Effects on Electronic Properties of Molecule Adsorption on CuO Surfaces and Nanowires

First-principles calculations were performed to study the stabilities, electronic structures, and chemical activities of various CuO surfaces for the understanding of the gas-induced change of conductance of CuCo nanowires. It was found that CuO(111) ancl CuO((1) over bar 11) have the lowest surface energies under ambient conditions and hence should be the most preferential facets of CuO nanowires. While band gaps of these surfaces are narrower than that of bulk CuO, they maintain the semiconductor feature. Adsorption of oxidizing gas such as 0, or NO2 on the CuO(11) and CuO((1) over bar 11) surfaces induces metallic behavior, and molecules gain electrons from the substrates. These two effects result in an increase of hole density ancl hence enhance the surface conductivity of CuO nanowires as observed in our experiments, On the electrons adsorption of H2O molecules on CuO(111) not only widens the band gap but also donates electrons to the surface, which Icads to reduction of surface conductivity. In addition, we found that CuO(111) is potentially an efficient catalyst for CO oxidation through the Mars-van Krevelen mechanism.