分子动力学模拟Ag-Pd双金属团簇中不同位置Ag原子偏析诱导的异常熔化

Molecular dynamics simulation of the irregular melting in Ag-Pd bimetallic cluster induced by the segregation of Ag atoms with different positions

在双金属团簇中任意两种元素表面能的差别都会在团簇形成时产生偏析,从而影响团簇的熔化、原子排布和结构.因此双金属团簇中原子偏析行为的研究可以为新型纳米结构的可控制备提供理论基础.本文用分子动力学结合嵌入原子方法研究了分布在团簇的核心层和亚表面层的Ag原子偏析对(AgPd)147团簇熔化的影响.结果表明Ag在Pd团簇的不同位置时能量不同,在表面层时最稳定,其次是核心层,最后是亚表面层.这造成了核心层的Ag原子偏析到团簇的亚表面层时,团簇原子能量随温度的增加而增大.而亚表面层Ag原子的偏析会使团簇原子能量随温度的增加而减小.这种异常熔化的程度与偏析原子个数有关.这为双金属团簇熔化行为的调节提供了有效途径.

Segregation occurs in bimetallic clusters during the formation process due to the difference in surface energies between two random elements.It will influence the melting,chemical ordering and structure of the cluster.Research on the atomic segregation in bimetallic cluster plays a key role in the controllable design of new nano-structure.The influence of the segregation of Ag atoms with Ag embedding in core layer and subsurface layer on the melting of the（AgPd）147 is studied by molecular dynamics simulation.It is found that atomic energies in the cluster are different for Ag embedding in differerent positions of Pd cluster.The most stable position is surface layer,then the core layer,and finally the subsurface layer.This leads to the sharp increase of atomic energy with the increase of the temperature when the Ag atoms in the core layer segregate to the subsurface layer.The atomic energy sharply decreases with the increase of the temperature when the atoms in the core layer segregate to the surface layer.The irregular phenomenon during the melting is strongly related to the segregated atomic numbers.This gives an effective method to tune the melting of the bimetallic clusters.