Abstract
The surface diffusion coefficient for hydrogen on Ni(100) at low coverage has been measured between 223 and 283 K. A pulsed laser is used to desorb hydrogen from a small, well defined, region on the surface without perturbing the ambient surface temperature. Hydrogen from nearby regions on the surface migrates into the vacant area and the time required to refill that area is determined by subsequent laser-induced-desorption measurements. The diffusion coefficient is obtained using an equation derived from Fick's Second law with non-stationary boundary conditions. The temperature dependence of the diffusion coefficients yields a value of 4.0±0.5 kcal/mol for the energy barrier to diffusion. A value of roughly 3×10 13 s -1 for the site-to-site hopping frequency is derived when the pre-exponential for diffusion is fit to a random-walk mechanism.
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