Growth mechanism of Te nanotubes by a direct vapor phase process and their room-temperature CO and NO2 sensing properties

The growth of Te nanotubes by the direct vapor phase process is dominated by the vapor-solid mechanism, where the intrinsic anisotropic crystal structure of tellurium and axial dislocations contained in the Te nanostructures should play crucial roles. During the growth process, Te nanoparticles will nucleate on the growth substrate in the initial stage, and then grow into nanoflakes and two-faced nanoscreens lying horizontally on the substrate until they fully cover the substrate. Some of the nanoscreens with certain horizontal angles with respect to the substrate surface will protrude out of the growth substrate and become preferential absorption sites for the incoming Te atoms. The two-faced nanoscreens then gradually develop into three-faced nanoscreens, four-faced nanogrooves, and finally perfect hexagonal nanotubes due to the lateral diffusion of Te atoms. Upon exposure to CO and NO2 at room temperature, Te nanotube sensors showed the same direction of resistance change, adequate sensitivities, and fast response and recovery times, making them promising candidates for use in air-quality single sensors.