Development of CNT-ISFET based pH sensing system using atomic force microscopy

In recent years, there has been an increasing interest in the monitoring and controlling of pH. It has become an important aspect of many industrial wastewater treatment processes as well as a drinking water quality issue. At the same time, the demand for smaller electronic devices used for various industrial and commercial applications has greatly increased. Nanomaterials such as Carbon Nanotubes (CNTs) are well known for their excellent electrical, mechanical, and thermal properties. Therefore, CNTs are good candidates for the manufacturing of small devices. In this paper, a novel concept combining CNT and Ion Sensitive Field Effect Transistor (ISFET) is proposed for pH-sensing application. Atomic Force Microscope (AFM) based manipulation and electrical property measurements in nano level are involved. Nanochannels are created by AFM-based nanoscratching, and the electrical properties of both multi-walled and single-walled CNTs are tested using Current Sensing AFM. FETs are fabricated to test the possibility of the CNTs’ alignment between the source and the drain electrode using Dielectrophoresis (DEP). The experimental results reveal that CNT is a promising material for improving the performance and lowering the cost of existing pH chemical sensors.     

Design and Evaluation of a Carbon Nanotube-Based Programmable Architecture

In the hunt to find a replacement to CMOS, material scientists are developing a wide range of nanomaterials and nanomaterial-based devices that offer significant performance improvements. One example is the Carbon Nanotube Field Effect Transistor, or CNFET, which replaces the traditional silicon channel with an array of semiconducting carbon nanotubes (CNTs). Given the increased variation and defects of nanometer-scale fabrication, and the regular nature of bottom-up self-assembly, field programmable devices are a promising initial application for such technologies. In this paper, we detail the design and evaluation of a novel nanomaterial-based architecture called FPCNA (Field Programmable Carbon Nanotube Array). New nanomaterial-based circuit building blocks are developed and characterized, including a lookup table created entirely from continuous CNT ribbons. To accurately determine the performance of these building blocks, we create variation-aware physical design tools with statistical timing analysis that can handle both Gaussian and non-Gaussian random variables. When the FPCNA architecture is evaluated using this CAD flow, we see a 2.75× performance improvement over an equivalent CMOS FPGA at a 95% yield. In addition, FPCNA offers a 5.07× footprint reduction compared to the baseline FPGA.     

碳纳米管制备及其复合材料导热性能研究进展

随着高集成、高功率电子器件的飞速发展,电子器件对高导热材料需求更加迫切。碳纳米管 因具有独特的一维纳米结构,同时兼具优异的导热、导电和机械性能等,近年来备受国内外科研工作 者广泛的研究关注。该文主要介绍了碳纳米管的 3 种制备方法：石墨电弧法、化学气相沉积法和激光 蒸发法,同时阐述了碳纳米管导热基本机理以及碳纳米管应用于复合材料热传导性能研究,并对碳纳 米管在进一步导热研究中进行了展望。     

Water transport through (7,7) carbon nanotubes of different lengths using molecular dynamics

Non-equilibrium molecular dynamics simulations are used to investigate water transport through (7,7) CNTs, examining how changing the CNT length affects the internal flow dynamics. Pressure-driven water flow through CNT lengths ranging from 2.5 to 50?nm is simulated. We show that under the same applied pressure difference an increase in CNT length has a negligible effect on the resulting mass flow rate and fluid flow velocity. Flow enhancements over hydrodynamic expectations are directly proportional to the CNT length. Axial profiles of fluid properties demonstrate that entrance and exit effects are significant in the transport of water along CNTs. Large viscous losses in these entrance/exit regions lead into central “developed” regions in longer CNTs where the flow is effectively frictionless.     

Gas sensing properties of platinum derivatives of single-walled carbon nanotubes: A DFT analysis

The limitations of intrinsic carbon nanotube (CNT) based devices to examine toxic gases motivate us to investigate novel sensors which can possibly overcome sensitivity problems. Pt–CNT assemblies (with Pt deposited externally as well as internally Pt-doped ones) interacting with NO₂ and NH₃ are studied and compared with unmodified CNTs. DFT calculations show that Pt can enhance adsorption and charge transfer processes to a very large degree. Incoming gas molecules cause changes in the electronic structure and charge distribution of the Pt-substituted CNTs that are both larger and more far-reaching than in their unmodified counterparts. Their relatively high stability is unaffected by the complexation with NO₂ and NH₃. CNTs with defective surface were also investigated. The sensing performance of Pt-doped CNT is found to be superior to defected CNTs.     

Numerical processing of CNT arrays using 3D image processing of SEM images

This paper outlines an image processing based technique to characterize carbon nanotube (CNT) array devices for enhanced cell transfection. Investigating how manufacturing parameters affects CNT array geometry, and how geometry affects transfection, requires the arrays to be measured. Obtaining a statistically sufficient number of measurements by hand is tedious and subject to human error. An automated system to characterize the arrays facilitates data collection of numerous pore properties. Scanning electron microscopy (SEM) micrographs are pre-processed to identify the location of CNTs which are then measured individually to obtain their characteristics. The data from single pores is aggregated to generate a numerical summary of the array parameters. Stereomicroscopy techniques are used to measure the heights of the CNTs using pairs of tilted images. The overall technique accurately measures the parameters relevant to cell transfection significantly faster than manual measurements while eliminating human error and bias.     

Performance of nanocomposites stacked with carbon nanotubes and Nafion films

Nanocomposites stacked layer-by-layer with carbon nanotubes (CNTs), referred to as CNT–Nafion?, are prepared using a spray and reproducible spin-cast deposition methodology. The CNTs used for the nanocomposite film were cylindrical with diameters in the range of 10–15 nm and lengths of up to several micrometers. The CNTs had a high purity of more than 95%. CNT–Nafion? nanocomposites with uniformly spray-coated CNTs provide sufficiently high electrical conductivity throughout, and show enhanced mechanical strength due to laterally aligned CNTs between each interface of the spin-coated Nafion film. Our results indicate that such a layer-by-layer film composed of CNTs and Nafion? is suitable for potential transducer applications at the microscale.     

The effect of protonation of cytosine and adenine on their interactions with carbon nanotubes

Placing electrical charges on nanomaterials is a means to extend their functional capabilities in nanoelectronics and sensoring applications. This paper explores the effect of charging nitrogen bases cytosine (Cyt) and adenine (Ade) via protonation on their noncovalent interaction with carbon nanotubes (CNT) using quantum chemical calculations performed at the M05-2X/6-31++G** level of theory alongside with a molecular graphics method. It is shown that the protonation of the bases causes threefold increase of the interaction energy in the CNT·Cyt·H⁺ and СNT·Ade·H⁺ complexes as compared to the CNT complexes formed with neutral bases. There is also some shortening of the base-CNT distance by ca 0.13 Ǻ. The visualization of the electrostatic potential distribution with the molecular graphics reveals that the positive potential due to the protonated bases extends to a cylindrical domain of the nanotube segment adjacent to the base binding site. Furthermore, subtraction of the electrostatic potential maps of the protonated bases from the maps of their complexes with CNTs reveals an area of negative potential on the CNT surface, which reflects the location of the adsorbed base. The positive charge transfer of ca 0.3 e from the protonated bases to the CNT strengthens the interaction in the CNT·Cyt·H⁺ and СNT·Ade·H⁺ complexes. The analysis of the frontier orbitals shows that the LUMOs of the complexes mainly reside on the CNT, while the HOMOs spread over both components of each complex. The observed effects may facilitate the design of nanomaterials involving nitrogen bases and CNTs.     

Batch welding of aligned carbon nanotube onto metal electrodes

A novel batch welding of aligned carbon nanotubes (CNTs) onto metallic electrodes is developed by radio frequency induction heating. The experiments had achieved optimum contact between CNTs and metal electrodes, two hundred samples had the same trend of reduction of contact resistance after heating process, and this reduction was irreversible, which demonstrated good reproducibility of induction heating for CNT welding. Because of its non-contact and selective heating, induction heating provide a potential approach to reproducible large-scale fabrication and wide applications of CNTs devices.     

A new numerical approach for low velocity impact response of multiscale-reinforced nanocomposite plates

In this paper, the low velocity impact analysis of carbon nanotube (CNT)/carbon fiber (CF)-reinforced hybrid nanocomposite plates is presented using variational differential quadrature (VDQ) method due to its numerical essence and the framework of implementation. The hybrid nanocomposite plate deformation is formulated based on classical plate theory and the contact force between the plate and projectile is estimated using Hertzian contact law. Also, a new micromechanics approach is presented to calculate the effective mechanical properties of the CNT/CF polymer hybrid nanocomposites. Five important factors including, random orientation and random distribution of CNTs, CNT/polymer interphase region, waviness and transversely isotropic behavior of CNT are incorporated in the micromechanical analysis. The accuracy of the present approach is verified with the available open literature results showing a clear agreement. The effects of various factors such as volume fraction and non-straight shape of CNT, CNT/polymer interphase region, CF volume fraction, random and regular arrangement of CFs, plate geometrical parameters and impactor velocity on the low velocity impact behavior of the CNT/CF-reinforced hybrid nanocomposite plates are studied.

     

Estimation of average contact number of carbon nanotubes (CNTs) in polymer nanocomposites to optimize the electrical conductivity

The present paper suggests an equation for the average contact number of carbon nanotubes (CNTs) in CNT-reinforced polymer nanocomposites (PCNT) by two developed equations for electrical conductivity. Several novel parameters in PCNT such as CNT size, CNT concentration, network fraction, interphase depth, tunneling effect, and CNT wettability by the polymer medium are considered to define the average contact number (m). “m” is calculated for some samples and the variation of “m” is explored over a range of parameters’ values. The results show that dense interphase, high fraction of networked CNTs, reedy and short CNTs, low CNT surface energy, high polymer surface energy, low tunneling distance, and small contact diameter increase the “m” improving the conductivity. Moreover, tunneling distance and CNT contact diameter have the greatest effects on the “m”. The optimized level for “m” is necessary to control the nanocomposite’s conductivity.

     

A simplified approach for heat conduction analysis of CNT-based nano-composites

The unique thermal properties of carbon nanotubes (CNT) may offer possibilities for the development of fundamentally new composite materials. Numerical simulation for such CNT-based composites usually demands extremely large and expensive computer resources. In preliminary computations, temperature distribution in the CNT has been turned out to be almost uniform, due to its exceptionally high heat conductivity in comparison with the host polymer. This feature allows us to considerably simplify the mathematical model of the heat conduction in CNT composites. In the proposed approach, the host polymer is the only domain which is modeled, while the CNTs are treated as heat superconductors with constant and unknown temperatures constrained at their surfaces. As a result, the computational scale is reduced substantially. The hybrid boundary node method is applied in this study. Numerical examples clearly demonstrate the efficiency and sufficient accuracy of the proposed approach.     

Large‐area FEDs with carbon‐nanotube field emitter

Abstract— Application of carbon nanotubes (CNTs) as field emitters for large‐area FED panels is described. In 1998, we presented the first experimental devices: light‐source tubes for outdoor large‐area displays and a diode‐type flat‐panel display, both with screen‐printed CNT cathodes. The fisrt practical high‐luminance color CNT‐FED panel was built in 1999. It employed the new triode‐structure panel was x‐y addressable. The CNT‐FED structure was further optimized for large‐area display panels by improving the luminous uniformity. This paper also describes the design and performance of a new, experimental, 40‐in.‐diagonal panel, which showed that the CNT‐FED technology is suitable for use in large‐area displays.     

Lumped modeling of carbon nanotubes for M/NEMS simulation

This paper presents a lumped model of a single walled carbon nanotube (CNT) using structural matrix mechanics. We implement the CNT model in Sugar and SugarCube to facilitate the design, modeling and simulation of combined micro and nano-scale systems. That is, where users can explore the application of CNTs as components of an electromechanical system. Our lumped CNT model is able to represent the dynamic response of a zigzag or armchair chirality, with the desired diameter, length, and distributed loading parameters. Our present dynamic CNT model is limited to small deflections and user-defined geometric properties. Our tools are accessible through the Web with remote computation at http://www.nanoHUB.org.     

Parameter Identification and Adaptive Control Of Carbon Nanotube Resonators

In this paper, we exploit an adaptive control scheme to adjust highly sensitive oscillations of fluid conveying carbon nanotube (CNT) resonators. Firstly, we focus on the nonlinear vibrations of the fluid conveying CNTs, considering an added mass using nonlocal Euler‐Bernoulli beam theory. CNT rests on nonlinear Winkler and Pasternak foundations. We use the Galerkin method to extract the nonlinear ordinary differential equation models of the CNT oscillations. We elicit a linear parametric model for estimating the added mass and other parameters of the system. Numerical simulations delineate that the developed model has sensitivity to added mass at the yoctogram level. It is known that CNT vibrations are very sensitive to small perturbations. Accordingly, a small perturbation results in significantly abrupt changes in the vibrational parameters of the targeted system. For that reason, it is crucial to have a potent apparatus for identifying the system parameters in case of sudden changes in the vibrational parameters. For such parameter identification, a least squares (LS) parameter identification algorithm and an extended Luenberger observer are integrated to a pole placement controller for online estimation of the system parameters as well as vibration control of the objective system. It is well‐known that CNTs are potentially ideal atomic force microscopy (AFM) probes, and accordingly, the proposed method is potentially beneficial for identifying highly sensitive motions in AFM. In addition, numerical simulations are presented, showing that the proposed adaptive controller has the potential to be used for vibration control of the CNT resonators even in the case of chaotic motions.     

Suspension‐deposited carbon‐nanotube networks for flexible active‐matrix displays

Abstract— The unique properties of carbon nanotubes (CNTs) promise innovative solutions for a variety of display applications. The CNTs can be deposited from suspension. These simple and low‐cost techniques will replace time‐consuming and costly vacuum processes and can be applied to large‐area glass and flexible substrates. Single‐walled carbon nanotubes (SWNTs) have been used as conducting and transparent layers, replacing the brittle ITO, and as the semiconducting layer in thin‐film transistors (TFTs). There is no need for alignment because a CNT network is used instead of single CNTs. Both processes can be applied to glass and to flexible plastic substrates. The transparent and conductive nanotube layers can be produced with a sheet resistance of 400 Ω/□ at 80% transmittance. Such layers have been used to produce directly addressed liquid‐crystal displays and organic light‐emitting diodes (OLED). The CNT‐TFTs reach on/off ratios of more than 10⁵ and effective charge‐carrier mobilities of 1 cm²/V‐sec and above.     

Vapor sensing properties of thermoplastic polyurethane multifilament covered with carbon nanotube networks

The volatile organic compound (VOC) vapor sensing properties of a novel kind of thermoplastic polyurethane multifilament - carbon nanotubes (TPU-CNTs) composites is studied. And the sensing is based on changes in the electrical resistance of the composites due to vapor contact. The composites were readily obtained by adhering CNTs on the surface layer of TPU by means of simply immersing pure TPU multifilament into CNT dispersion. The uniformly formed nanotube networks on the outer layer of composite multifilament are favorable for providing efficient conductive pathways. The resulting TPU-CNTs composites show good reproducibility and fast response (within seconds) of electrical resistance change in cyclic exposure to diluted VOC and pure dry air. The vapor sensing behaviors of the composites are related to CNT content, vapor concentration, and polar solubility parameters of the target vapors. A relatively low vapor concentration of 0.5% is detectable, and a maximum relative resistance change of 900% is obtained for the composite with 0.8 wt.% CNT loading when sensing 7.0% chloroform. It is proposed that both the disconnection of CNT networks caused by swelling effects of the TPU matrix and the adsorption of VOC molecules on the CNTs are responsible for the vapor sensing behavior of TPU-CNTs composite, while the former effect plays the major role.     

Application of the Green function method to flow-thermoelastic forced vibration analysis of viscoelastic carbon nanotubes

In this paper, the Green function method (GFM) is implemented for forced vibration analysis of carbon nanotubes (CNTs) conveying fluid in thermal environment. The Eringen’s nonlocal elasticity theory is used to take into account the size effect of CNT with modeling the CNT wall–fluid flow interaction by means of slip boundary condition and Knudsen number (Kn). The derived governing differential equations are solved by GFM which demonstrated to have high precision and computational efficiency in the vibration analysis of CNTs. The validity of the present analytical solution is confirmed by comparing the results with those reported in other literature, and good agreement is observed. The analytical examinations are accomplished, while the emphasis is placed on considering the influences of nonlocal parameter, boundary conditions, temperature change, structural damping of the CNT, Knudsen number, fluid velocity and visco-Pasternak foundation on the dynamic deflection response of the fluid-conveying CNTs in detail.     

A novel technique for fabrication of micro- and nanofluidic device with embedded single carbon nanotube

This paper describes a novel technique for fabrication of micro- and nanofluidic device that consists of a carbon nanotube (CNT) and a polydimethylsiloxane (PDMS) microchannel. Single CNT was placed at desired locations using dielectrophoresis (DEP) and PDMS microchannel was constructed on the aligned CNT via photolithography and soft lithography techniques. This technique enables a CNT to be seamlessly embedded in a PDMS microchannel. Moreover, controlling the PDMS curing condition enables the construction of the device with or without a CNT (the device without CNT has a trace nanochannel in PDMS). Preliminary flow tests such as capillary effect and pressure-driven flow were performed with the fabricated devices. In the capillary effect tests, the flow stopped at the nanochannel in both devices. In the pressure-driven flow lower flow resistance was observed in the device with a CNT.     

Carbon‐nanotube film on plastic as transparent electrode for resistive touch screens

Abstract— Carbon‐nanotube (CNT) films on plastic are incorporated as the touch electrode in a four‐wire resistive touch panel. Single‐point actuation tests show superior mechanical performance to ITO touch electrodes, with no loss of device functionality up to 3 million actuations. Sliding‐stylus‐pen tests reveal no loss of device linearity after 1 million stylus cycles. A CNT refractive index of ～1.55 leads to CNT touch panels with low reflection (<9% over the visible range) without costly anti‐reflective coatings. CNT films on PET currently have 86% total transmission (including the PET) over the visible and 600 Ω/□, with lab scale tests giving 88% at 500 Ω/□. CNT films are neutrally colored (a^* ～ 0, b^* ～ 1.5), low haze (<1%), uniform, and both chemically and environmentally stable. Unidym's solution‐based coatings can be printed directly onto both flexible and rigid polycarbonate using solution coating processes. Unidym films can be patterned using subtractive methods such as laser ablation with resolution down to 10 μm, or additive methods such as patterned gravure. CNTs are grown, purified, formulated into inks, and coated using scalable processes, allowing films to be attractive from a cost perspective as well.