异质原子在Cu(001)表面扩散的分子动力学模拟

Molecular dynamics simulation of heterogeneous adatom diffusion on Cu(001) surface

采用分子动力学方法模拟单个增原子Ag,Pd和Cu在Cu(001)表面上的扩散过程.通过对自扩散和异质扩散过程中扩散机制的观察,统计三种不同的增原子在不同温度下的扩散频率,拟合给出扩散势垒和扩散频率的指前因子,并与扩散势垒的静力学计算结果进行比较.结果表明:在800K以下时,三种增原子均以简单跳跃机制为主扩散,与衬底不互溶的Ag增原子的跳跃频率最大,与衬底互溶的Pd增原子的跳跃频率最小.同质增原子与异质增原子的扩散频率和温度的关系均较好地符合Arrhenius公式,由Arrhenius公式拟合给出的三种不同增原子的扩散势垒与表面结构和增原子表面结合能有关.Pd和Cu增原子从跳跃机制为主向交换机制为主的转换温度分别在825和937K左右.

The diffusion processes of single adatoms Ag,Pd and Cu on Cu（001）surface are investigated by molecular dynamics.By observing the mechanisms of self-diffusion and heterogeneous diffusion,the diffusion frequencies of three kinds of adatoms under different temperatures are counted and diffusion barriers and the pre-exponential factors of diffusion frequency are fitted.The results of diffusion barriers are compared with those from the static calculation.The results show that：Under 800 K,the dominant diffusion mechanism of adatom Ag,Pd and Cu is the simple hopping mechanism.The hopping frequency of adatom Ag is the biggest,and that of adatom Pd is the smallest.For homogeneous and heterogeneous adatom diffusion processes,the relationship between diffusion frequency and temperature obeys the Arrhenius formula.The diffusion barriers fitted from Arrhenius formula are relevant to the surface structure and the cohesive energy of adatom on the surface.The transition temperatures of diffusion from the jump-mechanism-dominant to the exchange-mechanism-dominant are about 825 K and 937 K for Pd and Cu adatoms respectively.