Effect of Water Adsorption on the Structural and Optical Properties of Silicon and Titanium Dioxide Nanoclusters

摘要

The formation of the structure and infrared (IR) spectra of (SiO_2)_n (n = 1–4) and (TiO_2)_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 (SiO_2)_n and (TiO_2)_n clusters are in good agreement with the bands observed in the IR spectra of the SiO_2 and TiO_2 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 tita- nium centers. As a result of H_2O adsorption, the electronic structure of TiO_2 undergoes a transition from the semiconductor state to the dielectric one. The traces of water adsorbed at the titanium centers can be identi- fied by the IR absorption spectra of samples due to a multiple (up to two orders of magnitude) increase in the intensities of the H_2O molecule vibrations within the adsorption complex.