First Principle Study of Surface Structure and Elementary Process of Crystal Growth

阐明外延生长的微观基本过程，被认为是生长高度可控的晶体和超晶格的关键。本课题的研究内容是同时优化吸附过程中的电子态和原子排布，以阐明影响吸附的关键因素，采用密度泛函理论和分子动力学方法，结合共轭梯度法进行优化。通过优化Si（100）表面上吸附原子的坐标和衬底中原子的坐标，确定了Si原子在Si（100）表面上的吸附能。确定了表面扩散势垒在二聚体方向为2.0eV，垂直于二聚体方向为0.6eV，并对台阶流动机制进行了模拟，得到了与实验一致的结果。我们在类似的理论框架下研究了GaAs表面硫原子钝化和氢气氛下金刚石薄膜生长的问题。我们还研究了具有大各向异性的系统。Nakao和Fujita在正方晶格中进行了插层化合物C_4KH_X的第一原理能带计算和Hubbard模型的自旋密度波分析。Hiramoto阐明了电子-电子相互作用对一维准周期系统电子结构的影响。

To clarify the microscopic elementary processes of epitaxial growth, is considered to be a key for growing highly controlled crystals and superlattices. Our subject is the simultaneous optimization of the electronic states and the atomic arrangements to clarify the key factor of the adsorption.We used the density functional theory and the molecular dynamics, with the conjugate gradient method for optimization. Adsorption energy of Si adatom on the Si(100) surface is determined by optimizing the coordinates of the adsorption atom, and the atoms in the substrate. We determined that the potential barrier of the surface diffusion to be 2.0eV in the dimer direction and 0.6eV in the perpendicular to it. We made simulation of step flow mechanism and obtained the results consistent with the experiments. We are investigating the problems of the passivation of the GaAs surface by sulfur atoms and thin film growth of diamond in hydrogen atmosphere in a similar theoretical framework.Surface is different from the crystal in strong anisotropy. We also studied the systems with large anisotropy. Nakao and Fujita perfoiw the first principle band calculation of intercalation compound C_4KH_X and spin-density-wave analysis of the Hubbard model in the square lattice. Hiramoto clarified the effect of electron-electron interaction on the elctronic structure of the one dimensional quasi periodic system.