Density and thickness of the host matrix

The host matrix in the current work was a-SiO₂ with a density of 2.2 g.cm⁻³ and a thickness of 140 ± 15 nm. The thickness was calculated by applying the log-ratio method to the collected EELS spectrum and using an inelastic mean free path from the literature²⁵ (specimen thickness is given by the product of the “inelastic mean free path” and “relative thickness” calculated from the EELS spectrum: 250 nm × 0.55 = 137 nm). However, during annealing, the specimens were observed to curl and bend as evidenced by the focus variation at the specimen edges and a progressive darkening due to a drop in the transmitted intensity. It was assumed that the centres of the precipitates remained stationary and, by measuring the distance between the centres of the precipitates, an approximate estimate of the tilt angle and effective specimen thickness was obtained. The effective specimen thickness after 30 minutes of annealing was estimated to be about 160 nm. Therefore, the image simulation at 973 K considers a specimen thickness of 160 nm.