Individual Single-walled Nanotubes Research Articles

One-Dimensional Poole-Frenkel Conduction in the Single Defect Limit.

A single point defect surrounded on either side by quasi-ballistic, semimetallic carbon nanotube is a nearly ideal system for investigating disorder in one-dimensional (1D) conductors and comparing experiment to theory. Here, individual single-walled nanotubes (SWNTs) are investigated before and after the incorporation of single point defects. Transport and local Kelvin Probe force microscopy independently demonstrate high-resistance depletion regions over 1.0 μm wide surrounding one point defect in semimetallic SWNTs. Transport measurements show that conductance through such wide depletion regions occurs via a modified, 1D version of Poole-Frenkel field-assisted emission. Given the breadth of theory dedicated to the possible effects of disorder in 1D systems, it is surprising that a Poole-Frenkel mechanism appears to describe defect scattering and resistance in this semimetallic system.

Systematic determination of absolute absorption cross-section of individual carbon nanotubes.

Optical absorption is the most fundamental optical property characterizing light-matter interactions in materials and can be most readily compared with theoretical predictions. However, determination of optical absorption cross-section of individual nanostructures is experimentally challenging due to the small extinction signal using conventional transmission measurements. Recently, dramatic increase of optical contrast from individual carbon nanotubes has been successfully achieved with a polarization-based homodyne microscope, where the scattered light wave from the nanostructure interferes with the optimized reference signal (the reflected/transmitted light). Here we demonstrate high-sensitivity absorption spectroscopy for individual single-walled carbon nanotubes by combining the polarization-based homodyne technique with broadband supercontinuum excitation in transmission configuration. To our knowledge, this is the first time that high-throughput and quantitative determination of nanotube absorption cross-section over broad spectral range at the single-tube level was performed for more than 50 individual chirality-defined single-walled nanotubes. Our data reveal chirality-dependent behaviors of exciton resonances in carbon nanotubes, where the exciton oscillator strength exhibits a universal scaling law with the nanotube diameter and the transition order. The exciton linewidth (characterizing the exciton lifetime) varies strongly in different nanotubes, and on average it increases linearly with the transition energy. In addition, we establish an empirical formula by extrapolating our data to predict the absorption cross-section spectrum for any given nanotube. The quantitative information of absorption cross-section in a broad spectral range and all nanotube species not only provides new insight into the unique photophysics in one-dimensional carbon nanotubes, but also enables absolute determination of optical quantum efficiencies in important photoluminescence and photovoltaic processes.

Carbon Single Wall Nanotubes As a Low-Barrier, Copper-Free Back Contact to CdTe Solar Cells

With a 1.45 eV band gap, a high absorption coefficient, and proven low-cost, high-volume manufacturing, CdTe-based photovoltaic (PV) technology accounted for more than 7% of the 100 GW of solar power generating capacity that was installed worldwide by the end of 2012. Copper doping of CdTe assists in forming back contacts to CdTe, but Cu is known to diffuse through the device and produce junction-shunting pathways. Because of the detrimental effects of Cu, several material systems have been investigated for use as the back contact for Cu-free CdTe devices. If long-term degradation of the photovoltaic performance could be eliminated, the levelized cost of electricity would be subtantially reduced without, in this case, significant changes in the device architecture or manufacturing process flow.Here, we discuss results1 that demonstrate that carbon single-wall nanotube (SWNTs) films can make a high-performance electrical back contact to CdTe solar cells without the use of Cu. Back contacts formed with SWNT films showed improved open circuit voltage in comparison to cells fabricated with standard Au/Cu back contacts and, once overcoated with a thin metal layer, the solar-to-electric conversion efficiency was higher as well. The results are understood by considering that individual SWNTs within the film extend through the film’s thickness and make barrier-less contacts to individual CdTe grains in the active layer of the device.This work was supported by the U.S. Department of Energy under Award Number DE-SC0006349 and by faculty start-up funds from the University of Toledo, and was conducted in collaboration with the Wright Center for Photovoltaics Innovations and Commercialization (http://www.utoledo.edu/research/pvic/)(1) Phillips, et al., Nano Lett., 2013, 13 (11), pp 5224–5232

Production single-walled carbon nanotubes by chemical vapor deposition from mechanism to patterned growth for electro devices

The ability to controllably obtain ordered carbon nanotube architectures is important to fundamental characterizations and potential applications of electrical devices. Controlled synthesis involving chemical vapor deposition (CVD) has been an effective strategy to order singlewalled nanotubes (SWNTs) on patterned catalyst. In this paper, Single-walled carbon nanotubes are synthesized by chemical vapor deposition of methane at controlled locations on a silicon substrate. This synthetic approach has allowed individual SWNT wires to be grown from controlled surface sites by catalyst patterning and has led to interconnecting SWNT electrical devices. The combined synthesis and microfabrication technique presented here allows a large number of ohmically contacted nanotube devices with controllable length to be placed on a single substrate.

A new lower limit for the bond breaking strains of defect-free carbon nanotubes: Tight binding MD simulation study

The Order(N) Tight Binding Molecular Dynamics (TBMD) algorithms applied to simulate the tensile elongations of short (2–2.5nm) armchair and zigzag Single Walled Carbon Nanotubes (SWCNTs) without bond breakings or defect formation. Simulations are repeated at high temperatures. We fix the lower limit of breaking strains to short SWCNTs without bond breaking or 5–7 defects formation. At room temperature, the simulated (4,4) SWCNT is able to carry the strain up to 130% of the relaxed tube length without bond breaking or 5–7 defects formation. This value is 127% for (11,0) SWCNT, 125% for (17,0) SWCNT, 123% for (10,10) SWCNT. Bond breakings occur at lower strain values in defect-free, short nanotubes as the radii of the nanotubes increase, regardless of their chirality. This is true even when we heat the tubes to higher temperatures. Bond breaking strain values, tensile strength, Young’s moduli of the SWCNTs are obtained as functions of temperature. In general, defect-free zigzag nanotubes exhibit higher tensile strength than armchaired ones. Young’s moduli of defect-free individual single-wall nanotubes are found to be in the range of 0.400TPa within the elastic limit. At room temperature and experimentally realizable strain values, thinner tubes are more resistant to bond breaking and zigzag tubes over armchair ones. The same trend still holds at high temperatures although the resistance to strain gets lowered. We observe a slight decrease of the tensile strength with increasing temperatures. A similar behavior is also observed in Young’s moduli. These results are important in determining the true breaking strains of SWCNTs.

PATTERNED GROWTH OF SINGLE-WALLED CARBON NANOTUBES ON SILICON WAFER FOR ELECTRONIC DEVICES BY CHEMICAL VAPOR DEPOSITION PROCESS

The ability to controllably obtain ordered carbon nanotube architectures is important for fundamental characterizations and potential applications of electrical devices. Controlling the synthesis process applied chemical vapor deposition (CVD) has been an effective technique to order single-walled nanotubes (SWNTs) on patterned catalyst. In this paper, single-walled carbon nanotubes are synthesized by chemical vapor deposition of methane at positioned locations on a silicon substrate. This synthetic approach has allowed individual SWNT to be grown from appointed surface sites by catalyst patterning and has led to interconnecting SWNT electrical devices. The combined synthesis and microfabrication technique presented here enable the developing of many ohmically contacted nanotube devices that can be controlled the size . Base on TEM results, SWNTs are formed via an open-ended, base-growth mechanism (VLS mechanism).

Single-Walled Aluminosilicate Nanotube/Poly(vinyl alcohol) Nanocomposite Membranes

The fabrication, detailed characterization, and molecular transport properties of nanocomposite membranes containing high fractions (up to 40 vol %) of individually-dispersed aluminosilicate single-walled nanotubes (SWNTs) in poly(vinyl alcohol) (PVA), are reported. The microstructure, SWNT dispersion, SWNT dimensions, and intertubular distances within the composite membranes are characterized by scanning and transmission electron microscopy (SEM and TEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), XRD rocking curve analysis, small-angle X-ray scattering (SAXS), and solid-state NMR. PVA/SWNT nanocomposite membranes prepared from SWNT gels allow uniform dispersion of individual SWNTs in the PVA matrix with a random distribution of orientations. SAXS analysis reveals the length (∼500 nm) and outer diameter (~2.2 nm) of the dispersed SWNTs. Electron microscopy indicates good adhesion between the SWNTs and the PVA matrix without the occurrence of defects such as voids and pinholes. The transport properties of the PVA/SWNT membranes are investigated experimentally by ethanol/water mixture pervaporation measurements, computationally by grand canonical Monte Carlo and molecular dynamics, and by a macroscopic transport model for anisotropic permeation through nanotube-polymer composite membranes. The nanocomposite membranes substantially enhance the water throughput with increasing SWNT volume fraction, which leads to a moderate reduction of the water/ethanol selectivity. The model is parameterized purely from molecular simulation data with no fitted parameters, and shows reasonably good agreement with the experimental water permeability data.

Synthesis of single-walled carbon nanotubes by aerosol method

Two aerosol synthesis methods of carbon nanotubes are considered. The possibility of separation of individual single-walled nanotubes from the bundle in the gas phase and control of their parameters with the help of etching agents is shown. The advantage of the aerosol synthesis methods of nanotubes both for variation of parameters of carbon nanotubes (diameter and morphology) and for their subsequent use in hightech areas (electronics, optics, electrochemistry) is discussed.

ChemInform Abstract: Perspectives on Electrochemical Insertion of Lithium in Carbon Nanotubes

AbstractReview: 13 refs.

Electron Transport in Carbon Nanotubes

Over the past decade, transport measurements on individual single-wall nanotubes have played a prominent role in developing our understanding of this novel carbon conductor. These measurements have identified both metallic and semiconducting nanotubes, determined their dominant electronic scattering mechanisms, and elucidated in great detail the properties of their quantized energy spectrum. Recent technological breakthroughs in nanotube device fabrication and electronic measurement have made possible experiments of unprecedented precision that reveal new and surprising phenomena. In this review, we present the fundamental properties of nanotubes side by side with the newest discoveries and also discuss some of the most exciting emerging directions.

Calculation of the sizes of individual few-walled carbon nanotubes and their bundles

The temperature dependences of the number of nucleating single-walled and few-walled nanotubes and their diameter have been determined over a wide range of model parameters in the framework of the problem regarding the nucleation of carbon nanotubes from catalytic particles supersaturated with carbon. It has been demonstrated that, initially, individual nanotubes nucleate and grow and, then, they can be joined together into bundles. The mechanism of the formation of bundles in the proposed model follows from the quantum-chemical analysis of the steady-state growth of nanotubes at the level of release of individual carbon atoms. During the growth, the axis of the nanotube rotates about the normal to the surface of the catalytic particle. This leads to the cross-linking of nanotubes into bundles. The characteristic diagram of the regions of the existence of individual single-walled, few-walled, and multiwalled nanotubes and their bundles has been constructed as a function of the temperature and the size of catalytic particles.

Perspectives on Electrochemical Insertion of Lithium in Carbon Nanotubes

a single walled nanotube (SWNT) can be conceived as wrapping a one-atom-thick layer of graphite, called graphene, into a seamless cylinder with diameters in the range of 1-2 nm and lengths of several hundreds micrometer. They form long crystalline bundles consisting of a few to thousands of individual SWNTs packed in triangular lattices. The interstitial channels with a size of 0.6 nm provide the necessary intercalation sites analogous to those found in the interlayer galleries in graphite or the tetrahedral/octahedral vacancies in fcc C60. Lithium ion batteries are the main power source in today’s portable electronic devices. These also bear the great potential to take over as power sources of electric vehicles and hybrid electric vehicles. Owing to the successful development of carbon based anodes to be incorporated into lithium ion batteries,1 lithium intercalation into, for example, different carbon nanostructured materials emerged as an interdisciplinary topic to improve the overall device performances. Additionally, the outstanding electrical conductivity,

Cs corrected STEM EELS: Analysing beam sensitive carbon nanomaterials in cellular structures

Identification of individual single wall nanotubes (SWNTs) within a cellular structure can provide vital information towards understanding the potential mechanisms of uptake, their localisation and whether their structure is transformed within a cell. To be able to image an individual SWNT in such an environment a resolution is required that is not usually appropriate for biological sections. Standard transmission electron microscopy (TEM) techniques such as bright field imaging of these cellular structures result in very weak contrast. Traditionally, researchers have stained the cells with heavy metal stains to enhance the cellular structure, however this can lead to confusion when analysing the samples at high resolution. Subsequently, alternative methods have been investigated to allow high resolution imaging and spectroscopy to identify SWNTs within the cell; here we will concentrate on the sample preparation and experimental methods used to achieve such resolution.

Experimentally Determined Redox Potentials of Individual (n,m) Single‐Walled Carbon Nanotubes

Nanotubes reveal their potential: The fabrication of a thin film that retains isolated single-walled nanotubes (SWNTs) allows the experimental determination of the redox potentials of many individual SWNTs that have different chirality indexes (n,m). The method is simple and applicable to all individual SWNTs whose near-IR photoluminescence (PL) is detectable (see picture). Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

A "Blue" Shift of Optical Absorption Bands of Single-Wall Nanotubes Grown from C:BN Mixtures by Arc-Discharge Technique

The electron and phonon properties of single-wall nanotubes synthesized from C:BN mixtures by arc-discharge technique have been analyzed. The BN content was varied from 0 to 50 weight%. The direct measurements of the absorption spectra of hetero-tubes obtained were performed for the suspensions of individual single-wall nanotubes in 1%-SDBS/D2O solution. The main optical absorption bands E sem 11 , E sem 22 , E met 11 ... were shifted toward the part of the spectrum while the BN content was increased in the initial mixture used for synthesis. Under all BN contents (0-50%) the typical features of carbon single-wall nanotubes were observed in the Raman spectra of heterotubes grown. No significant changes in G-mode (at 1592 cm -1 ) have been detected. In a low-frequency range a position of the dominating Raman breathing mode showed a blue while the BN content in the initial mixture increased. This was interpreted as an evidence of the bandgap increase in C:BN heterotubes. The shift of the optical absorption bands (about 140 nm) has been ascribed to the effect of incorporation of B and N atoms or BN clusters into the graphitic lattice of the nanotube wall. This led to the bandgap enlarge.

Uptake of Noncytotoxic Acid-Treated Single-Walled Carbon Nanotubes into the Cytoplasm of Human Macrophage Cells

Water-soluble single-walled nanotubes (SWNTs) are being tested as contrast agents for medical imaging and for the delivery of therapeutically active molecules to target cells. However, before they become used commercially, it will be essential to establish their subcellular distribution and whether they are cytotoxic. Here we characterize uptake of unlabeled, acid-treated, water-soluble SWNTs by human monocyte derived macrophage cells using a combination of Raman spectroscopy and analytical electron microscopy and compare our findings to previous work on unpurified SWNTs. Raman spectroscopy demonstrated that acid-treated SWNTs had a greater number of functional groups on the carbon walls than nontreated SWNT. The acid-treated SWNTs were less aggregated within cells than unpurified SWNTs. Bundles, and also individual acid-treated SWNTs, were found frequently inside lysosomes and also the cytoplasm, where they caused no significant changes in cell viability or structure even after 4 days of exposure.

Electrical and magnetic interaction along a defective single-walled carbon nanotube channel

We study the electrical and magnetic interaction in a low conduction regime for laterally as-grown defective single-walled carbon nanotube channel as functions of bias and gate voltage, combined with direct current and magnetic phase image by current-atomic force microscopy and magnetic force microscopy. For the SWNT field effect transistor at very low bias direct imaging of the current flow on the 0.9 and 2 nm diameter single-walled nanotube (SWNT) devices revealed that locally conducting islands occur along the SWNT channel, and become an origin of electrical behavior in the stage of minimal conduction. In contrast, the homogenous magnetic interaction along the as-laterally-grown individual SWNT channel observed by magnetic force measurements suggest a hint that as-grown single SWNT channel may be a reliable candidate for use in magnetoelectronics, regardless of whether clean or defective SWNT.

Identifying Individual Single-Walled and Double-Walled Carbon Nanotubes by Atomic Force Microscopy

We show that the number of concentric graphene cylinders forming a carbon nanotube can be found by squeezing the tube between an atomic force microscope tip and a silicon substrate. The compressed height of a single-walled nanotube (double-walled nanotube) is approximately two (four) times the interlayer spacing of graphite. Measured compression forces are consistent with the predicted bending modulus of graphene and provide a mechanical signature for identifying individual single-walled and double-walled nanotubes.

Dynamic dielectric response and electron-energy-loss spectra of individual single-walled BN nanotubes

Motivated by the recent electron-energy-loss-spectroscopy (EELS) experiment of Arenal et al. [Phys. Rev. Lett. 95, 127601 (2005)], we investigate the collective $\ensuremath{\pi}$-electronic excitations in individual boron nitride single-walled nanotubes (BN-SWNTs) with a zigzag wrapping. The dynamic dielectric response of such tubes is treated within a self-consistent-field approach using the one-particle states of the $\ensuremath{\pi}$-electron system of the BN-SWNTs derived from a simple two-band tight-binding model. Based on this approach, we obtain explicit analytic expressions for the real and imaginary parts of the frequency- and wave-number-dependent dielectric function of the system, whereby the electron-energy-loss function can easily be calculated. Numerical results for this function are presented for several zigzag BN-SWNTs in order to illustrate the possible electron-energy-loss spectra, and each tube is found to support only one branch of the wave-number-dispersed collective $\ensuremath{\pi}$-plasmon mode for each transferred quantum angular momentum $L$. In this respect, our results are in good agreement with the experiment, where only one pronounced peak, which can presumably be attributed to the $\ensuremath{\pi}$-plasmon excitations with a small $L$ and a small transferred momentum $q$, dominates the electron-energy-loss spectra in the range up to $8\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The wave-number dispersion of the plasmon modes with different $L$'s is extracted from the calculated spectra of the real part of the dielectric function, and it is shown that the plasmon dispersion curves exhibit a number of unusual characteristics that could be observable in momentum-resolved EELS experiments.

Interactions between tripodal porphyrin hosts and single walled carbon nanotubes: an experimental and theoretical (DFT) account

We describe a strategy for dispersing single walled nanotubes (SWNTs) in organic solvents using supramolecular coating with tailor-made, structurally adjustable tripodal porphyrin receptors. These have the ability to recognise SWNTs from DMF–toluene mixtures. HR TEM, TM AFM and SEM measurements showed that the hosts wrap around individual arc-made SWNTs, giving monodispersed composites in DMF which are stable for weeks. The dispersed composites were studied by Raman and fluorescence spectroscopies, including laser scanning confocal microscopy (for aggregates incorporated in cells). These porphyrin hosts encapsulate SWNTs based on π–π type interactions in an analogous manner to those observed by single crystal X-ray diffraction in their C60 complexes. These interactions may be further reinforced by porphyrin–porphyrin stacking. Density functional theory (DFT) calculations predicted the structure of the SWNT : porphyrin host complex or composite formed and the binding energies of tripodal porphyrin hosts in composites with either C60 or SWNT as guests.