Gas bubbles in shaped sapphire |
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| Authors: | O.M. Bunoiu Th. Duffar I. Nicoara |
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| Affiliation: | 1. Physics Department, West University of Timi?oara, 300223 Timi?oara, Romania;2. SIMAP-EPM, BP75, 38402 Saint Martin d’Hères, France;1. Department of Materials Science and Engineering, Stanford University, 476 Lomita Mall, Stanford, CA 94305, USA;2. Stanford Synchrotron Radiation Laboratory, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, United States;3. Geballe Laboratory for Advanced Materials, Stanford University, 476 Lomita Mall, Stanford, CA 94305, United States;4. Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Avenue SE, Minneapolis, MN 55455-0132, USA;1. Department of Mechanical Engineering, National Central University, No. 300, Jhongda Road, Jhongli City, Taoyuan County 32001, Taiwan, ROC;2. Innovation Technology Research Center, Sino-American Silicon Products Inc., No. 8, Industrial East Road 2, Science-Based Industrial Park, Hsinchu, Taiwan, ROC;1. Faculty of Engineering, Shinshu University, Wakasato, Nagano 380-8553, Japan;2. Institute for Materials Research, Tohoku University, Katahira, Aoba-ku, Sendai 980-8557, Japan;1. Fujikoshi Machinery Corp., 1650 Kiyono Matsushiro-machi, Nagano 381-1233, Japan;2. Interdisciplinary Graduate School of Science and Technology, Shinshu University, Wakasato, Nagano 380-8533, Japan;3. Faculty of Engineering, Shinshu University, Wakasato, Nagano 380-8533, Japan;1. Fraunhofer THM, Am St.-Niclas-Schacht 13, 09599 Freiberg, Germany;2. Siltronic AG, Johannes-Hess-Straße 24, 84489 Burghausen, Germany;3. Fraunhofer IISB, Schottkystraße 10, 91058 Erlangen, Germany;4. Crystal Technology Consulting, Helga-Hahnemann-Str. 57, 12529 Schönefeld, Germany |
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| Abstract: | Shaped sapphire single crystals almost always contain a typical defect: small bubbles also known as “micro-voids”. The goal of this paper is to review the existing literature and give a survey of our recent work on this specific defect. As a conclusion to our review we propose a mechanism for bubble formation and its occurrence and distribution in shaped sapphire.The bubbles contain CO which originates as a result of complex reactions between the molten alumina, Mo crucible and graphite pieces. The CO dissolves in the molten alumina and is probably present as a saturated solution whatever the growth conditions. Then the dissolved gas is rejected at the solid–liquid interface and bubble nucleation occurs where the concentration of CO is highest. Therefore, the location of the bubbles in the crystal is governed by the hydrodynamics in the meniscus, which include Marangoni convection. The bubble is finally incorporated in the crystal when it reaches a critical size which depends only on the growth rate.When a central capillary channel is used, the bubbles are located in a layer close to the surface of the crystal from where they can be easily removed by polishing. Also, all the literature agrees on the fact that interface destabilization at high velocity results in the presence of bubbles throughout the entire crystal and should be avoided. |
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