RNL's High Temperature Superconductivity Center can boast its first commercial product--a software-driven, pulsed-laser system for depositing superconducting films of a desired composition and thickness. Called the Automated Multilayer Deposition Accessory (AMDA), the system was developed in collaboration with Neocera, Inc., of College Park, Maryland, through a cooperative agreement.

Robert Hawsey, center director, said, "This is a perfect example of technology transfer--a collaborative project in which two organizations shared their resources, combined their innovative ideas, and developed the technology, resulting in a product that will be useful for basic and applied research, as well as manufacturing."

Douglas Mashburn, a researcher with ORNL's Engineering Technology Division who formerly worked in the Applied Technology and Solid State divisions, came up with a new concept in 1987 while investigating better ways to deposit superconducting films. He conceived a computer-controlled system for conveniently predetermining the exact ratios of different materials making up the film deposited by pulsed laser ablation. The concept makes possible abrupt composition changes for growing superlattices as well as the gradual changes needed for a graded alloy. Precision is maintained by sensing deviations in process conditions, such as laser pulse energy, window fogging, and target wear, and correcting for them in their early stages (feedback compensation). A laser arrangement he devised in 1990 greatly reduces uneven target erosion, making it easier to maintain the desired composition during long runs. The concepts are applicable to a wide range of solid materials.

Neocera president T. Venkatesan, who pioneered the use of pulsed laser deposition for high-temperature superconductors before founding the company, recognized that these concepts were nearly ideal for multilayer deposition, one of Neocera's primary business interests. Together, Neocera and ORNL developed the concept into a business opportunity.

AMDA is compatible with laser deposition systems manufactured by Neocera and other suppliers. It includes a copyrighted, menu-driven software program that enables researchers to specify the number of layers in a film, the composition and thickness of each layer, the frequency of the laser light "boiling" off atoms of material to be deposited in each layer, and the deposition rate. The deposition system controls the positions of the various targets and triggers the laser to create films as thick as 1000 atoms automatically.

Without such a product, researchers typically specify the material for each layer by manually rotating a carousel to expose the appropriate target and then control the thickness by turning the laser beam on and off while keeping time with a stopwatch.

AMDA will be useful for basic and applied research in superconductors, semiconductors, magnetic materials, and optical materials. Neocera has tested the product extensively in the company's program to develop electronic devices from high-temperature superconductors. These devices are multilayer structures made from superconductors, dielectrics, buffer layers, passivation materials, and electrical contact pads. Neocera recently announced their first commercial sale of an AMDA to a European customer.

AMDA can control superconducting layers as thin as a single unit cell (12 angstroms). Its fine thickness control allows researchers to fabricate devices with reproducible properties. It can also automate and control deposition of superlattices--artificial materials created by laying down very thin layers of two or more materials in sequence.

AMDA's hardware components include a motor to move six targets through the laser beam and a plug-in board for an IBM PC/AT computer.

The software enables the user to define a layer as a thickness of a given material depositied at a specific rate. Information on a selected sequence of layers can be stored on a disk and recalled for future use, thereby ensuring reproducibility from run to run.

Superconducting Wire Technology Licensed

The first license of a superconducting wire manufacturing technology developed at ORNL has been issued. Energy Systems has signed a license agreement to commercialize the technology with Superconductive Components, Inc. (SCI), a Columbus, Ohio, firm. A superconductor is a rare material that conducts electricity without the energy-wasting resistance typical of copper and other common electrical materials.

ORNL researchers Don Kroeger and Jorulf Brynestad and ORNL consultant Huey Hsu have developed a process for producing superconducting powder precursors of BSCCO material, which contains bismuth, strontium, calcium, copper, and oxygen. The product is an oxide metal powder that can be doped with lead to improve its properties.

According to Kroeger, "The process can produce lead-doped powders without measurable lead loss. The distribution of the particle sizes is narrow, from 0.1 to 1.0 micron. The grain size within a particle is very fine. And the chemical homogeneity from grain to grain is good."

The process is scaleable to high powder production rates. SCI will further develop the process to produce powders for sales and for use in bearings, current leads, superconducting wire, and magnetic levitation demonstrations.

Edward R. Funk, president of SCI, says, "The licensing of the ORNL BSCCO process completes our line of high-quality superconductive powders. The ORNL process is an important technological advance in tailoring the BSCCO powder for specific applications."

According to Robert Hawsey, director of ORNL's High Temperature Superconductivity Technology Center, "The commercialization of this process will benefit American industry as a whole. The increased quality and availability of the BSCCO powders may make possible large-scale products."

Examples are bulk electrical conductors for magnetic levitation and propulsion of high-speed trains and for superconductive magnetic energy storage devices. These devices promise to make wind and solar power economical by efficient, clean storage of energy for use when needed rather than when produced.

The ORNL process was developed with funding from DOE's Office of Energy Management. --Carolyn Krause

Ultralight Shielding for Electromagnetic Interference Licensed

ORNL researchers have developed extremely lightweight shielding to protect electronic components in automobiles, aircraft, and spacecraft from stray electromagnetic signals that can cause equipment confusion or failure. Such shielding could also protect people from the electromagnetic fields of cellular phones and other electronic devices. The electromagnetic interference (EMI) shielding technology has been licensed by Energy Systems to Sigma Electromagnetic Shielding Technologies, Inc., headed by Victor Rivas of Nebraska and recently relocated to Oak Ridge.

Rivas had been making lightweight shielding by sandwiching iron foil and carbon cloth in epoxy. The carbon cloth gives structure to the shield, and the iron prevents electromagnetic signals from penetrating equipment by absorbing and conducting them to the ground. His goal has been to make EMI shielding as efficient and light as possible for automobiles, aircraft, and spacecraft to reduce its adverse impact on fuel efficiency. Other applications could include communications satellites, electronically guided weapons, and electronic components within a room or enclosure.

Jim Weir of ORNL's Metals & Ceramics (M&C) Division learned of Rivas's work in December 1990 at a National Aeronautics and Space Administration conference. Weir suggested that ORNL has the capabilities to develop shielding of even lower weights. So he asked David Stinton of the M&C Division to pursue development of an ultralight shielding that uses the minimum amount of iron needed.

Stinton and Millicent Clark found that ultralight shielding could be made by depositing iron on carbon cloth using a low-temperature process called chemical vapor deposition. In this process, the carbon cloth is heated to around 200deg.C using sunlamps. Vapors of a heated liquid, iron pentacarbonyl [Fe(CO)5], are carried by argon gas into the chamber containing the heated carbon cloth.

If the temperature is right, a layer of iron as thin as 0.1 to 2 microns is evenly deposited on the fibers in the cloth, and the carbon monoxide in the compound is drawn out of the chamber. If the temperature is too high, carbon will also deposit on the cloth, resulting in a poor shield. Stinton and his colleagues are experimenting to determine the best temperatures for obtaining desired thicknesses and purity of the iron layers.

Stinton says that researchers in ORNL's Instrumentation and Controls Division are working with him to determine the shielding capabilities of carbon-iron composites of different thicknesses. They place a source of electromagnetic radiation on one side of the ultralight EMI shield and measure the amount of radiation that actually gets through the shield.

"It is important that the deposited iron is stable, or else it will rust and lose its ability to conduct stray electromagnetic signals to the ground," Stinton says. "If the iron is dense and not porous, it will not oxidize and it will stay magnetic. If it's unstable, it will lose its magnetism."

As soon as he obtains financing and organizes a management team, Rivas plans to produce prototype ultralight EMI shielding at the Valley Park incubator building operated by the city of Oak Ridge. Sigma will manufacture multiple layers of iron-coated carbon cloth or iron-coated fiberglass (which is less expensive than carbon cloth) and glue these layers together to make a rigid epoxy composite. Then the company will develop commercial shielding products for multiple applications.--Carolyn Krause

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