Damages of screen-printed carbon nanotube cold cathode during the field emission process

The field emission properties of the screen-printed carbon nanotube (CNT) composite cathode have close relationship with its microstructure. In this study, carbon nanotube composite cold cathode with ZnO nano-particles as binding material was prepared using screen-printing method. Electric field cycles were used to post-treat the carbon nanotube composite cold cathode. During the process of electric field cycle treatment, obvious heat-induced damages were observed from the cathode. Scanning electron microscope and transmission electron microscope were employed to analyze the morphology and microstructure of the cathode. The possible mechanisms responsible for damages were discussed.     

Predictive carbon nanotube models using the eigenvector dimension reduction (EDR) method

It has been reported that a carbon nanotube (CNT) is one of the strongest materials with its high failure stress and strain. Moreover, the nanotube has many favorable features, such as high toughness, great flexibility, low density, and so on. This discovery has opened new opportunities in various engineering applications, for example, a nanocomposite material design. However, recent studies have found a substantial discrepancy between computational and experimental material property predictions, in part due to defects in the fabricated nanotubes. It is found that the nanotubes are highly defective in many different formations (e.g., vacancy, dislocation, chemical, and topological defects). Recent parametric studies with vacancy defects have found that the vacancy defects substantially affect mechanical properties of the nanotubes. Given random existence of the nanotube defects, the material properties of the nanotubes can be better understood through statistical modeling of the defects. This paper presents predictive CNT models, which enable to estimate mechanical properties of the CNTs and the nanocomposites under various sources of uncertainties. As the first step, the density and location of vacancy defects will be randomly modeled to predict mechanical properties. It has been reported that the eigenvector dimension reduction (EDR) method performs probability analysis efficiently and accurately. In this paper, molecular dynamics (MD) simulation with a modified Morse potential model is integrated with the EDR method to predict the mechanical properties of the CNTs. To demonstrate the feasibility of the predicted model, probabilistic behavior of mechanical properties (e.g., failure stress, failure strain, and toughness) is compared with the precedent experiment results.     

Eshelby-Mori-Tanaka approach for vibrational behavior of functionally graded carbon nanotube-reinforced plate resting on elastic foundation

In this study, based on the three-dimensional theory of elasticity, free vibration characteristics of functionally graded (FG) nanocomposite plates reinforced by randomly-oriented straight single-walled carbon nanotubes (SWCNTs) resting on an elastic foundation are considered. Material properties are graded in the thickness direction of the plate according to the volume fraction power law distribution. An embedded carbon nanotube (CNT) in a polymer matrix and its surrounding inter-phase which is perfectly bonded to surrounding resin is replaced with an equivalent fiber to predict the mechanical properties of the carbon nanotube/polymer composite. The Mori-Tanaka approach is employed to calculate the effective elastic moduli of the plate. The natural frequencies of the plate are obtained by means of the generalized differential quadrature (GDQ) method. Detailed parametric studies have been carried out to investigate the influences of the CNT volume fraction, Winkler foundation modulus, shear elastic foundation modulus and various geometrical parameters on the vibration behavior of the functionally graded carbon nanotube-reinforced (FG-CNTR) plates.     

Measurement of residual stress in thick section composite laminates using the deep-hole method

The deep-hole method is a method of measuring residual stress in large metallic components. In this paper, an extension to the deep-hole method is described to allow the residual stresses in thick section composite laminated plates to be evaluated. The method involves first drilling a small hole through the laminate perpendicular to the surface. The material around the hole is then machined away, resulting in a change in diameter of the hole due to the release of residual stress. This change in diameter is measured and used to calculate the residual stress. The calculation requires the evaluation of coefficients that depend on the properties of the composite. In this work, the finite element method is used to evaluate these coefficients. Using this method, the residual stresses in a 22 mm thick carbon/epoxy composite plate are measured and reported.     

Application of response surface methodology in the optimization of laser treatment in buckypaper lighting for field emission displays

Carbon nanotube field emission backlight (CNT-BLU) is promising to replace traditional backlighting devices in liquid crystal display (LCD) industry. This study reports a laser irradiation process to enhance field emission properties of buckypaper, a thin sheet of high-loading carbon nanotube network. The scanning laser treated the selected region of buckypaper to activate CNT emitters. The improvement of phosphorescence luminance intensity, uniformity, and the reduction of turn-on field were achieved by adjusting machining parameters of laser power, laser lens motion speed, laser resolution, laser beam size, and pattern orientation. Design of experiment and response surface methodology provided ways to rapidly search the feasible laser parameter setting for processing buckypaper field emitters and improving field emission properties within fewer experimental runs. 2^5?1 Fractional fracotrial design presented the initial models of five repsponses. In addition, the face-centered central composite design is applied since the 2^5?1 factional factorial design showed curvature significance. It assisted to give the scientifical insight of the following conclusions. High-energy laser treatment damages and burns the CNTs into carbon oxide materials; furthermore, it loses the effective CNTs. Low-energy laser treatment performs CNT activation and produced low field emission performance. In this study, we succeeded to apply statistical analysis methods to understand the physics and mechanics of laser-activated buckypaper field emission and, furthermore, improve, optimize, and demonstrate performance by material selection, process development, and characterization.     

Dry friction and wear characteristics of nickel/carbon nanotube electroless composite deposits

Ni/carbon nanotube (Ni/CNTs) composite coatings were deposited on carbon steel plate by electroless deposition. The friction and wear properties were examined under dry sliding conditions using the ball-on-disk configuration. For reference, carbon steel plate was coated with Ni, Ni/SiC and Ni/graphite. The results show that the Ni/CNT coating has a microhardness value of 865 Hv, greater than for SiC reinforced composite deposits. The Ni/CNTs composite coating possesses not only a higher wear resistance but also a lower friction coefficient, resulting from their improved mechanical characteristics and the unique topological structure of the hollow nanotubes.     

Mechanics of single-walled carbon nanotubes inside open single-walled carbon nanocones

This study investigates the mechanical characteristics of single-walled carbon nanotubes (CNTs) inside open single-walled carbon nanocones (CNCs). New semi-analytical expressions are presented to evaluate van der Waals (vdW) interactions between CNTs and open CNCs. Continuum approximation, along with the the Lennard-Jones (LJ) potential function, is used in this study. The effects of geometrical parameters on alterations in vdW potential energy and the interaction force are extensively examined for the concentric CNT-open CNC configuration. The CNT is assumed to enter the nanocone either through the small end or the wide end of the cone. The preferred position of the CNT with respect to the nanocone axis is fully investigated for various geometrical parameters. The optimum nanotube radius minimizing the total potential energy of the concentric configuration is determined for different radii of the small end of the cone. The examined configuration generates asymmetric oscillation; thus, the system constitutes a nano-oscillator.     

Ionization gauge by carbon nanotube field emission

A newly developed ionization gauge using carbon nanotube (CNT) field emission effect has been designed and manufactured. The fabricated ionization gauge is of a triode type, consisting of a cathode (carbon nanotube field emitter arrays), a grid and a collector. The principle involved here is that for a constant number of electrons available for ionization emitted from carbon nanotube arrays by the grid potential, a constant fraction of gas will be ionized and the number of ions collected in the collector will be proportional to the number of gas molecules in the chamber traversed by the electrons. Due to the excellent field emission characteristics of CNT, it is possible to make a cost effective cold cathode ionization gauge. A screen-printing method has been used to make the CNT cathode. The glass grid with Cr deposited by E-beam has been put on the cathode with a gap of 200 μm between the two electrodes. Using the voltage applied to the grid, the electrons emitted from the carbon nanotube ionize gas molecules in the chamber and the ionized molecules are gathered in the collector. At this time, the collector voltage is maintained at a lower level than that of the grid voltage to obtain a large ionization ratio. The current detected in the collector is proportional to the pressure in the chamber. The ionization characteristics are dependent on the gas and the voltage applied to the grid and collector. In this paper we have shown the various metrological characteristics of the simple pressure sensor utilizing carbon nanotube.     

溶胶-凝胶法制备碳纳米管/SiO_2复合材料过程的TG-DSC-MS研究

利用热重 -差示扫描量热 -质谱 ( TG-DSC-MS)联用技术对溶胶 -凝胶 ( Sol-Gel)法热压烧结制备碳纳米管 ( CNT) /Si O2 复合材料过程中的热分解行为特性进行了表征研究。采用多离子检测模式预定测量热分解生成的 C+ ( m/z1 2 )、OH+ ( m/z1 7)、H2 O+ ( m/z1 8)、CO2 + ( m/z2 8)等 9种正离子。实验发现 :用溶胶 -凝胶法制备 CNT/Si O2 复合材料过程中 ,在 5 0 0℃以下生成 Si O2 ,CNT在 5 0 0～ 73 0℃左右氧化燃烧。在 5 0 0℃条件下煅烧 1 h,凝胶 Si O2 完全转变成玻璃粉。选择在 5 0 0℃条件下煅烧 CNT/Si O2 复合粉体 1 h可作为CNT/Si O2 复合材料的煅烧工艺     

单壁碳纳米管与石墨基底间摩擦的模拟研究

采用分子动力学模拟方法研究了常温300 K时,公度、不公度情况下,单壁碳纳米管CNT(10,10)在石墨基底上的运动、摩擦行为。计算中首先使碳纳米管在基底上弛豫平衡,而后施加持续时间500 fs的固定外力,撤去外力后碳纳米管在基底上减速至相对基底静止。结果表明,碳纳米管在石墨基底上不同的放置位置决定了它与基底接触面的微观构型,从而决定了碳纳米管的运动、摩擦规律。公度时,碳纳米管先在基底上滑动,摩擦力、平动能均呈现周期性起伏,之后碳纳米管在基底上滚动、滑动、翻转,滑动、转动之间运动形式的转变提高了能量耗散,增大了摩擦力,非公度时摩擦力约为公度时的70%。非公度时碳纳米管一直在基底上滑动,平动能和摩擦力不具有周期性。     

Tribological properties of carbon nanotube-doped carbon/carbon composites

Carbon nanotube (CNT)-doped carbon/carbon (C/C) composites were fabricated by the chemical vapor infiltration (CVI) method to investigate the effect of CNTs on tribological properties of C/C composites. CNTs, which had been synthesized by catalytic pyrolysis of hydrocarbons, were added to carbon fiber formed preforms before CVI process. Ring-on-block-type wear tests were performed to evaluate the frictional properties of CNT-doped C/C composites. Results show that CNTs can not only increase wear resistance of C/C composites but also maintain stable friction coefficients under different loads. Polarized light microscopy, X-ray diffraction, scanning electron microscopy and Raman spectroscopy analyses demonstrate that favorable effects of CNTs on tribological properties of C/C composites have been achieved indirectly by altering microstructure of pyrocarbons and directly by serving as high-strength lubricative frictional media at the same time. Electron dispersive spectroscopy (EDS) analyses verify the existence of adhesive wear mechanism in both pure C/C composites and CNT-doped C/C composites albeit the two-body abrasive mechanism dominates in pure C/C composites.     

The effect of CNT volume fraction on the magneto-thermo-electro-mechanical behavior of smart nanocomposite cylinder

In this article, using analytical approach, the stress analysis of a long piezoelectric polymeric hollow cylinder reinforced with carbon nanotube (CNT) under combined magneto-thermo-electro-mechanical loading is investigated. Considering three combined loading conditions such as pressure-electric, pressure-electric magnetic and pressure-electric thermal, the governing equation of the problem is obtained. The rule of mixture and modified multiscale bridging model are used to predict effective properties of nanocomposite. The magneto-thermo-electro-mechanical stresses in hollow cylinder are discussed in detail. It can be concluded that increasing CNT volume fraction enhances strength of the nanocomposite cylinder. The results of this work could be useful in view of optimum design of the smart nanocomposite cylinder under magneto-thermo-electro-mechanical loadings and could also be as a reference for future related works.     

In situ synthesis of carbon nanotubes on heated scanning probes using dip pen techniques

Carbon nanotubes (CNT) were synthesized on heated scanning probes and under ambient conditions without requiring Chemical vapor deposition (CVD) apparatus or process gases. In this study, dip pen nanolithography (DPN) techniques were utilized for deposition of catalyst precursors on the scanning probe tips in the form of aqueous solution of metal salts--prior to the synthesis of the CNT. A layer of fullerene (C(60)) of approximately 200 nm thickness was vapor deposited on the scanning probe tip prior to the deposition of the metal catalyst. During the in situ synthesis of the CNT on the scanning probes, the temperature of the heated scanning probes reached 350-400 degrees C. Hence the scanning probes were heated in an inert atmosphere to prevent potential oxidation of the deposited fullerene layer. The synthesized CNTs were subsequently characterized using SEM and Raman spectroscopy. The Raman spectroscopy showed peaks in the Radial breathing mode (RBM), as well as the defect (D) and graphitic (G) bands. The RBM peaks indicate that the single walled carbon nanotube (SWCNT) ranged in diameter from 0.9-1.5 nm. The peaks in the Raman spectra are indicative of SWCNT mixtures (metallic and semconducting) and possibly multiwalled carbon nanotube (MWCNT). Hence this process can be optimized to synthesize SWCNT of a specific chirality (metallic or semiconducting). This study differs from an earlier study reported in the literature involving synthesis of CNT on scanning probes where the process temperatures typically exceeded 700 degrees C, and resulted in synthesis of highly graphitic MWCNT (Sunden, et al., 2006).     

Role of Carbon Nanotube Tribolayer Formation on Low Friction and Adhesion of Aluminum Alloys Sliding against CrN

This work investigates the role of carbon nanotube (CNT) tribolayer formation in reducing friction and adhesion of an Al-alloy engine block material (Al-6.5% Si, 319 Al) sliding against a common piston ring coating, namely, CrN coated steel, when tested under a boundary lubricated condition. Coefficient of friction (COF) values were determined using pin-on-disk type tests as a function of sliding distance using CNT added to ethanol and ethanol without CNT addition. Boundary lubricated tests that used ethanol with 0.14 wt.% CNT resulted in a steady-state COF of 0.16, and reduced Al adhesion to the CrN due to the formation of CNT tribolayers on the Al-alloy contact surfaces. Raman spectroscopy and high resolution SEM suggested the CNT fibers in the tribolayers were damaged and possibly subjected to plastic deformation, and the carbon bonds were possibly passivated by the -H and -OH dissociated from ethanol as suggested by FTIR. The low friction and adhesion observed when ethanol with 0.14 wt.% CNT was used was attributed to the sliding-induced bending and curling of the CNT tribolayers, leading to the formation of rolled sections of tribolayer with a cylindrical morphology (diameter of ~?1 µm) that reduced direct contact between Al-alloy and CrN surfaces.     

Modeling of interfacial friction damping of carbon nanotube-based nanocomposites

Carbon nanotube-based composite is becoming increasingly popular and offers great potential for highly demanding practical high strength and high damping applications. The excellent damping capacity of CNTs is primarily due to the interfacial friction between carbon nanotubes and polymer resins and the extremely large interfacial surface area over a given specific mass (specific area). In this paper, damping characteristics of carbon nanotube-based composites have been investigated, with an objective of developing an effective and accurate analytical model, which can be used as a design tool for the damping design of such materials. Based on the interfacial slips between the resin and nanotubes and between the nanotubes themselves, a micro stick-slip damping model has been developed. Such a physically derived model is believed to be appropriate and representative of the actual complex damping mechanism of the material system. The model, developed for the first time, is analytical and relates explicitly the material properties of the resin and nanotubes and the processing parameters to the overall material damping loss factor and hence it offers the possibility for material engineers to possibly optimize the damping for required applications. Due to the nonlinear force–displacement relationship derived under the micro stick-slip, a harmonic linearization method, the Describing Function method, has been employed to analyse its vibration characteristics and to derive the required damping loss factors. From the analytical formula, it can be seen that the damping loss factor of the material system depends on the individual material properties of the resin and the nanotubes, structural deformation, nanotube volume fraction and the critical shear stresses at which interfacial slips take place. By taking careful considerations of these design parameters, optimized carbon nanotube-based composites for advanced damping applications can be developed.Extensive numerical simulations have been carried out to establish the practical applicability of the proposed analytical model. Based on realistic material properties of carbon nanotubes and polymer resins, damping characteristics have been predicted which compare well with existing results from open literature. The results have shown that for a volume fraction as small as 1%, a damping loss factor as high as 20% can be achieved which is adequate for most practical applications. The model has been further developed to deal with bending vibrations where different parts of the material are subject to different vibration strain levels. A practical case of cantilevered beam vibration has been employed to demonstrate the practical application of the proposed model.     

Method of reducing the gap between chips in mosaic photodetector modules

A method is proposed to shape the edges of chips in order to reduce the gap between chips in infrared-sensitive mosaic photodetectors modules. The method involves laser scribing of asymmetric grooves, splitting-off of the edge of the chip surface going under the chip, and the subsequent vertical alignment of the edges using laser radiation. The width of the gap between chips is 1–3 μm.     

Modeling the electron field emission from carbon nanotube films.

A theoretical framework for the electron field emission from carbon nanotubes (CNTs) is discussed. Using the tunneling theory, the influence of the detailed electron energy dispersion is proven to be of little importance for the electron field emission. By means of numerical computations in a simplified model, the influence of the environment on the local field on a CNT is discussed for an aligned CNT film. In a simple triangular model for the potential energy barrier at the tube end, a tunneling probability was obtained. A statistical model was developed for the structural and functional parameters of aligned CNT films. Practical CNT films of excellent alignment, obtained directly on a tungsten wire by plasma-enhanced chemical vapor deposition, were analyzed by this statistical model. Their distribution in the enhancement factors was thus deduced. An indirect method to get the average electrical parameters of the film using only a limited amount of experimental data was thus established.     

Synergetic effect of BN for the electrical conductivity of CNT/PAN composite fiber

Carbon nanotube (CNT) fillers in composite materials improve electrical conductivity, thermal stability, and mechanical properties. Boron nitride (BN) is an insulating material that is also thermally stable. Therefore, CNT and hexagonal boron nitride (hBN) fillers have been used to obtain composite materials’ high electrical conductivity. In this study, CNT-hBN/polyacrylonitrile (PAN) fibers were spun using simple wet-spinning and the effect of hBN on the electrical conductivity of the CNT-hBN/PAN composite was investigated. Contrary to predictions, as the content of the insulating material, BN, increased up to 15 wt%, the electrical resistance of the composite fiber decreased.

     

Structural instability of carbon nanotubes embedded in viscoelastic medium and subjected to distributed tangential load

In this paper, the nonlocal Euler-Bernoulli beam model is used to predict the static and dynamic structural instability of carbon nanotubes (CNTs) subjected to a distributed tangential compressive load. The CNT is considered to be embedded in a Kelvin-Voigt viscoelastic medium. Equation of motion and boundary conditions are obtained using the extended Hamilton’s principle and the extended Galerkin’s method is applied in order to transform the resulting equations into a general eigenvalue problem. The derived equations are validated by comparing the results achieved from the new derivations with existing solutions in literature. Effects of several experimentally interesting boundary conditions are considered on the stability characteristics of the CNT. Moreover, the influences of small scale parameter and material properties of the surrounding viscoelastic medium on the stability boundaries are examined.     

溶剂对碳纳米管/环氧树脂复合材料力热性能的影响

制备了碳纳米管／环氧树脂复合材料，分析了分散碳纳米管的溶剂对复合材料热学，力学行为的影响。溶剂效应由大到小依次为DMF，乙醇和丙酮，与三种溶剂的沸点顺序一致。溶剂效应被认为是未挥发完全的残留溶剂对环氧树脂固化反应的影响，从而导致了固化机理的不同。FTIR通过对比不同溶剂分散的复合材料的分子结构，证明了溶剂效应与复合材料中未反应完的环氧树脂及固化反应的完全程度有关，因而导致了不同的热、力学行为。