katsuno kiiko

To explore the relaxation process of percolating labyrinthine submonolayer films, we observe in real-time the evolution of a submonolayer film with a coverage of ∼ 0.7 monolayer on SrTiO3(001) at 670 C using scanning tunneling microscopy. We find that the characteristic length begins to increase after an incubation time. During the incubation time, percolating grooves are segmented by local pinch-off events predominantly driven by thermal fluctuations. The occurrence frequency of the pinch-off events markedly decreases with an increase in the characteristic length. In the second stage, reshaping of the disconnected irregular vacancy islands occurs by edge diffusion. Finally, small vacancy islands disappear via Ostwald ripening by terrace diffusion. © 2012 Elsevier B.V. All rights reserved.

We study the dependence of the critical size of the nucleus on the density of impurity by carrying out a Monte Carlo simulation. We assume that the impurities are fixed on a crystal surface, and neglect restoration of bonds between an impurity atom and an adsorbed atom. We initially prepare one cluster in the system and investigate the change of the cluster size. When the cluster size is the critical value, the frequency of increasing the cluster size is equal to that of decreasing the size. With increasing the impurity density, the critical nucleus becomes large. When the impurity density is sufficiently high, regardless of the initial cluster size, the cluster vanishes after a long time interval, namely, the critical cluster size is diverged.

Predicting the composition of a solid solution during its growth has been one of the principal themes in the study of crystal growth. The interface kinetics, which influences the element partitioning between a crystal and mother phases, has been poorly understood in spite of many theoretical and experimental studies. In the present paper, we introduce our recent study of the Monte Carlo simulation which was applied to clarify the essential processes for the incorporation of atoms on growth layers of a binary ideal solid solution growing from its vapor. The simulation reveals that the detachment of atoms from terrace sites, especially around kink sites, strongly controls the bulk composition of a growing solid solution.

Smoothing of an atomically rough vicinal surface of SrTiO3 is studied by scanning tunneling microscope (STM) observation and by Monte Carlo (MC) simulation. A complex step pattern that resembles a two-dimensional phase separation pattern is observed on the surface. Analysis of the step pattern during annealing obtained by the STM in comparison with the MC simulation reveals an asymmetry of the relaxation pattern between islands and holes. The asymmetry is attributed to the difference of the mobility of an adatom and an atomic hole, and the asymmetry is enhanced by the step edge diffusion barrier. Values of an effective bond energy and an effective diffusion barrier as well as the surface diffusion coefficient are deduced from the relaxation pattern. (C) 2008 Elsevier B.V. All rights reserved.

The growth of a binary ideal solid solution crystal from its vapor in a wide range of supersaturation is simulated using the Monte Carlo simulation method. The growth rate and surface structure obtained in the present simulation show that the growth mechanism changes from the layer-by-layer growth of smooth surfaces, through multinuclear layer-by-layer growth, to normal growth of rough surfaces, with increased supersaturation. The effective distribution coefficients for bulk., terrace, step, and kink sites show not simple dependence on supersaturation. The dependence is interpreted in the relation with the growth mechanisms, by taking account of both the kink kinetics and the relaxation by direct exchange of atoms between each kind of growth site and a vapor. (C) 2007 Elsevier B.V. All rights reserved.

Effective distribution coefficients of a binary ideal solid solution growing from dilute surroundings are investigated using the Monte Carlo simulations. To explain the gap between the published theories and our simulation results, the relaxation processes of the composition of the terrace by the desorption of atoms during the growth were formulated. (c) 2004 Elsevier B.V. All rights reserved.

Two dimensional nucleation process on substrate is investigated by Monte Carlo simulation, and the critical nucleus size and its waiting time are measured with a high accuracy. In order to measure the critical nucleus with a high accuracy, we calculate the attachment and the detachment rate to the nucleus directly, and define the critical nucleus size when both rate are equal. Using the kinematical nucleation theory by Nishioka, it is found that our obtained kinematical two dimensional critical nucleus size are about ten percent smaller than the thermodynamically defined one. The dependence on the chemical potentials for the critical nucleus size is good agreement with the classical nucleation theory. For the surface diffusion dependence of the critical nucleus size, it is found that the critical nucleus size increases as the surface diffusion length to long distance.