**5.4 Sensitization**

The sensitivity and the selectivity of the sensor can be improved by different strategies such as incorporating dopants, applying ultraviolet (UV) irradiation, and sensitizing the sensing layer with noble metals (Au, Pt, Pd) and metal oxides (CuO, SnO2). It is known that sensitizing the sensing layer by noble metals is most

**Figure 12.**

*Comparison of H2S sensing between ZnO and ZnO:Pd nanorod structures at (a) 300°C and (b) room temperature.*

**Figure 13.** *Response of sensors based on pure and Au-modified ZnO samples versus different concentrations of H2S gas.*

effective. The sputter deposition of Au layer with different nominal thicknesses on ZnO nanorods enhanced the sensing response to H2S at room temperature (25°C). When Au layer with 6 nm nominal thickness is deposited, higher response and selectivity to H2S than those reported in the literature are obtained. The sensing response at room temperature was enhanced because Au islands formed Schottky barriers at Au-ZnO interface, introduced surface active sites, and increased effective surface area through surface coarsening. The response of both pure and Au-sensitized rods increases with the gas concentration as shown in **Figure 13**. The fabricated sensor based on the Au-sensitized ZnO nanorods is able to detect H2S gas of ppb level [1].
