O2 Oxidation and Sublimation Kinetics of Single Silicon Nanoparticles at 1200 to 2050 K: Variation of Reaction Rates, Evolution of Structural and Optical Properties, and the Active-to-Passive Transition

Sublimation and O2 etching kinetics for a series of individual silicon (Si) nanoparticles (NPs) were studied for NP temperatures (TNP) from 1200 to 2050 K, using a single NP mass spectrometry technique. Sublimation was significant for TNP > 1700 K, with rates reasonably well fit to Arrhenius kinetics, but evolving, particularly during initial heating. O2 etching efficiencies varied from NP-to-NP and with changing TNP, but also evolved dramatically over time. For TNP ≤ 1500 K, NPs were observed to passivate after losing 30 to 50% of the initial NP mass. At higher TNP, etching efficiency decreased over time, but never passivated. Interestingly, bulk Si passivation has not been observed for the range of TNP and O2 pressures used here, and a model was developed to test the effects of several NP-specific mechanistic parameters on both the initial and time-dependent etching behavior. The optical properties of the hot NPs were also found to evolve as the NPs etched, particularly during the initial fast mass loss, and correlations between emission intensities and etching kinetics were examined.