Computational study of NO 2 sensing on the WO 3 (001) surface is presented. Our ab initio calculations reveal a two-step process of NO 2 detection on the WO 3 surface. In a first step the NO 2 molecule is dissociated at an oxygen vacancy site, but a NO molecule remains adsorbed. In a second step NO is re-oxidized into NO 2 by O 2 of the surrounding air leading to the resistance increase which is experimentally observed. We also calculate the adsorption energy of NO on stoichiometric and non-stoichiometric WO 3 surfaces and propose a method for the NO detection.

Combining experiments and first-principles calculations, we present in this paper a detailed study of the O 3 detection mechanism on the CuO (111) surface. The exchange-correlation functional is treated within both the LDA and the GGA including the spin polarization. In order to better take into account the on-site electronic interactions between 3d electrons of Cu atoms a Hubbard term U has to be added in all calculations. We show that the O 3 molecule is reduced to a O 2 molecule with an enthalpy of reaction of −1.11 eV (−1.15 eV) within LDA+U (GGA+U). Along the reaction path, the O 3 molecules are first physisorbed with a large adsorption energy of −1.83 eV (−1.03 eV) and a significant charge transfer from the surface to the molecule. The p-doping strengthening is compared to the electrical response of a CuO based sensor under O 3 exposure.

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