Excimer-laser pulses clean carbon nanotubes

Researchers at the National Institute of Standards and Technology (NIST; Boulder, CO) and the National Renewable Energy Laboratory (NREL, Golden, CO) have demonstrated and verified a simple method of cleaning single-walled carbon nanotubes using excimer laser pulses with photon energy near the pi-plasmon resonance (about 5 eV) of the nanotubes.

Feb 1st, 2007

Researchers at the National Institute of Standards and Technology (NIST; Boulder, CO) and the National Renewable Energy Laboratory (NREL, Golden, CO) have demonstrated and verified a simple method of cleaning single-walled carbon nanotubes using excimer laser pulses with photon energy near the pi-plasmon resonance (about 5 eV) of the nanotubes. During fabrication of nanotubes, contaminants such as catalyst, amorphous carbon and other particles are also formed, necessitating purification prior to commercial use. The new method, based on 20 ns pulses from a 248 nm laser with a 10 Hz repetition rate, is believed to work because laser irradiation near the pi-plasmon resonance preferentially transfers momentum to the bonding orbitals of the impurities that are more defective and less stable than nanotubes. Consequently the impurities tend to get oxidized by the surrounding air, as well as ozone generated by the laser beam.

Efficacy and lack of damage to nanotubes was assessed through resonant Raman spectroscopy in the backscattering configuration using a 7 mW beam from a 488 nm argon-ion laser. The general approach is simpler and less costly than conventional wet-chemistry processes, which can damage the nanotubes and also require removal of solvents afterward. Contact John Lehman at lehman@boulder.nist.gov.

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