AVS 50th International Symposium
    Surface Science Monday Sessions
       Session SS3-MoM

Paper SS3-MoM4
Dynamics of Surface Alloys: Decay of 2D Islands on Pb/Cu(111)

Monday, November 3, 2003, 9:20 am, Room 328

Session: Surface Diffusion and Wetting
Presenter: M.L. Anderson, Sandia National Laboratories
Authors: M.L. Anderson, Sandia National Laboratories
N.C. Bartelt, Sandia National Laboratories
G.L. Kellogg, Sandia National Laboratories
B.S. Swartzentruber, Sandia National Laboratories
Correspondent: Click to Email
To achieve control of nanostructure formation via self-assembly or growth processes, it is critical to gain an understanding of the complex physics governing mass transport. Observing thermal decay of 2D islands has proven useful to quantify atomic mechanisms of surface diffusion in single component systems. In this work we use this method to study more complicated issues of diffusion in multi-component systems. Using both STM and LEEM, we studied thermal decay of Pb-overlayer and Pb-Cu alloy islands on Pb/Cu(111). By combining techniques we extend the length scale from nanometers to microns and measure decay rates over 4 orders of magnitude. When Pb atoms are deposited on Cu(111), they place exchange with surface Cu atoms, forming a 2D surface-alloy phase. At Pb coverages above 0.22 ML, the surface alloy is saturated and further deposition causes Pb to de-alloy and form overlayer (pure Pb) islands. Despite large differences in structure, measured decay rates of both overlayer and alloy islands as a function of temperature follow an Arrhenius form with the same activation barrier (~0.8 eV). Equivalent barriers indicate that the same rate-limiting process is effective for both types of islands. The measured energy is comparable to DFT calculations of Cu adatom formation plus diffusion energies@footnote 1@ suggesting that transport of Cu is the rate-limiting process. Although the barriers are the same, the absolute rate at a given temperature is ~20 times slower for the alloy than for the overlayer islands. The rate difference is partially accounted for by the fact that, for equal size islands, there are 5 times more Cu atoms to transport in the coarsening of alloy islands. Sandia is a Lockheed Martin Company, operated for the U.S. DOE under Contract DE-AC04-94AL85000. This work was supported in part by the Division of Materials Science and Engineering, Office of Science, U.S. DOE. @FootnoteText@@footnote 1@ P. J. Feibelman, private communication.