Effect of water adsorption on the structural and optical properties of silicon and titanium dioxide nanoclusters

Abstract

The formation of the structure and infrared (IR) spectra of (SiO2)n (n = 1–4) and (TiO2)n (n = 1–3) clusters with an increase in their size n has been simulated using the B3LYP/6-31G* method of the density functional theory. The effect that water adsorption has on the structural and optical properties of silicon and titanium dioxide nanoclusters has been studied by this method as well. The calculated IR absorption bands for the structures of the (SiO2)n and (TiO2)n clusters are in good agreement with the bands observed in the IR spectra of the SiO2 and TiO2 films. It has been shown that the dissociative adsorption of the water occurs at the silicon centers, while the molecular form of adsorption is more energetically favorable at the active titanium centers. As a result of H2O adsorption, the electronic structure of TiO2 undergoes a transition from the semiconductor state to the dielectric one. The traces of water adsorbed at the titanium centers can be identified by the IR absorption spectra of samples due to a multiple (up to two orders of magnitude) increase in the intensities of the H2O molecule vibrations within the adsorption complex.