Diffusion studies on copper/ruthenium(001) and single-crystal ice on ruthenium(001)

The surface diffusion of H and CO on Cu/Ru(001) was studied using laser-induced thermal desorption (LITD) techniques. The mobilities of H and CO on the Ru(001) surface were dramatically attenuated by submonolayer copper coverages. The coverage dependence of hydrogen and CO mobility for fixed copper coverages suggests that hydrogen and CO are trapped by copper on Ru(001). Monte Carlo simulation results argue for a long-ranged perturbation of {dollar}sim{dollar}200 A induced by addition of copper to the ruthenium substrate. These results indicate that copper seriously perturbs the surface electronic properties of Ru(001).; The condensation of H{dollar}sb2{dollar}O on ice multilayers on Ru(001) was studied using both molecular beam and optical interference techniques. The sticking coefficient was measured to be essentially unity at temperatures between 97-145 K. The refractive index, n, and density, {dollar}rho,{dollar} for ice were evaluated and varied from n = 1.27-1.31 and {dollar}rho{dollar} = 0.82-0.93 g/cm{dollar}sp3{dollar} between 97-130 K. Low energy electron diffraction investigations confirmed that ice multilayers grown on Ru(001) above 160 K were crystalline to thicknesses of at least 105 Bilayers.; The surface and bulk diffusion of H{dollar}sb2{dollar}O on single-crystal ice grown epitaxially on Ru(001) were measured by creating a concentration gradient of {dollar}rm Hsb2Osp{lcub}18{rcub}{dollar} on an ice surface. Scanning LITD 2 measurements were used to map the {dollar}rm Hsb2Osp{lcub}18{rcub}{dollar} coverage profile versus diffusion time at 140 K. No relaxation of the {dollar}rm Hsb2Osp{lcub}18{rcub}{dollar} concentration gradient was observed, indicating that H{dollar}sb2{dollar}O may be diffusing into the ice bulk. LITD was used to monitor the diffusion and desorption of a single bilayer of {dollar}rm Hsb2Osp{lcub}18{rcub}{dollar} deposited on a crystalline {dollar}rm Hsb2Osp{lcub}16{rcub}{dollar} multilayer during isothermal desorption at 160 K. The {dollar}rm Hsb2Osp{lcub}18{rcub}{dollar} was present until all of the {dollar}rm Hsb2Osp{lcub}16{rcub}{dollar} ice multilayer desorbed, indicating that {dollar}rm Hsb2Osp{lcub}18{rcub}{dollar} is diffusing into the underlying {dollar}rm Hsb2Osp{lcub}16{rcub}{dollar} bulk. The bulk diffusion coefficient of H{dollar}sb2{dollar}O into crystalline ice was determined to be D = {dollar}2.0 times 10sp{lcub}-15{rcub}{dollar} cm{dollar}sp2{dollar}/s at 160 K. An Arrhenius analysis of the bulk diffusion data yielded an activation barrier for diffusion of E{dollar}sb{lcub}rm dif{rcub}{dollar} = 13.1 kcal/mol.