Lateral displacement of adsorbates induced by collisions with energy-controlled rare gas atoms was examined in an ultra high vacuum chamber using Fourier-transform infra-red spectroscopy and a supersonic molecular beam apparatus. A stepped Pt(997) surface was exposed to CO molecules and subsequently to energy-controlled Ne or Ar atoms. There was no change in the CO stretching mode region of the Fourier-transform infra-red spectrum of the Pt(997) surface after Ne atoms having an average translational energy of 0.23eV were collided with it. However, when Ne atoms having an average translational energy of 0.56eV were collided with the surface, the intensity of the peak assigned to the CO stretching mode at terrace sites decreased, while that at step sites increased with increasing the exposure to the Ne atoms. This was the demonstration of collision-induced migration, showing that CO molecules adsorbed at the terrace sites migrate laterally to the step sites upon collision with high-energy Ne atoms. In addition, the experimental results demonstrated the existence of an additional energy barrier for jumps across the steps. This investigation demonstrated an advantage of using a molecular beam for studying adsorbate migration.

Collision-Induced Migration of CO on Pt(997) Surface. T.Takaoka, T.Komeda: Surface Science, 2007, 601[4], 1090-100