Growth of Aligned Carbon Nanotubes through Microwave Plasma Chemical Vapor Deposition

Aligned carbon nanotubes (CNTs) were synthesized on glass by microwave plasma chemical vapor deposition (MWPCVD) with a mixture of methane and hydrogen gases at the low temperature of 550~C. The experimental results show that both the self-bias potential and the density of the catalyst particles are responsible for the alignment of CNTs. When the catalyst particle density is high enough, strong interactions among the CNTs can inhibit CNTs from growing randomly and result in parallel alignment.     

A study on bactericidal properties of Ag coated carbon nanotubes

A silver layer is coated on carbon nanotubes (CNTs) by ion beam assisted deposition (IBAD). Standard agar dilution method is used to evaluate the bactericidal rate against Gram positive S. aureus and negative E. coli. The structure and the chemical states are investigated by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The results show that Ag coated CNTs possess very high bactericidal rate. In comparison with the Ag coated pyrolytic carbon sample, the Ag coated CNTs show stronger bactericidal property.     

Enhanced field emission from nano-graphite coated carbon nanotubes

An effective method by low energy carbonhydrogen ion treatment to enhance field emission of the carbon nanotubes (CNTs) is demonstrated. Comparing with control, field emission (FE) currents of the CNTs by carbonhydrogen ion irradiation increased, and the turn-on field and the threshold field decreased significantly. The structure characteristic revealed by transmission electron microscopy demonstrates that CNTs are coated by nano-graphite particles after being treated with low energy carbonhydrogen ion and that there are large quantities of defects and grain boundaries in the coated layer. It is considered that the coating layer can decrease the effective surface work function of CNTs and correspondingly increase field emission. In addition, the defects, the grain boundaries and the C-H dipoles forming in the process of the low energy ions irradiation can effectively enhance the field emission.     

Ion sputtered surfaces as templates for carbon nanotubes alignment and deformation

Starting from their discovery in 1991, carbon nanotubes have attracted a great attention, thanks to their peculiar mechanical, electrical and elastic properties that could be used to realize new devices in many different fields.

For nanotechnology applications it is very important to be able to control not only shape and position but also alignment and orientation of carbon nanotubes, both during the growth and after it.

Here we present preliminary results obtained by depositing carbon nanotubes (CNT) solutions on ion sputtered quartz substrates. Atomic force microscopy (AFM) images allow to study both CNTs positioning on the “ripples” generated by Ar⁺ sputtering on the SiO₂ surface and their radial deformation induced by the “rough” surface.

Work is now in progress to optimize the sputtering parameters and solution treatment (purification and functionalization) in order to get single CNTs regularly arranged on a patterned surface.     

Influence of Reaction Pressure on Nucleation Rate of Diamond on Silicon Substrates

1.IntroductionDiamond,duetoitsexcellentproperties,hasmanypotentialapplicationsinthefieldsofmechanics,electronics,optics,astronautics,etc.Now,diamondfilmshavebeensuccessfullypreparedonllondiarnondsubstratesundertheconditionofasubatmospherepressurebyavarietyofchemicalvapordeposition(CVD)methods,amongwhichthemicrowaveplasmaCVD(MWPCVD)isthenoveltechnique,preeminentespeciallyfortheformationofahighqualityfilm[l].InCVDofdiamondfilm,similartothoseofothermaterials'films,thediamondnucleationmustbe…     

用碳纳米管从硝酸溶液中回收镅

研究了用碳纳米管从放射性废硝酸溶液中进行镅的回收。在浓硝酸溶液中,碳纳米管对镅的吸附率小于1％;随着硝酸浓度的降低,镅的吸附率迅速升高,当溶液的pH值大于5时,碳纳米管对镅的吸附率达到99.95％以上。用1．5mol／L硝酸进行解吸,一次解吸能够从碳纳米管回收99％以上的镅。     

碳纳米管的放射性材料填充

开口纯化后的碳纳米管(CNTs)用放射性(^125I)NaI和(^110Ag^m)AgNO3溶液进行了浸泡、洗涤和洗脱研究，用高分辨透射电镜(HREM)和X射线散射能谱(EDS)对CNTs的填充情况进行了表征；使用放射性同位素示踪技术确定了CNTs内部样品的填充量。结果显示用本工作所采用的简单水溶液浸泡技术能将水溶性无机盐材料填充到CNTs中空结构内。实验表明，放射性核素示踪技术能有效地应用于CNTs的填充、释放等行为的研究。     

同位素示踪法在碳纳米管填充释放行为研究中的应用

应用同位素示踪技术,以^110Ag^m-AgNO3溶液填充、NANO3或HNO3溶液洗涤氧化开口后的碳纳米管(CNTs),研究了填充物^110Ag^m-AgNO3在水溶液中从碳纳米管中的释放情况;用高分辨透射电镜(HREM)、扫描电镜(SEM)、X射线衍射(XRD)、X射线能量色散谱(EDS)对CNTs的填充情况进行了表征;根据放射分析测量结果计算了CNTs腔内部样品的填充量。结果表明,CNTs腔内有银材料填充并且在水溶液中不会释放出来;示踪技术能有效地应用于CNTs的填充、释放等行为的研究及材料填充量的定量测定。     

AFM and STM investigation of carbon nanotubes produced by high energy ion irradiation of graphite

Carbon nanotubes (CNT) were produced by high energy, heavy ion irradiation (215 MeV Ne, 246 MeV Kr, 156 MeV Xe) of graphite. On samples irradiated with Kr and Xe ions large craters were found by atomic force microscopy, these are attributed to sputtering. Frequently one or several CNTs emerge from the craters. Some of the observed CNTs showed a regular vibration pattern. No other carbon based materials, like amorphous carbon or fullerenes were evidenced. Focused ion beam cuts were used to compare CNTs with surface folds on graphite.     

碳纳米管/聚丙烯酰胺复合水凝胶的制备及性能

通过活度2.072×1015 Bq、剂量率2 k Gy·h-1的钴-60进行辐照接枝和辐照交联两步法制备了碳纳米管复合水凝胶。使用傅里叶红外光谱(Fourier Transform Infrared spectroscopy,FTIR)、热释重分析(Thermal gravimetric analysis,TGA)、透射电子显微镜(Transmission electron microscope,TEM)、X射线衍射(X-ray diffraction,XRD)、BET比表面积(Brunauer-Emmett-Teller Specific Surface Area)等方法对样品进行了表征。结果显示,改性后的碳纳米管(Carbon nanotubes,G-CNTs)的管壁出现了明显的链段,其傅里叶红外光谱在1 452 cm-1和1 726 cm-1处多了两个吸收峰;碳纳米管复合水凝胶的BET值(30 m2·g-1)比聚丙烯酰胺水凝胶的(12 m2·g-1)提高了一倍多。实验结果表明丙烯酸被成功接枝到CNTs的管壁上。G-CNTs在凝胶中均匀分散,并提高了复合水凝胶的比表面积和机械强度。     

金属离子在碳纳米管上的吸附及其对环境毒理学的影响

碳纳米管(NTs)易吸附环境中各种有毒金属离子,形成复合物,其生物效应和毒性有别于CNTs和金属离子单独作用及两重材料简单生物效应的叠加效果.阐述了金属离子在CNTs上吸附概况以及影响吸附的若干因素,分析了吸附作用对CNTs和金属离子环境毒理学的可能影响,指出了放射性核素示踪和同步辐射等核分析技术在相关研究中的重要作用...     

SiC/SiC composite fabricated with carbon nanotube interface layer and a novel precursor LPVCS

Continuous SiC fiber reinforced SiC matrix composites (SiC/SiC) have been studied as promising candidate materials for nuclear applications. Three-dimensional SiC/SiC composite was fabricated via polymer impregnation and pyrolysis (PIP) process using carbon nanotubes (CNTs) as the interface layer and LPVCS as the polymer precursor. The microstructural evolution of the fiber/matrix interface was studied. The porosity, mechanical properties, thermal and electrical conductivities of the SiC/SiC composite were investigated. The results indicated that the high densification efficiency of the liquid precursor LPVCS resulted in a low porosity of the SiC/SiC composite. The SiC/SiC composite exhibited non-brittle fracture behavior, however, bending strength and fracture toughness of the composite were relatively low because of the absence of CNTs as the interface layer. The thermal and electrical conductivities of the SiC/SiC composite were low enough to meet the requirements desired for flow channel insert (FCI) applications.     

A molecular dynamics study of the clustering of implanted potassium in multiwalled carbon nanotubes

We have studied the low energy irradiation of carbon nanotubes (CNT) with K ions using classical molecular dynamics simulations with analytical potentials. The studied CNTs had diameters of about 0.5–1.2 nm and single or multiple walls. The average penetration depth and probabilities to introduce an impurity atom into CNT were studied with simulations on irradiating the CNT with single K ion. The number of potassium clusters, their average sizes and the damage produced into the CNT due to the irradiation were studied using multiple K ion irradiations. We found that the K ions are mobile in CNTs right after the implantation event and that they cluster together. For CNTs with 1–3 coaxial tubes, the highest ratio of K atoms in clusters per total number of K ions was obtained by using an irradiation energy of about 100 eV. Also the least damage per K ion was found to be produced into the CNT with this energy when those energies high enough for the ion to penetrate the outermost wall of the CNT were considered.     

RBS/EBS/PIXE measurement of single-walled carbon nanotube modification by nitric acid purification treatment

Single-walled carbon nanotubes (SWCNTs) have many potential applications, including a number of promising biological applications. Nitric acid treatment solubilises CNTs by introducing functional groups, as well as removing amorphous carbon contaminants. Here, we report simultaneous RBS/EBS/PIXE measurements of nitric acid treated SWCNTs, focussing on the metal, nitrogen and oxygen content. We found that nitrogen remains constant in the samples despite washing and dialysis indicating it has either bound irreversibly via intercalation with the SWCNT and/or has been included in functional groups. We also found that the ratio between oxygen and platinum (catalyst) remains constant with treatment time (sampled at 2, 4, 6 h), indicating no more functional groups are made after 2 h exposure.     

The electrical conductivity of carbon nanotube sheets by ion beam irradiation

A method for improving the electrical conductivity of carbon nanotube (CNT) sheets by ion beam irradiation is reported. CNT sheets prepared by a vacuum filtration method were irradiated by Ar and H ion beams at different temperatures. The electrical conductivity of the irradiated CNT sheets at a temperature of 800 K can be improved. The conductivity improvement can be ascribed to the formation of covalent bond crosslinks between CNTs induced by the ion beam irradiation at the elevated temperature.     

Integrated carbon nanotubes electrodes in microfluidic chip via MWPCVD

An on-chip electrochemical detector for microfluidic chips was described, based on integrated carbon nanotube (CNT) electrodes directly onto the chip substrate through microwave plasma chemical vapor deposition (MWPCVD). The attractive performance of the integrated CNT electrodes was demonstrated for the amperometric detection of sucrose, glucose and D-fructose. The integrated CNT electrodes showed stronger electrocatalytic activity than gold electrodes.     

Synthesis of (B-C-N) Nanomaterials by Arc Discharge Using Heterogeneous Anodes

In spite of the current prevalence of the CVD-based processes,the electric arc remains an interesting process for the synthesis of carbon nanoforms,thanks to its versatility,robustness and easiness.It also allows performing in-situ substitution of carbon atoms by hetero-elements in the graphene lattice.Our work aims to establish a correlation between the plasma properties,type and chemical composition (and the substitution rate) of the obtained single-wall carbon nanotubes.The plasma was characterized by optical emission spectroscopy and the products were analyzed by high resolution transmission electron microscopy and core level Electron Energy-Loss Spectroscopy (EELS).Results show that a high boron content leads to a plasma temperature decrease and hinders the formation of nanotubes.This effect can be compensated by increasing the arc current and/or yttrium content.The optimal conditions for the synthesis of boron-and/or nitrogen-substituted nanotubes correspond to a high axial plasma temperature associated to a strong radial gradient.EELS analysis confirmed that the boron incorporates into the graphenic lattice.     

Electron spin resonance investigations on ion beam irradiated single-wall carbon nanotubes

ESR investigations on single-wall carbon nanotubes irradiated with accelerated protons, helium ions, and neon ions are reported. All spectra were accurately simulated assuming that the resonance line is a convolution of up to 4 lines originating from catalyst residues, amorphous carbon, and electrons delocalized over the conducting domains of nanotubes. The faint line observed in irradiated nanotubes at g > 2.25 was assigned to magnetic impurities. However, there are no sufficient data to confirm that this line is connected to radiation-induced magnetism in carbon nanotubes. The generation of paramagnetic defects due to the bombardment of single-wall carbon nanotubes by accelerated ions is reported. These data correlate with previous Raman and thermal investigations on the same single-wall carbon nanotubes and reveals their sensitivity to ionizing radiation. The temperature dependence of ESR spectra in the range 25-250 K was used to identify the components of the ESR spectra.     

On the anomalous stress-dependence of creep rate in precipitation strengthened alloys

The stress and temperature dependence of secondary creep rate have been analysed in the temperature range of 773–823 K for a 22% Cr-34% Ni austenitic steel (alloy 800) strengthened by a small volume fraction of γ′(Ni₃Ti, Al). In this respect two regimes have been distinguished at low and high stresses with the activation energies corresponding to those of the grain boundary and bulk diffusions, respectively. The very high stress-dependence (20) observed at elevated stresses, in comparison with those at low stresses (3–5), is shown to be enhanced by the metastability of the matrix and the resultant marked deformation inequalities during secondary creep. The effect of prior cold working and ageing are discussed. A correlation between low stress and high stress data through internal friction stress estimations is sought, and the possibility of the Coble creep mechanism becoming operative at low stresses is foreseen.     

Kinetic Monte Carlo simulation of hydrogen diffusion on tungsten reconstructed (0 0 1) surface

A kinetic Monte Carlo (KMC) algorithm has been developed to study the hydrogen diffusion on tungsten reconstructed (0 0 1) surface in the temperature range 220–300 K. The hydrogen diffusion coefficients predicted by the developed KMC code match the experimental values very well at low hydrogen coverage of a fraction of monolayer. A diffusion coefficient formula as a function of temperature and hydrogen coverage was derived from KMC simulations. Due to the very low probability of hydrogen occupying the long bridge adsorption sites, the rates of hydrogen atom having 3 or 4 neighbors are found to be zero for hydrogen coverage much less than a monolayer, while the rates of hydrogen atom having 0–2 neighbors are linear with respect to the hydrogen coverage. The calculated average rates of hydrogen located at the LB sites are very close to zero for low hydrogen coverage. Hydrogen only starts to occupy the LB sites after almost all SB sites are occupied.