Thin films of metallic carbon nanotubes and their optical spectra
  We show that separating metallic from semiconducting carbon nanotubes by dielectrophoresis is developing towards a bulk separation method, which allows for the first time to produce thin films of only metallic single-walled carbon nanotubes and to measure their optical absorption spectra. The data proofs that the selectivity of the separation scheme is independent from the nanotube diameter. 
Ralph Krupke, Stefan Linden, Michael Rapp, Frank Hennrich