Yuko Inatomi

The refractive index of GaP single crystal was measured through room temperature (300K) to 1200K at a wavelength of 780 nm by using an interferometry with a laser diode. To get a more accurate result, the thermal expansion coefficient of GaP crystal, which would be one parameter for the measurement of the refractive index, was measured by a diratometer equipped with laser interferometry against temperature in the range from room temperature to 973K. It was confirmed that the linear thermal expansion coefficient was a function of temperature. In this report, an empirical function was obtained to calculate the refractive index at any temperature for GaP crystal. The result shows that the refractive index of GaP varies from 3.1907 to 3.3354 in the temperature range from 300K to 1200K at the wavelength of 780nm.

The influence of the high static magnetic field to the crystal growth processes of the hen-egg-Lysozyme was studied by method of the observation such as microscopic interferometry to make the mechanism of the crystallographic orientation clear. As a result, orientation of the crystals was obviously controlled by the direction of a magnetic induction under 6.0T, but the magnetic field gives the crystal orientation only and never changes a condition figure.

Natural convection of liquid metal in a cubic enclosure heated from one vertical wall and cooled from an opposing vertical wall is studied under a horizontal lateral magnetic field parallel to the heated and cooled walls. The Seebeck effect is further considered for the present system. The Seebeck effect means the electric current induced having temperature difference in the two metals between two points. This effect may be induced for the liquid and solid boundaries of metals. This system was modeled and numerically computed. When the Seebeck effect is not considered, the Lorentz force increases with the Hartmann number, Ha, to decrease the average Nusselt number. When the Seebeck effect was considered, the average Nusselt number at Ha = 200 decreased. However at Ha = 400, the average Nusselt number increased with the Seebeck effect. This peculiar characteristic is due to the complicated convection of the Seebeck effect on the heat transfer surface.

Microgravity experiments are carried out mainly by shuttles in outer space, sounding rockets and airplanes in a ballistic orbit, and drop-shaft type facilities. Considering the frequency, condition of microgravity environment, and expenses, an inexpensive means with longer duration of microgravity than by an airplane or a drop type facility is expected. In 1980s three scientific balloons were launched with microgravity capsules which were dropped in the stratosphere to make a microgravity environment of 0.01g for 18 seconds. A long duration (more than 30 seconds) will be useful for such type of microgravity experiments. The conditions of duration, microgravity level, and experimental units loaded in a microgravity capsule were obtained by numerical simulations for free-fall capsules using the results of wind tunnel tests and the real condition of the upper air and wind over Sanriku Balloon Center. The results show that a microgravity experimental unit with 0.4m in diameter and 40kg in weight can make a 0.01g-microgravity environment for 30 seconds while a 0.125m and 10kg one can last for 35 to 40 seconds.

<br /> Step kinetic coefficient of GaP/GaP(111)B surface in liquid phase epitaxy growth was estimated by an in situ observation technique using a near-infrared microscopic interferometer under a reduced convection condition by utilizing a strong static magnetic field. Morphological stability of solid/liquid interface during the growth was evaluated based on a linear perturbational approach taking account of the step kinetic coefficient. The estimated value of the macrostep wavelength agreed well with the measured one.

An in situ observation setup for the growth process based on near-infrared microscopic interferometry was modified for a short-duration low-gravity experiment. Subsequently the observation in the environments were performed to reveal the influence of strongly-damped fluid flow on the growth process using the parabolic flights of an airplane and the free-fall of a drop capsule. As a result, the dissolution and growth rates were successfully obtained using the setup with a high accuracy. It was also found that the rates were strongly decelerated during the low gravity conditions.

Crystal growth processes of hen-egg-Lysozyme under high static magnetic field were studied by microscopic interferometry and dynamic light scattering measurements in order to control the crystallographic orientation. As a result, orientation of the crystals was obviously controlled by the direction of a magnetic induction under 6T, and few differences of the growth rates were observed from several nm to 400nm in the Lysozyme diameters under 0.6T.

In the present study, the morphological changes of a semiconductor growth interface from a solution were observed by near-infrared microscopy in rotating and static magnetic fields generated by two kinds of electromagnetic setups. The rotating magnetic setup had a maximum magnetic induction of 12 mT with a frequency of 50 Hz at the center of the furnace. The static magnetic field was produced by a single solenoid with a maximum magnetic induction of 800 mT. The growth of GaP/GaP (111) B was performed by a linear cooling method at the rate of 1 K/min under a starting growth temperature of 1173 K. The results revealed few differences in the morphological changes during growth under constant rotating magnetic fields of 0 and 12 mT. It was shown that the transverse static magnetic field of 800 mT reduced the growth rate and suppressed the appearance of macrosteps on the facet region. © 1999 Elsevier Science B.V. All rights reserved.

Growth and devolution rates on GaP(111)B facet surface during solution growth have been measured using near-infrared (NIR) microscopic field. We show that the possibility of solutal convection in the liquid causes the difference between the growth and dissolution rates.

The initial transient solute redistribution during directional solidification with liquid flow is analyzed and approximate solutions for both finite and infinite sample length are given, based on two assumptions: (1) there exists a solute transport boundary layer within which diffusion is the only solute transport mechanism, while beyond which convective mixing makes the solute distribution completely uniform; (2) the concentration profile inside the diffusion boundary layer is of exponential form and the diffusion length is a function of time during the initial transient process. The solution for infinite sample length comes back to Warren and Langer's approximate solution for pure diffusion when thickness of the boundary layer approaches infinity, and back to Burton et al.'s accurate solution for steady state when time approaches infinity. The calculation results according to the models for initial transient solute redistribution during directional solidification with liquid flow fit well with Inatomi et al.'s experimental results.

In situ observation of directional solidification of salol was carried out at a centrifuge acceleration of 10 G (G = 9.81 m/s2). Growth rate, temperature distribution and flow pattern in front of the solid-liquid interface could be simultaneously measured and visualized using a microscopic interferometer and thermocouples. The specimens were transparent, faceting organic compounds, which develop cellular arrays. These materials of commercial grade were purified by several zone-refining cycles on a laboratory scale and were enclosed in quartz glass cells. The solidification were controlled by the imposed temperature gradient in the cell and cooling rate at the both side of the cell. The growth direction was adjusted to opposite to the acceleration vector. We found appearance of a local recalescence region in front of the growing surface not only under 1 G but 10 G. The uniformity of the recalescence region along the interface seemed to be defined by the flow induced by the centrifuge acceleration. We considered the non-uniform temperature distribution ahead of the interface as one of the driving forces of the interface breakdown.

A setup for in situ observation was developed which makes possible the optical visualization of a solid-liquid interface during solution growth of semiconductors in an external magnetic field. This setup consisted of an optimized monoellipsoidal mirror furnace, a near-infrared optical system, and static or rotating electromagnetic facility. The target crystals were GaP, GaAs and CdTe.

In situ observation of directional solidification of transparent, faceting organic materials was carried out in a centrifuge at accelerations from 2 to 10 g. The solidification rate, temperature and concentration distributions, and now pattern in front of the solid-liquid interface were simultaneously measured and observed using a microscopic interferometer. Temperature oscillations occurred in this high Prandtl number melt from 2 to 10 g. Non-uniform temperature and concentration distributions in front of the interface were considered as the driving forces for interface breakdown at high acceleration.

Dynamic light scattering experiments were conducted to understand the phenomena of liquid phase separation. The alloy of succinonitrile-ethanol, which is in monotectic composition, was cooled from mono-phase temperature to two-phase region. The scattering intensity increased drastically near the critical temperature. The self-correlation function of the scattering intensity shows two peaks in the particle size distribution, one is less than 50 nm and the other is from 150 nm to 200 nm. The former is from residual impurities, and the latter is attributed to the concentration fluctuation near the critical temperature. It was concluded that the dynamic light scattering experiments has a high potential in phase separation phenomena studies, particularly in a microgravity environment.

In materials whose entropy change due to fusion are rather large, such as semiconductor, oxide superconductor and other crystalline materials, faceted cellular morphology is often observed on the advancing solid/liquid interface. The machanism to maintain this faceted morphology at the steady state growth had been believed to be solute pile-up and the subsequent undercooling at the bottom side of the cellular interface. Higashino, Inatomi and Kuribayashi (HIK), however, showed the appearance of a recalesced region ahead of the faceted interface in transparent organic compounds using the optical interferometer. In the present paper, precise measurement of the temperature distribution ahead of the advancing interface was carried out by means of the interferometric visuallization technique as well as the conventional temperatere measurement technique using micro-thermocouples. The result is that the influence of latent heat on the temperature distribution ahead of the interface was correlated qualitatively with the non-dimensional parameter defined by the release rate and the diffusion flux of latent heat. In addition morphologocal instabilities of the faceted interface were attributed to the change of the temperature distribution.

In the transparent organic crystal known as succinonitrile-acetone binary alloy, transient behavior of unidirectional solidification is directly observed within the range where the planar interface is stable, by means of a microscopic interferometer. Interface morphology and solidification rates are obtained by bright-field observations. Interference fringes are used to determine the gradient of the temperature and of the solute concentration in the liquid ahead of the solid-liquid interface. Although the solidification direction is taken such that the thermal convection is suppressed, experimental data on solidification rates and concentration gradients agree well with numerical values based not on the diffusion-controlled model, but on the boundary layer model which assumes fluid mixing beyond the boundary layer. One of the reasons why fluid mixing occurs is thought to be the thermosolutal convection induced by the concentration gradient built up ahead of the solid-liquid interface. Thickness of the boundary layer estimated from experimental data of solidification rates agrees quantitatively with those obtained from interference fringes and from tracer analysis. © 1993.

In-situ observation of unidirectional solidification was carried out in the transparent organic compound salol which develops faceted cellular arrays. Growth rate and the profiles of temperature and solute concentration in the vicinity of the solid-liquid interface could be simultaneously measured in a microscopic interferometer. Displacement of interference fringes was observed at large growth rates. This implied that the distribution of temperature ahead of the interface was influenced by the released latent heat. It was found that faceted interface was kept isothermal during the solidification and that there was the reversed profile of temperature around the concave of the interface. © 1993.

On the surface of LPE grown crystals, macrosteps are frequently observed. Macrosteps vary with the growth conditions of the process morphologically and induce the segregation of dopant atoms. The influence of the growth rate and temperature gradient on the surface morphology during LPE growth have been studied by in-situ observation technique with an infrared microscopic interferometer. It was shown that the positive temperature gradient in the liquid tends to suppress the appearance of macrosteps. © 1993.

There has been an increasing interest in understanding the underlying mechanisms and obtaining accurate data on mass and heat transport in liquid. All terrestrial experiments are distored by gravity-driven flow, which makes it virtually impossible to carry out precise measurements. In the transparent organic crystal of succinonitrile-acetone binary alloy, transient behavior of unidirectional dissolution is directly observed in order to precisely determine diffusion controlled mass transport properties in microgravity environment.

The effect of the surface kinetics upon the dissolution and growth rates on the faceted surface during the LPE growth process in GaP has been studied by means of the real-time measurement setup, which was composed of an infrared microscope with an interferometer. The measured dissolution rates agree remarkably well with the present model, in which it is assumed that solute concentration in the liquid ahead of the diffusion layer is homogenized by convection and the surface concentration is not equal to the equilibrium value. It was concluded from the values of kinetic coefficients that the rate controlling process may be the transportation of solute atoms in the liquid phase for both the dissolution process and the growth process. © 1991.

The effect of mixing in liquid upon the dissolution and growth rates on the faceted surface during solution growth process in GaP has been studied by means of the in situ observation setup, which was composed of an infrared microscope with an interferometer. The measured dissolution rates agree remarkably well with the boundary layer model, in which it is assumed that solute concentration in the liquid ahead of the boundary layer is homogenized by convection and the surface concentration is not equal to the equilibrium value. The estimated thickness of the boundary layer suggests the existence of the convective flow in the liquid, and this effect is certified with unidirectional solidification in succinonitrile-acetone, which is a transparent alloy system, by means of the in situ observation technique with a common-path microscope interferometer.

Most semiconductor crystals are transparent to infrared radiation. Using infrared radiation, it is possible to observe the liquid/solid interface from the bottom side of the substrate during the process of LPE growth of semiconductor crystals. The in-situ observation technique, which was developed in the present investigations, successfully gives clear images of morphological variations during the LPE GaP crystal growth process. © 1990.