SURFACE-DIFFUSION OF POTASSIUM ON RU(001)

The surface diffusion of potassium on Ru(001) was studied using laser- induced thermal desorption (LITD) techniques. The potassium surface mo bility was very dependent on the potassium surface coverage. The cover age dependent surface diffusion coefficients were obtained from an ite rative analysis based on surface diffusion measurements performed at d ifferent initial coverages. At 220 K, the surface diffusion coefficien t increased dramatically as the potassium coverage increased from thet a(K) = 0.08 to 0.33 ML. The surface diffusion coefficients also displa yed Arrhenius behavior at various temperatures and potassium coverages . As the potassium coverage increased from theta(K) = 0.15 to 0.33 ML, the surface diffusion activation energy decreased slightly and the di ffusion pre-exponential increased by a factor of 35. The diffusion act ivation energies were E(dif) = 9.0 +/- 0.4, 8.5 +/- 0.3 and 8.1 +/- 0. 4 kcal/mol and the corresponding pre-exponentials were D0 = 0.40 +/- 0 .06, 4.4 +/- 0.3 and 14.0 +/- 0.5 cm2/s at theta(K) = 0.15, 0.25 and 0 .33 ML, respectively. The coverage dependence of the potassium surface diffusion on Ru(001) was attributed to strong repulsive interactions between potassium adatoms. These interactions most likely originate fr om repulsions between dipoles formed by partially ionized potassium ad atoms and their surface image charges.