Hydromechanic instability of crystals growth by Czochralski method

Рассмотрен один из механизмов гидромеханической неустойчивости при выращивании кристаллов из расплава методом Чохральского, связанный с явлением образования «холодных термиков» в подкристальной области. С этой целью проанализированы результаты, полученные по двум математическим моделям: 1 - без и 2 - с учетом процесса кристаллизации. В первом случае модельной жидкостью был этанол, а положение фронта кристаллизации задавалось изотермой кристаллизации и было неизменным. В рамках такого подхода были исследованы особенности перехода от стационарного течения жидкости к его неустойчивым модам, сопровождающимся формированием, развитием и отрывом «холодного термика» от фронта (изотермы) кристаллизации. Во втором случае модельными расплавами были два материала с температурой плавления, близкой к комнатной: гептадекан и галлий, которые существенно различаются коэффициентами теплопроводности. В этом случае было изучено влияние термомеханических параметров на формирование формы фронта кристаллизации и возникновение гидромеханической неустойчивости в виде «холодных термиков». The mechanism of hydromechanical instability during Czochralski crystal growth from a melt is considered, which is associated with the formation of “cold plumes” under the crystal. For this purpose, the results obtained by two mathematical models: 1 - without and 2 - taking into account the crystallization process are analyzed. In the first case, an ethanol was as the model fluid, and the position of the crystallization front was set by the crystallization isotherm and was unchanged. Within the framework of this approach, the features of a transition from a stationary fluid flow to its unstable modes were studied, which are accompanied by the formation, development, and separation of “cold plumes” from the crystallization front (isotherm). In the second case, the model melts were as two materials with a melting point close to room temperature: heptadecane and gallium, which significantly differ in thermal conductivity. In this case, the influence of thermomechanical parameters on the formation of the crystallization front shape and the occurrence of hydromechanical instability in the form of "cold plumes"was studied.

Mixed Oscillation Flow of Binary Fluid with Minus One Capillary Ratio in the Czochralski Crystal Growth Model

This work presented a series of three-dimensional unsteady numerical simulations on the characteristics of the mixed oscillation flows of binary mixture in a Czochralski crystal growth model. The silicon-germanium melt is investigated and the capillary ratio is minus one. The simulation results showed that, for the special capillary ratio, the thermal and solutocapillary forces are imposed in opposite directions and counteract each other. With the effect of buoyancy, the balance between the capillary forces is disturbed. Mixed with the forced convection driven by rotation, the capillary-buoyancy convection is complex. The basic mixed flow streamlines are presented as various rolling cells. The directions of the rolls are dependent on the combinations of surface and body forces. With the increase of temperature gradient, the basic flow stability is broken, and the oscillations occur. The crucible rotation has an effective influence on the stability enhancement. However, affected by the crystal rotation, the critical condition experiences an increase to a turning point, and then undergoes a sharp reduction to zero. Once the instability is incubated, the surface oscillations are analyzed. For the three-dimensional steady flow, only spatial oscillations are observed circumferentially, and the surface patterns of spokes, rosebud, and pulsating ring are obtained. For the unsteady oscillation flow, the spiral hydrosoultal waves, rotating waves, and superimposition of spirals and spokes are observed, and the oscillation behaviors are also discussed.

Controlled growth of single-crystalline metal nanowires via thermomigration across a nanoscale junction

Mass transport driven by temperature gradient is commonly seen in fluids. However, here we demonstrate that when drawing a cold nano-tip off a hot solid substrate, thermomigration can be so rampant that it can be exploited for producing single-crystalline aluminum, copper, silver and tin nanowires. This demonstrates that in nanoscale objects, solids can mimic liquids in rapid morphological changes, by virtue of fast surface diffusion across short distances. During uniform growth, a thin neck-shaped ligament containing a grain boundary (GB) usually forms between the hot and the cold ends, sustaining an extremely high temperature gradient that should have driven even larger mass flux, if not counteracted by the relative sluggishness of plating into the GB and the resulting back stress. This GB-containing ligament is quite robust and can adapt to varying drawing directions and velocities, imparting good controllability to the nanowire growth in a manner akin to Czochralski crystal growth.

Improving the Dipping Step in Czochraski Process Using Haar-Cascade Algorithm

Czochralski crystal growth has become a popular technique to produce pure single crystals. Many methods have also been developed to optimize this process. In this study, a charge-coupled device camera was used to record the crystal growth progress from beginning to end. The device outputs images which were then used to create a classifier using the Haar-cascade and AdaBoost algorithms. After the classifier was generated, artificial intelligence (AI) was used to recognize the images obtained from good dipping and calculate the duration of this operating. This optimization approach improved a Czochralski which can detect a good dipping step automatically and measure the duration with high accuracy. Using this development, the labor cost of the Czochralski system can be reduced by changing the contribution of human specialists’ mission.

Czochralski crystal growth and characterization of large langatate (La3Ga5.5Ta0.5O14, LGT) crystals for SAW applications

1.5 and 2 inch LGT, langatate (La3Ga5.5Ta0.5O14) crystals along the X[100], Y[120] and Z[001]-directions were successfully grown by the Czochralski technique.