A Study Of Enhancement Of Adatom Incidence On Formation Of Misfit Dislocations In Epitaxial Aluminum Films

Misfit dislocation is one of the key researches in thin film field. They mostly form in the atomic deposition processes, while current experimental means do not have enough resolution power in both space and time to analyze any processes at atomistic scale. Using three dimensional molecular dynamics method, taking FCC aluminium as prototypes, we have carried out atomistic simulation studies of some factors on formation of misfit dislocations in epitaxial aluminum films. An embedded atom method (EAM) potential is used to calculate the interaction of aluminum atoms. The work mainly include establishing the molecular dynamics model of epitaxial growth; choosing the parameters for the model; enhancement of the positions of adatom incidence on formation of misfit dislocation in the epitaxial thin films; influence of kinetic energy of adatom incidence on formation of misfit dislocation in the epitaxial thin films. The results show that:(1) Incubation time of misfit dislocation is related to deposition temperature and film thickness in the epitaxial aluminum thin films which mismatch is -0.06. The higher temperature or thicker film, incubation time of misfit dislocation will be shorter, and it is easier to format misfit dislocations in the thin film.(2) Only one adatom incidence can break the stabile crystalline structure of epitaxial aluminum film, which is 15 layers thickness, smooth surface and with f_x = -0.06 mismatch.(3) The enhancement on formation of misfit dislocation is related to the incidence position of adatom. The {111} surface has four characteristics positions for <111> growth of FCC crystalline and the order of their enhancement is as following: FCC positions, HCP positions, positions upon the surface atoms, positions upon the middle point of two adjacent surface atoms.(4) Adatom incidence induces a misfit dislocation formation through squeezed out an inverse mini-tetrahedron atomic group in epitaxial thin films with compressive strain. When the adatom deposited on FCC or HCP, the bottom plane of the inverse mini-tetrahedron inclines to the surface of thin films; while on the middle point of two adjacent surface atoms, the bottom plane of the inverse mini-tetrahedron is parallel to the surface of thin films.(5) The enhancement effect of adatom on formation of misfit dislocations will be increase as the incident kinetic energy of adatom increasing. As soon as the kinetic energy is greater than or equal to 0.14eV, the misfit dislocation will be induced to form at 600K in the aluminum film with f_x =-0.06 mismatch, 15 atomic layers thickness and smooth surface.(6) There are two different squeezed out inverse mini-tetrahedron atomic group as the adatom with different incident kinetic energy deposited on FCC position of (111) surface of the epitaxial aluminum thin film. One is that, the inverse mini-tetrahedron is squeezed out by both the incident kinetic energy and the pressure of the adatom, and the adatom is close to one edge of the tetrahedron, when the kinetic energy of adatom is 0.14eV; the other is that, the inverse mini-tetrahedron is squeezed out by only the incident kinetic energy, and the adatom is far away to the tetrahedron, when the kinetic energy of adatom is more than 1.4eV.