Plasma meets nano at PPPL
Scientists at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) have launched a new effort to apply expertise in plasma to study and optimize the use of the hot, electrically charged gas as a tool for producing nanoparticles. This research aims to advance the understanding of plasma-based synthesis processes, and could lead to new methods for creating high-quality nanomaterials at relatively low cost.
Nanomaterials, which are measured in billionths of a meter, are prized for their use in everything from golf clubs and swimwear to microchips, paints and pharmaceutical products, thanks to their singular properties. These include exceptional strength and flexibility and high electrical conductivity. Carbon nanotubes, for example, are tens of thousands of times thinner than a human hair, yet are stronger than steel on an ounce-per-ounce basis.
PPPL researchers have launched a nanotechnology laboratory that they envision as a step toward research capabilities that could serve as a resource for institutions and industries around the world. “It could be a test bed for new technologies and devices,” said PPPL Deputy Director Adam Cohen. Users could include laboratories looking for small amounts of nanomaterial, “or companies interested in using plasmas in large-scale nanomanufacturing, or anyone in between.”
The facility will explore so-called low-temperature plasmas that are frequently used to synthesize nanomaterials. Plasmas consist of atoms and detached electrons and atomic nuclei called ions. While the heat in low-temperature plasmas can measure tens of thousands of degrees Celsius, they are colder than fusion plasmas, which contain a much higher percentage of ions and can register temperatures greater than tens of millions of degrees Celsius.
Little is known about how low-temperature plasmas function as synthesizing material, said physicist Yevgeny Raitses, the principal investigator for nanoparticle research at PPPL. “We want to understand just what plasma does in order to use it in the best way possible,” Raitses said.
PPPL scientists are poised for this task. Laboratory researchers possess decades of experience working with plasmas in fusion experiments and in other areas, ranging from studies of low-temperature plasmas for thrusters for space vehicles and particle beams, to the analysis of astrophysical phenomena. All such work uses electric and magnetic fields to control the plasma, which flows along the magnetic field lines because it is electrically charged.
Magnets are among the key components of PPPL’s new two-room nanotechnology laboratory, which the DOE has approved for producing engineered nanoparticles. Magnetic fields control the flow of plasma inside the laboratory’s two enclosures, enabling researchers to influence the synthesis of nanoparticles. This control could allow the facility “to fabricate nanomaterials that are not easily fabricated by other means,” said lead engineer Charles Gentile, who oversaw the development of the new laboratory.
The facility has produced test batches of nanoparticles that include carbon nanotubes and nanofibers. Both have widespread uses. Future applications could range from body armor to cancer treatments to flexible computer screens.
The production of nanomaterials involves complex transitions between different states of matter when plasma serves as a synthesizing medium. One method vaporizes a substance such as a rod of carbon with a lightning-like electric arc, transforming the carbon from a solid to a plasma. The plasma then condenses back into a solid as nanomaterial. Accompanying these transitions are little-understood chemical, kinetic and electrical interactions that need to be controlled to ensure the quality and purity of the nanomaterial.
PPPL researchers will seek to better understand these interactions to conduct controllable synthesis of nanomaterials with precisely prescribed properties. This research will employ a three-pronged approach that draws upon the resources of many collaborators. Contributions to plasma theory and computer modeling will come from PPPL physicists Igor Kaganovich and Edward Startsev, together with PPPL engineer Andrei Khodak and physicist Predrag Krstić of the Joint Institute of Computational Sciences at the University of Tennessee in Knoxville.
Other disciplines will contribute to the research. Included will be diagnostic techniques developed by physicists Mikhail Shneider of Princeton University and Benoit LeBlanc of PPPL, and by engineer Michael Keidar of George Washington University, who previously collaborated with Raitses on the plasma-based synthesis of carbon nanotubes and graphene, a nanomaterial. Princeton University chemical and biological engineer Bruce Koel, and Princeton geophysicist Thomas Duffy will join the research effort, as will engineer Mohan Sankaran of Case Western Reserve University, who has pioneered methods for synthesizing nanomaterial with plasma. All studies will be conducted under the aegis of the PPPL Department of Plasma Science and Technology, headed by physicist Philip Efthimion.
Discussions for the new PPPL laboratory began in 2009. “The question I always had,” recalled Deputy Director Cohen, “is that if nanoparticles and nanotubes are going to be in everything from car cylinders to medical equipment to nano-robots, who’s going to ensure that these materials are made consistently with the highest quality? That seemed like an opportunity for us.”
Designing and installing the new facility took more than a year. Included is an ultra-low particulate filter ventilation system that ensures the safe operation of the laboratory. Inspiration for much of the overall design of the laboratory came from the Center for Functional Nanomaterials at Brookhaven National Laboratory.
The new facility could serve as the forerunner of a larger one at PPPL. “For me, we’ve opened up a potential niche with a large area for growth,” Cohen said. That growth could include the use of nanomaterial in fusion experiments. “Fusion needs materials that can survive extreme environments, and some of these materials will very likely have ‘nano’ in their names,” Cohen said. “So we’re developing ways to make this stuff, and we could be end-users as well.”