Subramanian Shrijay, Wang Jee-Ching
Department of Chemical and Biological Engineering, University of Missouri-Rolla, Rolla, Missouri 65409-1230, USA.
J Chem Phys. 2005 Jul 1;123(1):014706. doi: 10.1063/1.1949170.
The diffusion of single n-butane and n-decane molecules on a model stepped surface, Pt655, and on a corresponding flat surface, Pt111, is investigated using molecular-dynamics simulations and anisotropic united atom model. The surface step on Pt655 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 Pt111, 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.
使用分子动力学模拟和各向异性联合原子模型，研究了单个正丁烷和正癸烷分子在模型阶梯表面Pt655以及相应的平面Pt111上的扩散情况。Pt655上的表面台阶使得烷烃分子以全反式构象吸附在较低台面上，其长分子轴与台阶边缘相邻且平行，并通过持续的摆动运动沿表面台阶各向异性扩散，而不发生旋转或明显偏离平行吸附构型。在相对较高的温度下，烷烃分子可以暂时脱离台阶边缘，但无法沿下楼或上楼方向越过台阶边缘迁移。与在Pt111上的扩散相比，正癸烷的扩散率因表面台阶而降低，但其扩散势垒几乎不受影响。然而，对于较短的正丁烷，表面台阶显著降低了扩散能垒，并在较低温度下产生了更高的扩散系数。讨论了模拟结果的重要意义。
