Transparent boron-doped carbon nanotube films

We report results of studies on the sheet resistance and optical transmission of thin films of boron-doped single-walled carbon nanotubes (SWNTs). Boron doping was carried out by exposure of SWNTs to B ₂O ₃ and NH ₃ at 900 °C and 1-3 atom % boron was found in the SWNT bundles via electron energy loss spectroscopy (EELS). Boron doping was found to downshift the positions of the optical absorption bands associated with the van Hove singularities (E ₁₁ ^s E ₂₂ ^S and E ₁₁ ^m) by ∼30 meV relative to their positions in acid-treated and annealed SWNTs. Raman spectroscopy, EELS, and optical data are consistent with the picture that a few atom % boron has been substituted for carbon in the sp ² framework of SWNTs. Finally, our results show that boron doping does not significantly affect the optical transmittance in the visible region. However, boron doping lowers the sheet resistance by ∼30% relative to pristine SWNT films from the same batch. Boron-doped SWNT may provide a better approach to touch-screen technology.