New Insights Towards Electron Transport Mechanism of Highly Efficient p-Type CuO (111) Nanocuboids-Based H2S Gas Sensor

Charge transport and adsorption kinetics of wet-chemically synthesized CuO nanocuboids have been explored. The growth direction of CuO nanocuboids was found to be (111) plane, which exhibited predominant surface catalytic activity toward the dissociation of H2S and O-2. Temperature-dependent adsorption studies revealed the adsorption kinetics of (111) grown p-type CuO nanocuboids toward H2S gas. Adsorption of oxygen (O-2) on the CuO (111) surface resulted in the formation of ionosorbed O-2(-) species, which increased the hole density and enhanced the surface conductivity of CuO nanocuboids. H2S molecules were found to interact well with CuO (111) surface, donating electrons to the material and reducing the hole-accumulation layer width. Investigation of electrical characteristics of p-type CuO nanocuboids revealed absence of any structural phase transitions under H2S environment. The H2S sensing mechanism was found to be associated with local suppression/expansion of the hole-accumulation layer of p-CuO nanocuboids rather than the thermally activated carriers. Exposure to H2S gas molecules was found to decrease the band bending energy as a function of concentration. The distinctive (111) surface reactivity of p-CuO nanocuboids toward H2S and their unique electron transport properties makes them highly amenable for fabricating high-performance gas sensors.