HiPco Single-walled Carbon Nanotube Research Articles

Improved Laser‐Based Photoluminescence on Single‐Walled Carbon Nanotubes

Photoluminescence (PL) is a common tool to characterize various properties of single‐walled carbon nanotube (SWCNT) chirality distribution and the level of tube individualization in SWCNT samples. Most PL studies use conventional lamp light sources whose spectral distribution is filtered with a monochromator, but this results in a still impure spectrum with a low spectral intensity. Tunable dye lasers offer a tunable light source which cover the desired excitation wavelength range with a high spectral intensity, but their operation is often cumbersome. Herein, the design and properties of an improved dye‐laser system which is based on a Q‐switch pump laser are presented. The high peak power of the pump provides an essentially threshold‐free lasing of the dye laser, which substantially improves the operability. It allows operation with laser dyes, such as Rhodamin 110 and Pyridin 1, which are otherwise on the border of operation of the laser. The system allows to cover the 540–730 nm wavelength range with four dyes. In addition, the dye laser output pulses closely follow the properties of the pump, which directly provides a time‐resolved and tunable laser source. The performance of the system by measuring the PL map of a HiPco SWCNTs sample is demonstrated.

Systemic Delivery of Sirna-Based Therapeutics Using Single-Walled Carbon Nanotubes

Background: Carbon nanotubes (CNTs) are potential candidates for drug, antigen and nucleic acid delivery vehicle in nanomedicine. The large surface of CNTs provides structural advantages and allows loading of functional groups or therapeutics such as nucleic acid, drugs and proteins. Aim: Our study is to deliver siRNA to cells using single walled carbon nanotube (SWNT) to achieve gene silencing effect. Methods: SWNT was functionalized by dissolving 1 mg of HiPCo SWNTs and 5 mg of PL-PEG-NH or PL-PEG-maleimide in 5 mL of water, sonicated for 60 min at room temperature and centrifuged for 6 h. The supernatant were collected and measured their concentration at 808 nm by ultraviolet-VIS-NIR spectrometer. The resulted noncovalent functionalized SWNTs were further conjugated with a 5′-thiolated siRNA against GFP (siGFP) and RFP (siRFP). In vitro silencing of GFP and RFP expression by SWNT-siRNA were evaluated in stable expression cell lines by fluorescence spectroscopy. Results: A range of 50%–80% GFP expression knocked down was observed in H1299, HeLa, MCF-7 and 293T cells by SWNT-siGFP. SWNT conjugated with both siGFP and siRFP were shown knocking down both GFP and RFP simultaneously in H1299 stable coexpression cell line. Also, gene silencing was observed despite incubation with inhibitors on different cellular internalization pathways. They are chlorpromazine for clathrin-mediated endocytosis inhibitor, genistein for caveolae-mediated endocytosis inhibitor and sodium azide for energy depletion agent. We also found that the internalization of SWNT by the nonphagocytic cells (H1299) did not solely depend on single cellular entry pathway to achieve the gene silencing effect. Conclusion: The successful knockdown of GFP expression in different cell lines indicated that siRNA were released from the conjugated SWNT-siRNA in the cytoplasm and silent the gene expression. It is also indicated that 2 different types of siRNA targets could be conjugated with SWNT and achieved 2 different gene silencing effects simultaneously.

Electronically Pure Single Chirality Semiconducting Single-Walled Carbon Nanotube for Large Scale Electronic Devices

Abstract Carbon nanotube thin film transistors (TFTs) with characteristics resembling those of TFTs constructed on amorphous silicon, low-temperature polycrystalline silicon and metal oxides were fabricated on (6,5) single chirality single-walled carbon nanotube (SWCNT) thin film deposited from electronically pure semiconducting (6,5) single chirality single-walled carbon nanotube (SWCNT) ink. This ink was extracted in industrial scale from raw SWCNTs produced using high pressure carbon monoxide conversion, and deposited on pretreated substrates to form uniform and consistent (6,5) HiPCO SWCNT thin film using solution process. The (6,5) HiPCO SWCNT thin films were characterized as pure semiconductor without metallic impurities showing classic nonlinear current-bias curves in Schottky-type diodes. Both N-type and P-type (6,5) HiPCO SWCNT TFTs were fabricated with femto Ampere off-current and ION/IOFF ratio of 108 by depositing SiNx and HfO2 dielectrics on the top of (6,5) HiPCO SWCNT thin films, respectively. The (6,5) HiPCO SWCNT inverter with voltage gain of 52 was also demonstrated by wire-bonding one P-type HiPCO SWCNT TFT to one N-type HiPCO SWCNT TFT.

Quantitative investigation of mineral impurities of HiPco SWCNT samples: Chemical mechanisms for purification and annealing treatments

HiPco single-walled carbon nanotube samples contain a non-negligible amount (about 30wt.%) of metal-based impurities. These impurities are prejudicial to the development of CNT-based applications. In the literature, there is no agreement for their nature and their relative content. Consequently, the standard purification treatments could not be selective enough and they lead to damage the carbon nanotubes. In this work, we have deeply investigated the mineral impurities of a raw HiPco SWCNT sample by means of several techniques. We were able to identify and quantify at least six iron-based phases that coexist in the HiPco SWCNT samples. The raw SWCNTs were submitted to a selective purification treatment involving a high temperature treatment under chlorine. The results show that the efficiency of the metal removal is improved by increasing the temperature of treatment leading to a purification yield of 95.4%, while preserving the structural quality of the SWCNTs. The analysis of the mineral residues in the purified and annealed SWCNT samples allows to propose the chemical mechanisms involved during the chemical treatments.

Controlling the adsorption and desorption of double-stranded DNA on functionalized carbon nanotube surface

We demonstrated controlled adsorption and desorption of double-stranded DNA (dsDNA) on single-walled carbon nanotube (SWNT) surface functionalized with polyethyleneglycol (PEG SWNT). First, when dsDNA molecules were mixed with the PEG SWNT solution, the DNA molecules spontaneously adsorbed onto the PEG SWNT surface and formed dsDNA–PEG SWNT conjugates without sonication. Next, we succeeded in detaching the dsDNA adsorbed on PEG SWNT by annealing at 95°C for 30min. These results were confirmed using atomic force microscopy, agarose gel electrophoresis, and micro-Raman spectroscopy. In contrast, when we used the usual SWNT produced by the high-pressure carbon monoxide method (HiPco SWNT), the DNA molecules were fragmented during the adsorption process as sonication was necessary for the hybridization of DNA–SWNT conjugates. Furthermore, detachment of DNA molecules from HiPco SWNT by annealing was impossible. Our method may be useful for developing DNA devices using SWNTs as substrates when it is combined with previously established various biochemical techniques.

Demetalization of single-walled carbon nanotube thin films with microwave irradiation

The microwave irradiation effects on purified HiPCO and CoMoCat single-walled carbon nanotube (SWNT) thin films are investigated. The surface conductivities of the SWNT films are extracted from the measured THz transmission coefficients to provide a direct indication of the metallic content in the films. The observed drastic conductivity decrease indicates a significant metallic content reduction after the microwave irradiation. Two different laser excitations are applied for Raman spectroscopy to reveal the response of different nanotube species. The Raman spectra of both HiPCO and CoMoCat thin films confirm the decrease of metallic carbon nanotubes. The observed microwave-induced effects may potentially lead to a convenient scheme for demetalization of single-walled carbon nanotube mixtures.

Single-Walled Carbon Nanotube Materials as T2-Weighted MRI Contrast Agents

With their unique nanoscalar properties, single-walled carbon nanotube (SWNT) materials are widely studied for various biological applications. Herein, we report the efficiency of full-length HiPco SWNTs and ultra-short SWNTs (US-tubes) as T2-weighted MRI contrast agents. Analysis has concluded that the superparamagnetic SWNT materials (especially US-tubes) are a new class of high-efficacy contrast agents having performance contributions from both the iron catalyst nanoparticles (originating from the synthesis of SWNT materials) and the carbon SWNT material itself. The superparamagnetic US-tubes with their short length (<100 nm), negligible metal content (<1% Fe (wt %)), and superior T2 relaxation efficiency (T2 = 31.7 ms per mg SWNT at 3 T and 37 °C) are the most promising candidates for advanced applications such as molecular and cellular imaging using MRI.

Synthesis and Characterization of FePt Nanoparticle/Single Walled Carbon Nanotube Composites

We report the synthesis and characterization of FePt nanoparticles (NPs)/single walled carbon nanotube (SWNTs) nanocomposites, which might have important potential applications to orient CNTs and the development of new catalysts. The crystallite size of FePt NPs is about 2.5-4 nm and the Fe atom content ranges from 50% to 65%. HiPCO SWNTs have been decorated with FePt nanoparticles under mild conditions without any pretreatment. When the bundle size of HiPCO SWNTs is about 20 nm, FePt NPs mostly attach on the sidewalls of SWNTs. The loading of FePt nanoparticles on the SWNTs bundles can be conveniently controlled by adjusting the initial amount of FePt NPs. The nanocomposite showed magnetic properties in a magnetic field. TEM, HRTEM, and EDS spectra were performed to observe the nanostructure of these nanocomposites.

Assessment of Chemically Separated Carbon Nanotubes for Nanoelectronics

It remains an elusive goal to obtain high performance single-walled carbon-nanotube (SWNT) electronics such as field effect transistors (FETs) composed of single- or few-chirality SWNTs, due to broad distributions in as-grown materials. Much progress has been made by various separation approaches to obtain materials enriched in metal or semiconducting nanotubes or even in single chiralties. However, research in validating SWNT separations by electrical transport measurements and building functional electronic devices has been scarce. Here, we performed length, diameter, and chirality separation of DNA functionalized HiPco SWNTs by chromatography methods, and we characterized the chiralities by photoluminescence excitation spectroscopy, optical absorption spectroscopy, and electrical transport measurements. The use of these combined methods provided deeper insight to the degree of separation than either technique alone. Separation of SWNTs by chirality and diameter occurred at varying degrees that decreased with increasing tube diameter. This calls for new separation methods capable of metallicity or chirality separation of large diameter SWNTs (in the approximately 1.5 nm range) needed for high performance nanoelectronics. With most of the separated fractions enriched in semiconducting SWNTs, nanotubes placed in parallel in short-channel (approximately 200 nm) electrical devices fail to produce FETs with high on/off switching, indicating incomplete elimination of metallic species. In rare cases with a certain separated SWNT fraction, we were able to fabricate FET devices composed of small-diameter, chemically separated SWNTs in parallel, with high on-/off-current (I(on)/I(off)) ratios up to 105 owing to semiconducting SWNTs with only a few (n,m) chiralities in the fraction. This was the first time that chemically separated SWNTs were used for short channel, all-semiconducting SWNT electronics dominant by just a few (n,m)'s. Nevertheless, the results suggest that much improved chemical separation methods are needed to produce nanotube electronics at a large scale.

Diameter-Selective Fractionation of HiPco Single-Walled Carbon Nanotubes in Repeated Functionalization Reactions

The functionalization reaction of the diamine-terminated oligomeric poly(ethylene glycol) with a purified HiPco single-walled carbon nanotube sample was repeated multiple times to yield the corresponding number of soluble fractions and the final insoluble residue. According to results from the characterization with various instrumental techniques, these soluble fractions and the final residue all have different nanotube diameter distributions from that found in the starting sample. A general conclusion is that the functionalization and solubilization are selective toward smaller diameter nanotubes, regardless of their being semiconducting or metallic. Mechanistic implications, especially with respect to the post-production separation in terms of the nanotube metallicity, are discussed.

The effect of purification of single-walled carbon nanotube bundles on the alcoholsensitivity of nanocomposite Langmuir–Blodgett films for SAW sensing applications

HiPco (high-pressure CO dissociation process) single-walled carbon nanotube (SWCNT)bundles containing Fe particles were purified in a two-step purification process by thermalannealing in oxygen and post-treatment in HCl. Nanocomposite films of pristine andpurified SWCNTs embedded in an organic matrix of cadmium arachidate (CdA) wereprepared by a Langmuir–Blodgett (LB) molecular engineering technique with a fixedweight filler content of 75 wt% onto a surface acoustic wave (SAW) transducer operatingas an oscillator at a frequency of 433 MHz. The raw and purified samples werecharacterized at various stages of the purification process using thermogravimetricanalysis (TGA), high-resolution transmission electron microscopy (HR-TEM), alongwith energy-dispersive x-ray spectroscopy (EDS), field emission scanning electronmicroscopy (FE-SEM) and x-ray diffraction (XRD). Functional characterizations of theSWCNT–nanocomposite-based SAW sensors were investigated towards methanol,isopropanol and ethanol, and demonstrated high sensitivity, reversibility, fastresponse and ppm level detection at room temperature. Results indicate that thesensitivity of the SAW sensors based on a nanocomposite film of oxygen-annealedSWCNTs is enhanced to the alcohols tested at room temperature. Purification of theSWCNTs in the nanocomposite film affects the SAW sensitivity to alcohol bymodulating the sensing properties. The sensing mechanisms are analysed anddiscussed.

Aggregation Effects on the Raman Spectroscopy of Dielectrophoretically Deposited Single-Walled Carbon Nanotubes

The effect of aggregation on surfactant-suspended individual single-walled carbon nanotube (SWNT) Raman spectroscopy has been explored in the context of dielectrophoretic separation. The Raman spectra of individual surfactant-suspended HiPco SWNTs deposited on a substrate and the same suspension deposited via dielectrophoresis were compared as a function of iterative aggregation states. The evolution of the samples' radial breathing modes and tangential modes at multiple excitation wavelengths (514, 633, and 785 nm) illustrates a direct correlation between changes in the Raman spectra and a broadening and downshifting of resonance transition energies. Dielectrophoresis samples exhibited Raman changes similar to control samples, indicating characterization of electronic separation is compromised by aggregation effects.

Characterization of Single-walled Carbon Nanotube Fibers and Correlation with Stretch Alignment

AbstractStructural, electrical and thermal methods are applied to characterize single-walled carbon nanotube (SWNT) fibers with post-extrusion stretching as the independent variable. HiPco SWNTs are dispersed in water using sodium dodecyl sulfate (SDS), and then co-extruded with polyvinyl alcohol (PVA)/water through a long syringe into a rotating water/PVA coagulation bath. Partial axial alignment is thereby achieved, and further enhanced by applying tension to the flexible green fibers in the coagulation bath. Our findings include: (1) X-ray diffraction shows that the full width at half maximum (FWHM) of the Bragg peaks decreases from 55 (as-extruded) to less than 30 degrees by 80% elongation. That is, SWNT alignment increases linearly with stretch (up to 80%). (2) In resistivity at room temperature vs. stretch ratio, result shows an initial rapid decrease followed by saturation; essentially all the improvement in electronic transport is obtained once alignment reached 40° FWHM. (3) Annealing in hydrogen at 1000°C is performed to drive out PVA, to improve inter-tube and inter-bundle contacts, and to heal damage on the tube walls. Such annealing is found to increase conductivity by at least 4 orders of magnitude. (4) Below 25 K, resistivity vs. temperature of the annealed fiber is well-represented by Coulomb gap variable range hopping (CG-VRH). It is rationalized that the Coulomb interactions in disordered systems open a gap at the Fermi energy. Above 25 K, the thermal energy is greater than the Coulomb gap, so thermal activation is more probable than correlated electron hops. (5) Finally, a measurable thermal conductivity is observed as stretch alignment increases.

Surface chemistry and pore structure of purified HiPco single-walled carbon nanotube aggregates

HiPco single-walled carbon nanotube (HCNT) containing about 30 wt% of Fe were purified by the 2-step process of air oxidation and successive washing with hydrochloric acid. The surface chemistry and pore structures of HCNT aggregates before and after purification were examined by X-ray photoelectron spectroscopy (XPS) and N 2 adsorption at 77 K. XPS results show that the purification treatment introduces carbon-based oxides groups on the surface of HCNT and removes the Fe from the HCNT aggregates. The N 2 adsorption isotherm on HCNT is of Type II and it changes to Type IV as a result of purification. Purification decreases the average pore width from 3.5 to 1.0 nm and develops the micropore structure.

Effect of Purification on Pore Structure of HiPco Single-Walled Carbon Nanotube Aggregates

HiPco single-walled carbon nanotube (HPNT) containing Fe was purified by one-step purification with HCl-washing (D-method) and two-step purification with HCl-washing after air oxidation (GD-method)...