Temperature Growth Of Carbon Nanotubes Research Articles

촉매 화학기상증착 공정에서 온도구배 설정을 통한 타이타늄 기판에서의 CNT 성장 거동

In this study, modified catalytic chemical vapor deposition (CCVD) method was applied to control the CNTs (carbon nanotubes) growth. Since titanium (Ti) substrate and iron (Fe) catalysts react one another and form a new phase (<TEX>$Fe_2TiO_5$</TEX>) above <TEX>$700^{\circ}C$</TEX>, the decrease of CNT yield above <TEX>$800^{\circ}C$</TEX> where methane gas decomposes is inevitable under common CCVD method. Therefore, we synthesized CNTs on the Ti substrate by dividing the tube furnace into two sections (left and right) and heating them to different temperatures each. The reactant gas flew through from the end of the right tube furnace while the Ti substrate was placed in the center of the left tube furnace. When the CNT growth temperature was set <TEX>$700/950^{\circ}C$</TEX> (left/right), CNTs with high yield were observed. Also, by examining the micro-structure of CNTs of <TEX>$700/950^{\circ}C$</TEX>, it was confirmed that CNTs show the bamboo-like structure.

Low temperature growth of carbon nanotubes on tetrahedral amorphous carbon using Fe–Cu catalyst

We report the growth of carbon nanotubes on tetrahedral-amorphous carbon using a Fe–Cu catalyst system at temperatures <500°C. By X-ray photoemission spectroscopy, we show that Cu forms an alloy with Fe during the process of catalyst pretreatment. This not only dramatically enhances the catalytic activity of Fe towards the nucleation of nanotubes at low temperatures, but simultaneously reduces its propensity to diffuse into the bulk of carbon-based substrates, thus minimising support damage. Such results prove the feasibility of growing nanotubes directly on carbon fibres, highlighting their potential for use in composites and fuel cell electrodes.

Photomask-based integration process of low-defect suspended carbon nanotubes into SOI MEMS

A fully-developed photomask-based integration process is reported. The process can integrate suspended carbon nanotubes (CNTs) into micro-structures on silicon-on-insulator chips. The process features batch-compatible fabrication and post-growth metallization of suspended CNTs, which has never been demonstrated by any other processes. The post-growth metallization avoids deterioration of the metals at the elevated CNT growth temperature and enables mechanically robust double-clamped configuration. Two key steps ensure a significant reduction of the risk for damage or contamination of the CNTs during post-growth processing. SiO2 bridges were fabricated to physically support CNTs during the wet processing, and a protective Al2O3 layer (∼40 nm) was deposited to prevent resist contamination during lithography. The combination of these two steps enables the removal of the unprotected suspended segments of unwanted CNTs by oxygen plasma ashing, improving device yield by a factor of six. The electrically interfaced suspended CNT device possessed high CNT quality (D/G+ intensity ratio of 1/224 in Raman spectroscopy) and good electrical properties, such as low device resistances as low as 105 kΩ and reduced gate hysteresis as low as 65 mV in ambient air. Measurements of eights devices indicate that the release step did not have a systematic influence on the device resistances.

Vertically Aligned Carbon Nanotubes Transfer with Glass Frit

Nanogetters, based on carbon nanotubes (CNTs) coated Ti films, do have higher pumping speed and possibly larger sorbed quantity compared with traditional getters, such as St175 of SAES [1]. Although the nanogetter is with the outstanding performance, it is still hard to be integrated into micro electro mechanical systems (MEMS) packaging and devices due to high growth temperature of CNTs (&gt;700°C) [2], poor adhesion with substrate [3, 4], vulnerability to pollute the wafers and difficulty to pattern. Therefore, this paper proposes a promotion of nanogetter based on transferring out vertically aligned CNTs (VA-CNTs) utilizing the glass frit. Compared with the conventional nanogetters, the promotion processes have advantages of (1) compatibility to the MEMS materials with controllable melting temperature and coefficient of thermal expansion (CTE), (2) Enhancement of the adhesion between CNTs and substrate, (3) Avoiding polluting the package wafer during CNTs growth. The results indicate that the promotion processes can be fulfilled by the silicon wafers and have wide applications such as nanogetters, field emission display, etc.

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.

Preparation and growth mechanism of carbon nanotubes via catalytic pyrolysis of phenol resin

Using nickel nitrate as catalyst precursor, a cost effective method for large scale preparation of carbon nanotubes (CNTs) was investigated through catalytic pyrolysis of phenol resin in the temperature range of 600–1200°C under an Ar atmosphere. The morphology and structure of pyrolysed resin were characterised by X-ray diffraction, scanning electron microscope, transmission electron microscope and energy dispersive X-ray spectroscopy. The results show that the morphology and structure of CNTs depend on pyrolysis temperature, and the starting growth temperature of CNTs is ∼600°C. When the pyrolysis temperature is raised, the length and crystallinity of CNTs increase remarkably. High aspect ratio and well crystallised CNTs with average diameter of about 50–60 nm and micrometer scale length could be obtained at 1000°C. Scanning electron microscopy and transmission electron microscopy analysis reveals that the catalyst particle was located at the top of each CNT, which indicates the tip growth mechanism for CNTs. The growth process of CNTs will go through the following stages: decomposition of hydrocarbon components into the carbon atoms, dissolution, diffusion and segregation. The growth of CNTs agrees with vapour–solid (V-S) model.

Application of CNT Enhanced Carbon Fibers in Hybrid Composites with Improved Interfacial Properties

Growing carbon nanotubes (CNT) on the surface of high performance carbon fibers (CF) offers a means to tailor the mechanical properties of the fiber-matrix interface of a composite. In the context of this work, a floating catalyst chemical vapor deposition (CVD) unit was utilized to grow CNT onto the surface of CF. The surface and mechanical properties of the resultant fibers, CNT density and alignment morphology were explained to depend on the CNT growth temperature, growth time, and atmospheric conditions within the CVD chamber. Single fiber/Epoxy composite coupons were fabricated by using both neat and CNT-coated CF to conduct single fiber fragmentation test (SFFT). It was observed that the coating of CNT onto CF surface improves the IFSS between CF and matrix when compared with neat-CF. Particularly, CF treatment condition for CNT-coating with 700 °C reaction temperature and 30 minutes reaction time has shown a considerable increase in IFSS approximately of 45% over that of the untreated fiber from which it was processed. The fiber-matrix adhesion was analyzed by using SEM on cryogenically fractured surface of both types of composites. The proper justification of fiber-matrix adhesion featured by composite interfacial properties was explained through IFSS.

Effect of fibre coating and geometry on the tensile properties of hybrid carbon nanotube coated carbon fibre reinforced composite

Hierarchically structured hybrid composites are ideal engineered materials to carry loads and stresses due to their high in-plane specific mechanical properties. Growing carbon nanotubes (CNTs) on the surface of high performance carbon fibres (CFs) provides a means to tailor the mechanical properties of the fibre–resin interface of a composite. The growth of CNT on CF was conducted via floating catalyst chemical vapor deposition (CVD). The mechanical properties of the resultant fibres, carbon nanotube (CNT) density and alignment morphology were shown to depend on the CNT growth temperature, growth time, carrier gas flow rate, catalyst amount, and atmospheric conditions within the CVD chamber. Carbon nanotube coated carbon fibre reinforced polypropylene (CNT-CF/PP) composites were fabricated and characterized. A combination of Halpin–Tsai equations, Voigt–Reuss model, rule of mixture and Krenchel approach were used in hierarchy to predict the mechanical properties of randomly oriented short fibre reinforced composite. A fractographic analysis was carried out in which the fibre orientation distribution has been analyzed on the composite fracture surfaces with Scanning Electron Microscope (SEM) and image processing software. Finally, the discrepancies between the predicted and experimental values are explained.

Carbon nanotube growth from Langmuir–Blodgett deposited Fe3O4 nanocrystals

We investigate colloidal Fe3O4 nanocrystals as a catalyst system for carbon nanotube (CNT) growth that allows for decoupling the CNT growth step from the catalyst shaping and activation step. The system consists of 6.4 nm Fe3O4 nanocrystals synthesized using a solution-based thermal decomposition reaction and, subsequently, transferred as hexagonally ordered Langmuir–Blodgett (LB) monolayers on TiN substrates. We demonstrate for the first time aligned CNT growth from LB deposited nanocrystals on a metallic underlayer. The hexagonally ordered monolayers of catalyst particles show promising stability up to the CNT growth temperature. In situ TEM heating experiments were performed to find this onset of particle deformation and showed stability of the nanoparticles up to 600 °C. The particle coalescence at high temperatures was also evidenced by the increasing CNT diameter, from 9.5 nm at 580 °C to 16 nm at 630 °C. By choosing to work at temperatures below the onset particle coalescence temperature, equivalent CNT diameters were obtained under different catalyst activation and growth conditions. The high stability of the catalyst on the metallic underlayer enables us to study CNT growth kinetics independently of the catalyst shaping step. This work opens a route towards combining growth studies with an electrical evaluation of the CNT growth as the TiN can be used as the bottom contact.

Controlling the size and the activity of Fe particles for synthesis of carbon nanotubes

The properties of carbon nanotubes (CNTs) are controlled by their structure and morphology. Therefore, their selective synthesis, using catalytic chemical vapor deposition, requires precise control of a number of parameters including the size and activity of the catalyst nanoparticles. Previously, an environmental scanning transmission electron microscope (ESTEM) has been used to demonstrate that electron beam-induced decomposition (EBID) of Fe containing precursor molecules can be used to selectively deposit Fe catalyst nanoparticles that are active for CNT growth. We have extended these in situ ESTEM observations to further our understanding of the EBID parameters, such as deposition time, and substrate temperature, that control the size and placement of Fe catalyst particles for two precursors, namely diiron nonacarbonyl (Fe2(CO)9) and ferrocene (Fe(C5H5)2). We found that the diameter of deposited particles increased with increasing deposition time. Electron energy-loss spectra, collected during deposition, show the incorporation of C in the Fe particles. The C content decreased as the substrate temperature was increased and was negligible at 100°C for Fe2(CO)9. However, C and Fe were co-deposited at all temperatures (up to 450°C) when Fe(C5H5)2 was used as an iron source. After deposition, the substrate was heated to the CNT growth temperature in flowing hydrogen to remove the co-deposited C, which was an important step to activate the deposited Fe catalyst for the growth using acetylene. Our measurements revealed that the Fe nanoparticles fabricated from Fe2(CO)9 had higher activity for CNT growth compared to the ones fabricated using Fe(C5H5)2. We also found that the co-deposited carbon could not be removed by heating in hydrogen in the case of Fe(C5H5)2. The particles deposited from Fe(C5H5)2 at 300°C to 450°C formed a core–shell structure with Fe surrounded by graphitic carbon. We speculate that the reduced activity for Fe(C5H5)2 is due to the C content in the deposit.

Growth of Carbon Nanotubes on Carbon Fiber by Thermal CVD Using Ni Nanoparticles as Catalysts

Nickel nanoparticles and thin film on carbon fiber have been prepared through electroless deposition. Moreover, carbon nanotubes were grown on carbon fiber covered by nickel nanoparticles using thermal chemical vapor deposition. The effects of changes in the thickness of the nickel catalyst layer and the growth temperature of carbon nanotubes were studied systemically, and the results are discussed in the present work.

Hierarchical carbon nanostructure design: ultra-long carbon nanofibers decorated withcarbon nanotubes

Hierarchical carbon nanostructures based on ultra-long carbon nanofibers (CNF)decorated with carbon nanotubes (CNT) have been prepared using plasma processes.The nickel/carbon composite nanofibers, used as a support for the growth ofCNT, were deposited on nanopatterned silicon substrate by a hybrid plasmaprocess, combining magnetron sputtering and plasma-enhanced chemical vapordeposition (PECVD). Transmission electron microscopy revealed the presence ofspherical nanoparticles randomly dispersed within the carbon nanofibers. The nickelnanoparticles have been used as a catalyst to initiate the growth of CNT by PECVD at600 °C. After the growth of CNT onto the ultra-long CNF, SEM imaging revealed the formationof hierarchical carbon nanostructures which consist of CNF sheathed with CNTs.Furthermore, we demonstrate that reducing the growth temperature of CNT to less than500 °C leads to the formation of carbon nanowalls on the CNF instead of CNT. This simplefabrication method allows an easy preparation of hierarchical carbon nanostructures over alarge surface area, as well as a simple manipulation of such material in order to integrate itinto nanodevices.

Low‐temperature growth of single‐wall carbon nanotubes inside nano test tubes

AbstractFrom nano‐test tube chemistry we determine details of low temperature growth of carbon nanotubes. Single‐walled carbon nanotubes of various diameters are grown at different temperatures from a Pt organometallic precursor encapsulated inside template single‐walled tubes. At the low temperature limits where the reactions are slower and milder, the inner‐tube diameters are optimally determined by the outer‐tube diameter. The growth temperature is determined for a given tube chirality and is found to be dependent on the diameter. It is lower for thinner tubes and can be as low as 600 °C for the (7.3) tube. In situ nano‐test tube chemistry within a state‐of‐the‐art microscope provides an idealistic nano‐clean room experiment, which allows monitoring of a snapshot in the catalytic growth of a single‐walled tube out of a Pt nanocrystal.

An intermetallic Fe–Zr catalyst used for growing long carbon nanotube arrays

Metallic nanoparticles containing single and binary components have been known for their catalytic properties to grow carbon nanotube (CNT) arrays. In this paper, an intermetallic catalyst consisting of iron and zirconium was used to grow millimeter long, well aligned arrays. The Fe–Zr catalysts enabled the growth of 1.7 mm-long carbon nanotube arrays in 45 min. A comparison with pure iron catalyst indicated that adding Zr to iron can stabilize the Fe catalyst at the CNT growth temperature and moderate its reactivity. SEM images showed the different growth behaviors for Fe–Zr and Fe catalysts. The long, uniform CNT arrays grown here have potential applications in many advanced composites.

Synthesis and Enhanced Field-Emission of Thin-Walled, Open-Ended, and Well-Aligned N-Doped Carbon Nanotubes

Thin-walled, open-ended, and well-aligned N-doped carbon nanotubes (CNTs) on the quartz slides were synthesized by using acetonitrile as carbon sources. As-obtained products possess large thin-walled index (TWI, defined as the ratio of inner diameter and wall thickness of a CNT). The effect of temperature on the growth of CNTs using acetonitrile as the carbon source was also investigated. It is found that the diameter, the TWI of CNTs increase and the Fe encapsulation in CNTs decreases as the growth temperature rises in the range of 780–860°C. When the growth temperature is kept at 860°C, CNTs with TWI = 6.2 can be obtained. It was found that the filed-emission properties became better as CNT growth temperatures increased from 780 to 860°C. The lowest turn-on and threshold field was 0.27 and 0.49 V/μm, respectively. And the best field-enhancement factors reached 1.09 × 105, which is significantly improved about an order of magnitude compared with previous reports. In this study, about 30 × 50 mm2 free-standing film of thin-walled open-ended well-aligned N-doped carbon nanotubes was also prepared. The free-standing film can be transferred easily to other substrates, which would promote their applications in different fields.

Low temperature growth of carbon nanotubes from methane catalytic decomposition overnickel supported on a zeolite

Multi-walled carbon nanotubes from 8 to 63 nm in diameter and from 60 to 413 nmin length, were synthesized over nickel supported on a zeolite by the chemicalvapor deposition of methane in the relatively low temperature range 400–550 °C. The carbon deposited was analyzed by x-ray powder diffraction, Raman spectroscopy, andscanning and transmission electron microscopy. The effects of the reaction temperature onthe carbon nanotube formation and relative purity were evaluated.

Wafer-Scale Growth and Transfer of Aligned Single-Walled Carbon Nanotubes

Experimental demonstration of wafer-scale growth of well-aligned, dense, single-walled carbon nanotubes on 4 ST-cut quartz wafers is presented. We developed a new carbon nanotube (CNT) wafer-scale growth process. This process allows quartz wafers to be heated to the CNT growth temperature of 865degC through the alpha-beta phase transformation temperature of quartz (573degC) without wafer fracture. We also demonstrate wafer-scale CNT transfer to transfer these aligned CNTs from quartz wafers to silicon wafers. The CNT transfer process preserves CNT density and alignment. Carbon nanotube FETs fabricated using these transferred CNTs exhibit high yield. Wafer-scale growth and wafer-scale transfer of aligned CNTs enable carbon nanotube very large-scale integration circuits and their large-scale integration with silicon CMOS.

Hierarchical composites of carbon nanotubes on carbon fiber: Influence of growth condition on fiber tensile properties

Growing carbon nanotubes (CNT) on the surface of high performance carbon fibers (CF) provides a means to tailor the thermal, electrical and mechanical properties of the fiber–resin interface of a composite. However, many CNT growth processes require pretreatment of the fiber, deposition of an intermediate layer, or harsh growth conditions which can degrade tensile properties and limit the conduction between the fiber and the nanotubes. In this study, high density multi-wall carbon nanotubes were grown directly on two different polyacrylonitrile (PAN)-based carbon fibers (T650 and IM-7) using thermal Chemical Vapor Deposition (CVD). The influence of CVD growth conditions on the single-fiber tensile properties and CNT morphology was investigated. The mechanical properties of the resultant hybrid fibers were shown to depend on the carbon fiber used, the presence of a sizing (coating), the CNT growth temperature, growth time, and atmospheric conditions within the CVD chamber. The CNT density and alignment morphology was varied with growth temperature and precursor flow rate. Overall, it was concluded that a hybrid fiber with a well-adhered array of dense MWCNTs could be grown on the unsized T650 fiber with no significant degradation in tensile properties.

Optimization of water assisted chemical vapor deposition parameters for super growth of carbon nanotubes

The optimization of water assisted chemical vapor deposition (WA-CVD) was carried out to synthesize ultra long, vertically aligned, densely packed carbon nanotube (CNT) forests. The effect of various WA-CVD parameters (viz. the flow rate of the reactant gas mixture and its injection temperature, growth kinetics, ramp rate and growth temperature) on the height of the CNTs was studied. A hypothesis for catalytic activity is proposed on the basis of the X-ray photoelectron spectroscopic analysis of the CNT grown substrates and further verified at the optimum condition. The effect of temperature on the growth of the CNTs is studied. The gas flow rate and injection temperature influence the onset of oxidation of the substrates, which in turn affects the CNT growth rate. A growth kinetics study is performed in order to monitor the growth temperature. The role of the onset of oxidation of the iron catalyst in the growth of the CNTs is studied by varying the ramp rate. The precise CNT growth temperature for WA-CVD is determined by growth temperature studies. The optimum condition allows ∼2.2 ± 0.002 mm long CNTs to be obtained.

Low temperature growth of carbon nanotubes using Ni nanopowder mixed with Ag-paste as catalyst

Growth of carbon nanotubes (CNTs) at low temperature is a critical issue in the development of CNTs for diversified applications. The screen printing method, which used silver paste mixed with CNTs and glass powder as the raw material, was usually adopted for fabricating cathode of field emission device. In this work, Ni nanopowder mixed with commercial Ag-paste was prepared and screen-printed on the glass substrate, and then subjected to sintering in air at 500 °C. Growth of CNTs was performed in a self-designed cold-walled chemical vapour deposition (CVD) chamber at 500 °C under a pressure between 1 and 10 Torr. Field emission property was tested and the turn-on field of 2.4 V/μm was obtained for the specimen containing 2.7 wt.% Ni nanopowder. CNT density can be controlled by adjusting the concentration of Ni nanopowder in silver paste. This method proposed a simple route for synthesizing CNTs at relatively low temperature in a conventional CVD system, which is capable of fabricating large area cathode with proper CNT density.