HiPco Single-walled Carbon Nanotubes Research Articles

Degradation of optical properties of a film-type single-wall carbon nanotubes saturable absorber (SWNT-SA) with an Er-doped all-fiber laser

Single-wall carbon nanotubes (SWNTs) are promising materials for saturable absorbers (SAs) in mode-locked lasers. However it has been widely recognized that the degradation of optical properties of film-type SWNTs used in femtosecond mode-locked lasers limits the achievable long-term stability of such lasers. In this paper, we study the degradation of optical properties of SWNT-SA fabricated as sandwich type using HiPCO SWNTs with an Er-doped all-fiber laser. The thresholds of laser pump power are examined to avoid the damage of the SWNT-SA. Based on the proposed analysis, it is shown that all-fiber laser pulses of 300 fs pulse width, 3.85 mW average output power, 211.7 MW/cm² peak intensity and 69.9 MHz repetition rate can be reliably generated without any significant damage to the SWNT-SA film.

Comparative study on raman and photoluminescence spectra of carbon nanotubes dispersed in different surfactant solutions

Raman and photoluminescence (PL) spectra of HiPCO and CoMoCat single-walled carbon nanotubes (SWCNTs) dispersed in 1 wt% aqueous surfactant solutions with five different surfactants were studied. The SWCNT suspensions exhibit almost the same Raman spectra, regardless of the surfactant used, but the PL peak positions of all the observed (7,5), (6,5), (8,3), (9,1), and (6,4) SWCNTs show strong surfactant-dependent shifts as large as ∼19 meV, known as solvatochromic shifts. For SWCNTs dispersed in deoxycholate sodium salts and sodium dodecyl sulfate solutions, the amount of the solvatochromic shift decreases as the excitation laser power is increased.

Selective dispersion of single-walled carbon nanotubes via easily accessible conjugated click polymers

To date synthetic methods to selectively produce specific (n, m) single-walled carbon nanotubes (SWCNTs) are not available. Therefore, post-processing of SWCNTs including solubilization and sorting by metallicity, length, diameter, chirality or (n, m) is necessary for further applications. To reach the goal of sorting SWCNTs, we have synthesized various conjugated polymers consisting of alternating 9,9-dialkyl fluorene and 1,2,3-triazole units via copper catalyzed alkyne–azide conjugation chemistry. Their ability to selectively wrap specific (n, m) SWCNTs is investigated towards HiPco SWCNT raw materials which contain more than 40 (n, m) species and are found to be comparable to fluorene based triazole free polymers, which are typically prepared via Suzuki-type polymerization. However, the herein reported triazole-linked click polymers are significantly simpler to prepare than their Suzuki-analogs. Fluorescence and UV/Vis NIR spectroscopy were employed to analyze the SWCNTs–polymer suspensions and demonstrate their selectivity for dispersing SWCNTs.

Polymer Library Comprising Fluorene and Carbazole Homo- and Copolymers for Selective Single-Walled Carbon Nanotubes Extraction

To date, (n, m) single-walled carbon nanotubes (SWNTs) cannot be selectively synthesized. Therefore, postprocessing of SWNTs including solubilization and sorting is necessary for further applications. Toward this goal, we have synthesized a polymer library consisting of fluorene- and carbazole-based homo- and copolymers. Variations of the connection of these aromatics together with the incorporation of further conjugated monomers give access to a broad diversity of polymers. Their ability to selectively wrap specific (n, m) species is investigated toward HiPco SWNTs raw material which contains more than 40 (n, m) species. Absorption and fluorescence spectroscopies were used to analyze SWNTs/polymer suspensions. These results provide evidence for selective SWNTs/polymer interactions and allow a more detailed assessment of polymer structure–property relationships, thus paving the way toward custom synthesis of polymers for single (n, m) SWNTs extraction.

One‐step separation of high‐purity (6,5) carbon nanotubes by multicolumn gel chromatography

AbstractWe investigated the separation of the (6,5) chirality from a commercially available (6,5)‐enriched CoMoCAT single‐wall carbon nanotubes (SWCNTs) by the multicolumn gel chromatography method. Results show that several (6,5) fractions with different purities were sorted across the different gel columns. The metallic SWCNTs were collected as the finally unbound SWCNTs. The highest chirality purity of the (6,5) fractions after one‐step separation was 74.5%, which is much higher than that (∼53.8%) of the (6,5) fraction separated from HiPco SWCNTs which contain a broad chirality distribution. This result indicates that the multicolumn method can highly improve the separation yield and efficiency of a specific (n,m) species if it is present at a high level in the starting material.

High yield fabrication of semiconducting thin-film field-effect transistors based on chemically functionalized single-walled carbon nanotubes

Here we report a simple and scalable method to fabricate high performance thin-film field-effect transistors (FETs) with high yield based on chemically functionalized single-walled carbon nanotubes (SWNTs) by organic radical initiators. The UV-Vis-NIR spectra, Raman spectra and electrical characterization demonstrated that metallic species in CoMoCat 65 and HiPco SWNTs could be effectively eliminated after reaction with some organic radical initiators. The effects of the substrate properties on the electrical properties of FET devices were investigated, and the results showed that the electrical properties of FET devices fabricated on high hydrophobic substrates were better than those on low hydrophobic substrates. Furthermore, it was found that FET devices based on 1,1′-azobis(cyanocyclohexane)(ACN)-modified CoMoCat 65 SWNTs exhibited more excellent electrical performance with effective mobility of ∼11.8 cm2/Vs and on/off ratio of ∼2×105 as compared with benzoyl peroxide (BPO)-modified CoMoCat 65 SWNTs and lauoryl peroxideand (LPO)-modified HiPco SWNTs, likely due to the introduction of the electron-withdrawing groups (CN group) on the SWNT surface. This method does not require nontrivial reaction conditions or complicated purification after reaction, therefore promising low-cost production of high-performance devices for macroelectronics.

Magnetic Properties of Iron Catalyst Particles in HiPco Single Wall Carbon Nanotubes

We have investigated the magnetic response of residual metal catalyst in the raw and super purified HiPco single wall carbon nanotubes (HiPco_raw and HiPco_SP SWCNTs). It has been shown that the residual metal catalyst is in the form of nanoparticles, even in the HiPco_SP SWCNTs that should contain a minimal amount of the metal. Mössbauer spectroscopy of the HiPco_raw SWCNTs proved the catalyst nanoparticles are in the form of Fe3C. Analysis of the synchrotron X-ray diffraction data provided an average diameter of nanoparticles about 1.9 nm. Magnetic studies by means of temperature dependence of magnetization, magnetization isotherms and susceptibility suggested that the nanoparticles obey the behavior of weakly interacting superparamagnetic systems in both samples. Further analysis of the data revealed a core–shell structure of the nanoparticles in the HiPco_raw nanotubes, with a magnetically oriented core and a paramagnetic shell, which is almost removed in the case of the HiPco_SP catalyst nanoparticles.

Ethylene Films Adsorbed onto Purified HiPco Single Walled Carbon Nanotubes: A Comparison with Ethane and Longer Alkanes

The results of adsorption isotherm measurements for ethylene on purified HiPco SWNTs conducted at 11 different temperatures (between 110 K and 220 K) are reported, together with a comparison with the results we have obtained for ethane on the same substrate. Two groups of distinct binding sites were observed for ethylene on bundles of carbon nanotubes; this is in agreement with previously reported observations for ethane on this same sorbent. In addition, a consistent value of the specific surface area of the substrate was obtained from the ethylene and ethane data measured at approximately the same temperature. We have also determined the coverage dependence of the isosteric heat of adsorption for ethylene on the HiPco nanotube bundles. The reported experimental isosteric heat results are compared with simulation results for ethane and ethylene.

Investigation of the electrical resistance of single-walled carbon nanotube films in the temperature range 4.2–290 K

Electrical resistance of films made of the source material and purified HiPCO and Arc single-walled carbon nanotubes (SWCNTs) with a thickness of 20−40 μm is 2.4 to 45 Ω (electrical conductivity of 0.42 × 103 to 5.03 × 103 S/m) at room temperature. The films have been formed by vacuum microfiltration of SWCNT suspensions in toluene and characterized by Raman and X-ray photoelectron spectroscopy and scanning electron microscopy. The conductivity of the films at room temperature depends on the type and degree of purity of the material of nanotubes. The resistance of the films decreases with the increasing temperature over the range of 4.2–290 K, and the rate of the step-down decreases with increasing purity of the material of the nanotubes. The conductivity of the films is semiconducting in character, and the electron transport is consistent with three-dimensional hopping conductivity.

Copolymer-Controlled Diameter-Selective Dispersion of Semiconducting Single-Walled Carbon Nanotubes

The ability of a series of strictly alternating copolymers to selectively enwrap single-walled carbon nanotubes (SWNTs) is investigated. Seven copolymers comprising either fluorene or carbazole subunits separated by naphthalene, anthracene, and anthraquinone spacers are obtained in good yields via a Suzuki cross-coupling protocol. The 1,5-linked naphthalene, anthracene, and anthraquinone units are introduced to favor a spiral conformation of the polymer backbone in order to improve its SWNT wrapping features. Particularly high yields of polymers are obtained using the naphthalene-1,5-ditriflate precursor, highlighting the potential of bifunctional aryltriflates as precursors of copolymers. All polymers disperse HiPco SWNTs in toluene. The obtained dispersions are purified by density gradient centrifugation and their compositions are analyzed by photoluminescence (PL) spectroscopy. In their dispersing ability the polymers display more or less pronounced SWNT diameter selectivity. In particular, poly(9,9-di...

Coherent injection and control of ballistic charge currents in single-walled carbon nanotubes and graphite

We report results from a comprehensive set of experiments to study coherently controlled electrical current injection in single-walled carbon nanotubes (SWNTs) and graphite. Photocurrents were injected at room temperature through the quantum interference of single- and two-photon absorption pathways induced by 150-fs optical pulses with 660--980 and 1320--1960-nm central wavelengths, respectively, and with maximum intensities of 10 and 0.15 GW cm${}^{\ensuremath{-}2}$, respectively. Detection of the photocurrents was achieved via the emitted terahertz radiation. For bulk graphite samples and collinearly polarized 750- and 1500-nm pulses incident along the $c$ axis, injected current densities up to 12 kA cm${}^{\ensuremath{-}2}$ have been observed just under the surface, independent of crystal azimuthal orientation and comparable to those generated in InP or GaAs. Current densities are \ensuremath{\sim}5 times smaller for cross-polarized pulses. A vertically aligned forest of carbon nanotubes (tube diameters \ensuremath{\sim}2.5 \ifmmode\pm\else\textpm\fi{} 1.5 nm) illuminated with 700- and 1400-nm pulses collinearly polarized along the alignment direction yields a maximum current of 8 nA per tube (current density of 35 kA cm${}^{\ensuremath{-}2}$). Terahertz emission drops by only 3.5 times after 90\ifmmode^\circ\else\textdegree\fi{} sample rotation about the normal, which is explained in terms of an imperfect alignment distribution (angular spread \ensuremath{\sim}19.5\ifmmode^\circ\else\textdegree\fi{}) and sample birefringence. Unaligned arc discharge and HiPco SWNTs with diameters of 1.44 \ifmmode\pm\else\textpm\fi{} 0.15 and 0.96 \ifmmode\pm\else\textpm\fi{} 0.15 nm, respectively, were sorted into semiconducting and metallic tubes. Photocurrents injected with collinearly polarized 750- and 1500-nm pulses in such semiconducting SWNTs showed peak current magnitudes similar to those in the aligned nanotubes, while metallic tubes yielded currents at least ten times smaller. Semiconducting SWNT currents showed spectral features as the second-harmonic wavelength varied from 660 to 980 nm, which were more consistent with current injection based on band-band transitions than on excitonic absorption effects.

Adsorption Characteristics of Linear Alkanes Adsorbed on Purified HiPco Single-Walled Carbon Nanotubes

We present the results of adsorption isotherm measurements for propane films on single-walled carbon nanotubes, for coverages limited to the first layer. Isotherms were measured at six different te...

Photoluminescence of single‐wall carbon nanotube films

AbstractIn this work, we report the photoluminescence (PL) studies of the films produced by different methods from pristine single‐wall carbon nanotubes (SWNTs). The suspensions of CoMoCAT and HiPCO SWNTs were used to make two different types of films: the polymer films with embedded SWNTs and the SWNT films deposited onto quartz substrates through filtration. A density gradient ultracentrifugation (DGU) has been used for enrichment of the initial carbon nanotube suspensions with semiconducting SWNTs and extraction of various diameter nanotubes to reveal a role of the nanotube interaction in the films. Optical diagnostic techniques including Raman spectroscopy, UV–VIS–NIR absorption spectroscopy, and PL have been used for characterization and comparison of the initial suspensions and films formed from them. A PL mapping has revealed an arrangement of carbon nanotubes inside the films. A cross‐linkage between the individual SWNTs appeared to be higher inside the films deposited via filtration than in the polymer films with dispersed SWNTs. magnified image The images of objects under investigation (from left to right): a SWNT suspension after DGU; a film deposited onto quartz substrate and a polymer film with embedded SWNTs

The influence of oxygen-containing functional groups on the dispersion of single-walledcarbon nanotubes in amide solvents

Surface composition plays an important role in carbon nanotube dispersibility in differentenvironments. Indeed, it determines the choice of dispersion medium. In this paper theeffect of oxidation on the dispersion of HiPCO single-walled carbon nanotubes (SWNTs) inN-methyl-pyrrolidinone (NMP),N, N-dimethylformamide (DMF),N, N-dimethylacetamide(DMA), N-dodecyl-pyrrolidinone (N12P) and cyclohexyl-pyrrolidinone (CHP) was systematicallystudied. During the oxidation process, similar amounts of carboxylic acid and phenolicgroups were introduced to mostly already existing defects. For each solvent thedispersion limits and the absorption coefficients were estimated by optical absorptionanalysis over a range of SWNT concentrations. The presence of acid oxygenatedgroups increased SWNT dispersibility in NMP, DMF and DMA, but decreased inN12P and CHP. The absorption coefficients, however, decreased for all solventsafter oxidation, reflecting the weakening of the effective transition dipole of theπ–π transition with even limited extension functionalization and solvent interaction. Theanalysis of the results in terms of Hansen and Flory–Huggins solubility parametersevidenced the influence of dipolar interactions and hydrogen bonding on the dispersibilityof oxidized SWNTs.

Diameter-Dependent Solubility of Single-Walled Carbon Nanotubes

We study the solubility and dispersibility of as-produced and purified HiPco single-walled carbon nanotubes (SWNTs). Variation in specific operating conditions of the HiPco process are found to lead to significant differences in the respective SWNT solubilities in oleum and surfactant suspensions. The diameter distributions of SWNTs dispersed in surfactant solutions are batch-dependent, as evidenced by luminescence and Raman spectroscopies, but are identical for metallic and semiconducting SWNTs within a batch. We thus find that small diameter SWNTs disperse at higher concentration in aqueous surfactants and dissolve at higher concentration in oleum than do large-diameter SWNTs. These results highlight the importance of controlling SWNT synthesis methods in order to optimize processes dependent on solubility, including macroscopic processing such as fiber spinning, material reinforcement, and films production, as well as for fundamental research in type selective chemistry, optoelectronics, and nanophotonics.

Silver Nanorod Array Substrates Fabricated by Oblique Angle Deposition: Morphological, Optical, and SERS Characterizations

A comparative study of the solubilizing effect of polycyclic aromatic hydrocarbon (PAHs) on single-walled carbon nanotubes (SWCNTs) produced by the high-pressure decomposition of carbon monoxide (HiPco) and the arc discharge (AD) method has been carried out with the aid of fluorescence and Raman spectroscopy. For this study, polyphenyl and polyacene PAHs of different lengths are used. From the study it has been found that the binding energy of PAHs with AD SWCNTs is the same as that with HiPco SWCNTs. Shorter PAHs molecules better solubilize SWCNTs and in general smaller-diameter SWCNTs. Thus, given their smaller-diameter profile, significantly larger numbers of HiPco SWCNTs are solubilized compared to the number of AD SWCNTs.

Systematic Study of the Dispersion of SWNTs in Organic Solvents

Dispersions of as-produced HiPco single-walled carbon nanotubes (SWNTs) in a series of organic solvents were prepared by dilution with the aid of tip sonication. Mild centrifugation (∼945 g) was carried out to remove large bundles. Atomic force microscopy (AFM) studies revealed that the bundle size decreased as the dispersion was diluted. By measuring the UV−vis−NIR absorption before and after centrifugation as a function of the concentration, the dispersion limit of SWNTs in each solvent can be determined. Correlations between the dispersion limit and solvent solubility parameters, including the Hildebrand solubility parameter and three-dimensional Hansen solubility parameters, are explored, demonstrating that SWNTs are easily dispersed in solvents with Hildebrand solubility parameter range from ∼22−24 MPa1/2 and Hansen polarity component (δP) ∼12−14 MPa1/2. No clear correlation between dispersion limits and the dispersion force (δD) or hydrogen bonding force (δH) are evident. It is found, however, that the degree of dispersion depends critically on sample preparation conditions and in particular sonication time. Increased sonication times increase the amount of SWNTs debundled and solubilized but do not appear to affect the dispersion limit. However, increased sonication also induces discernible changes to the SWNTs themselves and in itself influences their solubility, under which conditions no clear solubility parameters can be determined.

Chemical Vapor Deposition Synthesis of Carbon Nanotubes Using Iron Catalysts

Single-walled carbon nanotubes (SWNTs) were synthesized via a novel chemical vapor deposition (CVD) technique incorporating iron catalysts. Stable aqueous solutions of the nanotubes using the anionic surfactant sodium dodecylbenzene sulfonate were also obtained, and the properties of as-produced SWNTs were documented through atomic force microscopy and Raman spectroscopy and compared with purified HiPCO SWNTs as a reference.

Enrichment of (8,4) Single‐Walled Carbon Nanotubes Through Coextraction with Heparin

Heparin sodium salt is investigated as a dispersant for dispersing single-walled carbon nanotubes (SWNTs). Photoluminescence excitation (PLE) spectroscopy is used for identification and abundance estimation of the chiral species. It is found that heparin sodium salt preferentially disperses larger-diameter Hipco SWNTs. When used to disperse CoMoCAT nanotube samples, heparin has a strong preference for (8,4) tubes, which have larger diameter than the predominant (6,5) in pristine CoMoCAT samples. PLE intensity due to (8,4) tubes increases from 7% to 60% of the total after threefold extractions. Computer modeling verifies that the complex of (8,4) SWNTs and heparin has the lowest binding energy amongst the four semiconducting species present in CoMoCAT. Network field-effect transistors are successfully made with CoMoCAT/heparin and CoMoCAT/sodium dodecylbenzene sulfonate (SDBS)-heparin (x3), confirming the easy removability of heparin.

Insights into the physics of spray coating of SWNT films

Spray coating is a scalable and high-throughput process for fabrication of transparent and conducting coatings (TCCs) composed of single-walled carbon nanotubes (SWNTs). Presently the fundamentals of this process are not well understood. We show that suppression of coalescence of spray droplets by sufficiently rapid heat- and mass-transfer yields homogeneous SWNT films by preventing the formation of ‘coffee stains’ of larger length scale. Such heat and mass transfer is driven by differential evaporation between the top and edges of the drops, whereas thermal and compositional effects on surface tension and buoyancy are weak. Ultrasonic spraying ensures that the droplets are deposited without significant splashing, and delayed splashing at higher Weber number is evidenced. We find that the performance of spray-coated TCCs made from HiPCO SWNTs is limited by bundle diameter rather than length of the constituent SWNTs and bundes. Vapor acid doping with concentrated sulfuric acid roughly doubles the conductivity of the TCCs.