An Atomistic Simulation Of Surface Self-diffusion On Re And Mg Clusters And Growth Of Al Adatom On Mg Clusters

In this work, the analytic embedded atom method (EAM) has been used to studysome surface phenomenon systematically, such as the self-diffusion processes of Reand Mg metallic clusters with HCP structure, the diffusion and growth processes of Aladatoms on Mg cluster.The self-diffusion processes of Re and Mg clusters have been studied bycombining with the diffusion theory and the analytic EAM. The Re adatom intrafacetand interfacet self-diffusion processes on the4061-atom Re clusters with hexahedralstructure (Re HEX4061) have been studied. The mechanisms of these diffusionprocesses have been analyzed and some corresponding diffusion energy barriers havebeen calculated, which are in accord with the experimental results. The self-diffusionprocesses of Mg adatom on the587-atom Mg clusters with hexahedral structure（MgHEX587) have been studied. Diffusion energy barriers on Mg clusters are much lowerthan on Re clusters, especially on the (0001) facet, the value is0.02eV. We findhopping mechanisms play an important role for an adatom jumps across the step edgesbetween two facets of Re and Mg clusters. It means that the adatom on these clustersis difficult to penetrate into the cluster at low temperature.The anisotropic diffusion processes of Al adatom on the Mg HEX587cluster havebeen studied. Comparing with the results about self-diffusion processes of Mg and Reatom, there are some similarities and differences. On the (0001) facet, the diffusionprocesses are all easy to occur and there are some lower energy potential well on the(1101) facet on these cluster, the diffusion processes are hindered by the potentialwell. The main difference is that interfacet diffusion processes of Al adatoms on Mgcluster take place by exchange mechanisms mainly. We note that the ES barrier of Aladatom on the one path of Mg HEX587cluster by the exchange mechanism is0.049eV.The value of the ES barrier is so low that Al adatom is easy to push out Mg atom onthese steps and then occupy the sites. Comparing with the results about anisotropicdiffusion processes of single Al adatom, the anisotropic diffusion processes of Aldimers on the Mg HEX587cluster have been studied.The growth of Al adatom on Mg clusters has been studied. Many factorsinfluence on the growth of cluster, such as the size, temperature and shape of clustershave been considered. At the same temperature, the shape of clusters is important to the growth of clusters. For example, cluster with561atoms obtain a transition from acuboctahedron (CUB561) to an icosahedraon (ICO561). The growth of Al adatom ontruncated decahedraon cluster with561atoms (TDEC561) is similar to that on HEX587.An Mg-core/Al-shell cluster is also obtained. It is shown that the larger the cluster is,the more stable the cluster is. At low temperature, we can obtain an Mg-core/Al-shellcluster. As the temperature rise to250K, Al adatoms begin to enter the cluster, moreand more Mg atoms occur on the surface of cluster and the cluster ofMg-core/Al-shell can not be obtained. In addition, the growth of Al adatom on MgHEX967cluster at150K has been chosen to be discussed. At the beginning of thesimulation, a little of Al atoms deposes on the cluster, the mechanism of growth on theclusters have been researched. After being continuously deposited, the number of theAl atoms is600, the surface of the Mg cluster was almost occupied by the Al atomsand an Mg-core/Al-shell cluster with HEX structure was obtained. The results verifiedour analysis of the three factors of growth on the clusters.There are various kinds of theories related to the surface diffusion and growth，which mostly concentrated on face-centered cubic (FCC) metal clusters andbody-centered cubic (BCC) metal clusters, as far as we know, the study of hexagonalclose packed (HCP) metals is limited. Only fitting the bulk properties of metals, theanalytic EAM can predict surface dynamic properties for clusters in our paper withoutany parameter about surface properties. Our work is very important for developing thediffusion and growth theories and for guiding the diffusion and growth experiments.