TNP during CO2 laser pre-heating is estimated to have reached as high as ~2000 K, near Tmelt for silica, and in a range where decomposition/desorption have been observed for bulk SiO2. For example, Porter et al. reported that the vapor over bulk SiO2 in this temperature range contained SiO, SiO2, O2, and O. Thermodynamic analysis by concluded that for T < Tmelt, SiO and O2 are the primary gaseous products, followed by SiO2 and O at ~10 times lower concentrations, with trace amounts of atomic Si and Si2O2. Because the main products are SiO and O2, the net effect is that the composition of the near-surface layers becomes more Si rich, and for NPs this "near-surface" region may encompass a substantial fraction of the NP volume. The conclusion that the NP surfaces became Si-rich during pre-heating is consistent with the observation that pre-heated silica NPs have O2 etching chemistry that is similar in many, but not in all ways, to that for pure Si NPs (see below). Furthermore, as shown in Figs. and, the optical properties and sublimation kinetics of pre-heated silica NPs undergo only modest additional changes during prolonged heating at TNP up to 2350 K, indicating that CO2 pre-heating during trapping had already largely transformed at least the NP surface layers.