Gold Catalyzed Growth of Zinc Oxide Nanowires: Effect of Catalyst Thickness

Gold (Au) catalyzed zinc oxide (ZnO) nanowires (NWs) were synthesized onto silicon (Si) substrates using a thermal evaporation technique. The effect of different Au film thicknesses (1, 3, 5, and 7 nm) on the physical features of ZnO NWs is studied in detail. The surface morphology, elemental composition, crystalline structure, optical behavior, and crystallographic information of the grown samples are evaluated using field emission scanning electron microscope (FESEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray diffractometer (XRD), photoluminescence (PL) spectroscopy, and high-resolution transmission electron microscope (HRTEM). FESEM images shown that the thickness of the Au film is a critical factor in forming Au nanoparticles (NPs) for growing ZnO NWs with different diameters (ranging from ~31 to ~83 nm) and lengths (ranging from ~318 to ~2923 nm). Based on microscopic analysis, the growth of NWs could be controlled by the vapor-liquid-solid (VLS) nucleation mechanism. EDX spectra showed the expected elements (O, Zn, and Au) in the synthesized NWs structure. XRD analysis disclosed that the grown samples are polycrystalline in nature and had a hexagonal wurtzite structure, with the (002) plane as the dominant preferred direction. PL characterization demonstrated that the concentration of surface oxygen vacancies (V_ο) in smaller NWs is higher than in larger NWs. HRTEM images indicated that the ZnO NWs had a high crystallinity and grew along the [0001] direction.