Simulation of nanochannel membrane formation

Abstract

Monte Carlo simulations of atomic processes on the surface of silicon nanochannel membranes during molecular-beam epitaxy and subsequent thermal oxidation are performed. It is demonstrated that silicon deposition on Si(001) wafers with 1–100 nm cylindrical pores results in constriction of channel inlets. The rates of reduction of the nanochannel diameter are estimated as functions of the wafer temperature, silicon deposition rate, and initial nanochannel diameter. Optimal conditions of silicon deposition on nanochannel membranes are determined: the wafer temperature of 250–450°C and silicon flux intensity of 10−2 to 10 monolayers (ML) per second. Under these conditions, the rate of reduction of the nanochannel inlet diameter is 0.13–0.15 nm/ML, which allows membrane channel modifications over a wide range down to several nanometers. Simulations of nanochannel membrane oxidation in an oxygen flux shows that precise reduction of nanochannel inlet diameters down to complete sealing of the channel due to oxide growth is only possible for small diameters of the initial pores. For channels with large lateral sizes, the effect of reduction of the channel inlet diameter due to oxidation is insignificant. Oxidation of pores enhances their stability to subsequent high-temperature treatment.