AVS 45th International Symposium
    Surface Science Division Thursday Sessions
       Session SS1-ThA

Paper SS1-ThA10
Potassium Surface Diffusion by Optical Techniques

Thursday, November 5, 1998, 5:00 pm, Room 308

Session: Surface Diffusion
Presenter: W. Zhao, The Hebrew University, Israel
Authors: W. Zhao, The Hebrew University, Israel
M. Asscher, The Hebrew University, Israel
Correspondent: Click to Email
Coverage grating-optical second-harmonic diffraction method has been used to measure the diffusion of pure potassium and coadsorbed with CO on Re (001) surface in the potassium coverage range of 0.6-1 ML. The activation energy (E@sub d@) and the preexponential factor (D@sub 0@) for diffusion in both show a clear compensation effect. For the pure potassium case, E@sub d@ and D@sub 0@ change quadratically with the coverage, having a minimum in the potassium coverage of 0.75 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, the preexponentials are 5.6x10@super -3±0.3@, 3.5x10@super -4±1.1@, 5.8x10@super -4±0.3@, and 3.7x10@super -1±1.9@ cm@super 2@/s corresponding to potassium coverages of 0.93, 0.84, 0.73, and 0.59, respectively. The results are discussed in terms of electrostatic dipole-dipole repulsive interactions among neighboring adsorbates. In the coadsorption case, it is found that CO hinders potassium surface diffusion significantly, with the effective activation energy for 0.8 ML K rising to 15 kcal/mol for CO average coverage of 0.06 ML. The attractive interaction and complex formation (observed by TPD) of CO-K are proposed as the main reasons for the increasing E@sub d@.