共查询到20条相似文献，搜索用时 15 毫秒
1.
To simulate thermocapillary magnetohydrodynamic (MHD) convection in different shallow annular enclosures filled with silicon melt, a 3D numerical approach using an implicit finite volume formulation is used. Radiation is emitted upward from the annular enclosure's free top surface, the bottom one heated vertically and is subjected to an external magnetic field. The steady and unsteady thermocapillary MHD flow in four annular enclosures (R = 0.5, 0.6, 0.7, and 0.8) field is studied. The effects of varying the annular gaps, R, on the hydrothermal wave number and azimuthal pattern are obtained. The effects of the magnetic field on azimuthal velocity, temperature disturbances, and the transition from oscillatory to steady flow are also depicted. The results reveal that: hydrothermal waves m = 4, m = 6 and m = 8 are observed in steady flow for R = 0.7, R = 0.6 and R = 0.5, respectively. Oscillatory flows dominated by a hydrothermal wave m = 3 are found also when R = 0.8. The azimuthal velocity and temperature fluctuations at the free surface decrease as the magnitude of the magnetic field (Ha) increases, and the oscillatory flow would turn steady when Ha exceeds a critical value. 相似文献
2.
《Crystal Research and Technology》2018,53(9)
This paper presents a set of numerical simulations on the effect of rotation on thermal convection in a shallow model Czochralski configuration with a heated crucible bottom. Results show that when the bottom is heated by low heat flux, the temperature fluctuation can be significantly weakened and the melt can be kept from solidifying. Once the heat flux exceeds a threshold value, the thermocapillary convection will transit to the Benard–Marangoni convection. The temperature fluctuation is amplified by increasing crystal rotation rate or heat flux. The crystal rotation can restrain the azimuthal traveling of the waves. However, the propagating direction of the waves is related to the temperature gradient and the crucible rotation, and is independent of the crystal rotation. The wavenumber is reduced by the crystal rotation individually. Furthermore, the crucible rotation can reduce the effect of the crystal rotation on the wavenumber. 相似文献
3.
为了更好地了解轴向磁场对温度梯度作用下Marangoni-热毛细对流的影响,采用有限差分法对环形浅液池内硅熔体制单晶的流动进行了数值模拟.研究了三种不同边界条件下,Ha数分别为0、10、20、30对应下硅熔体内部流动强度和自由表面速度.结果表明,轴向磁场对浅液池内的Marangoni对流、热毛细对流和耦合的Marangoni-热毛细对流都有较好的抑制作用,且随着磁场强度的增强,抑制作用增加,更有利于提高晶体的结晶质量.当磁场强度和底部热流密度一定时,随着水平温度梯度的增加,靠近内壁的流动得到增强,外壁附近流动反而减弱. 相似文献
4.
A. Crll A. Mitric O. Aniol S. Schütt P. Simon 《Crystal Research and Technology》2009,44(10):1101-1108
Surface tension gradients in free crystal growth melts give rise to convective flow. If these gradients are due to thermal gradients, the well known thermocapillary (Marangoni) convection ensues. Concentration gradients due to segregation at the interface during growth can lead to additional solutocapillary convection. A system with large solutocapillary convection is Ge‐Si due to the pronounced segregation and the strong difference in surface tension; solutal buoyancy convection is also present due to the large density difference between Ge and Si. Solutocapillary convection will oppose thermocapillary convection in the Ge‐Si system since Si, having the higher surface tension, is preferentially incorporated into the crystal. A set of experiments directly proving and partially quantifying the effect has been conducted under microgravity during a parabolic flight campaign by recrystallizing Ge‐Si mixtures of different compositions, between 3% and 9% Si, in a crucible with tracers to visualize the movement. Solutocapillary flow with initial flow rates in excess of 5.5 cm/s at the onset of crystallization was measured. A slight dependence of the flow velocity on the initial Si content has been found. Experiments on the ground showed the same effect but with overall smaller speeds; this difference can be explained by the additional action of solutal buoyancy convection. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
5.
本文通过数值模拟的方法,研究了零重力条件下半浮区液桥内熔体热毛细对流的演化规律。在液桥的高度L和温差ΔT保持不变的情况下,通过改变液桥的半径R来改变液桥的高径比(Ar=L/R)。随着高径比Ar的变化,液桥内的对流表现出不同的流动特征。在Ar=0.5时,热毛细对流处于三维稳态;在Ar=1时,流场和温度场从稳态模式向非稳态周期多频振荡模式转变,它们之间的频率关系满足倍频关系(fn=nf1);在Ar=1.25时,监测点的速度振荡频率增大,表现为较小幅度的振荡模式,且温度振荡消失。 相似文献
6.
利用基于有限元的软件COMSOL Muhiphysics对多晶硅定向凝固过程进行了一系列二维数值模拟,研究了勾形磁场(CMF)对多晶硅定向凝固过程的影响.模拟分别在线圈电流设为0A、10 A、20A、30 A和40A的情况下进行.结果表明:CMF能有效抑制熔体的对流,特别是对坩埚侧壁附近的熔体.CMF可以影响结晶时的固液界面,使结晶初期凸形结晶界面变得平滑.电流从0A逐渐均匀增加到40A时,施加于熔体上的磁场也逐渐增加,熔体的最高流速逐渐减小,而且最高流速的减小量呈现出先增加后减小的趋势. 相似文献
7.
The result of a μg‐experiment on the Gradient‐Freeze growth of Ge:Zn with doping from the vapour phase shows a homogeneous distribution of the zinc in the melt, indicating the dominating role of a gravity‐independent transport mechanism. This effect is investigated numerically on the basis of a global model of the growth setup. The numerical simulation includes the melt flow and the transport of the dopant taking into account buoyant and thermocapillary forces. The results confirm the minor influence of gravity on the species transport. The complete mixing of the melt can be explained by thermocapillary (Marangoni) convection only. 相似文献
8.
Takashi Horiuchi Lei Wang Atsushi Sekimoto Yasunori Okano Takuya Yamamoto Toru Ujihara Sadik Dost 《Crystal Research and Technology》2019,54(5)
The top‐seeded solution growth method is a promising technique for growing high‐quality silicon carbide single crystal. Some inherent issues in this growth process, such as morphological instability, polycrystalline growth, and low growth rate, should be clarified. A high temperature difference between the seed and the crucible wall in this system is needed to enhance growth. However, such a high temperature gradient makes the radial growth rate profile non‐uniform due to the effect of Marangoni convection below the seed crystal, which leads to poor crystal quality. In the present work, the effects of crucible size and crucible rotation are numerically investigated to minimize the effect of Marangoni convection. The possibilities of the occurrence of growth‐rate non‐uniformity and undesired impurity incorporation are examined. A smaller crucible (in radius) leads to a more uniform growth rate profile. However, it gives rise to a higher possibility of impurity incorporation. It is also predicted that crucible rotation is ineffective in suppressing the Marangoni flow near the seed edge. This leads to a flow stagnation in the center of the melt, and consequently, it does not enhance the carbon transport below the seed. It also does not reduce the possibility of undesired impurity incorporation. 相似文献
9.
Claudia Cancellieri Daniel Ariosa Aleksandr V. Druzhinin Yeliz Unutulmazsoy Antonia Neels Lars P.H. Jeurgens 《Journal of Applied Crystallography》2021,54(1):87-98
Thin films generally contain depth‐dependent residual stress gradients, which influence their functional properties and stability in harsh environments. An understanding of these stress gradients and their influence is crucial for many applications. Standard methods for thin‐film stress determination only provide average strain values, thus disregarding possible variation in strain/stress across the film thickness. This work introduces a new method to derive depth‐dependent strain profiles in thin films with thicknesses in the submicrometre range by laboratory‐based in‐plane grazing X‐ray diffraction, as applied to magnetron‐sputtering‐grown polycrystalline Cu thin films with different thicknesses. By performing in‐plane grazing diffraction analysis at different incidence angles, the in‐plane lattice constant depth profile of the thin film can be resolved through a dedicated robust data processing procedure. Owing to the underlying intrinsic difficulties related to the inverse Laplace transform of discrete experimental data sets, four complementary procedures are presented to reliably extract the strain depth profile of the films from the diffraction data. Surprisingly, the strain depth profile is not monotonic and possesses a complex shape: highly compressive close to the substrate interface, more tensile within the film and relaxed close to the film surface. The same strain profile is obtained by the four different data evaluation methods, confirming the validity of the derived depth‐dependent strain profiles as a function of the film thickness. Comparison of the obtained results with the average in‐plane stresses independently derived by the standard stress analysis method in the out‐of‐plane diffraction geometry validates the solidity of the proposed method. 相似文献
10.
Liping Yao Zhong Zeng Yi Zhang Zhouhua Qiu Hiroshi Mizuseki Yoshiyuki Kawazoe 《Crystal Research and Technology》2012,47(8):816-823
Under a rotating magnetic filed (RMF), the instability of thermocapillary flow and its evolution with increasing Marangoni number (Ma) for semiconductor melt (Pr = 0.01) in a floating liquid bridge model (As = 1) are investigated numerically. Under 5 mT RMF, the thermocapillary flow is steady and axisymmetric with Ma < Mac, and the critical Marangoni number Mac for convection instability is 29.5, which is obtained by the direct numerical simulation. When the Ma is a little bit beyond the Mac, the thermocapillary flow loses stability to become a three‐dimensional rotating oscillatory convection, and a periodic oscillation is confirmed by the fast Fourier transform analysis, the oscillatory main frequency decays with increasing Ma. Under 1 mT–6 mT RMF, the Mac increases roughly with the magnetic strength except the Mac at 4 mT, where the corresponding change of flow mode after the instability is observed. The oscillatory convection occurs with a smaller Ma in the RMF than that without magnetic field. In addition, no instability toward a three‐dimensional steady convection, which is the state of thermocapillary flow without magnetic field after the first instability, is observed under the RMF. 相似文献
11.
12.
T. Duffar M. D. Serrano L. Lerin J. L. Santaller 《Crystal Research and Technology》1999,34(4):457-465
GaSb:Te and GaInSb samples have been solidified under microgravity conditions during the D2 Spacelab mission. Experimental design and parameters are described. Analysis of the thermal data taken during the flight, associated to numerical simulations of heat transfer in the experiment, with the help of FIDAP, gave the experimental conditions (thermal gradients and growth rate). Quantitative chemical analyses of the samples show a chemical segregation characteristic of strong mixing in the melt during crystal growth. Silica crucibles with an internal screw thread groove on the inner wall were used in order to get dewetting of samples from the crucible. It was therefore supposed that Marangoni convection on the free surface associated to the groove might have been the source of convection. This hypothesis has been studied by numerical simulation using FIDAP and the velocity field obtained is in agreement with a strong perturbation of the solutal boundary layer ahead the solid-liquid interface. This can explain the observed chemical segregation. 相似文献
13.
为了了解微重力条件下新型分离结晶生长过程中熔体热毛细对流的基本特征,利用有限差分法进行了三维数值模拟.当熔体顶部分别为自由表面及固壁边界条件时,得到了新型分离结晶Bridgrnan生长过程中熔体热毛细对流的速度分布和温度分布.结果表明:熔体顶部为自由表面时,当Marangoni数较小时,在上自由表面和下部狭缝处自由表面的表面张力的驱动下,熔体内部产生了逆时针和顺时针两个流动方向相反的流胞,此时熔体内的流动状态为稳态;随着Marangoni数进一步的增大,流胞的流动逐渐增强并逐步向熔体内部扩展,熔体内部温度分布非线性增强,上自由表面和下部狭缝处自由表面处速度增大;当Marangoni数超过某一临界值后,流动转化为非稳态流动.当熔体顶部为固壁时,与熔体顶部为自由表面时相比,临界Marangoni数增大.流动失稳的物理机制是流速的变化和阻力的变化之间存在滞后. 相似文献
14.
《Journal of Applied Crystallography》2017,50(1):265-277
The different approaches for separating residual stress and composition gradients introduced in the first part of this series [ Klaus & Genzel (2017). J. Appl. Cryst. 50 , 252–264 ] are demonstrated with the experimental example of a graded Ti(C,N) coating layer deposited by a modified high‐temperature chemical vapour deposition process on a cemented carbide substrate. The coating layer features a depth gradient in the lattice parameter in the strain‐free direction of the biaxial stress state, ψ*,hkl , and tensile residual stresses σ|| which are nearly uniform over the coating thickness but drop down significantly towards the free surface. On the assumption that the out‐of‐plane stress component σ33 can be neglected, the gradient is related to the variation in the chemical composition with depth. Therefore, the example considered here corresponds to case (d ) of possible combinations of residual stress and composition gradients discussed in the first part of this series. The comparison of the results achieved by means of the different methods reveals the importance of choosing appropriate experimental conditions that fit best to the sample to be investigated. For the case of thin‐film analysis, it is shown that the X‐ray information depth is the crucial parameter which should match the film thickness. 相似文献
15.
《Journal of Applied Crystallography》2017,50(1):252-264
Different X‐ray measurement and data evaluation concepts are presented, which allow for residual stress analysis in thin films with pronounced gradients in chemical composition. These gradients lead to a variation in the strain‐free lattice parameter a 0 with respect to the film thickness and superimpose the lattice strain induced by the film's inherent stresses. Non‐consideration of a 0(z ) gradients is shown to lead to considerable errors (`ghost stresses') in the residual stress depth profiles. With the simulated example of a TiCx N1−x film with a pronounced carbon gradient, the first part of this series introduces four approaches, which permit the separation of residual stress and composition depth distributions at different levels of approximation. They are based on lattice spacing depth profile measurements performed in either the sin2ψ mode or the scattering vector mode, or in combinations of these two scanning modes. Depending on the approach used for separating the residual stress and composition gradients, angle‐ or energy‐dispersive diffraction has to be applied, employing monochromatic X‐ray sources available in the laboratory or either white high‐energy synchrotron radiation or the Bremsstrahlung of conventional X‐ray tubes, respectively. The methods introduced here assume a biaxial residual stress state within the film. For a triaxial residual stress state with σ33 ≠ 0, a separation of stress and composition gradients is not straightforward, because an a 0(z ) gradient cannot be distinguished from the hydrostatic part of the stress tensor. 相似文献
16.
采用磁控共溅射沉积法,以Si靶和SiC靶为靶材,单晶Si(100)和石英为衬底,在不同衬底温度下沉积了富硅SiCx薄膜.在氮气氛下于1100 ℃退火,得到包含硅量子点的SiCx薄膜.采用傅立叶变换红外吸收光谱、拉曼光谱、掠入射X射线衍射和吸收谱对退火后的SiCx薄膜进行了表征.结果表明:当衬底温度从室温(25℃)升至300℃时,薄膜的晶化率增至71.3;,硅量子点尺寸增至8.9 nm,而光学带隙则减至2.42 eV;随着衬底温度进一步升高,薄膜的晶化率降至63.1;,硅量子点尺寸减小至7.3 nm,而光学带隙却增加至2.57 eV;当衬底温度从室温(25℃)升至400℃时,薄膜的吸收系数呈先增大后减小趋势.在本实验条件下,最佳衬底温度为300℃. 相似文献
17.
Wenjia Su Wei Yang Jiulong Li Xiaomin Han Junfeng Wang 《Crystal Research and Technology》2021,56(2):2000180
2D global transient model for generation-six (G6) GT-style furnace and upgraded generation-seven (G7) ALD-style furnace in which all types of heat transfer and flow are included is established to investigate the thermal field, melt convection, melt–crystal (m–c) interface shape, thermal stress, growth rate, and Voronkov ratios in the growing silicon ingot. The modeling is verified by the heater power and temperature experiment. Simulation results show that the melt flow is relatively stronger as the furnace upgrades. For G7, a relatively higher thermal stress and growth rate are found due to the higher temperature gradient both in the horizontal and axial directions. Furthermore, unlike the optimized G6, G7 shows the overly convex m–c interface in the initial stage and edge nucleation throughout crystal growth stage. 相似文献
18.
在直拉单晶硅生长的过程中,自然对流对晶体界面的形状、温度场及应力分布影响很大。本文采用二维模型对熔体内自然对流对单晶硅的影响作了数值模拟,在低雷诺数时采用层流模型,高雷诺数时采用紊流模型,Gr的变化范围从3×106到3×1010,这样涵盖了从小尺寸到大尺寸的直拉单晶硅生长系统。数值结果表明熔体的流动状态不仅与熔体的Gr有关,还与熔体高度和坩埚半径的比值密切相关。当Gr>108时,熔体内确实存在紊流现象,层流模型不再适合,随着Gr的增大,紊流现象加剧,轴心处的等温线变得更为陡峭,不利于晶体生长。 相似文献
19.
以Au膜作为催化剂和大晶粒多晶Si薄膜为衬底,利用固-液-固生长机制,制备出直径在30～ 100 nm和长度为几百微米的高密度Si纳米线.实验研究了退火温度、生长时间和N2流量对Si纳米线生长的影响.结果表明,随着退火温度的升高,生长时间的延长和N2流量的增加,Si纳米线的长度和密度都显著增加.对不同生长时间下获得的Si纳米线样品进行了X射线衍射测量,结果显示随着生长时间的延长,多晶Si薄膜和表面的Au膜成分都在减少.光致发光谱则显示出弱的蓝光发射和强的红光发射特性,前者应是由非晶SiOx壳层中的氧空位发光中心引起,后者则应归因于Si纳米线芯部与非晶SiOx壳层之间界面区域附近中的Si =O双键态或非桥键氧缺陷中心. 相似文献
20.
The concept of a physical model experiment is introduced and discussed in the context of melt and gas flows in bulk crystal growth processes. Such experiments allow one to \"extract\" selected physical phenomena from the full complexity of a real crystal growth process and “transfer” them to material systems with an easier access for experimental measurements. Model experiments for the main techniques of melt growth are summarized in a literature review, and the applicability of the results to real crystal growth systems is analyzed. Recent examples of model experiments for melt and gas flows in Czochralski growth of silicon are used to demonstrate the state of the art and show the potential of such experiments to improve the understanding of complex multi-physical multi-scale phenomena occurring in every crystal growth process. 相似文献