The formation and the suppression of type II striation in compound semiconductors grown by travelling heater method (THM) are studied. The work was done by an international cooperation between Germany and Japan supported by Science and Technology Agency of Japan. GaSb and InP crystals grown by SL-1 and D-1 missions and on ground by German group are studied with differential interference microscope and specially resolved photoluminescence spectrometer. By comparing theory and experiment, it is concluded that the suppression of type II striation is possible by applying a temperature gradient and keeping the growth velocity lower than a certain value.
Electrochemical informations under microgravity are of great interest and importance for science and technology in space; however few studies have been reported except for a sounding rocket experiment (TEXUS 1 Program) in 1978. As an example of electrochemical reactions under microgravity, an experiment of water electrolysis under microgravity by parabolic flights has been performed. Bubble evolved on a gold electrode have been observed and the formation process of a bubble has been discussed. Current-Voltage relationships of water electrolysis under terrestrial and microgravity conditions have been also discussed.
An experimental study of the gravitational effects on the property of the thermal convection in vapor phase is performed utilizing the MU-300 airplane. This experiment is conducted as the preliminary study of SFU / EEFU /GDEF (Space Flyer Unit / Exposed Facility Flyer Unit / Gas Dynamics Experiment Facility) mission. The visualization of gas flow at low pressure shows that the thermal convection is immediately reduced in microgravity condition. The relaxation time of convection is estimated to 2 - 3 second. The fluctuation of temperature distribution of gas is observed only in microgravity condition. It is synchronized with the residual gravity (g-jitter) simultaneously measured in the airplane. This effect is enhanced in the region of low frequency, and it can not be observed in both 1 g and 2 g conditions. This phenomenon is interpreted by the order of magnitude analysis.
An apparatus was developed for containerless material processing in space. The apparatus was constructed of a sample supplier and recovery system, an electrode system for the sample levitation, observation system and power sources. The principle for the levitation was the appliance of an alternating current (ac) and a direct current (dc) electric field which is produced by a set of two dimensional quadrupole electrode and a sphere electrode couple respectively. The as field is for confinement of the sample and the dc field makes a Coulomb repulsion force to counterbalance to the gravity. The sample with a 10mm diameter, of which the diameter will satisfy a material experiment in space, levitated statically in a terrestrial experiment and the levitation characteristics were obtained on the applied voltage, frequency of power source, specific charge and levitation height. Furthermore, the levitation was analyzed theoretically and the qualitative coincidence was obtained on the motion and the levitation position. It was found that the combination of ac and dc voltage with this electrode system was an excellent for the stable levitation.
As a part of a containerless melting experiments in space, a 65CaO-25Ga2O3-10GeO2 (mol %) composition will be melted in an acoustic levitation furnace (ALF). The effect of the acoustic field on the crystallization tendency of this composition has been investigated as a function of sound pressure level (SPL) and frequency. The critical cooling rate for glass formation, as measured in ALF without the acoustic field, was the same as that measured previously. Sound pressure levels up to 155 dB, frequency of 11 to 11.1 kHz at 5Hz steps has no effect on the temperature of crystallization for a melt cooled at 200 deg C/min nor on the tendency to form a glass for melts cooled at 1000 deg C/min. Sound fields with a frequency between 11 and 15 kHz had no effect on the crystallization for melts cooled at 500 deg C/min. Similarly the crystallization was un affected when that was swept at either 5 or 20 Hz.