Crystal growth experiments in Kibo
Number of nation/area participating in the ISS program is 15 including the U.S., Russia, Europe, Canada, and Japan. The most advanced technologies of the participators are brought together to the ISS. The Japanese-first manned experiment facility “Kibo” is the largest experiment module in the ISS.
The crystal growth experiments in Kibo have been conducted until now in the following two phases. In the “first term utilization” from 2008, when the use of Kibo started, to the middle of 2010, research objectives were to perform real-time observations of the morphology of growth interface and temperature concentration in order to identify the limit of roughness of the crystal growth face and to elucidate the formation of structure after that. In the “second term utilization” from the middle of 2010 to 2012, the experiments were focused on, based on the first term results, understanding of the crystal growth phenomena by observing the microscopic behaviors of atoms and molecules on the phase boundary and obtaining of the knowledge on high-quality crystal growth technology.
Crystal growth experiment facilities already installed on Kibo is categorized into three equipments (Fig. 2): Solution Crystallization Observation Facility (SCOF); Protein Crystallization Research Facility (PCRF); and Gradient Heating Furnace (GHF). SCOF is a microscope system, which allows us to measure simultaneously crystal shape and temperature/concentration in the environment phase. PCRF is literally to conduct multiple- and simultaneous-crystallization of protein. With GHF, we can perform automatically high-temperature heating of test samples by radiation from heater in the large vacuum chamber.
Examples of experiments to have performed in Kibo includes the ice, facet crystal, and protein crystal experiments using SCOF (abbreviated as 的ce Crystal?Facet?Nano Step・ and the semiconductor crystal growth experiment using the temperature gradient furnace (called 滴icari?Alloy Semiconductor・. For the detail of these experiments, please visit 的SAS News・of JAXA web site.
Future crystal growth research using the space environment
Other than ISS, methods using the space environment include sounding rockets, scientific balloons, aircraft, and the short-duration microgravity by drop tower. On the other hand, international cooperation research using new flight opportunities is expected in the future.
Here, I would like to discuss some of the future research themes that are now in my mind.
i) Growing of high-quality crystal and searching for new materials
As an international prototype meter was adopted as a standard of length, it is thought to develop a crystal that will have ideal characteristics as a standard. This is a research theme aiming for the practical application of the crystal. In order to produce high-quality crystal on the ground, it is indispensable to identify accurately the thermophysical properties of the environment phase (e.g., surface tension, specific heat, density, thermal conductivity), not only growing an ideal crystal. With the collaboration of crystal growth in space, thermophysical property measurement, knowledge obtained through fluid science experiment, and numerical simulation, this will contribute to making it efficient the crystal growth process on the ground, which has been made by trial and error in the past.
Other related theme includes quest for metastable phase by levitation technique. The technique using electromagnetic force, electrostatic force, or aerodynamic force by gas jet does not require container to sustain test samples. Thus, with this method we can expect to create the metastable phase, of which production is thought to be difficult by the conventional method to melt raw materials in containe