Growth Of Multi-walled Carbon Nanotubes Research Articles

The enhanced growth of multi-walled carbon nanotubes using an atmospheric pressure plasma jet

The growth of multi-walled carbon nanotube (MWCNT) forests was investigated using an atmospheric pressure plasma jet (APPJ) system with a mixture of helium and acetylene gases. The MWCNT forests grown on Fe catalyst were compared with those grown on Ni. The growth of MWCNT forests using Fe as the catalyst was better than the growth of MWCNT forests using Ni. The MWCNT forests grown using Fe catalyst and with a plasma power of 30 W were about 17 ± 9% taller than for the plasma off. We were unable to grow MWCNTs using Ni catalyst with the plasma power off; but curly MWCNTs were grown using Ni catalyst if the plasma power was 30 W. It is found that MWCNT growth is enhanced using an APPJ. The height of the forests produced using this APPJ system was also better than that reported by other researchers using either CVD or PECVD systems.

Growth Mechanism of Carbon Nanotubes over Gold-Supported Catalysts

Carbon nanotubes have been widely synthesized by chemical vapor deposition (CVD) in the presence of transition-metal catalysts, such as Fe and Co, because they have strong catalytic activities for both the decomposition of hydrocarbon feedstock and the formation of graphitic carbons. Recently, gold (Au) was reported to catalyze the growth of multi-wall and single-wall carbon nanotubes (MWNTs and SWNTs, respectively). Because of the low solubility of carbon in Au and the unique catalytic activity observed for Au nanoparticles, the growth mechanism and yield of nanotubes over Au catalysts are intriguing. In this paper, we investigated the catalytic activity of Au supported on various metal oxides, alumina (Al2O3), silica (SiO2), titania (TiO2), and magnesia (MgO), with different hydrocarbon feedstocks, methane (CH4), ethylene (C2H4), and acetylene (C2H2). We found that Au-supported catalysts have limited activity for the decomposition of the carbon source from the gas analyses and that only the catalyst supported on Al2O3 and SiO2 gave a small number of MWNTs when reacted with C2H4 or C2H2. The formation mechanism of MWNTs over the Au-supported catalysts is also discussed.

Growth of carbon nanotubes on carbon fibre substrates to produce hybrid/phenolic composites with improved mechanical properties

Carbon nanotubes were grown by chemical vapor deposition (CVD) on different carbon fibre substrates namely, unidirectional (UD) carbon fibre tows, bi-directional (2D) carbon fibre cloth and three dimensional (3D) carbon fibre felt. These substrates were used as the reinforcement in phenolic resin matrix to develop hybrid CF–CNT composites. The growth morphology and other characteristics of the as grown tubes were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermal gravimetry (TGA) which confirmed a copious growth of multiwalled carbon nanotubes (MWNTs) on these substrates. The mechanical properties of the hybrid composites was found to increase with the increasing amount of deposited carbon nanotubes. The flexural strength (FS) improved by 20% for UD, 75% for 2D and 66% for 3D hybrid composites as compared to that prepared by neat reinforcements (without CNT growth) under identical conditions. Flexural modulus (FM) of these composites also improved by 28%, 54% and 46%, respectively.

Theoretical and experimental evidence of a metal-carbon synergism for the catalytic growth of carbon nanotubes by chemical vapor deposition

The nucleation and growth of carbon nanotubes (CNTs) using chemical vapor deposition with a metal-carbon catalyst have been studied experimentally and theoretically. Results suggest that the nucleation and growth of multiwalled CNTs are not due to the metal alone, but that carbon nuclei (once formed) also contribute to radial and axial growth. Metal particles mainly promote the nucleation and growth of the innermost carbon shell(s), and catalyze the ordering of the carbon atoms to form graphene structures. The intrinsic difference between multiwalled CNT formation and single-walled CNT formation seems to be associated with a self-catalytic function of carbon nuclei.

The role of hydroxyl and atomic oxygen in multiwall carbon nanotube growth

Multiwall carbon nanotubes (CNTs) were grown by the plasma-enhanced chemical vapor deposition (PECVD) method in downstream on the p-Si (100) substrate. Besides precursors, methane as the carbon source and hydrogen as the ablation, oxygen or H2O was alternatively inlet into the reactive chamber at the pressure of 0.05 MPa. Given characterizations of the tube structure and tube mass weight, the role of radical atomic O, hydroxyl and perhydroxyl in multiwall CNT growth was explored. In addition to a small amount of O2 (∼0.67%) or H2O (∼0.1%), it was found that a high quantity of pure nanotubes can be grown in the downstream. However, no nanotube could be formed or even the carbon matrix generated when the concentration of O2 or H2O exceeded a proper value in the mixture. The mechanism of multiwall CNT growth controlled by active radicals was explored in this paper.

Effects of oxygen on multiwall carbon nanotubes growth by PECVD

Multiwall carbon nanotubes (MWCNTs) were grown by dielectric barrier discharge (DBD)-type plasma enhanced chemical vapor deposition (PECVD) method in downstream. The temperature was 973 K and the compositions of gases were methane, hydrogen and oxygen in the total pressure of 0.05 MPa. The effect of O2 concentration in the mixture on the configuration of carbon nanotubes (CNTs) was investigated in detail. Results from scanning electron microscope (SEM) and transmission electron microscope (TEM) showed that CNTs grown in CH4/H2 (38.6%/61.4%, volume) mixture have many defects and contained disordered graphitic materials. With the addition of appropriate amount of O2 (∼0.67%), high-purity CNTs could be obtained. However, no CNT, even no carbon matrix existed under the condition of an excessive oxygen concentration (>1.0%, volume) in the mixture. In order to understand the role of O2 during CNTs growth, optical emission spectroscopy (OES) was in-situ employed and the results predicted that the improvement of CNTs quality in O2 addition was attributed to the effect of OH oxidation from the reaction of atomic oxygen with hydrogen in the plasma.

Electrochemical Growth of Pd for the Synthesis of Multiwall Carbon Nanotubes

Palladium nanostructures with variation in shape and size have been synthesized using an electrochemical deposition method. Cyclic voltammetry and linear sweep voltammetry have been used to study the growth of Pd nanoparticles on Si substrates and tungsten wire. Different sets of solutions containing PdCl2, Pd(NO3)2, and PdSO4, respectively, have been used to grow the Pd nanoparticles. Field emission scanning electron microscopy was used to visualize the Pd nanostructures on various substrates. The Pd nanostructures were used as a catalyst to grow the multiwall carbon nanotubes (MWCNT) by a microwave plasma enhanced chemical vapor deposition method. Dependence of the Pd nanoparticle shape on the architecture of MWCNTs is discussed. Carbon nanotubes were also grown on the tungsten tips. Development of Pd into Pd2Si during growth of MWCNT on Pd-coated Si has been studied. The nanotubes were observed to be filled by Pd2Si. Raman spectroscopy has been used to study the structure of the Pd2Si filled carbon nan...

Mechanism growth of multiwalled carbon nanotubes on carbon black

The growth of multiwalled carbon nanotubes (MWCNTs) on carbon black has been studied using a combustion oxygen/acetylene flame method. Different types of carbon black and reaction temperatures were evaluated for the growth of carbon nanotubes. The reaction was stopped after different short duration times of deposition in an attempt to observe the growth of carbon nanotubes. The samples were characterized by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and by Raman Spectroscopy. We have observed the transformation of the carbon black surface into graphitic sheets and the start formation of tubes from these graphitic sheets. The length of the tubes is increased but the diameter is decreased with increased deposition times. Carbon nanotubes with 10–20 nm of diameter and a length of about 50 µm are obtained after 1 min deposition. The growth of multiwalled carbon nanotubes on carbon black is a phenomenon that can not be fully explained by carbon nanotubes growth models currently known. Our results lead us to propose a mechanism for the solid-state transformation of the carbon black particles surface into nanotubes in the oxygen/acetylene flame.

Time and temperature dependence of multi-walled carbon nanotube growth on Inconel600

The growth kinetics of vertically aligned multi-walled carbon nanotubes (MWNTs) onconductive substrates is investigated by synthesizing MWNTs at different growthtemperatures and measuring ex situ the length of the nanotubes as a function of growthduration. A typical ‘root growth’ mechanism (saturation of MWNT lengths withincreasing growth duration) was observed. The value of the activation energy(Ea≈136 ± 5 kJ mol−1) of the MWNT growth reaction is suggestive of carbon diffusion through the bulk of theiron catalyst particle versus diffusion on its surface. These findings will help inoptimizing MWNT growth on conductive substrates for various applications.

Electrochemically Grown Pd Nanoparticles Used for Synthesis of Carbon Nanotube by Microwave Plasma Enhanced Chemical Vapor Deposition

Pd nanoparticles of well-defined shapes with face centered cubic structure were grown electrochemically on silicon substrates with high degree of reproducibility. As direct application of these electrochemically grown Pd nanostructures they have been used as catalyst for the growth of multi wall carbon nanotube (MWCNT). It is observed that the MWCNTs are filled with a Pd based material during growth by microwave plasma enhanced chemical vapor deposition (MPECVD) technique. High-resolution transmission electron microscopy, used to study the material inside MWCNT suggests the formation of PdH0.649 or Pd2Si during the growth of carbon nanotube. Raman spectroscopy has been used to study the structure of the MPECVD grown carbon nanotubes.

Iron assisted growth of copper-tipped multi-walled carbon nanotubes

Carbon nanotubes incorporating copper are highly sought after for nanoelectronicapplications. Indeed, several recent studies have demonstrated the production ofcopper-tipped nanotubes using the chemical vapor deposition method. Here we present thegrowth and detailed characterization of such copper-tipped nanotubes. The nanotubesgrown were of a ‘bamboo-like’ structure, consisting of stacked cups of graphene, and wereproduced by chemical vapor deposition employing iron and copper nanoparticlesas a catalyst and metal source respectively. Transmission electron microscopyand electron holography analysis of the tips of these nanotubes revealed a smallcrystalline iron particle on the inner side of the copper tip, with the nanotubestructure encapsulating the iron. This form of growth may allow the formationof similar structures with various other metal-tipped carbon nanotubes to bemanufactured.

In situmanipulation and electrical characterization of multiwalled carbon nanotubes by using nanomanipulators under scanning electron microscopy

The results of in situ manipulation and electrical transport characterization of individual multiwalled carbon nanotubes (MWCNTs) grown on a nickel tip by using a piezoelectric nanomanipulation system operating in a scanning electron microscope chamber have been reported. The growth of MWCNT directly on nickel wire by chemical vapor deposition technique ensures good electrical contact with the catalyst substrate. Using the electron beam induced welding, a full characterization of electronic properties of several MWCNTs has been explored without the usual postprocessing methods which may alter, in principle, the intrinsic properties of the carbon nanotube (CNT). Thanks to the high mechanical and electrical stability ensured by the electron beam welding procedure, a detailed study of the modification of CNT electrical transport properties under CNT buckling has been performed. The crucial role played by the structural defects in determining an irreversibility of a long MWCNT $I\text{\ensuremath{-}}V$ characteristic under mechanical stress has been clearly evidenced. Finally, by a proper sequence of CNT/tip welding and movement, the potential in creating an Ohmic junction between two nanotubes has been demonstrated, opening the route to a systematic investigation of one of the most fundamental aspect of CNT physics.

Chemical kinetic considerations for postflame synthesis of carbon nanotubes in premixed flames using a support catalyst

Multiwalled carbon nanotubes (MWCNTs) on a grid supported cobalt nanocatalyst were grown, by exposing it to combustion gases from ethylene/air rich premixed flames. Ten equivalence ratios ( ϕ ) were investigated, as follows: 1.37, 1.44, 1.47, 1.50, 1.55, 1.57, 1.62, 1.75, 1.82, and 1.91. MWCNT growth could be observed for the range of equivalence ratios between 1.45 and 1.75, with the best yield restricted to the range 1.5–1.6. A one-dimensional premixed flame code with a postflame heat loss model, including detailed chemistry, was used to estimate the gas phase chemical composition that favors MWCNT growth. The results of the calculations show that the mixture, including the water gas shift reaction, is not even in partial chemical equilibrium. Therefore, past discussions of compositional parameters that relate to optimum carbon nanotube (CNT) growth are revised to include chemical kinetic effects. Specifically, rapid departures of the water gas shift reaction from partial equilibrium and changes in mole fraction ratios of unburned C 2 hydrocarbons to hydrogen correlate well with experimentally observed CNT yields.

Dendrimer-assisted controlled growth of carbon nanotubes for enhanced thermal interfaceconductance

Multi-walled carbon nanotubes (MWCNTs) with systematically varied diameter distributionsand defect densities were reproducibly grown from a modified catalyst structure templatedin an amine-terminated fourth-generation poly(amidoamine) (PAMAM) dendrimer bymicrowave plasma-enhanced chemical vapor deposition. Thermal interface resistances of thevertically oriented MWCNT arrays as determined by a photoacoustic technique reveal astrong correlation with the quality as assessed by Raman spectroscopy. This studycontributes not only to the development of an active catalyst via a wet chemical route forstructure-controlled MWCNT growth, but also to the development of efficient and low-costMWCNT-based thermal interface materials with thermal interface resistances≤10 mm2 K W−1.

Growth of Carbon Nanotubes on Nanoporous Titania Templates

This work reports the synthesis of multiwalled carbon nanotubes (MWCNTs) on nanoporous titanium dioxide (TiO2) templates. TiO2 nanotubular templates for MWCNTs are produced by anodization of titanium followed by pulsed electrodeposition (PED) of cobalt inside the TiO2 nanotubes. Cobalt acts as a catalyst for the growth of MWCNTs using chemical vapor deposition (CVD) technique. The cobalt catalyst initiates the growth of well graphitized MWCNTs inside the titania pores as well as beyond the titania pores. These materials have been characterized by SEM, EDS, GXRD, XPS, TEM, and ED techniques. The MWCNTs were about 10 mu in length and 80-120 nm in diameter.

Effect of carbon deposits on the reactor wall during the growth of multi-walled carbon nanotube arrays

The effect of carbon deposits on the reactor wall during the growth of multi-walled carbon nanotube (MWCNT) arrays was studied. It was found that the carbon deposits were helpful in converting the continuous catalyst film into carbon-containing nanoparticles before growth started, which was beneficial for the nucleation of MWCNT arrays. As a result, MWCNT arrays synthesized in a reactor with carbon deposits were well aligned with high nucleation density. Further study revealed that this effect could be probably ascribed to some activated species adsorbed in the carbon deposits. These results will be helpful in the repeatable synthesis of high quality MWCNT arrays and in understanding the nucleation process of MWCNT arrays.

In situ growth rate measurements during plasma-enhanced chemical vapour deposition ofvertically aligned multiwall carbon nanotube films

In situ laser reflectivity measurements are used to monitor the growth ofmultiwalled carbon nanotube (MWCNT) films grown by DC plasma-enhancedchemical vapour deposition (PECVD) from an iron catalyst film depositedon a silicon wafer. In contrast to thermal CVD growth, there is no initialincrease in the growth rate; instead, the initial growth rate is high (as much as10 µm min−1) and then drops off rapidly to reach a steady level(2 µm min−1) for times beyond 1 min. We show that a limiting factor for growing thick films ofmultiwalled nanotubes (MWNTs) using PECVD can be the formation of an amorphouscarbon layer at the top of the growing nanotubes. In situ reflectivity measurementsprovide a convenient technique for detecting the onset of the growth of this layer.

Simple model of the interrelation between single- and multiwall carbon nanotube growth rates for the CVD process

Recent time-resolved measurements of carbon nanotube (CNT) growth on Fe and $\mathrm{Fe}∕\mathrm{Mo}$ catalysts have identified a maximum growth rate and temperature corresponding to the onset of small-diameter, single-wall CNT (SWNT) formation. A simple model described here emphasizes the essential role of the SWNTs in the growth process of CNTs. Remarkably, it shows that the growth rate (i.e., the time derivative of the length) of a multiwalled CNT is the same as that of a SWNT at the carbon flux and diffusion coefficient corresponding to a given temperature. Moreover, below $\ensuremath{\sim}700\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, the temperature above which SWNT growth is observed for a $6\phantom{\rule{0.3em}{0ex}}\mathrm{sccm}$ (cubic centimeter per minute at STP) ${\mathrm{C}}_{2}{\mathrm{H}}_{2}$ flow rate, the number of walls as a function of temperature is uniquely determined by the interplay of the incident flux of atomic C and diffusion rates consistent with bulk diffusion. Even partial melting of the catalytic particle is unnecessary to explain the experimental results on growth rate and number of walls. Above $700\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, where severe catalyst poisoning ordinarily begins, the growth rate without poisoning is consistent with recent results of Hata and co-workers [Science 306, 1362 (2004); Phys. Rev. Lett. 95, 056104 (2005)] for ``supergrowth.''

The use of camphor-grown carbon nanotube array as an efficient field emitter

Three-dimensional growth of well-aligned high-purity multiwall carbon nanotubes (CNTs) is achieved on silicon, nickel-coated silicon and cobalt-coated silicon substrates by thermal decomposition of a botanical carbon source, camphor, with different catalyst concentrations. Field emission study of as-grown nanotubes in a parallel-plate diode configuration suggests them to be an efficient emitter with a turn-on field of ∼1 V/μm (for 10 μA/cm 2) and a threshold field of ∼4 V/μm (for 10 mA/cm 2). Maximum current density lies in a range of 20–30 mA/cm 2 at 5.6 V/μm with significant reversibility. Prolonged stability test of camphor-grown CNT emitters suggests a life time of ∼5 months under continuous operation. A new feature, metal-assisted electron emission from CNTs, has been addressed. Isolated nanotubes used as a cold cathode in a field emission microscope reveal the pentagonal emission sites and hence the atomic structure of the nanotube tips.

Effects of gas composition on the growth of multi-walled carbon nanotube

This paper studies the effects of different gas compositions on the growth of multi-walled carbon nanotube (MWCNT) films by using an electron cyclotron resonance chemical vapor deposition (ECR-CVD) method. The Raman spectrum was employed to explore the composition of the MWCNT films grown under different mixtures of C 3H 8 and H 2. The results showed that the optimum relative intensity ratio of the D band to G band (i.e., I D/ I G) is 2 for the cases considered in this study. In addition, the morphology and microstructure of the MWCNTs were examined by field emission scanning electron microscopy (FE-SEM) and field emission gun transmission electron microscopy (FEG-TEM). Furthermore, atomic force microscopy (AFM) and scanning thermal microscopy (SThM) were used to study the surface topography and thermal properties of the MWCNTs.