Aligned Single-walled Carbon Nanotubes Research Articles

The production of large scale ultrathin aligned CNT films by combining AC electric field with liquid flow

We report a simple and versatile technique combining the use of an AC electric field with a liquid shear force to prepare ultrathin aligned CNT films on solid substrates. Multiwalled carbon nanotubes (MWCNTs), which were synthesized by a template method and acid-treated single walled carbon nanotubes (SWCNTs) were dispersed in water and used for the ultrathin film fabrication. A solid substrate was immersed in the CNT dispersions and withdrawn at constant speed under AC electric field. SEM images of the substrate showed that CNTs were aligned with the AC electric field and the withdrawal direction and formed uniform films with a thickness around 10nm for SWCNTs and 90nm for MWCNTs. Repeating the deposition process increases the density and size of the film while also maintaining nanometer-scale thickness. Unidirectional alignment of CNTs was also confirmed by Raman spectra and electric conductivity measurements. It was found that ultrathin films of aligned SWCNTs exhibited very high anisotropic electrical conductivity with conductivity measured parallel to the alignment direction 3.3×105 times higher than that measured in the perpendicular direction. We demonstrate that use of the aligned ultrathin SWCNT film for a unidirectional alignment of liquid crystal.

Torsion-Sensing Material from Aligned Carbon Nanotubes Wound onto a Rod Demonstrating Wide Dynamic Range

A rational torsion sensing material was fabricated by wrapping aligned single-walled carbon nanotube (SWCNT) thin films onto the surface of a rod with a predetermined and fixed wrapping angle without destroying the internal network of the SWCNTs within the film. When applied as a torsion sensor, torsion could be measured up to 400 rad/meter, that is, more than 4 times higher than conventional optical fiber torsion sensors, by monitoring increases in resistance due to fracturing of the aligned SWCNT thin films.

Synthesis and Characterization of Carbon Nanotubes from Palm Oil by Aerosol-Assisted CVD

This paper will report on the synthesis of bundles of aligned single wall carbon nanotubes (SWCNTs) and multiwall carbon nanotubes (MWCNTs) from palm oil precursor and ferrocene as catalyst source by two stage aerosol-assisted CVD system at various deposition temperature ranging from 700-900oC. Palm oil was pyrolised into the furnace which contained the catalyst source producing black substances at the wall of the reaction furnace which were then collected to be characterized. Field emission scanning electron microscopy equipped with energy dispersive X-ray was used to obtain weight percentage, identification of samples and image of CNTs which showed different structures and diameters of CNTs relative to the deposition temperature of furnace. Raman Spectroscopy was used to further study the quality and identification of samples and finally X-ray powder diffraction was used to determine the crystalinity of samples. Individual micrograph of MWNTs at optimized deposition temperature was also obtained from the high resolution transmission electron microscopy.

Site-Specific Immobilization of Single-Walled Carbon Nanotubes onto Single and One-Dimensional DNA Origami

Development of a simple and efficient methodology to control the placement, spacing, and alignment of single-walled carbon nanotubes (SWCNTs) is essential for nanotechnology device application. Building on the growing understanding that the strong π-π interaction between the bases of single-stranded DNA (ssDNA) and CNTs is sufficient not only to drive CNT solubility in water but also to stabilize individual nanotubes against clustering in aqueous solution, a new motif for functionalizing DNA origami (DO) with CNTs is demonstrated. CNTs solubilized via wrapping with ssDNA react with DO constructs displaying linear arrays of ssDNA, leading to immobilization of the CNTs onto the DO scaffold. This study demonstrates the immobilization of ssDNA-wrapped CNTs at specific positions on single DO constructs. Furthermore, multiple DO constructs assembled into extended one-dimensional arrays have been used to successfully align pairs of CNTs exceeding 500 nm in length in a parallel orientation. This result provides a simplified, alternative approach to immobilization of CNTs with programmed spacing and orientation.

Free Vibration Analysis of Nanocomposite Plates Reinforced by Graded Carbon Nanotubes Based on First-Order Shear Deformation Plate Theory

AbstractBased on the Mindlin’s first-order shear deformation plate theory this paper focuses on the free vibration behavior of functionally graded nanocomposite plates reinforced by aligned and straight single-walled carbon nanotubes (SWCNTs). The material properties of simply supported functionally graded carbon nanotube-reinforced (FGCNTR) plates are assumed to be graded in the thickness direction. The effective material properties at a point are estimated by either the Eshelby-Mori-Tanaka approach or the extended rule of mixture. Two types of symmetric carbon nanotubes (CNTs) volume fraction profiles are presented in this paper. The equations of motion and related boundary conditions are derived using the Hamilton’s principle. A semi-analytical solution composed of generalized differential quadrature (GDQ) method, as an efficient and accurate numerical method, and series solution is adopted to solve the equations of motions. The primary contribution of the present work is to provide a comparative study of the natural frequencies obtained by extended rule of mixture and Eshelby-Mori-Tanaka method. The detailed parametric studies are carried out to study the influences various types of the CNTs volume fraction profiles, geometrical parameters and CNTs volume fraction on the free vibration characteristics of FGCNTR plates. The results reveal that the prediction methods of effective material properties have an insignificant influence of the variation of the frequency parameters with the plate aspect ratio and the CNTs volume fraction.

Diameter-controlled growth of aligned single-walled carbon nanotubes on quartz using molecular nanoclusters as catalyst precursors

Molecular nanoclusters containing Fe and Mo atoms have been used as catalyst precursors for the growth of single-walled carbon nanotubes (SWNTs) on stable temperature (ST)-cut quartz substrates by chemical vapor deposition. Attribute to the uniform catalyst nanoparticles and the confinement effect of the crystalline substrates, well-aligned SWNTs with narrow diameter distribution have been synthesized. Atomic force microscopy measurements show that the mean diameter of the nanotubes obtained by thermal decomposition of ethanol at 900°C is 0.76 ± 0.16 nm, which is the smallest among all reported results for aligned SWNTs. The mean diameter of the nanotubes increases with growth temperature. In addition to using identical nanoclusters as the catalyst precursors, the avoidance of annealing treatment of catalyst precursors is also a key point for obtaining SWNTs with controlled diameters. Using these identical nanoclusters as catalyst precursors and carefully tuning the growth parameters make us closer to the ultimate goal of controlling the chirality of SWNTs.

Molecular-level computational studies of single wall carbon nanotube–polyethylene composites

Minimum energy structures of short (3,3) single wall carbon nanotube (SWCNT)–polyethylene (PE) structures, as well as the binding energy between the SWCNT and PE, were obtained from three commonly used molecular mechanics force fields and first principles methods. The molecular force fields were the Dreiding, Universal and Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS) force fields and the first principles methods included the B3LYP density functional and MP2 post-Hartree Fock methods with, typically, 6-311G, 6-311G(d,p) and 6-311G(2d,2p) basis sets. These calculations show that the results obtained from all force fields are in qualitative agreement with the first principles results, and that PE prefers to be aligned with a non-zero angle along the SWCNT axis, where the angle depends on the force field or first principles method used. This indicates that longer PE chains may wrap around SWCNTs. This was studied using the COMPASS force field with longer (5,5) SWCNTs interacting with a PE chain and, in agreement with the minimum energy calculations, the PE wrapped around the SWCNT thereby increasing the radius of gyration of the PE. This force field was also used to assess the effect of (5,5) SWCNTs on the mechanical properties of PE nanocomposites. The calculated interfacial shear stress and interfacial bonding energy of SWCNT–PE structures was 141.09MPa and 0.14N/m. The simulations show that using short SWCNTs as reinforcement does not increase the Young’s modulus for the systems studied here, whereas longer, aligned SWCNTs increased the Young’s modulus in the SWCNT axial direction.

Precise Alignment of Individual Single‐Walled Carbon Nanotube Using Dielectrophoresis Method for Development and Fabrication of pH Sensor

Development and fabrication of single‐walled carbon nanotube (SWNT) based pH sensor were reported. The precise alignment of individual SWNT using dielectrophoresis method between the two microgap electrodes was conducted, and the effects of precise alignment of individual SWNT on impedance, long term stability, and capacitance of the sensor were studied. The pH sensor was fabricated using conventional photolithography and wet etching process. The impedance values were found to decrease in the order of distilled water > pH 10 > pH 5 > pH 3 > air. Without the alignment of SWNT, the capacitances values decreased with increasing of pH values at low frequency. All the impedance and capacitance results were highly repeatable.

The Role of Electric Field and Ultrasonication in the Deposition and Alignment of Single-Walled Carbon Nanotube Networks Using Dielectrophoresis

The effects of electric field and ultrasonication on the deposition and alignment of single-walled carbon nanotubes (SWCNTs) across a 10 μm electrode gap have been studied. It was found that a frequency of ~1 MHz of the applied field yields the largest current independent of the magnitude of the voltage or the ultrasonication time of the sample. Increasing the ultrasonication time of a SWCNT solution changes the I-V characteristics of the deposited nanotubes from linear to nonlinear for all the voltages and frequencies of the applied field. Even in the absence of an electric field, SWCNTs bridged the electrode gap up to a critical sonication time which depends on the concentration of nanotubes in the solution.

Aligned carbon nanotubes: from controlled synthesis to electronic applications

Single-wall carbon nanotubes (SWNTs) possess superior geometrical, electronic, chemical, thermal, and mechanical properties and are very attractive for applications in electronic devices and circuits. To make this a reality, the nanotube orientation, density, diameter, electronic property, and even chirality should be well controlled. This Feature article focuses on recent achievements researchers have made on the controlled growth of horizontally aligned SWNTs and SWNT arrays on substrates and their electronic applications. Principles and strategies to control the morphology, structure, and properties of SWNTs are reviewed in detail. Furthermore, electrical properties of field-effect transistors fabricated on both individual SWNTs and aligned SWNT arrays are discussed. State-of-the-art electronic devices and circuits based on aligned SWNTs and SWNT arrays are also highlighted.

Electrical Resistivity of Pristine and Functional Single‐Wall Carbon Nanotubes

The resistance of several pristine and functional single‐wall carbon nanotubes (SWNTs) deposited and dried on interdigitated electrode (IDE) chips was investigated to better understand how functional groups influence their resistivity. Without the external electrical field, the resistance was generally increased for the sulfonated and fluorinated SWNTs but not for COOH‐SWNTs. With a 3 V electric field applied during depositing, while no change in resistance was found for the purified pristine SWNTs, fluorinated SWNTs, COOH SWNTs, and Ni‐SWNTs, a significant decrease in resistance was observed in sulfonated SWNTs and unpurified pristine SWNTs, which could be due to the alignment of SWNTs in an electric field. The alignment of the sulfonated SWNTs is most likely due to the charge of the sulfate functional group. It is interesting to note that the alignment was found in the unpurified pristine SWNTs but not in the purified pristine ones which have lessened resistivity. The lower resistivity in the purified pristine SWNTs may be due to the smaller number (<5%) of impurities. The significance of this research is that hydrophilic COOH‐SWNTs could be a better candidate than the hydrophobic pristine SWNTs for being used in many applications, especially in polymer nanocomposites.

Label-free electronic detection of bio-toxins using aligned carbon nanotubes

A facile route for sensitive label-free detection of bio-toxins using aligned single walled carbon nanotubes is described. This approach involves patterning of a catalyst on the surface of a quartz substrate using a sub-100μm stripe-patterned polydimethylsiloxane stamp for aligned carbon nanotube generation followed by fabrication of field effect transistor (FET). Atomic force microscopy, field emission scanning electron microscopy and Raman spectroscopy are employed to characterize the synthesized nanotubes. Unlike previous reports, the adopted approach enables direct electronic detection of bio-toxins with sensitivities comparable to ELISA. As a proof of concept, the fabricated FET responds to nM concentration levels (with a LOD of ∼2nM) of epsilon toxin produced by Clostridium perfringens and a prominent food toxin. This facile approach could be customized to detect other classes of toxins and biomarkers upon appropriate functionalization of the aligned carbon nanotubes. Finally, we demonstrate the use of the FET-platform for detection of toxin in more complex matrices such as orange juice.

Dielectrophoretic Alignment and Pearl Chain Formation of Single-Walled Carbon Nanotubes in Deuterium Oxide Solution

Dielectrophoretic filtering and alignment of single-walled carbon nanotubes (SWCNTs) were tested using deuterium oxide as a solvent. A solution of deuterium oxide-SWCNTs was dropped on top of a silicon chip and an ac electric field was applied between pre-defined electrodes. Deuterium oxide was found to be a better solvent than hydrogen oxide for the dielectrophoresis process with higher efficiency of filtering. This was demonstrated by comparing Raman spectra measured on the initial solution with those measured on the filtered solution. We found that the aligned nanotubes along the electric field were not deposited on the substrate but suspended in solution, forming chain-like structures along the field lines. This so-called pearl chain formation of CNTs was verified by electrical measurements through the aligned tubes. The solution was frozen in liquid nitrogen prior to the electrical measurements to maintain the chain formation. The current-voltage characteristics for the sample demonstrate the existence of conduction channels in the solution, which are associated with the SWCNT chain structures.

ChemInform Abstract: Optoelectronic Properties of Single‐Wall Carbon Nanotubes

AbstractReview: 288 refs.

On the polarization-dependent Raman spectra of aligned carbon nanotubes

We perform polarized Raman spectroscopy on aligned single-walled carbon nanotubes. This test system allows us to empirically address if resonant Raman scattering from on-axis dipole transitions follows a cos2 or a cos4 mosaic spread. We observe in the polar plots a clear cos4 dependence, in agreement with the equivalency of incoming and outgoing dipole transitions.

Simultaneously grown single wall carbon nanotube channel and electrodes in a thin film transistor

Abstract

Optoelectronic Properties of Single‐Wall Carbon Nanotubes

Single-wall carbon nanotubes (SWCNTs), with their uniquely simple crystal structures and chirality-dependent electronic and vibrational states, provide an ideal laboratory for the exploration of novel 1D physics, as well as quantum engineered architectures for applications in optoelectronics. This article provides an overview of recent progress in optical studies of SWCNTs. In particular, recent progress in post-growth separation methods allows different species of SWCNTs to be sorted out in bulk quantities according to their diameters, chiralities, and electronic types, enabling studies of (n,m)-dependent properties using standard macroscopic characterization measurements. Here, a review is presented of recent optical studies of samples enriched in 'armchair' (n = m) species, which are truly metallic nanotubes but show excitonic interband absorption. Furthermore, it is shown that intense ultrashort optical pulses can induce ultrafast bandgap oscillations in SWCNTs, via the generation of coherent phonons, which in turn modulate the transmission of a delayed probe pulse. Combined with pulse-shaping techniques, coherent phonon spectroscopy provides a powerful method for studying exciton-phonon coupling in SWCNTs in a chirality-selective manner. Finally, some of the basic properties of highly aligned SWCNT films are highlighted, which are particularly well-suited for optoelectronic applications including terahertz polarizers with nearly perfect extinction ratios and broadband photodetectors.

Electrochemical detection of hepatitis B and papilloma virus DNAs using SWCNT array coated with gold nanoparticles

This study investigated electrochemical detection of human hepatitis B and papilloma viruses using electrochemical impedance spectroscopy technique. The sensor was fabricated by electrochemically depositing Au nanoparticles on the in situ prepared single walled carbon nanotube (SWCNTs) arrays, followed by the self-assembly of single-stranded probe DNA on the SWCNTs/Au platform. The as-prepared electrochemical sensor could detect lower than 1 attomole complimentary hepatitis B single-stranded DNA (ssDNA), which corresponds to having 600 ssDNA molecules in a 1.0mL sample. For a 1-base mismatched hepatitis B ssDNA, the experimental detection limit is 0.1pmol. When being applied to detect 24-base papilloma virus ssDNA, the experimentally determined low detection limit is 1 attomole. In addition to the low detection limit, the SWCNTs/Au/ssDNA sensor also showed great stability, where after being kept in a refrigerator for a month at a temperature 4–8°C its charge transfer resistance decreased by less than 1%. The sensor could be conveniently regenerated via dehybridization in hot water. Both aligned and random SWCNTs arrays have been investigated in this study and there was nearly no difference in the low limit in the detection of hepatitis B and papilloma viruses. This study illustrates that combining Au nanoparticles with the in situ fabricated SWCNTs array is a promising platform for ultrasensitive biosensing.

Improved field emission stability from single-walled carbon nanotubes chemically attached to silicon.

Here, we demonstrate the simple fabrication of a single-walled carbon nanotube (SWCNT) field emission electrode which shows excellent field emission characteristics and remarkable field emission stability without requiring posttreatment. Chemically functionalized SWCNTs were chemically attached to a silicon substrate. The chemical attachment led to vertical alignment of SWCNTs on the surface. Field emission sweeps and Fowler-Nordheim plots showed that the Si-SWCNT electrodes field emit with a low turn-on electric field of 1.5 V μm−1 and high electric field enhancement factor of 3,965. The Si-SWCNT electrodes were shown to maintain a current density of >740 μA cm−2 for 15 h with negligible change in applied voltage. The results indicate that adhesion strength between the SWCNTs and substrate is a much greater factor in field emission stability than previously reported.

Alignment of Single-Walled Carbon Nanotubes with Ferroelectric Liquid Crystal

Single-walled carbon nanotubes (SWCNTs) are aligned by using a ferroelectric liquid crystal (FLC) named [4-(3)-(S)-methyl-2-(S)-chloropentanoyloxy)]-4′-nonyloxy-biphenyl. The scanning electron microscope (SEM) is utilized to investigate the alignment of the SWCNTs in the smectic A phase. Fourier Transform Infrared spectroscopy (FTIR) and Raman spectroscopy are utilized to investigate the interaction between these two species. The SEM images show that SWCNTs can be well aligned along the smectic layers. A new peak appears at 1702 cm–1 in the FTIR spectra in the SWCNT hybrids, which indicate that charge transfer occurring from the hexagonal rings of the SWCNTs to the C═O groups of the FLC molecules that contact directly with the SWCNTs. To our knowledge, this is the first time we observe the charge transfer effect by FTIR. Similarly, a new peak at 763 cm–1 is also found in the Raman spectrum of the SWCNT hybrid that results from the charge transfer effect between the SWCNTs and the C–Cl groups of the FLC. The π–π stacking and charge transfer effect together make the SWCNTs align unidirectionally along the smectic layers instead of in the direction of the molecular long axis.