Molecular Dynamics Simulation Study Of Single Cu Clusters Deposit On Different Structure Fe And Clusters Deposit Continuously Into Films

Fe/Cu magnetic multilayers are widely used in hard disk,magnetic sensor,magnetic storage and other devices because of the great magnetoresistance effect in Fe/Cu magnetic multilayers.This makes the study of Fe/Cu multilayer films always a hot topic in materials science.The results show that the structure of the film will seriously affect the giant magnetoresistance effect of metal multilayer films.However,due to the limitation of experimental equipment and conditions,the microscopic process of film growth cannot be observed directly in the experiment.This limits the understanding of the mechanism by which thin film structures are formed.In this paper,Molecular Dynamics MD is used to reproduce the microscopic process of film growth at the atomic and molecular level.It is helpful to reveal the growth law of thin film and the formation mechanism of thin film structure.MD simulation is a deterministic simulation method,which can determine the motion process and state of the system according to reasonable initial conditions and rigorous mathematical calculation.It can show the microscopic mechanism of the interaction between atoms and molecules at the level of atoms and molecules.Therefore,a lot of research work has been done on atomic or cluster deposition using molecular dynamics simulation method.Based on the self-compiled molecular dynamics simulation software package for cluster deposition,part of the program was modified using FORTRAN 95 language to simulate Cu cluster deposition on Fe substrates with different structures.After debugging verification,to meet the needs of the research work.Three regular icosahedral structures of Cu13,Cu55 and Cu147 were selected as sedimentary clusters,and F-S potential functions were used to describe the atomic interactions among Fe-Fe,Fe-Cu and Cu-Cu.The cluster incidence direction is vertical(VV)substrate surface incidence.The initial incident energies of the cluster were selected as 0.1,1.0,2.5,5.0,10.0,15.0 and 20.0e V/atom.The substrate is body centered cubic(bcc)crystal structure Fe(001)and face centered cubic(fcc)crystal structure Fe(001),and the substrate temperature is selected as 300 K.The simulation results show that when the incident energy is low,the single cluster mainly presents surface reconstruction after deposition.When the incident energy increases,the potential field distribution is different due to the difference in the structure of the deposition substrate.This makes the interaction between cluster atoms and substrate atoms to form plateau sub-density regions different during deposition contact.Therefore,the high atomic density region in the fcc structure Fe substrate diffused deeper along the Z axis and was more concentrated in the XY plane.Therefore,the single cluster deposition in the XY plane of fcc structure Fe is less than that in bcc structure,while the Z-axis diffusion is greater than that in bcc structure.The epitaxial degree formed on fcc structure Fe is better,so it can be considered that the lattice matching between bcc structure Fe substrate and Cu cluster is higher.On the Z-axis,the fcc structure has a deeper plateau subdensity area,and the damage degree to the substrate structure is lower,which can help to form a film with high mixing degree,good epitaxial degree and fewer defects.Based on the existing molecular dynamics simulation program,the molecular dynamics simulation program of Cu cluster deposition on Fe(001)surface was developed.The effects of deposition energy and cluster size on the growth pattern and quality of the films were studied.In the simulation model,the cluster size was Cu6,Cu13,Cu26 and Cu39,and the deposition energy was 0.1,1,2.5,5,10,15 and20 e V/atom.The substrate is a 300 K bcc structure Fe(001)surface.The main conclusions are as follows: when the incident energy is low or the Cu cluster size is small,only part of the cluster atoms collide directly with the substrate.Since the plateau subdensity region formed by the collective collision cannot provide enough energy for atoms to migrate,the deposited clusters of atoms accumulate continuously on top of the bottom atoms to form island structures.The resulting film has poor epitaxy and large surface roughness.With the increase of incident energy,the epitaxial degree of the deposited films first increases and then decreases,and the surface roughness decreases.The Cu films formed by smaller clusters grow in two modes: island mixing or layer growth.However,with the increase of incident energy,larger clusters undergo three processes of island-like,layer-island mixing and layer-like growth successively,and the epitaxy of the films formed is smaller than that of the films formed by smaller clusters.The simulation results show that the smaller the cluster size,the better the ductility,smoother,fewer defects and stronger the bond strength of the film formed.In the simulation model,the films deposited by Cu clusters with a size of 6 and medium energy(5.0 ～ 10.0 e V/atom)have the highest epitaxy,the lowest roughness and the least defects,and the best performance can be obtained.