Photoluminescence and electrical properties of bidirectional ZnO nanowires on Zn foils via a thermal oxidation method
ZnO nanowires (NWs) were directly grown on ductile zinc foils through a two-step process: (a) large, thin, and ductile Zn foils were fabricated from a mixture of Zn and ZnO powders; and (b) ZnO NWs were produced by thermal oxidation at temperatures of 300–600 °C. The ZnO NWs presented preferential growth in the  orientation. The highly crystalline NWs synthesized at 500 °C exhibited a bidirectional mode with an angle of approximately 60° between their longitudinal axes. On foils oxidized at 600 °C, the NWs evolved into nanotowers. The photoluminescence (PL) spectra showed strong peaks at approximately 368 nm and weaker peaks at approximately 374 nm in the UV region; moreover, a broad deep-level-related green emission peak was recorded at approximately 520 nm in the visible region. The PL green emission line was strongly suppressed for the samples produced at higher oxidation temperatures, which indicated good optical qualities. These good optical qualities, combined with the bidirectional mode and the ductility of the foil, are expected to be useful for flexible planar device applications. The electrical properties of a single ZnO NW were investigated. I–V measurements revealed the Schottky characteristics of the NWs and the resistivity of the ZnO NWs was measured to be ∼93 Ω cm.