Hydrogen-Induced Rupture of Strained Si─O Bonds in Amorphous Silicon Dioxide

Using ab initio modeling we demonstrate that H atoms can break strained Si─O bonds in continuous amorphous silicon dioxide ($a\text{−}{\mathrm{SiO}}_2$) networks, resulting in a new defect consisting of a threefold-coordinated Si atom with an unpaired electron facing a hydroxyl group, adding to the density of dangling bond defects, such as $E^{\prime }$ centers. The energy barriers to form this defect from interstitial H atoms range between 0.5 and 1.3 eV. This discovery of unexpected reactivity of atomic hydrogen may have significant implications for our understanding of processes in silica glass and nanoscaled silica, e.g., in porous low-permittivity insulators, and strained variants of $a\text{−}{\mathrm{SiO}}_2$.

Figure 1

Atomic configuration and spin density of the hydrogen-induced defect: the hydroxyl $E^{\prime }$ center. The Si atoms are the bigger yellow balls, the O atoms are the smaller red balls and the H atom is the small white ball. The spin density is the blue, transparent polyhedron. It is clearly localized on the threefold-coordinated Si and its three O neighbors which faces a hydroxyl group.

Figure 2

Correlations between the one-electron levels and relative stabilities of the hydroxyl $E^{\prime }$ center with the nonbonding Si-O interaction. (a) A histogram of the distribution of the Si-O distances of the dissociated Si─O bond in the hydroxyl $E^{\prime }$ center [see Fig. 1]; (b) energies of the one-electron defect levels with respect to the top of the $a\text{−}{\mathrm{SiO}}_2$ valence band plotted against the Si-O distance; (c) the relative stability of the hydroxyl $E^{\prime }$ with respect to an interstitial H atom, plotted against the Si-O distance.