Simulation of gas diffusion and sorption in nanoceramic semiconductors

Gas diffusion and sorption in nanoceramic semiconductors are studied using atomistic simulation techniques and numerical results are presented for a v ariety of sorbate-sorbent systems. SnO2, BaTiO3, CuO, and MgO substrates ar e built on the computer using lattice constants and atomic parameters that have been either measured or computed by ab initio methods. The Universal f orce field is employed here for the description of both intramolecular and nonbonded interactions for various gas sorbates, including CH4, CO, CO2, an d O-2, pure and in binary mixtures. Mean residence times are determined by molecular dynamics computations, whereas the Henry constant and the isoster ic heat of adsorption are estimated by a Monte Carlo technique. The effects of surface hydroxylation on the diffusion and sorption characteristics are quantified and discussed in view of their significance in practical gas se nsing applications. The importance of fast diffusion on the response time o f the sensitive layer and of the sorption efficiency on the overall sensiti vity as well as the potential synergy of the two phenomena are discussed. ( C) 1999 American Institute of Physics. [S0021-9606(99)70418-6].