Division of Materials Technology, Department of Materials Science and Engineering, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden.
Phys Chem Chem Phys. 2018 Nov 28;20(46):29549-29557. doi: 10.1039/c8cp04519d.
We performed a density functional theory (DFT) investigation of the mechanisms of oxide growth at Al(100), Al(110) and Al(111) up to 1 monolayer (ML) coverage of O-atoms with 0.125 ML increments. We found that the surface binding site preferences of O-atoms are largely affected by the presence of neighboring O-atoms. Based on this we constructed two oxide growth models: the formation of clusters that evolve to stripes with increasing coverage and the formation of a more homogeneous distribution of O-atoms. While the former model is characterized by a lower symmetry of distribution of O-atoms at the surfaces, the latter corresponds to higher symmetries. We found that the prevalence of each oxide growth mode depends on the coverage of O-atoms and that this dependency is different for each surface. For Al(100) and Al(110), up to coverages of 1 ML the oxide grows preferably via the formation of clusters that evolve to stripes with increasing coverage, while for Al(111) the stripes and clusters are the preferred growth mode for coverages up to 0.375 ML, beyond which the homogeneous growth mode is energetically favored. The calculated Al-O pair distribution functions show that the formation of clusters and stripes leads to shorter Al-O bond lengths when compared to the homogeneous growth. The oxides formed at Al(100) and Al(110) have Al-O bond lengths and geometries typical of the shorter bonds of α-alumina while at Al(111) the bond lengths are typical of γ-alumina and β-alumina. These results suggest that for low coverages, the oxides formed at Al(100) and Al(110) are resemblant of defective α-alumina while the oxide formed at Al(111) is similar to less disordered γ-alumina and β-alumina. For Al(111), the small energy difference between the growth of clusters and stripes and homogeneous growth does not exclude the coexistence of both growth modes; this could lead to the formation of a defective or amorphous oxide.
我们采用密度泛函理论（DFT）对 Al(100)、Al(110)和 Al(111)表面在原子层覆盖度为 0.125 ML 的情况下，氧原子的单层（ML）到 1 ML 覆盖度的氧化物生长机制进行了研究。我们发现，氧原子的表面结合位点偏好受相邻氧原子的存在影响较大。基于这一点，我们构建了两种氧化物生长模型：随着覆盖度的增加，团簇的形成逐渐演变为条纹状，以及氧原子更均匀分布的形成。虽然前一种模型的氧原子在表面的分布对称性较低，但后一种模型的对称性较高。我们发现，每种氧化物生长模式的盛行取决于氧原子的覆盖度，并且这种依赖性在每个表面上是不同的。对于 Al(100)和 Al(110)，在 1 ML 覆盖度之前，氧化物的生长主要通过形成团簇来进行，这些团簇随着覆盖度的增加逐渐演变为条纹状，而对于 Al(111)，在 0.375 ML 覆盖度之前，条纹状和团簇是首选的生长模式，超过这个覆盖度后，均匀生长模式在能量上更有利。计算得到的 Al-O 配分函数表明，与均匀生长相比，团簇和条纹的形成导致 Al-O 键长变短。在 Al(100)和 Al(110)上形成的氧化物具有 Al-O 键长和几何形状，与 α-氧化铝的较短键长典型特征相似，而在 Al(111)上形成的氧化物具有 γ-氧化铝和 β-氧化铝的典型键长。这些结果表明，在低覆盖度下，在 Al(100)和 Al(110)上形成的氧化物类似于有缺陷的 α-氧化铝，而在 Al(111)上形成的氧化物类似于无序程度较低的 γ-氧化铝和 β-氧化铝。对于 Al(111)，团簇和条纹以及均匀生长的生长能差异较小，不能排除这两种生长模式共存的可能性；这可能导致形成有缺陷或非晶态的氧化物。
