The inelastic and reactive scattering dynamics of O(³P) atoms on a 6H-silicon carbide (SiC) surface were investigated as a function of temperature with a molecular beam-surface scattering technique that employed a rotatable mass spectrometer detector. One set of experiments used a pulsed hyperthermal beam that produced ∼8 km s^–1 O atoms, and another set of experiments used a continuous beam that contained O atoms with a nominal velocity of ∼2 km s^–1. When exposed to the relatively low-flux, pulsed hyperthermal O-atom beam, a passive oxide layer on the SiC that formed at lower temperatures decomposed as the temperature increased above 1673 K. Instead of entering an active oxidation regime, a graphitic layer formed on the surface and largely protected the underlying SiC from incoming O atoms. Investigation of the oxide decomposition without O-atom bombardment revealed volatile Si and SiO products at the moment that the oxide decomposed, implying that Si sublimation occurs concurrently with oxide decomposition. In the experiment with the continuous (higher flux) O-atom beam, volatile SiO and CO products were observed after the passive oxide decomposed, indicating that active oxidation was reached. The results of this study provide evidence for the importance of Si sublimation within the active oxidation regime. Above the passive-to-active transition temperature, Si sublimation is an ongoing process, and continuous active oxidation will only occur if sufficient oxygen reacts with the surface to produce SiO more quickly than a graphitic layer can form. Thus, accurate models of SiC ablation by atomic oxygen must account for multiple competing mechanisms that depend on the surface temperature and incident O-atom flux.

中文翻译：

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碳化硅与原子氧通过被动到主动转变的氧化


采用可旋转质谱仪检测器的分子束面散射技术研究了 O（³P） 原子在 6H-碳化硅 （SiC） 表面上的非弹性和反应散射动力学随温度的变化。一组实验使用脉冲高温束，产生 ∼8 km s^–1 个 O 原子，另一组实验使用连续束，其中包含标称速度为 ∼2 km s^–1 的 O 原子。当暴露于相对低通量的脉冲超热 O 原子束时，SiC 上在较低温度下形成的钝化氧化层会随着温度升高到 1673 K 以上而分解。表面形成石墨层，而不是进入活性氧化状态，并在很大程度上保护底层 SiC 免受 O 原子的进入。对没有 O 原子轰击的氧化物分解的研究揭示了在氧化物分解的那一刻挥发性 Si 和 SiO 产物，这意味着 Si 升华与氧化物分解同时发生。在连续（较高通量）O 原子束的实验中，观察到钝化氧化物分解后挥发性 SiO 和 CO 产物，表明达到了主动氧化。这项研究的结果为活性氧化过程中 Si 升华的重要性提供了证据。在被动到主动转变温度以上，硅升华是一个持续的过程，只有当足够的氧气与表面反应以比石墨层形成更快的速度产生 SiO 时，才会发生连续的主动氧化。因此，原子氧烧蚀 SiC 的准确模型必须考虑取决于表面温度和入射 O 原子通量的多种竞争机制。