Diffusion Dynamics Behaviors Of Two Dimension Atomic Clusters On Typical Metal And Alloy Surface

The performance and life of material closely relate to the surface morphology and growth pattern, which are invovled with the surface diffusion, especially in atomic level. It is believed that understanding and predicting of the surface diffusion of the materials is very beneficial not only to the material fabrication, but also to the applicatons in modern industries. Based on the Terrace_Ledge_Kink (TLK) model, the surface diffusion dynamics behaviors of metal and alloy are studied with the modified analytic embedded-atom method (MAEAM) and molecular dynamics (MD) simulation in this thesis. It is hoped that there are some guidance in crystal epitaxial growth.The expression of the Einstein relation is improved according to the simulation time in MD simulation. According to the TLK model, the self-diffusion dynamics behaviors of Pd adadtom and dimer are studied in the low-index Pd surface. The self-diffusion behaviors of Pd adatom are studied in the step and kink. The self-diffusion of Pd adatom and dimer is through the simple exchange mechanism in Pd(001) surface, and the migration energy and prefactor are deduced by Arrhenius relation. The migration energy of Pd dimer is slightly lower than that of the single Pd adatom. The diffusion of Pd adatom is anisotropic in Pd(110) surface. On Pd(110) surface, the adatom diffuses through the hopping mechanism along channel direction, and it do through the simple exchange mechanism across the channel. For self-diffusion dynamics behaviors of the small two-dimensional cluster on the Pd(111) surface, wth increasing size, the migration energies increase monotonically, but the increase is noticeably bigger from Pd6 to Pd₇. The prefactor of Pd₇ cluster is 2 orders of magnitude greater than that for the single Pd adatom. The analysis of trajectories shows the noncompact clusters diffuse by the local diffusion mechanism but the compact clusters diffuse mainly by the whole gliding mechanism. Based on the Pd(111) surface, Pd₇ clusters can be the nucleus in the room temperature range according to nucleation theory in homeepitaxial growth experiments.The Pd adatom diffuses along all of the step direction through the hopping mechanism on the low-index Pd surface, and the diffusion rates are lower than these on corresponding terrace at the same temperature. When going across the step, the single Pd adatom must overcome the additional ES energy barrier, and the kink at the step may effectively reduce the ES barrier. In the homeepitaxial crystal growth, it can form the dense and uniform film on the Pd(001) surface, in the low temperature range the film easily forms the pyramid appearance on the Pd(111) surface, and it forms peak-appearance film on the Pd(110) surface.The self-diffusion dynamics behaviors of the Re and Zr clusters are studied in low index surface and the corresponding step. In HCP(0001) surface, wth increasing size, the migration energies increase monotonically, but the increase is noticeably bigger from hexamer to heptamer. The prefactor of heptamer is 2 or 3 orders of magnitude greater than that for the corresponding single adatom. The analysis of trajectories shows the noncompact clusters diffuse by the local diffusion mechanism but the compact clusters diffuse mainly by the whole gliding mechanism, simllar to the diffusion behaviors of the Pd clusters on Pd(111) surface. In the homeepitaxial crystal growth, Re₃ cluster can be the nucleus on the Re(0001) surface in the room temperature range according to nucleation theory, but Zr7 cluster cannot be the nucleus on Zr(0001) surface.Re adatom and dimer always diffuse along the channel on Re(1 010) surface through the hopping mechanism. The diffusion mechanism of the dimer is that both of atoms simultaneously hop to the neighboring sites, and the migration energy is almost 2 times of that of the adatom. On Re(0001) surface, the adatom diffuses through the hopping mechanism not only along the step, but also across the step. Using the diffusion dynamics equation, the diffusion rates of the adatom are changed with substrate temperature along A-type and B-type step. The critical temperature (1670±20 K) is gained, which is a very important result. When substrate temperature T < (1670±20 K), the diffusion rate along B-type step is faster than that along A-type step; when substrate temperature T > (1670±20 K), the diffusion rate along A-type step is faster than that along B-type step. Corresponding to the barrier on the terrace, the ES barrier of the adatom is very high across the step, and the kink only descends slightly the ES barrier. It is difficult that the adatom goes across the step, and the mass transport of interlayer is very difficult. In the homeepitaxial crystal experiment, the film easily forms the pyramid appearance on the Re(0001) surface, simllar to homeepitaxial growth on Pd(111) surface.The heterogeneous diffusion dynamics behaviors of Pt2 and Pt3 clusters are studied on Pd(111) surface, and the diffusion mechanisms are similar to these of Pd2 and Pd₃ clusters on Pd(111) surface. The heterogeneous diffusion rates are lower than these of the homerogeneous diffusion on the Pd(111) surface at the same temperature. The characteristic temperature is higher than these of the homerogeneous diffusion.The diffusion dynamics behaviors of Al and Fe adatom are studied on B2-FeAl(110) and B2-FeAl(001) surface. The migration energy of the Fe adatom is lower than that of Al adatom on B2-FeAl(110) surface,. At the same temperature, the diffusion rate of Fe adatom is faster than that of Al adatom. For the diffusion behaviors on the B2-FeAl(001) surface that the outermost are all of Al atoms, the migration energy of Fe adatom (0.79 eV) is much higher than that of Al adatom (0.30 eV). For the diffusion behaviors of Fe₂ dimer on B2-FeAl(110) surface, the lower migration energy compared with the single Fe adatom is that the coordination number is higher for the migrating atom because the average bond strength typically decreases with higher coordination number, weaker bonds can be broken easily to form the dimer transition state, similar to the diffusion behaviors of Fe adatom and Fe₂ dimer on the Fe(110) surface.