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ABSTRACT: A novel method to separate metallic and semiconducting single-wall carbon nanotubes (SWCNTs) by free solution electrophoresis was investigated. A vertical electrophoretic cell was used to separate SWCNT aqueous solution by the application of electric field along the vertical cell. In contrast with conventional electrophoresis, electric-field-induced layer formation was found in the cell with clear horizontal boundaries. Both the optical absorbance spectra and resonant Raman spectra of these layers revealed the enrichment of metallic and semiconducting SWCNTs with 95% semiconducting SWCNTs in a layer. This method was successfully applied for SWCNTs with diameters from 1.0 to 1.7 nm. Thin-film transistors fabricated by the direct deposition of the semiconductor-enriched nanotubes onto the substrate showed excellent transport properties with an on/off current ratio of 4.4 × 105 and a mobility of 6.8 cm2 V–1 s–1.
10/2011;
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Advanced Materials 09/2011; 23(40):4631-5. · 13.88 Impact Factor
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Haruka Kyakuno,
Kazuyuki Matsuda,
Hitomi Yahiro,
Yu Inami,
Tomoko Fukuoka,
Yasumitsu Miyata,
Kazuhiro Yanagi,
Yutaka Maniwa,
Hiromichi Kataura, Takeshi Saito,
Motoo Yumura,
Sumio Iijima
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ABSTRACT: Studies on confined water are important not only from the viewpoint of scientific interest but also for the development of new nanoscale devices. In this work, we aimed to clarify the properties of confined water in the cylindrical pores of single-walled carbon nanotubes (SWCNTs) that had diameters in the range of 1.46 to 2.40 nm. A combination of x-ray diffraction (XRD), nuclear magnetic resonance, and electrical resistance measurements revealed that water inside SWCNTs with diameters between 1.68 and 2.40 nm undergoes a wet-dry type transition with the lowering of temperature; below the transition temperature T(wd), water was ejected from the SWCNTs. T(wd) increased with increasing SWCNT diameter D. For the SWCNTs with D = 1.68, 2.00, 2.18, and 2.40 nm, T(wd) obtained by the XRD measurements were 218, 225, 236, and 237 K, respectively. We performed a systematic study on finite length SWCNT systems using classical molecular dynamics calculations to clarify the effect of open ends of the SWCNTs and water content on the water structure. It was found that ice structures that were formed at low temperatures were strongly affected by the bore diameter, a = D - σ(OC), where σ(OC) is gap distance between the SWCNT and oxygen atom in water, and the number of water molecules in the system. In small pores (a < 1.02 nm), tubule ices or the so-called ice nanotubes (ice NTs) were formed irrespective of the water content. On the other hand, in larger pores (a > 1.10 nm) with small water content, filled water clusters were formed leaving some empty space in the SWCNT pore, which grew to fill the pore with increasing water content. For pores with sizes in between these two regimes (1.02 < a < 1.10 nm), tubule ice also appeared with small water content and grew with increasing water content. However, once the tubule ice filled the entire SWCNT pore, further increase in the water content resulted in encapsulation of the additional water molecules inside the tubule ice. Corresponding XRD measurements on SWCNTs with a mean diameter of 1.46 nm strongly suggested the presence of such a filled structure.
The Journal of chemical physics 06/2011; 134(24):244501. · 3.09 Impact Factor
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ABSTRACT: The main gas phase intermediates, leading the efficient chemical vapor deposition (CVD) growth of single wall carbon nanotubes (SWCNTs), have been explored through systematic experimental and theoretical studies. The growth efficiencies of the basic radical/neutral species (sp2 C2: C2H3/C2H4, sp3 C2: C2H5/C2H6, and sp3 C1: CH3/CH4) have been compared by supplying C2H4, C2H6, and CH4, as carbon sources to grow SWCNTs. The gaseous composition of the exhaust was analyzed by an in situ direct sampling mass spectrometric technique using vacuum ultraviolet (VUV)-single photon ionization (SPI)-time-of-flight mass spectrometry (TOFMS). For verification via theoretical prediction, a CHEMKIN calculation was performed. A kinetic analysis of the experimental and theoretical results was compared with thermal decomposition phenomena of the used hydrocarbons, and hence, it was concluded that the key gas phase intermediates produced from the complex gas phase reactions as a final and efficient species capable of initiating the CVD growth of SWCNTs are sp2 C2 species, C2H3/C2H4. Additional significance is the production of highly pure SWCNTs from C2H6 since to date production of either only multiwall carbon nanotubes (MWCNTs) or a mixture of MWCNTs and SWCNTs have been reported. This result will be beneficial for selecting suitable hydrocarbons for the efficient growth of SWCNTs.
10/2010;
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Advanced Materials 08/2010; 22(29):3156-60. · 13.88 Impact Factor
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ABSTRACT: A novel system for fractionating single wall carbon nanotubes (SWCNTs) by length via a three-step cross-flow filtration has been developed in which three membrane filters of different pore sizes, 1.0, 0.45, and 0.2 microm, were used. SWCNTs dispersed in water with the help of sodium carboxymethylcellulose (CMC) detergents were successfully sorted into four samples, and the atomic force microscopy (AFM) observation of those samples confirmed that their length distribution peaks are within the expected ranges from pore sizes of used filters. However, the result of the similar filtration process using a different detergent, sodium dodecylbenzenesulfonate (SDBS), showed no pronounced correlation between the length distribution of SWCNTs and the pore size. The observed difference in the sorting phenomena caused by the detergent type suggests that the permeation property depends on the complex structure resulting from the dispersed SWCNTs and detergent molecules.
ACS Nano 07/2010; 4(7):3606-10. · 10.77 Impact Factor
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Small 06/2010; 6(12):1279-82. · 8.35 Impact Factor
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ABSTRACT: For precise characterizations of single-walled carbon nanotubes (SWCNTs) by optical absorption spectroscopy, the background extinction that originated from precipitable impurities and SWCNT bundles has been experimentally determined by the interval centrifugation and difference spectrum (IC-DS) technique. The baseline correction using the line shape of the obtained background extinction revealed the actual absorption spectrum of absolutely debundled SWCNTs with detailed features. The chirality distribution, including both semiconductive and metallic SWCNTs, was evaluated by deconvoluting the corrected absorption spectrum into multiple Lorentzian lines, which was well consistent with the result of photoluminescence (PL) mapping measurements. Another peculiarity is that the UV absorption characteristics of SWCNTs hidden in the original observed spectra by overlapping the background extinction also appeared. The baseline correction by the IC-DS technique provides a useful analysis method for characterizing SWCNTs, a complement/alternative to the similar analysis done by PL spectroscopy.
05/2010;
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ABSTRACT: We report the synthesis and characterization of single-walled carbon nanotubes (SWNTs) filled with a zinc-containing quaternary ammonium based ionic liquid (ChZnCl(3)) inside. The threshold SWNT diameter for efficient encapsulation was determined to be ca. 0.97 nm. Different morphologies of the encapsulated ChZnCl(3) such as single-chain, double-helix, zigzag tubes, and random tubes were observed. The melting of ChZnCl(3) ionic liquid into "nanofluid" inside SWNTs was investigated by in situ TEM electron beam irradiation and compared with a high-temperature heat treatment. The thermal-decomposition temperature of the ChZnCl(3) ionic liquid confined in the SWNTs was much higher than in the bulk system. Furthermore, the doping effect of the encapsulated ChZnCl(3) on the host SWNTs can be varied (from p-type to n-type) by gradually reducing the filling ratio. The versatility of ionic liquids and the unique phase transition observed inside the SWNTs provide a new opportunity for modulating the electronic properties of carbon nanotubes.
Journal of the American Chemical Society 09/2009; 131(41):14850-6. · 9.91 Impact Factor
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ABSTRACT: The potentiality of optical absorption spectroscopy (OAS) for the
estimation of mean diameter of single-wall carbon nanotubes (SWCNTs)
from electronic transition energies has been explored. The observed
dependence of electronic transition energies of both metallic and
semiconducting SWCNTs on their mean diameters clearly showed that
transition energies scale inversely with the tube diameter. In the
present study, the applicability of this estimation method has been
experimentally confirmed for the diameter range of 1--2 nm and is
expected to be useful for the characterization of wide range of
diameters of SWNCTs.
Applied Physics Express 08/2009; 2(9):5006. · 3.01 Impact Factor
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ABSTRACT: The sp(2) C(2) species, C(2)H(3)/C(2)H(4), has been found as a key precursor for the efficient growth of single-wall carbon nanotubes (SWCNTs) by chemical vapor deposition (CVD) from hydrocarbons.
Chemical Communications 07/2009; · 6.17 Impact Factor
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ABSTRACT: A novel approach for selective diameter control of single-walled carbon nanotubes (SWNTs) is performed in the gas-phase growth using two kinds of carbon sources with different decomposition properties; the one carbon source (1st carbon source) is the organic solvent which is difficult to decompose in the reactor and the another carbon source (2nd carbon source) is facile to decompose. The diameter distributions of SWNTs synthesized with various conditions of the flow rate of the 2nd carbon source were investigated by resonant Raman scattering, optical absorption, and photoluminescence (PL) mapping measurements. It was found that increasing the flow rate of the ethylene tends to decrease the diameter of synthesized SWNTs, probably due to the earlier nucleation of SWNTs induced by the ethylene addition. The controlling the flow rate of the ethylene used as a 2nd carbon source can selectively tune the diameter distribution of SWNTs in our growth system.
Journal of Nanoscience and Nanotechnology 12/2008; 8(11):6153-7. · 1.56 Impact Factor
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ABSTRACT: Crystalline ErCl3 nanowires have been fabricated in single-walled carbon nanotubes (SWCNTs) with high yield (∼90%), and the structural and
magnetic properties of the resulting ErCl3 nanowires encapsulated in SWCNTs (ErCl3@SWCNTs) characterized. Encapsulation under high temperature and vacuum using high quality SWCNTs results in a high filling-ratio
of ErCl3 nanowires in the SWCNTs. The high filling-ratio of ErCl3 nanowires and the use of highly pure SWCNTs with only a small amount of residual Fe catalyst nanoparticles enabled us to
observe the magnetic properties of ErCl3@SWCNTs. Structure determination based on simulated annealing calculations and high-resolution transmission electron microscope
(HRTEM) image simulations revealed that the structure of the ErCl3 nanowires is unusual with respect to the coordination environment of the Eu3+ ions. This work opens up new possibilities to fabricate various metal complex nanowires with high yield and may also be of
more general importance in understanding and exploring magnetic properties in low-dimensional magnetic systems.
Nano Research 07/2008; 1(2):152-157. · 6.97 Impact Factor
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ABSTRACT: Substantial progress on field effect transistors ͑FETs͒ consisting of semiconducting single wall carbon nanotubes ͑s-SWNTs͒ without detectable traces of metallic nanotubes and impurities is reported. Nearly perfect removal of metallic nanotubes is confirmed by optical absorption, Raman measurements, and electrical measurements. This outstanding result was made possible in particular by ultracentrifugation (150 000 g) of solutions prepared from SWNT powders using polyfluorene as an extracting agent in toluene. Such s-SWNTs processable solutions were applied to realize FET, embodying randomly or preferentially oriented nanotube networks prepared by spin coating or dielectrophoresis. Devices exhibit stable p-type semiconductor behavior in air with very promising characteristics. The on-off current ratio is 10^5, the on-current level is around 10 µA, and the estimated hole mobility is larger than 2 cm2 / V s.
Applied Physics Letters 06/2008; · 3.84 Impact Factor
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Advanced Materials 05/2008; 20(13):2475 - 2479. · 13.88 Impact Factor
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ABSTRACT: We report optical band gap modifications of single-walled carbon nanotubes upon C60 insertions by using photoluminescence and the corresponding excitation spectroscopy. The shifts in optical transition energies strongly depend on the tube diameter (dt) and the "2n + m" family type, which can be explained by the local strain and the hybridization between the nanotube states and the C60 molecular orbitals. The present results provide possible design rules for nanotube-based heterostructures having a specific type of electronic functionality.
Journal of the American Chemical Society 04/2008; 130(12):4122-8. · 9.91 Impact Factor
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ABSTRACT: A simple and efficient technique is described for measuring photoluminescence (PL) maps of carbon nanotubes (NTs) in the extended IR range (1-2.3 mum). It consists of preparing an NT/surfactant/gelatin film and measuring PL spectra using a combination of a tunable Ti-sapphire laser excitation and FTIR detection. This procedure has been applied to a wide range of single- and double-wall NTs unveiling chirality and diameter distributions that have so far been very difficult to measure. The problems associated with deducing these distributions are discussed by comparing absorption and PL mapping data for NT samples prepared under different conditions.
The Journal of Physical Chemistry B 10/2006; 110(35):17420-4. · 3.70 Impact Factor
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ABSTRACT: Reversed micelles containing metallic ions have been used as precursors of novel catalysts for the gas-phase synthesis of single-walled carbon nanotubes (SWNTs). This technique possesses the following advantages: (i) excellent solubility in organic solvents, which are used as reactants and (ii) facile preparation of multicomponent catalysts enabling systematic screening of catalyst compositions for the synthesis of SWNTs. In this study, we report the results of the screening study on the catalytic behavior of Fe-Mo binary catalysts during the synthesis of SWNTs. The results suggested that the catalytic ability was closely related to the strain of the crystal structure of Fe-Mo catalysts formed in the reaction and/or the phase transition caused by dissolution of the Mo atoms. The addition of lithium to the Fe-Mo binary catalysts has revealed an increase in the yield of SWNTs.
The Journal of Physical Chemistry B 04/2006; 110(12):5849-53. · 3.70 Impact Factor
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ABSTRACT: Band gap photoluminescence (PL) is observed from "as-grown" single-walled carbon nanotubes (SWNTs) in solid form. The relative PL intensities for six specific semiconducting SWNTs are compared directly to those of the micelle-encapsulated SWNTs' solutions to investigate the influence of the micelle dispersion process on PL measurements. The results indicate that sodium dodecyl sulfate (SDS) and sodium cholate (SC) selectively solubilize smaller-diameter nanotubes, whereas sodium dodecylbenzene sulfonate (SDBS) solution does not exhibit significant diameter selectivity within the diameter range studied here (d(t) = 0.829-0.966 nm).
Nano Letters 01/2006; 5(12):2618-23. · 13.20 Impact Factor
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ABSTRACT: Nanoparticle catalysts are essential and indispensable for all syntheses of single-walled carbon nanotubes (SWCNTs). We have prepared size-controlled Co, Co-Mo, and Fe-Mo nanoparticles by the reversed micelle method as the catalysts for the gas-phase pyrolytic synthesis of SWCNTs. From the investigation of the relation between the sizes of the nanoparticles and the alkyl-chain lengths of the cationic surfactants, dialkyldimethylammonium bromides, it has been found that the alkyl groups of the surfactants could play a role in controlling the sizes of the nanoparticles and that the alkyl chain of the surfactant should be preferably less than 10 carbon atoms at most to prepare smaller-size nanoparticles with a narrow size distribution. The reduction of the particle size increases the number of nanoparticles in the colloidal solution and leads to a higher yield of SWCNTs.
The Journal of Physical Chemistry B 07/2005; 109(21):10647-52. · 3.70 Impact Factor
