Abstract
Single crystalline TiO2 nanowires/nanorods were synthesized by radio frequency plasma enhanced physical vapor deposition (PVD). TiO2 nanostructured materials often have unusual electronic, optical and mechanical properties as well as a wide range of potential applications. This study encompasses: two-step thermal evaporation for growing TiO2 nanowires; incorporation of nitrogen (N) to the TiO2 during the growth and substrate effect of the TiO2 for the growth of the TiO2 nanowires; performance characterization in TiO2 nanostructures.The TiO2 layer and two-step thermal evaporation process were developed to grow the TiO2 nanwires. Accordingly, the selected-area growth of TiO2 nanowires was achieved. Both cathodoluminescence (CL) and photoluminescence (PL) indicated that TiO2 nanowires exhibit a blue shift of the emission peak owing to the size effect. Conversely, bulk TiO2 exhibited no luminescence. The nanowires exhibited luminescence, which was associated with their good crystallinity. The N-doped TiO2 nanowires was shown a red shift effect under CL examined. The red shift demonstrated that doping with nitrogen narrowed the band gap of TiO2 nanowires. The high photocatalytic activity of TiO2 nanowires can be obtained by increasing the specific surface area of nanowires and by improving their crystallinity. The high-resolution transmission electron microscopy (HRTEM) demonstrated that the nanowires are grown along the [110] axis, which is the most thermodynamically stable direction and to form the single crystalline TiO2. The Au-doped TiO2 layer enables to increase the electric conductivity. The electron field-emission properties of TiO2 nanowires are for the first time to be correlated by the Folwer-Nordheim (F-N) theory. A low turn-on field was thus found to be ~ 5.7 V/μm at a current density of 10 μA/cm2.More importantly, a mechanism of utilizing the vapor phase deposition for the synthesis of single crystalline TiO2 nanowires have been addressed throughout this work. It would be exciting to enlarge the current investigation into the studies of the nanodvice fabrication in the near future.