Optimum shell thickness and underlying sensing mechanism in p–n CuO–ZnO core–shell nanowires

Abstract We report on the sensing properties of p – n CuO–ZnO core–shell nanowires (C–S NWs) for reducing gases. The C–S NWs were synthesized by a two-step process: first, core p –CuO nanowires were prepared by thermal oxidation on patterned interdigital electrodes, forming a network; and second, the n –ZnO shell layers were subsequently deposited by atomic layer deposition (ALD). The ZnO shell thickness was controlled by changing the number of ALD cycles between 5 and 110 nm. The sensing properties of the C–S NWs were investigated for the typical reducing gases CO and C 6 H 6 . At 35 nm shell thickness, the C–S NWs showed the highest CO and C 6 H 6 sensing ability, superior to that of pristine p –CuO nanowires. The sensing mechanism of the p – n C–S NWs is based on the radial modulation of an electron-depletion region in the ZnO shell layer, which occurs during the interaction between the reducing gas molecules and the adsorbed oxygen species and causes a pronounced change in resistance. This demonstrates that the radial modulation of the conducting channel is a universal sensing principle operating in p – n type C–S structures.