ENHANCED CO AND CO2 GAS SENSITIVITY OF THE CUO ZNO HETEROCONTACT MADEBY QUENCHED CUO CERAMICS/

The CuO/ZnO heterocontacts for carbon monoxide (GO) gas sensors were m ade using CuO ceramics with different histories, and their gas sensing characteristics were evaluated. The CuO/ZnO heterocontact made by the quenched CuO sintered compact showed enhanced CO and CO2 gas sensitiv ity, while that made by slowly cooled CuO showed no selective CO gas-s ensing characteristics with no CO2 gas sensitivity. The quenched CuO c eramics were thermodynamically stable but the slowly cooled ones were not; therefore the adsorbed CO molecules on the quenched CuO are thoug ht to be stable and have longer lifetimes. The specific reaction betwe en the adsorbed CO on CuO and adsorbed oxygen on ZnO would be promoted by long lifetime adsorbed CO on CuO and that may be the origin of the enhanced CO gas sensitivity of the quenched-CuO/ZnO heterocontact. Th e concentrations of cation vacancies of the quenched CuO ceramics can be controlled by controlling the firing temperatures. However, when th e CuO ceramics for the CuO/ZnO heterocontact were made by firing and q uenching, the ability to be selective in CO gas sensing of the heteroc ontact was not easily controlled by the control of the defect concentr ations of the CuO ceramics.