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Dysprosium disilicide can form nanowires and three dimensional (3D) islands on the Si(001) surface. The nanowire density and width are metal coverage dependent. Various superstructures are observed on the nanowires. The Si substrate is also reconstructed in either 2×4 or 2×7 superstructures. The nanowires have a minimum height of about 0.5 nm with respect to the Si surface; and the heights of the additional layers growing atop nanowires are quantized, consistent with the hexagonal AlB2 type silicide structure. Longer annealing time and higher coverage promote 3D island growth.

Tilt boundaries have been observed on the (0001) surface of graphite by scanning tunneling microscopy (STM). Rotation angles about the c axis of 6.5°, 8°, and 19° were found, indicating no preferential orientation of grains in the basal plane of graphite. The grain boundary region between crystallites appears disordered with a width varying between 10 and 100 Å. Moiré patterns are observed near grain boundaries when multiple tips scanning over different grains contribute to the image simultaneously. Such images support the theory that multiple isolated tips, occasionally hundreds of angstroms apart, can contribute to STM images.

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Deposition at room temperature of Ga on Si(100) produces single-atom-wide metal rows orthogonal to the Si-dimer rows. Detailed analysis using scanning tunneling microscopy reveals a monotonically decreasing size (i.e., length) distribution for these rows. This is unexpected for homogeneous nucleation without desorption, conditions which are operative in this system. Kinetic Monte Carlo simulation of an appropriate atomistic model indicates that this behavior is primarily a consequence of the feature that the capture of diffusing atoms is greatly inhibited in the Ga∕Si(100) system. The modeling also determines activation barriers for anisotropic terrace diffusion, and recovers the experimental distribution of metal rows. In addition, we analyze a variety of other generic deposition models and determine that the propensity for a large population of small islands in general reflects an enhanced nucleation rate relative to the aggregation rate. Disciplines Chemistry CommentsThis article is from Physical Review B 72 (2005) Deposition at room temperature of Ga on Si͑100͒ produces single-atom-wide metal rows orthogonal to the Si-dimer rows. Detailed analysis using scanning tunneling microscopy reveals a monotonically decreasing size ͑i.e., length͒ distribution for these rows. This is unexpected for homogeneous nucleation without desorption, conditions which are operative in this system. Kinetic Monte Carlo simulation of an appropriate atomistic model indicates that this behavior is primarily a consequence of the feature that the capture of diffusing atoms is greatly inhibited in the Ga/ Si͑100͒ system. The modeling also determines activation barriers for anisotropic terrace diffusion, and recovers the experimental distribution of metal rows. In addition, we analyze a variety of other generic deposition models and determine that the propensity for a large population of small islands in general reflects an enhanced nucleation rate relative to the aggregation rate.

Holmium deposition on the Si͑001͒ surface at elevated temperature results in the formation of Ho silicide islands coexisting with a Ho reconstructed substrate surface. At metal coverages below a monolayer, most of the islands are highly elongated nanowires. Structural details of both the reconstructions and the nanowires derived from scanning tunneling microscope data are presented. In addition, scanning tunneling spectroscopy shows that the nanowires are more metallic than either the reconstructed surface, or large silicide islands.