Manipulation Of Carbon Nanotubes Research Articles

Metallic CNT Tolerant Field Effect Transistor Using Dielectrophoresis

The performance of silicon-based transistors is reaching its limit, and new materials like carbon nanotubes (CNTs) have started emerging to replace them in electronic products. However, the precise manipulation of CNTs requires complicated techniques, which increases process variation. These variations can lead to a decrease in the overall yield of the field-effect transistor (FET). This study shows how a low-frequency signal may regulate the number of CNTs on electrodes with a nanometer scale. We also demonstrate using an interdigitated electrode to reduce the shorts caused by metallic CNTs. The fabricated CNFETs were characterized using SEM, AFM, and I-V measurements. The study also demonstrates how the duration and amplitude of the applied signal impact the density of CNTs on the electrodes. Finally, finite element analysis was used to evaluate the electric field parameters during DEP. This technique will lead to precise CNTs per unit area, which can help fabricate transistors, sensors, and other electronic components.

Optimization of Surfactant Concentration in Carbon Nanotube Solutions for Dielectrophoretic Ceiling Assembly and Alignment: Implications for Transparent Electronics.

Surfactants such as sodium dodecyl sulfate (SDS) are used to improve the dispersity of carbon nanotubes (CNTs) in aqueous solutions. The surfactant concentration in CNT solutions is a critical factor in the dielectrophoretic (DEP) manipulation of CNTs. A high surfactant concentration causes a rapid increase in the solution conductivity, while a low concentration results in undesirably large CNT bundles within the solution. The increase in the solution conductivity causes drag velocity that obstructs the CNT manipulation process due to the electrothermal forces induced by the electric field. The presence of large CNT bundles is undesirable since they degrade the device performance. In this work, mathematical modeling and experimental work were used to optimize the concentration of the SDS surfactant in multiwalled carbon nanotube (MWCNT) solutions. The solutions were characterized using dynamic light scattering (DLS) and ultraviolet–visible spectroscopy (UV–Vis) analysis. We found that the optimum SDS concentration in MWCNT solutions for the successful DEP manipulation of MWCNTs was between 0.1 and 0.01 wt %. A novel DEP configuration was then used to assemble MWCNTs across transparent electrodes. The configuration was based on ceiling deposition, where the electrodes were on top of a droplet. The newly proposed configuration reduced the drag velocity and prevented the assembly of large MWCNT bundles. MWCNTs were successfully assembled and aligned across interdigitated electrodes (IDEs). The assembly of MWCNTs from aqueous solutions across transparent electrodes has potential use in future transparent electronics and sensor devices.

Controlled manipulation of CNTs in glass/epoxy composites with cut-outs using non-uniform electric field

In this work, an effective methodology to incorporate aligned carbon nanotubes (CNTs) in long fiber composites in the presence of geometric discontinuities has been studied. Unidirectional (UD) glass/CNT-epoxy composites containing circular cut-outs were used as representative of a common discontinuity. Multi-walled (MW) CNTs were introduced in the composites via the epoxy matrix and aligned using low-frequency non-uniform AC electric field. This work discusses the methodology to control CNT alignment around the cut-out with the objective of enhancing the stiffness locally. The effectiveness of CNT alignment was assessed indirectly through the mapping of electrical resistance and polarized Raman spectroscopy. A strong correlation was found between the targeted CNT alignment state and the measured resistance values around the cut-out. As a precursor to developing glass/CNT-epoxy hierarchical composites, the response of MW-CNTs in the epoxy resin system was assessed at various input voltage levels in correlation with the weight fraction (wt.%) of CNTs. While a change in electrical resistance by ~3 orders of magnitude was found along the direction of CNT alignment in the hierarchical composites, a change in electrical resistance by ~5 orders of magnitude was observed in the CNT-epoxy composites in comparison with that of the respective control samples.

Characterization of the Resistance and Force of a Carbon Nanotube/Metal Side Contact by Nanomanipulation.

A high contact resistance restricts the application of carbon nanotubes (CNTs) in fabrication of field-effect transistors (FETs). Thus, it is important to decrease the contact resistance and investigate the critical influence factors such as the contact length and contact force. This study uses nanomanipulation to characterize both the resistance and the force at a CNT/Au side-contact interface inside a scanning electron microscopy (SEM). Two-terminal CNT manipulation methods, and models for calculating the resistance and force at contact area, are proposed to guide the measurement experiments of a total resistance and a cantilever's elastic deformation. The experimental results suggest that the contact resistance of CNT/Au interface is large (189.5 kΩ) when the van der Waals force (282.1 nN) dominates the contact force at the interface. Electron-beam-induced deposition (EBID) is then carried out to decrease the contact resistance. After depositing seven EBID points, the resistance is decreased to 7.5 kΩ, and the force increases to 1339.8 nN at least. The resistance and force at the contact area where CNT was fixed exhibit a negative exponential correlation before and after EBID. The good agreement of this correlation with previous reports validates the proposed robotic system and methods for characterizing the contact resistance and force.

Nanomanipulation of Carbon Nanotubes with the Vector Scanning Mode of Atomic Force Microscope

The miniaturization of electronics devices into the nanometer scale is indispensable for next generation semiconductor technology, and CNTs are considered to be the promising candidates for the future nanoelectronics devices with being manipulated to the appropriate location in the manufacturing process of nanodevices. So the new vector scanning mode nanomanipulation is proposed and studied through the nanomanipulation experiments of nanoparticles and carbon nanotubes. According to the specific vectors, carbon nanotubes can accurately achieve the specified operation. And in the movement of carbon nanotubes, the deformation and rotation appear at times, which is caused by many factors, such as material itself properties, the size and direction of propulsive force of AFM tip, the adhesion between carbon nanotubes and substrate surface. In addition, under the influence of many factors, the carbon nanotubes can be manipulated without the indentation or other mechanical damages at the contact position between carbon nanotubes and AFM probe tip due to high elasticity and strength, etc, but the indentation become obvious in the nanomanipulation process of polystyrene nanoparticles because of own property. So, the new vector scanning mode nanomanipulation, based on AFM system, is demonstrated that it is an effective and reliable technique for manipulation of carbon nanotubes for the future nanodevices.

Recent Simulation Study on Precise Positioning of Carbon Nanotubes by Dielectrophoresis

Carbon nanotubes (CNTs) have been widely studied for their unique size-dependent electrical, mechanical, and chemical properties. However, CNTs need to be precisely positioned in complex device structures. Dielectrophoresis (DEP) is an effective and practical method for precise assembly of CNTs. In this paper, the researches on simulation of precise positioning of CNTs by DEP are reviewed. Single electrode pairs include those with round, triangle, and rectangular tip shapes and electrode arrays such as comb electrodes are also taken accounted. The moving trajectories of CNTs during DEP from the selected literature are introduced. The effect of floating electrodes on precise manipulation of CNTs is examined as well.

Construction of carbon nanotube-based microcapsules by self-assembly

Carbon nanotubes possess unique structures and outstanding properties. However, dispersion and manipulation of carbon nanotubes in solvents severely limit their application. A solution is building carbon nanotube-based microcapsules that combine both the properties of carbon nanotubes and capsules. Carbon nanotube-based microcapsules have indeed great potential applications including catalysts, adsorbents, and controlled-release materials. Here, we built carbon nanotube-based microcapsules by electrostatic self-assembly to develop novel composite materials. The construction and morphology of microcapsules were characterized by Raman spectroscopy, infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. Pre-films composed of poly(sodium 4-styrenesulfonate) and poly(diallyldimethylammoinum chloride) were assembled onto calcium carbonate (CaCO3) microparticles to construct positive solid templates. The carboxylated carbon nanotubes were then successfully assembled on the CaCO3 template using a self-assembly technique. Ethylene diamine tetraacetic acid (EDTA) was used as a powerful chelating agent to remove the CaCO3 cores by chelation between EDTA and calcium, thus completing the construction of carbon nanotube-based hollow microcapsules. The spherical shapes of the microcapsules were well retained, and the carbon nanotubes were anchored evenly in the polyelectrolyte layers.

Removal of copper (II) ions from aqueous solutions onto chitosan/carbon nanotubes composite sorbent

Carbon nanotubes (CNTs) have been considered as promising materials in various applications including water treatment. Manipulation of CNT’s with polymer offers unique properties as a composite in treatment of wastewater and removal of heavy metal ions. In the present work, we have developed a chitosan (CS)/multiwall carbon nanotubes (MWCNTs) composite sorbent by mixing the naturally occurring biopolymer CS and functionalized MWCNTs in 1% acetic acid solution. The obtained composite adsorbent was used successfully for the removal of copper (II) ions from aqueous solutions. The influence of variable parameters like pH, concentration of the metal ion, amount of adsorbent, and contact time on the extent of adsorption was investigated by batch method. Graphical correlations of various adsorption isotherm models such as Langmuir and Freundlich have been carried out. The data were analyzed by the Lagergren pseudo-first-order and pseudo-second-order kinetic models. Further the adsorption performance of the CS/MWCNTs composite was compared with CS and cation exchange resin. The maximum monolayer capacity of CS/MWCNTs composite and CS was found to be 454.55 and 178.57 mg/g, respectively. The prepared adsorbents were characterized by fourier transform infrared spectroscopy and scanning electron microscopy analysis.

Optical visualization of individual ultralong carbon nanotubes by chemical vapour deposition of titanium dioxide nanoparticles

Direct visualization and manipulation of individual carbon nanotubes in ambient conditions is of great significance for their characterizations and applications. However, the observation of individual carbon nanotubes usually requires electron microscopes under high vacuum. Optical microscopes are much more convenient to be used, yet their resolution is low. Here we realize the visualization and manipulation of individual ultralong carbon nanotubes under optical microscopes by deposition of TiO2 nanoparticles on them. The strong scattering of TiO2 nanoparticles to visible light renders them visible by optical microscopes. Micro-Raman-spectroscopy measurement of individual carbon nanotubes is greatly facilitated by their optical visualization. With the assistance of TiO2 nanoparticles, individual carbon nanotubes can be easily manipulated under an optical microscope at macroscopic scale and in ambient conditions. Based on our approach, various manipulation of ultralong carbon nanotubes, including cutting, transfer, fabrication of structures/devices and pulling out inner shells of multiwalled carbon nanotubes, are demonstrated.

Automated Manipulation of Carbon Nanotubes Using Atomic Force Microscopy

The manipulation of carbon nanotubes is an important and essential step for carbon-based nanodevice or nanocircuit assembly. However, the conventional push-and-image approach of manipulating carbon nanotubes using atomic force microscopy has low efficiency on account of the reduplicated scanning process during manipulation. In this article, an automated manipulation system is designed and tested. This automated manipulation system, which includes an atomic force microscope platform and a self-developed computer program for one-dimensional manipulation, is capable of automatically moving any assigned individual carbon nanotube to a defined target location without any intermediate scanning procedure. To demonstrate the high-efficiency of this automated manipulation system and its potential applications in nanoassembly, two experiments were conducted. The first experiment used this system to manipulate a carbon nanotube to a defined target location. In the second experiment, this system was used to automatically manipulate several carbon nanotubes for generating and translating a defined pattern of nanotubes.

Virtual Manipulation of Multi-Wall Carbon Nanotubes with Atomic Force Microscope

This paper describes a virtual reality (VR) simulator for the manipulation of carbon multi-wall nanotubes with atomic force microscope (AFM). Major challenges in interfacing a human operator with tasks of manipulating nanotubes via a haptic VR interface are outlined. After a review of our previous efforts, we present the current state of our VR simulator for multi-wall nanotube manipulation. The collision detection, interaction force modeling, deformation simulation and haptic rendering of nanotubes are then discussed. Results of virtual manipulation of carbon nanotubes are presented within an immersive VR set-up.

The manipulation of carbon nanotubes on a polymer surface using a laser beam

Controlled noninvasive manipulation of porphyrin-doped single-walled carbon nanotubes (SWCNT) by laser beam is described. SWCNT/porphyrin complexes have been deposited on a polymer surface and irradiated by a scanning beam of laser light with the wavelength of 405 nm. Laser energy was absorbed by the porphyrin and converted into heat through an energy transfer within the complexes. This led to periodical deformation of the initially flat polymer surface. As a result of the surface deformation the SWCNTs or SWCNT bundle move in the direction given by the laser scanning. It was proved that SWCNTs can be moved to a desired position using the focused laser beam.

Immobilization of Chitosan onto Carbon Nanotubes for Lead Removal from Water

Carbon nanotubes (CNTs) are interesting materials which are being researched intensively in the past few year. Application of CNTs in water treatment with their unique properties has attracted the attention of many scientists and engineers. Moreover, manipulation of CNTs with other polymers has been done for different applications. This study describes the use of carbon nanotubes with attached Chitosan for lead removal from aqueous solution. The CNTs were functionalized with chitosan via covalent link. The immobilization was characterized by Fourier Transform Infrared Spectroscopy (FTIR) and Field Emission Scanning Electron Microscope (FESEM). The obtained nanocomposite was used as an adsorbent material for lead removal from aqueous solutions and its removal capacity was tested. The results show an optimum removal percentage (98.4%) at the center point conditions.

A multiscale simulation study of carbon nanotube interactions with designed amphiphilic peptide helices

The dispersion and manipulation of carbon nanotubes (CNTs) are of great importance if we are to utilise the unique properties of CNTs in a range of biological, electrical and mechanical applications. Recently, a designed amphiphilic peptide helix termed nano-1 has been shown to solubilise CNTs in aqueous solution. Furthermore, the peptide is capable of assembling these coated tubes into fibres. We use a multiscale molecular dynamics approach to study the adsorption profile of nano-1 on a CNT surface. We find that nano-1 interacts with a CNT in a preferred orientation, such that its hydrophobic surface is in contact with the tube. The adsorption profile is unchanged upon increasing the number of peptides on the CNT. Interestingly, when few peptides are adsorbed onto the CNT surface we find that the secondary structure of the peptide is unstable. However, the helical secondary structure is stabilised upon increasing the number of peptides on the CNT surface. This study sheds light on the adsorption of peptides on CNTs, and may be exploitable to enhance the selective solubilisation and manipulation of CNTs.

Chemistry of carbon nanotubes in biomedical applications

Carbon nanotubes (CNTs) have attracted great interdisciplinary interest due to their peculiar structural, mechanical and electronic properties. Applications of CNTs in biomedical research are being actively explored by many scientists worldwide. However, manipulation of CNTs is impeded by several problems, such as 1) formation of complex and entangled bundles; 2) very low solubility of CNTs in organic solvents and water; 3) inert properties of pristine CNTs under many chemical reaction conditions, etc. Chemical modification of CNTs has partly solved the above issues and is still one of the most effective means of manipulating and processing CNTs. Many bioapplications of CNTs rely on successful outer/inner surface functionalizations. This Feature Article is comprised of two main parts. In the first part, we briefly review the covalent surface chemistry for the CNT functionalization; in the second part, we focus on the biomedical applications of surface chemistry for CNTs, in particular, the chemistry for controlling biomedical functions and meanwhile lowering nanotoxicity of CNTs. We also analyze the underlying factors that led to the controversy in the previous experimental data of safety studies of CNTs.

In-situ monitoring of optical deposition of carbon nanotubes onto fiber end

Carbon nanotubes (CNTs) emerged as an attractive material for nonlinear optical devices. Their quasi-one-dimensional structure provided their unique nonlinear characteristics. However, one of their drawbacks is the handling method. We have proposed and demonstrated optical manipulation of CNTs to deposit them onto cores of optical fiber ends with a simple technique. Although the method is very simple, it requires precise control of the optical power. The method does not posses controllability of the CNT-layer properties. In this paper, we employed optical reflectometry to solve these problems. A 15 microm diameter circular region was area-selectively coated by CNTs using highly uniform solution. The preferentially-deposited CNTs were directly, for the first time, observed by a field emission scanning electron microscope (FE-SEM).

Depth-detection methods for microgripper based CNT manipulation in a scanning electron microscope

Current research work on the development of different depth-detection methods for supporting pick-and-place manipulations of carbon nanotubes (CNTs) in a scanning electron microscope (SEM) is presented. A nanorobot station capable of performing this manipulation task in the SEM’s vacuum chamber has been developed, consisting of two cooperating nanorobots. One robot carries an electrothermal microgripper and also performs the coarse approach between microgripper and CNT. The second robot serves as sample holder and realizes the fine positioning of the CNT sample. For a reliable fine approach between microgripper and CNT as well as an intended future automation of handling tasks, depth-detection methods are required in order to precisely measure and align the z-position of microgripper and CNT. Two different methods for z-position estimation are proposed. The depth from focus method uses the focusing information of SEM images whereas the touchdown sensor concept relies on a bimorph piezo bending actuator. The feasibility of both approaches is shown and first experimental results are discussed. Future work has to show how the proposed methods will increase the efficiency of nanorobotic manipulation and how these methods can advance the automation of nanohandling tasks.

Electrothermal microgrippers for pick-and-place operations

Manipulation of carbon nanotubes to assemble functional devices can be done inside a scanning electron microscope in which a suitable combination of visual resolution and sample space allows macros...

Manipulation and soldering of carbon nanotubes using atomic force microscope

Manipulation of carbon nanotubes (CNTs) by an atomic force microscope (AFM) and soldering of CNTs using Fe oxide nanoparticles are described. We succeeded to separate a CNT bundle into two CNTs or CNT bundles, to move the separated CNT to a desirable position, and to bind it to another bundle. For the accurate manipulation, load of the AFM cantilever and frequency of the scan were carefully selected. We soldered two CNTs using an Fe oxide nanoparticle prepared from a ferritin molecule. The adhesion forces between the soldered CNTs were examined by an AFM and it was found that the CNTs were bound, though the binding force was not strong.

Special Issue on the Magnetic and Electric Field Effects at the Micro- and Nano-Scale Systems and Flows in Material Processing

Special Issue on the Magnetic and Electric Field Effects at the Micro- and Nano-Scale Systems and Flows in Material Processing