No abstract

O2 oxidation and sublimation kinetics for >30 individual nanoparticles (NPs) of five different feedstocks (graphite, graphene oxide, carbon black, diamond, and nano-onion) were measured using single-NP mass spectrometry at temperatures (T NP) in the 1100–2900 K range. It was found that oxidation, studied in the 1200–1600 K range, is highly sensitive to the NP surface structure, with etching efficiencies (EEO2 ) varying by up to 4 orders of magnitude, whereas sublimation rates, significant only for T NP ≥ ∼1700 K, varied by only a factor of ∼3. Its sensitivity to the NP surface structure makes O2 etching a good real-time structure probe, which was used to follow the evolution of the NP surface structures over time as they were either etched or annealed at high T NP. All types of carbon NPs were found to have initial EEO2 values in the range near 10–3 Da/O2 collision, and all eventually evolved to become essentially inert to O2 (EEO2 < 10–6 Da/O2 collision); however, the dependence of EEO2 on time and mass loss was very different for NPs from different feedstocks. For example, diamond NPs evolved rapidly and monotonically toward inertness, and evolution occurred in both oxidizing and inert atmospheres. In contrast, graphite NPs evolved only under oxidizing conditions and were etched with complex time dependence, with multiple waves of fast but non-monotonic etching separated by periods of near-inertness. Possible mechanisms to account for the complex etching behavior are proposed.

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.

O2-oxidation and sublimation kinetics for >30 individual nanoparticles (NPs) of five different feedstocks (graphite, graphene oxide, carbon black, diamond, and nano-onion) were measured using single nanoparticle mass spectrometry at temperatures (TNP) in 1100 – 2900 K range. It was found that oxidation, studied in the 1200 to 1600 K range, is highly sensitive to NP sur-face structure, with etching efficiencies (EEO2) varying by up to four orders of magnitude, whereas sublimation rates, significant only for TNP ≥ ~1700 K, varied by only a factor of ~3. Its sensitivity to NP surface structure makes O2 etching a good real-time structure probe, which was used to follow evolution of the NP surface structures over time as they were either etched or an-nealed at high TNP. All types of carbon NPs were found to have initial EEO2 values in the range near 10-3 Da/O2 collision, and all eventually evolved to become essentially inert to O2 (EEO2 < 10-6 Da/O2 collision), however, the dependence of EEO2 on time and mass loss was very different for NPs from different feedstocks. For example, diamond NPs evolved rapidly and monoton-ically toward inertness, and evolution occurred in both oxidizing and inert atmospheres. In contrast, graphite NPs evolved only under oxidizing conditions, and etched with complex time dependence, with multiple waves of fast-but-non-monotonic etching, separated by periods of near-inertness. Possible mechanisms to account for the complex etching behavior are pro-posed.

Sublimation and O 2 etching kinetics for a series of individual silicon (Si) nanoparticles (NPs) were studied for NP temperatures (T NP ) from 1200 to 2050 K using a single NP mass spectrometry technique. Sublimation was significant for T NP > 1700 K, with rates reasonably well fit to Arrhenius kinetics but evolving, particularly during initial heating. O 2 etching efficiencies varied from NP-to-NP and with changing T NP , but they also evolved dramatically over time. For T NP ≤ 1500 K, NPs were observed to passivate after losing 30−50% of the initial NP mass. At higher T NP , etching efficiency decreased over time but never passivated. Interestingly, bulk Si passivation has not been observed for the range of T NP and O 2 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.