Photoconducting tellurium for submillimeterwave detectors

Vapor-solid growth of p-Te/n-SnO2 hierarchical heterostructures and their enhanced room-temperature gas sensing properties

We have synthesized brushlike p-Te/n-SnO2 hierarchical heterostructures by a two-step thermal vapor transport process. The morphologies of the branched Te nanostructures can be manipulated by adjusting the source temperature or the argon flow rate. The growth of the branched Te nanotubes on the SnO2 nanowire backbones can be ascribed to the vapor-solid (VS) growth mechanism, in which the inherent anisotropic nature of Te lattice and/or dislocations lying along the Te nanotubes axis should play critical roles. When exposed to CO and NO2 gases at room temperature, Te/SnO2 hierarchical heterostructures changed the resistance in the same trend and exhibited much higher responses and faster response speeds than the Te nanotube counterparts. The enhancement in gas sensing performance can be ascribed to the higher specific surface areas and formations of numerous Te/Te or TeO2/TeO2 bridging point contacts and additional p-Te/n-SnO2 heterojunctions.

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.