Diffusion of potassium on Re(001) investigated by coverage grating-optical second-harmonic diffraction

Using the coverage grating-optical second-harmonic diffraction method, we have measured the diffusion rate of potassium on Re(001) in the coverage range of 0.6-1 ML. We observe a minimum in both the activation energy for diffusion and the diffusion preexponential at an initial potassium coverage of 0.75 ML. For potassium coverages of 0.93. 0.84. 0.73. and 0.59 ML, the activation energies for diffusion are determined to be 5.0±0.2, 3.9±0.7, 3.6±0.2, and 5.0±1.0 kcal/mol, and D₀ is 5.6×10^-3±0.3, 3.5×10^-4±1.1, 5.8×10^-4±0.3, and 3.7×10^-1±1.9 cm²/s, respectively. The results are discussed in terms of electrostatic dipole-dipole repulsive interactions among neighboring adsorbates.