by josh perry, editor
[email protected]

scientists at the u.s. department of energy (doe) princeton plasma physics laboratory (pppl) in princeton, n.j. have developed diagnostic tools to improve the production of nanomaterials with specific characteristics through plasma-based synthesis.

members of the plasma nanosynthesis team. front row from left: alexandros gerakis, vladimir vekselman, shurik yatom. back row from left: yevgeny raitses, bruce koel, igor kaganovich, alexander khrabry, brent stratton, rachel selinsky, andrei khodak.
(elle starkman/office of communications)

according to a report from the pppl, the research will make it easier for nanomaterials to be fabricated in controllable and selective ways.

“the papers report unique observations of the synthesis in carbon plasma generated by an electric arc in situ, or as the process unfolds,” the report explained. “researchers create the plasma arc between two carbon electrodes, producing a hot carbon vapor composed of atomic nuclei and molecules that cool and synthesize — or condense — into particles that grow into nanostructures by bunching together.”

this research was published in three papers that covered different aspects of the study.

the first paper revealed details of how carbon nanotubes form in the vapor during synthesis. the creation of nanotubes is controlled by dimers, which are molecules formed by two carbon atoms. using computer simulations, researchers can predict the amount and type of nanotubes being formed, which can now be tested and validated.

the second paper described a “unique table-top laser technique for in situ detection of nanoparticle growth” that monitors the process of nanoparticle creation from nanometer down to the atomic scale. the method detects “particles that flow within and from the electric arc.”

the third paper explores how the synthesis of single-walled carbon nanotubes on an industrial scale is limited by impurities. the researchers found that the unstable behavior of carbon arcs causes impurities 80 percent of the time.

“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 report continued.

researchers also built a prove that collected synthesized nanotubes to be evaluated. the research showed that stabilizing the arc is the key to producing larger amounts of pure carbon nanotubes and proposes several possible solutions for future work.

one of the research papers was recently published in physical review applied. the abstract stated:

“we report on the development and experimental validation of a laser-based technique which uses coherent rayleigh-brillouin scattering (crbs) to detect nanoparticles with characteristic sizes ranging from the atomic scale to tens of nanometers.

“this technique is aimed (nonexclusively) at the detection of nanoparticles produced by volumetric nanoparticle synthesis methods. using crbs, carbon nanoparticles of dimensions less than 10 nm and concentrations of 1010  cm−3 are detected in situ in a carbon arc discharge with graphite electrodes.

“this four-wave-mixing approach should enable advances in the understanding of nanoparticle growth that could potentially lead to improved modeling of the growth mechanisms, and thus to improve synthesis selectivity of nanoparticles and yield.”