Ion bombardment can be used to regulate the submonolayer island growth through vacancy production and by breaking up islands. In the same way as islands grow due to adatom diffusion, mobile vacancies lead to formation of vacancy islands during ion bombardment assisted deposition (IBAD) of thin films. In addition, vacancies will recombine with islands, and thus smoothen the surface. The recombination process is slower than simple aggregation because of the strong Ehrlich-Schwoebel barrier between islands and vacancies.
We consider a reaction kinetic model (RKM) for submonolayer island growth in IBAD on metallic surfaces in a simple case, which shows the dynamics of interplay between vacancies and islands. The RKM is used to compute the island/vacancy size distribution function on the surface in IBAD, and to examine the effects of the Ehrlich-Schwoebel barrier of the island-vacancy recombination process as well as the asymmetry between the island and vacancy diffusion on the growth of the vacancy/adatom submonolayer islands.
In absence of recombination between adatom islands and vacancies, the size distribution of islands retain the scaling form as expected. With moderate recombination rate, while
vacancy production is low compared to the adatom deposition flux, the island size distribution continues to evolve as in normal deposition case, but the vacancy islands gradually vanish by filling. During growth the mean size of vacancy islands reach
a maximun value at some specific coverage, and then starts to diminish. These values for maximum vacancy size and coverage at this maximum have a regular dependence on
control variables. This dependence can be fitted with general exponential forms.
These results and the regularities contained in them in the form of the coverage for maximum island size help to estimate the role of vacancy production in IBAD to the properties of the film growth in different conditions of growth.
[1] I. T. Koponen, M. O. Jahma, M. Rusanen, T. Ala-Nissila, Phys. Rev. Lett. 92, 086103, 2004
[2] A. Petersen, C. Busse, C. Polop, U. Linke, T. Michely, Phys. Rev. B 68, 245410, 2003 |