Study On Diffusion Behavior Of Adatom On Cu(001) Surface By Molecular Dynamics

Diffusion behavior of adatom and ad-dimer is one of the main researching object in the field of thin film physics. Study on the diffusion of adatom and ad-dimer at atomic level is the primary task of simulating the mechanism of thin film growth by computer and it will have significant instructional meaning for our understanding of the physical essence of thin film growth. With the atomic interaction potential with the embedded atom methods, molecular dynamics simulation was used to study the variation of Cu (001) surface caused by a Cu adatom and the hoping barriers of another Cu adatom in the vicinity of the Cu adatom. Then the concept of temporary steady states of ad-dimer is put forward, and the diffusion of homo-ad-dimer and hetero-ad-dimer with temporary steady states is studied, including their lifespan and diffusion coefficients.The major points of this work were summarized as follows:1. Distortion of lattice caused by a single adatomThe results show that the Cu adatom may enable the positions of Cu atoms in the substrate rising in a range of 2 lattice constants and the influence is as deep as 10 layers.2. The influence of a single adatom on self-diffusion of another adatomDue to the interaction of the stress field between two adatoms, the hoping diffusion barriers of the adatoms are decreased and the adatoms are more active in diffusion than a single adatom. By comparing the difference of hoping barriers toing-and-froing along a same diffusion path, the migrating behavior of the adatoms can be divided into two kinds of diffusion, depending on the distance between the two adatoms. If they are in a distance longer than the effective distance of the atomic interaction potentials, the diffusion of adatoms is affected only by the interaction of the stress field between two adatoms. If they are in a distance shorter than the effective distance of the atomic interaction potentials, the two adatoms should be considered as an ad-dimer in different temporary steady states.3. Diffusion of ad-dimer with temporary steady statesWhen the temperature is lower than 400K, the ad-dimer will exist for infinite long time for the lifespan is long enough in the micro-timescale. The coefficient of the ad-dimer is considerably small which indicates weak diffusivity. So the second and third temporary steady states has nothing to do with the diffusion of the ad-atom. However, when the temperature is higher than 400K, sometimes the ad-dimers will die and with the increase...