Indeed, pre-heated silica NPs at 1200 K had initial EEO2 substantially higher than Si NPs, which we attribute to rougher surface layers with more sites capable of dissociatively adsorbing O2. The pre-heated silica NPs passivated substantially faster than Si NPs under the same conditions, which is attributed to participation of subsurface oxygen in the etching/passivation process. After passivation, the NPs remain "black", demonstrating the presence of a substantial residual Si-rich volume.