Quasi-collective motion of nanoscale metal strings in metal surfaces

Abstract

Mass transport processes on metal surfaces play a key role in epitaxial growth and coarsening processes. They are usually described in terms of independent, statistical diffusion and attachment/detachment of individual metal adatoms or vacancies. Here we present high-speed scanning tunnelling microscopy (video-STM) observations of the dynamic behaviour of five-atom-wide, hexagonally ordered strings of Au atoms embedded in the square lattice of the Au(100)-(1x1) surface that reveal quasi-collective lateral motion of these strings perpendicular to as well as along the string direction. The perpendicular motion can be ascribed to small atomic displacements in the strings induced by propagating kinks, which also provides a mechanism for the exchange of Au atoms between the two string ends, required for motion in string direction. In addition, quasi-one-dimensional transport of Au adatoms along the string boundaries may contribute to the latter phenomenon according to density functional calculations.

Thermodynamic and kinetic properties of surface dislocations on Au(001) from atomistic simulations

“…The main difference between the structures of the cores of the two surface dislocations is the core width ͑narrower in type II than in type I͒. The structure of type II surface dislocation obtained in the present study is again in good agreement with the HREM images of Zandbergen et al 15 ͑the side view͒ and the "double-ridge" configuration observed by Labayen et al 13 ͑the top view͒.…”

“…In this view, we see that the surface layer buckles around the dislocation core as a result of the injection of an extra atomic column to form the surface dislocation. The structure of type I surface dislocation is in fairly good agreement with high-resolution electron microscopy ͑HREM͒ images ͑viewed along ͗110͘, the side view͒ obtained by Zandbergen et al 15 and is also consistent with the "single-ridge" configuration observed by Labayen et al 13 ͑viewed along ͗001͘, the top view͒. The relaxed structure of type II surface dislocation is shown in Fig.…”

“…There have been a number of embedded atom method-type potentials for Au which generate the ͑5 ϫ 1͒ reconstruction of Au ͑001͒. [18][19][20][21] However, these potentials fail to replicate the surface structures observed by Labayen et al 13 and Zandbergen et al, 15 e.g., the instability of the ͑1 ϫ 1͒ unreconstructed surface at finite temperature ͑i.e., T Ͼ 0 K͒. Therefore, the present studies were performed using the modified embedded atom method potential ͑MEAM͒ for Au, 22 which replicates the finite temperature ͑5 ϫ 1͒ reconstruction on Au ͑001͒ ͓the MEAM potentials also provide a reasonable description of the ͑001͒ surfaces of several transition metals͔.…”

“…Labayen et al 13,14 reported mobile isolated strings on Au ͑001͒ surface that can move either perpendicular to or along the string direction. Zandbergen et al, 15 using high resolution electron microscopy, observed during the evaporation of a Au film that Au adatoms are collectively injected from the surface into the terrace and these form highly mobile surface dislocations on Au ͑001͒.…”

Anomalous Fast Dynamics of Adsorbate Overlayers near an Incommensurate Structural Transition

“…The observed rate of island growth requires a rate of mass transport orders of magnitude faster than the usual diffusion picture. Similar anomalously fast transport has also been invoked in other adsorption systems [11]. In a set of recent experiments [7,9], the dynamics in the submonolayer regime for Pb=Sið111Þ was studied by following the refilling of a hole region.…”