Tracer surface diffusion at high pressures: Molecular-dynamics study

Abstract

Molecular-dynamics simulations were employed to investigate the influence of high pressure on tracer surface diffusion. A model potential was used to describe the interaction among the various species in the system. The different binding energy values and masses used in this model simulation correspond to surface diffusion of N2 on Ru(001) surface under pressure of Ar. A pronounced enhancement in the magnitude of the diffusion coefficients was observed when pressure increased from P=0 to P=200 atm. The relationship between diffusion coefficient and three parameters that characterize the system was explored. It was found that the gas temperature and the nature of gas–adsorbate interaction (i.e., attractive or repulsive) have only a negligible influence on the diffusion coefficient. However, a marked variation in the diffusion coefficient was observed when the magnitude of gas-substrate binding energy was altered. The temperature dependence of the surface diffusion coefficient exhibits an Arrhenius behavior for all cases investigated. The relationship between the pressure and both pre-exponential factor and activation energy for surface diffusion was discussed based on a detailed analysis of the diffusion mechanism. The diffusion mechanism was deduced by careful examination of large number of individual trajectories.