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The chemical reactions of halogen molecules on a nano-graphite cluster are calculated using a semi-empirical calculational method. A real time calculation of the chemical reaction of halogen molecules up to 200 fs which is performed by the dynamic reaction coordinates (DRC) method of the quantum chemistry library shows that the iodine molecule exhibits a special reaction involving the removal of hydrogen atoms from edge carbon atoms. This result might be relevant to recent experiments on the graphitization of pitch at a low temperature of 400°C. We discuss the deformation of the nano-graphite cluster upon the intercalation of halogen atoms.

Femtosecond pump-probe studies provide a sensitive characterization tool for the study of ultrafast relaxation processes in intercalation compounds, more specifically in the alkali metal intercalated fullerenes K 3 C 60 and Rb 3 C 60 . Films of these materials were excited with femtosecond optical pulses and the induced transient changes in the optical properties were then monitored with a delayed probe pulse, revealing excited state relaxation dynamics occurring on a picosecond or femtosecond time scale. Room temperature measurements with a 20 fs pulse show extremely long-lived coherent phonon oscillations of the Ag molecular mode at -492 cm -1 . Information about a highly damped vibrational mode involving an alkali metal cation beating against a C 60 anion has also been obtained. Low temperature measurements were also performed, yielding new information about the quasi-particle dynamics in the superconducting state and across the normal to superconducting phase transition. These results are discussed in the context of intercalation compounds based on carbon.

Chirality-dependent van Hove singularities (vHs) of the one-dimensional electronic density of states (DOS) are discussed in connection with resonant Raman spectroscopy. The effect of trigonal warping on the energy dispersion relations near the Fermi energy splits the peaks of the density of states for metallic nanotubes, and the magnitude of this effect depends on the chiral angle of the carbon nanotube. The width of the peak splitting has a maximum for metallic zigzag nanotubes, and no splitting is obtained for armchair nanotubes or semiconducting nanotubes. We also find an additional logarithmic singularity in the electronic DOS for carbon nanotubes that is related to a two-dimensional singularity, which does not depend on either the diameter or the chirality.

Variations of the properties of submicron vapor-grown carbon fibers (VGCFs) and nanofibers, with diameters around 0.1–0.2 μm and 80–100 nm, respectively, are observed by Raman spectroscopy as a function of heat-treatment temperature. The microstructural evolution strongly depends on the original properties of the material, such that the main transition temperatures associated with the onset for establishing two-dimensional graphene ordering are defined below 1500 °C for the nanofibers and 2000 °C for the submicron VGCFs, respectively. The relative intensities (ID/IG) of the as-grown phase for submicron VGCFs and nanofibers are 3.44 and 1.35, while those for the corresponding graphitized samples are 0.393 and 0.497, respectively.

Fracture modes in a model glass–polymer coating–substrate system indented with hard spheres are investigated. The large modulus mismatch between the glass and polymer results in distinctive transverse fracture modes within the brittle coating: exaggerated circumferential (C) ring cracks that initiate at the upper coating surface well outside the contact (as opposed to the near-contact Hertzian cone fractures observed in monolithic brittle materials); median–radial (M) cracks that initiate at the lower surface (i.e., at the substrate interface) on median planes containing the contact axis. Bonding between the coating and substrate is sufficiently strong as to preclude delamination in our system. The transparency of the constituent materials usefully enables in situ identification and quantification of the two transverse fracture modes during contact. The morphologies of the cracks and the corresponding critical indentation loads for initiation are measured over a broad range of coating thicknesses (20 mm to 5.6 mm), on coatings with like surface flaw states, here ensured by a prebonding abrasion treatment. There is a well-defined, broad intermediate range where the indented coating responds more like a flexing plate than a Hertzian contact, and where the M and C cracks initiate in close correspondence with a simple critical stress criterion, i.e., when the maximum tensile stresses exceed the bulk strength of the (abraded) glass. In this intermediate range the M cracks generally form first—only when the flaws on the lower surface are removed (by etching) do the C cracks form first. Finite element modeling is used to evaluate the critical stresses at crack initiation and the surface locations of the crack origins. Departures from the critical stress condition occur at the extremes of very thick coatings (monolith limit) and very thin coatings (thin-film limit), where stress gradients over the flaw dimension are large. Implications of the results concerning practical coating systems are considered.

Raman and resonance Raman spectra of ${\mathrm{MoS}}_{2}$ nanoparticles, in the form of inorganic fullerenelike nanoparticles with diameters ranging from 200 to 2000 \AA{} in size, and platelets ranging from 50 to 5000 \AA{} in size, are presented. Off resonance, the first-order Raman bands are broadened, but not significantly shifted, and no additional bands are observed, indicating that the atomic structure is preserved, at least locally, in the nanoparticles. The broadening effect is assigned to phonon confinement by facet boundaries. In the resonance Raman spectra of the nanoparticles, several additional first-order peaks are observed. The electron-phonon coupling responsible for the strong-resonance conditions is identified through dynamic band calculations. Using temperature-dependent resonance Raman measurements, we assign these peaks to zone-boundary phonons activated by disorder and finite-size effects. By analyzing the position of the dispersive peak at 429 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ under resonance conditions, it was possible to probe the softening of modes propagating in the c-axis direction.

The electronic structure of fluorine-doped graphite nanoclusters is calculated by a semi-empirical quantum calculation. We find a local deformation of the graphite nanocluster upon fluorine doping resulting from a change in the electronic structure of the host carbon atoms from sp2 to sp3 hybridization. By adding fluorine atoms one by one, we found that the fluorine atoms first terminate at edge sites of the nanographite cluster, and then interior carbon atoms become doped by the added fluorine atoms by breaking the π bonds between a carbon atom and its neighboring carbon atoms. We also discuss the occurrence of unpaired spins in the graphite nanoclusters arising from F doping.

We demonstrate that scanning probe electrostatic force microscopy applied to a nanoscale electronic structure can be used for studying the spatially resolved carrier quantized states as determined by the screening properties of local surface regions of the structure. The results presented for the cross-sectional surface of Bi quantum wires elucidate the microscopic nature of quasi-one-dimensional confined states excited by an applied bias voltage, where the single-particle-in-a-box energy quantization competes with the wire boundary enhanced intercarrier Coulomb repulsion.

Using nonresonant bond polarization theory, we have calculated the Raman intensity of a single-wall carbon nanotube of finite length. The calculations show that the Raman peaks in the intermediate frequency range $(500--1200{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1})$ have no intensity for infinite nanotubes, but do have some intensity for finite nanotubes. These intermediate frequency modes, which are sensitive to the nanotube length, correspond to vibrations along the nanotube axis. We also found an edge state of the breathing phonon mode at an open end of the carbon nanotube, which is Raman active.

A circuit model is presented for Josephson junctions (JJs) that solves the nonlinear long-junction equation, driven by a nonuniform current distribution. This extended resistively shunted junction (ERSJ) model consists of a parallel array of ideal resistively shunted JJs coupled by inductors. The junction array is connected to an array of current sources that simulate the time- and space-dependent current distribution in a stripline. The rf-current dependent complex impedance of a long JJ calculated using this model agrees with measured data on a YBCO grain-boundary JJ and provides an explanation of the measured steps in the resistance resulting from the creation, annihilation, and motion of Josephson vortices under the influence of rf currents. This model contributes to a better understanding of the power-handling characteristics of high-Tc microwave devices, in which the power losses are believed to result from JJ effects associated with imperfections in the films. The model also predicts second-harmonic generation with a highly nonlinear and nonmonotonic power dependence. Details of the dynamics of Josephson vortices are presented and discussed.

The anomalous resonant behavior of the tangential Raman modes of carbon nanotubes has been studied in the critical region of laser energies 1.7‐2.2 eV. The special enhancement of the Raman modes is explained by a model that takes into account the transition between the singularities in the one-dimensional density of electronic states for the metallic nanotubes and the distribution of diameters in the sample. The results agree with direct measurements of the electronic density of states for the metallic nanotubes and establish their association with the specially enhanced high frequency, first-order Raman modes. @S0163-1829~98!50848-X# Resonant Raman spectroscopy is a very useful tool for the characterization of the one-dimensional ~1D! properties of carbon nanotubes. It has been used to study multiwall nanotubes ~MWNT!, 1 single-wall nanotubes ~SWNT!, 2‐5 and was recently examined theoretically. 6 We show here evidence that special tangential phonon modes of metallic carbon nanotubes are enhanced in a narrow range of laser energies between 1.7 and 2.2 eV by electronic transitions between the first singularities in the 1D electronic density of states ~DOS! in the valence and conduction bands v 1!c 1 . This result establishes the association of the specially enhanced highfrequency, tangential modes with the metallic carbon nanotubes.

The optical properties of inorganic fullerene-like and nanotube MS2 (M = Mo, W) material are studied through absorption and resonance Raman, and compared to those of the corresponding bulk material. The absorption measurements show that the semiconductivity is preserved. Nevertheless, the positions of the excitons are altered in comparison to the bulk. The Raman spectra of the nanoparticles show a close correspondence to that of the bulk. However, the first-order peaks are broadened and, under resonance conditions, new peaks are observed. The new peaks are assigned to disorder-induced zone edge phonons.

Image analysis has been applied to the TEM observation of activated carbon fibers, in order to evaluate the pore structure visually. It is suggested that the present method can show the shape of the pores as well as providing a quantitative estimation of the pore structure. The results are consistent with those obtained by common gas adsorption method and with synthesized molecular graphics TEM images of pores. The pore analysis on activated carbon fibers by TEM combined with image processing can provide a powerful tool to characterize the porous structure of activated carbons from a different new viewpoint.

Long and wide ropes/ribbons of single-walled carbon nanotube (SWNT) bundles with rope diameters of 100 mu m and lengths to 3 cm were synthesized by the catalytic decomposition of hydrocarbons. These ropes/ribbons consist of roughly-aligned bundles of aligned SWNTs. The SWNT diameters, as determined from HRTEM images, are 1.69 +/- 0.34 nm, which, in combination with resonant Raman scattering measurements, indicates that our SWNTs have larger diameters than those synthesized by other techniques. The larger SWNTs are promising for gas-storage applications. The easy manipulation of the ropes offer special opportunities for their characterization and applications. (C) 1998 Published by Elsevier Science B.V. All rights reserved.

Room-temperature Raman-scattering spectra are reported for the type-II superconductors ${\mathrm{M}}_{x}{\mathrm{Ba}}_{y}{\mathrm{Si}}_{46}$ (M=Na,K) that were recently shown to exhibit ${T}_{c}$'s \ensuremath{\sim}3.5 K. These spectra are compared to those of ${\mathrm{Na}}_{8}{\mathrm{Si}}_{46}$ and ${\mathrm{K}}_{7}{\mathrm{Si}}_{46}$ clathrates that exhibit normal metallic behavior down to 2 K. In the ${\mathrm{Si}}_{46}$ system, fifteen of the eighteen Si related first-order Raman frequencies predicted by group theory have been detected, and the frequencies are found to be sensitive to the particular dopants. The Raman linewidths observed for the ${\mathrm{M}}_{x}{\mathrm{Ba}}_{y}{\mathrm{Si}}_{46}$ system are comparable to those observed for ${\mathrm{Na}}_{8}{\mathrm{Si}}_{46}$ and ${\mathrm{K}}_{7}{\mathrm{Si}}_{46}.$ The data, taken collectively, suggest that the line broadening in the metallic Si clathrates is due to important contributions from both the electron-phonon interaction as well as from a random filling of the Si cages and charge-transfer disorder.

Using nonresonant bond-polarization theory, the Raman intensity of a single-wall carbon nanotube is calculated as a function of the polarization of light and the chirality of the carbon nanotube. The force-constant tensor for calculating phonon dispersion relations in the nanotubes is scaled from those for two-dimensional graphite. The calculated Raman spectra do not depend much on the chirality, while their frequencies clearly depend on the nanotube diameter. The polarization and sample orientation dependence of the Raman intensity shows that the symmetry of the Raman modes can be obtained by varying the direction of the nanotube axis, keeping the polarization vectors of the light fixed.

We report the results of a study of the nonlinear microwave surface impedance Z{sub s}, i.e., its dependence on microwave current Z{sub s}(I{sub rf}), resulting from vortex motion in YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} thin films in a dc magnetic field applied parallel to the film{close_quote}s c axis. Using the technique of stripline resonators we have measured the nonlinear Z{sub s} at frequencies of 1.23{endash}8.45 GHz, at temperatures from 5 to 30 K, and in magnetic fields from 0 to 4 T. In the mixed state, there is a significant increase in R{sub s} from the zero-field value, particularly at lower frequencies, causing an R{sub s}{proportional_to}f{sup 1.2} dependence at all measured temperatures and microwave powers. We also review our previously reported measurements and modeling of the linear Z{sub s} because the nonlinear results can be explained by an extension of the model that we have previously used to describe the dependence of Z{sub s} on frequency, temperature, and magnetic field in the linear I{sub rf} regime. This model explains the linear Z{sub s} data through the thermal activation of vortex segments between metastable vortex states separated by distances of order of the coherence length {approximately}{xi} and by a distribution of energymore » barriers U{sub b} whose magnitudes extend from U{sub b}{approximately}0 K to at least several hundred K. We further show that the behavior of Z{sub s} at high microwave powers is fully consistent with the same thermal activation of vortex segments, but the effective magnitudes of the energy barriers {tilde U}{sub b} have been reduced in proportion to the microwave current density J{sub rf}(r,t) such that {tilde U}{sub b}=U{sub b}{minus}J{sub rf(}r,t){phi}{sub 0}{xi}l. {copyright} {ital 1997} {ital The American Physical Society}« less

We calculate the optimized geometry and the corresponding electronic structure of Li ions doped in a small graphite cluster with dangling bonds or hydrogen terminations at the edge surrounding the cluster. The calculations imply both covalent and ionic bonds of Li ions to carbon atoms, which may be relevant to explaining the broad signal of the 7Li NMR Knight shift spectra. Li intercalation, in particular, is possible even at the hydrogen-terminated edges. Because of the finite size effect of the cluster, the ionicity of intercalated Li ions has a large distribution of values, ranging from positive values close to that in graphite intercalation compounds to even slightly negative values, depending on the bonding geometry. We propose that the cluster edge surface plays a special role in accommodating excess Li ions in the disordered graphite system.

A wide range of nanostructured π-bonded carbon-based materials,with unique physical properties is presented, including carbon fibers,carbon nanoparticles, porous carbons, fullerenes and carbon nanotubes.Particular emphasis is given to future research directions in thesenanostructured carbon-based materials and to energy-related applicationsthat may result.

This article reviews carbon materials from the standpoint of nanotechnology. The unusual features of carbon materials stem from the ability of carbon to form materials with vastly different structures and hence with vastly different proper ties. The major focus of this review is on the ability of carbon to form zero dimensional quantum dots of subnanometer dimensions in the form of fullerenes, and one-dimensional quantum wires in the form of carbon nanotubes. The struc ture and properties of fullerenes and carbon nanotubes are reviewed in this article in the context of nanotechnology.

We report femtosecond time-resolved pump-probe DECP experiments using a colliding pulse mode-locked laser performed on ${\mathrm{Ti}}_{2}$${\mathrm{O}}_{3}$ as the sample lattice temperature ${\mathit{T}}_{\mathit{L}}$ is raised from 300 K through the ``soft transition'' at 450 K to a temperature of 570 K. We have observed DECP spectra through the transition, with oscillations in reflectivity of a few percent associated with the low frequency ${\mathit{A}}_{1\mathit{g}}$ mode. A thermodynamic relation is found between the low frequency ${\mathit{A}}_{1\mathit{g}}$ equilibrium displacement and the number of excited electrons removed from the valence band. When applied to ${\mathit{T}}_{\mathit{L}}$-dependent equilibrium coordinate data for ${\mathrm{Ti}}_{2}$${\mathrm{O}}_{3}$ obtained in x-ray experiments, the theory allows a determination of the band overlap vs lattice temperature. The band overlap at ${\mathit{T}}_{\mathit{L}}$=621 K is found to be \ensuremath{\sim}0.06 eV. The ${\mathit{A}}_{1\mathit{g}}$ mode frequency ${\ensuremath{\nu}}_{\mathrm{ph}}$, the electronic relaxation rate (1/${\mathrm{\ensuremath{\tau}}}_{\mathrm{el}}$), and the phonon relaxation rate (1/${\mathrm{\ensuremath{\tau}}}_{\mathrm{ph}}$) have all been followed through the transition. ${\ensuremath{\nu}}_{\mathrm{ph}}$ decreases, and shows a partial recovery in agreement with other Raman studies. The behavior of (1/${\mathrm{\ensuremath{\tau}}}_{\mathrm{}\mathrm{el}}$) can be understood as due to an increase in available states for interband electron-phonon scattering as the band crossing takes place. Applying a deformation potential model to the data for (1/${\mathrm{\ensuremath{\tau}}}_{\mathrm{el}}$) before band crossing, with the low frequency ${\mathit{A}}_{1\mathit{g}}$ mode as the dominant scattering mechanism, a value of |D|\ensuremath{\simeq}2.0 eV is obtained for the valence band deformation potential associated with this mode. (1/${\mathrm{\ensuremath{\tau}}}_{\mathrm{ph}}$) does not show a clearcut correlation with bandcrossing due to greater scatter in the data. The temperature dependence is partially explained by the two-phonon decay of the coherent phonon excited in DECP, and may also have a component due to interaction with hot electrons as well as a dephasing contribution. \textcopyright{} 1996 The American Physical Society.

The optical properties of C60 are reviewed with regard to their intrinsic interest as molecular solids exhibiting high symmetry. Modifications to these properties due to phototransformation and alkali metal doping are summarized. These optical properties provide background to current studies on C60-polymer composites, with their focus on potential applications.

Since the discovery in 1990 of a relatively simple arc method to synthesize gram quantities of carbon cage molecules (fullerenes), considerable research effort has been expended to understand the molecular and solid-state properties of fullerenes and fullerene-derived materials. Raman scattering has played an important role in this effort which has focused on the fullerene C60, and to a lesser extent C70. From Raman spectra and their comparison with model andab initiocalculations, fundamental questions regarding the intramolecular bonds, the structure and properties of crystalline, fullerene-derived solids, including the superconducting K3C60 and Rb3C60 compounds, have been addressed and largely understood. Raman scattering has also been used to probe pressure- and temperature-driven phase transitions and the photopolymerization of fullerenes in the solid state, in addition to the bonding of fullerene molecules to metal substrates. In this review the highlights of this Raman scattering research are discussed. Brief introductory remarks concerning the discovery and structure of fullerenes are also given.

We report the results of a study of the complex microwave surface impedance {ital Z}{sub {ital S}} resulting from vortex motion in YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} thin films in a dc magnetic field applied parallel to the film {ital c} axis. Using the technique of stripline resonators we have measured {ital Z}{sub {ital S}} at frequencies from 1.2 to 22GHz and at temperatures from 5 to 65K in magnetic fields from 0 to 4 T. We find that both the surface resistance {ital R}{sub {ital S}} and the surface reactance {ital X}{sub {ital S}} increase almost linearly with the magnetic field. In zero applied magnetic field we find the frequency dependence of the surface resistance to be {ital f}{sup 2}. In the mixed state, however, there is a significant increase in {ital R}{sub {ital S}}, particularly at lower frequencies, causing {ital R}{sub {ital S}} to be approximately proportional to {ital f}{sup 1.2} at all measured temperatures. We show that fits of these data to models which include only a single pinning energy and a single characteristic pinning frequency are not able to explain our results. We propose that these data indicate the existence of a large number of metastable boundmore » vortex states separated by energy barriers {ital U}{sub {ital b}} whose magnitudes extend from {ital U}{sub {ital b}}{approximately}0 K to several hundred K, and that the dominant part of {ital R}{sub {ital S}} arises from vortex transitions between these states. {copyright} {ital 1996 The American Physical Society.}« less

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.

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.

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.

This work discusses new results obtained from analysis of Raman signal from isolated single wall carbon nanotubes. (1) Study of tangential (G band) modes frequency dependence on tube diameter and lineshape dependence on scattering polarization geometry shows clear observation of symmetry selection rules at the single nanotube level. Observation of E2 phonon modes indicates Raman spectra coming from cross-polarized light, i.e. from Eμv→Eμ±1c electronic transitions. (2) Study of the disorder induced (D) band and other small intensity features show strong dependence of Raman frequencies of nanotube chiral angle.

Activated carbon fibers (ACF's), already used widely as absorbent materials, are now expected to be useful as new electrical and electronic materials, for their very large specific surface areas (SSA). Chemical adsorption as well as x-ray diffraction have been mainly used for characterizing the ACF structure. While TEM observations reveal the texture of ACF's, such observations have not yet yielded quantitative information about the microstructure. To promote the quantitative interpretation of the TEM images, computer image analysis is used in this work to clarify the pore structure of ACF's. The microstructures of three samples, which are all isotropic pitch-based ACF's but with different SSA values, have been investigated. Operations such as noise reduction, low frequency cut-off filtering, and binary image formation are used to clarify the pore images of the ACF's. The distribution of the ACF porosity size is clearly shown by a frequency analysis of the two-dimensional fast Fourier transform (FFT). The results suggest that TEM images include contributions from many different pore sizes. Pores in different size ranges are extracted by the inverse FFT (IFFT) operation by selecting the specific frequency range, and by-this analysis the pore structure is shown to have fractal characteristics.

We review results obtained from our laboratory regarding the optical properties of C 60 - and C 70 -based thin solid films, including alkali metal (M) doped compounds. The films were deposited on various substrates (e.g. KBr, Si(100), quartz, Cu) by vacuum sublimation. First- and higher-order IR and Raman spectroscopies were used to determine values for most of the 46 intra-molecular vibrational modes of the pristine solid, and the results are compared with theory. Doping (M)-induced shifts and splittings of these mode frequencies are also discussed. Finally, results of UV-visible-IR reflection-transmission spectroscopies and ellipsometry are presented which reveal structure in the dielectric function due to electronic absorption. For pristine C 60 , the Clausius-Mossotti relation is used to extract the frequency-dependent molecular polarizability. Results from these studies of the electronic contribution to the optical dielectric function are discussed in connection with recent calculations.

The optical absorption (OA) and photoluminescence (PL) spectra of pristine, oxygen-free ${\mathrm{C}}_{60}$ films in the vicinity of the absorption edge across the highest-occupied-molecular-orbital to lowest-unoccupied-molecular-orbital (HOMO-LUMO) gap are studied to elucidate the nature of these electronic states. Structures observed in both the OA and PL spectra are identified with Herzberg-Teller vibronic coupling of the respective singlet electronic states to intramolecular vibrational modes. Similarities and differences among the PL and OA spectra of ${\mathrm{C}}_{60}$ in solution, solid films, and single crystals are discussed. The larger linewidth of the ${\mathrm{C}}_{60}$ film spectra is attributed to the presence of defects, presumably associated with numerous grain boundaries. Finally, the OA and PL spectra of photopolymerized ${\mathrm{C}}_{60}$ solid films are presented. The features in both the OA and PL spectra are observed to broaden considerably. In addition, two of the OA bands blueshift slightly (400--800 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$) and the PL features downshift by \ensuremath{\sim}330 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ upon polymerization. These results are consistent with the intermolecular oligomerization bond disorder and reduced symmetry of the ${\mathrm{C}}_{60}$ shell imposed by the covalent bonds between ${\mathrm{C}}_{60}$ molecules in the polymeric phase.

The fundamental relations governing the geometry of carbon nanotubes are reviewed, and explicit examples are presented. A framework is given for the symmetry properties of carbon nanotubes for both symmorphic and non-symmorphic tubules which have screw-axis symmetry. The implications of symmetry on the vibrational and electronic structure of 1D carbon nanotube systems are considered. The corresponding properties of double-wall nanotubes and arrays of nanotubes are also discussed.

The vibrational properties of oxygen-free C60 films indicate the nearly ideal molecular nature of solid C60. Numerous sharp Raman lines (∼98) and infrared lines (∼98) were observed and assigned to first-order modes, or combination and overtone intramolecular mode frequencies of C60. Analysis of these vibrational modes yields a complete, self-consistent set of the 46 fundamental intramolecular mode frequenciesof a C60 molecule. Irradiation of oxygen-free C60 films with visible or ultraviolet light phototransformed C60 to a new polymeric phase. We present experimental evidence which suggests the formation of covalent C-C bonds between C60 molecules in the polymeric phase. Furthermore, the rate for thermal dissociation of these intermolecular bonds is found to follow an Arrhenius' type behavior with an activation energy Ea = 1.25 eV. Our experimental results will also be compared to recent thcoretical calculations and connected with the photophysical bchavior of C60.

The infrared absorption intensity of a C 70 molecule is calculated by a semi-empirical molecular orbital calculation library, mopac93. Geometrical optimization for C 70 is obtained by the MNDO and PM3 methods. The calculated molecular vibration frequencies of C 70 at the optimized geometry are shifted to higher frequency by about 15.5% compared with the experimental result. The calculated result of the infrared absorption intensity shows that there are only 17 modes which have a large intensity among the 31 infrared-active modes predicted by group theory. A comparison of the intensities of the infrared absorption spectra between theory and experiment is satisfactory.

Hindered rotation is combined with the vibrations of a C[sub 60] molecule and is discussed in the context of icosahedral symmetry. A large difference is predicted for the occurrence of vibrations and rotations between a pure [sup 12]C[sub 60] molecular solid and a solid containing molecules with the [sup 13]C isotope.

We report measurements of the surface impedance ${\mathit{Z}}_{\mathit{s}}$=${\mathit{R}}_{\mathit{s}}$+i\ensuremath{\omega}\ensuremath{\lambda}' of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ thin films in an externally applied dc magnetic field B (parallel to the c axis) using a stripline resonator. At T=4.3 K we obtain the surface resistance ${\mathit{R}}_{\mathit{s}}$ and the microwave penetration depth \ensuremath{\lambda}' as a function of applied dc field up to 5 T and as a function of microwave frequency f from 1.2 to 20 GHz. While \ensuremath{\lambda}' increases linearly with B for Bg1 T at all frequencies, ${\mathit{R}}_{\mathit{s}}$ is found to be roughly \ensuremath{\propto}${\mathit{B}}^{\mathrm{\ensuremath{\alpha}}(\mathit{f})}$, where \ensuremath{\alpha}(f)1 for f\ensuremath{\le}10 GHz and \ensuremath{\alpha}(f)\ensuremath{\approxeq}1 for f\ensuremath{\ge}10 GHz. In zero dc field, ${\mathit{R}}_{\mathit{s}}$\ensuremath{\propto}${\mathit{f}}^{2}$. For Bg1 T, ${\mathit{R}}_{\mathit{s}}$ shows a much weaker dependence on f. The results for ${\mathit{Z}}_{\mathit{s}}$(f,T,B) have been quantitatively explained using a model developed by Coffey and Clem, based on a self-consistent treatment of vortex dynamics that includes the influence of vortex pinning, viscous drag, and flux creep. The pinning force constant ${\mathrm{\ensuremath{\alpha}}}_{\mathit{p}}$, the pinning frequency ${\mathrm{\ensuremath{\omega}}}_{\mathit{p}}$, and the pinning activation energy ${\mathit{U}}_{0}$(T,B) are obtained through the fitting procedure. We find that the effects of thermally activated flux creep at 4.3 K upon the surface resistance are significant. The low ${\mathit{U}}_{0}$\ensuremath{\approxeq}35 K that we determine is interpreted as arising from the interaction of the vortex lattice with a dense random pinning potential as described in the collective-pinning theory.

The symmetry properties of chiral monolayered carbon nanotubes, along with the method of zone-folding, are used to study their electronic and lattice properties. The energy bands and phonon modes are classified according to the irreducible representations of the 1D periodicity of the chiral nanotubes.

Transport properties of K x C 70 thin films doped to their maximum conductivity are studied. At this doping level, K x C 70 (nominally K 4 C 70 ) is characteristic of a disordered metal with roomtemperature conductivity close to 600 S/cm. The conduction bandwidth is estimated as 0.5-0.6 eV. The thermopower and magnetoconductance data are similar to those of K 3 C 60 and intercalated carbon materials. No superconducting transition is observed above 1.35 K

Carbonaceous material including nanoscale soot, carbon-coated nanoscale Co particles and nanotubes have been generated from a dc arc discharge between carbon electrodes. Sharp first- and second-order lines are observed in the Raman scattering spectra of the arc-derived carbons only when Co metal is present in the core of the anode. The sharp lines in the Raman spectrum of the Co-catalyzed, arc-derived carbons have not been observed previously in carbonaceous materials and are tentatively assigned to carbon nanotubes on the basis of a zone-folded model for the vibrational spectra of armchair tubules.

Since the start of this decade (the 1990's), intercalation has become a more important tool for modifying the structure and properties of host materials, both because of the important new systems to which intercalation has been applied and because of the new science and technology that has been made possible by these discoveries. Recently, the intercalation of fullerenes by alkali metals have demonstrated intercalation in zero-dimensional systems. The observation of relatively high Tc superconductivity in certain alkali metal intercalated fullerenes has attracted much attention. Even more recent is the introduction of guest species into one-dimensional carbon nanotubules. Intercalation has also been used to gain insights into the properties of high Tc cuprates. A review is given here of recent advances in the intercalation of GICs and of new materials systems with particular relevance to the implication of this work on more traditional areas of intercalation physics.

A thermodynamic model of the rotational phase transition in solid ${\mathrm{C}}_{60}$ is presented. The phase transition which appears at 257 K is a first-order phase transition in which a competition occurs between entropy gain by rotation and energy gain by intermolecular attraction. The anomaly in the specific heat, and the entropy and enthalpy changes observed at the critical temperature are well reproduced in the present numerical results.

The double resonance Raman spectra of the overtone of the out-of-plane tangential optical (oTO) phonon and of combinations of the LO, ZO, and ZA phonons with one another are calculated for bilayer graphene. In the case of the bilayer graphene, these Raman peaks are observed in the energy region between $1600$ and $1800$ cm${}^{\ensuremath{-}1}$. We obtain results for both the fixed $q=0$ and the dispersive $q=2k$ peaks of the overtones of the oTO phonon of bilayer graphene. We calculate the double resonance Raman spectra of the combination modes coming from the LO, iTO, LA, and iTA phonons in bilayer graphene. The calculated Raman peaks are compared with the experimental results.

From the basic physical concepts relating to the Raman spectra of graphene, we can develop characterization methods for point defects and the edge structure. Furthermore, the Fermi energy can be studied by the phonon softening phenomena of the Raman spectra. Finally, we also discuss recent progress on near-field optics.

The Raman spectra of pristine ${\mathrm{C}}_{70}$ films and ${\mathrm{K}}_{\mathit{x}}$${\mathrm{C}}_{70}$ doped to the maximum-conductivity phase (nominally ${\mathrm{K}}_{4}$${\mathrm{C}}_{70}$) are studied. All the Raman modes for ${\mathrm{C}}_{70}$ are only moderately broadened upon K doping, distinctively different from the superconducting ${\mathrm{K}}_{3}$${\mathrm{C}}_{60}$ where several ${\mathit{H}}_{\mathit{g}}$ modes are broadened to the extent that they have almost disappeared from the spectrum. Assuming that the electron-phonon interaction is responsible for the broadening, the electron-phonon coupling strength is found to be comparable to the Coulomb repulsion. These results are important for understanding the absence of superconductivity in ${\mathrm{K}}_{\mathit{x}}$${\mathrm{C}}_{70}$.

An expression for the electron-phonon coupling strength in fullerene nanotubules is derived within the tight-binding model. It is shown that the interaction of electrons with longitudinal acoustic phonons gives rise to intraband scattering but not to interband scattering; the reverse is true for interaction of electrons with transverse phonons in the tangential direction. It is estimated that under ideal circumstances, the electrical conductivity of metallic fullerene nanotubules could be more than an order of magnitude larger than that of copper.

Transport properties of ${\mathrm{K}}_{\mathit{x}}$${\mathrm{C}}_{70}$ thin films doped to their maximum conductivity are studied. At this doping level ${\mathrm{K}}_{\mathit{x}}$${\mathrm{C}}_{70}$ (nominally ${\mathrm{K}}_{4}$${\mathrm{C}}_{70}$) is characteristic of a disordered metal with room-temperature conductivity close to 600 S/cm. The conduction bandwidth is estimated as 0.5--0.6 eV. The thermopower and magnetoconductance data are similar to those of ${\mathrm{K}}_{3}$${\mathrm{C}}_{60}$ and intercalated carbon materials. No superconducting transition is observed above 1.35 K.

Temperature (T) -dependent Raman scattering from ${\mathrm{C}}_{60}^{3\mathrm{\ensuremath{-}}}$ intramolecular modes and simultaneous electrical resistivity measurements were made on ${\mathrm{Rb}}_{3}$${\mathrm{C}}_{60}$ films which exhibited a superconducting transition temperature ${\mathit{T}}_{\mathit{c}}$=28 K. ${\mathrm{K}}_{3}$${\mathrm{C}}_{60}$ films were studied for comparison, but at T=300 K only. Weak, or no T dependence in the intramolecular modes is observed through ${\mathit{T}}_{\mathit{c}}$, consistent with the fact that the mode frequencies \ensuremath{\omega}g2\ensuremath{\Delta} (superconducting gap). By comparing the linewidths of the modes in ${\mathit{M}}_{3}$${\mathrm{C}}_{60}$ to values in pristine ${\mathit{C}}_{60}$ we have estimated their contributions to the electron-phonon coupling constant \ensuremath{\lambda}. Values of \ensuremath{\lambda} have been found to be 0.6 and 0.5 for ${\mathrm{K}}_{3}$${\mathrm{C}}_{60}$ and ${\mathrm{Rb}}_{3}$${\mathrm{C}}_{60}$, respectively, in good agreement with the theoretical value \ensuremath{\lambda}=0.6 obtained previously by Schl\"uter and co-workers. The ${\mathit{H}}_{\mathit{g}}$(2)-derived mode is found to make the dominant contribution to \ensuremath{\lambda}. A line-shape analysis of the ${\mathit{H}}_{\mathit{g}}$(1)-derived mode suggests that this mode is a Breit-Wigner-Fano resonance. The radial ${\mathit{A}}_{\mathit{g}}$(1)-derived mode linewidth in ${\mathrm{Rb}}_{3}$${\mathrm{C}}_{60}$ is anomalously narrow (\ensuremath{\sim}0.1 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$), and found to be very sensitive to sample quality, i.e., strongly correlated with the width of the superconducting transition.

We present measurements of the surface impedance as a function of frequency (1--17 GHz), temperature (4.2--91 K), and peak rf magnetic field (0${\mathit{H}}_{\mathrm{rf}}$500 Oe) for high-quality epitaxial ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathit{x}}$ thin films using a stripline-resonator technique. The lowest surface resistance at 1.5 GHz was 15 \ensuremath{\mu}\ensuremath{\Omega} at 77 K and 3 \ensuremath{\mu}\ensuremath{\Omega} at 4.3 K. The results for the low- and intermediate-field regions (${\mathit{H}}_{\mathrm{rf}}$50 Oe at 77 K) are explained by a coupled-grain model, which treats the film as a network of superconducting grains connected by grain boundaries acting as resistively shunted Josephson junctions. Quantitative agreement has been obtained between the model and the measurements. The effective junction critical current density, grain size, and shunt resistance are used in the model to characterize the films. The high-field region may be explained by flux penetration into the grains but is not modeled in detail here.