Optical properties and energetics of oxygenated silicon ring-shaped clusters

The optical absorption spectra of equilibrium Si-based ring-shaped clusters have been calculated with the semi-empirical quantum mechanical Intermediate Neglect of Differential Overlap method and Configuration Interaction. The Neglect of the Diatomic Differential Overlap based AM1 geometry optimization calculations show that it is energetically favorable to attach the OH group to an isolated Si ring and to further incorporate the oxygenated Si clusters into an amorphous silica matrix. Substitution of oxygen atoms with nitrogen in such clusters lowers the binding energy of the participating atoms and therefore compromises the stability of the molecule. The calculated optical absorption spectra of the oxygenated Si-based rings consistently exhibit three peaks in the neighborhood of 200, 260 and 320 nm that are not influenced by the presence or absence of nitrogen atoms. A comparison has been made between the experimental results obtained and the properties of the spark-processed Si. The calculations suggest that Si ring clusters are contributing to the optical properties of this material.