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Kinetics and Mechanism of γ-Al2O3 Solid Phase Epitaxy on c-Plane α-Al2O3
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2023-06-28 , DOI: 10.1021/acs.jpcc.3c01695
Zhongyi Wan 1 , Rui Liu 2 , Donald E. Savage 2 , Thomas F. Kuech 2, 3 , Paul G. Evans 2 , J. R. Schmidt 1
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2023-06-28 , DOI: 10.1021/acs.jpcc.3c01695
Zhongyi Wan 1 , Rui Liu 2 , Donald E. Savage 2 , Thomas F. Kuech 2, 3 , Paul G. Evans 2 , J. R. Schmidt 1
Affiliation
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Experiments and molecular dynamics (MD) simulations show that crystallization of amorphous Al2O3 via solid phase epitaxy (SPE) on a (0001), c-plane, α-Al2O3 substrate forms a metastable γ-Al2O3 polymorph before transforming eventually to α-Al2O3. MD simulations over a wide range of crystallization temperatures above the glass transition point Tg show that the growth velocity of epitaxial γ-Al2O3 follows the Wilson–Frenkel relation. The barriers associated with interfacial reorganization processes are minimal, indicating that mass transport to the amorphous–crystalline interface is the rate-limiting step over the entire temperature range for γ-Al2O3 SPE. The mechanisms of transport depend on the temperature and have a significant effect in determining the crystallization velocity. Above Tg, mass transport is controlled by bulk diffusion. Below Tg, the crystallization velocity is faster than predicted from the Wilson–Frenkel relation in both the MD and experimental results. X-ray characterization shows that the growth of epitaxial γ-Al2O3 follows an Arrhenius dependence on crystallization temperature from 700 to 800 °C with an apparent activation energy of 3.1 eV. Despite the fact that MD shows essentially no bulk diffusion at temperatures below Tg, SPE growth is nonetheless observed. Our simulations show that this persistent growth is the result of kinetic heterogeneity between bulk and interface, with epitaxial growth governed by enhanced diffusion near the amorphous–crystalline interface. The rate of interfacial diffusion is computed using a hopping rate based on the first passage time of atoms moving to neighboring crystallization sites. The combination of conventional diffusion and interfacial hopping modes of mass transport within the Wilson–Frenkel model provides an accurate estimate of the SPE growth velocity of γ-Al2O3 both above and below Tg.
中文翻译：
c面α-Al2O3上γ-Al2O3固相外延的动力学及机理
实验和分子动力学 (MD) 模拟表明，非晶 Al 2 O 3通过固相外延 (SPE) 在 (0001)、c 面、α-Al 2 O 3衬底上结晶，形成亚稳态 γ-Al 2 O 3最终转变为α-Al 2 O 3之前的多晶型物。在高于玻璃化转变点T g的较宽结晶温度范围内的 MD 模拟表明，外延 γ-Al 2 O 3的生长速度遵循威尔逊-弗兰克尔关系。与界面重组过程相关的势垒很小，表明向非晶-结晶界面的传质是 γ-Al 2 O 3 SPE整个温度范围内的限速步骤。传输机制取决于温度，并且对确定结晶速度具有显着影响。高于T g时，传质受体扩散控制。低于T g时，结晶速度比 MD 和实验结果中的 Wilson-Frenkel 关系预测的要快。X射线表征表明外延生长的γ-Al 2 O 3遵循阿伦尼乌斯依赖于 700 至 800 °C 的结晶温度，表观活化能为 3.1 eV。尽管 MD 在低于T g 的温度下基本上没有表现出整体扩散，但仍然观察到 SPE 生长。我们的模拟表明，这种持续生长是体相和界面之间动力学异质性的结果，外延生长受非晶-晶体界面附近增强扩散的控制。界面扩散速率是使用基于原子移动到相邻结晶位点的首次通过时间的跳跃速率来计算的。Wilson-Frenkel 模型中质量传输的传统扩散和界面跳跃模式的组合提供了 γ-Al 的 SPE 生长速度的准确估计2 O 3高于和低于T g。
更新日期：2023-06-28
中文翻译：
c面α-Al2O3上γ-Al2O3固相外延的动力学及机理
实验和分子动力学 (MD) 模拟表明，非晶 Al 2 O 3通过固相外延 (SPE) 在 (0001)、c 面、α-Al 2 O 3衬底上结晶，形成亚稳态 γ-Al 2 O 3最终转变为α-Al 2 O 3之前的多晶型物。在高于玻璃化转变点T g的较宽结晶温度范围内的 MD 模拟表明，外延 γ-Al 2 O 3的生长速度遵循威尔逊-弗兰克尔关系。与界面重组过程相关的势垒很小，表明向非晶-结晶界面的传质是 γ-Al 2 O 3 SPE整个温度范围内的限速步骤。传输机制取决于温度，并且对确定结晶速度具有显着影响。高于T g时，传质受体扩散控制。低于T g时，结晶速度比 MD 和实验结果中的 Wilson-Frenkel 关系预测的要快。X射线表征表明外延生长的γ-Al 2 O 3遵循阿伦尼乌斯依赖于 700 至 800 °C 的结晶温度，表观活化能为 3.1 eV。尽管 MD 在低于T g 的温度下基本上没有表现出整体扩散，但仍然观察到 SPE 生长。我们的模拟表明，这种持续生长是体相和界面之间动力学异质性的结果，外延生长受非晶-晶体界面附近增强扩散的控制。界面扩散速率是使用基于原子移动到相邻结晶位点的首次通过时间的跳跃速率来计算的。Wilson-Frenkel 模型中质量传输的传统扩散和界面跳跃模式的组合提供了 γ-Al 的 SPE 生长速度的准确估计2 O 3高于和低于T g。
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