SURFACE-DIFFUSION OF NORMAL-ALKANES ON RU(001)

The surface diffusion of n-alkanes on Ru(001) was measured using laser-induced thermal desorption (LITD) techniques. The surface diffusion coefficients for propane, n-butane, n-pentane, and n-hexane all displayed Arrhenius behavior. The surface diffusion activation energies increased linearly with carbon chain length from Edif = 3.0 ± 0.1 kcal/mol for propane to Edif = 4.8 ± 0.2 kcal/mol for n-hexane. In contrast, the surface diffusion preexponentials remained nearly constant at D0≃0.15 cm2/s. Measurements performed at different coverages also revealed that the surface diffusion coefficients were coverage-independent for all the n-alkanes on Ru(001). The surface corrugation ratio Ω was defined as the ratio of the diffusion activation energy to the desorption activation energy, Ω = Edif/Edes. The surface corrugation ratio was observed to be remarkably constant at Ω≃0.3 for all the n-alkanes. This constant corrugation ratio indicated a linear scaling between the diffusion activation energy and the desorption activation energy. This behavior also suggested that the n-alkanes move with a rigid configuration parallel to the Ru(001) surface. © 1990 American Institute of Physics.