Mechanisms of growth and the structure of the adsorption layer of water at the surface of porous silicon

Model concepts of the formation and growth of a water adsorption layer at the surface of porous silicon with the use of the experimental data obtained by nuclear magnetic resonance are developed in this work. The proposed model is based on an approximation that water menisci formed at pore exits onto the surface are completely filled with water at specific values of humidity and play the role of immobile centers of nucleation for adsorbed water molecules. The fractal aggregates grow at these centers, whose modeling is carried out in a modified Witten-Sender model of diffusion-limited aggregation. In this case, the possibility of the simultaneous growth of several fractal aggregates at an array of nucleation centers by drawing the initial localization of a regular element of the fractal structure and finding the most probable site of its joining one of the growing aggregates is taken into account. The results of computer modeling are described within the context of percolation theory; they agree well with the experimental data and can be used for predicting the percolation properties of porous structures.