Size Of Carbon Nanotubes Research Articles

Electrochemical Tailoring of Catalyst Nanoparticles for CNT Spatial-Dimension Control

Electrodeposition is an excellent method for a site-selective and direct fabrication of catalyst nanoparticles for subsequent carbon nanotube (CNT) growth. Nickel nanoparticles with densities as high as and diameters down to are deposited on blanket and patterned TiN wafers. Ni nanoparticles are selectively placed at the bottom of submicrometer vias by through-mask electrodeposition. The spherical nanoparticles all produce aligned multiwalled CNTs. The CNT diameter is directly determined by the diameter of the as-deposited nanoparticles, which is tailored by the electrodeposition conditions. Such control of CNT size, density, and location represents an important step toward the implementation of CNTs in device fabrication.

Nanotoxicity Assessment toward the Applications of Carbon Nanotubes as a Small Biomolecule Carrier in Drug Delivery Systems

Carbon Nanotube (CNT) materials have superior properties in electric current carrying capacity, thermal conductivity, and thermal stability. Due to their structure with high aspect ratio, they have structural unusual toxicity and complicate safety issue in a target tissue. In optimized quantities with limited functionality, special type of CNT assembly such as “buckyball” can be used as a potential drug carrier of bioactive molecules and display with increased circulating time and acceptable functionality. We analyzed cytoxicity and inflammatory response following exposure of different size, mass, shape, and functionality of CNTs. We monitored the transport across skin, physiological perturbation of transepithelial electrical resistance (TER) during the exposure of different concentrations of CNTs. The mechanisms of CNTs’ toxicity are closely related to their structure, functional group, and surface charge on the molecule. We established the nanoscale toxicity of fullerenes of CNTs.

An investigation on dispersion of carbon nanotubes in chitosan aqueous solutions

The dispersion of carbon nanotubes (CNT) in water of different pH and in chitosan aqueous solution of three acids, acetic acid, formic acid, and hydrochloric acid, was investigated. Chitosan was soluble in water of pH ≤3 and could well disperse untreated CNT and acid-treated CNT, both of which had poor dispersion in water of pH ≤3. With the presence of 0.1 wt% chitosan in solution, particle sizes of the CNT dispersion were found to decrease with increasing COOH contents on the CNT. Particle sizes of CNT, untreated and acid-treated, in the three acidic aqueous solutions were found to increase with increasing chitosan contents in solutions. Among the three acids, hydrochloric acid gave the smallest particle size of the CNT dispersion. Without chitosan, the dispersibility of the acid-treated CNT in aqueous solutions of three acids was in the order of acetic acid > formic acid > hydrochloric acid.

Mechanical alloying of multi-walled carbon nanotubes and aluminium powders for the preparation of carbon/metal composites

Interactions between carbon nanotubes (CNTs) and aluminium particles during the mechanical alloying (MA) via ball milling have been investigated from the viewpoint of particle behaviour with the aim at developing CNT-dispersed Al matrix composites based on powder metallurgy routes. It was observed that the use of the curly small-diameter multi-walled carbon nanotubes (MWCNTs) in the MA prevented the agglomeration of composite powders, which is attributed to the beneficial role of the MWCNTs as grinding aids. It was also deduced from the mechanical properties of the composite samples, prepared from the ball-milled powders, that such prevention of the particle agglomeration did not hinder the homogeneous distribution of the CNT reinforcements within the Al matrix. It is suggested that careful choices of the sizes of CNTs and Al powders would allow fine-grinding of composite particles with uniformly distributed CNT reinforcements thereby ensuring improved properties of the final composites produced by low-temperature compacting.

Suspension of Multi-Walled Carbon Nanotubes (CNTs) in Freshwaters: Examining the Effect of CNT Size

Global demand for carbon nanotubes (CNTs) is increasing dramatically. As CNTs become commonplace, the range of uses is expected to expand as will the potential for release into ecosystems. Recent research suggests that CNTs display increased suspension in water in the presence of natural organic matter (NOM), thus increasing their ability for transport and dispersion. However, it remains unclear how CNT size will affect the suspension of CNTs in natural waters. Here we examine the effect of CNT diameter (10–500 nm) and CNT length (1–40 μm) in the presence of 1% sodium docecyl sulfate (SDS), and two different freshwater NOM extracts on suspension of CNTs in water. Absorbance spectrometry (UV-VIS) was used to determine CNT concentration in solutions over a 68 h period in the dark. Seventy to ninety-five percent of the CNTs settled out of the 1% SDS solution as compared to 23–54% in each of the NOM solutions. The half-life of suspension in solution increased with decreasing CNT diameter (from 13.9 to 138.8 h−1 for solutions containing NOM). These results demonstrate that settling rates are strongly determined by NOM presence in solution as well as CNT size.

The fabrication of carbon nanotube probes utilizing ultra-high vacuum transmissionelectron microscopy

An application of ultra-high vacuum transmission electron microscopy (UHV TEM) isdemonstrated for the fabrication of carbon nanotube (CNT) probes. In this study, all thefabrication processes—such as CNT attachment, CNT orientation manipulation, and apextrimming—are integrated into a single UHV TEM system. The in situ work under UHV conditions(<5 × 10−10 mbar) allows us to clean the tip surface at the start of the fabrication process to ensurea good contact between the tip and CNT. Furthermore, the CNT size can beuser-selected to meet the various needs for scanning probe microscopy (SPM). Mostimportantly, the in situ trimming enables a multi-walled CNT to have the sharpness of asingle-walled CNT. The three advantages mentioned above are designed to improveconventional methods and will be shown in detail as the procedures of CNT probefabrication by a series of high-resolution TEM images. Finally, we compare the scannedimage via our CNT probes and conventional probes, where the typical artefactscoming from the conventional ones are addressed. We believe the technique wehave developed here will further enhance the resolution of SPM measurements.

Adsorbate-Induced Defect Formation and Annihilation on Graphene and Single-Walled Carbon Nanotubes

We used density functional theory calculations to probe the chemical reactivity of graphene and single-wall carbon nanotubes (CNTs) toward the small molecules O(2), H(2), N(2), C(2)H(2), CO, and CO(2). We found that there is a threshold CNT size below which C(2)H(2) and CO, typical feedstock precursors for CNT growth, become trapped in decorated hillock-like defects on the side walls of CNTs. We also found that O(2), H(2), and CO(2) can etch isolated C adatoms and C adatom pairs. These processes play a role not only in the growth of CNTs, but also in the postgrowth evolution of defects on CNTs through exposure to typical ambient gases.

Automated process for selection of carbon nanotube by electronic property using dielectrophoretic manipulation

This paper presents a novel and an automated selection system to separate carbon nanotubes (CNTs) by their electronic properties using a dielectrophoresis-based method. CNTs have been found as promising materials for nanoelectronics due to their sizes and unique properties. Different CNTs have different electronic properties. Conventional electronic devices that are replaced by specific CNTs can possibly provide better performance and their sizes can be reduced. However, different types of CNTs aggregate together after synthesis processes, so the resulting electronic property of bundled CNTs cannot be predicted easily. Therefore, a novel classification method is necessary to separate different electronic properties of CNTs. Since the size of CNTs is in nanoscale, traditional robotic manipulation cannot be applied. Selection and manipulation of a single CNT with a specific electronic property are challenging. AC electrokinetic assembly is one of the promising methods to manipulate a CNT in the desired position. In this paper, a dielectrophoresis-based method is used to select and manipulate different types of CNTs across microelectrodes. By combining the separation and deposition system, it enables the possibility to manipulate a single CNT precisely and repeatedly, and potentially improve the yield for fabricating CNT based devices. It can also be integrated with a traditional robotic system and implemented in current manufacturing processes. As a result, a fast and batch nano-assembly of consistent nano-devices can be achieved.

Surface Chemical Modification of Multiwalled Carbon Nanotubes by a Wet‐Mechanochemical Reaction

A wet‐mechanochemical reaction for surface modification of multiwalled carbon nanotubes (CNTs) has been developed. In the treatment, CNTs reacted with potassium hydroxide in alcohol solvent at room temperature under mechanical milling. The results from Fourier transmission infrared spectroscopy demonstrate that the nonreactive surfaces of CNTs have been modified successfully by multiple hydroxyl groups. Functionalized carbon nanotubes exhibit higher zeta potential values indicating their high dispersibility in polar solvents. XRD studies corroborate that the surface functionalization does not affect the basic crystal domain size of CNTs. TEM observations reveal that CNTs have been cut into shorter ones by the milling. Shortened CNTs with functionalized surfaces show good dispersion properties.

Magnetism of linear Fe, Co, and Ni nanowires encapsulated in zigzag (n,0) carbon nanotubes (CNT) with n = 5 to 9: A first‐principles study

AbstractWe investigated the magnetic properties of linear Fe, Co, and Ni nanowires (NW) encapsulated in zigzag (n,0) (n = 5, 6, 7, 8, and 9) carbon nanotubes (CNT) using the first‐principles plane wave calculation with the generalized gradient approximation. The magnetic moments per atom for transition metal atoms in the zigzag (n,0) with n = 8 and 9 were slightly smaller than those of freestanding transition metal nanowires with the same bond length, but the values were decreased abruptly for the NW in (6,0) and (5,0). These results suggest that the magnetic properties of linear NW in zigzag CNT are mainly determined by the size of CNT and also by the electronic property of surrounding CNT. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Studies of the equilibrium and thermodynamics of the adsorption of Cu 2+ onto as-produced and modified carbon nanotubes

This study evaluates the Cu 2+ adsorption efficiency of as-produced carbon nanotubes (CNTs) and those modified by HNO 3 and NaOCl. The surface area, pH pzc, pore volume, FTIR analyses, and average pore size of CNTs were determined to compare the differences between nanotubes before and after HNO 3 and NaOCl modification. The HNO 3 and NaOCl modifications increased the pore volume and the average pore size of CNTs; in contrast, the pH pzc was decreased. The modification processes produced some functional groups. The adsorption capacity of Cu 2+ on as-produced and modified CNTs increased with the pH and temperature; however, the effects of the ionic strength on the adsorption of Cu 2+ on as-produced and modified CNTs were negligible. The linear correlation coefficients of Langmuir and Freundlich isotherms were obtained and the results revealed that the Langmuir isotherm fitted the experimental results better than did the Freundlich isotherm. The adsorption capacity of Cu 2+ followed the order NaOCl-modified CNTs > HNO 3-modified CNTs > as-produced CNTs. Changes in the free energy of adsorption ( Δ G o ) , enthalpy ( Δ H o ) , and entropy ( Δ S o ) were determined. All Δ G o values were negative; the Δ H o values of as-produced, HNO 3-modified, and NaOCl-modified CNTs were 10.84, 17.08, and 67.77 kJ/mol and the Δ S o values were 96.89, 122.88, and 319.76 J/mol K, respectively.

DYNAMIC RESPONSE OF CARBON NANOTUBES DISPERSED IN NEMATIC LIQUID CRYSTAL

The alignment and dynamic response of carbon nanotubes (CNTs) in nematic liquid crystal (NLC) medium induced by strong electric field have been observed through polarizing optical microscope. Density-functional calculations suggest that LC molecule anchors helically to the CNT wall to enhance π-stacking with a binding energy of nearly -2.0 eV due to a considerable amount of charge transfer from LC molecule to CNT, resulting in the formation of excess charges and permanent dipole moment in CNTs. Under strong electric field, the motion of CNTs distorted the director of adjacent LC molecules. Our detailed analysis of dynamics revealed that the four-lobe textures in vertical cell and two vertical stripes in in-plane switching cell were strongly correlated, i.e., the side view of textures by the vertical motion of CNTs in vertical cell was similar to the textures in in-plane switching cell. Interestingly, the magnitude of textures in microscope was strongly dependent on the size of CNTs and the applied field strength. The statistical size distribution of textures similar to that of CNTs provided information for the degree of dispersion of CNTs.

Vertically aligned carbon nanotubes synthesized by the thermal pyrolysis with an ultrasonic evaporator

Thermal pyrolysis process is a catalytic chemical vapor deposition (CVD) based method, involving pyrolysis of mixed solution composed of liquid carbon sources and catalysts. This paper is focused on the synthesis of carbon nanotubes (CNTs) by the thermal pyrolysis process with an ultrasonic evaporator that atomizes the mixed liquid solution. The merit of this approach is that the apparatus can produce aligned and clean CNTs which can be easily controlled in a cost-effective manner. CNT samples synthesized by introducing the atomized solution into the pyrolysis furnace were analyzed to understand and characterize the growth mechanism. HRTEM and high magnification SEM analysis indicate that the samples are multiwalled carbon nanotubes (MWNTs) grown through tip growth mechanism. The results were confirmed by Raman spectrum curve. In addition, the effects of experimental parameters on the structure of CNTs were investigated by SEM images and themogravimetric analysis. The results reveal that synthesis time and temperature have a key influence on the size of CNTs, and the concentration of catalyst determines the amount of the filling yield in the inner part of CNTs.

Fabrication of High Thermal Conductivity Carbon Nanotube Arrays by Self Assembled Fe 3O 4 particles

The outstanding properties of carbon nanotubes (CNTs) have induced widespread interest in researches and applications. A new approach of fabricating vertically aligned CNT arrays with good CNT size and distribution control, and enhanced substrate attachment is under development. This technique includes fabrication and size tuning of Fe 3O 4 nanoparticles, buffer layer preparation on Si substrates, self assembly of Fe 3O 4 nanoparticles on substrates, CNT synthesis by thermal CVD with optimized operation parameters. One application of the synthesized CNT arrays is serving as thermal interface material to meet the thermal management challenge in high power microelectronic packages. The thermal performance of the synthesized CNT arrays was evaluated.

Effect of substrate bias on growth and properties of carbon nanotubes deposited under no hydrogen introduction by MPCVD

In order to examine the consequence of replacing hydrogen gas with high substrate bias, processes were successfully demonstrated to fabricate various carbon catalyst-assisted nanostructures, including carbon nanotubes (CNTs), by microwave plasma chemical vapor deposition (MPCVD), under the pure CH 4 as the only source gas and without additional H 2 gas introduction. The Si wafers were first deposited with catalyst by physical vapor deposition (PVD), and then followed by H-plasma pretreatment to obtain the well-distributed catalyst particles on wafer. The pretreated specimens were then deposited in MPCVD to manipulate the various carbon nanostructures. The main process parameters include catalyst material (Co, Ni and Fe), the substrate bias (0 to − 320 V), and deposition time (1 to 20 min). The as-deposited nanostructures were characterized by SEM, HRTEM, Raman spectroscopy, and field emission I– V measurement. The results indicate that the various nanostructures on Si wafers can be manipulated under sufficient high negative substrate bias (> − 200 V) without the additional hydrogen introduction. These results also improve our understanding on growth mechanisms of CNTs or other nanostructures, where the most of the proposed mechanisms in the literature were too much emphasis on the role of hydrogen. On important process parameters, except the substrate bias, it is interesting to note that effect of deposition time on nanostructures is essentially to extend the more CNTs into the plasma zone, which can result in different purification effect on CNTs, vary the alignment and sizes of CNTs, and expose the more nanostructures near the substrate surface. Under the present deposition conditions, the best nanostructures with the best field emission properties (Turn-on field = 5 V/μm, maximum current density > 35 mA/cm 2) are the well-aligned CNTs with proper tube number densities, purities and sizes.

Adsorption of microcystins by carbon nanotubes

The production of cyanobacterial toxins microcystins (MCs) by cyanobacterial bloom which may promote the growth of tumor in human liver is a growing environmental problem worldwide. In this paper, the adsorption of MC-RR and LR, which were extracted from cyanobacterial cells in Dianchi Lake in China, by carbon nanotubes (CNTs), wood-based activated carbon (ACs) and clays were investigated. Compared with ACs and clay materials of sepiolite, kaolinite and talc tested, CNTs were found to have a strong ability in the adsorption of MCs. At the concentrations of 21.5 mg l −1 MC-RR and 9.6 mg l −1 MC-LR in 50 mmol phosphate buffer solution (pH 7.0), the adsorption amounts of MCs by CNTs with the range of outside diameter from 2 to 10 nm were 14.8 and 5.9 mg g −1, which were about four times higher than those by other adsorbents tested. It was shown that with the decrease of CNTs outside diameters from 60 to 2 nm, the adsorption amount of MCs was apparently increased, however the size of CNTs particles formed in solution declined. This result implies that the size of CNTs tube pore that is fit for the molecular dimension of MCs plays a dominant role. Furthermore the specific surface area of CNTs was also found to be a factor in the adsorption of MCs. The results suggested that the selection of suitable size of CNTs as a kind of adsorbent is very important in the efficient eliminating MCs from drinking water in future.

열 CVD법에 의한 CNTs/Metal/Al2O3나노복합분말의 합성 및 특성

An optimum route to synthesize composite powders with homogeneous dispersion of carbon nanotubes (CNTs) was investigated. nanocomposite powders were fabricated by thermal chemical vapor deposition of gas over nanocomposite catalyst prepared by selective reduction of metal powders. The FT-Raman spectroscopy analysis revealed that the CNTs have single- and multi-walled structure. The CNTs with the diameter of 25-43 nm were homogeneously distributed in the powders, and their characteristics were strongly affected by a kind of metal catalyst and catalyst size. The experimental results show that the composite powder with required size and dispersion of CNTs can be realized by control of synthesis condition.

Effects of deposition and synthesis parameters on size, density, structure, and field emission properties of Pd-catalyzed carbon nanotubes synthesized by thermal chemical vapor deposition

The effects of deposition parameters and NH3 pretreatment on the size and distribution of Pd catalytic particles and subsequently their effects on the characteristics of the synthesized carbon nanotubes (CNTs) were systematically investigated. It was found that the size of Pd particles decreases and the particle density (total number of Pd particles per unit area) increases as the Pd film thickness decreases. Moreover, pretreatment of Pd film in NH3 gas promotes smaller Pd particles and higher particle density which is beneficial for CNT growth. The CNTs were synthesized by thermal chemical vapor deposition at 750 °C using methane (CH4) as the carbon source, and a mixture of Ar/H2 (80 vol %: 20 vol %) as a carrier gas with NH3 serving as a processing reagent. The incorporation of NH3 in CNT synthesis, per the specific pretreatment of catalytic film, has a distinct effect on the size and morphology of CNTs produced. The interrelation between processing, structure and emission behavior of CNTs produced with different synthesis conditions was examined by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and field emission measurements.

The growth of bunched and multi-circularly wrapped carbon nanotubes on bulk magnetic alloys by microwave enhanced hot-filament CVD with a dilute gas of ammonia

Bunched and multi-circularly wrapped carbon nanotubes (CNT) are observed to grow on alloy substrates based on iron group metals and copper by a microwave enhanced hot-filament method with a dilute gas of ammonia at a proper RF self-bias. The grown size of CNTs embodied in the grain sizes of conducting bulk alloy catalysts such as Cu-Ni, Cu-Fe, Cu-Co, and Cu-Ni-Fe-Co are controlled by a precursor time of hydrogen plasma etching. Species with different structural features and homogenization of CNTs samples are produced crucially attributed to various reactant gases and self-bias induced by the radio frequency field.

Nanoscale Gap Fabrication by Carbon Nanotube-Extracted Lithography (CEL)

Carbon nanotube (CNT) -extracted lithography (CEL) was developed to create high-quality nanoscale gaps defined by the size of CNTs. An individual multiwalled CNT (MWCNT) was deposited across electrodes by the composite electric field guided assembly method (CEGA) developed previously. After blanket deposition of a metal layer, the MWCNT was removed to obtain a nanoscale gap. The CEL can provide a technique for the mass fabrication of well-defined and precisely positioned nanosized gaps in a reproducible manner.