分子动力学模拟Cu(010)基体对负载Co-Cu双金属团簇熔化过程的影响

纳米团簇负载到基体上的结构演化和热稳定性是其走向技术应用的关键. 本文用分子动力学结合嵌入原子方法模拟了具有二十面体初始结构的Co₂₈₁Cu₂₈₀ 混合双金属团簇在Cu(010)基体上的熔化过程, 考察了基体的Cu原子可以自由移动(自由基体)和固定(固定基体)两种条件对负载团簇熔化的影响. 发现基体条件对团簇的熔化有明显的影响. 在自由基体上团簇原子的温度-能量曲线存在明显的团簇熔化时的能量突变点, 熔点为1320 K, 低于固定基体上团簇的熔点1630 K. 在升温过程中团簇的二十面体结构会在基体表面发生外延生长. 外延团簇随着温度增加发生表面预熔, 预熔原子会逐渐向基体表面扩散形成薄层, 直至完全熔化. 自由基体上团簇原子的嵌入行为会使原子的分布状态产生不同于固定基体上的演变.

Molecular dynamics simulation of the influence of Cu(010) substrate on the melting of supported Co-Cu bimetallic clusters

Structural evolution and thermal stability of nanoclusters supported on the substrate play a key role in their applications. In this paper, we study the melting of the mixed Co₂₈₁Cu₂₈₀ bimetallic cluster with the icosahedral configuration by using molecular dynamics simulation with a general embedded atom method. The influence of the free or fixed Cu(010) substrate on the melting of the supported cluster is explored. It is found that the melting is strongly related to the substrate condition. There is a sharp increase in the temperature-energy curve for the cluster on the free substrate. The melting point (1320 K) is much lower than that (1630 K) of the cluster on the fixed substrate. The icosahedral configuration is converted into epitaxial cluster along the (010) of the substrate. Premelting occurs for the epitaxial cluster with the increase of temperature. The premelted atoms diffuse to the surface of the substrate and form surface layer until the cluster melt. The variation of the atomic spreading for the cluster on the free substrate is different from the case on the fixed substrate due to the atomic embedding into the substrate.