Quantum mechanical characterization of the microscopic structure and nonlinear optical properties of radiation-induced defects in a-SiO2

摘要

Abstract: We have used ab initio Hartree-Fock theory to characterize the microscopic structure and the nonlinear optical (NLO) properties of the over-coordinated oxygen hole center observed in radiation-exposed SiO$-2$/ films. Our calculations indicate that a proton (H$+$PLU$/) forms a stable bond with a divalent oxygen atom in the Si-O-Si network at an equilibrium r(O-H) approximately equals 1.005 angstrom and also leads to an enhancement in the microscopic NLO response of the local structure by a factor of 4 or more. In the absence of the over-coordinating H$+$PLU$/, the dipole, moment and the second-order NLO response of the Si- O-Si cluster is extremely small. Protonation of a bridging O atom distorts the electron charge cloud in the direction of the O-H bonding and also reduces the gap between the filled and the vacant energy levels. This leads to a substantial increase in the magnitude of the dipole moment vector and the component of the second-order NLO susceptibility along the O-H bond. !10