SURFACE-DIFFUSION OF K ON PD(111) - COVERAGE DEPENDENCE OF THE DIFFUSION-COEFFICIENT DETERMINED WITH THE BOLTZMANN-MATANO METHOD

The surface diffusion of potassium on Pd{111} has been studied with ph otoelectron emission microscopy (PEEM) for coverages up to one monolay er, The coverage dependence of the chemical diffusion coefficient is d etermined by analysis of the concentration profiles obtained from the PEEM images with the Boltzmann-Matano method. The diffusion coefficien t, D, decreases with increasing coverage but a local maximum is found at a coverage of theta approximate to 0.5 ML. The values of D at low c overages (theta < 0.3 ML) agree well with those obtained in a previous investigation for theta approximate to 0.12 ML. The maximum in D is i nterpreted in terms of an order-disorder phase transition in the adsor bed layer. (C) 1998 American Institute of Physics.