DIFFUSION OF POTASSIUM ON RE(001) INVESTIGATED BY COVERAGE GRATING-OPTICAL 2ND-HARMONIC DIFFRACTION

Using the coverage grating-optical second-harmonic diffraction method, we have measured the diffusion rate of potassium on Re(001) in the co verage range of 0.6-1 ML. We observe a minimum in both the activation energy for diffusion and the diffusion preexponential at an initial po tassium 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+/-0.71 3.6+/-0.2, and 5.0+/-1.0 kcal/mol, and D-0 is 5.6x10(-3+/-0.3), 3.5x10(-4+/-1.1), 5.8x10(-4+/-0.3), and 3.7x10(- 1+/-1.9) cm(2)/s, respectively. The results are discussed in terms of electrostatic dipole-dipole repulsive interactions among neighboring a dsorbates. (C) 1997 American Institute of Physics.