勝野 喜以子

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.

成長中の固溶体の結晶組成を予測することは,結晶成長の研究における主要なテーマの1つである.結晶と母相の間の元素分配に影響を及ぼす界面カイネティックスは,多くの理論的,実験的な研究が行われたにもかかわらず,十分に理解されてはいない.本稿では,気相成長する二成分理想固溶体の成長層での原子の取り込みに必要なプロセスを明らかにすべく,モンテカルロ・シミュレーションで行った我々の最近の研究を紹介する.本シミュレーションにより,テラス(特にキンクの周辺のテラス)からの原子の離脱が成長している固溶体のバルクの組成を強くコントロールしていることが明らかになった.

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.

基板面上に形成される微細構造を制御できれば,新たなデバイス開発に多くの進展が期待できる.それが自己形成であれば,生産コスト面でも大きな効果をもたらす.その可能性を探るためには,基板面上の二次元核形威遇程を原子レベルで理解することが重要である.モンテカルロ法を用いて,結晶表面の動的過程をシミュレートすることにより,エピタキシャル成長の初期段階である核形成週程の解析について述べる.

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.