18 October 1996 Quantum mechanical characterization of the microscopic structure and nonlinear optical properties of radiation-induced defects in a-SiO2
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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 SiO2 films. Our calculations indicate that a proton (H+) 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+, 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.
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Shashi P. Karna, Antonio Ferreira, Robert D. Pugh, Charles P. Brothers, Babu B.K. Singaraju, "Quantum mechanical characterization of the microscopic structure and nonlinear optical properties of radiation-induced defects in a-SiO2", Proc. SPIE 2811, Photonics for Space Environments IV, (18 October 1996); doi: 10.1117/12.254056; https://doi.org/10.1117/12.254056
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