DFT and experimental interpretations of silicon-based room-temperature NO2 sensors improving humidity independence

Insights toward detecting hazardous NO2 gas at room temperature with nearly humidity-independent sensing characteristics has been promisingly envisioned yet rare reports have been addressed. Here, the spatial configurations for favorable NO2 adsorption on the incorporated WOx/Si structures were studied using density functional theory (DFT) calculations. Results reveal that the more negative adsorption energy encountered for NO2 adsorption exists in exposed Si surfaces, which further show the largest magnitude of charge transfer (0.16 e), compared with WOx surfaces (0.08 e), and WOx/Si interfaces (0.02 e) evidenced from Bader charge analysis. To experimentally remedy the correlated sensing performances, incorporations of either dense or distributed WOx nanoparticles on aligned Si nanowires featuring z-scheme band structure were synthesized, where the coupled heterostructures with distributed WOx features display the environmentally stable gas-sensing characteristics by featuring trivial degradation of sensing response of 8.4% under high humidity of 83% compared with average response within humidity range of 24.5-55.2%, and such detection robustness is much superior than other oxide-based NO2-gas sensors in the literature. Examinations of band structures clarify that the rule of Si in such promising NO2 sensors behaves as a bridge that efficiently rectifies the hole flows for synergistically improving room-temperature detection.

Automated summary

This article investigates the spatial configurations of WOx/Si structures for favorable NO2 adsorption using density functional theory calculations. The results show that NO2 adsorption has a more negative adsorption energy and a larger charge transfer on exposed Si surfaces compared to WOx surfaces and WOx/Si interfaces. To improve the sensing performances, dense or distributed WOx nanoparticles were synthesized and incorporated on aligned Si nanowires, and the coupled heterostructures with distributed WOx features exhibit environmentally stable gas-sensing characteristics with minimal degradation in sensing response under high humidity conditions.