SURFACE-DIFFUSION OF H AND CO ON CU RU(001) - EVIDENCE FOR LONG-RANGETRAPPING BY COPPER ISLANDS (VOL 201, PG 273, 1995)/

The surface diffusion of H and CO on Cu/Ru(001) was studied using lase r-induced thermal desorption (LITD) techniques. The surface mobilities of H and CO on the Ru(001) surface were both dramatically attenuated by submonolayer copper coverages. At 300 K and Theta(H) = 0.25 ML, the H diffusion coefficient decreased by a factor of similar to 30 from D -H = 8.7 x 10(-7) cm(2)/s on clean Ru(001) to D-H = 3.0 x 10(-8) cm(2) /s at Theta(Cu) = 0.09 ML. At fixed copper coverages of Theta(Cu) = 0. 10 ML and Theta(Cu) = 0.25 ML, the hydrogen diffusion coefficient was negligible at low hydrogen coverages and then increased at higher hydr ogen coverages. The copper coverages also increased the hydrogen diffu sion activation barrier from E(H) = 2.8 +/- 0.2 kcal/mol on clean Ru(0 01) to E(H) = 9.8 +/- 1.0 kcal/mol at Theta(Cu) = 0.15 ML. The depende nce of hydrogen mobility on hydrogen coverage and the increase in diff usion activation barrier at higher copper coverages suggest that hydro gen is trapped by copper on Ru(001). The copper coverage on Ru(001) al so reduced the CO diffusion coefficient. At 300 K and Theta(CO) = 0.41 ML, the CO diffusion coefficient decreased by a factor of 2400 as the copper coverage increased from Theta(Cu) = 0.00 ML to 0.10 ML. Recent scanning tunneling microscope (STM) studies have revealed that copper forms islands on Ru(001). Monte Carlo simulations of these surface di ffusion results are consistent with a trapping interaction between H a nd the copper islands. The Monte Carlo results also argue for a very l ong-ranged perturbation of similar to 200 Angstrom induced by the copp er islands. These experimental and theoretical results for dramatic an d long-ranged trapping indicate that copper seriously perturbs the sur face electronic properties of Ru(001).