Absence of Domain Wall Roughening in a Transverse Field Ising Model with Long-Range Interactions

We investigate roughening transitions in the context of transverse-field Ising models. As a modification of the transverse Ising model with short range interactions, which has been shown to exhibit domain wall roughening, we have looked into the possibility of a roughening transition for the case of long-range interactions, since such a system is physically realized in the insulator LiHoF4. The combination of strong Ising anisotropy and long-range forces lead naturally to the formation of domain walls but we find that the long-range forces destroy the roughening transition.Comment: 7 pages, 5 figures, revtex

Step Patterns on Vicinal Reconstructed Surfaces

Step patterns on vicinal $(2\times1)$ reconstructed surfaces of noble metals Au(110) and Pt(110), miscut towards the (100) orientation, are investigated. The free energy of the reconstructed surface with a network of crossing opposite steps is calculated in the strong chirality regime when the steps cannot make overhangs. It is explained why the steps are not perpendicular to the direction of the miscut but form in equilibrium a network of crossing steps which make the surface to look like a fish skin. The network formation is the consequence of competition between the -- predominantly elastic -- energy loss and entropy gain. It is in agreement with recent scanning-tunnelling-microscopy observations on vicinal Au(110) and Pt(110) surfaces.Comment: 11 pages with 5 eps figures in text. Uses psfig and elsart.sty (ELSEVIER Science). To be published in Surf. Sc

Can one have preroughening of vicinal surfaces?

We discuss the possibility that, besides roughening, a vicinal surface could display preroughening (PR), and consider the possible mechanisms for its promotion. Within the framework of a terrace-step-kink model, it turns out that a PR transition is possible, and could be induced by a short-range repulsion between parallel kinks along the same step or on adjacent steps, or even by some kind of extended range step-step repulsion. We discuss the possible relevance of this phenomenon to the anomalous roughening behaviour recently reported for Ag(115).Comment: 9 pages, 3 postscript figures, submitted to Surface Scienc

Simulation temporelle du fraisage de parois minces

Quel que soit le secteur industriel concerné, la réduction de masse est un objectif récurrent dont la première conséquence est l'augmentation des parties à faibles épaisseurs sur les pièces à fabriquer. L'usinage de ces parois minces engendre fréquemment des problèmes vibratoires qui doivent être anticipés notamment à partir de simulations visant à prédire l'état des surfaces usinées. Cet article revient sur la simulation temporelle de l'usinage de parois minces et souligne que ce type de simulation est long et délicat à mettre en œuvre et à analyser. Une méthode permettant d'accélérer l'analyse et la prise de décision par l'orientation des calculs est proposée. Cette méthode est basée sur la recherche du régime stationnaire effectif. Initialisée à partir de ce régime, la simulation converge plus rapidement et conduit à l'état de la surface usinée. En confrontant les résultats obtenus par simulation à ceux obtenus expérimentalement, l'apport de cette méthode est prouvé

Adsorption induced reconstruction of the Cu(110) surface

The formation of the O/Cu(110)-(2 × 1) and H/Cu(110)-(1 × 2) superstructures has been investigated by a LEED beam profile analysis. The oxygen induced reconstruction proceeds at later stages by creation of holes on flat terraces. This could not be observed at the hydrogen induced missing row reconstruction. The formation of the missing row structure proceeds most probably via nucleation at steps and subsequent growth of (1 × 2) islands. The influence of different distributions of steps and islands on beam profiles is discussed

Scattering of hydrogen molecules from a reactive surface: Strong off-specular and rotationally inelastic diffraction

Six-dimensional quantum dynamical calculations of the scattering of H_2 from a Pd(100) surface using a potential energy surface derived from density-functional theory calculations are presented. Due to the corrugation and anisotropy of the PES strong off-specular and rotationally inelastic diffraction is found. The dependence of the diffraction intensitities on the incident kinetic energy is closely examined. In particular we focus on the quantum oscillations for normal and off-normal incidence.Comment: RevTeX, 5 pages, 5 figures, to appear in Chem. Phys. Let

Influence de la position de l'outil sur le comportement dynamique en fraisage de parois minces

Vibratory problems encountered when milling a thin walled structure affect the surface quality of the finished workpiece and to a lesser extent, the life of the tool and the spindle. This is why, it is necessary to be able to limit these problems by an appropriate choice of the cutting conditions. The stability lobes theory allows to choose the suitable cutting conditions according to the dynamic behaviour of the workpiece and the tool. We introduce here the variations of dynamic behaviour due to the tool position, in order to obtain optimum cutting conditions all along the machining. This general implementation of the classical stability lobes graph leads us to represent the lobes in three dimensions. These theoretical results are compared with experimental milling of thin walled structure, in down-milling

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

Changing shapes in the nanoworld

What are the mechanisms leading to the shape relaxation of three dimensional crystallites ? Kinetic Monte Carlo simulations of fcc clusters show that the usual theories of equilibration, via atomic surface diffusion driven by curvature, are verified only at high temperatures. Below the roughening temperature, the relaxation is much slower, kinetics being governed by the nucleation of a critical germ on a facet. We show that the energy barrier for this step linearly increases with the size of the crystallite, leading to an exponential dependence of the relaxation time.Comment: 4 pages, 5 figures. Accepted by Phys Rev Let

Diffraction of neon by a (117) copper surface

The diffraction pattern of a thermal beam of neon atoms by a (117) copper surface has been experimentally determined. This pattern is produced by the step lattice which characterizes the (117) face.On a déterminé expérimentalement la figure de diffraction d'un faisceau d'atomes de néon d'énergie thermique par une surface vicinale de cuivre (117). Cette figure de diffraction correspond bien au réseau formé par les marches atomiques equidistantes qui caractérisent cette surface