Temperature-dependent selectivity of bead-like TeO2 nanostructured gas sensors

Bead-like p-TeO2 nanowires (NWs) were obtained directly from Te powder by thermal evaporation along with assisting 40 sccm of O-2 gas. Scanning and transmission electron microscopy showed that the two different formation origins for the two types of bead-like TeO2 NWs take place at the vicinity of the surface and are characterized by (1) the presence of locally higher concentration and saturation of O-2, and (2) the surface state (terraces, ledges, and kinks (TLK)) of Te reacting with adsorbed oxygen atoms. In the present work, the gas-sensing performances of bead-like p-TeO2 NW gas sensors fabricated using a facile and low-temperature route has been investigated for the detection of nitric dioxide (NO2), ethanol (C2H5OH), and hydrogen sulfide (H2S) gases contained in human breath. Specifically, this work systematically investigates the gas response of bead-like p-TeO2 NW sensors in dependence of temperature in the range from 200 degrees C to 400 degrees C. The sensing capabilities of bead-like p-TeO2 NWs are investigated with respect to C2H5OH, NO2, and H2S without any artificial handling, such as surface modification, n-and/or p-type doping, and heterostructure formation. The selectivity of bead-like p-TeO2 NWs by adjusting the operating temperature is dependent on the target gas, which is attributed to an interaction between p-TeO2 NWs and gas molecules at a specific operating temperature. In particular, the bead-like p-TeO2 NWs show quite superior sensitivity and selectivity to C2H5OH, NO2, and H2S at 250, 350, and 400 degrees C, respectively. Thus, bead-like TeO2 NWs are promising for the detections of C2H5OH, NO2, and H2S with high selectivity at the ppm level and may contribute to the realization of more selective NW sensors.