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

Abstract

Bead-like p-TeO₂ nanowires (NWs) were obtained directly from Te powder by thermal evaporation along with assisting 40 sccm of O₂ 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 O₂, 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 °C to 400 °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 °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.