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This article examines the optical properties of single-wall carbon nanotubes (SWNTs) and nanographene. It begins with an overview of the shape of graphene and nanotubes, along wit the use of Raman spectroscopy to study the structure and exciton physics of SWNTs. It then considers the basic definition of a carbon nanotube and graphene, focusing on the crystal structure of graphene and the electronic structure of SWNTs, before describing the experimental setup for confocal resonance Raman spectroscopy. It also discusses the process of resonance Raman scattering, double-resonance Raman scattering, and the Raman signals of a SWNT as well as the dispersion behavior of second-order Raman modes, the doping effect on the Kohn anomaly of phonons, and the elastic scattering of electrons and photons. The article concludes with an analysis of excitons in SWNTs and outlines future directions for research.

This paper reviews progress that has been made in the use of Raman spectroscopy to study graphene and carbon nanotubes. These are two nanostructured forms of sp2 carbon materials that are of major current interest. These nanostructured materials have attracted particular attention because of their simplicity, small physical size and the exciting new science they have introduced. This review focuses on each of these materials systems individually and comparatively as prototype examples of nanostructured materials. In particular, this paper discusses the power of Raman spectroscopy as a probe and a characterization tool for sp2 carbon materials, with particular emphasis given to the field of photophysics. Some coverage is also given to the close relatives of these sp2 carbon materials, namely graphite, a three-dimensional (3D) material based on the AB stacking of individual graphene layers, and carbon nanoribbons, which are one-dimensional (1D) planar structures, where the width of the ribbon is on the nano...

Using the Bethe-Salpeter equation, we have calculated the exciton energies of (i) bright exciton states; (ii) 2g exciton energies; and (iii) the energy difference between dark and bright exciton states for single wall carbon nanotubes (SWNTs) as a function of diameter. By adjusting the dielectric constant, we can reproduce the observed exciton energies in the resonance Raman spectra and two-photon absorption spectra for SWNTs. The environmental effect on the transition energies can be explained by a diameter-dependent dielectric constant. However, the energy difference between the dark and bright exciton states cannot be reproduced simply by changing the dielectric constant consistently. Thus we need to consider the evaluation of the Coulomb interaction, especially with regard to the surrounding materials.

The use of the Fourier expansion technique, which is based entirely on crystal symmetry, is studied by application of the technique to the phonon dispersion relations in silicon and germanium. In order to facilitate the convergence of the Fourier expansion, the interaction between the phonons and the low-lying electronic excitations is explicitly considered in terms of a Fourier expansion of this interaction. In the present approach, which only treats short-range forces, the simplest model which provides an adequate fit to the known experimental data utilizes nine adjustable parameters. By comparing certain tunneling and inelastic neutron scattering data, the location of the conduction band minima in germanium along the Δ axis is determined. The fractional distance to the X point for these minima is 0.82 ± 0.04.

An effective Hamiltonian which yields the observed optical properties of silicon and germanium is presented. The form of the Hamiltonian depends upon crystal symmetry and is based on a Fourier expansion for the energy bands. This Hamiltonian is closely related to the Slater-Koster interpolation scheme and has been applied as an interpolation scheme for experimental data.

Recent Raman scattering studies in different types of graphene samples are reviewed here. We first discuss the first-order and the double resonance Raman scattering mechanisms in graphene, which give rise to the most prominent Raman features. The determination of the number of layers in few-layer graphene is discussed, giving special emphasis to the possibility of using Raman spectroscopy to distinguish a monolayer from few-layer graphene stacked in the Bernal (AB) configuration. Different types of graphene samples produced both by exfoliation and using epitaxial methods are described and their Raman spectra are compared with those of 3D crystalline graphite and turbostratic graphite, in which the layers are stacked with rotational disorder. We show that Resonance Raman studies, where the energy of the excitation laser line can be tuned continuously, can be used to probe electrons and phonons near the Dirac point of graphene and, in particular allowing a determination to be made of the tight-binding parameters for bilayer graphene. The special process of electron–phonon interaction that renormalizes the phonon energy giving rise to the Kohn anomaly is discussed, and is illustrated by gated experiments where the position of the Fermi level can be changed experimentally. Finally, we discuss the ability of distinguishing armchair and zig-zag edges by Raman spectroscopy and studies in graphene nanoribbons in which the Raman signal is enhanced due to resonance with singularities in the density of electronic states.

We have measured the Raman spectra of one to three layer graphene as a function of laser excitation energy. The observed G ′ band Raman peak (∼2650 cm −1 ) intensity decreases with increasing numbers of graphene layers. The electronic energy band structure calculated by the extended tight binding model shows that there are four and nine possible optical processes in double resonance theory for the Raman G ′ band of double and triple layers graphene, respectively. Raman intensity calculations show that each peak position depends on its wavevector, and then the G ′ band of double and triple layer graphene has three and five components, respectively.

The higher lying exciton energies ( E 33 S and E 44 S ) of single wall carbon nanotubes (SWNTs) are calculated by solving the Bethe–Salpeter equation within an extended tight binding method. For E 11 S and E 22 S transitions, the chirality dependence of the exciton binding energy for each ( n , m ) SWNT is almost cancelled by that of the self energy. Thus the origin of the family pattern for E 11 S and E 22 S can be understood by the chirality dependence of the single particle energies. However, for E 33 S and E 44 S transitions, since the self energy becomes larger than the exciton binding energy, the chirality dependence of many body effects becomes important to analyze the transition energies.

A big picture view of Raman scattering in carbon nanotubes is presented, starting from its early history and the discovery of the unique Raman spectra of carbon nanotubes, and following on to the discovery of Raman spectra at the single nanotube level and a more detailed understanding of the scattering mechanism in terms of the excitonic picture. Recent developments and an outlook to the future of the field are emphasized along with the special role that Brazilian researchers have played in the development of the field. Both the advance in our understanding of Raman scattering in 1D systems and the use of Raman scattering to advance carbon nanotube research and sample characterization are discussed.

Over the last 10 years, carbon nanotubes have offered a unique system for the study of Raman spectra in one-dimensional systems, and at the same time Raman spectroscopy has provided a widely used and powerful tool for the characterization of single walled carbon nanotubes (SWNTs). The 10 year history of Raman scattering in SWNTs is reviewed here and future prospects for the field are discussed.

Resonance Raman studies have been carried out on length-sorted single walled carbon nanotubes (SWNTs). For nanotubes much shorter than the wavelength of light, a large increase in Raman intensity is observed for several features in the intermediate frequency mode (IFM) region. The changes in IFM intensities are found to be highly dependent on the laser excitation energies, the (n, m) indices, and the specific Raman features. A direct correlation is found between the amount of IFM intensity increase as a function of the average nanotube length, as well as the symmetry of the physical origin for the specific IFM feature.

Although the Raman effect was discovered nearly 80 years ago, it is only recently that the special characteristics of Raman scattering for one-dimensional systems have been seriously considered. This review focuses on the special interest of the Raman effect for one-dimensional systems that is of particular relevance to carbon nanostructures. Two examples of Raman scattering in one-dimensional systems are given. The first illustrates the use of Raman spectroscopy to reveal the remarkable structure and properties of carbon nanotubes arising from their one-dimensionality. Some of the recent advances in using Raman spectroscopy to study doping and intercalation to modify nanotube properties are reviewed, in the context of a one-dimensional system. The second example is the Raman spectra of a linear chain of carbon atoms and the special properties of this interesting system. New approaches toward applying Raman spectroscopy to carbon nanostructures are also emphasized.

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.

The Raman intensity of the disorder-induced D-band in graphitic materials is calculated as a function of the in-plane size of the graphite nanoparticles (La) and as a function of the excitation laser energy. Matrix elements associated with the double resonance Raman processes, i.e., electron–photon, electron–phonon and electron–defect processes are calculated based on the tight binding method. The electron–defect interaction is calculated by considering the elastic scattering at the armchair edge of graphite, adopting a nanographite flake whose width is La. We compare the calculated results with the experimental results obtained from the spectra for different laser lines and La.

We describe the synthesis of N-doped single-walled carbon nanotubes (N-SWNTs), that agglomerate in bundles and form long strands (

The photoluminescence (PL) intensity of a single-wall carbon nanotube (SWNT) is calculated for each ( n , m ) by multiplying the photon-absorption, relaxation and photon-emission matrix elements. The intensity depends on chirality and “type I vs type II” for smaller diameter semiconducting SWNTs (less than 1 nm). By comparing the calculated results with the experimental PL intensity of SWNTs prepared by chemical vapor deposition at different temperatures, we find that the abundance of ( n , m ) nanotubes with smaller diameters should exhibit a strong chirality dependence, which may be related to the stability of their caps.

A review is given of how resonance Raman spectroscopy (RRS) and photoluminescence (PL) can be used to reveal unique information about nanostructures, 1 nm in diameter, thus providing new techniques for probing the electronic and vibrational properties of nanostructures. Special attention is given to recent advances made in this field.

The use of Raman spectroscopy to reveal the remarkable structure and the unusual electronic and phonon properties of single wall carbon nanotubes (SWNTs) is reviewed comprehensively. The various types of Raman scattering processes relevant to carbon nanotubes are reviewed, and the theoretical foundations for these topics are presented. The most common experimental techniques used to probe carbon nanotubes are summarized, followed by a review of the novel experimental findings for each of the features in the first order and second order Raman spectra for single wall carbon nanotubes. These results are presented and discussed in connection with theoretical considerations. Raman spectra for bundles of SWNTs, for SWNTs surrounded by various common wrapping agents, and for isolated SWNTs at the single nanotube level are reviewed. Some of the current research challenges facing the field are briefly summarized.

The second order Raman signals around the G′-band region of graphite and carbon nanotubes have been investigated at more than 15 excitation laser lines. Two distinct Raman bands have been observed around 2700 cm−1; a prominent one is due to the so-called G′-band and the other is a weak band around 2450 cm−1. Both two bands can be from the double resonance process involving two phonons around the K-point in the phonon dispersion of a two-dimensional graphite. The 2450 cm−1-band has exhibited little power dependence, whereas the intensity of G′-band has shown large photon energy dependence as already reported. The 2450 cm−1-band and the G′-band correspond to non-dispersive q = 0 and fully-dispersive q = 2k, respectively. From the phonon dispersion and the corresponding phonon frequency, the 2450 cm−1-band can be assigned as an overtone mode of LO phonon (i.e. 2LO). This is revealed by calculated Raman spectra of graphite with proper electron–phonon matrix elements. The present study is the first report on the origin and assignment of the 2450 cm−1-band, which is based on the double resonance Raman scattering.

Optical characterization of DNA-wrapped CoMoCAT carbon nanotube hybrids (DNAOCNT) and semiconductor-enriched DNAOCNT was carried out using resonant Raman spectroscopy (RRS) and photoluminescence (PL) experiments. The values of radial breathing modes frequency xRBM were found to be relatively insensitive to the type of wrapping agents surrounding the nanotube. The values of xRBM and the irst and second resonant interband transitions, E11 and E22, for a particular (n,m) tube for all sample types in RRS and PL measurements are found to correspond to the values obtained for SDS-dispersed nanotubes measured with PL, but with a shift in Eii ranging from 10 to 80 meV. The DNA-wrapping has shown not only to provide good isolation to the individual nanotube in a bundle, but the DNA wrapping mechanism for the CoMoCAT sample has also been shown to be diameter selective.

A review of the electronic, thermal and mechanical properties of nanotubes is presented, with particular reference to properties that differ from those of the bulk counterparts and to potential applications that might result from the special structure and properties of nanotubes. Both experimental and theoretical aspects of these topics are reviewed.

▪ Abstract The unusual structure and properties of carbon nanotubes are presented, with particular reference to single-wall nanotubes (SWNTs) and nanotube properties that differ from those of their bulk counterparts. The atomic structure; electronic structure; and vibrational, optical, mechanical, and thermal properties are discussed, with reference made to nanotube junctions, nanotube filling, and double-wall nanotubes (DWNTs). Special attention is given to resonance Raman spectroscopy at the single nanotube level. The status of current research in this field is assessed and opportunities for future research are identified.

The electron–phonon (e–ph) interaction and the relaxation time of photo-excited electrons are calculated in graphite within the tight-binding scheme. The e–ph matrix element thus obtained, shows anisotropy in k-space. The calculated relaxation time is of the same order of magnitude as the experimental one. Moreover, below an energy close to the Fermi energy, the absorption rate exceeds the emission rate, which indicates that graphite can emit far infra-red electro-magnetic waves by absorbing heat. We also compare this result with Planck's formula for black-body radiation.

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.

We calculated the resonance condition for the radial breathing Raman mode for single wall carbon nanotube (SWNT) bundles for light polarization parallel and perpendicular to the tube axis. The radial breathing modes that are not observed in isolated SWNTs, but are observed in SWNT bundles, are assigned to a resonance process for light with perpendicular polarization. Asymmetry between the valence and conduction π energy bands becomes essential for obtaining resonance conditions. We find that due to a high joint density of states, armchair SWNTs have the largest optical transition intensities.

In single-walled carbon nanotubes (SWNTs), their electronic and vibrational structure as well as their charge-carrier dynamics are crucial for potential ultrasmall optical device applications. SWNT properties have now been obtained from optical absorption and time-resolved photoemission and, at the single-nanotube level, by resonance Raman scattering and photoluminescence studies. This article presents an overview of SWNT photophysics, discussing important findings for the characterization of carbon nanotube properties and directions for future research and potential applications. The unique optical properties observed in SWNTs are due to the one-dimensional confinement of electronic states, resulting in van Hove singularities in the nanotube density of states. Optical measurements of phonons, charge-carrier dynamics, and the electronic transition energy van Hove singularities are discussed.

The optical absorption matrix element as a function of one-dimensional (1D) wave vector k, and subband index μ of a single wall carbon nanotube is given analytically for linearly polarized light with polarization parallel to the nanotube axis. For armchair nanotubes, it is found that the optical transitions for non-degenerate A symmetry bands are forbidden over the whole 1D k region and the transitions for all other bands are also forbidden at the k = 0 point. Near the Fermi level, the absorption for all metallic nanotubes is found to be approximately zero. For both metallic and semiconducting nanotubes, it is found that the absorption matrix element has a maximum absolute value at the van Hove singularity (vHS) k point around the Fermi energy for each band. The absorption dependence on diameter and chiral angle is also presented for semiconducting nanotubes. For light polarization perpendicular to the nanotube axis, on the other hand, the absorption for nanotubes is generally weak near a vHS.

We report a new method for the fabrication of carbon aerogels. Resorcinol and furfural were polymerized in isopropanol using HCl as a catalyst and the resulting alcogels were then dried directly using supercritical isopropanol, followed by carbonization under a nitrogen atmosphere. The carbon aerogels can be prepared over a range of densities (0.148–0.746 g/cm3), depending on the gelation temperature and the mass content of the reactants. The textural and transport properties of the aerogels materials were characterized by nitrogen adsorption/desorption analysis, high-resolution transmission electron microscopy (HRTEM), magnetic susceptibility, and resistivity measurements. TEM observations show that the carbon aerogels are composed of interconnected nanoparticles with diameters ranging from 20 to 30 nm. All of the aerogel samples exhibit high Brunauer– Emmett–Teller (BET) surface areas in the range of 557–656 m2/g. The carbon aerogels produced by this new method have similar transport properties to those of carbon aerogels prepared by the traditional method.

Efficient solid state energy conversion based on the Peltier effect for cooling and the Seebeck effect for power generation calls for materials with high electrical conductivity σ, high Seebeck coefficient S, and low thermal conductivity k. Identifying materials with a high thermoelectric figure of merit Z(= S2σ/k) has proven to be an extremely challenging task. After 30 years of slow progress, thermoelectric materials research experienced a resurgence, inspired by the developments of new concepts and theories to engineer electron and phonon transport in both nanostructures and bulk materials. This review provides a critical summary of some recent developments of new concepts and new materials. In nanostructures, quantum and classical size effects provide opportunities to tailor the electron and phonon transport through structural engineering. Quantum wells, superlattices, quantum wires, and quantum dots have been employed to change the band structure, energy levels, and density of states of elect...

A review is presented of the resonance Raman spectra from individual isolated single-wall carbon nanotubes (SWNTs). A brief summary is given of how the measurements are made. Why the resonance Raman effect allows single-carbon nanotube spectra to be observed easily and under normal operating conditions is summarized. The important structural information that is provided by single-nanotube spectroscopy using one laser line is discussed, and what else can be learned from tunable laser experiments is reviewed. Particular attention is given to the determination of the nanotube diameter and of the energy of its van Hove singularities Eii. Applications of single-nanotube spectroscopy are emphasized, such as measurements of isolated SWNTs connected with circuit-based samples and of isolated SWNTs mounted on an atomic force microscope tip. A critical assessment of the opportunities and limitations of the resonance Raman method for structural (n, m) identification is presented. The trigonal warping effect, which is central to the (n, m) identification in resonance Raman spectroscopy, is discussed in simple terms, and the importance of this effect in nanotube science and applications is reviewed.

Nanowires and nanotubes are now at the forefront of materials science at the nanoscale. This article starts with introductory comments about nanowires and nanotubes and then addresses in more detail the special structure and properties of bismuth nanowires and carbon nanotubes, which are considered as prototype examples of nanowires and nanotubes. Both nano-materials are important for the new nanoscience concepts that they introduce and for their promise for practical applications. Both provide a system that is simple enough so that detailed calculations of their properties can be carried out, and predictions about their physical behavior can be made. The occurrence and control of unusual and unique properties of specific nanostructures are the drivers for the exploitation of nanoscience in nanotechnology applications.

The use of Raman spectroscopy to elucidate the vibrational and electronic structure of single wall carbon nanotubes is reviewed. The special role played by single nanotube spectroscopy in the (n,m) structural characterization of individual nanotubes and in the elucidation of the spectra of nanotube bundles is emphasized.

The disorder-induced D-band and some other non-zone center Raman modes of graphite and single wall carbon nanotubes are assigned to phonon modes in their respective Brillouin zones. In disordered graphite, the weak, dispersive phonon modes, which have been known but never assigned so far, are well described by the double resonance Raman process. All weak Raman peaks observed for sp2 carbons are useful for determining the phonon dispersion relations of graphite. In carbon nanotubes, all semiconducting nanotubes and some metallic nanotubes have van Hove singular k points for their electronic and phonon energy dispersion curves at the Γ point of the Brillouin zone. A corresponding Raman process is relevant to explain the observed D-band and intermediate frequency spectra.

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.

We performed polarized Raman scattering studies on 0.4 nm diameter single wall carbon nanotubes (SWNTs) grown inside the pores of zeolite crystals, using several different laser lines (1.92⩽Elaser⩽2.71 eV). The strong diameter-selective resonant behavior of typical SWNTs (1

A broad review of recent research work on the preparation and the remarkable properties of intercalation compounds of graphite, covering a wide range of topics from the basic chemistry, physics and materials science to engineering applications.

The Raman spectra of the disorder-induced D-band and some other non-zone-center phonon modes of graphite and single wall carbon nanotubes are discussed using double resonance Raman theory. For two-dimensional disordered graphite, two D-band peaks and one G′-band peak are predicted. The trigonal warping effect of the constant energy contours in graphite and the van Hove singularities in the electronic and phonon energy dispersion of carbon nanotubes are of importance for discussing the line width and possible numbers of Raman peaks which come from inequivalent Raman processes.

A review is presented on the resonance Raman spectra from one isolated single wall carbon nanotube. The reasons why it is possible to observe the spectrum from only one nanotube are given and the important structural information that is provided by single nanotube spectroscopy is discussed. Emphasis is given to the new physics revealed by the various phonon features found in the single nanotube spectra and their connection to spectra observed for single wall nanotube bundles. The implications of this work on single wall carbon nanotube research generally are also indicated.

Single-walled carbon nanotube samples produced in the presence of different combinations of metal catalysts have been studied by resonant Raman spectroscopy. The diameter distribution of different samples has been determined by analysis of the laser excitation energy dependence of the tangential modes associated with metallic nanotubes. These modes are resonantly enhanced over a narrow range of the exciting energies, which shifts for different samples. The Raman cross-section expression has been used to fit the experimental Raman excitation profiles. This procedure was used to determine the mean value and the width of the distribution of diameters within each sample.

The stable structure of a double-wall carbon nanotube (DWNT) is calculated for various chirality pairs, (n,m) – (n ′ ,m ′ ) , of inner and outer constituent layers. The stability of a double-wall nanotube is found not to depend on chirality, but rather on the diameter difference between inner and outer layers. However, the potential barrier for the relative displacement of the inner and outer nanotube layers is found to depend significantly on the chirality difference of the pair. Mechanical motions like a bolt–nut pair or discrete rotations can be expected for special pairs of chiralities in double-wall nanotubes, and these special motions will be important for nano-technology.

We show that the Raman scattering technique can give complete structural information for one-dimensional systems, such as carbon nanotubes. Resonant confocal micro-Raman spectroscopy of an (n,m) individual single-wall nanotube makes it possible to assign its chirality uniquely by measuring one radial breathing mode frequency omega(RBM) and using the theory of resonant transitions. A unique chirality assignment can be made for both metallic and semiconducting nanotubes of diameter d(t), using the parameters gamma(0) = 2.9 eV and omega(RBM) = 248/d(t). For example, the strong RBM intensity observed at 156 cm(-1) for 785 nm laser excitation is assigned to the (13,10) metallic chiral nanotube on a Si/SiO2 surface.

We report measurements and modeling of microwave-frequency vortex dynamics in YBCO grain boundaries that are modeled as long Josephson junctions by numerically solving the sine-Gordon equation. YBCO bicrystal grain boundaries with misorientation angles from 2 to 24° have been studied experimentally using microwave resonator measurement techniques. Comparison between the measured and calculated microwave impedance and the harmonic generation of the 24° grain boundaries indicates that the 24° grain boundaries are weakly coupled long Josephson junctions. The corresponding results of lower angle grain boundaries are also presented. A transition from strong-coupled single-crystal-like behavior to weak-coupled Josephson-junction-like behavior has been observed in a 10° grain boundary between 55 and 75 K. The physics of Josephson-vortex dynamics and its impact on the microwave properties of superconducting thin films are discussed.

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) [E-2(E-2g)], 1567 cm(-1) [A(A(1g)) + E-1(E-1g)], 1590 cm(-1) [A(A(1g)) + E-1(E-1g)] and 1607 cm(-1) [E-2(E-2g)]. The frequency shifts of the tangential G modes from the 2D graphitelike E-2g2 frequency are discussed in terms of the nanotube geometry.

We report the results of a detailed experimental and theoretical study of the ultrafast relaxation processes in superconducting ${\mathrm{K}}_{3}{\mathrm{C}}_{60}$ and ${\mathrm{Rb}}_{3}{\mathrm{C}}_{60}$ films. Room temperature pump-probe spectra were obtained for different pump and probe wavelengths. Low-temperature measurements through the phase transition temperature ${T}_{c}$ were performed to monitor the quasiparticle dynamics in the superconducting state. For comparison we performed measurements on ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ under similar conditions. An intuitive model is presented to explain the temperature and wavelength dependence of our experimental results for both the superconducting and normal phases.

In this work we have studied the dispersion of the disorder-induced (D) and the second-order (G') Raman bands in single wall carbon nanotubes using several laser excitation energies (E laser) in the range 1.5-3.0 eV. An anomalous step-like behavior was observed in the E laser dependence of the G'-band frequency. This result is interpreted as a manifestation of the one-dimensional (1D) behavior of the phonon spectrum in carbon nanotubes.

The surface-enhanced resonant Raman-scattering (SERRS) spectra of single-walled carbon nanotubes (SWNT's) adsorbed on silver and gold metal island films and on colloidal silver cluster substrates were investigated using different laser excitation wavelengths. The observed enhancement in the SERRS signal of the SWNT's results from: (i) an ``electromagnetic'' surface-enhanced Raman spectral (SERS) enhancement due to resonances between optical fields and the electronic excitations in the metallic nanostructures, (ii) a ``chemical'' SERS enhancement due to the interaction between the SWNT's and the metal surfaces, and (iii) a selective resonance Raman effect between the incident and scattered photons and electronic transitions between the one-dimensional van Hove singularities in the electronic density of states of metallic and semiconducting nanotubes. We have observed changes in the relative intensities and shifts in the peak frequencies of several vibrational modes of the SWNT's upon adsorption on a metal surface, which indicate a specific interaction of the nanotubes with the metal surface. Changes in the resonant Raman spectra due to interaction with the silver or gold surfaces are apparent in the second-order Raman bands, especially in the dispersive features, such as the second-order Raman ${G}^{\ensuremath{'}}$ band, which upshifts in the SERRS spectra relative to the resonant Raman-scattering (RRS) spectra, providing evidence for a significant perturbation of the electronic levels for the adsorbed nanotubes. In addition, the SERRS spectra show an additional enhancement of the Raman signal for specific features in the vibrational spectra of the metallic nanotubes, in contrast to the case for the semiconducting nanotubes for which the normal RRS and SERRS spectral profiles are very similar. These results can be explained in terms of a specific charge-transfer enhancement effect for the metallic nanotubes.

Surface enhancement factors of at least ${10}^{12}$ for the Raman scattering of single-walled carbon nanotubes in contact with fractal silver colloidal clusters result in measuring very narrow Raman bands corresponding to the homogeneous linewidth of the tangential C--C stretching mode in semiconducting nanotubes. Normal and surface-enhanced Stokes and anti-Stokes Raman spectra are discussed in the framework of selective resonant Raman contributions of semiconducting or metallic nanotubes to the Stokes or anti-Stokes spectra, respectively, of the population of vibrational levels due to the extremely strong surface-enhanced Raman process, and of phonon-phonon interactions.