The influence of Ni catalyst on the growth of carbon nanotubes on Si substrates

This article treats the influence of the treatment of a Ni catalyst upon the growth of carbon nanotubes in alcohol catalytic chemical vapour deposition (AC CVD) equipment. Prior to the growth of diamond, a thin film of Ni was deposited on a silicon substrate by magnetron sputtering. We observed that a combination of annealing of the Ni catalyst in vacuum and NH₃ had a positive effect upon the growth of carbon nanotubes (CNTs). The prepared CNTs were analysed by scanning electron microscopy and Raman spectroscopy.     

The preparation of carbon nanotube/linear low density polyethylene composites by a water-crosslinking reaction

A novel method to prepare the carbon nanotube (CNT)/linear low density polyethylene (LLDPE) composite is demonstrated. The combination of free radical reaction and water-crosslinking reaction to prepare the CNT/LLDPE composite was characterized by Raman and FT-IR. Mechanical properties and thermal stability of the composite were significantly improved after silane modification and water-crosslinking reaction.     

Synthesis of Heterogenous Multi-Walled Carbon Nanotubes in a Carbon Arc in Water

Boron-doped multi-walled carbon nanotubes (MWCNTs) were generated by arc discharge in water by using B-doped graphite electrodes. The product morphology was studied by SEM and HRTEM microscopy. The electronic features were determinated by Raman and EELS spectroscopy. Optical emission spectroscopy (OES) was used to evaluate the temperature and C₂ content distributions in arc plasma.     

Effects of oxygen annealing on gas sensing properties of carbon nanotube thin films

Carbon nanotubes (CNTs) thin films deposited by plasma enhanced chemical vapor deposition have been investigated as resistive gas sensors towards NO₂ oxidizing gas. Effects of air oxidative treatment dramatically influence the nanotubes’ electrical resistance as determined by volt-amperometric measurements. In particular the electrical measurements show that electrical behavior of the CNT films can be converted from semiconducting to metallic through thermal treatments in oxygen. The electrical response was then measured exposing the films to sub-ppm NO₂ concentrations (100 ppb in air) at 165 °C. Upon exposure to NO₂, the electrical resistance of CNTs was found to decrease. The obtained results demonstrate that nanotubes could find use as a sensitive chemical gas sensor for (a) the fast response accompanied by a high sensitivity to sub-ppm NO₂ exposure, and (b) the precise recover of the base resistance value in absence of NO₂ at a fixed operating temperature, likewise indicating that intrinsic properties measured on as prepared nanotubes may be severely changed by extrinsic oxidative treatment effects.     

Effect of intense laser and energetic ion irradiation on Raman modes of Multiwalled Carbon Nanotubes

The effects of intense laser and energetic ion irradiation on Raman vibrational modes of Multiwalled Carbon Nanotubes have been investigated. The intensity ratio of D and G modes decreases with increase in laser power density and remains almost constant with decrease of laser power density. The intensity ratio of D mode to G mode for ion irradiated Multiwalled Carbon Nanotubes decreases at low fluence (4 × 10¹¹ ions/cm²) and increases further with increase in ion fluence. The results show that ion irradiation at low fluence and laser irradiation lead to purification/ordering of the nanotubes.     

炭纤维表面生长碳纳米管

采用化学气相沉积工艺在炭纤维表面生长了碳纳米管,并观察了它的微观形貌,且对其影响因素进行了初步研究.结果表明:纤维表面的纵向沟槽可以负载催化剂粒子,是生长碳纳米管的物理基础;催化剂的浓度太高,金属粒子容易团聚长大,所得碳纳米管的管径较大;而催化剂浓度太低,则不能在炭纤维整个表面均匀生长碳纳米管;最佳的催化剂溶液的浓度是0.05mol/L的硝酸钴.比较了铁、钴、镍三种过渡金属催化剂,从形成的碳纳米管的质量来看,钴催化剂最佳.     

Influence of co-catalyst on growth of carbon nanotubes using alcohol catalytic CVD method

This paper describes the influence of a co-catalyst on growth of carbon nanotubes (CNTs) by alcohol catalytic chemical vapour deposition (ACCVD) method. Silicon wafers covered with thermal oxide or polycrystalline diamond thin film were used as substrates. Ni thin film supported with Al, Cu or Ti was used as a catalyst. The films were deposited by pulsed laser deposition technique. Comparison of the various types of the co-catalyst (Al, Cu, Ti) leads to the conclusion that Cu co-catalyst is suitable for producing very thin single wall carbon nanotubes (SWCNTs) and combination of Al and Ni provide a good condition to the catalytic growth of CNTs. In addition, we observed also the influence of the various diffusion barriers (thermal oxide and polycrystalline diamond) on growth of CNTs. Prepared samples were analysed by Raman spectroscopy (RS) and scanning electron microscopy (SEM).     

Formation of Transition Metal Cluster Adducts on the Surface of Single-walled Carbon Nanotubes: HRTEM Studies

We report the formation of chromium clusters on the outer walls of single-walled carbon nanotubes (SWNTs). The clusters were obtained by reacting purified SWNTs with chromium hexacarbonyl in dibutyl ether at 100°C. The functionalized SWNTs were characterized by thermogravimetic analysis, XPS, and high-resolution TEM. The curvature of the SWNTs and the high mobility of the chromium moieties on graphitic surfaces allow the growth of the metal clusters and we propose a mechanism for their formation.     

Adaptive Neuro-Fuzzy Modeling of Mechanical Behavior for Vertically Aligned Carbon Nanotube Turfs

Several characterization methods have been developed to investigate the mechanical and structural properties of vertically aligned carbon nanotubes (VACNTs).Establishing analytical models at nanoscale to interpret these properties is complicated due to the nonuniformity and irregularity in quality of as-grown samples.In this paper,we propose a new methodology to investigate the correlation between indentation resistance of multi-wall carbon nanotube (MWCNT) turfs,Raman spectra and the geometrical properties of the turf structure using adaptive neuro-fuzzy phenomenological modeling.This methodology yields a novel approach for modeling at the nanoscale by evaluating the effect of structural morphologies on nanomaterial properties using Raman spectroscopy.     

Functionalized Multi‐Wall Carbon Nanotubes for Lipase Immobilization

We examine the immobilization of lipase B from Candida antarctica on functionalized multi‐wall carbon nanotubes (MWCNTs) through physical adsorption. MWCNTs functionalized with carboxyl‐, amine‐ and ester‐ terminal groups on their surface are used as immobilization carriers. Dispersion of the nanotubes and the immobilization procedure take place in aqueous and low‐water media. High enzyme loadings are attained, up to 25% of the weight of the carbon nanotubes. These novel biomaterials are characterized though FT‐IR and Raman spectroscopy. The MWCNT–lipase bioconjugates exhibit high catalytic activity and increased storage and operational stability. The biomaterials retain more than 55% of their initial activity after 6 months at 4 °C, while they retain approximately 25% of their initial activity after 30 d of incubation in hexane at 60 °C. The catalytic behaviour of the immobilized enzyme depends on the terminal group of the carbon nanotubes, the concentration of the enzyme and the immobilization method employed.     

Microwave-Assisted Synthesis of a Soluble Single Wall Carbon Nanotube Derivative

The development of a novel procedure based on microwave (MW) heating allowed to obtain a soluble derivative of Single Wall Carbon Nanotubes (SWNTs) by grafting poly(ethylene glycol) (PEG) chains to shortened SWNTs. The use of MW irradiation remarkably enhanced reaction rates compared to similar syntheses based on conventional heating.     

Carbon dioxide as a carbon source for synthesis of carbon nanotubes by chemical vapor deposition

Carbon dioxide was successfully used as carbon source in the synthesis of carbon nanotubes (CNTs) by chemical vapor deposition (CVD) over Fe/CaO catalyst. The product was evaluated using both transmission electron microscopy (TEM) and Raman spectroscopy. Crooked and branching structures of multi-walled carbon nanotubes (MCNTs) with diameters of around 50 nm were observed on the TEM micrographs. Raman spectrum results show that the nanotubes have small defects, which is in agreement with the results of TEM. The influence of reaction variable such as furnace temperature and types of support media was also studied and the reaction mechanism was then discussed in this paper.     

Carbon nanotube forest growth on NiTi shape memory alloy thin films for thermal actuation

Actuation frequencies in thermally triggered Shape Memory Alloy (SMA) thin films are limited by the slow heat transport into/out of the films. Carbon Nanotubes (CNTs) are known to exhibit an exceptionally high thermal conductivity. Thus, we propose to thermally contact SMA films with CNTs to increase SMA actuation frequencies by enhanced heat transport through the CNTs. The basic requirement for this envisaged nanotube application is to obtain CNT forest growth on a SMA material while retaining a reversible martensitic transformation, as required for Shape Memory Effect exploitation. We show how such growth can be achieved on thin films of the SMA material NiTi. Future work is needed to measure thermal properties and obtainable cycling frequencies of CNT-SMA structures.     

Spark plasma sintered tantalum carbide-carbon nanotube composite: Effect of pressure, carbon nanotube length and dispersion technique on microstructure and mechanical properties

TaC-4 wt.% CNT composites were synthesized using spark plasma sintering. Two kinds of CNTs, having long (10-20 μm) and short (1-3 μm) length, were dispersed by wet chemistry and spray drying techniques respectively. Spark plasma sintering was carried out at 1850 °C at pressures of 100, 255 and 363 MPa. Addition of CNTs leads to an increase in the density of 100 MPa sample from 89% to 95%. Short CNTs are more effective in increasing the density of the composites whereas long CNTs are more effective grain growth inhibitors. The longer CNTs are more effective in increasing the fracture toughness and an increase up to 60% was observed for 363 MPa sample. Hardness and elastic modulus are found to increase by 22% and 18% respectively for 100 MPa samples by addition of long CNTs. Raman spectroscopy, SEM and TEM images indicated that the CNTs were getting transformed into flaky graphitic structures at pressure higher than 100 MPa.     

Enhanced electron emission from titanium coated multiwalled carbon nanotubes

Enhanced field emission properties and improved crystallinity of titanium (Ti) coated multiwalled carbon nanotubes (MWCNTs), prepared by microwave plasma enhanced chemical vapour deposition have been observed. Ti films of extremely low thicknesses (0.5 nm, 1.0 nm and 1.5 nm) were coated over carbon nanotubes (CNTs) and their field emission behaviour was investigated. The turn on field of Ti coated CNTs was found to be low (~ 0.8 V/μm) as compared to pristine CNTs (~ 1.8 V/μm). The field enhancement factor for Ti coated CNTs was quite large (~ 1.14 × 10⁴) as compared to pristine CNTs (~ 6 × 10³). This enhancement in electron emission is attributed to the passivation of defects and improved crystallinity of CNTs. Surface morphological and microstructural studies were carried out to investigate the growth of pristine and Ti coated CNTs. It was observed that Ti nanoclusters adsorb on the edges of MWCNTs and increase their crystallinity. This increase is directly correlated with the thickness of Ti film deposited. Micro Raman spectroscopy confirmed the improved crystallanity of Ti coated CNTs.     

Influence of Bias on the Properties of Carbon Nitride Films Prepared by Vacuum Cathodic Arc Method

Carbon nitride films have been synthesized in a wide range of biases from 0 to -900 V by vacuum cathodic arc method. The N content was about 12.0-22.0 at. pct. Upon increasing the biases from 0 to -100 V, the N content increased from 15.0 to 22.0 at. pct which could be attributed to the knot-on effect. While the further increasing biases led to the gradual falling of the N content to 12.0 at. pct at -900 V due to the enhancement of the sputtering effect. Below -200 V, with the increasing biases the sp2C fraction in the films decreased, as a result of vvhich the I(D)/I(G) fell in the Raman spectra and the sp peaks also showed the decreasing tendency relative to the s peaks in the VBXPS (valence band X-ray photoelectron spectroscopy). While above -200 V, the sp2C fraction increased and the films became graphitinized gradually, accompanying which the I(D)/I(G) rose from -200 V to -300 V and the Raman spectra even shovved the graphite characteristic above -300 V and the sp peaks rose again relative to the s     

Preparation of carbon nanotube by rotary CVD on Ni nano-particle precipitated cBN using nickelocene as a precursor

Ni nano-particles were deposited on hexagonal boron nitride (hBN) and cubic boron nitride (cBN) powders by rotary chemical vapor deposition (RCVD) using nickelocene as a precursor. Ni nano-particles precipitated on hBN and cBN powders were about 20 nm and 10 to 50 nm in diameter, respectively. Carbon nanotubes (CNTs) were grown from relatively large Ni particles about 50 nm in diameter on cBN powder, whereas carbon layers surrounded Ni nano-particles on the surface of hBN powders.