Fabrication of Cu oxide/TiO2 p–n nanojunctions by stress-induced migration

Abstract

Many Cu oxide/TiO2 p–n nanojunctions were fabricated by introducing the concept of using n-type TiO2 layers to the fabrication method of p-type Cu oxide nanowires by stress-induced migration. Cu oxide/TiO2 nanojunctions were formed along with nanowire growth by heating a Cu thin film with TiO2 passivation layers of different thicknesses. The presence of p–n nanojunctions at the Cu oxide/TiO2 interface was analyzed by current–voltage and electrochemical impedance measurements. The sheet resistance of the samples decreased as the TiO2 thickness increased from 0 to 20 nm and then increased with increasing TiO2 thickness. The shapes of Nyquist plots consisted of two semicircles, one distorted semicircle, and two distorted semicircles for samples without a TiO2 layer, with 2 or 20 nm TiO2 layer, and with 100 or 200 nm TiO2 layer, respectively. The TiO2 thickness dependence of these electrical characteristics suggests that electrical conduction in the sample heated with a TiO2 passivation layer was through the Cu oxide grain surface, Cu oxide/TiO2 interface, and Cu oxide nanowires. In the equivalent circuit representing this electrical conduction, the capacitance values at the Cu oxide/TiO2 interface decreased with increasing TiO2 thickness. These results suggest that a thicker TiO2 passivation layer led to the formation of more p–n nanojunctions at the Cu oxide/TiO2 interface.