Ge. G. Samsonidze

Double resonance Raman spectroscopy of single-wall carbon nanotubes

A review of double resonance Raman spectroscopy is presented. Non-zone centre phonon modes in solids can be observed in the double resonance Raman spectra, in which weak Raman signals appear in a wide frequency region and their combination or overtone modes can be assigned. By changing the excitation laser energy, we can derive the phonon dispersion relations of a single nanotube.

Raman spectroscopy for probing chemically/physically induced phenomena in carbon nanotubes

The use of recent advances in resonance Raman spectroscopy studies on isolated carbon nanotubes and the scientific knowledge achieved so far from these studies is discussed in the context of advancing carbon nanotube-based technology. Changes in the Raman spectra can be used to probe and monitor structural modifications of the nanotube sidewalls that come from the introduction of defects and the attachment of different chemical species. The former effect can be probed through the analysis of the disorder-induced Raman modes and the latter through the upshifts/downshifts observed in the various Raman modes due to charge transfer effects.

Family behavior of the optical transition energies in single-wall carbon nanotubes of smaller diameters

Using the extended tight-binding model that allows bond lengths and angles to vary, the optical transition energies Eii in single-wall carbon nanotubes are calculated as a function of inverse tube diameter. After geometrical structure optimization, the 2n+m=constant family behavior observed in photoluminescence (PL) experiments is obtained, and detailed agreement between the calculations and PL experiments is achieved after including many-body corrections.

Potential dependent surface Raman spectroscopy of single wall carbon nanotube films on platinum electrodes

The analysis of the resonance Raman spectra of single-walled carbon nanotubes in an electrochemically controlled aqueous H2SO4 environment using different laser excitation energies shows major reversible and irreversible differences in the main vibrational features regarding their intensities, lineshapes, and frequencies for different applied potentials. These differences arise from the electrochemically induced changes in the occupation of electronic states for metallic and semiconducting nanotubes.

Quantitative evaluation of the octadecylamine-assisted bulk separation of semiconducting and metallic single-wall carbon nanotubes by resonance Raman spectroscopy

The selective stabilization of octadecylamine (ODA) on semiconducting (S) single-wall carbon nanotubes (SWNTs) has been reported to provide a means for the bulk separation of S from metallic (M) SWNTs. Utilizing resonance Raman spectroscopy and, in particular, the relative changes in the integrated intensities of the radial-breathing mode region, a generic method has been developed to provide quantitative evaluation of the separation efficiency between M and S SWNTs along with diameter separation. The ODA-assisted separation is shown to provide S enrichment by a factor of 5 for SWNTs prepared by high pressure CO decomposition and greater S enrichment for SWNTs with diameters below 1nm.

Probing the electronic trigonal warping effect in individual single-wall carbon nanotubes using phonon spectra

Abstract We have studied the trigonal warping effect in metallic carbon nanotubes using resonance Raman scattering and examining the G′-band profile for individual metallic single-wall carbon nanotubes. We show that the observed splitting in the G′-band phonon spectra is directly correlated with the splitting in the singularities of the joint density of electronic states, i.e., detailed information about the 1D electronic structure is extracted from a phonon measurement. By correlating the phonon data with the calculated electronic structure for several (n,m) nanotubes, we were able to determine the G′-band dispersion [( ∂ ω G ′ / ∂ E laser )=108±6 cm −1 / eV ] by using a single laser energy.

Environment effects on the Raman spectra of individual single-wall carbon nanotubes: Suspended and grown on polycrystalline silicon

An enhanced Raman signal is observed from individual suspended single-wall carbon nanotubes (SWNTs) and from isolated SWNTs grown on an n-doped polycrystalline silicon film used in standard silicon processing. The radial breathing modes of the Raman spectra taken from suspended SWNTs exhibit narrow linewidths, which indicate a relatively unperturbed environment for suspended SWNTs. Clear Raman signals from intermediate frequency modes in the frequency range from 520to1200cm−1 are presented, which might allow a detailed study of the phonon band structure of individual SWNTs.

Intermediate Frequency Raman Modes in Metallic and Semiconducting Carbon Nanotubes

Resonance Raman spectra of bundled and isolated single‐wall carbon nanotubes (SWNTs) have been investigated in the spectral range between 600 and 1100 cm−1, associated with intermediate frequency modes (IFM). The IFMs have been poorly studied before despite the rich set of spectral features and their relation to defects and finite size effects in SWNTs. Different kinds of samples and many laser excitation energies (Elaser) have been used in the experiments. The differences in the IFM spectra for different SWNT samples are discussed, and from a line‐shape analysis of the spectra we get an (n,m) assignment based on IFM features.

Trigonal Anisotropy in Graphite and Carbon Nanotubes

We discuss here how the trigonal warping effect of the electronic structure is relevant to optical processes in graphite and carbon nanotubes. The electron-photon, electron-phonon, and elastic scattering matrix elements have a common factor of the coefficients of Bloch wave funtions of the A and B atoms in the graphite unit cell. Because of the three fold symmetry around the Fermi energy point (the K or K′ point), the matrix elements show a trigonal anisotropy which can be observed in both resonance Raman and photoluminescence spectroscopy. This anisotropy is essential for understanding the chirality dependence of the Raman intensity and the optical response of single wall carbon nanotubes.

Spectroscopy of small diameter single‐wall carbon nanotubes

Resonance Raman spectroscopy of small diameter (below 1.2 nm) single‐wall carbon nanotubes (SWCNT) is presented. The diameter and chirality dependent many‐body corrections to the tight binding based Kataura plot are discussed. The radial breathing modes also show small chirality dependence, giving evidence for the deviations of the small nanotube diameters from the ideal folded graphene structure. The use of spectroscopy for the characterization of small environmental effects and the (n,m) population on HiPco and CoMoCAT SWNT samples is pointed out. The richness of the intermediate frequency modes is highlighted.