Magnetization of carbon nanotubes

For narrow-gap carbon nanotubes, the curvature effect due to the misorientation of 2p_z orbitals dominates over electronic structures and thus magnetic properties. It significantly changes magnetization and magnetic susceptibility, and creates special structures in them. There exists a critical field direction in changing magnetism. The critical angle strongly depends on the chiral angle, the nanotube radius, and the temperature. One-dimensional carbon nanotubes are quite different from zero-dimensional carbon tori, such as in terms of special structures in magnetization, the strength of the magnetic response, and the critical angle.     

Terahertz oscillations in semiconducting carbon nanotube resonant-tunneling diodes

The paper presents the simulation and possible physical implementation of a resonant tunneling diode based on a semiconducting single-walled carbon nanotube, which exceeds the performance of similar resonant tunneling devices based on semiconductor heterostructures. In this respect, the oscillation frequency and the output power are predicted to be greater by one order of magnitude, attaining 16 THz and 2.5 μW, respectively. The generated THz signal is directly radiated into free-space through the injection contacts of the resonant tunneling diode, which have the shape of a bowtie antenna.     

Microwave-assisted functionalization of single-walled carbon nanotubes with 3-chloropropene

We have reported a highly efficient approach to functionalize single-walled carbon nanotubes by electrophilic addition polymerization of 3-chloropropene under microwave irradiation. Using Lewis acids as catalysts, 3-chloropropene can undergo polymerization followed by hydrolysis with alkaline methanol, and thus the reaction results in the attachment of polymer chains and hydroxyl groups to the surface of the nanotubes. The resulting nanotubes were characterized with Fourier transform infrared spectroscopy, thermogravimetric analysis, Raman spectroscopy, high-resolution transmission electron microscopy, and atomic force microscopy. The result shows that 30 min of irradiation time is enough to bring the reaction to the end and a longer time did not improve the degree of functionalization.     

Synthesis and characterization of carbon nanotubes on carbon microfibers by floating catalyst method

In this paper, carbon nanotubes were synthesized on carbon microfibers by floating catalyst method with the pretreatment of carbon microfibers at the temperature of 1023 K, using C₂H₂ as carbon source and N₂ as carrier gas. The morphology and microstructure of carbon nanotubes were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The composition of carbon nanotubes was determined by energy dispersive X-ray spectroscopy (EDX). The results showed that the surface of treated carbon microfibers was thickly covered by carbon nanotubes with diameters of about 50 nm. EDX image indicated that the composition of carbon nanotubes was carbon. In comparison with the sample grown on untreated carbon microfibers surface, it was found that after carbon microfibers were boiled in the solution of sulfur acid and nitric acid (VH₂SO₄:VHNO₃ = 1:3) and immersed in the solution of iron nitrate and xylene, carbon nanotubes with uniform density can be grown on carbon microfibers surface. Based on the results, we concluded that the pretreatment of carbon microfibers had great effect on the growth of carbon nanotubes by floating catalyst method.     

Functionalization of carbon nanotubes with silver clusters

In this paper, an advanced method of one-step functionalization of single and multi walled carbon nanotubes (SWCNTs and MWCNTs) using γ-irradiation was described. Two synthesis procedures, related with different reduction species, were employed. For the first time, poly(vinyl alcohol) PVA is successfully utilized as a source to reduce silver (Ag) metal ions without having any additional reducing agents to obtain Ag nanoparticles on CNTs. The decoration of carbon nanotubes with Ag nanoparticles takes place through anchoring of (PVA) on nanotube's surface. Optical properties of as-prepared samples and mechanism responsible for the functionalization of carbon nanotubes were investigated using UV-vis and FTIR spectroscopy, respectively. Decorated carbon nanotubes were visualized using microscopic techniques: transmission electron microscopy and scanning tunneling microscopy. Also, the presence of Ag on the nanotubes was confirmed using energy dispersive X-ray spectroscopy. This simple and effective method of making a carbon nanotube type of composites is of interest not only for an application in various areas of technology and biology, but for investigation of the potential of radiation technology for nanoengineering of materials.     

One-step preparation of water-soluble single-walled carbon nanotubes

A novel one-step process using potassium persulfate (KPS) as oxidant is proposed in this paper to prepare water-soluble single-walled carbon nanotubes (SWNTs). The process without the need for organic solvents and acids is a low-cost, eco-friendly, facile method. Morphology observation by atomic force microscopy (AFM) indicates that the KPS-treated SWNTs were effectively debundled without obvious shortening in their length. The functional groups and thermal stability of the treated SWNTs were analyzed by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). XPS results show that several functional groups such as potassium carboxylate (-COOK), carbonyl (-CO) and hydroxyl (-C-OH) groups were formed on the surfaces of the SWNTs, while the TGA results reveal that the quantity of the functional groups can reach to approximately 20%.     

Damping of electron Zitterbewegung in carbon nanotubes

Zitterbewegung (ZB, trembling motion) of electrons in semiconductor carbon nanotubes is described taking into account dephasing processes. The density matrix formalism is used for the theory. Differences between decay of ZB oscillations due to electron localization and that due to dephasing are discussed.     

Investigation of electrical transport in hydrogenated multiwalled carbon nanotubes

Highly disordered multiwalled carbon nanotubes of large outer diameter (∼60 nm) fabricated by means of chemical vapor deposition process inside porous alumina templates exhibit ferromagnetism when annealed in a H₂/Ar atmosphere. In the presence of an applied magnetic field, there is a transition from positive to negative magnetoresistance. The transition may be explained in terms of the Bright model for ordered and disordered carbon structures. Additionally, temperature dependent electrical transport experiments exhibit a zero-bias anomaly at low temperature.     

Biological functionalization and fluorescent imaging of carbon nanotubes

Biofunctionalization and manipulating of carbon nanotubes (CNTs) is important for biomedical research and application. Cy5 labeled goat anti-rabbit IgG (anti-IgG-Cy5) is chemically bonded to CNTs via a two-step process of diimide-activated amidation. This process can avoid the intermolecular connection of proteins. Fluorescent imaging of CNTs in aqueous solution has been demonstrated using anti-IgG-Cy5 immobilized CNTs (IgG-CNTs) as the model. The biologically functionalized carbon nanotubes (f-CNTs) in solution have been observed successfully using fluorescence microscopy. The fluorescent image of highly oriented f-CNTs is obtained at first time. The influencing factors on fluorescent imaging including oxidation duration, background noise and reactant concentration are discussed.     

碳纳米管在储氢上的应用

氢能是一种理想的能源载体,而经济有效的储氢手段是氢能实现规模应用急需解决的关键问题之一。碳纳米管在存储氢气上表现出来的独特性质,使其最有希望成为一种新的高效的储氢材料。从实验、理论研究两个方面总结了前人在碳纳米管储氢上的研究成果,并对碳纳米管储氢吸附方式,吸附量影响因素等方面做出分析。最后指出为实现碳纳米管储氢大规模应用仍需做的一些基础性研究工作。     

不同参数多壁碳纳米管太赫兹谱特性

探索不同管径和长度的多壁碳纳米管（MWCNT）的太赫兹（THz）谱特性,采用透射型太赫兹时域光谱系统研究了5个不同管径和长度的MWCNT样品的太赫兹吸收谱和折射率谱,并对比和分析了它们的差异。结果表明：在0.2～2.0 THz内,多壁碳纳米管太赫兹吸收没有特征吸收峰,吸收强度随着频率的增加而增加,并可以拟合为不同斜率的直线,且MWCNT在THz波段的吸收强度与管径和长度成正比。折射率随着频率的增加呈指数衰减,同时,管径是影响其折射率的一个重要因素,而长度对其影响不大。     

不同参数多壁碳纳米管太赫兹谱特性

探索不同管径和长度的多壁碳纳米管(MWCNT)的太赫兹(THz)谱特性,采用透射型太赫兹时域光谱系统研究了5个不同管径和长度的MWCNT样品的太赫兹吸收谱和折射率谱,并对比和分析了它们的差异。结果表明:在0.2~2.0THz内,多壁碳纳米管太赫兹吸收没有特征吸收峰,吸收强度随着频率的增加而增加,并可以拟合为不同斜率的直线,且MWCNT在THz波段的吸收强度与管径和长度成正比。折射率随着频率的增加呈指数衰减,同时,管径是影响其折射率的一个重要因素,而长度对其影响不大。     

Preparation of carbon nanosheets deposited on carbon nanotubes by microwave plasma-enhanced chemical vapor deposition method

Carbon nanosheets were synthesized by microwave plasma-enhanced chemical vapor deposition method on carbon nanotubes substrate which was treated by hydrogen plasma. The results showed that the diameters of carbon nanotubes first got thick and then “petal-like” carbon nanosheets were grown on the outer wall of carbon nanotubes. The diameters of carbon nanotubes without and with carbon nanosheets were 100-150 and 300-500 nm, respectively. Raman spectrum indicated the graphite structure of carbon nanotubes/carbon nanosheets. The hydrogen plasma treatment and reaction time greatly affected the growth and density of carbon nanosheets. Based on above results, carbon nanosheets/carbon nanotubes probably have important applications as cold cathode materials and electrode materials.     

Optical studies of carbon nanotubes and nanographites

Resonance Raman and photoluminescence excitation (PLE) spectroscopies are used to study the optical properties of different types of carbon nanostructures such as carbon nanotube, nanoribbons, nanographites and graphite edges. In the resonance Raman experiments of carbon nanotubes, the (n,m) assignment is obtained by comparing the experimental and theoretical diameter and chirality dependence of the optical transitions. The influence of the environment on the optical transitions of the nanotubes is also obtained in the Raman experiments. The PLE measurements in different samples of carbon nanotubes show both direct and phonon-assisted optical transitions, and the results give new evidences that the optical transitions in nanotubes have an excitonic character, which is very strong for the low energy transitions. We also analyze the Raman spectra of nanoribbons and nanographites, showing that this technique is an important tool for defect characterization in graphitic materials, and can be used to distinguish the atomic structure of the graphite edges.     

Preparation and characterization of biocompatible magnetic carbon nanotubes

Magnetic carbon nanotubes consisting of multi-wall carbon nanotubes (MWNTs) core and Fe₃O₄ shell were successfully prepared by in situ thermal decomposition of Fe(acac)₃ or FeCl₃ or Fe(CO)₅ in 2-pyrrolidone containing acid treated MWNTs at 240 °C with the protection of nitrogen gas. The samples were characterized by TEM, XRD, SEAD, XPS and superconducting quantum interference device. Also, their biocompatibility was compared with naked carbon nanotubes. The results showed that after coated with Fe₃O₄ nanoparticles, the obtained magnetic carbon nanotubes show superparamagnetic characteristic at room temperature, and their blocking temperature is about 80 K. The magnetic properties of the nanotubes are relevant to the content of magnetic particles, increasing content of magnetic nanoparticles leads to higher blocking temperature and saturation magnetization. The results of antimicrobial activities to bacterial cells (Escherichia coli) showed that the MWNTs have antimicrobial activity, while the magnetic nanotubes are biocompatible even with a higher concentration than that of MWNTs.     

Purification of carbon nanotubes grown by thermal CVD

We show the results of a set of purifications on carbon nanotubes (CNT) by acid and basic treatments. CNTs were obtained by thermal decomposition of camphor at 850 °C in a CVD growth system, by means of a growth process catalyzed by iron clusters originating from the addition of ferrocene in the precursors mixture. The purification procedures involved HNO₃, H₂SO₄, HSO₃Cl and NaOH for different process temperatures.As-grown CNTs showed a consistent presence of metal catalyst (about 6 wt%), evidenced by TGA. The purification treatments led to a certain amount of opening of the CNT tips, with a consequent loss of metal catalyst encapsulated in tips. This is also confirmed by BET analysis, which showed an increase of the surface area density of CNT after the purification.FT-IR and XPS revealed the presence of carboxylic groups on the CNT surface chemically modified by the harsh environment of the purification process.Among the various treatments that have been tested, the 1:3 solution of nitric and sulphuric acid was the most effective in modifying the CNT surface and inducing the formation of functional groups.     

碳纳米管负载矾的第一性原理研究

本文基于密度泛函第一性原理研究了原始和带有缺陷的(Stone-Wales缺陷和单空位缺陷)碳纳米管负载金属V的稳定构型.对于V吸附在原始碳纳米管(CNT)上时,V在内表面的吸附比外表面的吸附有更强的相互作用力,且六元环内表面结构最稳定.当V与Stone-Wales缺陷碳纳米管相互作用时,V原子易吸附在管外七元环C-C键的外表面和内表面处,这说明缺陷位置的有效结合使之局域化加强.而以单空位缺陷碳纳米管为载体时V最易吸附在外缺陷处,相当于碳纳米管的一个C被金属V原子取代,形成了3个V-C_(sur)键,这进一步表明SV管外吸附比管内吸附更容易.我们从上述三种构型载体中发现,金属V吸附在缺陷碳纳米管时的稳定性要优于原始碳纳米管,且SV缺陷对金属V的固定效果最好.     

Electric resistivity of multi-walled carbon nanotubes at high temperatures

The electric resistivity of a clean multi-walled carbon nanotube (MWNT) mat sample was studied at temperatures T between 300 and 1900 K. We found that the resistivity ρ decreases monotonously with increasing temperature without showing any sign of turn up. Our results can be well fitted with a power law of T^−α within the framework of one dimensional Luttinger liquid theory with α = 0.13 or with a simple thermally activated inter shell hopping model.     

Terahertz Time-Domain Spectroscopy of Solids: A Review

Recent development of the terahertz time domain spectroscopy (THz-TDS) and its application to solids have been reviewed. This spectroscopy is unique in that the time-domain wave forms are measured at first and the complex optical constants are deduced directly by the Fourier transformation of them without resort to the Kramers-Kronig analysis. Various types of the THz-TDS systems are briefly described. Applications of the THz-TDS to various solids, i.e., semiconductors, superconductors, polymers, photonic crystals, and so on are also presented to demonstrate how widely this spectroscopy is applicable to characterization of solids.     

Multiwall carbon nanotubes synthesized by RF-CCVD on novel CaO supported catalysts

Multiwall carbon nanotubes were synthesized on the FeCoCaO and FeMoCaO catalysts by RF-CCVD at 750 °C, 850 °C and 950 °C, using acetylene as the carbon source. Analytically, it was found that the nanotubes are well crystallized, with outside diameters ranging between 10 and 60 nm and a ratio of the outside to the inside diameters of 2 to 3. The nanotubes did not present amorphous carbon and their purity increased with the temperature of synthesis. A relatively large number of metallic nanoparticles of various dimensions and shapes encapsulated inside the nanotubes were observed by TEM in most of the nanotube samples.