Calculation And Simulation Of The Coalescence And Deposition Of Clusters And Nanometer Indentation

The coalescence and the deposition of nanometer-size paticles or clusters are simulated by using molecular dynamics method in the frame work of embedded atom method. The processes of initial plastic deformation of single crystal Cu in nanoindentation are simulated by using quasicontinuum method.As the basis of the simulation of coalescence and deposition of the clusters the processes of melting and solidification of Cu cluster are simulated by using molecular dynamics in the frame of embedded atomistic method. The Cu clusters (initial FCC spherical structures) with the diameters of 2.89,3.61 and 4.33 nm are choosen as samples to study the melting and the solidification processes. The resuslts show that the melting poits is increase with the increase of the sizes of the clusters. Different size clusters present almost the same solidification point during the cooling processes.The coalescences simulation are carried out at 300K for the Cu clusters with the diameters of 2.17,2.89 and 3.61nm to study the size effects. The results show that the degree of coalescence is higher for the small clusters than that for the large clusters to the simulation at the same initial temperature. The coalescence simulation of the clusters with the diameters of 2.17nm (456 Cu atoms) the coalescence simulation are carried out at 300K,600K and 900K initial temperatures respectively, which shows the degree of the coalescence rises when the initial temperatures are increased. The degree of the coalescence the culsters at liquid state is remakble higher than that of the clusters at solid state.Small cluster is the basic unit in many processes of preparation of film material. Based on the study of melting and coalescence the processes of deposition of Cu cluster with low energy are investigated with emphasis on the effect of the surface orientation of the substrates. The simulaiton results show that among the depositions of Cu cluster at lquid state on the three low index surfaces the atoms rearreangement on the (111) suface share the relatively higher fitness with the atoms arrangement of the substrate. The epitaxial degree of the cluster deposited on the surface is remarkably influenced by the initial translational energy of the cluster.Molecular dynamics method investigates the materials behavior at the atomistic level and is successfully in studying the issuses relevant to clusters. However, it is resstrained in studying the meso and macro dimenssion system. It is also restrained by simulation time. Quasicontinuum method is one of the multiscale simulation methods, which embedded an area (the vinicity of the defect) directly described at atomistic level into a continuum medium described in finite elements method. It has remarkable advantages in studing materials with defect.The processes of initial plastic deformation of single crystal Cu in nanoindentation are simulated by using quasicontinuum method. The results show the critical loads of dislocation emissions for the systems with widths of 0.835,1.252 andl.670 nm nanometer indenters are are 27.36,29.85 and 32.39 N/m respectively determined by the curves of load-displacement, which is basically agreement with the values of critical loads calculated from the energy points of view.The general regularity of the increase of geometrically necessary dislocations beneath the indenter obtained in the simulation is basically agreement to that predited by using the model of Francois et al.. By analyzing the plot of this displacement field and with the guide of theory of FCC dislocation nucleation it is concluded that Shockley partial dislocation is the basic structure of the dislocations emitted in the simulations.The characteristics of the staking fault in quasicontimuun method simulation and in molecular dynamics simulation are analyzed. The reuslts show that the values of center symmetry parameter reflecting the change of anti-symmetry are about 0.042 to both simulations with different methods, which is basically agreement with the value of theoretical calculation to the intrinsic stacking fault of fcc crystal.The direction change of the motion and the annihilations of dislocations in the unloading show that the crystal experienced the initial plastic deformation can still restor its ogiginal state to some extent...