Mass Transport of Xe Multi-layers on Cu(111) X.D. Zhu , Department of Physics, University of California at Davis Intralayer and interlayer transport play critical roles in thin film growth and fabrication of novel material structures.  It remains a challenge to experimentally determine kinetic parameters that characterize these processes for a set of host and guest materials of practical interest. The decay of adsorbate multilayer gratings can be used to study intralayer and interlayer mass transport kinetics of the adsorbates.  Such a decay can be measured either directly by following the diffraction of an optical beam from the grating or indirectly by following the amplitude of the grating-coupled surface plasmon polariton wave (SPPW) if the solid substrate such as Cu(111) supports SPPW. Using a combination of optical diffraction and excitation/detection of an adsorbate-thickness-grating-coupled surface-plasmon polariton wave on Cu(111) (Fig. 1), we studied the mass transport of Xe multi-layers on Cu(111) at low temperatures (from 45 to 53 K). The activation energy that dominates the decay kinetics is Ea = 3.5 kcal/mol or 150 meV/atom (Fig. 2). This value is high for Xe intralayer diffusion, suggesting that the decay is rate-limited by interlayer mass transport and/or desorption. Gray and Zhu measured the thermal desorption kinetics of Xe multilayers and found the activation energy for those Xe above the first monolayer on Ni(111) (similar to Cu(111)) was also characterized by an activation energy of 3.5 kcal/mol (unpublished). This suggests that both the thermal desorption and the decay of Xe multi-layer gratings are rate-limited by the detachment of Xe from step edges, instead of surface diffusion or detachment from the terraces.