Growth Behavior Of Carbon Nanotubes Research Articles

Solution Combustion Synthesis of Ni-Based Nanocatalyst Using Ethylenediaminetetraacetic Acid and Nickel-Carbon Nanotube Growth Behavior.

We studied the influence of the ethylenediaminetetraacetic acid (EDTA) content used as combustion fuel when fabricating nickel oxide (NiO) nanocatalysts via solution combustion synthesis, as well as the growth behavior of carbon nanotubes (CNTs) using this catalyst. Nickel nitrate hexahydrate (Ni(NO3)2∙6H2O) was used as the metal precursor (an oxidizer), and the catalysts were synthesized by adjusting the molar ratio of fuel (EDTA) to oxidizer in the range of 1:0.25 to 2.0. The results of the crystal structure analysis showed that as the EDTA content increased beyond the chemical stoichiometric balance with Ni(NO3)2∙6H2O (F/O = 0.25), the proportion of Ni metal within the catalyst particles decreased, and only single-phase NiO was observed. Among the synthesized catalysts, the smallest crystallite size was observed with a 1:1 ratio of Ni ions to EDTA. However, an increase in the amount of EDTA resulted in excessive fuel supply, leading to an increase in crystallite size. Microstructure analysis revealed porous NiO agglomerates due to the use of EDTA, and differences in particle growth based on the fuel ratio were observed. We analyzed the growth behavior of CNTs grown using NiO nanocatalysts through catalytic chemical vapor deposition (CCVD). As the F/O ratio increased, it was observed that the catalyst particles grew excessively beyond hundreds of nanometers, preventing further CNT growth and leading to a rapid termination of CNT growth. Raman spectroscopy was used to analyze the structural characteristics of CNTs, and it was found that the ID/IG ratio indicated the highest CNT crystallinity near an F/O ratio of 1:1.

Synthesis of nonstoichiometric NiO nanocatalysts and growth of bamboo‐like carbon nanotubes

AbstractThe growth behavior of carbon nanotubes from NiO nanoparticles was investigated in terms of vacancy concentration and nanostructure. The NiO nanoparticles were prepared using anhydrous ethanol as a solvent to lower hydroxyl groups, compared to distilled water. The Ni vacancies in NiO via less hydrolysis were confirmed by lattice expansion and the increased mean oxidation state of Ni3+ through X‐ray absorption spectroscopy. The increased Ni3+ ratio determined from the photoelectron spectrum and ferromagnetism implied a high concentration of Ni vacancies on the surface. Nonstoichiometric NiO exhibited a small particle size of 10.13 nm and a narrow size distribution. For the growth of CNTs, the NiO nanocatalysts with vacancies resulted in thinner CNTs. The internal structures of the CNTs obtained from the defective particles were grown into bamboo‐like CNTs, identifying the variation in the carbon diffusion path.

Effect of Reaction Temperature on Carbon Yield and Morphology of CNTs on Copper Loaded Nickel Nanoparticles

This investigation was attempted to introduce carbon nanotubes (CNTs) onto surface of copper powders in order to improve heat transfer performance of copper matrix for engineering application of electrical packaging materials. The Ni/MgO catalyst was formed on the copper powders surface by means of codeposition method. CVD technique was executed to fabricate uniform CNTs on copper powders and effect of reaction temperature on the morphology of CNTs was surveyed. The results showed that CNTs products on the copper powder surface were distributed uniformly even if reaction temperature was different. The diameter dimension of CNTs was within the scope of 30~60 nm. Growth behaviors of CNTs by CVD method were considered to be “tip-growth” mechanism. Raman spectra of CNTs proved that intensity ratio of D-band to G-band (ID/IG) increased as deposition reaction temperature increased, which implied that order degree of graphitic structure in synthesized CNTs improved.

Measuring the Electrical Conductivity of Carbon Nanotubes Grown on Sodalime Glass Substrates using Cu as Catalyst

We have studied the electrical resistance of carbon nanotubes (CNTs) grown on sodalime glass using Cu as catalyst at 580°C temperature. The conductivity was measured at room temperature using four point probe technique. The Cu catalyst was coated on glass substrate by using dc magnetron sputtering system and etched by hydrogen (H2) gas in order to form nanometer sized catalytic particles. Mixture of C2H2/H2/Ar (20:80:100 standard centimeter cubic per minutes) gases were heated at 580°C for growth of CNTs on a glass substrate by using Thermal Chemical Vapor Deposition (TCVD). The temperature dependence of sheet resistance and current-voltage characteristics of the film were measured by a four point probes method. The morphology of the catalyst surface was probed by Atomic Force Microscopy (AFM), and the growth behavior of CNTs was investigated by scanning electron microscopy (SEM).

Various temperature effects on the growth of carbon nanotubes (CNTs) by thermal chemical vapor deposition (TCVD) method

The growth behavior of carbon nanotubes synthesized from C2H2 at the temperature range of 700 to 900°C and using thermal chemical vapor deposition (TCVD) method has been investigated. Thin films of nickel (Ni) catalyst, were coated on SiO2 substrates by ion beam sputtering technique. The formation of catalytic nickel nanoparticles was much increased when using NH3 as the environment gas which implies both the formation and the separation of graphitic layer. Scanning electron microscopy (SEM) and Raman results show that the temperature of growth is the effective parameter on the formation of carbon nanotubes (CNTs). Key words: Carbon nanotubes, chemical vapor deposition, temperature.

Effect of Electron Beam Bombarding of the Catalyst Layer on the Growth of Carbon Nanostructures by TCVD Method

The growth behavior of carbon nanotubes (CNTs) grown on electron bombarded catalyst layer has been investigated in this paper. A hot cathodic electron beam facility was employed to electron bombarding of catalyst layer before stage of CNTs growth. The growth of carbon nanotubes was performed on the Fe catalyst layer with sio2 substrate in an environment of different mixed gases (H2, NH3 and C2H2) by Thermal Chemical Vapor Deposition (TCVD) system. The pretreated substrates were probed by Atomic Force Microscopy (AFM) and CNTs grown was confirmed by Raman spectroscopy. Moreover, all samples were analyzed by Scanning Electron Microscopy (SEM) before and after growth of CNTs. SEM analyzes clarified that the catalyst grains has been smaller under effect of electron beam bombardment.

Investigation on Growth Behavior of CNTs Synthesized by Atmospheric Pressure Plasma Enhanced Chemical Vapor Deposition System on Fe Catalyzed Substrate

We have studied growth behavior of carbon nanotubes (CNTs) on iron (Fe) catalyzed substrate using newly developed atmospheric pressure plasma enhanced chemical vapor deposition (AP-PECVD) system. To investigate the improved growth performance with simple equipment and process on large scale, a new AP-PECVD system containing different concept on downstream gas was designed and manufactured. As a catalyst, either sputtered or evaporated Fe thin film on SiO2/Si substrate was used and acetylene gas was used as a carbon source. We observed growth behavior of CNTs such as height, rate and density were strongly affected by plasma power. The maximum height of 427 microm and 267 microm was synthesized under RF plasma power of 30 W for 30 min and 40 W for 3 min, respectively. The growth rate dramatically increased to 6.27 times as plasma power increased from 30 to 40 W which opens the possibility the mass production of CNTs. By SEM and TEM observation, it was verified the grown CNTs was consists of mixture of single-wall and multi-wall CNTs. The graphitization ratio was measured to be 0.93, indicating that the graphitized CNTs forest was formed and relatively high purity of CNTs was synthesized, being useful for nano-composite materials to reinforce the strength. From our experiments, we can observe that the height and growth rate of CNTs is strong function of plasma power.

Effect of different metal deposition methods on the growth behaviors of carbon nanotubes

It is generally known that the catalyst particles promote tip or base growth of carbon nanotubes depending on the contact force between the catalyst particles and the substrate. We have investigated the correlation between the growth modes of vertically aligned carbon nanotubes (CNTs) and the adhesion of Ni catalyst particles to the Si substrates. It is shown that Ni films (10 nm thick) deposited by pulsed laser deposition (PLD) and electron beam evaporation are broken up into nanoparticles and/or islands when pretreated in NH3 gas ambient at 850 °C for 20 min. It is found that CNT growth on the PLD substrate proceeds by base growth mode, whereas CNT growth on the electron-beam evaporated substrate is operated by tip growth mode. The different CNT growth behaviors are explained in terms of the difference of the adhesion between the Ni catalyst particles and the substrate due to the different kinetic energy of depositing Ni particles.

Effect of Thickness Ration of Ni Layer to Ti Layer in Ni/Ti/Si Substrate on the Growth Behavior of Carbon Nanotubes

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Effect of Thickness of Ni Layer in Ni/TiO2/Ti/Si Substrate on the Growth behavior of Carbon Nanotubes

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Selective growth of carbon nantoubes on SiO 2/Si substrate

Three-step raising temperature process was employed to fabricate carbon nanotubes by pyrolysis of ferrocene/melamine mixtures on silica and single crystalline silicon wafers respectively. Then the morphologies, structures and compositions of obtained carbon nanotubes are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscope (EDX) and electron energy-loss spectroscopy (EELS). TEM and SEM observation shows that on silica substrate, high-oriented carbon nanotube can grow compactly to form continuous film on both frontal and cross-section surfaces, but on silicon substrate, only can form on cross-section surface. These carbon nanotubes have much irregular cup-like structure, and with outer diameter varying from 25 nm to 35 nm. At the top end of carbon nanotube there is a catalyst particle. EDX analysis reveals that the particle are iron cluster, and EELS spectrum indicates that the nanotube is composed of pure carbon. Finally, the effect of substrate surface roughness on the growth behavior of carbon nanotubes has been discussed.

Deposition of carbon nanotubes by capillary-type atmospheric pressure PECVD

In this study, the growth behavior of carbon nanotubes(CNT) deposited from C 2H 2 by an atmospheric pressure plasma enhanced chemical vapor deposition (AP-PECVD) method was investigated. The deposition was performed at 400 °C using a modified dielectric barrier discharge using He/C 2H 2 with additive gases such as N 2 and NH 3. The effect of the pretreatment on the surface morphology of the Ni catalyst was also investigated. Treatment of the Ni catalyst surface with a He (6 slm)/NH 3 (90 sccm) atmospheric pressure plasma for 5 min at 400 °C transformed the Ni surface into more uniformly agglomerated small Ni particles required for the enhanced carbon diffusion during the CNT formation. The CNTs grown by using He (6 slm)/C 2H 2 (90 sccm) AP-PECVD with additive gases (NH 3, N 2) for 5 min at 400 °C after the pretreatment showed uniform 1.5–2 μm long and 20–50 nm diameter multi-layer CNTs. By the application of − 1.2 kV of dc bias to the substrate during the growth CNTs by the AP-PECVD, more vertical CNTs could be obtained. FT-Raman data showed the grown CNTs are muti-wall CNTs and have the intensity ratio of D-band/G-band was 0.8–0.9, so defects were involved in the grown CNTs. This study provides a new method growing CNTs at atmospheric pressure and at low temperature, which has special advantages for large scale applications using conventional glass substrates.

Carbon nanotubes synthesized by CVD method on Au/Ni films and the field emission properties

Carbon nanotubes (CNTs) are prepared on Au/Ni films covered by a mask by the hot filament chemical vapor deposition (HFCVD) method using CH 4 and H 2 as reaction gases, the various thickness ratios of Ni and Au layers in Au/Ni films are deposited on Si (001) substrates by the magnetic sputtering method. The growth behaviors of CNTs on Au/Ni films are investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate that the multi-wall CNTs are formed, and the thickness ratio of Au and Ni layers is responsible to the diameter and electrical properties of synthesized CNTs. Furthermore, the electron field emission from the CNTs present the properties of low threshold voltage and high emission current density compared with those of the CNTs synthesized on pure Ni films, which can be attributed to the formation of nano-sized Au–Ni alloy particles at a suitable thickness ratio of Au and Ni layers in Au/Ni film and rich-hydrogen growth condition, which play an important roles in modifying the growth and electrical properties of CNTs.

Effects of the Applied Bias Voltage on the Formation of Vertically Well-Aligned Carbon Nanotubes

Carbon nanotubes were formed on silicon substrate using microwave plasma-enhanced chemical vapor deposition method. The possibility of carbon nanotubes formation was related to the thickness of nickel catalyst. The growth behavior of carbon nanotubes under the identical thickness of nickel catalyst was strongly dependent on the magnitude of the applied bias voltage. High negative bias voltage (-400 V) gave the vertically well-aligned carbon nanotubes. The vertically well-aligned carbon nanotubes have the multi-walled structure with nickel catalyst at the end position of the nanotubes.

Growth behavior of carbon nanotubes on multilayered metal catalyst film in chemical vapor deposition

The temperature and time dependences of carbon nanotube (CNT) growth by chemical vapor deposition are studied using a multilayered Al/Fe/Mo catalyst on silicon substrates. Within the 600–1100 °C temperature range of these studies, narrower temperature ranges were determined for the growth of distinct types of aligned multi-walled CNTs and single-walled CNTs by using high-resolution transmission electron microscopy and Raman spectroscopy. At 900 °C, in contrast to earlier work, double-walled CNTs are found more abundant than single-walled CNTs. Defects also are found to accumulate faster than the ordered graphitic structure if the growth of CNTs is extended to long durations.

Effect of NH 3 and thickness of catalyst on growth of carbon nanotubes using thermal chemical vapor deposition

The growth behavior of carbon nanotubes synthesized from C 2H 2 using thermal chemical vapor deposition method has been investigated. The formation of catalytic cobalt nanoparticles was much enhanced when using NH 3 as the environment gas, whereas NH 3 introduced during nanotubes growth does not play a key role in growing the vertically aligned nanotubes. The role of NH 3 is to obtain the high density of nucleation sites for nanotube growth by inhibiting amorphous carbon generation in the initial stage of synthesis. We found unexpected behavior in terms of the length and growth time during nanotube growth. The length of the nanotubes is inversely proportional to the size of nanoparticle just in the initial stages of growth and thick catalyst.

Effect of catalyst on growth behavior of carbon nanotubes synthesized by microwave heating thermal chemical vapor deposition process

Influence of morphology of Fe-catalyst on the microstructure and electron field emission properties of carbon nanotubes were systematically investigated. H2-plasma treatment imposed a most significant effect on the morphology of Fe clusters. The 1200 W H2-plasma treated Fe catalysts are nanosized (40–80 nm), isolated, and uniformly distributed, which result in carbon nanotubes of highest purity and most density population, exhibiting the largest electron field emission capacity (Je=3600 μA/cm2 at 6 V/μm applied field). Too low (1000 W) or too high (1400 W) H2-plasma treated Fe catalysts are interconnected or coarsened particulates, which result in large proportion of carbon soots, in addition to the carbon nanotubes. The electron field emission capacity of the films is thus markedly decreased. The prebaking process before H2-plasma treatment also imposes a marked effect on those characteristics. These results imply that spin coating of Fe(OR)3 is a simple and inexpensive method for producing catalyst of good quality, provided that the Fe(OR)3 was well pretreated.

Formation of carbon nanotubes by plasma enhanced chemical vapor deposition: Role of nitrogen and catalyst layer thickness

The growth behavior of carbon nanotubes (CNTs), produced by radio frequency plasma enhanced chemical vapor deposition, is studied here as a function of the CH4/N2 ratio and Ni catalyst layer thickness. Scanning electron microscopy shows that by employing a suitable deposition (methane) to etching (nitrogen) gas ratio, it is possible to obtain the growth of nanotubes with a limited presence of amorphous carbon on the substrate surface. In particular a progressive transition from random to aligned CNTs is observed when nitrogen is added to the plasma atmosphere. The electronic structure was then investigated by C 1s and valence band photoemission spectroscopy. The results show a shift of the overall spectral to a higher-binding-energy side and a larger density of the states at the Fermi level indicating the formation of metallic aligned tubes with increasing nitrogen fraction in the plasma atmosphere. The electronic structure indicates the insertion of odd-member rings in the graphene network leading to an improvement of the mechanical properties. The thickness of the Ni layer has a strong influence on the CNTs growth showing maximum value for nanotube formation at 20 nm.

Electron field emission properties of carbon nanotubes grown on tungsten wire

Carbon nanotubes have been successfully grown on the tip of wires by using a novel technique, which heated up the tip of wire locally via the absorption of microwaves. Effect of processing parameters such as microwave power, gas species and catalyst on the growth behavior of carbon nanotubes on the tip of wire was examined. The bare Fe-needles, which possess essentially no electron field emission capacity, were converted into good emitters, which exhibited large electron field emission current density ( J e=45 mA/cm 2), due to the formation of carbon nanotubes on their tip.

Growth behavior of carbon nanotubes on Fe-deposited (001) Si substrates

Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) are used to investigate the growth behavior of carbon nanotubes on the Fe-deposited Si (001) substrates by thermal chemical vapor deposition (CVD). The Fe films are deposited for 20 s–20 min by pulse-laser deposition. SEM results show that the growth characteristics of carbon nanotubes strongly depend on the Fe film deposition time. TEM results show that the CVD growth at 800 °C causes the continuous Fe films to be broken up into nanoparticles 10–50 nm across and discontinuous islands 100 nm–1.1 μm in size. It is shown that the Fe nanoparticles are essentially required for the formation of aligned carbon nanotubes. We show direct evidence that a base growth mode is responsible for the growth of carbon nanotubes in the present work.