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Raman spectra of single‐walled carbon nanotubes (SWNTs) in aqueous solutions with sodium dodecylsulfate (SDS) or fragmented single‐stranded DNA (ss‐DNA) and films obtained from these solutions have been studied. Scanning electron microscope (SEM) film study shows that micelles formed by SDS molecules around SWNT in solution do not keep individual nanotubes from sticking together in bundles during drying out the film. DNA wrapped around SWNT precludes the full nanotubes sticking in the film that facilitates the following splitting of these bundles.

The switching of resistance between two discrete values, known as random telegraph noise (RTN), was observed in individual single-walled carbon nanotubes (SWNTs) and C60-filled SWNTs (the so-called peapods). The RTN has been studied as a function of bias-voltage and gate-voltage as well as temperature. By analyzing the features of the RTN, we identify three different types of RTN existing in the SWNT related systems. While the RTN can be generated by the various charge traps in the vicinity of the SWNTs, the RTN for metallic SWNTs is mainly due to reversible defect motions between two metastable states, activated by inelastic scattering with ballistic electrons. On the other hand, the noise for peapods can be attributed to the motion of C60 molecules in hollow space of SWNTs.

Raman spectra of SWNTs suspended in aqueous solutions containing fragmented single-stranded DNA (SWNT:DNA), and films obtained from this suspension have been obtained. SEM study of the dried films indicated that the nanotubes tend to aggregate into bundles which results in the enhancement of the Raman intensity of the G− tangential band, and an upshift and broadening of the G+ band. The intensity of radial breathing modes of metallic SWNTs is higher in the SWNT:DNA films as compared to that of the SWNT:DNA solution. The Raman spectra of SWNT:PVP and SWNT:agaroza samples exhibit similar changes as the SWNT:DNA samples when films are cast from the corresponding solutions. Both films and the solution forms of SWNT:DNA yield luminescence spectra which indicates the presence of individual tubes or small bundles in the films. The luminescence bands of SWNT:DNA films are relatively wider and is attributed to the interaction of DNA with the nanotube surface in the solid state.

The thermal stability of initial and purified samples of single-walled carbon nanotubes prepared through gas-phase disproportionation of carbon monoxide CO in the presence of iron particles under high pressure (the HiPCO method) is investigated using optical absorption spectroscopy and thermogravimetry. An analysis of the optical absorption spectra demonstrates that thermal oxidation of the initial material proceeds rather rapidly and uniformly owing to the catalytic effect caused by the presence of iron particles in the sample. The destruction of the carbon nanotubes contained in the as-prepared and purified samples begins at temperatures of ∼250 and ∼300°C, respectively. It is shown that single-walled metallic nanotubes undergo faster oxidation as compared to the single-walled semiconducting nanotubes.

We performed two different types of composites using single wall carbon nanotubes: 1) transparent electrodes, using a thin network of carbon nanotubes as electrode on which we can grow a conducting polymer electrochemically on it, polyaniline or polypirrole, CNT-CP; the obtained thin films are both transparent (transmission coefficient T from 70% to 95%) and electrically conducting. The samples were observed by AFM, optical and Raman spectroscopy, room temperature electrical conductivity were performed. 2) CNT with a metal, copper in our case (CNT-Cu), as a material with high electrical and thermal conductivity and low coefficient of thermal expansion (CTE), to be used in electronic packaging. We observed the samples by AFM and SEM.

Anelastic spectroscopy experiments in HiPco carbon nanotubes from room temperature to 3 K displayed a thermally activated relaxation process at about 25 K for frequencies in the kHz range. The activation energy obtained by the peak shift with frequency is E a = 635 K and reveals the presence of a very mobile species performing about 103 jumps/s at the peak temperature. The derived value of the pre-exponential factor of the Arrhenius law for the relaxation time, τ 0 = 1 0 − 14 s, is typical of point defect relaxation and suggests that the process is originated by the dynamics of hydrogen or H complexes. The peak is much broader than a single Debye-relaxation process, indicating the presence of intense elastic interactions in the highly disordered bundle structure. There are clear, but not conclusive, indications that the relaxation process is governed by a quantum mechanism.

We investigated the switching of resistance between two discrete values, known as random telegraph noise (RTN), observed in carbon nanotube peapod transistors [single‐walled carbon nanotubes (SWNTs), C60‐peapods, and Cs‐encapsulated SWNTs (so‐called Cs‐peapods)]. By analyzing the features of the RTN, we suggest that this noise for SWNTs is due to the random transition of defects between two metastable states, activated by inelastic scattering with ballistic electrons. The noise for C60‐peapods (Cs‐peapods) is attributed to the motion of C60s (Cs) in the nanotubes.

The electronic structure of purified single-wall carbon nanotubes obtained from HiPco process has been probed by X-ray fluorescent spectroscopy. The CKa spectrum of the HiPco nanotubes revealed a significant enhancement of the high-energy maximum intensity compared with the graphite spectrum. Quantum chemical calculations of carbon nanotube models show the spectral variations could be caused by vacancies in the tube walls developed with the thermal and acid treatment of the sample.

Raman spectra of HiPco SWNT and SWNT-pyrene films were measured in the 160–1800 cm−1 range. Due to the non-covalent interaction between SWNT and pyrene the most intensive component of the SWNT G mode (1590 cm−1) is downshifted by 2 cm−1 and becomes narrower. Also the intensity of the low-frequency component of the G mode (1550 cm−1) decreases by about 30%. Structures and interaction energies in the complexes of pyrene and zigzag (n, 0) SWNTs [6 ≤ n ≤ 20] were determined at the MP2 level of theory. The BSSE-free geometry optimization of the pyrene-zigzag (12,0) SWNT complex converged to a structure with a 1/2staggered conformation and with an intermolecular distance of 3.5 A. The BSSE-free interaction energy in the complex is −30.8 kj mol−1. Increasing of the nanotube diameter leads to a higher interaction energy. This energy becomes equal to −37.2 kJ mol−1 in the case of a planar carbon surface.

Hydrogen storage in new nano-structured carbonic materials is a topic for lively discussion. The measured storage capacities of these materials, which have been announced in the literature during the last ten years are spread over an enormous range from about 0.1 wt% up to 67 wt%. This paper will give a report on the state of the art of hydrogen storage in carbon nano-structures. We shall critically review the recent ‘key publications’ on this topic, which claim storage capacities clearly above the technological bench mark set by the US Department of Energy, and we shall report new results which have been obtained in a joint project sponsored by the Federal Ministry for Education and Research in Germany (BMBF). To cite this article: M. Becher et al., C. R. Physique 4 (2003).

Single-walled carbon nanotubes (SWNTs) produced by the high pressure CO disproportionation (HiPCO method) and purified by controlled thermal oxidation in air have been studied by Raman spectroscopy at 300 and 5 K. Raman spectra have been observed at λexc=632.8 and 441.6 nm laser excitation in the range of 160–1800 cm−1. In the low-frequency part of the spectra (the radial breathing mode range) eleven narrow lines can be detected at low temperatures, enabling an estimation of nanotube diameters (0.8–1.3 nm) and chirality. The width at half-maximum intensity of these spectral lines is about 3–4 cm−1 at 5 K. The Stokes and anti-Stokes spectra are measured at λexc=632.8 nm at room temperature. The most intense lines in these spectra are caused with the resonant Raman-scattering process. With increasing temperature from 5 to 300 K the shift (3–4 cm−1) of the most intense high-frequency component of the tangential mode (G mode) to lower frequency is observed. Based on the analysis of the Stokes/anti-Stokes spectra and the G band shape, the corresponding lines were identified with metallic or semiconducting type of nanotubes.

The transport properties of siloxene (as-grown and annealed) are investigated. The dark conductivity is thermally activated with an activation energy of about 1 eV for as-prepared siloxene, in accordance with the insulating nature of this material and its energy gap of about 2.6 eV. The conductivity is very sensitive to the presence of ambient gases. The spectral and temperature dependence of photoconductivity is also discussed.

We investigated a series of nanocomposites, built of the hydrogen-bonded liquid crystal (LC) p-n-heptyloxybenzoic acid (7OBA) and single-walled carbon nanotubes (SWCNTs) by optical microtexture analysis and other complementary methods. The surface orientation strength of the LC cell and the bulk interaction of the dimeric LC molecules with the SWCNTs turn out to mainly govern the type (symmetry), thermal stability, and chirality of the LC states induced in these nanocomposites. As a result, a cascade of phase transitions and phases not typical for pristine 7OBA were observed and additionally confirmed by temperature-dependent Raman spectroscopy and differential scanning calorimetry. The most effective SWCNT concentrations in the LC matrix, ensuring both the necessary conformability between these materials and induction of liquid crystal phases with unique optical and electro-optical properties, were found to be in the range of 0.01-0.007 wt%. Reversal of smectic phases into reentrant nematic states as well as induction of chirality in all LC phases were observed in the SWCNT-7OBA nanocomposite, even though pure 7OBA is typically achiral. However, our most intriguing result is the detection below the reentrant nematic of a triclinic smectic-C(G) phase, which is chiral and biaxial, and exhibits bulk ferroelectricity.

AC dielectrophoresis (DEP) is a useful method to fabricate single wall carbon nanotube (SWCNT) network structures on various kinds of substrates. We report on the fabrication of SWCNT networks with varying densities, on transparent and flexible polyether sulfone (PES) substrates by using DEP. From the scanning electron microscope observations and current‐voltage measurements of the fabricated SWCNT network, we obtain the contour map of the density and conductance as functions of Vp‐p and f. Our results show that the maximum density does not necessarily imply the maximum conductance. We find that there exists an optimum density for the maximum conductance.

A thermally activated relaxation process has been found in the anelastic spectrum of HiPco carbon nanotubes at 25 K. This peak is depressed in the hydrogenated samples, but grows after subsequent thermal treatments which partially remove hydrogen. The activation energy obtained by the peak shift with frequency is E-a = 54.7 meV, and the pre-exponential factor of the Arrhenius relaxation time is tau(0) = 10(-14) s, which is typical of point defect relaxation. The observation of an isotope peak shift confirms that the relaxation is due to hydrogen. The height of the peak firstly increases with decrease of c(H) as more free sites are made available for the H jumps. On further reducing the hydrogen content, the peak height decreases, as a small number of relaxing species is left in the sample. The high mobility of the species giving rise to this peak indicates that it can hardly be ascribed to a hydrogen molecule. Moreover, classical models cannot reproduce the peak, suggesting a dynamics of atomic hydrogen governed by quantum tunneling, (C) 2006 Elsevier B.V. All rights reserved.

We investigate the magnitude and temperature dependence of electrical conductivity, the optical and infrared absorption, and the Raman spectra of single-walled carbon nanotube (SWNT) bucky-paper after chemical treatment and determine the correlations between the changes in these properties. Ionic-acceptor doping of the SWNT bucky-paper (with SOCl(2), iodine, H(2)SO(3), etc.) causes an increase of electrical conductivity that correlates with an increase of the absorbance in the far-IR region and an increase in the frequency of Raman spectral lines. Conversely, treatment with other molecules (e.g., aniline, PyPhF(5), PhCH(2)Br, etc.) leads to a decrease in both conductivity and far-IR absorption. The temperature dependence of the conductivity gives a good indication of the presence of metallic charge carriers and is in agreement with the model of interrupted metallic conduction.

The anelastic spectrum of carbon nanotubes produced by the high-pressure CO method is reported for the first time in the temperature range from 10 up to 700 K. A series of peaks in the elastic dissipation are ascribed to the dynamics of atomic and molecular hydrogen, the adsorption of air, the surfactant melting and to a glassy dynamics, involving either the bundles of nanotubes or the molecular groups attached to the tubes. (c) 2006 Elsevier B.V. All rights reserved.

The first mechanical spectroscopy experiments in HiPco carbon nanotubes from room temperature to 3 K revealed a thermally activated relaxation process at about 25 K for frequencies in the kHz range. The peak is due to the presence of a very mobile species performing about 103 jumps per second at the peak temperature. The activation energy obtained by the peak shift with frequency is Ea = 54.7 meV; the value of the pre-exponential factor of the Arrhenius law for the relaxation time, τ0 = 10-14 s, which is typical of point defect relaxation and suggests that the process is originated by the dynamics of hydrogen or by H complexes. The peak is much broader than a single Debye relaxation process, indicating the presence of intense elastic interactions in the highly disordered bundle structure. There are indications that the relaxation process is governed by a quantum mechanism.

We report on our experience using a preliminary protocol for quality control of bulk single wall carbon nanotube (SWNT) materials produced by the electric arc‐discharge and laser ablation method. The first step in the characterization of the bulk material is mechanical homogenization. Quantitative evaluation of purity has been performed using a previously reported procedure based on solution phase near‐infrared spectroscopy. Our results confirm that this method is reliable in determining the nanotube content in the arc‐discharge sample containing carbonaceous impurities (amorphous carbon and graphitic particles). However, the application of this method to laser ablation samples gives a relative purity value over 100 %. The possible reason for that might be different extinction coefficient meaning different oscillator strength of the laser ablation tubes. At the present time, a 100 % pure reference sample of laser ablation SWNT is not available, so we chose to adopt the sample showing the highest purity as a new reference sample for a quantitative purity evaluation of laser ablation materials. The graphitic part of the carbonaceous impurities has been estimated using X‐ray diffraction of 1:1 mixture of nanotube material and C60 as an internal reference. To evaluate the metallic impurities in the as prepared and homogenized carbon nanotube soot inductive coupled plasma (ICP) has been used.We report on our experience using a preliminary protocol for quality control of bulk single wall carbon nanotube (SWNT) materials produced by the electric arc‐discharge and laser ablation method. The first step in the characterization of the bulk material is mechanical homogenization. Quantitative evaluation of purity has been performed using a previously reported procedure based on solution phase near‐infrared spectroscopy. Our results confirm that this method is reliable in determining the nanotube content in the arc‐discharge sample containing carbonaceous impurities (amorphous carbon and graphitic particles). However, the application of this method to laser ablation samples gives a relative purity value over 100 %. The possible reason for that might be different extinction coefficient meaning different oscillator strength of the laser ablation tubes. At the present time, a 100 % pure reference sample of laser ablation SWNT is not available, so we chose to adopt the sample showing the highest purity as...

We have shown recently that ionic doping (with SOCl2, iodine, HNO3) of single wall carbon nanotubes (SWNT) buckypaper causes an increase of electrical conductivity (factor of 5 for SOCl2‐doping). Optical absorption spectra of ionic‐doped SWNT show a vanishing of the first peak of van Hove singularities for semiconducting tubes, and at the same time a significant increase of the absorbance in the infrared region. In contrast, molecules forming covalent bonds with SWNT affect the properties of buckypaper so that electrical conductivity decreases (factor of 9 for aniline‐functionalization) and the absorbance in the infrared region of the optical absorption spectra is reduced, unlike what is observed for ionic doping.

Electronic state of carbon in HiPco nanotubes before and after purification was examined using X‐ray fluorescent spectroscopy. The CKα‐spectrum of as prepared HiPco nanotubes was shown to be similar to the spectrum of graphite. The purification of carbon nanotubes by thermal and acid treatment was found to result in an enhancement of high‐energy maximum in the CKα‐spectrum. Quantum‐chemical calculation revealed such enhancement can be attributed to the sp‐hybridized carbon atoms, which are likely to compose the open tube ends and boundaries of pores developed in the tube walls during the purification.

A diameter‐dependent oxidative etching of the smallest HipCO nanotubes (diameters 8–10 A) has been observed by in situ Raman measurements both in a laser beam with a variable power density and in an optical oven with a variable temperature. The effect manifested itself as an irreversible disappearance of the Raman breathing modes with frequencies > 220 cm−1. The small tube degradation (up to their complete disappearance) took place at temperatures 150–400°C. Statistical averaging of HRTEM images of HipCO nanotubes, taken after successive temperature steps, has confirmed an obvious shift of the tube diameter distribution maximum toward higher values.

The set of samples with a calibrated nanotube content has been prepared by mixing pure HipCO nanotubes and an amorphous carbon. The samples have been studied by a Raman‐based method for purity estimation, based on a measurement of the tangential Raman mode shift depending on the laser power density applied. The nanotube content values estimated by the Raman‐based method have coincided well with the preset ones. The model of a homogeneous two‐component medium was used to describe a thermal conductivity of the mixed samples.

The liquid crystalline (LC) nature of alkyloxybenzoic acids is preserved after adding of any mesogenic or non-mesogenic compound through hydrogen bonding. However, this noncovalent interaction provokes a sizable effect on the physical properties as, e. g. melting point and mesomorphic states. In the present work we investigate nanocomposites, prepared by mixture of the eighth homologue of p-n-alkyloxybenzoic acids (8OBA) with single-walled carbon nanotubes (SWCNT) with the purpose to modify the optical properties of the liquid crystal. We exercise optical control on the LC system by inserting SWCNT specially functionalized by carboxylic groups. Since the liquid crystalline state combines order and mobility at the molecular (nanoscale) level, molecular modification can lead to different macroscopical nanocomposite symmetry. The thermal properties of the functionalized nanocomposite are confirmed by DSC analyses. The mechanism of the interaction between surface-treated nanoparticles (functionalized nanotubes) and the liquid crystal 8OBA bent- dimer molecules is briefly discussed.

Single-walled carbon nanotubes (SWNTs) produced by arc-discharge and laser ablation were purified by selective oxidation in air at 350°C and subsequent HCl treatment at 120°C. Raw soot and purified samples were analyzed with X-ray diffraction, thermogravimetric analysis (TGA), chemical analysis and transmission electron microscopy (TEM). The optimized purification temperature of SWNTs in air, 350°C, has been determined from TGA curves. Repetition of the oxidation and acid treatment, larger than 95 wt.% purity of SWNTs has been obtained.

Characteristic peaks in the optical spectra of carbon nanotubes in the infrared region gives a tool to calculate the diameter distribution and to estimate the ratio between metallic and semi conducting tubes as well. Furthermore after chemical purification a shift of the fermi energy can be observed by changing of the peak intensities. This indicate a doping of such purified carbon nanotube material due to absorbed molecules on the surface and structural changing. We will present this behavior on carbon nanotubes from different production sources.

Well oriented distinct local single crystals were grown in smectic C liquid crystal (LC) (heptyloxybenzoic acid – 7OBA) using predefined orientation of the single-walled carbon nanotubes (SWCNT). The SWCNT/SiOx/ITO/glass surface is found to cause a substantial enlargement of the smectic C distinct local single crystals and to reinforce both surface memory effect and surface anchoring. We synthesized and examined a set of nanocomposites, built of LC with hydrogen-bonded in dimers molecules (7OBA) and SWCNT. We found that the surface orientation strength and the interaction of the dimeric molecules with the carbon nanotubes play a decisive role for the type (symmetry), thermal stability and chirality of the LC states induced in the nanocomposites. As a result, a set of phase transitions and new phases (chiral smectic C, reentrant nematic, reentrant chiral nematic and a unique low-temperature chiral biaxial fluid smectic phase CG) not typical for pristine 7OBA were found.

We have measured the modulus of the flexo-surface polarization term: 5.1 pC/m for the case of the nematic E7. The extension of the theory of Helfrich for the case of flexoelectric bending-splaying of a nematic layer permitted to measure also the modulus of the flexoelectric sum: 15 pC/m. The inclusion of minute amounts of single-walled carbon nanotubes (SWCNTs) with a concentration below 10−3 wt. % changes the results obtained as follows: 14.7 pC/m and 78.7 pC/m, respectively. Additionally we have measured the value of the surface energy for the pure nematic E7 and the E7/SWCNTs mixture.

Single-walled carbon nanotubes (SWNTs) and carbon black (CB) were used as conductive additives in lithium-ion batteries. Composites containing nanostructured LiCoO 2 and carbon additives were applied as positive electrodes in coin-type electrochemical cells with Li metal as a counter electrode. The conductive SWNTs with their wirelike shape and high aspect ratio are proved to have significant impact on the electrochemical performance of the electrode. The electrode composite containing 0.5 wt % of SWNTs has an internal resistance comparable to that of the 10 wt % of carbon black. Whereas the discharge capacity of the electrode containing 0.5 wt % of CB drops to 0 when increasing the rate to 5C, the capacity of the electrode containing the same weight fraction of SWNTs retains 67% of its initial capacity even at 18C. Cycling performance measured up to 23 cycles demonstrates that the SWNTs at a low concentration are as efficient in the capacity retention as the 10 wt % of carbon black. We interpret the SWNT-induced electrode performance by formation of a flexible, electrically wired network of conducting SWNTs in close contact with LiCoO 2 nano-particles, which accelerates the exchange of the Li ions and allows a rapid transfer of electrons throughout the electrode.

The influence has been studied of single-walled carbon nanotubes with a concentration between 0.0001 and 0.001 wt % and a dried zwitter-ionic phospholipid (SOPC: l-stearoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine) layer of thickness, smaller than 0.5 μm, deposited only on a half of one of the two glass plates, on the behaviour of the gradient flexoelectric and surface polarization induced domains arising in a homeotropic nematic E7 (a mixture of 5CB, 7CB, 8OCB and 5CT) layer. We have observed for the first time different polar on/off formation of the surface polarization induced domains in the region of the liquid crystal cell without surface deposited lipid SOPC layer. On the other hand, the SOPC layer strongly decreases the gradient of the electric field thus leading to less-pronounced flexoelectric domains. However, the SOPC layer does not influence the creation of surface polarization induced domains and of injection induced domains arising at voltages above 4V. Appropriate dynamic light transmitted curves have been recorded and typical microphotographs have been taken.

Electrical properties of C60 encapsulated peapod are investigated at various temperatures from room temperature down to T=1.8K. The current behavior induced by the applied gate and source-drain voltage shows that C60 peapods exhibit single-electron transistor properties. Gate-dependent conductance is enhanced at negative gate voltage and is suppressed and oscillate at positive gate voltage. This behavior is ascribed to the modulation of density of states by the insertion of C60s inside a carbon nanotube.