Computer simulation of vapor deposition

Abstract

The initial nucleation which occurs during vapor growth on a crystalline substrate has been simulated in a computer by the use of Monte Carlo methods. The crystalline surface is represented by a 30 × 30 array and the deposition site is selected randomly as is the alternative between adsorbed atom migration or evaporation. The output was programmed so as to be displayed graphically or tabulated. During each simulation run atoms were given the opportunity of moving between two and three thousand times. The result of simulations at three different temperatures where surface activation energies and binding energies were chosen so as to be on the range reported for silver on silver chloride showed that while good agreement between the simulation and the two-dimensional nucleation theory of Zinsmeister occured at the start of nucleation, agreement could only be obtained at later stages if direct impingement of depositing atoms is considered.In summary, the computer simulations were found to be in general agreement with two-dimensional nucleation theory. The most important points of disagreement are: (1) the temperature dependence of the total cluster concentration which is found is to be temperature-dependent at all temperatures investigated; and (2) the cluster size distribution, which is much broader than predicted. The simulation results indicate that the assumption of no direct impingement of depositing atoms is more critical than the assumption of the size independence of the collision cross section. Finally, it has been shown that the nucleation theory can be applied to the co-deposition of two different atomic species.