title: Effects of surfactant and boron doping on the BWF feature in the Raman spectrum of single-wall carbon nanotube aqueous dispersions.
abstract: We examine the Breit-Wigner-Fano (BWF) line shape in the Raman spectra of carbon single-wall nanotubes (SWNTs) dispersed in aqueous suspensions. Bundling and electronic effects are studied by comparing undoped SWNTs (C-SWNTs) to boron-doped nanotubes (B-SWNTs) in a variety of different surfactant solutions. For SWNTs dispersed with nonionic surfactants that are less effective in debundling than ionic surfactants, the Raman spectra retain a large BWF feature. However, we demonstrate that even for SWNTs dispersed as isolated nanotubes by ionic surfactants the BWF feature may be present and that the intensity of the BWF is highly sensitive to the specific surfactant. In particular, surfactants with electron-donating groups tend to enhance the BWF feature. Also, modification of the SWNT electronic properties by boron doping leads to enhanced surfactant dispersion relative to undoped C-SWNTs and also to modification of the BWF feature. These observations are in agreement with reports demonstrating an enhancement of the BWF by bundling but also agree with reports that suggest electron donation can enhance the BWF feature even for isolated SWNTs. Importantly, these results serve to caution against using the lack or presence of a BWF feature as an independent measure of SWNT aggregation in surfactant dispersions.
authors.affiliation: Center for Basic Science, National Renewable Energy Laboratory, Golden, Colorado 80401, USA.
authors.forename: Jeff L
authors.initials: JL
authors.lastname: Blackburn
authors.forename: Chaiwat
authors.initials: C
authors.lastname: Engtrakul
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: McDonald
authors.forename: Anne C
authors.initials: AC
authors.lastname: Dillon
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Heben
mesh_terms: D001557:Benzenesulfonates / Q000737:chemistry; D001895:Boron / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D015394:Molecular Structure; D037742:Nanotubes, Carbon / Q000737:chemistry*; D012680:Sensitivity and Specificity; D020358:Sodium Cholate / Q000737:chemistry; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry; D013059:Spectrum Analysis, Raman / Q000379:methods*; D013499:Surface Properties; D013501:Surface-Active Agents / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D001557:Benzenesulfonates; D037742:Nanotubes, Carbon; D013501:Surface-Active Agents; D014867:Water; D012967:Sodium Dodecyl Sulfate; C001114:dodecylbenzenesulfonic acid; D001895:Boron; D020358:Sodium Cholate