PubMed Health⌕ Search

Biomedical subjects

O Pierre-Louis

Publications and source records attributed to O Pierre-Louis.

10 recordsLinked to original sources
PubMed2004

Peculiar effects of anisotropic diffusion on dynamics of vicinal surfaces.

We report on peculiar behaviors due to anisotropic terrace diffusion on step meandering on a vicinal surface. We find that anisotropy triggers tilted ripples. In addition, if the fast diffusion direction is perpendicular to the steps, the instability is moderate and coarsening is absent, while in the opposite case the instability is promoted, and interrupted coarsening may be observed. Strong enough anisotropy restabilizes the step for almost all step orientations. These findings point to the nontrivial effect of anisotropy and open promising lines of inquiries in the design of surface architectures.

Journal Article↗
PubMed2004

Kinetic step pairing.

We report on the theoretical and experimental discovery of pairing of identical crystal steps. We first show that step bunching always occurs at long wavelength in the vicinity of an instability threshold when step dynamics is local. But an instability towards a stable train of pairs can be obtained when steps dynamics is nonlocal. This instability is shown to occur for transparent steps under electromigration. Observations on Si(111) under electromigration around 1230 degrees C show stable trains of pairs. By controlling both supersaturation and electromigration, we establish an experimental morphology diagram, from which we conclude that the transparency kinetic coefficient is negative.

Journal Article↗
PubMed2003

Phase field models for step flow.

The relation between phase field and discontinuous models for crystal steps is analyzed. Different formulations of the kinetic boundary conditions of the discontinuous model are first presented. We show that (i) step transparency, usually interpreted as the possibility for adatoms to jump through steps, may be seen as a modification of the equilibrium concentration engendered by step motion. (ii) The interface definition (i.e., the position of the dividing line) intervenes in the expression of the kinetic coefficients only in the case of fast attachment kinetics. (iii) We also identify the thermodynamically consistent reference state for kinetic boundary conditions. Asymptotic expansions of the phase field models in the limit where the interface width is small, lead to various discontinuous models. (1) A phase field model with one global concentration field and variable mobility is shown to lead to a discontinuous model with fast step kinetics. (2) A phase field model with one concentration field per terrace allows one to recover arbitrary step kinetics (i.e., arbitrarily strong Ehrlich-Schwoebel effect and step transparency). Quantitative agreement is found, in both the linear and nonlinear regimes, between the numerical solution of the phase field models and the analytical solution of the discontinuous model.

Journal Article↗
PubMed2003

Interrupted coarsening of anisotropic step meander.

We report on the effect of anisotropy on the step meandering instability on vicinal surfaces during molecular beam epitaxy growth. A scenario of interrupted coarsening is found: the lateral length scale of the structure first significantly increases with time and then freezes at a larger length scale. The wavelength selection mechanism results from a nontrivial nonlinear effect of anisotropy. Anisotropy also leads to solutions which drift sideways, resulting from the loss of the back-front symmetry of the meander and the nonvariational character of dynamics.

Journal Article↗
PubMed2001

Continuum model for low temperature relaxation of crystal steps.

High and low temperature relaxation of crystal steps are described in a unified picture, using a continuum model based on a modified expression of the step-free energy. Results are in agreement with experiments and Monte Carlo simulations of step fluctuations and monolayer cluster diffusion and relaxation. In an extended model where mass exchange with neighboring terraces is allowed, step transparency and a low temperature regime for unstable step meandering are found.

Algorithms↗
PubMed2001

Oscillatory driving of crystal surfaces: a route to controlled pattern formation.

We show that the oscillatory driving of crystal surfaces can induce pattern formation or smoothening. Depending on driving conditions, step bunching and meandering, mound formation, or surface smoothening may be seen in the presence of a kinetic asymmetry at the steps or kinks. We employ a step model to calculate the induced mass flux along misoriented surfaces, which accounts for surface dynamics and stability. Slope selection, surface metastability, and frequency-dependent surface stability are found. Quantitative predictions for pattern formation on metal surfaces in an electrolyte are provided.

Journal Article↗
PubMed2001

Unstable step meandering with elastic interactions.

We report on theoretical investigations of the influence of step interactions due to elasticity on unstable step meandering during molecular beam homoepitaxy. It is shown that elasticity causes coarsening of the cellular structure of the meander found in a previous work. The time dependence of step roughness is found to be robust, behaving as t(1/2). The lateral length scale coarsening is shown to be sensitive to the underlying physical mechanisms. In particular, the typical length follows the law t(alpha), with alpha = 1/6 or 1/4 depending on whether line diffusion is negligibly small or not.

Journal Article↗