• 대한기계학회논문집B
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• 제20권7호
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• pp.2397-2408
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• 1996

A numerical study was made of the control of transient oscillatory flow modes in Czochralski convection. The reduction of temperature oscillation was achieved by changing the rotation rate of crystal rod, .OMEGA.$_{S}$=.OMEG $A_{S0}$(1+ $A_{S}$sin(2.pi. $f_{S}$/ $t_{p}$t)). The temporal behavior of oscillation flow was scrutinized over broad ranges of two parameters, i.e., the rotation amplitude( $A_{S}$.leq.0.5) and the nondimensional frequency (0.9.leq. $f_{S}$.leq.1.5). The mixed convection parameter was ranged 0.225.leq.Ra/PrR $e^{2}$.leq.0.929, which encompassed the buoyancy-and forced-dominant convection regimes. Computational results revealed that the temperature oscillations could be reduced effectively by a proper adjustment of the control parameters. The uniformity of temperature distribution near the crystal rod was examined. The control of oscillatory flow modes was also made for a realistic, low value of Pr.

• 대한기계학회논문집B
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• 제20권3호
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• pp.988-1004
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• 1996

The characteristics of flow and oxygen concentration are numerically studied in Czochralski 8" silicon crystal growing process considering radiative heat transfer. The analysis of net radiative heat flux on all relevant surfaces shows growing crystal affects the heater power. Furthermore, the variation of the radiative heat flux along the crystal surface in the growing direction is confirmed and should be a cause of thermal stress and defect of the crystal. The calculated distributions of temperature and, heat flux along the wall boundaries including melt/crystal interface, free surface and crucible wall indicate that the frequently used assumption of the thermal boundary conditions of insulated crucible bottom and constant temperature at crucible side wall is not suitable to meet the real physical boundary conditions. It is necessary, therefore, to calculate radiative heat transfer simultaneously with the melt flow in order to simulate the real CZ crystal growth. If only natural convection is considered, the oxygen concentration on the melt/crystal interface decreases and becomes uniform by the application of a cusp magnetic filed. The heater power needed also increases with increasing the magnetic field. For the case of counter rotation of the crystal and crucible, the magnetic field suppresses azimutal flow produced by the crucible rotation, which results in the higher oxygen concentration near the interface.

• Journal of Radiation Protection and Research
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• 제34권2호
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• pp.83-86
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• 2009

The single crystal scintillator of bismuth germinate ($Bi_4Ge_3O_{12}$:BGO) was successfully grown by the conventional Czochraski technique. The characteristics of the grown BGO were evaluated and presented on the excitation, emission responses and energy spectra of the $\gamma$-rays from $^{241}Am$, $^{133}Ba$, $^{57}Co$, $^{22}Na$, $^{137}Cs$ and $^{54}Mn$ radio-isotopes. The energy resolution of grown BGO, $\Delta$E/E, was estimated to be 12.1% at 662 keV of $\gamma$-ray for $^{137}Cs$ nuclide. Compared to the commercial BGO crystal, we confirmed that the grown BGO has a good performance and is comparable to reference one.

• 한국세라믹학회:학술대회논문집
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• 한국세라믹학회 2003년도 춘계총회 및 연구발표회 초록집
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• pp.221.2-221
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• 2003

• 한국결정성장학회지
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• 제9권1호
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• pp.74-79
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• 1999

Langasite($La_3Ga_5SiO_14$)는 acoustic 특성에서 quartz, $LiTaO_3$ 와 $LiNbO_3$에 비교되는 새로운 압전재료이다. 본 연구에서는 새로운 Langasite 계열의 물질을 공기 중에서 고상반응법에 의해 합성하였고, 합성공정에서의 주요 확산종 을 조사하였다. 이때 합성된 물질의 소결체를 제조하여 각각의 유전적 성질을 비교평가하였다. 또한, Langasite 단결정 을 자체제작한 Czochralski 시스댐을 사용하여 성장시키는데 성공하였고, 성장된 결정의 물성을 평가하였다

• 한국결정성장학회지
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• 제7권3호
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• pp.359-365
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• 1997

$K_2CoCl_4$ 단결정을 Ar분위기에서 Czochralski법으로 육성하였다. 육성된 결정의 물리적 성질의 조사로서 먼저 유전적 특성을 조사하여 commensurate-incommensurate(C-INC) 상전이에서 유전율의 thermal hysteresis가 $5^{\circ}C$ 이하의 값을 가짐을 보였고, incommensurate(INC) 상에서 $K^+$ 이온에 의한 ionic hopping mechanism으로 전도도를 해석하였으며 이때 activation energy는 0.62 eV 이었다. 각각의 결정축으로 열팽창을 조사하여 c축으로 가장 큰 열팽창을 보였으며 열팽창계수를 계산하였다. 광학적 특성의 조사로서 200 nm~ 3000 nm 영역에서 흡수 스펙트럼을 측정하여 나타나는 흡수 peak을 결정장내의 에너지 준위의 분리에 따른 전이 에너지로 해석하였으며, 800 nm~ 1200 nm 영역의 투과특성으로 optical band filter로서의 가능성을 제시하였다.

• 한국결정성장학회지
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• 제9권2호
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• pp.149-156
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• 1999

초크랄스키 결정성장계의 산소농도에 영향을 주는 유동거동에 대한 정보를 얻기 위해 저온모델을 이용하여 실험적으로 초크랄스키 멜트에 내의 유속을 측정하였다. 실리콘 멜트와 유사한 프란틀(Pr) 수를 갖는 저 융점의 Woods metal을 작동유체로 채택하였다. 전기 전도성을 갖는 유체에서 속도 측정이 가능한 일체형 자석 프로우브(Incorporated magnet probe)를 제작하여 멜트 내부의 여러 지점에서 유속을 3차원저긍로 측정하였다. 측정 결과 관찰된 속도장은 자연대류가 지배적이며 비축대칭적인 유동양상을 나타내었다. 또한 멜트의 두 지점에서 동시에 측정된 온도 데이터로부터 상관계수 및 도가니 회전에 의한 온도 wave의전파를 분석한 결과 상관계수의 크기는 기존의 소형 실리콘 멜트의 연구에서 구한 값보다 작게 나타났으며 이러한 현상은 규모가 큰 멜트의 유동은 난류인 거동이 더 강해지기 때문에 발생하는 것으로 파악되었다.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1996년도 The 9th KACG Technical Annual Meeting and the 3rd Korea-Japan EMGS (Electronic Materials Growth Symposium)
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• pp.505-507
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• 1996

• 한국광학회:학술대회논문집
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• 한국광학회 1999년도 제16회 광학 및 양자전자 학술발표회Proceedings of 16th Optics and Quantum Electronics Conference, 1999
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• pp.220-221
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• 1999

Single crystals of Yttrium Calcium Oxyborate (YCOB) doped with different concentrations of Er3+ and Yb3+ ions were growth by Czochralski method. High qualities of crystals in morphology and transparency were obtained . Analysis on crystal structure and lattice parameters were performed by X-ray diffraction method. It was found that congruent melting composition is YCA4.2O1.2(BO3)3. Absorption and fluorescence properties of grown crystals were also reported.

• 한국결정성장학회지
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• 제6권2호
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• pp.155-165
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• 1996

Growth of $LiNbO_3$ single crystal by Czochralski method was carried out to study the piezoelectric effects. Piezoelectric coefficients and elastic compliances of the $LiNbO_3$ single crystal were determined by the resonance method of length-extentional mode of bar resonator from the room temperature up to $100^{\circ}C$. Two dielectric constants of $LiNbO_3$ were also determined by measuring the capacitance of the plate specimen. Measured constants were piezoelectric coefficients $d_{15},d_{22},d_{31},d_{33}$ elastic compliances $s^E_{11},s^E_{33},2s^E_{13}+2s^E_{44},s^E_{14}$ and dielectric constants $K^T_{11},K^T_{33}$. As temperature increased, elastic compliances changed very slowly while piezoelectric coeffiecients and dielectric constant $K^T_{33}$ changed very rapidly. Electromechanical coupling constant of zyw ($45^{\circ}C$)-bar was as high as 0.51 in room temperature and nearly constant up to $1000^{\circ}C$. The increase of piezoelectric coefficients was mainly due to the increase of dielectric permittivity.