| Dramatic increases in the average size of high-quality, arc-fusion-grown magnesium oxide single crystals have resulted from a cooperative research and development agreement between ORNL and Commercial Crystal Laboratories, a small U.S.-owned crystal-growth company in Naples, Florida. | |
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Boatner and Feenstra, both physicists in ORNL's Solid State Division, received a Federal Laboratory Consortium (FLC) Award for Excellence in Technology Transfer on April 15, 1997, in East Brunswick, New Jersey. The award citation reads, "For the development and production of new single-crystal substrates for the growth of epitaxial electro-optic and superconducting thin films." A substrate is an underlying template that lines up the atoms of a crystalline thin film grown on it, much as a waffle iron confers a grid pattern on batter poured into it while hot.
The FLC award specifically recognizes the ORNL scientists' research and development involving single crystals of magnesium oxide (MgO) for a wide range of uses and the development, patenting, and licensing of a new family of thin-film substrates based on the cubic-perovskite material, potassium requirements: It must have a crystalline structure that matches that of the thin film and that aligns the film's structure so that electrons or light can be conducted through the film. The substrate should also be chemically compatible—that is, when the film is deposited on the substrate at an elevated temperature, the substrate should expand at the same rate as the film when both are heated; if the thermal expansion rates are different, the substrate could break or strain the film.
Few compound crystals can meet these criteria in general, but single-crystal MgO is an excellent substrate that is used with barium titanate for optical modulators and switches, with yttrium-barium-copper oxides (YBCO) for superconducting thin films, and with other oxides as a substrate for optical waveguide films. However, for some devices, the typical MgO crystal size has previously been too small.
| The result of the ORNL CRADA was the growth of large optical-quality MgO crystals at the size that the customers sought. |
Through a three-year cooperative research and development agreement (CRADA), ORNL and its industrial partner succeeded in perfecting techniques for the reproducible growth of larger single crystals of MgO. The crystal industry had been making and marketing MgO crystals up to about 2.5 centimeter (1.0 inch) in diameter, but some customers wanted larger substrates in order to develop new electronic and optical devices. The result of the ORNL CRADA was the growth of large optical-quality MgO crystals at least 5 to 7.6 centimeter (2 or 3 inch) in diameter—the size that the customers sought (see photographs above). This new MgO crystal-growth technology will help U.S. high-technology firms avoid total reliance on foreign suppliers of MgO substrates.
Large MgO substrates for thin films of various materials could be used for devices based on high-temperature superconductors and for optical switches and modulators for light-based communication networks and all-optical computers. Because infrared light from heat sources can be passed through MgO at high temperatures (and is absorbed by most other crystals at the same temperature), MgO windows and lenses can be used for chemical analysis (infrared spectroscopy) and for satellite sensors for remote detection of heat-producing processes on the earth. Other existing and potential applications of large MgO single crystals include optical components in the aerospace and defense industries and as filters and monochromators in DOE-supported neutron-science research.
Crystals of potassium tantalate/niobate grown at ORNL have been shown to make excellent substrates to support thin films of superconducting material such as YBCO. As a result, these new substrates received an R&D 100 Award in 1996 and the technology for producing these crystals has been patented and licensed to Commercial Crystal Laboratories of Naples, Florida.
Potassium tantalate is an excellent substrate because it is mechanically stable (it provides good support to thin films) and it is chemically stable (it doesn't react with thin films during deposition or with water vapor in the air prior to film growth). As an atomic template, it properly arranges the film's atomic structure through epitaxial growth so that the ferroelectric, metal, or superconducting films can exhibit good electronic and optical properties.
In some of his early experiments while doing research in Lausanne, Switzerland, Boatner added elemental dopants such as calcium and barium to the potassium tantalate crystals. He found that the addition of various amounts of these impurities made the crystalline material semiconducting. Therefore, the substrates could be made in either an insulating or conducting form.
By adding niobium, it is also possible to turn the crystal into a ferroelectric material. Such a material exhibits a polar separation of positive and negative electrical charges and properties that can be switched when an electric field is applied.
These new substrates are useful because of the important applications of devices made using the thin films that are grown on them. High-temperature superconducting films are currently being developed for a variety of electronic devices such as magnetic sensors for medical, geological, and industrial applications; microwave components for radar and communication technologies; and ultrafast switches, interconnects, and current leads. Additionally, potassium tantalate can be used as a substrate for dielectric and ferroelectric materials, such as barium titanate and lead titanate, or for electro-optic materials such as pure potassium niobate. Applications for these materials include miniature "super" capacitors, digital circuitry devices for information storage, and integrated and hybrid optical components.
Potassium tantalate substrates can be produced as large wafers—with a diameter of 5 centimeter (2 inch) or more—because of the crucible-based fabrication method employed. In contrast, other candidate substrate materials, such as strontium titanate, require a flame-fusion fabrication process, which generally limits the crystal size to 2 centimeter or less (less than 1 inch in diameter). The larger wafer size of potassium tantalate substrates is advantageous because it reduces the fabrication cost of thin-film devices that are grown on the substrate material. Commercial Crystal Laboratories has developed improved ways to prepare epitaxial-quality surface finishes on these substrates and is currently marketing the material for commercial and research applications.—Carolyn Krause
On December 23, 1996, two licensing agreements were signed by Lockheed Martin Energy Research Corporation, which manages ORNL for DOE, and DeRoyal Industries, Inc., a Knoxville-based health care products manufacturer. DeRoyal Industries was granted rights to two new ORNL technologies for concentrating solutions of the technetium-99m radioisotope, the most widely used diagnostic radioisotope in nuclear medicine.
More than 36,000 diagnostic tests using technetium-99m agents are conducted daily in the United States (10 to 12 million tests annually). These agents are used for imaging the heart, liver, lungs, brains, and most other major organs in the body. The use of technetium-99m allows the diagnosis of many conditions, such as blockages of arteries of the heart or poorly functioning organs. Unlike techniques such as magnetic resonance imaging and X-ray scans, radioactive diagnostic agents such as technetium-99m can be used to evaluate tissue function rather than only the anatomical changes of diseased tissues. Because of the technetium isotope's short half-life, the patient's exposure to radiation is very low.
DeRoyal Industries, which was founded by Pete DeBusk in 1973, employs about 2000 people at its facilities in 38 countries. DeRoyal's international sales, which are in excess of $250 million, primarily involve soft goods such as operating room procedure trays, surgical accessories, and critical care and wound care products. The company also produces computer software for hospitals.
The new ORNL technologies are simple, efficient concentration methods that are required when dilute technetium-99m solutions are obtained from radionuclide generators. A generator is a device that contains a parent radioisotope and the decay product it yields. Technetium-99m solutions are prepared from the decay of the molybdenum-99 parent radioisotope, which is most often conventionally produced in a nuclear reactor as a byproduct of the fission of uranium-235.
Currently, the U.S. supply of molybdenum-99 comes from an aging Canadian reactor. To ensure a reliable future supply, DOE plans to produce the isotope using facilities at Los Alamos and Sandia national laboratories. There, stainless steel tube interiors will be coated with highly enriched uranium and irradiated in a reactor. The tubes will be opened, the enriched uranium coating dissolved, and the molybdenum-99 extracted from numerous fission products. The problem with this process is the large amount of radioactive waste that is generated.
In the envisioned Oak Ridge approach, an enriched molybdenum-98 product would be produced in ORNL's calutrons at the Oak Ridge Y-12 Plant, which separate stable isotopes electromagnetically. The molybdenum-98 would be placed in ORNL's High Flux Isotope Reactor (HFIR), where it would capture a neutron, forming molybdenum-99. This product would then be introduced into large-scale radionuclide generators from which dilute technetium-99m solutions would be extracted and concentrated. The generators and concentrators would be built by DeRoyal Industries near the HFIR.
| ORNL’s radionuclide generator technology for producing technetium-99m produces no highly radioactive waste that requires special storage and disposal. |
ORNL's radionuclide generator technology offers several advantages over the conventional technology planned for producing technetium-99m. It is simpler and faster. Highly enriched uranium is not required as the starting material. Perhaps most important, it produces no highly radioactive waste that requires special storage and disposal.
The new technology will require approval from the U.S. Food and Drug Administration prior to clinical use. It could make use of the HFIR and several other reactors in the United States, enabling the nation to avoid reliance on imports of molybdenum-99 from foreign sources.
Inventors for one patent for technology developed between ORNL's Chemical Technology and Life Sciences divisions for which exclusive rights were granted to DeRoyal Industries are Saed Mirzadeh, F. F. (Russ) Knapp, Jr., and Emory Collins. The inventors on a second patent for which non-exclusive rights were given for technetium-99m concentration technology are ORNL Nuclear Medicine Group members Knapp, Arnold L. Beets, Mirzadeh, and Stefan Guhlke, from the Clinic for Nuclear Medicine in Bonn, Germany, who worked with the Nuclear Medicine Group as a postdoctoral fellow for six months through July 1996.
Pete DeBusk, DeRoyal Industries president and chief executive officer, expects to develop a global market for this technology. He estimates that approximately 30 persons will be employed in the Oak Ridge area for production of the generator and concentrator units. Production is expected to begin within 2 to 3 years. Annual sales could reach about $75 million. DeRoyal also announced plans to invest $5 million to $10 million in the construction of a new processing facility at ORNL near the HFIR.
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