Si Ad-dimer Interactions with Steps and Islands on the Si(001) Surface*

B. S. Swartzentruber
Sandia National Laboratories
Albuquerque, NM 87185

This document contains the complete scanning tunneling microscopy (STM) movie image data that are used as figures in, Si Ad-Dimer Interactions with Steps and Islands on Si(001), B. S. Swartzentruber, Surf. Sci. 374, 277 (1997). In these experiments, the Si ad-dimer-substrate binding free energy as a function of location is extracted from measurements of the position and hop statistics of ad-dimers as they migrate on the Si(001) surface in the thermodynamic limit. This type of measurement introduces the idea of the "atom as a probe". In this context, the ad-dimers themselves are used to probe the substrate potential energy site-by-site, while the instrument continually monitors their positions. Much like dogs spend more time next to trees and bushes, diffusing adsorbates spend more time at energetically favorable locations on the surface.
[Dimers at Step]
Image 1: Filled-state movie of two ad-dimers diffusing in wells between an SA step and vacancy-type defects acquired at 110 C. The upper well contains 4 sites and the lower well contains 6 sites. (MPEG format 35kb)

[Dimer Diffusion #1] [Dimer Diffusion #2] [Dimer Diffusion #3]
Image 2(a), (b), (c): Empty-state movies of ad-dimers diffusing in wells with repulsive walls comprised of various surface defects acquired at 110 C. The wells contain (a) 10, (b) 12, and (c) 14 lattice sites among which the ad-dimers diffuse. (MPEG format 100kb, 108kb, 70kb)

[Binding Energy Plot]
Image 3: Plot of the relative binding energy as a function of the distance from the left wall. The circles, squares, and diamonds are from the wells shown in Image 2(a), 2(b), and 2(c) respectively. The crosses are the data from the 6 site well at the bottom of Image 1. These data are extracted from the site occupation probabilities measured by atom tracking the diffusing ad-dimers. (GIF 6kb)

Attribution: The reference for this document is: B. S. Swartzentruber, Si Ad-Dimer Interactions with Steps and Islands on the Si(001) Surface, SAND96-2258, Sandia National Laboratories, Albuquerque, NM, September 1996.
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