AVS 47th International Symposium
    Surface Science Wednesday Sessions
       Session SS3-WeA

Paper SS3-WeA4
Direct Observations of Ordered Domain Structures and their Dynamics : Pb on Cu(111)@footnote 1@

Wednesday, October 4, 2000, 3:00 pm, Room 210

Session: Surface and Interface Structure I
Presenter: R. Plass, Sandia National Laboratories
Authors: R. Plass, Sandia National Laboratories
N.C. Bartelt, Sandia National Laboratories
G.L. Kellogg, Sandia National Laboratories
Correspondent: Click to Email
There is considerable scientific interest in the spontaneous formation of two-dimensional periodic domain structures due to long-range interactions in two-phase systems. Theoretical investigations of the stability of periodic structures due to dipolar interactions predict a progression of droplet and striped phases as a function of area fraction@footnote 2@ but experimental verification has been elusive. Using low energy electron microscopy (LEEM), we find that the growth of Pb on Cu(111) reproduces this domain evolution with surprising accuracy. Above 25C, Pb on Cu(111) follows the SK growth mode@footnote 3@ with a disordered surface alloy saturating at 0.4 ML Pb and an incommensurate (incom. hereafter) overlayer covering the surface at 1.0 ML Pb. As Pb deposition proceeds on the surface alloy held at 385C, the density of incom. structure droplets (about 90 nm in diameter) increases steadily. The droplets clearly repel each other, and pack together into a fairly well ordered lattice. They achieve maximum density near 0.3 area fraction (incom.) after which there is an abrupt transition to a striped phase characterized by lengthening bands of surface alloy and incom. regions. The stripes completely cover the surface at 0.5 area fraction, after which another abrupt transition occurs between the striped phase and a conjugate droplet phase where the surface alloy forms droplets in the incom. matrix. The conjugate droplet maximum density is near 0.7 area fraction. The domain structures' spatial dimensions, as well as the size of their thermal fluctuations are temperature sensitive. We use this sensitivity to probe the energetics responsible for the domain structures. @FootnoteText@ @footnote 1@ Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin company, for the U.S. Dept of Energy, contract #DE-AC04-94AL85000 @footnote 2@ K.-O. Ng and D. Vanderbilt, PRB 52 (95) 2177. @footnote 3@ C. Nagl, et al., Surf. Sci. 321 (94) 237.