Direct observation of methyl radicals islanding on copper surface and its effects on the kinetics of catalytic reactions

The formation of methyl radicals into densely packed two-dimensional islands on the Cu(111) surface is directly observed for the first time by scanning tunneling microscopy (STM). It is shown that chemisorbed CH 3 (ads) molecules tend to aggregate into (√3 x √3) R30° structure in 2D islands at any coverage up to one saturation monolayer. The island sizes depend on the amount of gaseous exposure, and at a given exposure, the sizes are found to decrease when the surface temperature is raised to near the reaction temperature of CH 3 (ads). The adsorbate islanding behavior can be correlated with the first-order reaction kinetics in the generation of long-chain alkene products detected in the thermal desorption. From this and other related studies on methyl-solid interactions, we infer that the islanding phenomenon may be quite general in catalytic systems.