Conversion of stable crystals to metastable crystals in a solution by periodic change of temperature

Using a Becker-D\"oring type model including cluster incorporation, we study the possibility of conversion of stable crystals to metastable crystals in a solution by a periodic change of temperature. At low temperature, both stable and metastable crystals grow by coalescence with abundant clusters. At high temperature, a large amount of small clusters produced by the dissolution of crystals inhibits the dissolution of crystals, and the imbalance in the amount of crystals increases. By repeating this process, the periodic temperature change can convert stable crystals into metastable crystals

Kinematical Bound States of Steps Caused by Asymmetry in Step Kinetics

金沢大学総合メディア基盤センターWe study time evolution of parallel straight steps with repulsive interaction between steps. If step kinetics is asymmetric in the upper and the lower terraces (Schwoebel effect), a vicinal face becomes unstable when undersaturation exceeds a critical value, and an array of large bunches described by the Benney equation appears. In the one-sided model (the extreme limit of the asymmetry) a pairing instability occurs. In this case the instability always ends up with formation of step pairs, and with large undersaturation hierarchical bound states of step pairs are formed. On the contrary many-body bound states appear in the general asymmetric model

Control of chaotic wandering of an isolated step by the drift of adatoms

金沢大学総合メディア基盤センターThe drift of adatoms strongly influences the wandering pattern of an isolated step moving in a surface diffusion field. When the drift velocity has a component against the step motion and exceeds a critical value, the straight step becomes unstable with long wavelength fluctuations, and wanders. This wandering pattern can be controlled by changing the direction of the drift. When the drift has no component parallel to the step edge, the unstable step obeys the Kuramoto-Sivashinsky equation and shows a chaotic pattern. When the drift has a component parallel to the step edge, the step obeys the Benney equation. If the parallel component is sufficiently large, the step shows a regular pattern

Two mechanisms forming a comblike step pattern induced by a moving linear adatom source

We carry out phase field simulations to study properties of the comblike step patterns induced by an adatom source. When an adatom source advances right in front of a step, stepwandering is caused by the asymmetry of the surface diffusion field and small protrusions are formed. If the velocity of the source Vp is smaller than a critical value V c p , the protrusions follow the adatom source with coarsening of the step pattern, and a regular comblike pattern with finger-like protrusions is formed.With a sufficiently small Vp, the gap of the supersaturation is large at the adatom source. Since the period of protrusions, , decreases with increasing Vp, the coarsening of step pattern is irrelevant for the protrusions to catch up with the adatom source. Near V c p , the gap of the supersaturation at the adatom source is small. Taking account of the increase in with increasing Vp, the coarsening of the step pattern is essential for the protrusions to follow the adatom source

Effect of two-dimensionality on step bunching on a Si(001) vicinal face

金沢大学総合メディア基盤センターWe study the effect of two-dimensionality on step bunching on a Si(001) vicinal face heated by direct electric current. When the anisotropy of the diffusion coefficient changes alternately on consecutive terraces like a Si(001) vicinal face, bunching occurs with the drift of adatoms. If the wandering fluctuation of step bunches is neglected as in the one-dimensional model, the bunching with step-down drift is faster than that with step-up drift in contradiction with experiment (Latyshev et al.: Appl. Surf. Sci. 130-132 (1998) 139). In a two-dimensional model with a wide system width, the step bunches wander heavily with step-up drift, and the recombination of neighboring bunches occurs more frequently than those with step-down drift. The bunching with step-up drift is accelerated and can be faster than that with step-down drift. ©2006 The Physical Society of Japan.

Evaporation and impingement effects on drift-induced step instabilities on a Si(001) vicinal face

金沢大学総合メディア基盤センターWe theoretically study the effect of evaporation and impingement of atoms on step wandering induced by the drift of adatoms. With a Si(001) vicinal face in mind, the anisotropy in diffusion coefficient is assumed to alternate on consecutive terraces. Without evaporation, steps wander in-phase with step-up drift and grooves perpendicular to the steps appear. The form of the wandering steps is sinusoidal with the width increasing in time as t12. Evaporation of adatoms suppresses the step wandering and introduces two surface diffusion lengths. When they are longer than the step distance, the step width still increases in proportion to t12, but with a smaller coefficient than that in the case without evaporation. When one of the surface diffusion lengths is comparable or shorter than the step distance, the saturation of the step width occurs. Impingement of atoms, on the other hand, changes the form of the wandering steps: their front becomes flat and wide and the grooves become steep and narrow. The growth rate of the step width becomes small, but the step width increases with the same exponent 12.© 2005 The American Physical Society

Instabilities of steps induced by the drift of adatoms and effect of the step permeability

金沢大学総合メディア基盤センターWe theoretically study step wandering and step bunching induced by the drift of adatoms with attention to the permeability of steps. The critical drift velocity to induce the instability is calculated, and Monte Carlo simulation is performed to test the linear analysis. In sublimation, when the step distance is small in comparison with the surface diffusion length, the wandering and bunching of steps can occur simultaneously with the step-down drift if steps are impermeable. The instabilities do not occur simultaneously if steps are permeable: the bunching occurs with the step-up drift, and the wandering with the step-down drift. In growth, when the step distance is small, the bunching occurs with the step-down drift and the step wandering occurs with the step-up drift irrespective of the permeability, in agreement with Métois and Stoyanov [Surf. Sci. 440, 407 (1999)]. The change of the permeability with increasing temperature can explain the instabilities observed in Si(111) vicinal face

Repulsion-mediated step wandering on a Si(001) vicinal face

金沢大学総合メディア基盤センター　With a Si(001) vicinal surface in mind, we study step wandering instability on a vicinal surface with an anisotropic surface diffusion whose orientation dependence alternates on each consecutive terrace. In a conserved system step wandering takes place with step-up adatom drift. Repulsive interaction between steps is found indispensable for the instability. Monte Carlo simulation with a strong repulsive step interaction confirms the result of linear stability analysis, and further shows that in-phase step wandering produces straight grooves. Grooves widen as their amplitudes increase in proportion to the square root of time