Microscopic and spectroscopic study of self-ordering in poly(3-hexylthiophene)/carbon nanotubes nanocomposites

Poly(3-hexylthiophene)-single-walled carbon nanotubes (SWNTs) composites were studied using UV-visible absorbance and Raman spectroscopy, scanning tunneling microscopy (STM) and transmission electron microscopy (TEM). Monolayers of regioregular poly(3-hexyl thiophene) (rrP3HT) adsorbed on SWNTs have been imaged using scanning tunneling microscopy (STM) to obtain measurements of the chiral angles at which the thiophene polymer chains wrap around individual carbon nanotubes (41-48 degrees with respect to nanotube axis) and polymer interchain spacings (1.68 angstroms). The rrP3HT interchain distance is greater for rrP3HT monolayers adsorbed onto the curved surfaces of SWNTs than on the flat surfaces of highly ordered pyrolytic graphite samples (1.4 angstroms). UV-vis spectroscopic data provided strong evidence for increased interchain interactions in composites of rrP3HT and SWNTs compared to the pure polymer. The STM local-probe studies of the native polymer and the composites further confirmed that the rrP3HT interacts with carbon nanotubes to produce a highly ordered material at the molecular level.     

填充叠氮化铜的碳纳米管纳米材料的制备研究?

首先采用电化学沉积法在碳纳米管中沉积铜,再利用叠氮化反应制备填充叠氮化铜的碳纳米管纳米材料。利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、高分辨透射电镜(HRTEM)和X射线能谱(EDS)对样品的微观形貌和晶体结构进行表征。结果表明,利用电化学沉积方法在定向碳纳米管中空管腔内合成了针状纳米枝晶铜,非连续的枝晶结构有利于后续的气固叠氮化反应,最终制备得到填充叠氮化铜晶体的碳纳米管纳米材料。     

Direct synthesis of Y-junction carbon nanotubes by microwave-assisted pyrolysis of methane

Both Y-junction carbon nanotubes and individual carbon nanotubes were synthesized without any additive catalyst by microwave decomposition of methane. Detailed microstructures of as-synthesized products have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. The results show that these Y-junction CNTs possess an internal bamboo-shaped structure, and some three dimensional multi-terminal junctions are also observed on CNTs. As gas flow rate decreased to 15 sccm, only individual nanotubes could be obtained. A possible mechanism is proposed for the synthesis of the Y-junction carbon nanotubes on these observations. This technique may also have great potential in making other nano-structured carbon materials on a large scale and at low cost.     

Fabrication of flat capped carbon nanotubes using an arc-discharge method assisted with a Sm-Co catalyst

In this study, carbon nanotubes (CNTs) were fabricated using an arc-discharge method assisted with samarium-cobalt (Sm-Co) chloride as a catalyst. The optimal fabrication condition was determined through a series of experiments on various ambient conditions. Observations were completed using scanning electron microscopy (SEM), Raman spectroscopy, and tunneling electron microscopy (TEM); the main products we observed are well-structured multi-walled carbon nanotubes. By identifying the radial breathing modes (RBMs) of the Raman spectra with a TEM micrograph, we also observed a small number of single-walled carbon nanotubes. With the assistance of the Sm-Co chloride catalyst, the RBMs of the Raman spectra were measured in the ambient pressure of 760 torr. The TEM observations revealed that our nanotubes have good graphitic structures and almost no bamboo defects, which agrees with their Raman measurements with a high I_G/I_D ratio (~88). A perfect graphitic flat cap was found to be attached at the end of the nanotube. Simulation shows that by incorporating 5 carbon pentagons, it is possible to construct a flat capped carbon nanotube. The results of our experiment offer a unique approach to growing high quality CNTs. Such a flat capped structure may useful for further advanced application in nano-electronics and nano-optics.     

Analysis of non-planar graphitic structures: from arched edge planes of graphite crystals to nanotubes

A unified approach to the analysis of the mechanisms that lead to the edge reconstruction of graphite and growth of a variety of non-planar graphitic structures, such as nanotubes, is suggested. Transmission electron microscopy (TEM) shows that nano-arches are formed on the edge planes of natural and synthetic graphite, as well as graphite polyhedral crystals, which are built of graphene sheets; this makes the edge reconstruction of graphite different from the surface reconstruction of other crystals. A theoretical study of edge zipping in graphite and formation of tubular carbon structures has been performed using an integrated approach combining molecular dynamics simulation and analytical continual energetics modeling. The suggested theoretical framework describes the formation of curved surfaces in a wide range of dimensions, which is a general feature of the growth of layered materials. Layered materials isostructural to graphite, such as hexagonal BN, demonstrate similar edge structures and also form nanotubes. Thus, the ability of materials to form arches as a result of edge reconstruction points out to their ability to form nanotubes and vice versa. TEM studies of graphite and hexagonal boron nitride provide experimental verification of our analytical model. Received: 29 October 2001 / Accepted: 5 November 2001     

Fabrication and characterization of vertically aligned carbon nanotubes on silicon substrates using porous alumina nanotemplates

An ethylene-air laminar diffusion flame successfully provided silicon substrates of anodic aluminum oxide (AAO) template with vertically oriented well-aligned carbon nanotubes. Field emission scanning electron microscopy (SEM) showed that open-tipped carbon nanotubes consisting of tube elements with the same length and diameter uniformly coated the template. High-resolution transmission electron microscopy (TEM) analyses revealed these nanotubes to be multiwalled carbon nanotubes, some well graphitized. It was found that cobalt catalyst particles, but not the porous aluminum templates, helped the growth of carbon nanotubes through graphitization and bonding of carbon nanotubes to the silicon substrates.     

Hydrogen-acetylene gas ratio and catalyst thickness effect on the growth of uniform layer of carbon nanotubes

Effect of catalyst thickness (2, 4, and 6 nm) and acetylene-hydrogen gas ratio (1/4, 2/4, and 3/4) on the synthesis of carbon nanotubes is reported in this article. Synthesized nanotubes are characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy, and Raman effect. From SEM results, nanotubes growth is less for higher thickness, as at higher thickness catalyst nanoparticles agglomerate which suppress the growth of nanotubes. Raman spectroscopy results reveal that at higher thickness defects density increases. Nanotube of better crystallinity and graphitic outer walls grows for lower acetylene-hydrogen gas ratio and at smaller thickness of catalyst layer. The sheet resistance of carbon nanotube thin film is measured by using Hall effect measurement systems. Smallest sheet resistance among synthesized multi-walled carbon nanotubes sample is obtained for nanotubes grown on 2 nm thick catalyst film and is 0.9 kΩ/square.     

用DBD-PECVD方法合成碳纳米管

在大气压、较低温度下合成碳纳米管(CNTs),对于大规模的工业生产具有重要的意义.本文介绍了一种介质阻挡放电等离子体增强化学气相沉积(DBD-PECVD)的方法,并利用该方法制备碳纳米管.实验是在约0.5个大气压、700℃下,通入氢气和甲烷的混合气体(CH4/H2为1∶10～1∶20),产生DBD等离子体;衬底为硅片;催化剂是用磁控溅射制备的Ni/Al薄膜,厚度分别为3nm和10nm.在扫描电镜下观察发现,碳纳米管的生长符合底端生长模式.在透射电镜下观察,碳纳米管没有竹节状结构.拉曼光谱分析表明,这种碳纳米管的结构缺陷比较多.     

Monodisperse carbon microspheres synthesized from asphaltene

Carbon microspheres were synthesized from asphaltene by a chemical vapor deposition (CVD) method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy method. The results indicated the monodispersed spheres were almost curving graphitic structure with diameters from 300 to 400 nm. G mode centre of carbon microspheres had shifted upward compared with graphite. As an efficient precursor, asphaltenes were metastable structures at higher temperature. The aromatic carbon rings of asphaltenes promoted the formation of closed cage graphitic structures. The results provide a new perspective for the application of asphaltene.     

Catalyst-free synthesis of carbon and boron nitride nanoflakes using RF-magnetron sputtering

Catalyst-free boron nitride (BN) and carbon (C) nanoflakes have been produced by direct radio frequency (RF)-magnetron sputtering on molybdenum and tungsten substrates at or above temperatures of 1000 °C and 800 °C, respectively. Selected-area electron diffraction (SAED) shows that the films are polycrystalline and contain disordered graphite and hexagonal BN. Transmission electron microscopy (TEM) reveals curved or twisted flakes up to several hundred nanometres in length. High resolution transmission electron microscopy (HRTEM) confirms the nanoflake structure to be turbostratic, which is intermediate between an amorphous phase and the ordered layered phases of hexagonal BN or graphite.     

Synthesis and characterization of electrochemically-reduced graphene

Graphene has superior electrical conductivity than graphite and other allotropes of carbon because of its high surface area and chemical tolerance. Electrochemically processed graphene sheets were obtained through the reduction of graphene oxide from hydrazine hydrate. The prepared samples were heated to different temperatures such as 673 and 873 K. X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), transmission electron microscopy (TEM), Raman spectra and conductivity measurements were made for as-prepared and heat-treated graphene samples. XRD pattern of graphene shows a sharp and intensive peak centred at a diffraction angle (2θ) of 26·350. FTIR spectra of as-prepared and heated graphene were used to confirm the oxidation of graphite. TEM results indicated that the defect density and number of layers of graphene sheets were varied with heating temperature. The hexagonal sheet morphology and purity of as-prepared and heat treated samples were confirmed by SEM–EDX and Raman spectroscopy. The conductivity measurements revealed that the conductivity of graphene was decreased with an increase in heating temperature. The present study explains that graphene with enhanced functional properties can be achieved from the as-prepared sample.     

CNT composites for aerospace applications

Carbon nanotubes were synthesized by thermal arc plasma process after optimization of the synthesis parameters. These samples were then analysed by scanning and transmission electron microscopes (SEM and TEM), in order to establish the morphology of the nanostructures. Atomic force microscopy (AFM) and electron diffraction studies were also carried out before using the sample for the composite material preparation. Composites of epoxy resin with curing agent as well as a mixture of graphite and carbon nanotubes were prepared with varying proportions of the mixture. The electrical resistivity of the material was studied under varying pressure and voltage conditions. Preliminary results of these studies present interesting features which are reported here.     

The effect of substrate morphology on the diameter distribution of carbon nanotubes grown on silica and ceramic substrates

Large-scale well-aligned carbon nanotube film and carbon nanotube bundles have been fabricated on smooth silica and rough polycrystalline ceramic substrates by pyrolysis of ferrocene/melamine mixtures. The images of transmission electron microscopy (TEM) and scanning electron microscope (SEM) show that carbon nanotubes grown on the silica substrate have uniform outer diameters of about ∼ 25 nm and lengths of about 40 μm, while those on the ceramic substrate have outer diameters from 10 to 90 nm and lengths up to 100 μm. Electron energy-loss spectroscopy (EELS) spectra show that nanotubes grown on the two different substrates are pure carbon tubes. The effects of substrate micro-morphologies on the diameters of carbon nanotubes have been discussed.     

Scanning probe microscopy of intrafibrillar crystallites in calcified collagen

Vertebrate mineralized tissues are composite materials formed by the organized growth of carbonated apatite crystals within a matrix of collagen fibres. Calcified collagen from turkey tendon was investigated using scanning tunnelling microscopy (STM) and atomic force microscopy (AFM). Samples were treated with hydrogen peroxide to enhance the mineralized phase by removing part of the collagen matrix and the results compared with the untreated material. Plate-like crystalline entities with dimensions 35 nm × 5–8 nm by 1.5 nm were seen. These dimensions are consistent with previous reports using transmission electron microscopy (TEM) of calcified tendon and topographic imaging of tendon crystals. The resolution of the images obtained using STM is better than the previously reported pictures obtained using TEM or scanning electron microscopy (SEM). The value of 35 nm is the same as the gap region in the structure of the collagen fibrils. Stacking of plates and plate-aggregates are a dominant feature in the scanning images. These results support the concept of organized intra-fibril mineral crystals within the organic collagen matrix. Electron diffraction and X-ray diffraction were undertaken on the samples and the patterns recorded match those previously reported for carbonated apatite.     

Multiwall and bamboo-like carbon nanotube growth by CVD using a semimetal as a catalyst

Multiwall carbon nanotubes have been synthesized on silicon substrates via atmospheric pressure chemical vapour deposition technique using bismuth as a catalyst. Field emission scanning electron microscopy analysis suggests that the samples grow through a tip growth mechanism. High-resolution transmission electron microscopy analysis shows spaghetti-like multiwall carbon nanotubes and with a bamboo-like structure obtained using the Bi catalyst. The quality, in terms of the graphitic crystallinity of the as grown carbon nanotubes, was analyzed by Raman analysis. The study shows that the catalyst, namely bismuth strongly influences the growth density and graphitic crystallinity of the grown carbon nanotubes.     

Production of monolayer, trilayer, and multi-layer graphene sheets by a re-expansion and exfoliation method

Mass graphene sheets were obtained by a re-expansion and exfoliation method which uses the commercially available graphite intercalation compounds as the starting materials. The as-prepared samples have been characterized by scanning electronic microscopy, transmission electron microscope, atomic force microscope, Fourier transform infrared spectrometer spectroscopies, and Raman microscope. Using high resolution transmission electron microscopy on 60 samples, it was shown that the final samples exhibit 8 % monolayer, 19 % bilayer, and 77 % less than or equal to five layers, and the sheets are largely free of defects and chemical functional groups after thermal reduction.     

Effect of nano carbon additives on the microstructure of polyvinyl chloride heated up to 2000°C

Polyvinyl chloride (PVC) is one of the most commonly used thermoplastic materials among worldwide polymer consumption. The PVC exhibits particular inherent properties such as low cost and high performance, it can be obtained from different techniques. PVC products will finally become waste. As a result, the quantity of waste PVC is gradually increasing. The waste product PVC can be converted to graphite. Graphitic structure was obtained by carbonization of polymers to 1000°C, and subsequent heating to 2000°C. In this study the effect of carbon nanotube (CNT) and carbon black additives on the graphitic microstructure of PVC polymer was investigated. The solution of PVC in tetrahydrofuran (THF) was prepared then additives were dispersed in solution by ultrasonic. The additives were applied in the concentration between 1 and 3wt%. Changes in graphitic microstructure were studied via Raman spectroscopy, X-ray diffraction, and Transmission electron microscopy (TEM). Morphology of microstructures studies with scanning electron microscopy (SEM). The results show that the additives do not develop the graphitic microstructure and do not improve the formation of flaky graphite crystals.     

Macroscopic synthesis of onion-like graphitic particles

In this paper, we present a method for macroscopic synthesis of onion-like graphitic particles, which may be used to study physical properties. This method is based on annealing carbon nanotubes under high pressure. By transmission electron microscopy (TEM), the microstructure of carbon nanotubes is found to transform into quasi-spherical graphitic structures when the sample has been treated at 770 °C and 950 °C under 5.5 GPa. The high pressure assumes an important role in this transformation.     

The atomic structure of nanotubes synthesized from a carbon mix of high reaction ability

The surface of carbon nanotubes was studied on an atomic resolution level in a scanning tunneling microscope (STM) operating under atmospheric conditions. The nanotubes were synthesized from a carbon mix of high reaction ability. Factors determining distortion of the STM image are analyzed and the main parameters (chiral angle and diameter) of nanotubes are calculated.