SnO2nanoribbons with exposed (1 0 1h) and (0 1 0) surfaces have recently been demonstrated to be highly effective NO2sensors 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 an 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 O2and CO sensing are
also investigated.