Raman scattering in graphite intercalation compounds

Raman scattering results are reported on graphite intercalated with Br₂, ICℓ and IBr. In all of these acceptor compounds, the single E_2g2 Raman peak for pure graphite is replaced by a doublet structure identified with in-plane carbon atom vibrations. In addition, Raman peaks specific to the intercalate species are found at frequencies down-shifted from the stretching modes of the free intercalate molecules.     

Measuring the uniaxial strain of individual single-wall carbon nanotubes: resonance Raman spectra of atomic-force-microscope modified single-wall nanotubes

Raman spectroscopy is used to measure the strain in individual single-wall carbon nanotubes, strained by manipulation with an atomic-force-microscope tip. Under strains varying from 0.06%-1.65%, the in-plane vibrational mode frequencies are lowered by as much as 1.5% (40 cm(-1)), while the radial breathing mode (RBM) remains unchanged. The RBM Stokes/anti-Stokes intensity ratio remains unchanged under strain. The elasticity of these strain deformations is demonstrated as the down-shifted Raman modes resume their prestrain frequencies after a nanotube is broken under excessive strain.     

Optical absorption of graphite and single-wall carbon nanotubes

A review of the electronic dipole transitions in graphite and single-wall carbon nanotubes is presented. Because of its singular electronic structure, the optical absorption matrix element as a function of wave vector has a node in the two-dimensional Brillouin zone of graphite, which depends linearly on the optical polarization direction. In the case of the single-wall carbon nanotubes, the dipole selection rule and the van Hove singularity in the joint density of states will give a characteristic behavior, which is observed by luminescence and resonance Raman spectroscopy. PACS 78.30.Na; 78.20.Bh; 78.66.Tr; 63.22.+m; 36.20.Kd; 36.20.Ng     

Phonon-assisted excitonic recombination channels observed in DNA-wrapped carbon nanotubes using photoluminescence spectroscopy

By using a sample of DNA-wrapped single-wall carbon nanotubes strongly enriched in the (6,5) nanotube, photoluminescence emissions observed at special excitation energy values were identified with specific mechanisms of phonon-assisted excitonic absorption and recombination processes associated with (6,5) nanotubes, including one-phonon, two-phonon, and some continuous-luminescence processes. Such detailed processes are not separately identified in three-dimensional semiconducting materials. A general theoretical framework is presented to interpret the experimentally observed phonon-assisted processes in terms of excitonic states.