Nanostructured surfaces

Nano-structured thing films growth control in multi-layer anisotropic adsorptive systems 
Dvornichenko A.V., Kharchenko V.O.
Sumy State University, 2 Rimskii-Korsakov St., 40007 Sumy, Ukraine. 
E-mail: alina.dvorni4enko@ukr.net

We study pattern formation on a surface of thing films during adsorption/desorption processes at condensation from gaseous phase and in plasma-condensate systems by taking into account interaction between adatoms in the framework of generalized model of multi-layer adsorptive system. We discuss isotropic and anisotropic diffusion of adsorbate between layers, separately, in the framework of theoretical study and numerical simulations. 
By considering the condensation from the gaseous phase we take into account non-equilibrium quasi-chemical reactions, responsible for the formation of stable complexes on the current layer of the multi-layer system, leading to the stabilization of the adsorbate islands. In the isotropic case of the standard vertical diffusion we show that an increase in the adsorption coefficient reduced to the pressure of the gaseous phase leads to a change in the surface morphology from separated multi-layer adsorbate islands on a substrate towards separated vacancy islands inside adsorbate matrix. 
We show that in anisotropic gas-condensate system with preferential motion of adatoms from lower layers to upper ones, relevant to the principle of the minimization of the surface energy, the main conditions for the adsorbate island formation of the current layer are both the critical adsorbate concentration on the current layer and the critical size of the adsorbate island on the precursor layer. We discuss an influence of the anisotropy strength onto critical size of adsorbate islands and perform statistical analysis of the multi-layer surface structures. 
By considering plasma-condensate systems we take into account that the electric field near substrate induces anisotropy in transference reactions between neighbor layers with preferential motion from lower to upper layers, where anisotropy strength relates to the strength of the electric field. Here we show that an increase in the anisotropy strength leads to the transformation of the surface morphology from the separated vacancy islands inside the adsorbate matrix towards separated adsorbate islands on the substrate. The linear size of adsorbate islands decreases with anisotropy strength growth.