Controlled growth of high-quality TiO2 nanowires on sapphire and silica

The vapour-liquid-solid (VLS) growth of TiO2 nanowires (NWs) was performed using a thermally evaporated Ti source and sputter-deposited Au catalysts under an O-2 gas flow. High-density single-crystalline TiO2 NWs having the rutile structure were successfully grown on sapphire (single-crystal alpha-Al2O3) and quartz ( amorphous SiO2) substrates. Ti buffer layers, deposited on the substrates to prevent undesirable reactions between the Ti vapour and substrates, were identified to promote the TiO2 NW growth by providing supplementary Ti vapour to the Au catalysts. Crystallinity of TiO2 NWs was investigated by x-ray diffraction ( XRD) and their morphological features were characterized by field emission scanning electron microscopy ( FESEM). High-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction ( SAED) analyses reveal growth of the rutile NWs having twofold twin structures along the growth direction on Ti/sapphire and the defect-free single-crystalline rutile NWs on Ti/quartz substrates. TiO2 NWs grown on Ti/quartz showed a short-wavelength (similar to 402 nm) and high-intensity photoluminescence (PL) emission compared to those grown on Ti/sapphire substrates. By introducing a Ti buffer layer and using quartz substrates, the crystallinity and PL properties were successfully improved for VLS-grown TiO2 NWs.