Simulation of adsorbate-induced faceting on curved surfaces

A simple solid-on-solid model, proposed earlier to describe overlayer-induced faceting of bcc(111) surface, is applied to faceting of spherical surfaces covered by adsorbate monolayer. Monte Carlo simulation results show that morphology of faceted surface depends on annealing temperature. At initial stage surface around the [111] pole consists of 3-sided pyramids and step-like facets, then step-like facets dominate and their number decreases with temperature, finally a single big pyramid is formed. It is shown that there is reversible phase transition at which faceted surface transforms to almost spherical one. It is found that temperature of this phase transition is an increasing function of surface curvature. Simulation results show that measurements of high temperature properties performed directly and after fast cooling to low temperature lead to different results.Comment: 8 pages, 10 figure

X-ray scattering from stepped and kinked surfaces: An approach with the paracrystal model

A general formalism of X-ray scattering from different kinds of surface morphologies is described. Based on a description of the surface morphology at the atomic scale through the use of the paracrystal model and discrete distributions of distances, the scattered intensity by non-periodic surfaces is calculated over the whole reciprocal space. In one dimension, the scattered intensity by a vicinal surface, the two-level model, the N-level model, the faceted surface and the rough surface are addressed. In two dimensions, the previous results are generalized to the kinked vicinal surface, the two-level vicinal surface and the step meandering on a vicinal surface. The concept of crystal truncation rod is generalized considering also the truncation of a terrace by a step (yielding a terrace truncation rod) and a step by a kink (yielding a step truncation rod).Comment: 33 pages, 18 figure

The phase diagram of the lattice Calogero-Sutherland model

We introduce a {\it lattice} version of the Calogero Sutherland model adapted to describe $1/d^2$ pairwise interacting steps with discrete positions on a vicinal surface. The configurational free energy is obtained within a transfer matrix method. The full phase diagram for attractive and for repulsive interaction is deduced. For attraction, critical temperatures of faceting transitions are found to depend on step density.Comment: latex PRBCalogSuth.tex, 6 files, 4 pages [SPEC-S00/900

Vicinal silicon surfaces: from step density wave to faceting

This paper investigates faceting mechanisms induced by electromigration in the regime where atomic steps are transparent. For this purpose we study several vicinal orientations by means of in-situ (optical diffraction, electronic microscopy) as well as ex-situ (AFM, microprofilometry) visualization techniques. The data show that faceting proceeds in two stages. The first stage is short and leads to the appearance of a step density wave, with a wavelength roughly independent of the surface orientation. The second stage is much slower, and leads to the formation of a hill-and-valley structure, the period of which depends on the initial surface orientation. A simple continuum model enables us to point out why the wavelength of the step density wave does not depend on the microscale details of the surface. The final wavelength is controlled by the competition between elastic step-step interaction and facet edge energy cost. Finally, the surface stress angular dependence is shown to emerge as a coarsed-grained picture from the step model.Comment: 26 pages, 9 figure

Ne diffraction from Cu(110)

Experimental results of diffraction of thermal energy (64 meV) Ne atoms from the (110) face of copper are presented Diffraction is observed up to fifth order and strong selective adsorption features were measured. The bound state energy levels are fitted using the shifted Morse hybrid potential. Diffraction intensities extrapolated to zero kelvin are fitted using the so called modified corrugated Morse potential (MCMP) which is a realistic soft potential. The potential is found to be more corrugated and steeper in its repulsive part than in the Cu(110)/He case. This shows that attractive forces play an important rôle in the corrugation of the potential.On présente les résultats expérimentaux de la rétrodiffusion d'atomes de néon d'énergie thermique (64 meV) sur la face (110) du cuivre. La diffraction est observée jusqu'au cinquième ordre, ainsi que le phénomène de résonance avec les états liés. On ajuste les niveaux d'énergie des états liés à l'aide du potentiel de Morse hybride déplacé. Les intensités diffractées extrapolées à zéro kelvin sont reproduites en utilisant le potentiel de Morse corrugué modifié (MCMP) qui est un potentiel non abrupt réaliste. On trouve que, dans sa partie répulsive, le potentiel est plus modulé que dans le cas de la diffraction de l'hélium par Cu(110). Ceci montre que les forces attractives influencent de manière importante la modulation du potentiel total