Using nanotechnology at 600,000°C per second, researchers are laying the groundwork for new consumer products.
Researchers at ORNL have developed a rapid heating technology that could revolutionize the manufacturing of products made of materials whose functionality is maintained at the nanoscale. Called pulsed thermal processing (PTP), the technology enables researchers to control precisely the diffusion of atoms and the merging of nanoparticles to generate desirable electrical, optical, and magnetic properties in thin films and nanoparticle systems.
The researchers believe PTP could be used to produce affordable and more efficient solar electric cells; flexible digital displays that can be rolled up; light-emitting diodes that make digital clocks and traffic lights glow; and thin-film batteries needed to energize medical implants and radiofrequency identification labels on consumer products.
ORNL's research tool used for PTP is the most powerful light source in the world—a high-density plasma arc lamp that provides "white light" nearly matching the sun's spectrum, including infrared, visible, and ultraviolet light. The light source produced by Mattson Technologies is a direct-current arc that ionizes gas inside a water wall–insulated quartz window.
ORNL's Materials Processing Group in the Materials Science and Technology Division has demonstrated that the latest upgrade of the Mattson lamp can make various nanomaterials functional by delivering a flash of light as short as 1 millisecond at a power density up to 20,000 watts per square centimeter over an area almost as broad as a flat-panel computer screen. The lamp can heat surfaces up to 600,000°C per second. "We are trying to reduce the flash time to 0.1 millisecond," says Craig Blue, the division's associate director for technology. Decreasing the pulse time generates less 'heat soaking'—the amount of heat absorbed by the layers underneath the surface.
Guided by computer modeling of materials' thermophysical properties, the group conducts experiments with funding from ORNL's Laboratory Directed Research and Development Program and industrial firms. Modeling enables prediction of the "thermal profile"—the temperature on the surface and underlying layers based on the lamp's distance and the selected wavelengths of light and power density delivered to the sample. "We can filter out wavelengths we don't want," Blue says.
Unlike laser processing, PTP can rapidly heat the entire surface area with one flash, potentially creating a uniform microstructure or nanocrystalline structure that has uniform electrical, optical, or magnetic properties. The technology is capable of thermally influencing the surface without thermally affecting the substrate.
"We have shown that the lamp can achieve critical annealing temperatures of 500 to 700°C for thin-film silicon in solar electric cells and thin-film silicon transistors for flat-panel displays," says team member Ron Ott. "The multibillion-dollar photovoltaic and thin-film transistor industry would like to anneal silicon on inexpensive polymer substrates, but inexpensive polymers cannot be heated to more than 150°C. PTP is the only process that can simultaneously heat the surface of the thin film or nanoparticle system to over 500°C and limit the substrate to 150°C over broad areas."
Laser processing currently used by the thin-film transistor industry is expensive, time consuming, and environmentally unfriendly because of the gases the technology uses. Laser light scanning surfaces creates non-uniform microstructures, resulting in non-uniform electrical and optical properties and stresses that can lead to cracking.
Solar cells made of inexpensive, amorphous silicon convert about 5% of sunlight into electricity. PTP, which offers high throughput at a low cost, introduces nanocrystals into the matrix, creating more charge carriers, increasing electron mobility, and doubling the photovoltaic efficiency to about 10%.
Ott proved in an LDRD project that the lamp could increase data storage 1000 times by chemically ordering magnetic iron-platinum nanoparticles.
Researchers from ORNL and Caterpillar, the world's largest manufacturer of construction equipment, worked together to use PTP to coat bearings. Caterpillar now owns a Mattson lamp and is prototyping the technology.
Researchers already are thinking beyond the laboratory. "We and Mattson envision a third-generation lamp at ORNL that would be a dedicated user facility for industry," Blue says. "Before buying a lamp, each user could collaborate with us to develop the process science for making prototypes. The user's experiences could then be transferred to the factory environment to make marketable devices."
Web site provided by Oak Ridge National Laboratory's Communications and External Relations