| 日時： |
2006年08月07日（月） 15:00〜16:30 |
| 場所： |
京都大学 工学部物理系校舎 1階 112室 |
| 講演者： |
Professor Janusz S. Szmyd (AGH University of Science and Technology, Poland) |
| 講演題目： |
Unsteady character of 'spoke pattern' in the melt during growth of single crystals by Bridgman and Czochralski methods |
| 講演要旨： |
The currently most important techniques for growing bulk crystals use growth from melt. It is well known that the quality of substrates depends on crystal growth conditions such as crystal and crucible pull speed, and temperature distribution on the wall. It is therefore very important to understand melt motion and the fluctuation of temperature in the melt to obtain higher quality and larger single crystal substrates. Numerous studies on the dynamic patterns of convection in a melt have been carried out, and many on crystal growth have reported the occurrence of "spoke pattern" on the melt surface. The flow loses its stability and axisymmetric structures break its symmetry and become non-axisymmetrical. It has been observed that flow is divided into several identical rolls. Adjacent roll structures (sectors) have an opposed azimuthal velocity component. Moreover, computed results show that the azimuthal velocity of structure modifies the temperature profile from axisymmetric to non-axisymmetric. The numerical computation applied to the analysis of buoyancy driven flow in the vertical cylinder shows a non-axisymmetric character of the flow even for axisymmetric boundary conditions. The present work performed three-dimensional numerical computations of the unsteady flow and thermal fields of a melt in a vertical cylinder (like the Bridgman top seeding convection and Czochralski technique) in order to investigate the transient convection phenomena. The numerical analysis has shown that in Bridgman top seeding convection the Rayleigh-Benard instability is an indispensable factor in forming the surface spoke pattern. For Czochralski technique the temperature distributions on the vertical wall of the crucible and radiative heat transfer from the free surface of the melt were found to play a key role in forming the surface spoke pattern. |
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