The role of activation energy distributions in diffusion related annealing in SiO2

Abstract

Models for annealing processes in damaged, amorphous SiO2 are discussed. Using a series expansion approach, theories developed for diffusion-limited recombination are adapted to allow for a Gaussian distribution of activation energies. It is found that the effect of a distribution having deviation ΔE, and center EA can be accounted for by using an effective diffusion coefficient, D̃, such that in the series expansion any power (n) is defined by (D̃)n=Dn0 exp 1/2 (nΔE/kT)2 exp(−nEA/kT). This form is more complicated than that found previously for ‘‘pure’’ diffusion studies. The importance of the form of the distribution function for the activation energies is discussed in the context of the full diffusion-limited theory for annealing. It is argued that processes occurring at temperatures in excess of 500 °C are not due to diffusional recombination.

Solar Wind Implantation Into the Lunar Regolith: Monte Carlo Simulations of H Retention in a Surface With Defects and the H2 Exosphere

“…Upon integration over all energies, an effective diffusion coefficient is obtained . Similar approaches have been used in the studies of hydrogen diffusion in silica glass (Devine, ; Shelby & Keeton, ). Using equation , Farrell et al () define an analytical expression of the implanted density as a function of solar zenith angle assuming dynamic equilibrium on timescales much less than a lunation: where is defined as the diffusive velocity, or in terms of a diffusive lifetime .…”

“…Similar approaches have been used in the studies of hydrogen diffusion in silica glass (Devine, 1985;Shelby & Keeton, 1974). Using equation (6), Farrell et al (2017) define an analytical expression of the implanted density as a function of solar zenith angle assuming dynamic equilibrium on timescales much less than a lunation:…”

Optical nonlinearity of oxygen-rich SiOx thin films

“…Apart from the excess oxygen reactive species in the plasma, Ar þ and O þ ion bombardment to the growing film could be another factor causing the formation of the O-rich film, because high-degree O-rich films did not form at V b ¼ 0 V, but they did form at V b ¼ À100 V, as indicated in Fig. 1, and it has been found that O-rich related defects could be generated in silica by Ar þ implantation [5,6]. Optical absorption of the SiO x films deposited on bare silica plates was measured before and after thermal annealing at temperature of 400 C for 30 min.…”

“…These phenomena can be associated with the defects in the films. The defects in silica have been well-studied using electron-spin resonance technique [5,6]. It was found that there are three principal non-impurity-related defects in amorphous SiO 2 : paramagnetic oxygen vacancy centre (E 0 ) and its variants, non-bridging oxygen (NBO) hole centre and peroxy radical with trapped hole.…”

“…polar structure unites) are electrical dipoles [1]. It has been observed that, for temperature below 400 C, the concentration of peroxy radicals grows with annealing temperature, while in the same temperature range the concentration of E 0 and NBO centres decrease [5,6]. During the annealing process, O 2 may diffuse through the silica and combine with E 0 centres to form new peroxy radicals; existing bridging peroxy Si-O-O-Si linkages may be broken into non-bridging Si-O-O À peroxy radicals [5,6].…”