Low Temperature Growth Of Carbon Nanotubes Research Articles

Effect of HF wet-etching and H2-plasma polishing on the low-temperature growth of carbon nanotubes on stainless-steel substrates

Direct growth of carbon nanotubes (CNTs) on 316 stainless-steel (SS) substrates could facilitate versatile commercial applications. For the successful synthesis of CNTs on SS substrate, hydrofluoric acid (HF) etching renders suitable surface roughness to promote CNT growth. For catalyst preparation and also subsequent CNT growth, H2-plasma treatment plays essential roles. Reversing the aging effect of Fe/Ni from its unwanted oxides of reduced catalytic activity and formation of Fe nanoparticles from the sheet are accomplished using H2-plasma. High-density plasma, along with specific gas precursors with its energetic ions, required for uniform CNT growth is attained by microwave plasma-enhanced chemical vapor deposition. By using CO2, providing suitable oxidizer precursors, in (CH4 + H2) diffuse plasma, necessary ambience for low-temperature nucleation (300 °C) and high-yield CNT growth is obtained. Reduction in the deposition rate by highly-energetic ion collisions in high-power plasma is resolved by introducing remote plasma configuration using a specially designed mask assembly. Considering the optimum magnitudes of the intensity ratios of D- and 2D-peaks to the G-peak in the Raman spectra of CNTs, a time span of 2 h of HF-etching appears optimum for proper functioning of the Fe/Ni nanoparticle catalyst. Furthermore, H2-plasma polishing is effectively utilized as the last step of pretreatment, leading to the growth of lower-diameter CNTs. Finally, using a shadow mask assembly and weak oxidizing gas, low-temperature growth of CNTs is successfully accomplished on SS substrates, pretreated by optimum HF-etching and H2-plasma polishing on the Fe-nanoparticle catalyst layer, avoiding the conventional steps of high-temperature annealing for catalyst nanoparticle formation as well as high-temperature nucleation for CNT growth. Even without the use of a separate Fe-catalyst layer, CNT growth is accomplished directly on HF-etched and H2-plasma polished SS substrates, utilizing mostly Fe/Ni nano-grains that originate from the intrinsic composition of SS as the nucleation sites. Use of limited action-steps and of a low-temperature (~300 °C) distinguish this as a realistic avenue for commercial production of CNTs.

Electrical conductivity and mechanical property improvement by low-temperature carbon nanotube growth on carbon fiber fabric with nanofiller incorporation

Carbon fiber reinforced polymer composites offer many advantages due to their great combination of high strength and modulus combined with low density and light-weight; however, they typically feature low electrical conductivity. These advanced composites are often unsatisfactory compared to conventional conductive metals that are vulnerable to lightning strike damage. To develop a new generation of highly conductive carbon fiber composites that address these shortcomings, carbon nanotubes (CNTs) were grown on nickel-coated carbon fiber using low-temperature growth to create a fuzzy fiber surface. An additional conductive filler, graphene nanoplatelets (GNPs), was then dispersed on the fuzzy fiber surface to form synergistic physical interactions between two different low-dimensional carbon-based nanostructures. The results reveal a synergistic enhancement in both functional conductivity and mechanical properties. The electrical conductivity of composites with the inclusion of GNPs resulted in approximately 40%, 300%, and 190% enhancement in the fiber, surface, and through-thickness direction compared to the fuzzy fiber composites. Mechanical properties, including flexural, work of fracture, impact, and interlaminar shear stress properties were further enhanced. These results reveal that the presence of GNPs creates more electron transfer pathways, and also promotes a synergistic effect in physical interactions. Altogether, these enhancements provide avenues for future high-performance conductive carbon fiber composites in aircraft structures.

Low-temperature synthesis of carbon nanotubes on iron nanopowders

This work presents the results of experiments on synthesis of carbon nanostructures by the method of thermal chemical vapor deposition (CVD) using iron nanopowders obtained by the method of electrical explosion of wires as catalysts. The process parameters that are optimal for low-temperature growth of carbon nanotubes (CNTs) have been identified during performed experiments. Results of Raman spectroscopy and x-ray analysis showed that samples grown at temperatures below the normally used have the highest crystallinity. Studies by scanning electron microscopy using SE2 mode and results of transmission electron microscopy indicate that the synthesized structures are multi-walled CNTs with the metal clusters inside the channel of the tube. The experimental modes of synthesis of CNTs by low-temperature CVD using iron nanopowders as catalyst have been found for the first time.

Pulsed PECVD for Low‐temperature Growth of Vertically Aligned Carbon Nanotubes

Pulsed plasma‐enhanced (PE)CVD is used for the growth of vertically aligned multiwall carbon nanotubes (CNTs) at a low temperature range of 350–490 °C. A pulsed plasma is generated by the application of a rectangular negative pulse to the substrate electrode with an on time of 4.5 μs, off time of 5.5 μs, duty cycle of 45%, and pulse repetition frequency of 100 kHz. CNTs are synthesized from Ni catalyst film of 20–40 nm thickness deposited on a silicon substrate under pressures of 0.01 and 0.5 Torr by magnetron sputtering. The effect of Ni catalyst film morphology on low temperature growth of CNTs by pulsed PECVD is studied. It is found that CNTs grown from Ni catalyst films depend on the process pressure employed to prepare the film by magnetron sputtering. A comparison with the direct current (DC) discharge‐produced CNTs reveals that the growth rate of pulsed plasma‐produced CNTs is two times higher. CH species density is studied using optical emission spectroscopy (OES) by an actinometrical approach, which shows that DC discharge plasma has a higher CH concentration, but still has a lower growth rate. Further, it is observed that using pulsed plasma, growth of CNTs is possible at temperatures down to 350 °C, whereas in the case of DC discharge plasma, CNTs growth is possible only at temperatures down to 450 °C in the present experimental set‐up. Possible reasons for the better performance of pulsed plasma in respect of growth rate and low temperature growth are discussed.

Low temperature growth of carbon nanotubes on carbon fibre to create a highly networked fuzzy fibre reinforced composite with superior electrical conductivity

We report a method for the growth of carbon nanotubes on carbon fibre using a low temperature growth technique which is infused using a standard industrial process, to create a fuzzy fibre composite with enhanced electrical characteristics. Conductivity tests reveal improvements of 510% in the out-of-plane and 330% in the in-plane direction for the nanocomposite compared to the reference composite. Further analysis of current–voltage (I–V) curves confirm a transformation in the electron transport mechanism from charge – hopping in the conventional material, to an Ohmic diffusive mechanism for the carbon nanotube modified composite. Single fibre tensile tests reveal a tensile performance decrease of only 9.7% after subjecting it to our low temperature carbon nanotube growth process, which is significantly smaller than previous reports. Our low-temperature growth process uses substrate water-cooling to maintain the bulk of the fibre material at lower temperatures, whilst the catalyst on the surface of the carbon fibre is at optimally higher temperatures required for carbon nanotube growth. The process is large-area production compatible with bulk-manufacturing of carbon fibre polymer composites.

Plasma enhanced growth of single walled carbon nanotubes at low temperature: A reactive molecular dynamics simulation

Low-temperature growth of carbon nanotubes (CNTs) has been claimed to provide a route towards chiral-selective growth, enabling a host of applications. In this contribution, we employ reactive molecular dynamics simulations to demonstrate how plasma-based deposition allows such low-temperature growth. We first show how ion bombardment during the growth affects the carbon dissolution and precipitation process. We then continue to demonstrate how a narrow ion energy window allows CNT growth at 500K. Finally, we also show how CNTs in contrast cannot be grown in thermal CVD at this low temperature, but only at high temperature, in agreement with experimental data.

Low-Temperature Growth of Carbon Nanotubes on Bi- and Tri-metallic Catalyst Templates

Low temperature growth process of carbon nanotubes (CNTs) over bi-metallic (Co–Fe) and tri-metallic (Ni–Co–Fe) catalysts on Si/Al/Al2O3 substrates is carried out from acetylene precursor using hydrogen, ammonia or nitrogen as a carrier in a low pressure chemical vapor deposition system. Using the tri-metallic Ni–Co–Fe catalyst template, vertically aligned CNTs of ~700 nm length could be grown already at 450 °C within 10 min using ammonia as a carrier. Within the same period of time, on bi-metallic Co–Fe catalyst templates, ~250 nm long aligned nanotubes emerged already at 400 °C in nitrogen carrier. At low temperatures most of the catalyst materials were elevated from the support by the grown nanotubes indicating tip growth mechanism. The structure of catalyst layers and nanotube films was studied using scanning and transmission electron microscopy and atomic force microscopy.

Remote and direct plasma regions for low-temperature growth of carbon nanotubes on glass substrates for display applications

A novel method for growing carbon nanotubes (CNTs) on glass substrates is introduced in this study. A two-stage plasma was used to achieve low-temperature and vertically aligned CNTs. Ni deposited on indium tin oxide/glass substrate was used as the catalyst and hydrogen and acetylene were used as gas feeds. In this investigation a new technique was developed to grow vertically aligned CNTs at temperatures below 400 °C while CNT growth by plasma-enhanced chemical vapour deposition required high temperatures. Low-temperature growth of vertically aligned CNTs was suitable for the fabrication of micro-lens and self-oriented displays on glass substrates. Also, we have reported a new configuration for CNT-based display by means of controlling the refractive index of liquid crystal around the CNT by applying a proper voltage to the top and bottom array.

Growth of carbon nanotubes at temperatures compatible with integrated circuit technologies

The potential applications of carbon nanotubes grown for semiconductor and sensor devices are immense. But, this growth must be CMOS compatible and over large-areas, in excess of 4 inches in diameter, for any industrial interest. Reports of low-temperature growth of carbon nanotubes have mostly resulted in false dawns in the context of CMOS production, with direct integration for mass manufacturing remaining a challenge, as lower synthesis temperatures matched to manufacturing result in nanotubes with high defect levels. We report a unique ‘top-down’ synthesis method that allows energy delivery directly to the catalyst, resulting in higher quality nanotube growth at compatible low substrate temperatures. This growth is demonstrated over a large-area, whilst maintaining the silicon substrate below 350 °C. Long-range ordering of carbon nanotubes is supported by well developed second-order Raman peaks and HREM. The methodology developed is suitable to produce many nano-material systems, including graphene and silicon nanowires.

High emission current density, vertically aligned carbon nanotube mesh, field emitter array

A vertically aligned carbon nanotube mesh emitter array has been fabricated and tested, giving a current density of up to 1.5 A/cm2, and a threshold field of 1.5 V/μm for a current density 1 mA/cm2. Low temperature carbon nanotube growth is used to fabricate the carbon nanotube mesh emitter arrays significantly reducing the cost of the fabrication of large area electron emitters. This system exhibits ultralong lifetime.

Synergistic Effects in Bimetallic Nanoparticles for Low Temperature Carbon Nanotube Growth

Carbon nanotubes (CNTs) have been extensively studied in recent years for potential applications spanning from electronics to nanocomposites. Current synthesis approaches rely on transition metal catalysts to provide structural control, which has led to considerable efforts to understand and improve catalytic activity. While the most commonly used catalysts for CNT growth are Ni and Fe, experiments with metal alloys such as NiFe, NiCo, CoMo, and FeMo have been empirically observed to produce higher growth rates and lower growth temperatures. Recent molecular simulation results suggest that the unique catalytic properties of bimetallic nanoparticles may be a result of the role different metals play during critical steps in CNT growth. Therefore, dimensional and compositional tuning of catalyst nanoparticles is critical to precise control of CNT growth. The majority of efforts to study catalytic efficacy have been hampered by large variations in particle size and composition. Catalyst nanoparticles are often prepared in solution-phase routes where stabilizing molecules or oxidation on the particle surface are a source of contamination during CNT growth. Here, we report on a clean, gas-phase approach to synthesize tunable compositions of bimetallic nanoparticles at constant particle size. A continuous-flow, atmospheric pressure microplasma reactor is used to decompose organometallic precursors and prepare narrow dispersions of bimetallic nanoparticles in a single step. CNT growth is achieved by mixing the particle-laden flow exiting the microplasma reactor with acetylene and hydrogen gas and heating in a tubular flow furnace. To relate the catalytic properties of bimetallic nanoparticles to CNT growth, the flow system is integrated with aerosol instrumentation to ‘‘watch’’ CNT nucleation and growth. Kinetic studies are performed to obtain activation energies as a function of particle composition. We demonstrate that nanotubes can be grown at temperatures as low as 300 8C using Ni0.67Fe0.33 catalysts, which is significantly lower than temperatures normally required for thermal chemical vapor deposition (CVD) growth. Metal nanoparticles of varying chemical composition were synthesized at atmospheric pressure using a continuous-flow

Low Temperature Synthesis of Carbon Nanotube on Si substrate Using Alcohol Gas Source in High Vacuum

ABSTRACTConventional alcohol catalytic chemical vapor deposition (ACCVD) growth of carbon nanotubes (CNTs) have been carried out under ambient gases from 103 to105 Pa. These ambient gas pressures have prevented in situ observations using an electron beam during CNT growth, such as scanning electron microscopy (SEM), scanning tunneling microscopy (STM). Therefore, in order to realize the in situ observations and to clarify the growth mechanism of nanotube, CNT growth in a high vacuum is essential. In addition, the effects of residual gases also may be avoided in the growth under high vacuum. In this study, we carried out CNT growth under high vacuum using an alcohol gas source in an ultrahigh vacuum (UHV) chamber and we achieved CNT growth below 400°C without any excitation processes of carbon source. After deposition of Co catalyst of 1 nm in thickness on SiO2/Si substrate, ethanol gas was supplied to the substrate surface through a stainless steel nozzle in the UHV chamber. The growth temperature was monitored by a pyrometer during the growth, and set between 350 and 900°C. The supply of ethanol gas was controlled by monitoring an ambient pressure, which was varied from 1 ∼10-1 to 1 ∼10-4 Pa. The grown CNTs were characterized by SEM and Raman spectroscopy. The G/Si intensity ratio reached its maximum at 700°C, when the pressure was 1 ∼10-1 Pa. The maximum point of the G/Si peak intensity shifted to a lower temperature as the growth pressure decreased. When the pressure was 1 ∼10-4 Pa, the G/Si intensity ratio reached its maximum at 400°C, at which clear RBM peaks were observed in the Raman spectrum. From the RBM peaks, the CNT diameters were estimated to be between 0.9 to 1.7 nm, and CNTs of 1.2-1.4 nm in diameter were dominant at 1 ∼10-1 Pa, whereas thinner CNTs (diameter is below 1.0 nm) were increased with the reduction of the pressure. Our largest G/D ratio was about 40 for the sample grown at 1 ∼10-1 Pa, which is considerably larger than the reported value for the CNTs grown under low pressure. From these results, we conclude that the reduction of the growth pressure lowers the growth temperature. This technique can be applied to in situ observation, and may also be useful for low temperature growth of CNTs, which opens new possibilities for the fabrication of CNT based nanodevices.

Dendrimer-assisted low-temperature growth of carbon nanotubes by plasma-enhanced chemical vapor deposition

Using a shielded growth approach and N2-annealed, nearly monodispersed Fe2O3 nanoparticles synthesized by interdendritic stabilization of Fe3+ species within fourth-generation poly(amidoamine) dendrimers, carbon nanotubes and nanofibers were successfully grown at low substrate temperatures (200-400 degrees C) by microwave plasma-enhanced chemical vapor deposition.

A possible approach exploring the melting state of catalysts during the low-temperature growth of carbon nanotubes

A method to qualitatively examine the physical state of catalysts has been demonstrated by simultaneously supplying Ti species for carbon nanotube (CNT) growth. Under a TiCl 4/CH 4/H 2/N 2 plasma ambience, a continuous TiCN film was deposited on the Si substrate in the absence of catalysts; however, for the Ni-coated Si substrate, one-dimensional CNTs rather than TiC or TiCN nanofibers were grown through the catalytic vapor growth process, with the amorphous Ti-containing layers coated on their surfaces. The obtained coaxial CNT structure and the electron diffraction pattern analysis of catalysts support the factor that Ti atoms hardly dissolve into the catalyst and pass through it (or diffuse along the surface). Selective dissolution and diffusion between the Ti and C atoms in Ni nanoparticles suggest that catalysts during low-temperature growth of CNTs (580 °C) are not melted, instead they should be in solid state.

Hydrogen Radical Etching Effect on Carbon Nanotube Growth

ABSTRACTThe hydrogen microwave remote plasma CVD was introduced to fabricate carbon nanotubes(CNTs). C2H2 or CH4, used as source gas react with hydrogen radicals introduced from the cavity. In this experiment, hydrogen radical etching effect on the substrate surface could be controlled independently. We confirmed CNTs growth at 400°C under adequate hydrogen radical etching effect on the substrate surface. The result directly suggests that the etching effect of hydrogen radicals on the reaction surface contribute to the low temperature growth of CNTs. The CNT thickness did not depend on the hydrogen radical etching effect but the catalyst layer thickness.

Low-temperature growth of carbon nanotubes from the catalytic decomposition of carbon tetrachloride.

Multiwall carbon nanotubes (MWNTs) were synthesized via the decomposition of CCl4 in supercritical CO2 at 175 degrees C and 27.6 MPa using an iron-encapsulated dendrimer as a growth catalyst. The average diameter of resultant nanotubes was 20-25 nm, obtained after a 24-h reaction time. Our conditions represent the first application for CX4 precursors, as well as the lowest-reported temperature regime for carbon nanotube growth, allowing the use of other temperature-sensitive catalytic substrates.

Low-temperature growth of carbon nanotube by thermal chemical vapor deposition with FeZrN catalyst

Recently the direct growth of carbon nanotubes (CNT) on glass substrates by thermal chemical-vapor deposition at low temperatures has been researched for the fabrication of field-emission displays. We have achieved synthesis of CNT on soda lime glass with a catalyst: FeZrN at low temperature (500–550 °C). The FeZrN film deposited by sputtering is amorphous. However, this film changes into a crystalloid to separate out Fe fine particles by thermal treatment. This characteristic has been successfully applied to make the precursor of CNT. There is a possibility that the density and diameter of CNT can be controlled by varying the composition ratio of FeZrN. The emission from CNT has also been obtained. The turn-on electric field has been ∼2.5–3 V/μm. We have fabricated a microtriode structure and the emission has been also recognized.

Low-temperature growth of carbon nanotubes by plasma-enhanced chemical vapor deposition

Vertically aligned carbon nanotubes were grown at temperatures as low as 120 °C by plasma-enhanced chemical vapor deposition. A systematic study of the temperature dependence of the growth rate and the structure of the as-grown nanotubes is presented using a C2H2/NH3 system and nickel as the catalyst. The activation energy for the growth rate was found to be 0.23 eV, much less than for thermal chemical vapor deposition (1.2–1.5 eV). This suggests growth occurs by surface diffusion of carbon on nickel. The result could allow direct growth of nanotubes onto low-temperature substrates like plastics, and facilitate the integration in sensitive nanoelectronic devices.

Low-Temperature Growth of Carbon Nanotube by Plasma-Enhanced Chemical Vapor Deposition using Nickel Catalyst

Carbon nanotubes (CNTs) were grown on silicon (Si) substrates with a native oxide layer using a nickel (Ni) catalyst by the plasma-enhanced chemical vapor deposition method at 550 and 650°C. Multiwall CNTs with a large inside hollow core were observed with samples deposited on Si substrates with a native oxide layer. However, no CNT growth was observed with samples deposited on Si substrates without a native oxide layer due to the formation of Ni-silicide. The native oxide layer was believed to act as the diffusion barrier and to suppress the formation of Ni-silicide. The typical diameter and length of CNTs ranged from about 30 to 100 nm and 2 to 3 µm, respectively. The size of CNTs was more strongly dependent on the thickness of the Ni layer than on the growth temperature. The surface roughness and amount of surface defects decreased with increasing process temperature. We performed a post hydrogen plasma treatment for the purification of raw CNTs. The post hydrogen plasma treatment successfully removed residual graphite particles and/or metallic impurities without significant damage to the CNTs.

Low-Temperature Synthesis Multiwalled Carbon Nanotubes by Microwave Plasma Chemical Vapor Deposition Using CH4–CO2 Gas Mixture

Vertically aligned carbon nanotubes (CNTs) with multiwalled structures were successfully grown on a Fe-deposited Si substrate at low temperatures below 300°C by microwave plasma chemical vapor deposition using of a CH4–CO2 gas mixture. The low temperature would be beneficial for reducing the diameter of CNTs but it will also decrease the growth rate on the substrate. The low-temperature growth of CNTs was achieved by decreasing both the microwave power and the total gas pressure. The constituents of the gas mixture are also key factors in chemical vapor deposition. After deposition, the microstructure morphology of CNTs was observed by using scanning electron microscope and high-resolution transmission microscope. The results showed that even at low temperature a high yield of carbon nanotubes with a high emission current density and a small diameter is obtained. Vertically aligned multiwalled CNTs with a diameter about 12 nm were investigated by scanning electron microscope (SEM) and high-resolution transmission electron microscope (HRTEM).