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       Session SS1-FrM

Paper SS1-FrM1
Crossover from Surface- to Bulk-Diffusion-Limited Surface Dynamics on Pt(111)@footnote 1@

Friday, November 2, 2001, 8:20 am, Room 120

Session: Dynamics of Metal Surfaces
Presenter: G.L. Kellogg, Sandia National Laboratories
Authors: B. Poelsema, University of Twente, The Netherlands
J.B. Hannon, IBM T.J. Watson Research Center
N.C. Bartelt, Sandia National Laboratories
G.L. Kellogg, Sandia National Laboratories
Correspondent: Click to Email
Microscopic measurements of changes in surface morphology due to the motion of single-atom high steps provide detailed information on atomistic processes occurring at a crystal surface. In this study, we use low energy electron microscopy (LEEM) to measure the time-dependent changes in area of two-dimensional Pt islands on Pt(111) as a function of temperature. We find evidence for a crossover from step motion caused by surface diffusion to step motion caused by the flow of material to and from the bulk crystal as the temperature is raised. At temperatures in the range from 1100-1500 K, circular islands residing at the top of three-dimensional stacks exhibit a linear decay, as long as the stack diameter exceeds approximately 1.5 microns. The temperature dependence of the decay rate yields an activation energy of 1.7 eV. On the other hand, for stacks with smaller diameters and temperatures below 1350 K, the decay is non-linear, having a form more closely resembling surface diffusion-limited kinetics. The high-T behavior is similar to that recently observed for NiAl(110), where it was shown that bulk vacancy transport controls step motion on the surface.@footnote 2@ In support of the same interpretation for Pt(111), we observe that the islands grow upon increasing the temperature and shrink upon lowering the temperature in non-equilibrium experiments. The dynamics for Pt(111) are more complicated than NiAl(110), involving a competition between the diffusion of surface adatoms and bulk vacancies. However, preliminary modeling studies indicate that processes involving bulk vacancies can simultaneously explain the temperature dependence of island decay at fixed temperature and the non-equilibrium behavior of islands on Pt(111) as the temperature is varied. @FootnoteText@ @footnote 1@Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the U. S. DOE under Contract DE-AC04-94AL85000. @footnote 2@ K. McCarty, J.A. Nobel, and N.C. Bartelt, preprint.