Magic Islands and Barriers to Attachment: A Si/Si(111)7x7 Growth Model

Surface reconstructions can drastically modify growth kinetics during initial stages of epitaxial growth as well as during the process of surface equilibration after termination of growth. We investigate the effect of activation barriers hindering attachment of material to existing islands on the density and size distribution of islands in a model of homoepitaxial growth on Si(111)7x7 reconstructed surface. An unusual distribution of island sizes peaked around "magic" sizes and a steep dependence of the island density on the growth rate are observed. "Magic" islands (of a different shape as compared to those obtained during growth) are observed also during surface equilibration.Comment: 4 pages including 5 figures, REVTeX, submitted to Physical Review

Crater formation by fast ions: comparison of experiment with Molecular Dynamics simulations

An incident fast ion in the electronic stopping regime produces a track of excitations which can lead to particle ejection and cratering. Molecular Dynamics simulations of the evolution of the deposited energy were used to study the resulting crater morphology as a function of the excitation density in a cylindrical track for large angle of incidence with respect to the surface normal. Surprisingly, the overall behavior is shown to be similar to that seen in the experimental data for crater formation in polymers. However, the simulations give greater insight into the cratering process. The threshold for crater formation occurs when the excitation density approaches the cohesive energy density, and a crater rim is formed at about six times that energy density. The crater length scales roughly as the square root of the electronic stopping power, and the crater width and depth seem to saturate for the largest energy densities considered here. The number of ejected particles, the sputtering yield, is shown to be much smaller than simple estimates based on crater size unless the full crater morphology is considered. Therefore, crater size can not easily be used to estimate the sputtering yield.Comment: LaTeX, 7 pages, 5 EPS figures. For related figures/movies, see: http://dirac.ms.virginia.edu/~emb3t/craters/craters.html New version uploaded 5/16/01, with minor text changes + new figure

Atomic structures of Si() surface during silane UHV-CVD

International audienc

2D aggregation and selective desorption of nanoparticle probes: A new method to probe DNA mismatches and damages

A 2D colorimetric DNA sensor is reported based on the 2D aggregation of oligonucleotide-modified gold nanoparticle probes resulting from the molecular hybridization between these latest and their complementary single stranded DNA targets. To increase their mobility the nanoparticles are adsorbed on a fluid lipid bilayer, itself supported on a substrate. The hybridization between the target and the mobile nanoparticle probes creates links between the nanoparticles resulting in the formation of nanoparticle aggregates in the plane of the substrate. This aggregation is detected using a new method based on the selective desorption of non-aggregated nanoparticles. The addition of dextran sulfate induces the substitution of non-aggregated gold nanoparticles while aggregated ones are stable on the substrate. We show that this detection method is highly specific and allows the detection of DNA mismatches and damages

Scanning tunneling microscopy (S.T.M.) of semiconductor surfaces and metal-semiconductor interfaces

In this review paper, we present the basic features of scanning tunneling microscopy and spectroscopy and describe some illustrative applications on local characterization of clean semiconductor surfaces and metal overlayers on reconstructed silicon surfaces