First-principles investigation of facet-dependent anisotropic transport in SnO2 for intrinsic NO2 sensing

Identifying the surface origin of gas selectivity remains a challenge in the design of metal-oxide chemiresistive sensors. Although SnO 2 -based materials have shown promising performance for NO 2 detection, the individual roles of surface facet, oxygen vacancy, and anisotropic electron transport remain difficult to distinguish. Here, we combine density functional theory calculations with non-equilibrium Green's function transport calculations to examine NO 2 sensing on pristine and oxygen-vacancy SnO 2 (110), (100), and (101) facets. The results show that NO 2 adsorption strongly depends on surface orientation and the presence of oxygen vacancies, while the electrical response is governed by the coupling of NO 2 -induced electronic perturbations with facet- and direction-dependent transport channels under applied bias. Among the examined facets, SnO 2 (101) provides the most robust intrinsic NO 2 response, whereas SnO 2 (110) shows strong but more defect- and direction-dependent behavior. Comparison with NH 3 further supports that gas selectivity cannot be evaluated solely from adsorption energy. These findings clarify how adsorption chemistry, oxygen-vacancy states, and anisotropic electron transport jointly determine the intrinsic NO 2 response of SnO 2 , suggesting that morphology control toward transport-active facets may be a useful strategy for improving metal-oxide gas sensors.