For Si and silica NPs, EEO2 should be proportional to the O2 dissociative adsorption rate, which for constant PO2, is proportional to the sticking probability. The literature Si etching models assume that O2 sticks only at exposed Si sites, i.e., sticking is blocked by surface oxygen. For preheated Si NPs, any initial surface contamination (including oxides) would have been lost during pre-heating, when TNP was held in the temperature range where surface SiO2 is known to decompose and desorb, long enough (>10 minutes) to desorb several monolayers-worth of material. Furthermore, the lifetime of Oads at 1200 K with respect to desorption is short compared to the O2 sticking rate, thus the pre-heated Si NPs should have had few if any O2 adsorption sites blocked by oxygen or other adsorbates during the initial stage of etching. For silica NPs, preheating clearly results in an Si-rich surface, but Figs. 1 and 2 indicate that the ~100 milliseconds of pre-heating used in the etching experiments did not completely transform the NPs. Thus, the pre-heated silica NPs probably retained significant oxygen, most likely in the subsurface region, but possibly on the surface as well.