Big steps toward control of production of tiny building blocks
A chief source of these drawbacks is the unstable behavior of carbon arcs, PPPL has found. Such behavior creates two modes of production, which the laboratory calls “synthesis-on,” for pure nanotube fabrication, and “synthesis-off,” for impure results. “The synthesis in plasma arcs is 20 percent on and 80 percent off,” said physicist Shurik Yatom, lead author of the results published in the journal Carbon.
In these experiments, Yatom used a conventional arc synthesis technique and filled one of the two electrodes — called an “anode” — with graphite powder and a catalyst and found that the synthesis was erratic, switching between the dominant synthesis-off mode and the far less common synthesis-on mode. Fast-camera images, electric characteristics and emission spectra showed that the arc engaged the contents of the anode directly in the synthesis-on mode, but oscillated around the hollow anode in the synthesis-off mode and was unable to interact with the powdered graphite and catalyst inside.
The team also constructed a probing device to selectively collect the synthesized product between the two modes. Evaluating the synthesized nanomaterials was Rachel Selinsky of Princeton University, who found that the vast majority of nanotubes were collected during the “synthesis-on” mode.
The findings revealed the need for stabilizing the arc so that it constantly engaged the graphite and catalyst for the continuous production of single-wall carbon nanotubes. The paper proposes several pathways going forward, ranging from the use of thinner-walled to solid composite anodes for producing nanotubes in a continuous manner with fewer unwanted byproducts.
Finally, understanding the cause of such impurities is crucial for future research at PPPL and elsewhere. As scientists continue to develop methods of in situ characterization for nanostructures, they must monitor the arc behavior and distinguish between results obtained in the synthesis-on and synthesis-off modes.
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Going forward, PPPL conducts in situ measurements of plasma nanotubes synthesized from boron nitride, a promising material with aerospace and electronics applications. Collaborating on this work are professors Roberto Car of Princeton University, Predrag Kristic of the State University of New York at Stony Brook, and Bruce Koel of Princeton.
Overseeing PPPL nanosynthesis projects is Phil Efthimion, head of the PST Department. Following are coauthors of the papers. Nanoparticle precursors: Vladislav Vekselman, Alexander Khrabry, Igor Kaganovich, Brent Stratton and Yevgeny Raitses of PPPL, and Rachel Selinsky of Princeton University. Detecting nanoparticle growth: Alexandros Gerakis, James Mitrani, Brent Stratton, and Yevgeny Raitses of PPPL, Yao-Wen Yeh and Mikhail Schneider of Princeton University. Synthesis on and synthesis off: Shurik Yatom and Yevgeny Raitses of PPPL, Rachel Selinsky and Bruce Koel of Princeton University.
PPPL, on Princeton University’s Forrestal Campus in Plainsboro, N.J., is devoted to creating new knowledge about the physics of plasmas — ultra-hot, charged gases — and to developing practical solutions for the creation of fusion energy. The Laboratory is managed by the University for the U.S. Department of Energy’s Office of Science, which is the largest single supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.