A study of step edges in graphite with different atomic structures combining Raman spectroscopy and scanning probe microscopy is presented. The orientation of the carbon hexagons with respect to the edge axis, in the so-called armchair or zigzag arrangements, is distinguished spectroscopically by the intensity of a disorder-induced Raman peak. This effect is explained by applying the double resonance theory to a semi-infinite graphite crystal and by considering the one-dimensional character of the defect.

Polarized Raman spectra of high purity aligned arrays of multiwalled carbon nanotubes, prepared on silica substrates from the thermal decomposition of a ferrocene-xylene mixture, show a strong dependence of the graphitelike G band and the disorder-induced D band on the polarization geometry employed in the experiments. The experimental G-band intensity exhibits a minimum at straight theta(m) = 55 degrees in the VV configuration, in good agreement with theoretical predictions of a characteristic minimum at 54.7 degrees for A(1g) modes in single wall nanotubes, where straight theta(m) denotes the angle between the polarization direction and the nanotube axis.

Polarized Raman spectra were obtained from a rope of aligned semiconducting single-wall nanotubes (SWNTs) in the vicinity of the D band and the G band. Based on group theory analysis and related theoretical predictions, the G-band profile was deconvolved into four intrinsic SWNT components with the following symmetry assignments: 1549 cm(-1) [E2(E(2g))], 1567 cm(-1) [A(A(1g))+E1(E(1g))], 1590 cm(-1) [A(A(1g))+E1(E(1g))] and 1607 cm(-1) [E2(E(2g))]. The frequency shifts of the tangential G modes from the 2D graphitelike E(2g(2)) frequency are discussed in terms of the nanotube geometry.

In this work we analyze the room-temperature linewidth for several Raman features ͑i.e., the radial breathing mode, the G band, the D band, and the GЈ band͒ observed for individual isolated single-wall carbon nanotubes ͑SWNTs͒. Temperature-dependent measurements on SWNT bundles and isolated SWNTs show that anharmonic effects are not important for linewidth broadening at room temperature. Measurements on a large number of samples ͑170 isolated SWNTs͒ allow us to filter out the effect from extrinsic SWNT properties ͑e.g., defects, tube deformations, substrate roughness͒ and to obtain information about intrinsic properties related to phonon and electron dispersion relations, curvature and Breit-Wigner-Fano effects, single-vs double-resonance Raman scattering processes, and the resonance condition itself through a linewidth analysis. We also use observations at the single-nanotube level to understand linewidth effects in SWNT bundles.

Resonant Raman scattering ͑RRS͒ measurements made with a tunable laser provide a highly reliable technique to study the shape of the joint density of electronic states ͑JDOS͒ of isolated single-wall carbon nanotubes ͑SWNTs͒. RRS can be used to determine the energy value for the one-dimensional ͑1D͒ van Hove singularities of a SWNT with a precision better than 5 meV, thereby providing important information that could be used for subsequent measurements on this same SWNT. With RRS, the measured width of the JDOS is on the order of ϳ0.1Ϫ1.0 meV, further demonstrating that SWNTs really provide a remarkably good model for 1D mesoscopic systems.