Growth of well-aligned carbon nanotubes by RF-DC plasma chemical vapor deposition

Highly aligned carbon nanotubes (CNTs) were grown under high sheath electric field and gas pressure conditions by the radio frequency (RF) plasma-enhanced direct current (DC) plasma chemical vapor deposition (CVD) method due to a stabilized DC discharge. The uniform growth of highly aligned multi-walled CNTs was achieved over the entire surface area of a 50 × 50 mm² iron foil. The growth of multi-walled CNTs on a 75 × 75 mm² iron foil was also confirmed.     

A shear lag model of Piezoelectric composite reinforced with carbon nanotubes-coated Piezoelectric fibers

A novel hybrid piezoelectric composite in which the microscopic piezoelectric fiber reinforcements are coated with radially aligned carbon nanotubes (CNTs) is analyzed in this study. A shear-lag model is developed to analyze the load transferred to such coated fibers from the aligned-CNT reinforced matrix in a hybrid composite application in the absence and the presence of the electric field along the length of the fiber. It is found that if the aligned CNTs are radially grown on the surface of the piezoelectric fiber then the axial load transferred to the fiber is reduced in the absence of the electric field while the axial stress in the fiber increases in the presence of the electric filed only. The radial stress in the active piezoelectric fiber significantly increases due to the radial growth of aligned CNTs on the surface of the fibers. This indicates a probable critical window for engineering the surface of the piezoelectric fiber for improving the effective piezoelectric properties. Effects of the variation of the aspect ratio of the piezoelectric fiber and the CNT volume fraction on the load transferred to such CNT-coated piezoelectric fibers are also investigated.     

A Four-Wire Line as a Standard for Electric and Magnetic Field Strengths

It is shown that an unmatched four-wire transmission line can be used as a combined standard for electric and magnetic field strengths as well as for the energy density and energy flux density in that field. The control parameters can be the electric field strength at the maximum, the short-circuit current in the line, and the power absorbed in the load. The main advantages are the simple formulas relating the control parameters to the quantities reproduced and the ease of building a device to reproduce them.     

Electric-field-induced microstructure modulation of carbon nanotubes for high-performance supercapacitors

The growth direction, morphology and microstructure of carbon nanotubes (CNTs) play key roles for their potential applications in electronic and energy storage devices. However, effective synthesis of CNTs in high crystallinity and desired microstructure still remains a tremendous challenge. Here we introduce an electric field for controlling the microstructure formation of CNTs. It reveals that the electric field not only make CNTs aligned parallel but also improve the density of CNTs. Especially, the microstructures of CNTs gradually change under electrical field. That is, graphite sheets are transformed from the “herringbone” structure to a highly crystalline structure, facilitating the transportation of electrons. Due to the improved aligned growth direction, high density and highly crystalline microstructure, the electrochemical performance of CNTs is greatly improved. When the CNTs are applied in supercapacitors, they present a high specific capacitance of 237 F/g, three times higher than that of the CNTs prepared without electrical field. Such microstructure modulation of CNTs by electric field would help to construct high performance electronic and energy storage devices.     

Temperature alternation by an on-chip microheater to reveal enzymatic activity of beta-galactosidase at high temperatures

A method to measure enzymatic activity at high temperatures by rapid temperature alternation of a microreactor with a microheater is proposed. On-chip microreactor and microheater were integrated on a glass plate by MEMS technology; this microheater can control the temperature of the microreactor with a response speed of 34.2 and 31.5 K/s for temperature rise and fall, respectively, with an accuracy of 3 degrees C. The enzyme, beta-galactosidase, was revealed to survive short exposure (4-s pulses) to temperatures above that which would "normally" denature them. Its activity at 60 degrees C was revealed to be approximately 4 times greater than that at room temperature. This method not only gives new kinetic information in biochemistry but also enables application in highly sensitive biosensors.     

A self-assembled synthesis of carbon nanotubes for interconnects

We report a novel approach to grow highly oriented, freestanding and structured carbon nanotubes (CNTs) between two substrates, using microwave plasma chemical vapour deposition. Sandwiched, multi-layered catalyst structures are employed to generate such structures. The as-grown CNTs adhere well to both the substrate and the top contact, and provide a low-resistance electric contact between the two. High-resolution scanning electron microscope (SEM) images show that the CNTs grow perpendicular to these surfaces. This presents a simple way to grow CNTs in different, predetermined directions in a single growth step. The overall resistance of a CNT bundle and two CNT-terminal contacts is measured to be about 14.7?k Ω. The corresponding conductance is close to the quantum limit conductance G(0). This illustrates that our new approach is promising for the direct assembly of CNT-based interconnects in integrated circuits (ICs) or other micro-electronic devices.     

新型基于离子注入技术的用于微池芯片的微加热器(英文)

为了降低微型聚合酶链式反应(PCR)芯片的功耗,设计了一种嵌入硅基内部的微加热器.该加热器由采用离子注入技术制作的加热电阻并行排列构成.利用设计的热循环控制系统,对微加热器进行了热循环特性研究,包括功耗、不同加热功率下的温升速率以及样液对芯片温度及功耗的影响.实验结果表明,当加热功率为1.6 W时平均温升速率可达4.7℃/s,90℃时芯片功耗仅为0.67 W.最后获得了PCR循环试验曲线.因此,该加热器可以有效降低芯片的功耗,更好地满足微型PCR芯片的要求.     

Electric field induced growth of well aligned carbon nanotubes from ethanol flames

This paper introduces a process to synthesize well aligned carbon nanotubes (CNTs) from ethanol flames by using a uniform electric field generated from a DC power supply. It has been found that (1)?comparing with the other processes a small electric field is enough to align CNTs; (2)?the synthesis process becomes more controllable and repeatable; (3)?the electric field also improves the diameter uniformity and the crystallinity of graphite sheets. It is thought that the alignment mechanism is due to the electrostatic force acting upon the catalyst particles at the tips of CNTs. The present process has advantages such as convenience of applying electric field, simple experiment set-up, and large area synthesis of well aligned CNTs.     

Nonaligned carbon nanotubes anchored on porous alumina: formation, process modeling, gas-phase analysis, and field-emission properties

We have developed a chemical vapor deposition (CVD) process for the catalytic growth of carbon nanotubes (CNTs), anchored in a comose-type structure on top of porous alumina substrates. The mass-flow conditions of precursor and carrier gases and temperature distributions in the CVD reactor were studied by transient computational fluid dynamic simulation. Molecular-beam quadrupole mass spectroscopy (MB-QMS) has been used to analyze the gas phase during ferrocene CVD under reaction conditions (1073 K) in the boundary layer near the substrate. Field-emission (FE) properties of the nonaligned CNTs were measured for various coverages and pore diameters of the alumina. Samples with more dense CNT populations provided emitter-number densities up to 48,000 cm(-2) at an electric field of 6 V microm(-1). Samples with fewer but well-anchored CNTs in 22-nm pores yielded the highest current densities. Up to 83 mA cm(-2) at 7 V microm(-1) in dc mode and more than 200 mA cm(-2) at 11 V microm(-1) in pulsed diode operation have been achieved from a cathode size of 24 mm2.     

An apparatus for applying tensile,compressive and cyclic stresses on foil specimens during light ion irradiation

An apparatus is described which allows irradiation of thin folded foils under tensile, compressive or cyclic load by light ions at well defined temperatures. The foils are stabilized against buckling under compressive stresses by folding them at angles of 50° or 70°. By this means, more than 100 MPa compressive stress can be safely loaded on 50 μm foils of 20% cold worked stainless steel. Details are also given of the helium-gas cooling circuit, the temperature control device and the irradiation system.     

EPS控制器建模与动态性能试验仿真

电动助力转向(electric power steering,EPS)控制器动态性能直接影响EPS总成的快速响应性和平稳性.利用Matlab/Si mulink创建EPS控制器模型,设计了EPS基本助力特性和包含PID算法、电流反馈的控制策略;利用AMESi m创建EPS负载模型并组装系统仿真模型,定义软件的数据交换接口并进行联合仿真.通过仿真,研究了三种标准激励下控制器动态性能的评价方法,讨论了助力电机关键参数对控制器性能的影响.结果表明,依托特定负载建模构建半物理仿真系统,进行脱离EPS总成环境的控制器动态性能试验是可行的.     

Doping-free fabrication of carbon nanotube thin-film diodes and their photovoltaic characteristics

Random networks of single-walled carbon nanotubes (SWCNTs) were have been grown by chemical vapor deposition on silicon wafers and used for fabricating field-effect transistors (FETs) using symmetric Pd contacts and diodes using asymmetrical Pd and Sc contacts. For a short channel FET or diode with a channel length of about 1 μm or less, the device works in the direct transport regime, while for a longer channel device the transport mechanism changes to percolation. Detailed electronic and photovoltaic (PV) characterizations of these carbon nanotube (CNT) thin-film devices was carried out. While as-fabricated FETs exhibited typical p-type transfer characteristics, with a large current ON/OFF ratio of more than 10⁴ when metallic CNTs were removed via a controlled breakdown, it was found that the threshold voltage for the devices was typically very large, of the order of about 10 V. This situation was greatly improved when the device was coated with a passivation layer of 12 nm HfO₂, which effectively moved the threshold voltages of both FET and diode back to center around zero or turned these device to their OFF states when no bias was applied on the gate. PV measurements were then made on the short channel diodes under infrared laser illumination. It was shown that under an illumination power density of 1.5 kW/cm², the device resulted in an open circuit voltage V _OC = 0.21 V and a short circuit current I _SC = 3.74 nA. Furthermore, we compared PV characteristics of CNT film diodes with different channel lengths, and found that the power transform efficiency decreased significantly when the device changed from the direct transport to the percolation regime.     

Electric Current-induced Failure of 200-nm-thick Gold Interconnects

200-nm-thick Au interconnects on a quartz substrate were tested in-situ inside a dual-beam microscope by applying direct current, alternating current and alternating current with a small direct current component. The failure behavior of the Au interconnects under three kinds of electric currents were characterized in-situ by scanning electron microscopy. It is found that the formation of voids and subsequent growth perpendicular to the interconnect direction is the fatal failure mode for all the Au interconnects under three kinds of electric currents. The failure mechanism of the ultrathin metal lines induced by the electric currents was analyzed.     

DNA mutation detection in a polymer microfluidic network using temperature gradient gel electrophoresis

A miniaturized system for DNA mutation analysis, utilizing temperature gradient gel electrophoresis (TGGE) in a polycarbonate (PC) microfluidic device, is reported. TGGE reveals the presence of sequence heterogeneity in a given heteroduplex sample by introducing a thermal denaturing gradient that results in differences between the average electrophoretic mobilities of DNA sequence variants. Bulk heater assemblies are designed and employed to externally generate temperature gradients in spatial and temporal formats along the separation channels. TGGE analyses of model mutant DNA fragments, each containing a single base substitution, are achieved using both single- and 10-channel parallel measurements in a microfluidic platform. Additionally, a comprehensive polymer microfluidic device containing an integrated microheater and sensor array is developed and demonstrated for performing spatial TGGE for DNA mutation analysis. The device consists of two PC modular substrates mechanically bonded together. One substrate is embossed with microchannels, and the other contains a tapered microheater, lithographically patterned along with an array of temperature sensors. Compared with the external heating approaches, the integrated platform provides significant reduction in power requirement and thermal response time while establishing more accurate and highly effective control of the temperature gradient for achieving improved separation resolution.     

Electronic structure, electron field emission and magnetic behaviors of carbon nanotubes fabricated on La0.66Sr0.33MnO3 (LSMO) for spintronics application

This work elucidates the electronic structure, electron field emission and magnetic anisotropic behaviors of single wall carbon nanotubes (SWCNTs) for the spin-electronics device application grown on the La0.66Sr0.33MnO3 (LSMO)/SrTiO3 (STO) substrate. Micro-Raman spectroscopy, X-ray absorption near-edge structure (XANES) and valence-band photoemission spectroscopy (VBPES) were used for the study of electronics structure. The field emission characteristics were studied from the electron field emission current density (J) versus applied electric field (E(A)) from which the turn-on electric field (E(TOE)) was evaluated. The magnetization behaviors are also presented by the M-H hysteresis loop and were obtained by applying the magnetic field in the parallel and perpendicular direction of the CNTs at 305 K and 5 K temperatures. A magnetic measurement shows that the coercivity of the CNTs/LSMO/STO is higher and has hig anisotropic-nature than the composite LSMO/STO that could be the good material for the future possible spin-electronics device applications.     

Versatile transfer of aligned carbon nanotubes with polydimethylsiloxane as the intermediate

A simple technique to transfer aligned multi-walled carbon nanotubes (MWCNTs) is demonstrated in this work. With polydimethylsiloxane (PDMS) as the transfer medium, as-grown or patterned MWCNT arrays are directly transferred onto a wide variety of Pt-coated substrates such as glossy paper, cloth, polymers, glass slides, and metal foils at low temperatures. The surface of the transferred CNTs is cleaner with better alignment, compared with the as-grown one. Furthermore, the transferred CNTs show strong adhesion and good electric contact with the target substrates. A maximal current density of ～10(4)?A?cm(-2) has been achieved from the CNT interconnects prepared with this technique. Because of the lower density and open-ended structures, improved field emission performance has been obtained from CNTs transferred on polymers, based on which flexible emitter devices can be fabricated. In addition, the surface of transferred CNTs becomes more hydrophilic, with an averaged contact angle of 93.4 ± 5.8°, in contrast to the super-hydrophobic as-grown CNT surface (contact angle 151.6 ± 5.5°). With versatile properties and flexible applications, the technique provides a simple and cost-effective way towards future nanodevices based on CNTs.     

Flexible High‐Conductivity Carbon‐Nanotube Interconnects Made by Rolling and Printing

Applications of carbon nanotubes (CNTs) in flexible and complementary metal‐oxide‐semiconductor (CMOS)‐based electronic and energy devices are impeded due to typically low CNT areal densities, growth temperatures that are incompatible with device substrates, and challenges in large‐area alignment and interconnection. A scalable method for continuous fabrication and transfer printing of dense horizontally aligned CNT (HA‐CNT) ribbon interconnects is presented. The process combines vertically aligned CNT (VA‐CNT) growth by thermal chemical vapor deposition, a novel mechanical rolling process to transform the VA‐CNTs to HA‐CNTs, and adhesion‐controlled transfer printing without needing a carrier film. The rolling force determines the HA‐CNT packing fraction and the HA‐CNTs are processed by conventional lithography. An electrical resistivity of 2 mΩ · cm is measured for ribbons having 800‐nm thickness, while the resistivity of copper is 100 times lower, a value that exceeds most CNT assemblies made to date, and significant improvements can be made in CNT structural quality. This rolling and printing process could be scaled to full wafer areas and more complex architectures such as continuous CNT sheets and multidirectional patterns could be achieved by straightforward design of the CNT growth process and/or multiple rolling and printing sequences.     

Structural Investigation of Catalytically Grown Carbon Nanotubes

Carbon nanotubes (CNTs) having diameters in the range of 30–50 nm and few micrometers in length were synthesized in one step through a chemical-reduction route under autogenous pressure of H₂/CO₂. The synthesized materials prepared under different experimental conditions were characterized using different techniques. Results showed that V₂O₅ used as a catalyst for the nucleation of CNTs become carburized to vanadium carbide (V₈C₇) and provides a site for growth of CNTs. At high temperature, carbide particles thus formed become encapsulated at the tip of nanotube followed by the growth of CNTs through the tip-growth mechanism. Thermogravimetric analysis results showed that the CNTs obtained after the longer reaction time are more stable at high temperatures. Raman analysis showed a well-ordered graphite structure.