Dynamic Alignment of Single-Walled Carbon Nanotubes in Pulsed Magnetic Fields

We have used linear dichroism spectroscopy to measure the dynamic alignment of single-walled carbon nanotubes (SWNT) in pulsed magnetic fields up to 55 T. We make use of the fact that SWNTs absorb light only when the electric-field vector is oriented parallel to the tube axis. SWNTs thus produce a polarization dependent change of the optical transmission, that permits precise measurements of their orientation. In order to distinguish the influence of different mechanisms governing the alignment such as the external magnetic field, Brownian motion or the tube length, we have systematically varied parameters such as the viscosity of the aqueous solution and the sample temperature.     

Adsorption Properties of Multi‐wall Carbon Nanotubes

Abstract

Preparation of multi‐wall carbon nanotubes by means of arc‐discharge in He atmosphere was worked out and optimized. Electron micrographs show that electrode deposit consists of crossed multi‐wall carbon nanotubes. For study of adsorption properties of multi‐wall carbon nanotubes, the thermodynamic characteristics of adsorption of different classes organic compounds at small coverage were determined by gas chromatography and compared with those for graphitized carbon black and molecular crystals of fullerene C₆₀ (fullerite). The comparison of adsorption data for organic compounds with different functional groups on multi‐wall carbon nanotubes, on graphitized carbon black and fullerene C₆₀ shows the similarity of adsorption properties of multi‐wall carbon nanotubes and graphitized carbon black and the differences in molecular interaction of adsorbed molecules with crystal C₆₀.     

Carbon Nanotubes for Microelectronics?

Despite all prophecies of its end, silicon-based microelectronics still follows Moore's Law and continues to develop rapidly. However, the inherent physical limits will eventually be reached. Carbon nanotubes offer the potential for further miniaturization as long as it is possible to selectively deposit them with defined properties.     

One Step Synthesis and Growth Mechanism of Carbon Nanotubes

A simple one step,reproducible,synthesis route for carbon nanotubes was proposed.No external catalyst was used for the synthesis.These nanotubes were obtained after decomposition of acetone at 650 ℃ in a specially designed autoclave.The pressure generated due to decomposition of acetone played a vital role in the synthesis.The X-ray diffraction pattern and transmission electron microscopy of the sample showed that the diameter of nanotubes is in the range of 3—14 nm.The thermo gravimetric analysis showed 3%weight loss below500 ℃;the content of amorphous carbon is very less.The growth mechanism of CNTs was also proposed in the present paper.     

Single-walled Carbon Nanotubes Regularly Aligned in Channels of Zeolite Single Crystal

We report the synthesis of single-wall carbon nanotubes (SWCNs) formed in 1-nm-sized channels of zeolite crystal by pyrolysis of tripropylamine molecules. The SWCNs are mono-sized and parallelly aligned along the crystal direction. In the present paper, we report the polarized Raman spectra measured for the wellaligned SWCNs, which gives us information about structural symmetry. Electrical transport properties of the SWNTs are measured in the temperature range of 0.3 K ～ 300 K. The conductivity of the SWCNs is monotonically decreased with decreasing temperature. The observed temperature dependence of zero-field conductance, In(σ) ～ 1/√T, could be explained well in terms of electron localization caused by imperfections and impurities in the nanotubes.     

Dispersion of the Nonlinear Optical Susceptibility in Single‐Wall Carbon Nanotubes

Abstract

We have calculated the dispersive behavior of the third‐order nonlinear susceptibility χ⁽³⁾ (?ω₃; ω₁, ω₁, ?ω₂) in single‐wall carbon nanotubes (SWCNTs) responsible for optical frequency mixing of the form ω₃ = 2ω₁ ? ω₂. The dispersive resonance of χ⁽³⁾ (?ω₃; ω₁, ω₁, ?ω₂) is shown to occur when the frequency ω₃ = 2ω₁ ? ω₂ is generated near the band gap of SWCNTs due to three‐wave mixing. A very sharp peak of χ⁽³⁾ (?ω₃; ω₁, ω₁, ?ω₂) reaching extremely high values ～10^?4 esu at the newly generated frequency ω₃ can be observed when not only ω₃ is close to the band gap of the system, but also when the frequencies of incident fields are near such a resonance.     

Formation of Various Carbon Nanoclusters from Laser‐Produced Carbon Plasma

Abstract

Laser vaporization of graphite proved to be an unbelievably flexible instrument allowing selective fabrication of various novel forms of carbon (diamond or fullerenes or different types of carbon nanotubes). In this work, the extension of the laser vaporization method to composite fullerene‐containing carbon targets is presented. It is shown that, depending on the pressure in an experimental chamber, different products come out of the ablation plume and get deposited on the substrate. The experimental results of this work allow to suggest a mechanism of formation of different carbon forms from laser‐produced carbon plasma at different experimental conditions.     

Research on the Relationship between Density of States and Conducting Properties of Single-walled Carbon Nanotubes

The analytical expression of the electronic density of states (DOS) for single-walled carbon nanotubes (SWNTs) has been derived on the basis of graphene approximation of the energy E(k) near the Fermi level EF. The distinctive properties of the DOS, the normalized differential conductivity and the current vs bias for SWNTs are deduced and analyzed theoretically. The singularities in the DOS (or in the normalized differential conductivity) predict that the jump structure of current (or conductance)--bias of SWNTs exists. All conclusions from the theoretical analysis are in well agreement with the experimental results of SWNT‘s electronic structure and electronic transport. In other words, the simple theoretical model in this paper can be applied to understand a range of spectroscopic and other measurement data related to the DOS of SWNTs.     

Electroluminescent Polymers and Carbon Nanotubes for Flat Panel Displays

polymeric light-emitting diodes(LEDs) with sufficient brightness. efficiencies, low driving voltages, and various interesting features have been reported. The relatively short device lifetime, however, still remains as a major problem to be solved before any commercial applications will be realized. In this regard,carbon nanotubes have recently been proposed as more robust electron field emitters for flat panel displays. We have synthesised large arrays of vertically aligned carbon nanotubes, from which micropatterns of the aligned nanotubes suitable for flat panel displays were fabricated on various substrates. In this paper, we summarise our work on the synthesis and microfabrication of electroluminescent polymers and carbon nanotubes for flat panel displays with reference to other complementary work as appropriate.     

Individualization of Single‐Walled Carbon Nanotubes: Is the Solvent Important?

The influence of different solvents on the individualization of single-walled carbon nanotubes (SWNTs) was investigated by several methods. A stable solution of individual SWNTs in o-dichlorobenzene was obtained by a combination of ultrasonication and ultracentrifugation. Atomic force microscopy height analysis confirmed that the final supernatant solution contained 85 % of individual tubes with a diameter equal to or less than 1.5 nm, which is consistent with the average diameter of arc-discharge tubes. Both the solvent and the ultracentrifugation speed are important parameters in determining the final degree of individualized SWNTs. Notably, the SWNTs were stable in o-dichlorobenzene for more than eight months. This technique for obtaining highly individualized SWNTs in an organic solvent is expected to have great potential in many applications, such as functional materials and nanoelectronics.     

Synthesis and Hydrogen Storage in Single—walled Carbon Nanotubes

Single=walled carbon nanotubes(SWNTs) were synthesized by a hydrogen arc discharge method.A high yield of gram quantity of SWNTs per hour was achieved.Tow kinds of SWNT products:web-like substancea and thin films in large slices were obtained. Results of resonant Raman scattering measurements indicate that the SWNTs prepared have a wider diameter distribution and a larger mean diameter.Hydrogen uptake measurements of the two kinds of SWNT samples(both as prepared and pretreated) were carried out using a high pressure volumetric method,respectively.And a hydrogen storage capacity of 4 wt pct could be repeatedly achieved for the suitably pretreated SWMNTs,whicb indicates that SWNTs may be a promising hydrogen storge material.     

Infrared Reflectivity Spectra of Manganite Thin Films Grown on Different Substrates

We have measured the reflectivity infrared (IR) spectra of R_1−x Ca _x MnO₃ (R = La, Pr) manganite thin films grown on different substrates (SrTiO₃ (STO), LaAlO₃ (LAO) and SrLaGaO₄ (SLGO)) manganites over a wide frequency (50–5000 cm⁻¹) range. In the Far IR (FIR) region the substrates dominate over the manganite spectrum. However, the previously observed infrared active modes or mode pairs could be identified. In the mid-IR (MIR) region, a characteristic insulating gap at ∼700 cm⁻¹ is always present for all thin film studied, which shows substrate and thickness dependence.     

Characterization of the Response of CaWO4 on Recoiling Nuclei from Surface Alpha Decays

A potentially harmful background for experiments attempting direct dark matter detection like the CRESST (= Cryogenic Rare Event Search with Superconducting Thermometers) experiment is caused by recoiling nuclei from ²¹⁰Po alpha decays on surfaces close to the detector. In order to characterize this kind of background in CRESST, calibration measurements have been performed at the TU München. A for this purpose an optimized version of the CRESST detector has been developed consisting of a 38 g CaWO₄ crystal and a separate cryogenic light detector, both equipped with Ir/Au transition edge sensors (TESs). The simultaneous measurement of the phonon signal and the scintillation light from the CaWO₄ crystal allows to discriminate between electron and nuclear recoils using their different light outputs. The unexpected results of a first measurement with a ²¹⁰Po source can be understood with the help of a Monte Carlo simulation performed for a similar system.      

Synthesis of Hybrid Materials Based on Multiwalled Carbon Nanotubes Decorated with WC1 –x Nanocoatings of Various Morphologies

Technical Physics Letters - New hybrid materials based on multiwalled carbon nanotubes (MWCNTs) with a nonstoichiometric tungsten carbide coating (WC1 –x/MWCNTs) were synthesized by...     

Characterization of Thermal Conductivity of Carbon Fibers at Temperatures as Low as 10 K

Due to their excellent thermal structural properties, carbon fibers have been extensively applied in the fields of mechanical and aerospace engineering. Many studies have been conducted at room temperature or higher, yet the literature gives very few data on the measurement of thermophysical properties at very low temperatures. The thermal diffusivity of two kinds of carbon fibers was measured by the transient electrothermal technique at very low temperatures (down to 10 K) in the work, the ρCp followed the Debye T3 law dependence quite accurately in agreement with theoretical investigations at very low temperatures(<?10 K). The thermal diffusivity of carbon fiber almost increases linearly with decreasing temperature, but when the temperature drops down below 90 K, the thermal diffusivity rapidly decreases. The thermal expansion mismatch between the different materials present in carbon fibers may influence the change of thermal diffusivity. The relationship between the impurity concentration and the thermal transport of the carbon fibers is discussed.     

Optical Absorption of Single‐Wall Carbon Nanotubes Produced by Arc‐Discharge Method with Different Concentration of Ni/Co Catalyst

Abstract

Material containing single‐wall carbon nanotubes (SWNTs) was obtained by arc‐discharge method. The optical absorption spectra were measured. Several narrow absorption bands were observed in a range from 0.4 to 3 eV caused by optical transitions between van Hove singularities. Comparing the results of “tight‐binding” electronic structure calculation for SWNT with the experimental spectra we found that each feature of spectrum can be attributed to interband transition in SWNTs. We have also found that the total yield of SWNTs and their diameter distribution depend on the catalyst content.     

Carbon nanotube Schottky diode: an atomic perspective

The electron transport properties of semiconducting carbon nanotube (SCNT) Schottky diodes are investigated with atomic models using density functional theory and the non-equilibrium Green's function method. We model the SCNT Schottky diode as a SCNT embedded in the metal electrode, which resembles the experimental set-up. Our study reveals that the rectification behaviour of the diode is mainly due to the asymmetric electron transmission function distribution in the conduction and valence bands and can be improved by changing metal-SCNT contact geometries. The threshold voltage of the diode depends on the electron Schottky barrier height which can be tuned by altering the diameter of the SCNT. Contrary to the traditional perception, the metal-SCNT contact region exhibits better conductivity than the other parts of the diode.     

Thermophysical Properties of Binary Mixtures of Methanol with Chlorobenzene and Bromobenzene from 293 K to 313 K

Densities and viscosities have been measured for the binary mixtures of methanol with chlorobenzene and with bromobenzene from 293 K to 313 K over the complete composition range. Densities were used to compute the excess molar volume ( , for these binary systems. The results have been discussed in terms of molecular interactions. Furthermore, viscosity results were compared with a corresponding-states model. The average absolute deviation was found to be 1.9 %.     

Computation of the relaxation and creep functions of elastomers from harmonic shear modulus

The purpose of this paper is to compute the relaxation and creep functions from the data of shear complex modulus, G ^∗(iν). The experimental data are available in the frequency window ν∈[ν_min,ν_max] in terms of the storage G′(ν) and loss G″(ν) moduli. The loss factor h( n) = \fracG"( n)G￠(n)\eta( \nu) = \frac{G'( \nu )}{G'(\nu )} is asymmetrical function. Therefore, a five-parameter fractional derivative model is used to predict the complex shear modulus, G ^∗(iν). The corresponding relaxation spectrum is evaluated numerically because the analytical solution does not exist. Thereby, the fractional model is approximated by a generalized Maxwell model and its rheological parameters (G _k ,τ _k ,N) are determined leading to the discrete relaxation spectrum G(t) valid in time interval corresponding to the frequency window of the input experimental data. Based on the deterministic approach, the creep compliance J(t) is computed on inversing the relaxation function G(t).