  We investigated the atomic structures, Raman spectroscopic and electrical
transport properties of individual graphene nanoribbons (GNRs, widths ~10-30
nm) derived from sonochemical unzipping of multi-walled carbon nanotubes
(MWNTs). Aberration-corrected transmission electron microscopy (TEM) revealed a
high percentage of two-layer (2L) GNRs and some single layer ribbons. The
layer-layer stacking angles ranged from 0o to 30o including average chiral
angles near 30o (armchair orientation) or 0o (zigzag orientation). A large
fraction of GNRs with bent and smooth edges was observed, while the rest
showing flat and less smooth edges (roughness \leq 1 nm). Polarized Raman
spectroscopy probed individual GNRs to reveal D/G ratios and ratios of D band
intensities at parallel and perpendicular laser excitation polarization
(D///D\bot). The observed spectroscopic trends were used to infer the average
chiral angles and edge smoothness of GNRs. Electrical transport and Raman
measurements were carried out for individual ribbons to correlate spectroscopic
and electrical properties of GNRs.
