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In previous research, Indium iodide (InI) showed promise as a material for detecting nuclear radiation at room temperature. As a non-toxic, stable material with a relatively low melting point, it also is ideal for experiments aboard the space station. The Detached Melt and Vapor Growth of InI in SUBSA Hardware (Detached Melt and Vapor Growth of InI) investigation grows separate, high-quality InI crystals in microgravity in order to test it against more expensive and difficult-to-grow current detection materials such as Cadmium Zinc Telluride (CZT). This work advances the process of fabricating high-quality InI and other crystals on Earth for use as better and less expensive detectors of nuclear radiation.
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The following content was provided by Aleksander Ostrogorsky, Sc.D., and is maintained in a database by the ISS Program Science Office.
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Aleksander Ostrogorsky, Sc.D., Illinois Institute of Technology, Chicago, IL, United States
Illinois Institute of Technology, Chicago, IL, United States
NASA Marshall Space Flight Center, Huntsville, AL, United States
Tec-Masters Inc., AL, United States
Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)
National Laboratory (NL)
Earth Benefits, Scientific Discovery
ISS Expedition Duration
September 2016 - February 2017; March 2017
- September 2017
SUBSA initially launched on STS-111, ISS Flight UF2 in 2002. All hardware was returned on STS-113, ISS Flight 11A in 2002 and STS-114, ISS Flight LF-1.1 in 2005.
Indium iodide (InI) is ideal for space experiments in the SUBSA Transparent Furnace because it is non-toxic, and has a relatively low melting point of only 365°C (~150°C below the melting point of Indium antimonide (InSb) used in the SUBSA experiments in 2002). InI melts and evaporates congruently, allowing directional solidification from the melt at a rate of 5 mm/hr and growth from the vapor at ~ 5 mm/week. InI is considered to be one of the very few semiconductor materials that that could compete with Cadmium Zinc Telluride (CZT) and Mercury(II) iodide (HgI2) as detectors of nuclear radiation at room temperature. CZT is expensive, toxic and has to be grown very slowly (~ 5 mm/day). HgI2 is soft, toxic and has to be grown from the vapor phase at ~ 1 cm/month. The Detached Melt and Vapor Growth of InI in SUBSA Hardware (Detached Melt and Vapor Growth of InI) investigation will:
Verify that the SUBSA furnace is ideal for growing reference quality crystals, having higher crystalline and chemical perfection than the crystals grown on earth. This is especially true for simple congruently melting and/or evaporating materials.
Study the de-wetting and detached growth in the SUBSA furnace in the Microgravity Science Glovebox (MSG) on the ISS can help in the development of equipment for detached growth on Earth.
Following 6 years ground based research on InI crystals, sponsored by the Department of Energy’s National Nuclear Security Administration (NNSA), it is believed that InI is a promising semiconductor material for nuclear detector applications. Furthermore, InI is the only non-toxic material (excluding germanium) and has a melting point of only Tm=365°C .
InI is a binary compound semiconductor, which melts and evaporates congruently. Molten InI is stable, has low vapor pressure (at the melting point ~0.3 mmHg at 360°C), and does not react or stick to the silica crucible, allowing growth using the Bridgman and Cozhralski processes. InI has a demonstrated growth rate of 5 mm/hr [1,2]. The advantages InI properties compared to CZT are:
Its energy gap Eg=2.0 eV is above that of CZT, hence less leakage current.
Its density (5.31 g/cm3) is sufficiently high, although lower than density of CZT (5.78 g/cm3).
It is not toxic; it is not hydroscopic.
It is easy to grow from the melt since there are no problems related to compositional segregation, phase separation, volatility of Cadmium, Zinc and Tellurium. Post growth annealing is not needed.
The advantages of InI properties, compared to HgI2, is a non-layered structure and much superior mechanical properties.
InI crystals grown on Earth contain numerous defects, whose nature is not well understood at present. Therefore, the scientific goals are of the Detached Melt and Vapor Growth of InI in SUBSA Hardware (Detached Melt and Vapor Growth of InI) investigation are to:
Minimize the number of defects in InI crystals.
Determine the nature of the defects.
Produce reference quality InI (highest achievable crystalline and chemical perfection), in order to determine if such crystals can compete with CZT.
To determine if InI can compete with CZT as a room temperature detector material.
Microgravity, experiments should yield crystals with low level of dislocations, i.e. crystals having the highest achievable crystalline perfection. A significant increase in the mobility-lifetime (μ τ) product, and detector performance is expected. For example, van den Berg and Schnepple  reported a significant increase in mobility. The specific objectives include:
Detached melt growth of InI in microgravity.
Physical vapor transport growth of InI under diffusion controlled vapor transport conditions. Since InI evaporates congruently (vapor consist of InI molecules) the process is extremely simple. Molecules of InI sublime from a high purity solid source at the hot end of an evacuated ampoule, travel as vapor, and crystalize at the cold end of the ampoule. Diffusion transport (with no convection) is expected to increase crystalline perfection and reduce the concentration of impurities in the growing crystal.
The goal is to achieve:
Electrical resistivity to well above 5x1011 ohm-cm. Potential benefits are low leakage current. Note that resistivity of CZT is ~ 3x1010 Ohm-cm
Mobility-lifetime (μτ) product approaching that of CZT ( for electrons (μτ)e> 3 x10-3 cm2/V and for holes (μτ)h> 5 x10-5 cm2/V.
Detector energy resolution approaching 2% FWHM at 662 keV.
The SUBSA furnace was designed and built by Tec Masters Inc. (R. A. Spivey and G. Smith) for growing doped InSb crystal which melt at 512°C. The SUBSA team (PI A. Ostrogorsky, Project Manager, L. Jeter, Project Scientist M. Volz, Project Engineer P. Luz), prepared 17 ampoules, 12 for flight experiments and 5 for testing. W.A. Bonner of Crystallod Inc. grew the InSb seed crystals. Tec Masters Inc. fitted the ampoules into Sample Ampoule Assemblies (SAA). In 2002, astronaut Peggy Whitson conducted 8 crystal growth experiments. Solidification Using a Baffle in Sealed Ampoules (SUBSA) was the first project conducted in the Microgravity Science Glovebox (MSG) on board the ISS.
PROPOSED FLIGHT EXPERIMENTS AT ISS
Based on experience acquired during the original SUBSA investigation, the research team is planning to grow in microgravity:
Four InI crystals, by detached directional solidification. The growth rate will be 2 mm/hr. Each melt-growth experiment is expected to last ~ 24 hrs. The ampoules are produced at the Illinois Institute of Technology (IIT), by the PI and his student V. Riabov.
Two crystals are grown using physical vapor transport growth. As a rule, vapor-growth experiments conducted in microgravity are not affected by convection, and have produced crystals with superior properties. The experiments are expected to last 2 to 4 weeks, depending on the time available. The ampoules for vapor growth are produced at the Marshall Space Flight Center (MSFC) by M. Volz and A. Croell (international co-investigator, University of Freiburg, visiting MSFC and the University of Alabama at Huntsville). Dr. Lodewijk van den Berg, Constellation Technologies, is the consultant for vapor growth.
EXPERIMENTS IN SUBSA GROUND FACILITY AT TecMASTERS INC
The research team is conducting experiments in the SUBSA ground unit, to optimize the ampoule design for melt growth and vapor growth of InI. The key problem is the steep temperature gradient in the transparent section of the furnace.
Once the 6 flight ampoules are delivered to NASA (November 2016), 6 identical ampoules are prepared experiments in the SUBSA ground facility (TecMasters Inc. and MSFC).
FINITE ELEMENT MODELING
A finite element (FE) model of the SUBSA furnace is being developed, using the CrysMass code . The FE model of the SUBSA furnace is being used, along with the experiments in the SUBSA ground facility, to determine the optimal set point and the position of the crystal in the ampoule, to reduce the axial temperature gradient, etc.
The FE model of the furnace was be calibrated to match the temperature measured by 5 thermocouples. The FE model is used, along with temperature measurements, to optimize the seeding set point, to determine the optimal position of the charge, the cooling rate, etc.
CHARACTERIZATION AND DETECTOR FABRICATION
Characterization and detector fabrication will be conducted primarily by A. Chrilov, at Radiation Monitoring Devices, (RMD).
 I. Nicoara, D.Nicoara, C. Bertorello, G.A. Slack and A. G. Ostrogorsky, M. Groza and A. Burger “Czochralski Growth of Indium Iodide and other Wide Bandgap Semiconductor Compounds”, MRS Proc. 1341 (2011) 95-104.
 P. Bhattacharya, M. Groza, Y. Cui, D. Caudel, T. Wrenn, A. Nwankwo, A. Burger, G. Slack, A.G. Ostrogorsky, Growth of InI single crystals for nuclear detection applications’, J. Crystal Growth 312(2010)1228-1232
 Lodewijk van den Berg and W.F. Schnepple, “Mercuric Iodide Crystal Growth in Space”, Nuclear Instruments and Methods in Physics Research, A283(1989) 335-338
 CrysMAS Users Manual, Fraunhofer Institute, Erlangen, Gremany.
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Inexpensive InI-based detectors capable of operating at room temperature have many potential applications, including as medical sensors, in security inspections, for detection and evaluation of nuclear emergencies and detection of hard X- and γ-rays for astrophysical studies, and for surveillance of nuclear activity.
Operational Requirements and Protocols
There are a total of 6 crystal growth experiments planned. These consist of 2 experiments using a physical vapor transport method, and 4 experiments using a melt growth method. However, 1 spare ampoule for each of the methods is launched. So, a total of 3 vapor growth and 5 melt growth experiments are possible if time and resources permit.
The processing time for each of the melt growth experiments is approximately 24 hours. The processing time for each of the vapor growth experiments is up to 2 to 4 weeks. Crew time is required for installation of the sample ampoule assemblies (SAA’s) into the furnace and for their removal after sample processing is complete.
A nominal operating scenario for each of the crystal growth experiments is as follows:
Activate the Microgravity Science Glovebox (MSG).
Load a sample into the SUBSA furnace.
Establish processing conditions per Glovebox Investigator (GI) and safety requirements.
Request the recording of microgravity measurement data from the sensor in the MSG.
Ensure that commanding and data and video downlink is enabled for the required time periods.
Melt and re-solidify the sample or grow a sample from vapor transport.
Remove the sample and store.
Downlink SUBSA data and video not downlinked during the experiment.
The samples need to be transported back to Earth for characterization to complete the investigation.
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Decadal Survey Recommendations
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MMAE Professor Aleksandar Ostrogorsky Receives CASIS Grant for Out of this World Research with NASA
Growth of InSb and InI Crystals on Earth and in Microgravity Abstract
CASIS Announces Grant Awards for Materials Science Investigations
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