Dynamic analysis of fixed-free single-walled carbon nanotube-based bio-sensors because of various viruses

In the present study, the vibrations of the fixed-free single-walled carbon nanotube (SWCNT) with attached bacterium/virus on the tip have been investigated. To explore the suitability of the SWCNT as a bacterium/virus detector device, first the various types of virus have been taken for the study and then the resonant frequencies of fixed-free SWCNT with attachment of those viruses have been simulated. These resonant frequencies are compared with the published analytical data, and it is shown that the finite element method (FEM) simulation results are in good agreement with the analytical data. The results showed the sensitivity and suitability of the SWCNT having different length and different masses (attached at the tip SWCNT) to identify the bacterium or virus.     

Sharp burnout failure observed in high current-carrying double-walled carbon nanotube fibers

We report on the current-carrying capability and the high-current-induced thermal burnout failure modes of 5-20 μm diameter double-walled carbon nanotube (DWNT) fibers made by an improved dry-spinning method. It is found that the electrical conductivity and maximum current-carrying capability for these DWNT fibers can reach up to 5.9 × 10(5) S m(-1) and over 1 × 10(5) A cm(-2) in air. In comparison, we observed that standard carbon fiber tended to be oxidized and burnt out into cheese-like morphology when the maximum current was reached, while DWNT fiber showed a much slower breakdown behavior due to the gradual burnout in individual nanotubes. The electron microscopy observations further confirmed that the failure process of DWNT fibers occurs at localized positions, and while the individual nanotubes burn they also get aligned due to local high temperature and electrostatic field. In addition a finite element model was constructed to gain better understanding of the failure behavior of DWNT fibers.     

Graphene-on-diamond devices with increased current-carrying capacity: carbon sp2-on-sp3 technology

Graphene demonstrated potential for practical applications owing to its excellent electronic and thermal properties. Typical graphene field-effect transistors and interconnects built on conventional SiO(2)/Si substrates reveal the breakdown current density on the order of 1 μA/nm(2) (i.e., 10(8) A/cm(2)), which is ~100× larger than the fundamental limit for the metals but still smaller than the maximum achieved in carbon nanotubes. We show that by replacing SiO(2) with synthetic diamond, one can substantially increase the current-carrying capacity of graphene to as high as ~18 μA/nm(2) even at ambient conditions. Our results indicate that graphene's current-induced breakdown is thermally activated. We also found that the current carrying capacity of graphene can be improved not only on the single-crystal diamond substrates but also on an inexpensive ultrananocrystalline diamond, which can be produced in a process compatible with a conventional Si technology. The latter was attributed to the decreased thermal resistance of the ultrananocrystalline diamond layer at elevated temperatures. The obtained results are important for graphene's applications in high-frequency transistors, interconnects, and transparent electrodes and can lead to the new planar sp(2)-on-sp(3) carbon-on-carbon technology.     

Gecko-inspired carbon nanotube-based self-cleaning adhesives

The design of reversible adhesives requires both stickiness and the ability to remain clean from dust and other contaminants. Inspired by gecko feet, we demonstrate the self-cleaning ability of carbon nanotube-based flexible gecko tapes.     

Recent advances in carbon nanotube-based electronics

CNT-electronics is a field involving synthesis of carbon nanotubes-based novel electronic circuits, comparable to the size of molecules, the practically fundamental size possible. It has brought a new paradigm in science as it has enabled scientists to increase the device integration density tremendously, hence achieving better efficiency and speed. Here we review the state-of-art current research on the applications of CNTs in electronics and present recent results outlining their potential along with illustrating some current concerns in the research field. Unconventional projects such as CNT-based biological sensors, transistors, field emitters, integrated circuits, etc. are taking CNT-based electronics to its extremes. The field holds a promise for mass production of high speed and efficient electronic devices. However, the chemical complexity, reproducibility and other factors make the field a challenging one, which need to be addressed before the field realizes its true potential.     

Clamped-free double-walled carbon nanotube-based mass sensor

In this study, we investigate the vibrations of the cantilever double-walled carbon nanotube (DWCNT) with attached bacterium on the tip in the view of developing the sensor. This sensor will be able to help to identify the bacterium or virus that may be attached to the DWCNT. Four cases are considered; these are light or heavy bacteria attached to either inner or outer nanotube. The problem is solved by the finite difference method.     

Rapid assembly of carbon nanotube-based magnetic composites

The rapid assembly of magnetic carbon nanotubes is mediated through the electrostatic attraction of α-haematite nanoparticles to carboxylic groups decorating their outer surface. The system is then stabilised through covalently bonding a silica coat using a 3-aminopropyltriethoxysilane precursor, which creates a thin barrier protecting the α-haematite particles from aggressive pH solutions. The nanocomposites can be effectively dispersed in aqueous solution and can be attracted to an external magnetic field. The proposed method can be used for synthesis of magnetic CNTs suitable for assembling densely packed magnetic arrays, remotely guided drug delivery and organic chemical wastewater remediation with the added benefit of nanomaterial recovery. Therein, p-nitroaniline was demonstrated to still adsorb to uncoated areas of the silica-sheathed magnetic MWCNT composite.     

High-density carbon nanotube buckypapers with superior transport and mechanical properties

High-density buckypapers were obtained by using well-aligned carbon nanotube arrays. The density of the buckypapers was as high as 1.39 g cm(-3), which is close to the ultimate density of ideal buckypapers. Then we measured the transport and mechanical properties of the buckypapers. Our results demonstrated that its electrical and thermal conductivities could be almost linearly improved by increasing its density. In particular, its superior thermal conductivity is nearly twice that of common metals, which enables it a lightweight and more efficient heat-transfer materials. The Young's modulus of the buckypapers could reach a magnitude over 2 GPa, which is greatly improved compared with previous reported results. In view of this, our work provided a simple and convenient method to prepare high-density buckypapers with excellent transport and mechanical properties.     

Recent progress in carbon nanotube-based gas sensors

The development of carbon nanotube-(CNTs-)based gas sensors and sensor arrays has attracted intensive research interest in the last several years because of their potential for the selective and rapid detection of various gaseous species by novel nanostructures integrated in miniature and low-power consuming electronics. Chemiresistors and chemical field effect transistors are probably the most promising types of gas nanosensors. In these sensors, the electrical properties of nanostructures are dramatically changed when exposed to the target gas analytes. In this review, recent progress on the development of different types of CNT-based nanosensors is summarized. The focus was placed on the means used by various researchers to improve the sensing performance (sensitivity, selectivity and response time) through the rational functionalization of CNTs with different methods (covalent and non-covalent) and with different materials (polymers and metals).     

CMOS considerations in nanoelectromechanical carbon nanotube-based switches

In this paper, we focus on critical issues directly related to the viability of carbon nanotube-based nanoelectromechanical switches, to perform their intended functionality as logic and memory elements, through assessment of typical performance parameters with reference to complementary metal-oxide-semiconductor devices. A detailed analysis of performance metrics regarding threshold voltage control, static and dynamic power dissipation, speed, and integration density is presented. Apart from packaging and reliability issues, these switches seem to be competitive in low power, particularly low-standby power, logic and memory applications.     

Computational modeling of a carbon nanotube-based DNA nanosensor

During the last decade the design of biosensors, based on quantum transport in one-dimensional nanostructures, has developed as an active area of research. Here we investigate the sensing capabilities of a DNA nanosensor, designed as a semiconductor single walled carbon nanotube (SWCNT) connected to two gold electrodes and functionalized with a DNA strand acting as a bio-receptor probe. In particular, we have considered both covalent and non-covalent bonding between the DNA probe and the SWCNT. The optimized atomic structure of the sensor is computed both before and after the receptor attaches itself to the target, which consists of another DNA strand. The sensor's electrical conductance and transmission coefficients are calculated at the equilibrium geometries via the non-equilibrium Green's function scheme combined with the density functional theory in the linear response limit. We demonstrate a sensing efficiency of 70% for the covalently bonded bio-receptor probe, which drops to about 19% for the non-covalently bonded one. These results suggest that a SWCNT may be a promising candidate for a bio-molecular FET sensor.     

Effect of ion irradiation on the properties of carbon nanotube buckypapers

Optical, electrical and structural properties of argon (Ar) ion-irradiated buckypapers of multi-walled carbon nanotube (MWCNT) at various doses prepared by a vacuum filtration method were investigated. It was found that the direct current (DC) conductivity and absorption spectra in the visible range were decreased with an increasing Ar ion irradiation dose. A subsequent heating of nanotube buckypapers at 800 K in a vacuum at each irradiation dose improved the conductivity of buckypapers, whereas optical absorption was unchanged. Moreover, the graphite structure of MWCNTs was transformed to amorphous structure with an increasing Ar ion irradiation dose. The decrease of optical absorption and electrical conductivity of MWCNT buckypaper at room temperature can be ascribed to the increase of defects in the irradiated MWCNTs.     

Processing technique for single-walled carbon nanotube-based sensor arrays

We investigated a selective assembly method of fabricating single-walled carbon nanotubes (SWCNTs) on a silicon-dioxide (SiO2) surface by using only a photolithographic process; then, we fabricated 8 x 8 field-emission transistor (FET) arrays for sensor applications. Photoresist (PR) patterns were made on a SiO2-grown Si substrate by using the photolithographic process. This PR-patterned substrate was dipped into a SWCNT solution dispersed in dichlorobenzene (DCB). The PR patterns were removed by using acetone. As a result, selectively-assembled SWCNT channels in 8 x 8 FET arrays could be fabricated between source and drain electrodes without complicated chemical steps using octadecyltrichlorosilane (OTS). Finally, we successfully fabricated 8 x 8 SWCNT-based multi-channel FET arrays by using our novel self-assembly method.     

A wireless, passive carbon nanotube-based gas sensor

A gas sensor, comprised of a gas-responsive multiwall carbon nanotube (MWNT)-silicon dioxide (SiO₂) composite layer deposited on a planar inductor-capacitor resonant circuit is presented here for the monitoring of carbon dioxide (CO₂), oxygen (O ₂), and ammonia (NH₃). The absorption of different gases in the MWNT-SiO₂ layer changes the permittivity and conductivity of the material and consequently alters the resonant frequency of the sensor. By tracking the frequency spectrum of the sensor with a loop antenna, humidity, temperature, as well as CO₂ , O₂ and NH₃ concentrations can be determined, enabling applications such as remotely monitoring conditions inside opaque, sealed containers. Experimental results show the sensor response to CO₂ and O₂ is both linear and reversible. Both irreversible and reversible responses are observed in response to NH₃, indicating both physisorption and chemisorption of NH₃ by the carbon nanotubes. A sensor array, comprised of an uncoated, SiO₂ coated, and MWNT-SiO₂ coated sensor, enables CO₂ measurement to be automatically calibrated for operation in a variable humidity and temperature environment     

Nonlinear performance analysis of forced carbon nanotube-based bio-mass sensors

International Journal of Mechanics and Materials in Design - In this effort, an analytical solution is proposed for the large amplitude nonlinear vibrations of doubly clamped carbon nanotube...     

Continuous production of flexible carbon nanotube-based transparent conductive films

Abstract

This work shows a simple, single-stage, scalable method for the continuous production of high-quality carbon nanotube-polymer transparent conductive films from carbon feedstock. Besides the ease of scalability, a particular advantage of this process is that the concentration of nanotubes in the films, and thus transparency and conductivity, can be adjusted by changing simple process parameters. Therefore, films can be readily prepared for any application desired, ranging from solar cells to flat panel displays. Our best results show a surface resistivity of the order of 300 Ω square^-1 for a film with 80% transparency, which is promising at this early stage of process development.     

Performance of multi-walled carbon nanotube-based nanofluid in turning operation

This paper evaluates the performance of nanofluid using multi-walled carbon nanotubes (MWCNT) in distilled water and sodium dodecyl sulfate surfactant for turning operation on EN 31 material. Turning was performed without any fluid, with conventional, mineral oil–based cutting fluid, and with nanofluid. The flow rates of both fluids were limited to 1?L/h and these fluids were applied at the tool tip through gravity feed. Cutting forces, wear on tool, and surface finish on workpiece were measured as responses while turning under the three conditions. The responses obtained in three different conditions of turning are then compared. It is found that application of MWCNT-based nanofluid resulted in 49% and 30% lesser tool wear than machining without any fluid and machining with mineral oil–based fluid, respectively. The use of nanofluid also resulted in 5–8% lesser cutting force and 9–22% better surface finish of the workpiece as compared with conventional cutting fluid. Thus, MWCNT-based nanofluid performed better than the conventional, oil-based cutting fluid for turning of EN 31 bars.     

Continuous production of flexible carbon nanotube-based transparent conductive films

This work shows a simple, single-stage, scalable method for the continuous production of high-quality carbon nanotube-polymer transparent conductive films from carbon feedstock. Besides the ease of scalability, a particular advantage of this process is that the concentration of nanotubes in the films, and thus transparency and conductivity, can be adjusted by changing simple process parameters. Therefore, films can be readily prepared for any application desired, ranging from solar cells to flat panel displays. Our best results show a surface resistivity of the order of 300 Ω square^-1 for a film with 80% transparency, which is promising at this early stage of process development.     

Highly conductive carbon nanotube buckypapers with improved doping stability via conjugational cross-linking

Carbon nanotube (CNT) sheets or buckypapers have demonstrated promising electrical conductivity and mechanical performance. However, their electrical conductivity is still far below the requirements for engineering applications, such as using as a substitute for copper mesh, which is currently used in composite aircraft structures for lightning strike protection. In this study, different CNT buckypapers were stretched to increase their alignment, and then subjected to conjugational cross-linking via chemical functionalization. The conjugationally cross-linked buckypapers (CCL-BPs) demonstrated higher electrical conductivity of up to 6200?S?cm( - 1), which is more than one order increase compared to the pristine buckypapers. The CCL-BPs also showed excellent doping stability in over 300?h in atmosphere and were resistant to degradation at elevated temperatures. The tensile strength of the stretched CCL-BPs reached 220?MPa, which is about three times that of pristine buckypapers. We attribute these property improvements to the effective and stable conjugational cross-links of CNTs, which can simultaneously improve the electrical conductivity, doping stability and mechanical properties. Specifically, the electrical conductivity increase resulted from improving the CNT alignment and inter-tube electron transport capability. The conjugational cross-links provide effective 3D conductive paths to increase the mobility of electrons among individual nanotubes. The stable covalent bonding also enhances the thermal stability and load transfer. The significant electrical and mechanical property improvement renders buckypaper a multifunctional material for various applications, such as conducting composites, battery electrodes, capacitors, etc.     

Emitter spacing effects on field emission properties of laser-treated single-walled carbon nanotube buckypapers

Carbon nanotube (CNT) emitters on buckypaper were activated by laser treatment and their field emission properties were investigated. The pristine buckypapers and CNT emitters' height, diameter, and spacing were characterized through optical analysis. The emitter spacing directly impacted the emission results when the laser power and treatment times were fixed. The increasing emitter density increased the enhanced field emission current and luminance. However, a continuous and excessive increase of emitter density with spacing reduction generated the screening effect. As a result, the extended screening effect from the smaller spacing eventually crippled the field emission effectiveness. Luminance intensity and uniformity of field emission suggest that the highly effective buckypaper will have a density of 2500 emission spots cm(-2), which presents an effective field enhancement factor of 3721 and a moderated screening effect of 0.005. Proper laser treatment is an effective post-treatment process for optimizing field emission, luminance, and durability performance for buckypaper cold cathodes.