Temperature Growth Of Carbon Nanotubes Research Articles

Low temperature multi-catalytic growth and growth mechanism of carbon nanotubes on carbon fiber surfaces

In order to reduce the etching effect of the catalysts to carbon fibers caused by high temperature during the chemical vapor deposition (CVD) process, four multi-element catalysts, Fe–Co, Fe–Ni, Co–Ni and Fe–Co–Ni, were used to realize the low temperature growth of carbon nanotubes (CNTs) on carbon fibers at 350 °C–400 °C. The results show that the growth state of CNTs has a great relationship with the type of catalysts. The catalytic efficiency of Fe–Co catalysts is low, but the graphitization degree of CNTs is relatively high. The Fe–Co–Ni catalysts has high catalytic efficiency but low graphitization degree of CNTs. The tensile strength of carbon fiber/CNTs reinforcements prepared by Fe–Ni catalysts at 400 °C is the highest, reaching 3.99 GPa, which is 11.14% higher than that of desized fiber. The melt drop phenomenon of the catalysts was found by TEM, indicating the formation of the liquid phase catalysts during the growth of CNTs. This phenomenon can change the diffusion mode of carbon atoms in the catalyst and significantly reduce the growth activation energy of CNTs, so that CNTs can grow at lower temperatures. Based on the detailed analysis of the CVD process, a low temperature growth model of CNTs on carbon fibers was proposed.

The Advantages of Double Catalytic Layers for Carbon Nanotube Growth at Low Temperatures (<400 °C) in 3D Stacking and Power Applications

A double catalytic layer scheme is proposed and investigated for the low temperature growth of carbon nanotubes (CNTs) over Co (Cobalt), Al (Aluminum), and Ti (Titanium) catalysts on a silicon substrate. In this work, we demonstrate the growth of CNTs by a thermal chemical vapor deposition (TCVD) process at both 350 °C and 400 °C. Based on scanning electron microscopy (SEM) and Raman spectroscopy analyses, the good quality of the CNTs is demonstrated. This study contributes to the on-going research on integrating semiconductors into packaging and power-related applications, as demonstrated with the low resistance (~128 Ω) and high thermal conductivity (~29.8 Wm−1 K−1) of our developed CNTs.

Unique bubble-chain carbon nanotubes catalyzed by CoZn nanoparticles

Carbon nanomaterials with combined structures are highly desirable in both fundamental research and industrial applications. Herein, we report a unique carbon bubble-chain N-doped carbon nanotubes (CNTs) with features of both nanospheres and nanotubes prepared by a facile pyrolysis method. The in situ formed CoZn alloy which acts as a novel catalyst for the bubble-chain CNTs is found to be an intermetallic compound with a face-centered cubic structure. Compared with typical Fe, Co, and Ni catalysts, CoZn has larger unit cell parameters with larger tetrahedral and octahedral interstices, resulting in the fast C/N diffusion across the catalyst. In addition, CoZn catalyst is partially melted at the CNTs growth temperature. We demonstrate that the high N content, the fast C/N diffusion and the partially molten CoZn catalyst contribute to the growth of bubble-chain CNTs at moderate temperature. Bubble-chain nanotubes can be described as a unique carbon structure between carbon hollow nanospheres and nanotubes, which may have the advantages of both nanospheres and nanotubes. The formation mechanism of bubble-chain N-doped CNTs and the electrocatalytic properties towards oxygen reduction reaction were presented in this work.

Carbon nanotube-decorated glass fibre bundles for cure self-monitoring and load self-sensing of FRPs

Extra to serving as the reinforcement in polymer-based composites, glass fibres (GFs) are decorated with dense and uniform carbon nanotubes (CNTs) via chemical vapor deposition at a low CNT growth temperature (500 °C). The hairy CNT-decorated GF bundles measure the dynamic variation in electrical resistance using CNT-formed piezoresistive networks in the bundles, with which the resin flow front and cure progress of epoxy during fabrication are self-monitored by the composites. The bundles also precisely sense in-service loads applied to the composites, with a gauge factor as high as 30.2. Without intrusion to the original composites from sensors and sensor-associated electrodes/cables, the CNT-decorated GF bundles shed light on the use of nanocomposite-driven fibre decoration towards development of new functional composites.

Synthesis of Vertical Carbon Nanotube Interconnect Structures Using CMOS-Compatible Catalysts.

Synthesis of the vertically aligned carbon nanotubes (CNTs) using complementary metal-oxide-semiconductor (CMOS)-compatible methods is essential to integrate the CNT contact and interconnect to nanoscale devices and ultra-dense integrated nanoelectronics. However, the synthesis of high-density CNT array at low-temperature remains a challenging task. The advances in the low-temperature synthesis of high-density vertical CNT structures using CMOS-compatible methods are reviewed. Primarily, recent works on theoretical simulations and experimental characterizations of CNT growth emphasized the critical roles of catalyst design in reducing synthesis temperature and increasing CNT density. In particular, the approach of using multilayer catalyst film to generate the alloyed catalyst nanoparticle was found competent to improve the active catalyst nanoparticle formation and reduce the CNT growth temperature. With the multilayer catalyst, CNT arrays were directly grown on metals, oxides, and 2D materials. Moreover, the relations among the catalyst film thickness, CNT diameter, and wall number were surveyed, which provided potential strategies to control the tube density and the wall density of synthesized CNT array.

Catalytic Preparation of Carbon Nanotubes from Waste Polyethylene Using FeNi Bimetallic Nanocatalyst.

In this work, carbon nanotubes (CNTs) were synthesized by catalytic pyrolysis from waste polyethylene in Ar using an in-situ catalyst derived from ferric nitrate and nickel nitrate precursors. The influence factors (such as temperature, catalyst content and Fe/Ni molar ratio) on the formation of CNTs were investigated. The results showed that with the temperature increasing from 773 to 1073 K, the carbon yield gradually increased whereas the aspect (length-diameter) ratio of CNTs initially increased and then decreased. The optimal growth temperature of CNTs was 973 K. With increasing the Fe/Ni molar ratio in an FeNi bimetallic catalyst, the yield of CNTs gradually increased, whereas their aspect ratio first increased and then decreased. The optimal usage of the catalyst precursor (Fe/Ni molar ratio was 5:5) was 0.50 wt% with respect to the mass of polyethylene. In this case, the yield of CNTs reached as high as 20 wt%, and their diameter and length were respectively 20–30 nm, and a few tens of micrometers. The simple low-cost method developed in this work could be used to address the environmental concerns about plastic waste, and synthesize high value-added CNTs for a range of future applications.

One step synthesis and characterization of high aspect ratio network-like carbon nanotubes containing calcium aluminate cement composite powders

The poor water dispersion and oxidation resistance of carbon has restricted the widely industrial application of carbon containing castables. High aspect ratio network-like carbon nanotubes containing calcium aluminate cement composite powders were synthesized by carbon-bed sintering method using calcium acrylate and activated alumina as raw materials, and nickel nitrate as catalyst. Meanwhile the effects of catalyst content on the structure and morphology of carbon nanotubes were also studied. The synthesized products were characterized by X-ray diffraction, field-emission scanning electron microscopy, high-resolution transmission electron microscopy and Raman spectroscopy. The results indicated that the phase compositions of composite powders were similar to that of commercial Secar71. The length of carbon nanotubes was ca. 25 μm, and the diameter of carbon nanotubes was 55 nm. The aspect ratio of carbon nanotubes is ca. 450. The formation process and mechanism of carbon nanotubes was studied by thermogravimetric analysis coupled with Fourier transform infrared spectroscopy. The growth temperature of carbon nanotubes was 700 °C, and the growth of carbon nanotubes agrees with vapour–solid (V–S) model. In addition, the thickness of floating layer, floating ratio and oxidation ratios of the synthesized product were lower than those of the same carbon containing Secar71 cement (S71CB) composite powders, implying that the water dispersion and oxidation resistance of carbon nanotubes were improved because the high aspect ratio network-like carbon nanotubes were not easily separated from calcium aluminate cement and the carbon nanotubes were encased in calcium aluminate cement.

Growth and characterization of carbon nanotubes over CoFe2O4-MgO catalysts at different temperatures

A novel approach for synthesizing carbon nanotubes (CNTs) via chemical vapor deposition (CVD) technique has been elucidated. CNTs are catalytically grown on the CoFe2O4-MgO nano-catalyst at various growth temperatures (700 °C, 800 °C, 900 °C) to clarify the effect of temperature and to achieve the optimum CNT growth temperature. The structural properties of the catalyst and CNTs were studied with thermal analysis (TGA), X-ray diffraction (XRD), FTIR spectroscopy (IR), Raman spectroscopy, and High Resolution Transmission Electron Microscope (HRTEM). X-ray diffraction is used to study changes in the crystal structure of the CoFe2O4+MgO nano-catalyst. The obtained data ratifies the formation of MWCNTs over the nanocatalyst. The intensity of the main peak of CNTs decreases as well as the yield with increasing the growth temperature. The two main Raman modes, G band and the D band, can be identified in the spectra multi-walled carbon nanotubes .The lowest ID/IG ratio is obtained at the highest growth temperature. HRTEM images show that the growth temperature has a significant parameter on CNT quality. The average diameters of grown CNTs are 42, 32 and 16 nm for growth temperatures of 700 ̊C, 800 ̊C and 900 ̊C, respectively. The inner and outer diameters of MWCNTs become thinner and the quality of the tubes is enhanced with increasing the growth temperature. Additionally, it can be concluded from the temperature study that the balance between decomposition of acetylene gas and diffusion rate of manufactured carbon atoms in CoFe2O4-MgO catalyst nanoparticles occurs at the optimal growth temperature of 900 °C.

Chemical Vapor Deposition Synthesis of Carbon Nanotube Using Pyrolysis Gas Products of Apricot Kernel Shell

The results of a study of carbon nanotubes (CNTs) growth using apricot stone (AS) as a carbon source are presented. The described method here is two-zone thermal chemical vapor deposition (CVD) that uses cobalt acetate directly as deposition medium at different geometries under argon flow of 100 mL min–1. Argon gas was fed into the oven until pyrolysis of apricot kernel started. Since pyrolysis started, argon was passed through toluene immersed in hot water in the gas washing flask and sent to the furnace for CNT formation. This method allows the bulk metal acetate surface over a quartz road and in a quartz boat to act as catalyst for CNT growth. Our recent results obtained from the toluene assisted growth. The effect of growth temperature and purification of CNTs was studied. As-grown and purified CNTs were characterized by scanning electron microscopy (SEM), X-ray diffraction, differential thermal analysis and surface analysis. High yield of CNTs were obtained over quartz road at 900 °C and at the same temperature with 48 hours deposition time in quartz boat. The obtained CNTs were purified by refluxing using nitric acid.

Design and Fabrication of CMOS Microstructures to Locally Synthesize Carbon Nanotubes for Gas Sensing.

Carbon nanotubes (CNTs) can be grown locally on custom-designed CMOS microstructures to use them as a sensing material for manufacturing low-cost gas sensors, where CMOS readout circuits are directly integrated. Such a local CNT synthesis process using thermal chemical vapor deposition (CVD) requires temperatures near 900 °C, which is destructive for CMOS circuits. Therefore, it is necessary to ensure a high thermal gradient around the CNT growth structures to maintain CMOS-compatible temperature (below 300 °C) on the bulk part of the chip, where readout circuits are placed. This paper presents several promising designs of CNT growth microstructures and their thermomechanical analyses (by ANSYS Multiphysics software) to check the feasibility of local CNT synthesis in CMOS. Standard CMOS processes have several conductive interconnecting metal and polysilicon layers, both being suitable to serve as microheaters for local resistive heating to achieve the CNT growth temperature. Most of these microheaters need to be partially or fully suspended to produce the required thermal isolation for CMOS compatibility. Necessary CMOS post-processing steps to realize CNT growth structures are discussed. Layout designs of the microstructures, along with some of the microstructures fabricated in a standard AMS 350 nm CMOS process, are also presented in this paper.

Synthesis of a magnetic core–shell carbon nanotube@MgNi2FeO4.5 nanotube composite

In this paper, a magnetic core–shell composite with MgNi2FeO4.5 nanotubes as core and carbon nanotubes (CNTs) as shell was synthesized by in situ growth of CNTs on the surface of MgNi2FeO4.5 nanotubes via a catalytic chemical vapor deposition method. The MgNi2FeO4.5 nanotubes were prepared using a mixed aqueous solution of Mg(NO3)2, Ni(NO3)2 and Fe(NO3)3 (molar ratio of 1:2:1) and anodic aluminum oxide as template. Both the growth temperature and time of CNTs brought about effect on the structure and magnetic property of the composite were investigated. X-ray diffraction, transmission electron microscope, field emission scanning electron microscope, Raman spectroscopy and vibrating sample magnetometer were used to characterize the as-prepared samples. The MgNi2FeO4.5 nanotubes are parallel arranged, and the exterior surface of which is wrapped by CNTs when the growth temperature exceeding 480 °C. Magnetic measurement demonstrates the composite with higher growth temperature and shorter growth time possesses more excellent magnetic property.

Refractory-Metal Diffusion Inhibitors Slow Erosion of Catalytic Metal Particles in the growth of Carbon Nanotubes

ABSTRACTCatalytic growth of substantial amounts of Carbon Nanotubes (CNTs) to lengths greater than 1 – 2 cm is currently limited by several factors, including especially the deactivation of the catalyst particles due to erosion of catalyst atoms from the catalyst particles at elevated CNT growth temperatures. Inclusion of refractory metals in the CNT growth catalyst has recently been proposed as a method to prevent this catalytic particle erosion and deactivation, allowing the CNT to grow for greater times and reach substantially greater lengths. Here are presented results of recent investigations into this method. The system investigated employs Molybdenum as the erosion inhibitor and Iron as the CNT growth catalyst. Results show that inclusion of Mo leads to substantially longer catalyst particle lifetimes.

Low temperature growth of carbon nanotubes by microwave plasma stimulated by CO2 as weak oxidant and guided by shadow masking

Operating at a moderate MW power of 600 W and employing optimized Fe nanoparticles as catalyst, growth optimization of multi-wall CNTs at a relatively low substrate temperature has been performed using tubular microwave plasma enhanced-CVD system. Moderately high energy density plasma facilitates formation of essential precursors for CNT growth. Two intriguing techniques have been integrated in the growth process. Specific shadow masking arrangement by specially designed stainless steel multiple mask assembly protects the growth surface from etching by direct plasma bombardment. CO2 has been used as an auxiliary gaseous component added to the (CH4 + H2) plasma. Instrumental presence of CO2 as a weak oxidant in the plasma accomplishes the removal of a-C coverage from the Fe catalyst nanoparticles via etching by atomic O and thereby, re-triggers their catalytic reactivity and ensures the persistent growth of CNTs. Altogether, a perpetual growth of multiwall CNTs has been realized through tip-growth process at the lowest substrate temperature (300 °C) reported so far in PECVD.

Low temperature growth of carbon nanotubes using chemical bath deposited Ni(OH)2 – An efficient Pt-free counter electrodes for dye-sensitized solar cells

A simple and facile chemical bath deposition (CBD) process was employed to prepare Ni catalyst through Ni(OH)2 on fluorine-doped tin oxide (FTO) surface and CNTs were successfully grown on FTO substrate by low-temperature chemical vapor deposition (CVD) method. The formation and surface morphologies of as-fabricated Ni(OH)2/FTO and CNT/FTO substrates were analyzed by X-ray diffraction (XRD), Raman spectroscopy and field-emission scanning electron microscope (FE-SEM) analysis. The fabricated CNT/FTO substrate was directly applied for DSSC application as a counter electrode (CE) and the CE behavior of CNT/FTO was evaluated through the cyclic voltammetry (CV) measurements using I−/I3− redox couple. Electrochemical impedance spectroscopy (EIS) and Tafel studies were used to investigate the kinetics of electron transfer and Nernst diffusion process of CNT/FTO CE towards I−/I3− redox electrolyte. The photo conversion efficiency (PCE) of CNT/FTO (7.36%) CE based DSSC was found to be superior than that of Sputter-Pt (6.65%) and TD-Pt (6.72%) based DSSCs.

Gas phase infiltration of carbon nanotubes in Ni Nanofoam via liquid injection chemical vapor deposition

We demonstrate a new approach for improving the specific surface area of Ni nanofoam (NiNF) by exploiting its high void fraction for gas-phase infiltration of carbon nanotubes (CNTs) via liquid injection chemical vapor deposition (LICVD) process. To address the poor thermal stability of NiNF at CNT growth temperatures and low CNT nucleation density, a two-step pretreatment approach is implemented. First, a thin graphitic coating is deposited to stabilize NiNF via CH4 CVD at 550°C. Second, Fe catalyst is activated by depositing a thin layer of AlxOy (~2nm) on the graphite-coated NiNF. The infiltration of CNTs at 750°C increases the BET specific surface area of the resulting hybrid NiNF by a factor of over 20. A major appeal of this approach is that it can be utilized for tuning the structural properties of other nanostructures with relatively low temperature tolerance.

CMOS micro-heater design for direct integration of carbon nanotubes

Carbon nanotubes (CNTs) are nanomaterials that exhibit many remarkable electrical, mechanical and thermal properties, which can be exploited in various smart sensing applications by integrating them in standard CMOS processes. However, such integration technique is challenging since CMOS does not tolerate high temperatures required for local CNT synthesis. This work involves designing power efficient CMOS micro-heaters that can generate CNT growth temperature (~900°C) in a post-CMOS CNT fabrication step, while maintaining CMOS compatible temperature (<300°C) in the microsystem. One suitable metal interconnect layer and a polysilicon layer available in AMS 0.18μm CMOS technology have been used to design and simulate the micro-heaters. This paper proposes and compares six different optimal micro-heater designs alongside their thermal and thermomechanical analysis using multiphysics simulation software, ANSYS. Feasibility of implementing the designed micro-heaters in a real chip is discussed based on the analysis. Required CMOS post processing steps for the designed micro-heaters are also discussed. The promising results are expected to lead the way for successful implementation of carbon nanotube based sensors in a commercial CMOS process.

Fabrication of Low Temperature Carbon Nanotube Vertical Interconnects Compatible with Semiconductor Technology

We demonstrate a method for the low temperature growth (350 °C) of vertically-aligned carbon nanotubes (CNT) bundles on electrically conductive thin-films. Due to the low growth temperature, the process allows integration with modern low-κ dielectrics and some flexible substrates. The process is compatible with standard semiconductor fabrication, and a method for the fabrication of electrical 4-point probe test structures for vertical interconnect test structures is presented. Using scanning electron microscopy the morphology of the CNT bundles is investigated, which demonstrates vertical alignment of the CNT and can be used to tune the CNT growth time. With Raman spectroscopy the crystallinity of the CNT is investigated. It was found that the CNT have many defects, due to the low growth temperature. The electrical current-voltage measurements of the test vertical interconnects displays a linear response, indicating good ohmic contact was achieved between the CNT bundle and the top and bottom metal electrodes. The obtained resistivities of the CNT bundle are among the average values in the literature, while a record-low CNT growth temperature was used.

Fabrication of Low Temperature Carbon Nanotube Vertical Interconnects Compatible with Semiconductor Technology.

We demonstrate a method for the low temperature growth (350 °C) of vertically-aligned carbon nanotubes (CNT) bundles on electrically conductive thin-films. Due to the low growth temperature, the process allows integration with modern low-κ dielectrics and some flexible substrates. The process is compatible with standard semiconductor fabrication, and a method for the fabrication of electrical 4-point probe test structures for vertical interconnect test structures is presented. Using scanning electron microscopy the morphology of the CNT bundles is investigated, which demonstrates vertical alignment of the CNT and can be used to tune the CNT growth time. With Raman spectroscopy the crystallinity of the CNT is investigated. It was found that the CNT have many defects, due to the low growth temperature. The electrical current-voltage measurements of the test vertical interconnects displays a linear response, indicating good ohmic contact was achieved between the CNT bundle and the top and bottom metal electrodes. The obtained resistivities of the CNT bundle are among the average values in the literature, while a record-low CNT growth temperature was used.

Fabrication and electrical performance of through silicon via interconnects filled with a copper/carbon nanotube composite

In this work, through silicon vias (TSVs) were fabricated using a materials system consisting of a composite of copper (Cu) and vertically grown carbon nanotubes (CNTs) as a possible solution to the problems encountered when using Cu-based interconnects. A metallic seed layer, tungsten, was deposited prior to CNT growth. Tungsten replaces Cu as a seed layer due to the thermal sensitivity of Cu at CNT growth temperatures. CNTs were grown both on the wafer surface and inside the silicon vias by chemical vapor deposition. A self-directed densification process was applied to modify the shape of the CNTs from a forest with equal top and bottom dimensions into bundles with a significantly smaller dimension at the top compared to the bottom. This process maximizes the contact area between the Cu electroplating solution and the CNTs. Cu was deposited by periodic pulse electroplating after CNT growth to form the Cu/CNT composite. Wafer thinning and polishing completed the TSV fabrication forming a test configuration to evaluate electrical performance. Experimental results were compared for interconnects filled with pure Cu to those filled with the Cu/CNT composite. The results indicate potential application of the Cu/CNT composite as a TSV interconnect material.

Direct growth of carbon nanotubes on carbon fibers: Effect of the CVD parameters on the degradation of mechanical properties of carbon fibers

Grafting carbon nanotubes (CNTs) directly on carbon fibers represents a promising approach in order to strengthen the weak interface between carbon fibers and polymer matrix in carbon fiber reinforced polymer composites (CFRCs). We have carried out direct growth of CNTs on carbon fibers by using two different catalytic chemical vapor deposition (CVD) processes, namely the conventional CVD process based on catalytic thermal decomposition of ethylene and the oxidative dehydrogenation reaction between acetylene and carbon dioxide. The effect of various CVD growth parameters, such as temperature, catalyst composition and process gas mixture, was for the first time systematically studied for both processes and correlated with the mechanical properties of carbon fibers derived from single-fiber tensile tests. The growth temperature was found to be the most critical parameter in the presence of catalyst particles and reactive gasses for both processes. The oxidative dehydrogenation reaction enabled decreasing CNT growth temperature as low as 500°C and succeeded to grow CNTs without degradation of carbon fiber's mechanical properties. The Weibull modulus even increased indicating partial healing of present defects during the CVD process. The new insights gained in this study open a way towards simple, highly reproducible and up-scalable process of grafting CNTs on carbon fibers without inducing any damages during the CVD process. This represents an important step towards CNT-reinforced CFRCs with higher damage resistance.