Laser-induced defects on a Ni(100) surface: Effects on adsorption and surface diffusion of CO

Abstract

Pulsed-laser-induced desorption (LID), a method which has been used to measure surface diffusion, can cause changes in the morphology of the surface being studied. The object of this paper is to investigate the influence of laser-induced surface defects on the adsorption and diffusion of CO on Ni(100). The defects were produced by illuminating a Ni(100) surface with 73 MW/cm 2 of 1.06 microm radiation. Subsequent exposure of the surface to CO resulted in about 10% more adsorbed CO than without the laser-induced defects. The CO coverage on the laser pre-irradiated surface was further enhanced relative to the unirradiated surface by annealing the CO overlayer at 310 K. However, the degree of enhancement was dependent on the initial CO coverage. This increase in the local CO surface coverage was modelled by the presence of laser-induced surface defects which tightly bind the diffusing CO. From the coverage dependence of this phenomenon, we estimate that 2.4 ± 1% of the surface sites are tight binding defects. These defects have the greatest influence on LID diffusion coefficient measurements at low CO coverages where we estimate that the results may be in error by approximately a factor of 2 if one assumes an asymptotic limit equal to the initial coverage rather than experimentally determining the actual asymptotic coverage.