Pastes for electromagnetic interference shielding

A paste has been developed for electromagnetic interference shielding by mixing stainless steel fibers (8-μm diameter) and graphite flakes (5 μm) in a water-based graphite colloid (containing submicron graphite flakes and a binder) in a volume ratio 0.5:20:100. The resulting coating of thickness 0.1–0.2 mm after drying exhibits shielding effectiveness of 34 dB at 1 GHz, primarily due to reflection. The paste is superior to those containing graphite flakes or carbon filaments (0.1-μm diameter), due to the higher shielding effectiveness of the steel fibers. The graphite flakes in the paste serves to help suspend the steel fibers, in addition to contributing to shielding.     

The study of a BOCC m-ary spread spectrum scheme

M-ary spread spectrum technique has been found wide applications in wireless communications, but it needs too many orthogonal spreading codes, and its despreading/demodulation is quite complex computationally, which limit its wider applications. This paper proposes a novel scheme for Code Division Multiple Access （CDMA） communication systems based on M-ary spread spectrum, where only one prototype spreading code is assigned to each user and the codes for different users are orthogonal or quasi-orthogonal with each other. The M spreading codes of each user to represent K bits data are generated by circularly shifting the assigned code and reversing its polarity. The spreading codes generated like that are called as BiOrthogonal Cyclic Codes （BOCCs）. At the receiver of the system, a transform domain matched-filter implemented by means of Fast Fourier Transform （FFT） is employed to despread and demodulate the received signals, which has very low computational complexity. The results of simulation experiments and bit-error performance analysis show that the proposed scheme is practical and very useful in many cases.     

An optimized junctionless GAA MOSFET design based on multi-objective computation for high-performance ultra-low power devices

An analytical investigation has been proposed to study the subthreshold behavior ofjunctionless gates all around （JLGAA） MOSFET for nanoscale CMOS analog applications. Based on 2-D analytical analysis, a new subthreshold swing model for short-channel JLGAA MOSFETs is developed. The analysis has been used to calculate the subthreshold swing and to compare the performance of the investigated design and conventional GAA MOSFET, where the comparison of device architectures shows that the JLGAA MOSFET exhibits a superior performance with respect to the conventional inversion-mode GAA MOSFET in terms of the fabrication process and electrical behavior in the subthreshold domain. The analytical models have been validated by 2-D numerical simulations. The proposed analytical models are used to formulate the objectives functions. The overall objective function is formulated by means of a weighted sum approach to search the optimal electrical and dimensional device parameters in order to obtain the better scaling capability and the electrical performance of the device for ultra-low power applications.     

Correcting Image Distortion for Adaptive Cruise Control

One of the main drivers for intelligent transportation systems is safety.Adaptive cruise control,as a common solution for traffic safety,has extended from radars to cameras.Due to high mobility of vehicles and unevenness of roads,the picture quality of cameras has been great challenges for camera-based adaptive cruise control.In this paper,an image distortion correction algorithm is addressed.Our method is based on optical flow technology which is normally applied in motion estimation and video compression research.We are the first to attempt to adapt it in image distortion correction.Two optical flow approaches,the Lucas-Kanade method and the Horn-Schunck method,are selected and compared.The procedure of image distortion correction using the optical flow method has been tested by both synthetic test images and camera images.The experimental results show that the Lucas-Kanade method is more suitable in the correction of image distortion.     

An effective network congestion control method for multilayer network

The congestion control problem in a single node network has been solved by the nonlinear feedback control method,which has been proven to be effective and robust for different router’s queue size.However,these control models are based on the single layer network architecture,and the senders and receivers are directly connected by one pair of routers.With the network architecture being more and more complex,it is a serious problem how to cooperate many routers working in the multilayer network simultaneously.In this paper,an effective Active Queue Management（AQM）scheme to guarantee the stability by the nonlinear control of imposing some restrictions on AQM parameter in multilayer network is proposed.The nonlinear control can rely on some heuristics and network traffic controllers that appear to be highly correlated with the multilayer network status.The proposed method is based on the improved classical Random Early Detection（RED）differential equation and a theorem for network congestion control.The theorem proposed in the paper proved that the stability of the fluid model can effectively ensure the convergence of the average rate to its equilibrium point through many routers in multilayer network.Moreover,when the network capacity is larger,the proposed scheme can still approach to the fullest extensibility of utilization and ensure the stability of the fluid model.The paper reveals the reasons of congestion control in multilayer network,provides a theorem for avoiding network congestion,and gives simulations to verify the results.     

Analysis of dispersion in the nano-InP doped fiber

We propose that nanomaterials are used for fibers.A novel nano-InP doped fiber has been fabricated by the method of modified chemical vapor deposition(MCVD).It has been measured that the doping concentration of phosphorus element is 0.1%.The relationship between refractive index and the wavelength is obtained by fitting experimental data to Sellmeier equation.Dispersion of the fiber has been calculated in the wavelength range of 1.2-1.6 μm.As the wavelength varies from 1.20 μm to 1.60 μm,dispersion paramete...     

电力静电感应晶体管大电压特性的改善

A novel structure for designing and fabricating a power static induction transistor（SIT）with excellent high breakdown voltage performance is presented.The active region of the device is designed to be surrounded by a deep trench to cut off the various probable parasitical effects that may degrade the device performance,and to avoid the parallel-current effect in particular.Three ring-shape junctions（RSJ）are arranged around the gate junction to reduce the electric field intensity.It is important to achieve maximum gate–source breakdown voltage BVGS, gate–drain breakdown voltage BVGD and blocking voltage for high power application.A number of technological methods to increase BVGD and BVGS are presented.The BVGS of the power SIT has been increased to 110 V from a previous value of 50–60 V,and the performance of the power SIT has been greatly improved.The optimal distance between two adjacent ring-shape junctions and the trench depth for the maximum BVGS of the structure are also presented.     

A temperature window for the synthesis of single-walled carbon nanotubes by catalytic chemical vapor deposition of CH4 over Mo-Fe/MgO catalyst

A temperature window of single-walled carbon nanotubes （SWCNTs） growth has been studied by Raman spectroscopy. The results presented when temperature lower than 750℃, there were few SWCNTs formed, and when temperature higher than 900℃, mass amorphous carbons were formed in the SWCNTs bundles due to the self-decomposition of CH4. The temperature window of SWCNTs efficiently growth is between 800 and 900℃, and the optimum growth temperature is about 850℃. These results were supported by transmission electron microscope images of samples formed under different temperature. The temperature window is important for large-scale production of SWCNTs by catalytic chemical vapor deposition method.     

Preface to the Special Topic on Compound Semiconductor Materials and Devices on Si

The research in silicon photonics has been booming due to its potential for lowcost,reliable,energy-efficient and high-density chip-wise integration using widely available CMOS technology,featuring the tremendous success in modulator,detector and other passive waveguide components in industry.However,the absence of efficient and reliable electrical to optical converter on Si platform has been considered as“the last piece of the puzzle”,hindered by the in-direct bandgap property of Si bulk materials.CompoundⅢ–Ⅴsemiconductor devices offer highly efficient optical light emitting sources and optical amplifiers,hence the compound semiconductor materials and devices on Si platform are drawing more and more attention nowadays as it could make possible the long-dreamed light sources on Si substrates by combining their advantages with silicon ICs,enabling the fabrication of full functional optoelectronic circuits,chip-to-chip and even system-to-system optical chips.     

Delay Optimized Architecture for On-Chip Communication

Networks-on-chip （NoC）, a new system on chip （SoC） paradigm, has become a great focus of research by many groups during the last few years. Among all the NoC architectures that have been proposed until now, 2D-Mesh has proved to be the best architecture for implementation due to its regular and simple interconnection structure. In this paper, we propose a new interconnect architecture called 2D-diagonal mesh （2DDgl-Mesh） for on-chip communication. The 2DDglMesh is almost similar to traditional 2D-Mesh in aspects of cost, area, and implementation, but it can outperform the later in delay. The both architectures are compared by using NS-2 （a network simulator） and CINS1M （a component based interconnection simulator） under the same traffic models and parametric conditions. The results of comparison show that under the proposed architecture, the packets can almost always be routed to their destinations in less time. In addition, our archi- tecture can sometimes perform better than 2D-Mesh in drop ratio for special fixed traffic models.     

Electron-microscopic imaging of single-walled carbon nanotubes grown on silicon and silicon oxide substrates

Direct imaging of single-walled carbon nanotubes (SWNTs) suspended on pillar-patterned Si or SiO2 substrates is investigated using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The suspended nanotubes are successfully observed by direct TEM imaging and it is seen that they have either individual or bundles of SWNTs. Low energy (< or =2 keV) SEM produces high contrast images of suspended SWNTs. On the contrary, when SWNTs contact a SiO2 substrate, they are imaged using electron-beam induced current. The image brightness depends on the length of SWNTs.     

Polyazines and Polyazomethines with Didodecylthiophene Units for Selective Dispersion of Semiconducting Single‐Walled Carbon Nanotubes

Polymer wrapped single‐walled carbon nanotubes (SWNTs) have been demonstrated to be a very efficient technique to obtain high purity semiconducting SWNT solutions. However, the extraction yield of this technique is low compared to other techniques. Poly‐alkyl‐thiophenes have been reported to show higher extraction yield compare to polyfluorene derivatives. Here, the affinity for semiconducting SWNTs of two polymers with a backbone containing didodecylthiophene units interspersed with N atoms is reported. It is demonstrated that one of the polymers, namely, poly(2,5‐dimethylidynenitrilo‐3,4‐didodecylthienylene) (PAMDD), has very high semiconducting SWNT extraction yield compared to the poly(3,4‐didodecylthienylene)azine (PAZDD). The dissimilar wrapping efficiency of these two polymers for semiconducting SWNTs is attributed to the interplay between the affinity for the nitrogen atoms of the highly polarizable walls of SWNTs and the mechanical flexibility of the polymer backbones. Photoluminescence (PL) measurements demonstrate the presence of metallic tubes and SWNT bundles in the sample selected with PAZDD and higher purity of SWNT‐PAMDD samples. The high purity of the semiconducting SWNTs selected by PAMDD is further demonstrated by the high performance of the solution‐processed field‐effect transistors (FETs) fabricated using a blade coating technique, which exhibit hole mobilities up to 33.3 cm² V^?1 s^?1 with on/off ratios of 10⁶.     

Single-walled carbon nanotube transistors fabricated by advanced alignment techniques utilizing CVD growth and dielectrophoresis

Single-walled carbon nanotube field effect transistors (SWNT-FETs) are fabricated by two different alignment techniques. The first technique is based on direct synthesis of an aligned SWNTs array on quartz wafer using chemical vapor deposition. The transistor with three SWNTs and atomic layer deposited (ALD) Al₂O₃ gate oxide shows a contact resistance of 280 KΩ, a maximum on-current of ?7 μA, and a high I_on/I_off ratio (>10³). The second technique is based on room temperature self-assembly of SWNT bundles using dielectrophoresis. By applying AC electric fields, we have aligned nanotube bundles between drain and source contact patterns of a transistor at room temperature. Transistors based on twisted bundle of SWNTs show high contact resistance (MΩ range) and low current drive in the order of tens of nA.     

Super‐Fast Switching of Twisted Nematic Liquid Crystals on 2D Single Wall Carbon Nanotube Networks

We have developed a high performance liquid crystal (LC) alignment layer of ultra‐thin single wall carbon nanotubes (SWNTs) and a conjugated block copolymer nanocomposite that is solution‐processible for conventional twisted nematic (TN) LC cells. The alignment layer is based on the non‐destructive solution dispersion of nanotubes with a poly(styrene‐b‐ paraphenylene) (PS‐b‐PPP) copolymer and subsequent spin coating, followed by conventional rubbing without a post‐annealing process. Topographically grooved nanocomposite films with two dimensionally (2D) networked SWNTs embedded in a block copolymer matrix were created using a rubbing process in which bundles of SWNTs on the composite surface were effectively removed. The LCs were well aligned with a stable pre‐tilt angle of approximately 2° on our extremely transparent nanocomposite, which gave rise to superfast switching of the TN LC molecules that was approximately 3.8 ms, or four times faster than that on a commercial polyimide layer. Furthermore, the TN LCD cells containing our SWNT nanocomposite alignment layers exhibited low power operation at an effective switching voltage amplitude of approximately 1.3 V without capacitance hysteresis.     

High‐Tensile Strength,Composite Bijels through Microfluidic Twisting

Rope making is a millennia old technique to collectively assemble numerous weak filaments into flexible and high tensile strength bundles. However, delicate soft matter fibers lack the robustness to be twisted into bundles by means of mechanical rope making tools. Here, weak microfibers with tensile strengths of a few kilopascals are combined into ropes via microfluidic twisting. This is demonstrated for recently introduced fibers made of bicontinuous interfacially jammed emulsion gels (bijels). Bijels show promising applications in use as membranes, microreactors, energy and healthcare materials, but their low tensile strength make reinforcement strategies imperative. Hydrodynamic twisting allows to produce continuous bijel fiber bundles of controllable architecture. Modelling the fluid flow field reveals the bundle geometry dependence on a subtle force balance composed of rotational and translational shear stresses. Moreover, combining multiple bijel fibers of different compositions enables the introduction of polymeric support fibers to raise the tensile strength to tens of megapascals, while simultaneously preserving the liquid like properties of the bijel fibers for transport applications. Hydrodynamic twisting shows potentials to enable the combination of a wide range of materials resulting in composites with features greater than the sum of their parts.     

Charged Rod‐Like Nanoparticles Assisting Single‐Walled Carbon Nanotube Dispersion in Water

A new dispersant for stabilization of single wall carbon nanotubes (SWNTs) in water that simultaneously utilizes three different dispersion or stabilization mechanisms: surfactant adsorption, polymeric wrapping, and Coulomb repulsive interaction, has been demonstrated. The new dispersant, a charged rod‐like nanoparticle (cROD), is a cylindrical micelle wrapped by negatively charged polymers which is fabricated by the aqueous free radical polymerization of a polymerizable cationic surfactant, cetyltrimethylammonium 4‐vinylbenzoate (CTVB), in the presence of sodium 4‐styrenesulfonate (NaSS). The surface charge density of the cRODs is controlled by varying the concentration of NaSS. Dispersions of SWNTs are obtained by sonicating a mixture of SWNTs and cROD in water, followed by ultra‐centrifugation and decanting. While the cRODs with neutral or low surface change densities (0 and 5 mol % NaSS) result in very low dispersion power and poor stability, the cRODs with high surface charge densities (15, 25, and 40 mol % NaSS) produce excellent dispersions with SWNT concentration as high as 437 mg L^?1 and long term stability. The sharp van Hove transition peaks of the cROD assisted SWNT dispersions indicate the presence of individually isolated SWNTs. Atomic force microscopy and small angle neutron scattering analysis show that the dominant encapsulation structure of the cROD assisted SWNTs is surfactant assisted polymeric wrapping. SWNTs dispersed by the cRODs can be fully dried and easily re‐dispersed in water, providing enhanced processibility of SWNTs.     

掺杂单壁碳纳米管的电流特性

依据Boltzmann方程及单壁碳纳米管(SWNTs)能量色散关系,对单个掺杂SWNTs(金属型和半导体型)所加偏压、掺杂浓度及管口直径影响输运电流的性质进行数值计算.分析表明,掺杂SWNs中的电流随偏压变化呈现跃变结构;管口直径、掺杂后Fermi能级附近的态密度以及各通道输运电子的能力直接决定电流的特性,如电流强度、跃变间隔及跃变幅度;同时电流的特性也与温度有关.     

Capacitance–voltage characteristics of P3HT:PCBM bulk heterojunction solar cells with ohmic contacts and the impact of single walled carbon nanotubes on them

Capacitance–voltage (C–V) characteristics of P3HT:PCBM devices of two different thicknesses are correlated with current density–voltage (J–V) characteristics. The rising portion of the C–V characteristics coincides with the exponential current density below the built-in voltage. The negative capacitance (NC) of these devices is a low frequency phenomenon and it occurs in trap-free space charge limited current (SCLC) regime. The onset frequencies of NC for devices with and without SWNTs also do not follow direct relation with effective mobility. The NC in thin devices has non-monotonic change with voltage for thin devices showing that interface state kinetics can be the reason for its occurrence. The NC of thick devices, on the other hand, increases monotonically with voltage showing that bulk properties dominate in these. Addition of SWNTs to these devices for efficiency improvement does not modify their built-in voltage. Also, the SWNTs do not affect the forward NC behaviour. However, the devices containing SWNTs show NC in reverse bias also which has different frequency dependence with voltage. The reverse bias NC is attributed to the large non-linear reverse current by charge injection into the additional energy levels introduced by SWNTs.     

Electrode temperature decays of interrupted d.c. arcs of variable duration†

Results are given for the decay of electrode temperature for arcs of variable durations, 50–500 msec and current range 10–50 A. The working gas was air at atmospheric pressure and the electrodes were 3[sdot]2 mm φ graphite rods. The temperature decay values have been compared with other workers' measurements of arc re-ignition voltages, obtained under similar experimental conditions, and from this a strong functional dependence of the re-ignition voltage on cathode temperature has been detected.     

N‐Type Conjugated Polymer‐Enabled Selective Dispersion of Semiconducting Carbon Nanotubes for Flexible CMOS‐Like Circuits

Sorting of semiconducting single‐walled carbon nanotubes (SWNTs) by conjugated polymers has attracted considerable attention recently because of its simplicity, high selectivity, and high yield. However, up to now, all the conjugated polymers used for SWNT sorting are electron‐donating (p‐type). Here, a high‐mobility electron‐accepting (n‐type) polymer poly([N,N′‐bis(2‐octyldodecyl)‐naphthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl]‐alt‐5,5′‐(2,2′‐bithiophene)) (P(NDI2OD‐T2)) is utilized for the sorting of high‐purity semiconducting SWNTs, as characterized by Raman spectroscopy, dielectric force spectroscopy and transistor measurements. In addition, the SWNTs sorted by P(NDI2OD‐T2) have larger diameters than poly(3‐dodecylthiophene) (P3DDT)‐sorted SWNTs. Molecular dynamics simulations in explicit toluene demonstrate distinct linear or helical wrapping geometry between P(NDI2OD‐T2) and different types of SWNTs, likely as a result of the strong interactions between the large aromatic core of the P(NDI2OD‐T2) backbone and the hexagon path of SWNTs. By using high‐mobility n‐type P(NDI2OD‐T2) as the sorting polymer, ambipolar SWNT transistors with better electron transport than that attained by P3DDT‐sorted SWNTs are achieved. As a result, flexible negated AND and negated OR logic circuits from the same set of ambipolar transistors are fabricated, without the need for doping. The use of n‐type polymers for sorting semiconducting SWNTs and achieving ambipolar SWNT transistor characteristics greatly simplifies the fabrication of flexible complementary metal‐oxide‐semiconductor‐like SWNT logic circuits.