Formation and photoluminescence of single-crystalline rutile TiO2 nanowires synthesized by thermal evaporation

Uniform nanowires were grown over a selected area of a TiO2/sapphire substrate using a horizontal furnace system with a radio frequency (RF) heater. The growth of the nanowire was governed by a catalyst-free vapour-solid (VS) mechanism. The x-ray diffraction pattern showed that the nanowires comprised TiO2 in the pure rutile phase. The size of the TiO2 nanowires was verified using field emission scanning electron microscopy (FESEM), which showed that the diameters were in the range 50-100 nm and the lengths were in the range 1-2 mu m. The nanowire growth direction and its crystalline structure were examined using high-resolution transmission electron microscopy (HRTEM), indicating that these nanowires had a single-crystalline structure and grew along, the [110] axis. A blue emission peak at similar to 380 nm was obtained under examination by photoluminescence (PL), which revealed only single-crystalline rutile TiO2 nanowires, and thus indicated that the single-crystalline TiO2 nanowire could be a candidate for use in optoelectronic devices.