Growth of Vertically Aligned ZnONanowire Arrays Using BilayeredMetal Catalysts

Vertically aligned, high-density ZnO nanowires (NWs) were grown for the first time on c-plane sapphire using binary alloys of Ni/Au or Cu/Au as the catalyst. The growth was performed under argon gas flow and involved the vapor-liquid-solid (VLS) growth process.We have investigated various ratios of catalyst components for the NWs growth and results indicate that very thin adhesion layers of Ni or Cu deposited prior to the Au layer are not deleterious to the ZnO NW array growth. Significant improvement of the Au adhesion on the substrate was noted, opening the potential for direct catalyst patterning of Au and subsequent NW array growth. Additionally, we found that an increase of in thickness of the Cu adhesion layer results in the simultaneous growth of NWs and nanoplates (NPs), indicating that in this case the growth involves both the VLS and vapor-solid (VS) growth mechanisms. Energy dispersive X-ray spectroscopy (EDX) and surface-enhanced Raman scattering (SERS) studies were also performed to characterize the resulting ZnO NW arrays, indicating that the NWs grown using a thin adhesion layer of Ni or Cu under the Au show comparable SERS enhancement to those of the pure Au-catalyzed NWs.