Well-aligned Carbon Nanotube Arrays Research Articles

Carbon Nanotubes as Active Components for Gas Sensors

The unique structure of carbon nanotubes endows them with fantastic physical and chemical characteristics. Carbon nanotubes have been widely studied due to their potential applications in many fields including conductive and high‐strength composites, energy storage and energy conversion devices, sensors, field emission displays and radiation sources, hydrogen storage media, and nanometer‐sized semiconductor devices, probes, and quantum wires. Some of these applications have been realized in products, while others show great potentials. The development of carbon nanotubes‐based sensors has attracted intensive interest in the last several years because of their excellent sensing properties such as high selectivity and prompt response. Carbon nanotube‐based gas sensors are summarized in this paper. Sensors based on single‐walled, multiwalled, and well‐aligned carbon nanotubes arrays are introduced. Modification of carbon nanotubes with functional groups, metals, oxides, polymers, or doping carbon nanotubes with other elements to enhance the response and selectivity of the sensors is also discussed.

Facile Synthesis of Highly Aligned Multiwalled Carbon Nanotubes from Polymer Precursors

We report a facile one‐step approach which involves no flammable gas, no catalyst, and no in situ polymerization for the preparation of well‐aligned carbon nanotube array. A polymer precursor is placed on top of an anodized aluminum oxide (AAO) membrane containing regular nanopore arrays, and slow heating under Ar flow allows the molten polymer to wet the template through adhesive force. The polymer spread into the nanopores of the template to form polymer nanotubes. Upon carbonization the resulting multi‐walled carbon nanotubes duplicate the nanopores morphology precisely. The process is demonstrated for 230, 50, and 20 nm pore membranes. The synthesized carbon nanotubes are characterized with scanning/transmission electron microscopies, Raman spectroscopy, and resistive measurements. Convenient functionalization of the nanotubes with this method is demonstrated through premixing CoPt nanoparticles in the polymer precursors.

High dispersion of γ-MnO 2 on well-aligned carbon nanotube arrays and its application in supercapacitors

The well-aligned carbon nanotube arrays (ACNTs) were used as supporting material and the γ-MnO 2/ACNT electrode with high dispersion of γ-MnO 2 has been prepared by electrochemically induced deposition method. The crystal structure and morphology of the γ-MnO 2/ACNT electrode were investigated by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The capacitive properties of γ-MnO 2/ACNT electrode were characterized by cyclic voltammetry and galvanostatic charge–discharge method. The specific capacitance of the γ-MnO 2/ACNT electrode is as high as 784 F g − 1 based on γ-MnO 2 and 234 F g − 1 based on γ-MnO 2/ACNT composites in 0.1 M Na 2SO 4 aqueous solution from 0 to 1 V when the charge–discharge current density is 1 mA cm − 2 . Additionally, the electrode shows excellent power characteristics, high electrochemical reversibility and excellent long-term charge–discharge cycle stability.

Synthesis of well-aligned bamboo-like carbon nanotube arrays from ethanol and acetone

We report on a novel and facile thermal chemical vapour deposition method for fabricating dense and vertically well-aligned bamboo-like carbon nanotube (CNT) arrays on a copper substrate from ethanol and acetone for the first time. The effect of growth time, temperature and catalysts has been systematically studied. Using ethanol as the carbon source, well-aligned CNTs were produced at 800 °C, and random, long and large carbon fibres/tubes were formed at 900 °C. When acetone was used, mushroom-like carbon nanostructures were formed at 800 °C, and well-aligned CNTs were produced at 850 °C. In contrast, large amounts of random carbon micro-fibres were formed at 800 °C using ethanol as the carbon source when Fe or Ni was employed as the substrate. The electrochemical properties of the novel mushroom-like carbon nanostructures are presented; the growth mechanisms for the formation of the bamboo-like CNTs and the mushroom-like carbon nanostructures are discussed.

Selective growth of well-aligned carbon nanotubes by APCVD

Well-aligned good-quality carbon nanotube (CNT) array was grown on silicon substrate by atmospheric pressure chemical vapor deposition (APCVD) through SiO2 masking. First, the patterned substrate was pretreated with NH3 and then CNTs were synthesized at 800 °C using Ni as the catalyst, acetylene (C2H2) as the carbon source material and N2 as the carrier gas. Effects of the NH3-pretreatment time, the flow ratio of [C2H2]/[NH3] and the CNT growth time on the qualities of CNT array were analyzed in detail. It was found that good-quality CNTs with an average length of around 15 μm could be grown by pretreating the Si substrate with NH3 for 10 min and then conducting the CNT growth with a flow ratio of [C2H2]/[NH3] = 30/100. Furthermore, the field emission property of CNT array was investigated using a diode structure. It was found that the turn-on electric field decreased with increasing CNT length. The turn-on electric field as low as about 2 V/μm with an emission current density of 10 μA/cm2 was achieved for a CNT-array diode with the tube length near 18 μm. For the same device, the emission current density could be elevated to 10 mA/cm2 with the applied voltage of 3.26 V/μm.

A generic process of growing aligned carbon nanotube arrays on metals and metalalloys

Aligned carbon nanotube (CNT) arrays are integral towards the development of severalapplications such as field emission, interconnects in silicon technology, and chemicaland biological sensing. Even though the synthesis of CNTs has been describedextensively in the literature, there has not been significant success in growing uniform,well-aligned CNT arrays on pure metal surfaces other than metals that catalyseCNT growth themselves. In this paper, we describe a method of growing alignedCNT arrays on a variety of pure metals, metal alloys, and conductive ceramicsusing a bimetallic iron/alumina composite catalyst at low temperatures (550 to700 °C). We believe that the addition of alumina to the iron catalyst significantly reducescatalyst–metal underlayer interactions that have traditionally proven to be a barrier for thegrowth of CNTs on metals. The alumina also minimizes surface diffusion of iron and allowsthe formation of a high density of uniformly dispersed catalyst nanoparticles to act asnucleation sites for well-aligned CNT arrays. Despite the presence of non-conductingalumina from the catalyst, the contact resistance between the CNTs and the metalunderlayer was observed to be quite low, emphasizing the usefulness of this approach topractical applications. Our process was successful in growing aligned CNTs even oncommercial steel plates and may be applicable for substrates of any shape orsize.

Growth of well-aligned carbon nanotubes arrays by chemical vapor deposition

A non-template CVD method was used to synthesize well-aligned carbon nanotube (ACNT) arrays. Ferrocene was used as a catalyst, xylene as the carbon source. This process carried out in a single-furnace system. The products were characterized by Scanning Electron Microscopy(SEM), Transmission Electron Microscopy(TEM), Energy Dispersive Spectrometry(EDS) and Raman Spectroscopy. The effects of process parameters on ACNT arrays growth were also investigated. The results show that well-aligned carbon nanotubes can be easily grown on polished silicon substrate at 800℃ with catalyst concentration of 0.02mg/L. Under the above conditions the rate of growth of ACNT arrays can reach 25μm/min.

RETRACTED: Langmuir–Blodgett films of single-walled carbon nanotubes

Large arrays of well-aligned carbon nanotubes on glass, silicon, quartz, etc. have been successfully prepared by Langmuir-Blodgett deposition. The overall direction of the carbon nanotubes alignment can be controlled both by compression and dipping process. Several factors involved in the deposition process were investigated in an attempt to understand the deposition technique and to optimize the quality of the films. Deposition can be performed in a layer-by-layer fashion up to several hundreds layers, allowing to readily control the film thickness.

Preparation of Well-aligned CNT Arrays Catalyzed with Porous Anodic Aluminum Oxide Template

Well-aligned open-ended multi-walled carbon nanotube (MWCNT) arrays were prepared via chemical vapor deposition (CVD) method in porous anodic aluminum oxide (AAO) templates without depositing any transition metals as catalyst. Effects of the CVD temperature and heat treatment were studied in detail. Well-aligned open-ended MWCNT arrays were obtained at the CVD temperature above 600 C; when CVD temperature is reduced to around 550 C, CNTs, CNFs and other structures existed at the same time; no CNTs or carbon nanofibres (CNFs) could be found as the CVD temperature is below 500 C, and only amorphous carbon in the porous AAO template was found. Experimental results showed that the AAO template is catalytic during the CVD process, and it has the following two effects: to catalyze thermal decomposition of acetylene and to catalyze conversion of carbon decomposed from acetylene into CNTs or CNFs. Heat treatment could improve the graphitization degree, but it might also introduce new defects.

Growth of ZnO nanowires on modified well-aligned carbon nanotube arrays

Single-crystal ZnO nanowires were successfully grown on modified well-aligned carbonnanotube (CNT) arrays by a hydrothermal process. The pre-deposited ZnO grains on theCNTs served as the nucleation sites for the growth of ZnO nanowires. The attached growthof ZnO nanowires on the well-aligned CNT arrays formed a 3D configuration. The 3Dhybrid nanostructured material could find application in sensors and other electronic oroptoelectronic devices.

Effects of post treatment on the field emission properties of CNTs grown by ECR-CVD

Field emission display (FED) has been considered as one of the most promising application of carbon nanotubes. In FED application, the CVD assisted grown CNT cathodes have major problems, i.e., the screen effect of the well aligned CNT array reduces the field emission characteristics. The post treatments for cathode become necessary to improve the field emission characteristics and uniformity of the CNT emitters. In this study, well-aligned carbon nanotube array on Si substrate were synthesized by using a catalyst-assisted microwave plasma electron cyclotron resonance chemical vapor deposition (ECR-CVD) system with methane as source gas. Then a series of post treatment, including hydrogen plasma, oxygen plasma and electroless nickel plating, were conducted on the as grown CNT arrays. The results show that the H-plasma may damage the stems of CNTs at longer etching time. Consequently, the field emission characteristic of CNTs is reduced. In contrast, oxygen plasma increases the field emission characteristic of CNTs by reducing CNTs diameter and increasing inter-tube distance. Comparing to plasma post-treatment, electroless nickel-plating post-treatment is apparently improve the field emission characteristic of CNTs. This process results in the gathering of nickel catalysts at the top of CNTs and concentration CNTs field emission ability.

Electrochemical oxidation of glutathione at well-aligned carbon nanotube array electrode

Electrochemical oxidation and determination of glutathione (GSH) were investigated with well-aligned carbon nanotube (CNT) arrays. Square wave voltammetric and amperometric results suggest that aligned-CNT electrode exhibits excellent electrochemical activity and good anti-fouling property for direct electrochemical oxidation of glutathione. Also, the preliminary application of the aligned-CNT electrode for amperometric determination of glutathione was evaluated.

Deposition and electrocatalytic properties of platinum on well-aligned carbon nanotube (CNT) arrays for methanol oxidation

Well-aligned carbon nanotube (CNT) arrays were used as supporting materials for platinum (Pt) electrocatalysts. The microstructure of the resulting Pt/aligned-CNT electrode was characterized by scanning electron microscopy (SEM), and nano-scale Pt catalysts dispersed highly on CNT arrays by electro-deposition can be obtained. The electrocatalytic properties of the Pt/aligned-CNT electrode for methanol oxidation have been investigated by cyclic voltammetry (CV). Compared with Pt/graphite and Pt/tangled-CNT/graphite electrodes, higher electrocatalytic activity of the Pt/aligned-CNT electrode can be observed.

Efficient encapsulation of gaseous nitrogen inside carbon nanotubes with bamboo-like structure using aerosol thermolysis

High yields of dense, ‘clean’ and uniform arrays of well-aligned carbon nanotubes, with bamboo-like structure encapsulating gaseous nitrogen, were obtained by thermolyzing uniform aerosols of ferrocene/benzylamine solutions at 850 °C. Electron energy loss spectroscopy (EELS) studies reveal that up to 90% of these tubes contain molecular nitrogen in their cores. The materials were characterized by scanning electron microscopy, X-ray powder diffraction, high-resolution transmission electron microscopy, and EELS elemental mappings using an Omega Filter microscope. We envisage the material useful for storing large concentrations of relatively heavy gases such as nitrogen in confined volumes.

Synthesis of vertically aligned carbon nanotube arrays on silicon substrates

The growth of well-aligned carbon nanotube (CNT) arrays using a heat chemical vapor deposition system on silicon substrates is reported. The growth properties of CNT arrays are studied as a function of synthesis conditions. It is found that 750℃ and 10 nm Fe film are suitable conditions for the growth of well-aligned CNT arrays. CNT arrays with a uniform diameter, thick tube wall and firm cohesion to the Si substrate can be grown for C2H2 concentration of 27%. Based on the experiment, the processes of improving the alignment of CNT arrays and cohesion between CNT arrays and Si substrates are discussed.

High dispersion and electrocatalytic properties of platinum on well-aligned carbon nanotube arrays

Platinum (Pt) electrocatalyst was electrochemically dispersed on well-aligned carbon nanotube (CNT) arrays by a potential-step method. The structure and elemental composition of the resulting Pt/CNT electrode were characterized by scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. The electrocatalytic properties of the Pt/CNT electrode for oxygen reduction reaction have been investigated by linear sweep voltammetry. Compared with a Pt/graphite electrode, higher electrocatalytic activity of the Pt/CNT electrode can be observed. This may be attributed to the high dispersion of platinum catalysts and the particular properties of CNT supports. The results imply that the Pt/CNT has good potential applications in proton exchange membrane fuel cells.

Well-aligned carbon nanotube array grown on Si-based nanoscale SiO 2 islands

Well-aligned carbon nanotube (CNT) array grown on Si-based nanoscale SiO 2 islands was obtained by microwave plasma-enhanced chemical vapor deposition under low temperature of 520°C. Atomic force microscope observation and Raman spectroscopic analysis disclosed the formation of the CNTs. The SiO 2 islands formed by excess anodization of Si-based Al film were found to be the growth points of the CNTs, which was confirmed by the C–V curves without charge characteristics. Position-controllable growth of CNTs was attempted on silicon substrate so as to explore significant applications in nanoelectronics and nanodevices.

Low-temperature synthesis of large-area CNx nanotube arrays.

Well-aligned nitrogen-doped multiwall carbon nanotube arrays have been successfully grown over large areas on quartz and silicon wafers by floating-catalyst chemical vapor deposition at low temperatures (600 degrees C). These nitrogen-including nanotubes, derived from pyridine-ferrocene mixtures, have smaller outer diameters but larger inner diameters compared with carbon nanotubes grown from a xylene-ferrocene mixture under similar conditions. The N-doped nanotubes exhibit bamboo-like structures in the core. Elemental analysis and electron energy loss spectroscopy analysis show that the as-prepared nanotubes contain as much as 2.62 wt.% N, with most of the N concentrated in the inner few shells of the nanotube. Such large-scale arrays of well-aligned N-doped nanotubes on silicon wafers have a current density as high as 23.8 mA/cm2 at an applied electric field of 17 V/micron, which can be further improved by patterning the tubes and coating the silicon substrate with a conductive thin metal film for the fabrication of flat panel displays.

Photonic Crystals Based on Periodic Arrays of Aligned Carbon Nanotubes

We demonstrate here that large area periodic arrays of well-aligned carbon nanotubes can be fabricated inexpensively on Ni dots made by the process of self-assembly nanosphere lithography. These periodic arrays appear colorful due to their efficient reflection and diffraction of visible light. In addition, due to their honeycomb lattice structure, these arrays can act as photonic band gap crystals in the visible frequency range. In this report, we present the initial exploration of the optical properties of such arrays. Here we show that these potential 2D photonic band gap crystal arrays might find very important applications in optoelectronics.

Rapid growth of well-aligned carbon nanotube arrays

Vertically aligned carbon nanotube (CNT) arrays with high density were synthesized on quartz substrates in large areas ( 100×40 mm 2 ) by catalytic decomposition of a ferrocene–xylene mixture at 850 °C in a quartz tube reactor. The nanotubes grow at a high growth rate of ∼50 μm /min, and reach 1.5 mm in length in 30 min. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigations reveal that the nanotubes are high-purity multi-wall CNTs with well-ordered graphene sheets, and about 30–60 nm in diameter. This provides a simple way to synthesize well-aligned CNTs in large areas. A continuous rapid growth model is suggested for the CNTs in high growth rate under our experimental conditions.