GEC Conference Features Latest Research in Plasma Phenomena

Carbon nanowalls, space plasma propulsion, and applying cold plasmas to facilitate wound healing were among the highlights of the annual Gaseous Electronics Conference, held October 2-5 in Arlington, Virginia. The meeting’s focus is on basic phenomena and plasma processes in partially ionized gases, and on the theory and measurement of basic atomic and molecular collision processes. There are also sessions devoted to related applications, including plasma processing of materials, gas lasers, ion sources, gas discharge lamps, diagnostics, and plasma aerodynamics, among other topics.

Building Carbon Nanowalls.Carbon nanowalls (CNWs) are two-dimensional nanosctructures made of layers of graphene, with much potential as an ideal material for catalyst support for fuel cells and gas storage, thanks to their high surface-to-volume ratios. One graphene sheet could potentially demonstrate high electron mobility and large sustainable current, thereby enabling various kinds of electric devices using this material. Masaru Hori of Nagoya University reported on a novel plasma enhanced chemical vapor deposition (PECVD) technique to synthesize CNWs with a wide range of morphologies and structures, some with excellent characteristics for building new functional devices (such as biodevices), including good electron field emission and water repellency of the surface area. Exposing the surface to a plasma makes it hydrophilic.

Accelerating Ions for Plasma Propulsion. Edgar Choueiri of Princeton university reported on a recently discovered mechanism for ion acceleration that appears to occur naturally in Earth’s ionosphere, and holds promise as a means of energizing ions for thermonuclear fusion and electrodeless space plasma propulsion. Previous known mechanisms used electrostatic (ES) waves, which only accelerate ions with initial velocities above a certain threshold. This new mechanism involves pairs of beating ES waves, and is capable of accelerating ions with small initial velocities, thereby offering a more effective way to couple energy to plasmas. Choueiri believes this fundamental insight can be applied to develop novel plasma propulsion concepts.

Cold Plasmas Heal Wounds. Ten years ago, scientists found it a challenge to create plasmas at temperatures cool enough not to damage surfaces, but this can now be done fairly easily. Cold plasmas are proving useful as a means of sterilizing heat-sensitive medical tools, and decontaminating surfaces, particularly skin wounds. This has already been demonstrated in vivo, according to Eva Stoffels of Eindhoven University of Technology, who has developed a “cold plasma needle.” This is a specially designed plasma source with a low-power discharge below the threshold of tissue damage.

The plasma needle does not cause fatal cell injury and allows for precise and localized cell removal, as well as bacterial disinfection. Stoffels reported that the plasma does not necrotize the cells, has clear antimicrobrial effects, and stimulates fibroblast cells towards faster attachment and proliferation. Concerns remain about potential cytotoxicity, but Stoffels’ recently completed in vitro studies on long-term cellular damage were “satisfying,” paving the way for clinical applications such as disinfecting wounds and dental cavities.

Pattern Recognition. Deep etching of silicon is used widely to build MEMs and other microelectronics components, but Remi Dussart of the Université d’Orléans’ GREMI program is interested in developing the cryoetching process as a faster and cleaner alternative. A major challenge is achieving precise control of the formation of the wafer’s passivation layer. He and his GREMI colleagues have developed an improved cryoetching process using SF6 and O2 as basic gases that form an SiOxFy passivation layer in an inductively-coupled plasma (ICP) reactor at very low temperatures.

Despite the widespread use of plasma-based etching to produce device features with precisely controlled nanoscale dimensions, surprisingly little is known about the interaction of the plasma with the organic molecules arranged in the surface pattern, not to mention the chemical, morphological and topographic changes induced by these interactions. Gottlieb Oehrlein of the University of Maryland, College Park, described his recent collaborative work aimed at improving our understanding and control of plasma-surface interactions with advanced polymers for nanoscale patterning of materials.

According to Koichi Sasaki of Nagoya University’s Plasma Nanotechnology Research Center, laser-aided plasma diagnostics offers a powerful tool for exploring reactive plasmas, as well as for monitoring the operation of conditions of plasma processing tools in factories to achieve efficient mass production. He discussed two examples of laser-aided precise diagnostics for lab experiments, as well as a new method for monitoring reactive plasmas. The latter is based on diode laser absorption spectroscopy, enabling low cost, maintenance-free operation.