Coverage dependence of the surface diffusion coefficient for hydrogen on Ru(001)

The coverage dependence of the surface diffusion coefficient for hydrogen on Ru(001) was studied using laser-induced thermal desorption(LITD) techniques. The LITD measurements were performed for a wide range of initial hydrogen surface coverages in the temperature range 230–270 K. At a given temperature, the surface diffusion coefficient was found to be constant as a function of coverage. The absence of coverage dependence in the surface diffusion coefficient indicates that adsorbate-adsorbate interactions between adsorbed hydrogen atoms on Ru(001) are negligible. This observation suggests that the coverage-dependent features observed in work function, high resolution electron energy loss spectroscopy and possibly temperature programmed desorption studies of hydrogen on Ru(001) are associated with two inequivalent hydrogen sites rather than repulsive lateral hydrogen interactions. Monte Carlo simulations reveal that the surface diffusion coefficient should be coverage independent on a surface with two inequivalent sites in the absence of adsorbate-adsorbate interactions.