RESONANCE RAMAN SPECTROSCOPY OF LENGTH-SEPARATED AND ALIGNED SINGLE WALL CARBON NANOTUBES

 

J. R. Simpson and A. R. Hight Walker

Optical Technology Division, Physics Laboratory

 

Many potential advanced-technology applications of single wall carbon nanotubes (SWNTs) require a homogeneity of physical properties not presently found in bulk SWNT samples.  This work demonstrates mechanical alignment and length separation characterized via vibrational spectroscopy.  We measure resonance Raman scattering (RRS) using continuously tunable laser excitation, from NIR thru UV, coupled to a triple grating spectrometer.  This experimental setup permits observation of resonant low-frequency modes, such as the nanotube radial breathing mode (RBM), through higher frequency graphite modes. ..Our samples include HiPco, CoMoCat, and arc-discharge SWNTs wrapped with 30-mer 5'-GT(GT)13GT-3' single-stranded DNA and dispersed in aqueous solutions.  Size-exclusion chromatography collects length fractions ranging in size from less than 100 nm to approximately 600 nm as characterized by multi-angle and dynamic light scattering, AFM, and TEM.  All observed vibrational modes, including the RBMs, D-band, G-band, M-band, iTOLA, and D*, exhibit a monotonic increase of Raman scattering intensity with increasing nanotube length.  We discuss these results in terms of optical scattering models and the resonant behavior of the vibrational modes.  For alignment, the solutions are cast in polyacrylic acid and mechanically stretched into optically-transparent polymer composite films.  Polarized RRS (VV) reveals significant nematic SWNT alignment in these stretched films.

 

 

Author Information

Name:  Jeffrey R. Simpson

Mentor’s name:  Angela R. Hight Walker

Division:  Optical Technology, 844

Laboratory:  Physics (PL)

Building/Room:  216/B211

Mail Stop:  8443

Telephone #:  301-975-3140

Fax #:   301-975-6991

Email:  jeff.simpson@nist.gov

Sigma Xi:  not a member

Category:  Physics