Structure and diffusion of boron in amorphous silica: Role of oxygen vacancy related defects

Abstract

Based on first-principles density-functional calculations, we present the structure and diffusion of boron in amorphous silica, as well as in crystalline silica for comparison purpose. We find that incorporation of a boron atom into the amorphous silica matrix results in various minimum-energy configurations with and without oxygen deficient centers, and also the B-related defects can undergo interconversions at elevated temperatures. While B atoms preferentially remain in the trigonal BO 3 form in amorphous silica, our work shows that B diffusion may require transformation of the immobile BO 3 state to a mobile B state by capturing oxygen vacancy related defects equivalent to an S center, which is a combination of an oxygen vacancy and a trivalent Si defect with an unpaired electron. Considering an energy cost for S center creation, our predicted activation energy of B diffusion is in good agreement with experiments. In addition, the defect-mediated diffusion model can explain the observed correlation of B diffusion and Si self-diffusion in amorphous silica.

Stabilization of the GeO2/Ge Interface by Nitrogen Incorporation in a One-Step NO Thermal Oxynitridation

“…Uematsu and co-workers proposed that triply bonded nitrogen would hinder Si–O bond reconstruction, reducing SiO diffusivity to the surface. , The accumulation of SiO at the interface would reduce the rate at which the interfacial reaction occurs and thus inhibit film growth. The fact that nitrogen incorporation significantly lowers boron diffusivity inside SiO 2 supports these hypotheses, as the formation of oxygen vacancies related defects at the SiO 2 /Si interface enhances boron diffusion. − This complex mechanistic scenario taking place at the SiO 2 /Si system can serve as background for understanding the role of N in GeO 2 stabilization. Since the GeO 2 + Ge → 2GeO reaction is the source of thermal instability in GeO 2 /Ge structures, N incorporation must have an influence on this reaction.…”

Ab initiostudy of Cu diffusion inα-cristobalite

“…Some work has been published about the Cu/SiO 2 interface [18,19], but there is nothing available about Cu impurities or diffusion (employing either density-functional theory (DFT) or empirical calculations). On the other hand, many works based on DFT have been published about impurities and diffusion of lighter elements, such as oxygen [20], carbon [21], nitrogen [22], boron [23][24][25] and aluminum [26]. Also much attention has been paid to simulations of native defects in different SiO 2 modifications and their migration [27][28][29][30].…”