The role of surface stoichiometry in NO2 gas sensing using single and multiple nanobelts of tin oxide

Typically used semiconducting metal oxides (SMOs) consist of several varying factors that affect gas sensor response, including film thickness, grain size, and notably the grain-grain junctions within the active device volume, which complicates the analysis and optimisation of sensor response. In comparison, devices containing a single nanostructured element do not present grain-grain junctions, and therefore present an excellent platform to comprehend the correlation between nanostructure surface stoichiometry and sensor response to the depletion layer (Debye length, L-D) variation after the analyte gas adsorption/chemisorption. In this work, nanofabricated devices containing SnO2 and Sn3O4 individual nanobelts of different thicknesses were used to estimate their L-D after NO2 exposure. In the presence of 40 ppm of NO2 at 150 degrees C, L-D of 12 nm and 8 nm were obtained for SnO2 and Sn3O4, respectively. These values were associated to the sensor signals measured using multiple nanobelts onto interdigitated electrodes, outlining that the higher sensor signal of the Sn4+ surface (up to 708 for 100 ppm NO2 at 150 degrees) in comparison with the Sn2+ (up to 185) can be explained based on a less depleted initial state and a lower surface electron affinity caused by the Lewis acid/base interactions with oxygen species from the baseline gas. To support the proposed mechanisms, we investigated the gas sensor response of SnO2 nanobelts with a higher quantity of oxygen vacancies and correlated the results to the SnO system.

Automated summary

Semiconducting metal oxides (SMOs) used in gas sensors are affected by factors such as film thickness, grain size, and grain-grain junctions in the active device volume, complicating analysis and optimization of sensor response. Nanostructured devices with a single element offer a platform to understand the correlation between surface stoichiometry and sensor response. In this study, nanofabricated devices containing SnO2 and Sn3O4 nanobelts of different thicknesses were used to estimate their response to NO2 exposure, revealing differences in Debye length and sensor signals based on surface properties.