Molecular Dynamics Study of the Thin Film Formation Process

Abstract

The initial stage of thin film formation process was studied by the molecular dynamics method. The Morse function was assumed as the interaction potential between the substrate-substrate, substrate-deposited and deposited-deposited atoms. The interfacial structure of the calculated system was restricted to be coherent, i.e. the structures of the substrate and the deposited atoms were both fcc and had the same lattice constants. The depth of the potentials for the three types of interaction was changed to study its effects on the film structure. The substrate temperature was also varied to see the temperature dependence of the relaxation process of the film structure.

Two kinds of structure of the deposited films were considered; three atomic layers of fcc(111) and a monolayer of fcc(111). Both consisted of 19 atoms. They were considered as the nucleus of the film at the initial stage of the deposition process. The deposited nuclei were relaxed into equilibrium shapes such as the monolayer, the 3 dimensional island and the intermediate structure, which were determined by the ratios of the depths of the potentials for the deposited-deposited atoms D_ff and the deposited-substrate atoms D_fs . The relaxed structures were dependent upon the initial structure, but roughly speaking, D_ff/D_fs > 2 made the 3 dimensional island structure, D_ff/D_fs < 1 produced a monolayer and 1 < D_ff/D_fs < 2 the intermediate structure. The appropriate substrate temperature was necessary to accomplish such structural transitions. A low substrate temperature kept the film in the initial structure.

Key Words:

• Thin film formation
• molecular dynamics
• growth mode
• depth of potential
• substrate temperature