First principle study of electronic properties of ZnO nanoclusters with native point defects during gas adsorption

First principle investigations of adsorption processes of different gas molecules (NH3, CO, O-2, NO2) on native point defects in (ZnO)(n) nanoclusters (n = 34, 60) based on the density functional theory within the general gradient approximation plus Hubbard U corrections (GGA + U), for different types of isomers, were performed. For each type of defect an optimization (relaxation) of structures geometry was performed and then the molecules of O-2, CO, NO2, NH3, had been added to the surface. The values for adsorption energy, band gap energy, as well as, the charge transfer, and the bond length between the adsorbed molecule and the surface atom for each cluster were obtained to establish the influence of the defects on the electronic properties of the (ZnO)(n) nanoclusters during gas adsorption. The calculations showed the change in the concentration of majority carriers (electrons) in the sensory system depending on the type of gas adsorbed: CO and NH3 molecules increase the concentration, while O-2 and NO2 molecules decrease their concentration. A reduction of the band gap of nanoclusters was also observed during adsorption of molecules. The sharpest decrease for acceptor molecules was observed for the NO2 molecule, and among donor molecules the greatest influence was exerted by NH3 molecules.