SnO2 nanoribbons with exposed (1 0 1) and (0 1 0) surfaces have recently been demonstrated as highly effective NO2 sensors even at room temperature. The sensing mechanism is examined here through first-principles Density Functional Theory (DFT) calculations. We show that the most stable adsorbed species involve an unexpected NO3 group doubly bonded to Sn-centers. Significant electron transfer to the adatoms explains orders of magnitude drop in electrical conductance. X-ray absorption spectroscopy indicates predominantly NO3 species on the surface, and computed binding energies are consistent with adsorbate stability up to 700 K. Nanoribbon responses to O2 and CO sensing are also investigated.
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