Preparation and characterization of amorphous carbon (a-C) membranes by molecular dynamics simulation

Amorphous carbon (a-C) membranes with 1,728 particles were prepared from diamond at four different densities (1.8, 2.0, 2.28, and 2.4g/cm(3)) using molecular dynamics simulation. Stillinger and Weber potential for carbon was introduced with kinetic energy abided by classical Newton equation. Time mesh was chosen 0.01 or 1fs. The melt-quenching technology method was adopted with the corresponding cooling rate 5 and 0.05K/fs, respectively. Different membranes were obtained from higher initial temperature (7,500, 7,000, or 6,500K at different densities and cooling rates) to room temperature. We compared the radial distribution function, bond angle distribution, and pore size distribution with experimental data. The results agreed well and one membrane at lower density with larger pores was chosen to calculate the gas permeation further. Gas molecules (He, Ne, H-2, CO2, N-2, CH4, and SF6) permeation through the a-C membrane at low density (1.8g/cm(3)) when time mesh equal to 1fs were calculated at 300, 400, 473, 500, and 600K. The results of every gas species almost illustrated Knudsen diffusion well. And the number of permeated particles depended on the molecular weight.