanorods**

The two-step fabrication process of In2O3-core/ZnO-shell nanorods comprises the thermal evaporation of a 1:1 mixture of In2O3 and graphite powders and the atomic layer deposition of ZnO [39]. The core-shell nanorods have the diameter in the range of 100–200 nm and the length up to a few hundreds of micrometers. The thickness of the ZnO-shell layer in the core-shell nanorod ranged from 5 to 10 nm. The nanorods consist of bcc-structured polycrystalline In2O3 as cores and simple hexagonal-structured polycrystalline ZnO as shells. The responses of the multiple networked In2O3-core/ZnO-shell nanorod sensors at H2S concentrations of 10, 25, 50, and 100 ppm were 34.11, 34.55, 35.77, and 28.86%, respectively, at 300°C and 4.2, 4.0, 4.0, and 3.5 times larger than those of bare-In2O3 nanorod sensors, respectively. Based on the space-charge model, the In2O3-ZnO heterojunction acts as a lever to facilitate or restrain the electron transfer and thus enhances the sensing properties of the core-shell nanorod sensor. In addition, the In2O3-core/ZnO-shell nanorods sensor exhibits shorter response and recovery times than the bare-In2O3 nanorods for any H2S concentration.
