The diffusion of single n-butane and n-decane molecules on a model stepped surface, Pt(655), and on a corresponding flat surface, Pt(111), is investigated using molecular-dynamics simulations and anisotropic united atom model. The surface step on Pt(655) causes the alkane molecules to adsorb on the lower terrace in all-trans conformations with their long molecular axes adjacent and parallel to the step edge, and to diffuse anisotropically along the surface step via a constant wiggly motion without rotation or marked deviation from the parallel adsorption configuration. At relatively high temperatures, the alkane molecules can temporarily break away from the step edge but cannot migrate across the step edge in either the downstair or upstair direction. In comparison with the diffusion on Pt(111), the diffusivity of n-decane is reduced by the surface step but its diffusion barrier is hardly affected. In the case of the shorter n-butane, however, the surface step significantly reduces the diffusion energy barrier and gives rise to higher diffusion coefficients at lower temperatures. Important implications of the simulation results are discussed.
S. Subramaniyan and J. C. Wang, "Anisotropic Diffusion of n-Butane and n-Decane on a Stepped Surface," Journal of Chemical Physics, American Institute of Physics (AIP), Jan 2005.
The definitive version is available at http://dx.doi.org/10.1063/1.1949170
Chemical and Biochemical Engineering
Missouri Research Board
Keywords and Phrases
Surface Diffusion; Adsorption; Molecular dynamics -- Simulation method; Organic compounds; Platinum
Article - Journal
© 2005 American Institute of Physics (AIP), All rights reserved.