Oriented adsorption of NO2 on WSe2 monolayer

An oriented adsorption behavior of NO2 is disclosed on the WSe2 monolayer in this work regardless the monolayer is perfect or defective based on density functional theory study by large-scale sampling. The presence of typical defects, including selenium vacancy, tungsten vacancy, and antisite defect of selenium on tungsten site, does not modify the anisotropic adsorption behavior of NO2 molecule at all. The adsorbed NO2 exhibits similar behavior on the four kinds of monolayers with its extending orientation all main lines along the two directions of the Se–W bond and the Se–W–Se trough, in spite of the symmetry is decreased somewhat from trigonal of the perfect monolayer to bilateral of the defective monolayers. Molecular dynamic simulations well reproduce these trends. The anisotropic adsorption behavior can be attributed to the polar properties of both heteroatomic bond of the WSe2 monolayer and NO2 molecule itself. Out of plane polarization is believed to play key role in the vertical and then the oriented adsorption behavior formation. The sensitivity is estimated to be very good based on moderate adsorption energy (0.35, 0.42, 0. 95 and 0.78 eV on pure, selenium vacancy, tungsten vacancy, and selenium on tungsten site monolayers) and considerable charge transfer number (0.205, 0.208, 0.164, and 0.160 e, respectively), with different degrees of change by defect. These fantastic findings may provide substantial foundation for wide applications beyond thought.