Byoung Min Lee

Surface nucleation of the (111) plane of excimer laser annealed Si on SiO2 substrates: A molecular dynamics study

We have investigated the nucleation and crystallization processes of molten silicon (Si) on SiO2 substrates by performing molecular dynamics (MD) simulations based on the modified Tersoff potential parameters. A heat flow that leads to a steady fall of the local temperature in the molten Si is achieved by determining the atomic movements with the combination of Langevin and Newton equations. Good agreement is reached between the predictions of temperatures based on the kinetic energies and the velocity distributions of atoms at local regions. The results of simulations revealed that the (111) plane of the Si nuclei formed at the surface was predominantly parallel to the substrate of MD cell. The surface energies of the (100), (110), and (111) planes of Si at 77 K were calculated to be 2.27, 1.52, and 1.20u2009J∕m2, respectively, and they were in good agreement with the experimental results. The lowest value of surface energy, 1.20u2009J∕m2, for the (111) plane at 1700 K was obtained under the condition of elastic...

Molecular-dynamics simulations of nucleation and crystallization processes of laser crystallized poly-Si

The nucleation and crystallization processes of excimer-laser annealed Si on a SiO2 substrate for complete melting conditions have been investigated by using molecular-dynamics simulations. In the early stage of nucleation, the preferential growth of nuclei with a {111} face normal to the surface was originated from the {111} twin boundaries with a low surface energy. The partial rotation of the dimer leads to the growth of {111}-oriented nuclei along twins that have different stacking sequences. The recombination of vacancies and dimers at the solidification front is directly related to {111} growth from the twin boundaries.

Crystal Growth of Silicon Thin Films on Glass by Excimer Laser Annealing: A Molecular-Dynamics Study

We have investigated crystallization processes during excimer laser annealing of silicon (Si) thin films on glass by molecular-dynamics simulations and laser power dependence of the polycrystalline Si grain size was discussed. The temperature range for the highest growth rate was found to be approximately 500 degrees higher than that for the highest nucleation rate. It was also found that a steady state temperature gradient was obtained in the direction of the surface normal during laser irradiation. These results suggest that nucleation occurs in the Si/glass interface region and then crystallization proceed toward the high temperature region during laser irradiation in the near-complete melting condition.

Molecular-dynamics analysis of the structural properties of silica during cooling

The structural properties of SiO2 liquid during cooling have been investigated by molecular dynamics simulations. The interatomic forces acting on the particles are calculated by the modified Tersoff potential parameters. The glass transition temperature and structural properties of the resulting SiO2 system at various temperatures have been investigated. The fivefold coordinations of Si and threefold coordinations of O atoms were observed, and the coordination defects of system decrease with decreasing temperature up to 17 % at 300 K. The self-diffusion coefficients for Si and O atoms drop to almost zero below 3000 K. The structures were distorted at high temperatures, but very stable atomic network persisted up to high temperature in the liquid state.

Structural Properties and Diffusion Behaviors of Liquid Silica at Finite Temperatures

The structural properties of SiO₂ liquid at finite temperatures have been investigated by molecular dynamics (MD) simulations utilizing the Tersoff interatomic potential. During cooling process, the SiO₂ liquid structure quenched with a cooling rate of 1.0×10¹¹ K/sec shows the traditional properties observed in the experiments. The coordination defects of system decrease with decreasing temperature up to 17%. The SiO₂ glass quenched up to 1600 K contains defects consisting of the fivefold coordination of Si, and the threefold coordination of O atoms. The calculated diffusion coefficients which are calculated by monitoring the mean-square displacement of atoms drop to almost zero below 3000 K (＜10?? ㎠/sec) but has a fluctuations at low temperature. The structure properties of SiO₂ liquid shows a significant dependence on the temperature during cooling process. Bond-angle distribution at around 120° originate from the O and Si atoms consisting of the over-coordinated O atoms.