Solidification Using a Baffle in Sealed Ampoules (SUBSA) - 01.09.14
Science Objectives for Everyone Experimental methods of crystallizing melts in microgravity are expected to result in reduced fluid motion in the melt, leading to better distribution of subcomponents and the potential for improved technology used in producing semiconductor crystals.
Science Results for Everyone
Semiconductor components are made from large crystals formed by melting and solidification of various elements. Higher-quality crystals have enabled smaller and more powerful electronic devices. But the process can be affected by movement of molecules in the liquid phase (convection), which can be caused by spacecraft vibration. This investigation clarified the origin of convection in space and sought to reduce its effect. Researchers found that an automatic baffle minimized melt motion and produced, for the first time in space, reproducible, nearly identical crystals. The investigation increased our understanding of solidification phenomena and will contribute to production of higher-quality semiconductor crystals.
Marshall Space Flight Center, Huntsville, AL, United States
Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)
Human Exploration and Operations Mission Directorate (HEOMD)
ISS Expedition Duration
June 2002 - December 2002
Previous ISS Missions
Semiconductors have been studied before in microgravity but not with this hardware.
- In the space environment, accelerations produce circular motions that affect the solidification of crystal growth/semiconductor materials flight experiments, resulting in a material that is less useful.
- The objectives of SUBSA are:
- Test the performance of an automatically moving baffle (used to minimize melt motion).
- Visualization of the melting process to identify what causes the melt motion.
- Production of several crystals with reproducible properties.
- To determine the behavior and possible advantages of liquid encapsulation in microgravity conditions.
Material melt-growth experiments have been difficult to run in the space environment because there is just enough residual micro-acceleration (g-jitter) to produce natural convection that interferes with the structure and purity of the material. This convection is responsible for the lack of reliable and reproducible solidification data and, thus, for gaps in the solidification theory. The Solidification Using Baffle in Sealed Ampoules (SUBSA) experiment tested an automatically moving baffle (driven by melt expansion during freezing) that was designed to reduce thermal convection inside an ampoule to determine whether the baffle significantly reduces convection. Ground studies showed that the baffle reduces the movement of the material during its liquid phase, making the process easier to analyze and allowing more homogenous crystals to form.
The key goal of SUBSA was to clarify the origin of the melt convection in space and to reduce the magnitude to the point that it does not interfere with the transport phenomena.
The SUBSA furnace, with its capability to control and visualize melting and solidification of semiconductor crystals has increased our understanding of solidification phenomena. The transparent furnace coupled with the video downlink and real-time commanding capability provides a powerful tool for scientists and engineers. The scientists were able to watch the motion of the crystal-melt interface as semiconductor crystals were formed.
The design of the SUBSA ampoule which includes a baffle and a system that prevents de-wetting resulted in crystals whose properties have not been disrupted by micro-accelerations at the Station, making it possible for future researchers to produce the high-quality semiconductor crystals that are in demand on Earth.
Semiconductor materials can conduct, stop or modify a wide range of electrical and optical signals. Therefore, all computer chips, sensors, and wireless communication devices, etc. are built from tiny chips cut from large semiconductor crystals. Improved semiconductor quality, well-formed crystals with few or no imperfections, are the key reason that the electronic devices today are so much smaller and more powerful than their predecessors.
The MSG will provide safety containment, power, video, connection to the Station's Ethernet via a laptop, and storage space. A Space Acceleration Measurement System II (SAMS-II) sensor will be placed inside the MSG to monitor and record the acceleration environment.
This is a partially hands-on experiment. The crew will be responsible for loading and activating each individual experiment.
The crew will load the SUBSA hardware into the MSG work volume via a port. Once the parts are safely contained inside, the crew will load the samples into the furnace (using the glove ports to manipulate the parts) and activate the hardware using the laptop. They can monitor the experiment's progress through the work volume's Lexan window. A total of 10 to 12 experiments will be conducted.
The baffle proved successful. Eight single crystals of indium antimonide (InSb), doped with tellurium and zinc, were directionally solidified in microgravity. The molten semiconductor material solidified as expected, without separating from the ampoule walls or releasing the undesirable bubbles that have been reported in several previous microgravity investigations. Semiconductor crystals with reproducible, nearly identical composition were obtained for the first time in space. (Evans et al. 2009)
Ostrogorsky AG, Churilov AV. Model of Tellurium- and Zinc-Doped Indium Antimonide Solidification in Space. Journal of Thermophysics and Heat Transfer. 2005; 19(4): 542-547.
Ostrogorsky AG, Marin C, Churilov AV, Volz M, Bonner WA, Spivey RA, Smith GP. Solidification Using the Baffle in Sealed Ampoules. 41st Aerospace Sciences Meeting and Exhibit, Reno, NV; 2003
Churilov AV, Ostrogorsky AG. Solidification of Te and Zn doped InSb in space. 42nd Aerospace Sciences Meeting and Exhibit, Reno, NV; 2004 [Also published in the Journal of Thermophysics and Heat Transfer, 19(4);547-547, 2005.]
Spivey RA, Gilley S, Ostrogorsky AG, Grugel RN, Smith GP, Luz PL. SUBSA and PFMI Transparent Furnace Systems Currently in use in the International Space Station Microgravity Science Glovebox. 41st Aerospace Sciences Meeting and Exhibit, Reno, NV; 2003
Ground Based Results Publications
Flinn ED. Glovebox Fits Astronauts to a 'T'. Aerospace America. 2002; 40: 18-19.
SUBSA Principal Investigator, Aleksander Ostrogorsky, Ph.D. holding a SUBSA ampoule. Image courtesy of NASA.
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NASA Image: ISS005E07172 - Astronaut Peggy Whitson, in front of the MSG, working on SUBSA, at the International Space Station, July 2002.
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