Oxidation of aluminum nanoclusters
Oxidation of aluminum nanoclusters
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DOI：
10.1103/physrevb.71.205413
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发表时间：
2005-05-01
影响因子：
3.7
通讯作者：
Vashishta, P
中科院分区：
文献类型：
--
作者：
Campbell, TJ;Aral, G;Vashishta, P
采用平行分子动力学方法研究了铝纳米团簇（直径20 nm）的氧化动力学，该方法基于由Streitz和Mintmire引起的可变电荷原子间相互作用，包括离子和共价效应。模拟了分子氧（O-2）环境的正则系综和分子氧（O-2）和原子氧（O-1）环境的微正则系综。计算了氧化区的结构和动态相关性，以及电荷、表面氧化厚度、原子扩散率和局部应力的演变。在微正则系综中，由于Al-O键的巨大能量释放，氧化反应在分子氧和原子氧环境中都具有爆炸性。氧化层中的局部应力引起铝原子和氧原子的快速扩散。对氧化垢的分析揭示了从金属-氧化物界面到氧化物-环境界面的显著电荷转移和局部结构的变化。在正则系综中，氧化物深度随时间线性增长，直到接近30ps，随后氧化物深度饱和作为时间的函数。466 ps后形成厚度约为40埃的非晶态氧化层，与实验结果吻合较好。氧化层的平均质量密度为体积氧化铝密度的75%。通过径向分布和键角分析了氧化物中结构相关性的演变。通过对O原子轨迹及其OAln结构形成的详细分析，我们提出了一个氧化渗透的三步过程，该过程解释了典型系综中氧化物生长的减速。
The dynamics of oxidation of aluminum nanoclusters (20 nm diameter) is investigated using a parallel molecular dynamics approach based on variable charge interatomic interactions due to Streitz and Mintmire that include both ionic and covalent effects. Simulations are performed for both canonical ensembles for molecular oxygen (O-2) environments and microcanonical ensembles for molecular (O-2) and atomic (O-1) oxygen environments. Structural and dynamic correlations in the oxide region are calculated, as well as the evolution of charges, surface oxide thickness, diffusivities of atoms, and local stresses. In the microcanonical ensemble, the oxidizing reaction becomes explosive in both molecular and atomic oxygen environments due to the enormous energy release associated with Al-O bonding. Local stresses in the oxide scale cause rapid diffusion of aluminum and oxygen atoms. Analyses of the oxide scale reveal significant charge transfer and a variation of local structures from the metal-oxide interface to the oxide-environment interface. In the canonical ensemble, oxide depth grows linearly in time until similar to 30 ps, followed by saturation of oxide depth as a function of time. An amorphous oxide layer of thickness similar to 40 angstrom is formed after 466 ps, in good agreement with experiments. The average mass density in the oxide scale is 75% of the bulk alumina density. Evolution of structural correlation in the oxide is analyzed through radial distribution and bond angles. Through detailed analyses of the trajectories of O atoms and their formation of OAln structures, we propose a three-step process of oxidative percolation that explains deceleration of oxide growth in the canonical ensemble.