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A comparative photoemission study on RbxC60, RbxC70 and RbC8 (graphite intercalation compound) is reported. It was found that the Fermi level of Rb3C60 is located at the bottom of a valley of the density of states, while that of RbC8 is at a maximum point of the occupied states. This experimental result is explained in terms of the existence of a pseudo-gap at the Fermi level in the fulleride. This indicates that a rigid-band picture is not a good starting point for understanding the change of the electronic structure upon the alkaline-doping. It was also found that the density of states at the Fermi level is much smaller in RbxC70 than in RbxC60. This accounts for the less conductive nature and the absence of superconductivity in RbxC70.

We present a Raman scattering study of pristine and K doped C 60 at various doping levels by exciting in the near-IR at 1.16 eV. The normal metallic state of K 3 C 60 is characterized by a broad scattering background and by the resonance of low energy phonons in the range of 250–500 cm −1 . We assign the broad background to an electronic Raman scattering due to low energy electronic excitations. This spectral feature is indicative of an anomalous normal state behaviour and is similar to the case of high temperature ceramic superconductors. In the overdoped K 6 C 60 the squashing mode at 278 cm −1 shows a Fano resonance with the electronic scattering associated with localized electronic excitations which are characteristic of isolated regions of K 3 C 60 into the matrix of K 6 C 60 as a result of inhomogeneous doping. The Fano resonance indicates a specific electron-phonon coupling of this Jahn-Teller mode with low energy excitations and suggests that the symmetry of this electronic excitation is h g (i.e. the same of the coupled phonon mode). We discuss the nature of the anomalous electronic Raman scattering in terms of scattering from low energy excitations involving a low lying singlet band resulting from electron correlation and/or dynamical J-T distortion caused by the squashing mode.

We present 13 C-NMR investigation on CS 2 -grown crystal and benzene- grown crystal between 300K and 77K at 6.1T. The spin-lattice relaxation time T 1 and the NMR linewidth demonstrate molecular rotation in both of the crystals. It is assigned that a relaxation mechanism of T 1 is due to an anisotropic chemical shift modulated by the molecular rotation. The observed NMR shift, 142.9±0.8 ppm from TMS in both of the crystals, is close to those reported previously in solid C 60 ⧸C 70 mixture and solution. It was also suggested that a high temperature heat treatment may change the microscopic surrounding of C 60 in CS 2 -grown crystals irreversibly.

Electronic states of K 2p and C 1s core levels and valence bands for K χ C 60 ( χ =0≈6.3) have been studied by X-ray photoelectron spectroscopy (XPS). We find two different chemical states of potassium with binding energy 293.8 and 294.9 eV. The K 2p 3 2 line becomes a single peak at χ = 6.3. These results are discussed in terms of the sites occupied by K in K χ C 60 . The C 1s line (285.1 eV) for C 60 is shifted by 0.3 eV to the side of higher binding energy by a very small amount of K, which is consistent with the shift of the valence band. The other line at 284.4 eV appears at 10 min evaporation (χ = 0.8). The intensity of the former is reduced and that of the latter increases with the evaporation time.

New kinds of fullerenes were separated by HPLC with benzene from carbon soot. At least four fractions were well separated. Mass analysis confirmed the separation of C60, C70, C84 and the mixture of C76 and C78. Absorption spectra of C76, C78, and C84 were measured for the first time.

Two-photon transitions A 2 Σ + (ν′ = 0)-X 2 Π(ν″ = 0) of nitric oxide are investigated by high-resolution resonance-enhanced multiphoton ionization spectroscopy. The underlying causes behind observed anomalous intensity features of these two-photon transitions are discussed. Several new lines produced by the three-photon transitions “L 2 Π(ν = 4)-C 2 Π(ν = 6)” -X 2 Π(ν″ = 0) and K 2 Π(ν = 1) -X 2 Π(ν″ = 0) are assigned. The values for T ν and B ν of the K 2 Π(ν = 1) state are determi 66350 cm −1 has been resolved. It is suggested that several lines with anomalous intensity on the O 12 branch of the A 2 Σ + (ν′ = band should be interpreted as the result of an autoionization process rather than as the result of an accidental resonance of a third photon with rotational levels of the “L 2 Π(ν = 4)-C 2 Π(ν = 6) state as previously has been anticipated.

A detailed three-dimensional structural analysis of single-walled carbon nanotubes was carried out using a scanning tunneling microscope (STM) operated at room temperature in ambient conditions. On a microscopic scale, the images show tubes condensed in ropes as well as tubes which are separated from each other. For a single-wall nanotube rope, the outer portion is composed of highly oriented nanotubes with nearly uniform diameter and chirality. On separated nanotubes, atomically resolved images show variable chirality ranges between 0°–30°, and variable diameter (1–3 nm), with no one type dominant. From STM and scanning tunneling spectroscopy measurements we confirmed the correlation between chirality and the electronic properties, namely the tuning from metallic to semiconducting. We also observed a rectifying behavior correlated with the chiral angle of 25°, an important observation for nanodevices application.

The mass distribution of neutral carbon clusters generated by a laser vaporization of graphite in He was safely determined by a single photon (10.5 eV) ionization technique. The resulting mass distribution was surprisingly different from those reported in previous articles. It was found that the carbon clusters generated under a moderate laser fluence condition (0.1–1 J/cm2) consists of mostly even-numbered monocyclic rings with the cluster sizes of n=10–18. The formation mechanism of such neutral carbon clusters upon laser irradiation is discussed.

We report on the magneto‐optical properties of aligned single‐walled carbon nanotubes in polymer. With appling magnetic fields parallel to the aligned tube axis, the optical absorption spectra significantly change. The observed spectral change is explained by the magnetic‐field‐induced band splitting. The physical origin of energy splitting is discussed in relation to Aharanov‐Bohm and Zeeman effects.

Pristine single-wall carbon nanotubes (SWCNT's) filled with C 6 0 are investigated with resonance Raman spectroscopy. Both totally symmetric modes of C 6 0 exhibit a surprising splitting into two components with a slightly different resonance behavior and an apparent loss of polarization. The latter can be understood from a symmetry reduction of the fullerene molecules in the center of the tubes and/or by an anisotropy of the electric field seen by the C 6 0 peas inside the SWCNT pods due to depolarization effects. The splitting is explained from molecular-dynamics simulations which show that the two bands emerge from a coupling of the C 6 0 totally symmetric modes to the fullerene translational mobility inside the tube. The doublet is thus the spectroscopic fingerprint of different mobilities of C 6 0 fullerenes in the tubes.

Double wall carbon nanotubes were prepared by vacuum annealing of single wall carbon nanotubes filled with ${\mathrm{C}}_{60}$. Strong evidence is provided for a highly defect free and unperturbed environment in the interior of the tubes. This is concluded from unusual narrow Raman lines for the radial breathing mode of the inner tubes. Lorentzian linewidths scale down to $0.35\text{ }{\mathrm{c}\mathrm{m}}^{\ensuremath{-}1}$ which is almost $10$ times smaller than linewidths reported so far for this mode. A splitting is observed for the majority of the Raman lines. It is considered to originate from tube-tube interaction between one inner tube and several different outer tubes. The highest RBM frequency detected is $484\text{ }\mathrm{c}{\mathrm{m}}^{\mathrm{\ensuremath{-}}\mathrm{1}}$ corresponding to a tube diameter of only $0.50\text{ }\mathrm{n}\mathrm{m}$. Labeling of the Raman lines with the folding vector is provided for all inner tubes. This labeling is supported by density functional calculations.

We report on the doping dependence of so-called peapods where C 6 0 is encapsulated inside single-wall carbon nanotubes (SWCNT's) using Raman spectroscopy as probe. The charge transfer in intercalated C 6 0 peapods is analyzed as a function of doping with FeCl 3 (p type) and potassium (n type). A competition between a charge transfer to the SWCNT pods and to the C 6 0 peas is observed. At low intercalation levels, the charge transfer is predominantly to the SWCNT pods. The Fermi level shifts beyond the second van Hove singularity of the semiconducting tubes and below the first singularity of the metallic tubes, respectively. The doping of the valence band for FeCl 3 intercalation (p doping) and of the conduction band for K intercalation (n type) is symmetric. At high levels of potassium intercalation, the Fermi level shifts beyond the third singularity of the semiconducting tubes and the C 6 0 molecules are charged as well finally yielding a C 6 0 6- state that forms a one-dimensional metallic single-bonded C 6 0 polymer. For intermediate charging levels of the C 6 0 molecules, no line phases are observed in contrast to the fullerides. Rather, a quasicontinuous charge transfer is observed. This provides a unique procedure to establish a continuous charge transfer to C 6 0 by intercalation.

We present an ultra-fast saturable absorber device based on single-walled carbon nanotubes. The saturable absorbing effect was observed using 1 ps optical pulses at 80 GHz. This device possesses promising characteristics for applications such as a noise suppressor or a mode-locker.

We have performed the valence‐band photoemission spectroscopy on single‐wall carbon nanotubes. Characteristic peak structures originated from one‐dimensional van Hove singularities have been successfully observed. The peak structures are well reproduced by the calculation based on the tight‐binding model taking into account a diameter distribution of nanotubes.

By annealing fullerene peapods at high temperatures in a dynamic vacuum it is possible to produce double wall carbon nanotubes (DWCNTs). A Raman investigation revealed that the inner SWCNTs are remarkably defect free showing very strong and very narrow radial breathing modes (RBMs). Lorentzian line widths scale down to about 0.35cm−1 which is almost 10 times smaller than reported for single tubes so far. Also, the scattering intensities for the inner RBMs can be more than 10 times higher than those for the outer RBMs. Additionally, all radial modes of the inner tubes are split into at least two components.

Although the diameter dispersion of the phonons composing the Raman G‐band of single wall carbon nanotubes (SWCNTs) is well understood theoretically, systematic experimental studies on the subject are scarce. We investigated 6 different diameter samples between d=1.05−1.57 nm with several excitation lasers and used artificial neural networks (ANN) to explore if there is a connection between the fine structure of the G‐band and the sample diameter. An initial screening by a Kohonen self‐organizing map revealed that ANN technology is able to identify spectra measured on the same sample. Based on this result several supervised learning algorithms were tested and finally we succeeded in building a resilient propagation ANN with one hidden layer which is able to predict the diameter distribution of a macroscopic SWCNT sample from the structure of its Raman G‐band with acceptable accuracy. We suggest that with more extensive calibration this method could be developed into a useful auxiliary technique of SWCNT characterization.

We report a detailed analysis of the optical properties of single wall carbon nanotubes with different mean diameters as produced by laser ablation. From a combined study of optical absorption, high resolution electron energy-loss spectroscopy in transmission and tight binding calculations we were able to accurately determine the mean diameter and diameter distribution in bulk SWCNT samples. In general, the absorption response can be well described assuming a Gaussian distribution of nanotube diameters and the predicted inverse proportionality between the nanotube diameter and the energy of the absorption features. A detailed simulation enabled not only a determination of the mean diameter of the nanotubes, but also gives insight into the chirality distribution of the nanotubes. The best agreement between the simulation and experiment is observed when only nanotubes within 15$^\circ$ of the armchair axis are considered. The mean diameters and diameter distributions from the optical simulations are in very good agreement with the values derived from other bulk sensitive methods such as electron diffraction, x-ray diffraction and Raman scattering., 9 figures

We report recent measurements of the electronic and structural properties of bulk samples of ${\mathrm{C}}_{60}$ molecules encapsulated in single-wall carbon nanotubes (so-called peapods) using electron-energy-loss spectroscopy in transmission. We demonstrate that ${\mathrm{C}}_{60}$ peapods with a single-wall carbon nanotube (SWNT) diameter distribution of $1.37\ifmmode\pm\else\textpm\fi{}0.08 \mathrm{nm}$ have an average fullerene filling of 60%. Regarding the electronic and optical properties, the overall shape of the response of the SWNT and the peapods is very similar, but with distinct differences in the fine structure. The interband transitions of the SWNT are slightly downshifted in the peapods, which can be explained by either a small increase of the SWNT diameter or by a change of the intertube interaction. The electronic and optical properties of the encapsulated ${\mathrm{C}}_{60}$ peas closely resemble those of solid fcc ${\mathrm{C}}_{60}$ showing small changes in the relative intensities, peak positions, and peak width, which point to a weak van der Waals interaction between the tubes and the encapsulated fullerenes.

We report on the charge transfer in intercalated C60 peapods as a function of doping. A competition between a charge transfer to the SWCNT pods and one to the C60 peas is observed. At low intercalation levels the charge transfer is predominantly to the SWCNT pods. This leads to a shift of the Fermi level beyond the third van Hove singularity of the semiconducting tubes for potassium intercalation (n‐doping) and beyond the first singularity of the metallic tubes for FeCl3 intercalation (p‐doping), respectively. In addition at high levels of potassium intercalation the C60 pods are charged up to C606− and form a metallic one dimensional polymer.

Photoconducting and local transport properties of single‐wall carbon nanotubes (SWNTs) have been investigated. Two peaks in the photoconductivity excitation spectra around 0.7 and 1.2 eV are observed at room temperature, which can be interpreted as a photocurrent in semiconducting SWNTs. From the local transport measurements on SWNT bundles by the combination of atomic force microscopy and scanning tunneling spectroscopy, we find current flows through each SWNT separately rather than uniformly in the bundle. The results show that we can extract the transport properties of semiconducting or metallic SWNTs from the mixture of both phases by photoconductivity measurements and the local transport measurements.

The 129I-Mossbauer spectroscopy was applied to the iodine-doped single-walled carbon nanotubes (SWNTs) in the region of heavy and medium doping. Two kinds of SWNTs with different synthesis methods were used as samples. For both samples, the iodine in SWNTs in these doping levels was proved to work as electron acceptors in the forms of triiodides (I 3 − ) and pentaiodides (I 5 − ) and to exist as iodine molecules (I2) in addition. Moreover, monoiodide ions (I−) appear additionally. As the doping level decreases, the proportions of triiodide and monoiodide ions increase, whereas those of pentaiodide ions and iodine molecules decrease. This tendency is in common for both kinds of SWNTs. However, the charge distribution of iodides and the ratios of iodine forms are a little different between two kinds of SWNTs, probably because of difference in morphology and remaining catalysts.

It was found by photoemission and inverse photoemission that an energy gap with a finite density of states at the bottom (a pseudo-gap) opens at the Fermi level for alkali-doped solid C 60 at the composition A 3 C 60 (A = alkali metal). Strong electron correlation and lattice distortions (Jahn-Teller effect) are discussed as possible origins for the pseudo-gap.

Electrical transport properties of alkali metal-doped C 60 solids were studied. Single crystals obtained from a CS 2 solution show a metallic temperature dependence of the resistivity from room temperature to superconducting transition temperatures T c for samples optimally doped with potassium or rubidium. The thermoelectric power of potassium- or rubidium-doped crystals has a negative value and shows metallic behavior in the temperature range T c -300 K. Based on this result we estimate the Fermi energy EF to be 0.30-0.35 eV for a potassium doped crystal and 0.19-0.20 eV for a rubidium-doped crystal, assuming a three-dimensional free electron model

A hypothetical ring-stacking procedure combined with the isolated-pentagon rule(IPR) shows variety of formation pathways of many fullerene structures with a 5- and 6-membered ring carbon cage. Combining the ring-stacking procedure with energetic considerations, the numbers of possible reaction channels are dramatically reduced within the framework of the ring-stacking considerations. This, in turn, gives the results that only some specific isomers of large fullerenes are selectively produced. The resulting fullerene structures specified are surprisingly well consistent with the recent experimental results.

A simple threshold electron analyzer was constructed and laser photodetachment threshold electron spectra of Si− and Si4− were measured.

X-ray diffraction studies of an orthorhombic C 60 single crystal grown from CS 2 solution have revealed a phase transition to a monoclinic phase between 1.1 and 2.2GPa. Compressibility of three principal axes is measured up to 3GPa and found to be nearly isotropic. Its bulk modulus is obtained as 10.5±1.9GPa, and this crystal is more compressible than an fcc one. We discuss the structural characteristic differences under pressure between the orthorhombic crystal and the fcc crystal.

Doping induced polymerization of ${\mathrm{C}}_{60}$ inside single-walled carbon nanotubes is reported using Raman spectroscopy and resistivity measurements as a probe. The resistivity changes from semiconducting for the undoped system to metallic for the doped system. For full intercalation, we observe a chemical reaction inside the nanotubes which leads to a one-dimensional polymeric ${\mathrm{C}}_{60}^{\ensuremath{-}6}$ chain which has metallic character. The resonance and the oscillations of the radial breathing mode are lost suggesting an up-shift of the Fermi level to beyond the third Van Hove singularity in the semiconducting tubes. The linewidth of the radial breathing mode now represents directly the Gaussian distribution of tube diameters.

Dissociative ionization of highly charged ${\mathrm{CS}}_{2}^{q+}$ $(q=3--10)$ molecular ions produced in collisions of ${\mathrm{CS}}_{2}$ with ${\mathrm{Ar}}^{8+}$ ions is studied at 120 keV energy. Triple coincidence techniques have been applied to measure the velocity components of all three ionic fragments produced in the fragmentation process. The velocity measurements have been used to deduce the total kinetic energy released (KER) in the fragmentation of the molecular ion for each particular product channel. KER values were found to be similar to those predicted by a pure Coulomb explosion model, revealing the apparent unimportance of binding electronic interactions in highly charged, multielectron molecular systems. The propensity of fragmentation into symmetric and asymmetric channels depends only on energetics, with the most exothermic channel being favored. The velocity vectors of the ion fragments yield information on ion structure prior to fragmentation; results indicate that the ionization is impulsive and fragmentation is simultaneous.

Doping induced polymerization of C(60) inside single-walled carbon nanotubes is reported using Raman spectroscopy and resistivity measurements as a probe. The resistivity changes from semiconducting for the undoped system to metallic for the doped system. For full intercalation, we observe a chemical reaction inside the nanotubes which leads to a one-dimensional polymeric C(60)(-6) chain which has metallic character. The resonance and the oscillations of the radial breathing mode are lost suggesting an up-shift of the Fermi level to beyond the third Van Hove singularity in the semiconducting tubes. The linewidth of the radial breathing mode now represents directly the Gaussian distribution of tube diameters.

Single-wall carbon nanotubes (SWNTs) encapsulating fullerenes, so-called fullerene-peapods, were synthesized in high yield. High-resolution transmission electron microscopy revealed that almost all nanotubes are filled with high-density fullerene chains. We measured Raman spectra of C60- and C70-peapods. In the case of C60-peapods, C60 Raman active mode intensity decreased rapidly by laser irradiation at room temperature. The final spectrum is similar to that of orthorhombic polymer phase, which indicates one-dimensional photopolymerization. At liquid helium temperature, no photopolymerization was observed, and the Raman spectra obtained indicates a feature of C60-dimer phase. Furthermore, C60-C60 distance estimated from electron diffraction pattern measured at room temperature is consistent with C60-dimer phase. The spontaneous dimerization should be explained in part by internal high-pressure effect.

Raman spectroscopy provides a unique opportunity to investigate the intercalation process of alkali metals into single walled carbon nanotubes (SWNT). Particularly, E2g mode, which is characteristic of the graphene sheet, is highly informative on the intercalation processes. X-ray photoemission spectroscopy, on the other hand, is useful for determining the atomic ratio of K and C. The depth profile of K/C ratio determined by an Ar+ sputtering technique yields a reliable bulk stoichiometry of the sample. Combing the above information, a structural model is presented for a doped SWNT ropes.

Single-wall carbon nanotubes (SWNTs) encapsulating fullerenes, so-called fullerene-peapods, were synthesized in high yield by using diameter-selected nanotubes as pods. High-resolution transmission electron microscopy revealed high-density fullerene chains inside nanotubes. X-ray diffraction measurements indicate 60% filling of C 60 molecules in a macroscopic average. Room temperature Raman spectra show one-dimensional photopolymerization of C 60 inside nanotubes by blue laser irradiation, indicating molecular rotation inside. In C 70 -peapod case, Raman active modes peculiar to C 70 were strongly suppressed by encapsulation. The suppression is probably caused by deformation of molecule due to the anisotropic interaction between C 70 and SWNT. Anomalous resonance effects in C 70 -peas suggest hybridization of electronic states of C 70 and nanotubes. High-symmetry mode Raman intensity suggests the filling factor to be higher than 50%, which is consistent with the X ray diffraction analysis.

Time and space evolution of carbon species generated with a laser furnace apparatus was investigated using a high-speed video camera and an ICCD system combined with a laser-induced emission technique. It was found that the blackbody emission intensity increased at Δt>400 μ sec after laser vaporization of graphite rod under high ambient temperature condition, where fullerene formation was most favored. Additionally, a tunable light from an OPO laser was introduced in order to excite C2 (a3Πu) with a certain delay after laser vaporization of graphite target, and it was found that the amount of C2 (a3Πu) also increased at Δt>400 μ sec under high ambient temperature condition. These findings suggest that there exists some exothermic process related to the formation of fullerene species at Δt>400 μ sec after laser vaporization of graphite target.

Photoselective resonance Raman scattering is well known for C60 and pristine SWNTs and has been extensively studied. In this contribution we present a detailed study of the photoselective resonance Raman scattering for C60 encapsulated in single wall carbon nanotubes (SWNTs), so-called C60 peapods, when excited with 13 different laser lines. For the Ag(2) pinch mode of C60, which is most sensitive to resonance scattering, we observe a downshift of the main Raman resonance energy to lower energy. Interestingly a second component has an additional resonance in the optical gap of C60 at around 1.8 eV. The resonance scattering of the SWNT radial breathing mode (RBM) and G-line are only slightly changed compared to the pristine SWNT reference.

We report studies of the electronic structure and optical properties of single wall carbon nanotubes (SWNT) using high resolution electron energy-loss spectroscopy in transmission. We present new results of the dependence of the interband transition and π plasmon dispersion on the SWNT diameter as well as on the SWNT orientation. For the SWNT filled with C60 (so-called peapods) we are able to derive the bulk filling factor from an analysis of the C1s absorption edge.

The authors report the results of low energy (0-1 keV) collisions of negatively charged carbon clusters C{sub n} (n=2-18) with MoS{sub 2} solid surfaces, where what was observed was the electron emission. These carbon clusters represent several isometric structures. They observe two types of emission. One is related simply to the incident kinetic energy of the cluster ions. The second evidences narrow peaks, present for collisions of less than 100eV, and for only certain types of cluster.

Soft x-ray absorption and emission spectroscopy is being used to study and compare the electronic structure of (a) potassium doped single wall carbon nanotubes (interstitial dopant), (b) La@C82 (endohedral dopant) and (c) (C59N)2 (on-cage dopant).

The electronic properties of semiconducting (S) and metallic (M) single-wall carbon nanotube (SWCNT) films were modified either by chemical or electrochemical doping, while changes in their electronic structure were monitored in-situ by optical absorption spectroscopy. In both experiments the intensity of absorption features at 0.68, 1.2 and 1.8 eV were dramatically affected, demonstrating the possibility of tuning the Fermi level to specific bands in S- or M-SWCNTs.

Explosive fragmentation of highly charged molecular ions has been studied by a position sensitive time-of-flight (TOF) technique. The highly charged molecular ions of CO2, NO2, and CD4 were produced by 90–120 keV collisions of Arn+ (n=6,8). By the detailed analysis of the 3-dimensional velocity vectors of the fragment ions, molecular images at the instant of multiple ionization are “reconstructed,” which are consistent with known structure of the neutral molecules. This in turn means that the dissociation of the highly charged ions is reasonably described by the pure Coulomb explosion scheme.

Photodetachment spectra of negative carbon clusters are reported in the size range from 5 through 20 atoms. The clusters were prepared in a supersonic beam by laser vaporization and 2nd (2.3 eV) and 3rd (3.5 eV) harmonics of Nd-YAG laser were used for photodetachment. The resultant data indicate that carbon negative cluster ions in the 10–20 range take the forms of both linear chain and cyclic ring under a certain condition.

Electron emission efficiency induced by the collision of clusters with a solid surface was measured as a function of cluster size. Emitted electron energy distribution for the impact of mass selected negative ion clusters or mass selected neutral clusters was also measured in the energy region of 0–5 eV. The difference in the shape of the electron spectra was observed depending on the size and charge of the clusters.

Multi-walled carbon nanotubes synthesized by the carbon arc in hydrogen gas have very thin core channels. We have measured resonance Raman scattering of some samples synthesized in different conditions, and have observed radial breathing mode (RBM) peaks from 200 to 500 cm−1. Resonance effect of each peak is similar to that of single-walled nanotube. However, the peak frequencies are about 5 % higher than those of single-walled nanotubes, which is probably due to the inter-layer interaction. Further, the highest RBM peak splits in three peaks. The result on the resonance effect and the zone-folding band calculation suggest that the thinnest core nanotube is (4,3) that have four candidates of second outer nanotubes. This suggests that the different outer nanotube gives different degree of the interlayer interaction.

Recently we have succeeded to synthesize solvent-free single crystals of endohedral metallofullerene La@C82 with the size of 0.5×0.2×0.2 mm3 for the first time. We have investigated the low temperature (T) x-ray diffraction measurements (20K–300K), and have revealed that the solvent-free La@C82 crystal takes various structured phases, that is, (I) the face-centered cubic (fcc) phase (300K–180K), (II) the rhombohedral phase (180K–140K), (III) the triclinic phase (140K–20K) and (IV) the simple cubic (sc) phase (132K–20K). The rhombohedral and triclinic phases are characterized by the C82-cage orientational order, and the sc phase is characterized by the molecular electric dipole order, and in the fcc phase both are not in order. As for the two lowest-T phases, with slow cooling below 132K, the crystal remains in the triclinic phase. On the other hand with rapid cooling, the crystal undergoes the phase transition to the sc phase at 115K. Once the phase transition occurs, the sc phase is stable up to 132K, an...

Four kinds of single-walled carbon nanotubes (SWNTs) with different diameter distributions were synthesized using NiY, NiCo, Ni and RhPd catalysts. Optical absorption and resonance Raman spectra were measured. For all the samples, three large absorption peaks were observed from the infrared to visible region. From the band calculation, it was found that they could be explained by the optical transitions between mirror image spikes in density of states caused by the one-dimensional van Hove singularities. Lower two peaks are originating from the semiconductor phases and the third one is from the metallic phases. In the Raman spectra, indeed, broad and asymmetric Fano line shape was observed when the excitation was at the optical transition of metallic SWNTs. Preliminary results about resonance Raman scattering of multiwall carbon nanotubes that have small core diameter and of Br2 doped SWNTs are shown.

Single-wall carbon nanotubes (SWNTs) have been synthesized by laser ablation of Ni/Co catalyzed graphite target at 1200°C in argon gas. Raman spectroscopy has been used to study the effect of target position in the furnace and flow rate of argon gas on the diameter distribution of SWVNTs. It was found that yield of smaller diameter SWNTs relatively increases as target is placed away from the hot zone of the furnace. The relative yield of smaller diameter SWNTs decreases with increase in flow rate of the argon gas.