Changing Electric Resistance of ZnO Nano-Rods by Sulfur Compounds for Chemical Gas Sensor.

In this study, a zinc oxide (ZnO) single crystal rod was synthesized for applications as a gas-sensing material for hydrogen sulfide (H2S) and its H2S-sensing properties were investigated. H2S absorbed well on ZnO via a gas and solid chemical reaction, resulting in the conversion of ZnO to ZnS. ZnS is also oxidized easily to ZnO with O2 contained in air. ZnO and ZnS are semiconducting materials. The energy band gap of ZnS is higher than that of ZnO. Therefore, the electric conductivity of ZnS must be lower than that of ZnO. On the other hand, different results were obtained in the H2S sensing tests. The energy band gap of sulfur-absorbed ZnO nano-rods was 2.84 eV according to UV-Visible spectrophotometry. The electrical conductivity can be enhanced by sulfur doping on ZnO single crystal rods because the lattice oxygen on the surface of ZnO single crystal is replaced with the sulfur in H2S. The electrical conductivity of S-doped ZnO also decreased due to oxidation with the oxygen in air.