Vapour transport and inner walls covering in large aspect ratio macropores

A model for the covering of the inner surfaces of narrow and large aspect ratio tubes is developed. It considers diffusive vapour transport toward the bottom of the tubes and self-regulated adsorption at their walls. According to the growth conditions and the tubes geometry, Knudsen diffusion approximation is used. Pressure and coverage profiles, calculated for different geometries and sticking coefficients, allowed discriminating two well defined regimes. In these regimes, surface reaction or vapour diffusion are the corresponding limiting processes; then, a simple equation to estimate the walls covering time as a function of the growth parameters and tubes geometry is proposed. This model allowed revealing the main features guiding the deposition of CdSe semiconductor within commercial alumina membranes by the Isothermal Close Space Sublimation technique.

► Inner surface covering process in narrow and large aspect ratio tubes was modelled.
► Two covering regimes were identified depending on the sticking coefficient of the gas.
► A simple equation was found to reproduce more exact numerical calculations.
► Covering of the inner surfaces of alumina membranes with CdSe semiconductor is discussed.