碳纳米管介电电泳组装及过程控制研究进展

碳纳米管具有独特的结构和卓越的电学、热学、力学等性能,有望在微纳电子、微纳机电系统、传感器、新能源、光学等诸多领域获得具有深远影响的应用。碳纳米管的组装是其获得广泛应用的重要前提,基于介电电泳的组装和过程控制技术近年来得到了迅速发展。这些技术包括回路中串联自限制性电阻,间隙电信号实时监测和反馈控制,三维结构的组装和包覆,引入不同形状浮动电极等。对碳纳米管介电电泳组装及各种新技术做了系统介绍,并对各种方法的优缺点进行了对比与总结,为探索稳定、高效的碳纳米管自动组装方法提供帮助。     

Stretchable Electrode Based on Laterally Combed Carbon Nanotubes for Wearable Energy Harvesting and Storage Devices

Carbon nanotubes (CNTs) are a promising material for use as a flexible electrode in wearable energy devices due to their electrical conductivity, soft mechanical properties, electrochemical activity, and large surface area. However, their electrical resistance is higher than that of metals, and deformations such as stretching can lead to deterioration of electrical performances. To address these issues, here a novel stretchable electrode based on laterally combed CNT networks is presented. The increased percolation between combed CNTs provides a high electrical conductivity even under mechanical deformations. Additional nickel electroplating and serpentine electrode designs increase conductivity and deformability further. The resulting stretchable electrode exhibits an excellent sheet resistance, which is comparable to conventional metal film electrodes. The resistance change is minimal even when stretched by ≈100%. Such high conductivity and deformability in addition to intrinsic electrochemically active property of CNTs enable high performance stretchable energy harvesting (wireless charging coil and triboelectric generator) and storage (lithium ion battery and supercapacitor) devices. Monolithic integration of these devices forms a wearable energy supply system, successfully demonstrating its potential as a novel soft power supply module for wearable electronics.     

3D Microstructured Carbon Nanotube Electrodes for Trapping and Recording Electrogenic Cells

Electrogenic cells such as cardiomyocytes and neurons rely mainly on electrical signals for intercellular communication. Microelectrode arrays (MEAs) have been developed for long‐term recording of cell signals and stimulation of electrogenic cells under low‐cell‐stress conditions, providing new insights in the behavior of electrogenic cells and the operation of the brain. To date, MEAs are relying on flat or needle‐shaped electrode surfaces, mainly due to limitations in the lithographic processes. This paper relies on a previously reported elasto‐capillary aggregation process to create 3D carbon nanotube (CNT) MEAs. This study shows that CNTs aggregate in well‐shaped structures of similar size as cardiomyocytes are particularly interesting for MEA applications. This is because i) CNT microwells of the right diameter preferentially trap individual cardiomyocytes, which facilitates single cell recording without the need for clamping cells or signal deconvolution, and ii) once the cells are trapped inside of the CNT wells, this 3D CNT structure is used as an electrode surrounding the cell, which increases the cell–electrode contact area. As a result, this study finds that the recorded output voltages increase significantly (more than 200%). This fabrication process paves the way for future study of complex interactions between electrogenic cells and 3D recording electrodes.     

Water-Resistant Ionogel Electrode with Tailorable Mechanical Properties for Aquatic Ambulatory Physiological Signal Monitoring

Underwater electrocardiography (ECG) monitoring, which can monitor cardiac autonomic changes and arrhythmias during diving, is essential for sports management and healthcare. However, it is crucial yet rather challenging to achieve ECG monitoring in an aquatic environment because the interface electrodes may lose their functionality underwater. Here, an ionogel with tailorable mechanical properties is prepared by a facile one-step polymerization and used as water-resistant electrode. The Young's modulus and strain at break of the ionogel can be modulated in the range of 0.22–337 MPa and 349 to >10 000%, respectively. The hydrophobic polymer networks inside the ionogel endow this ionogel with excellent stability, adhesion, and self-healing ability underwater. The ionic conductivity imparted by the free ionic groups inside the ionogel allows the ionogel to detect and transmit physiological electrical signals. Compared with commercial gel electrodes, this ionogel electrode demonstrates better adhesion ability, conductivity, and stability underwater. The ionogel electrode can collect real-time ECG signals effectively both in the air and underwater, and the data can be used to warn users of the potential risk of a heart attack.     

Aligned Carbon Nanotube–Based Flexible Gel Substrates for Engineering Biohybrid Tissue Actuators

Muscle‐based biohybrid actuators have generated significant interest as the future of biorobotics but so far they move without having much control over their actuation behavior. Integration of microelectrodes into the backbone of these systems may enable guidance during their motion and allow precise control over these actuators with specific activation patterns. Here, this challenge is addressed by developing aligned carbon nanotube (CNT) forest microelectrode arrays and incorporating them into scaffolds for cell stimulation. Aligned CNTs are successfully embedded into flexible and biocompatible hydrogels exhibiting excellent anisotropic electrical conductivity. Bioactuators are then engineered by culturing cardiomyocytes on the CNT microelectrode‐integrated hydrogel constructs. The resulting cardiac tissue shows homogeneous cell organization with improved cell‐to‐cell coupling and maturation, which is directly related to the contractile force of muscle tissue. This centimeter‐scale bioactuator has excellent mechanical integrity, embedded microelectrodes, and is capable of spontaneous actuation behavior. Furthermore, it is demonstrated that a biohybrid machine can be controlled by an external electrical field provided by the integrated CNT microelectrode arrays. In addition, due to the anisotropic electrical conductivity of the electrodes provided by aligned CNTs, significantly different excitation thresholds are observed in different configurations such as the ones with electrical fields applied in directions parallel versus perpendicular to the CNT alignment.     

Performance improvement of organic thin film transistors with carbon nanotube/metal hybrid electrodes for S/D contacts

Electrode contact resistance is an important factor that seriously affects the performance of organic thin film transistors (OTFTs). In this paper, new low contact resistance carbon nanotube (CNT) based hybrid electrodes are introduced for the source and drain electrodes of OTFTs. The hybrid electrodes consist of solution-processed CNTs and a metal (Al; CNT/Al or Au; CNT/Au) layer evaporated on the CNTs. The contact resistance of the CNT/Al and CNT/Au hybrid electrodes was found to vary depending on the thickness of the Al and Au layer. The contact resistance of the CNT/Al hybrid electrodes exhibited a minimum of 2.9 kΩ cm at an Al thickness of 5 nm. It is notable that the minimum contact resistance of the CNT/Au was 0.9 kΩ cm at an Au thickness of 5 nm, and is the lowest value ever reported. It was lower than the 13 kΩ cm of the bare CNT electrodes, and tremendously less than the 4 MΩ cm of the pure Au electrode. The mobility of the OTFTs, which used pentacene as the semiconductor and polyvinylphenol as the gate dielectric, also followed the same dependence on metal thickness as the contact resistance. The maximum mobility of the OTFTs using CNT/Al and CNT/Au electrodes was 0.76 cm²/V sec and 1.0 cm²/V sec, respectively, at the same metal thickness of 5 nm, which was larger than 0.3 cm²/V sec of the bare CNT electrodes. The major origin of these enhancements was found to be the small energy difference between the work function of the CNT/metal hybrid electrodes and pentacene HOMO (5.1 eV), which was obtained at the metal thickness of 5 nm.     

Hierarchical Free‐Standing Carbon‐Nanotube Paper Electrodes with Ultrahigh Sulfur‐Loading for Lithium–Sulfur Batteries

The rational combination of conductive nanocarbon with sulfur leads to the formation of composite cathodes that can take full advantage of each building block; this is an effective way to construct cathode materials for lithium–sulfur (Li–S) batteries with high energy density. Generally, the areal sulfur‐loading amount is less than 2.0 mg cm^?2, resulting in a low areal capacity far below the acceptable value for practical applications. In this contribution, a hierarchical free‐standing carbon nanotube (CNT)‐S paper electrode with an ultrahigh sulfur‐loading of 6.3 mg cm^?2 is fabricated using a facile bottom–up strategy. In the CNT–S paper electrode, short multi‐walled CNTs are employed as the short‐range electrical conductive framework for sulfur accommodation, while the super‐long CNTs serve as both the long‐range conductive network and the intercrossed mechanical scaffold. An initial discharge capacity of 6.2 mA·h cm^?2 (995 mA·h g^?1), a 60% utilization of sulfur, and a slow cyclic fading rate of 0.20%/cycle within the initial 150 cycles at a low current density of 0.05 C are achieved. The areal capacity can be further increased to 15.1 mA·h cm^?2 by stacking three CNT–S paper electrodes—resulting in an areal sulfur‐loading of 17.3 mg cm^?2—for the cathode of a Li–S cell. The as‐obtained free‐standing paper electrode are of low cost and provide high energy density, making them promising for flexible electronic devices based on Li–S batteries.     

3D Interconnected Conductive Graphite Nanoplatelet Welded Carbon Nanotube Networks for Stretchable Conductors

Stretchable conductors with stable electrical conductivity under harsh mechanical deformations are essential for developing next generation portable and flexible wearable electronics. To achieve both high stretchability and conductivity with electromechanical stability, highly stretchable conductors based on 3D interconnected conductive graphite nanoplatelet welded carbon nanotube (GNP-w-CNT) networks are fabricated by welding the junctions of CNTs using GNPs followed by infiltrating with poly(dimethylsiloxane) (PDMS). It is observed that GNPs can weld the adjacent CNTs to facilitate the formation of continuous conductive pathways and avoid interfacial slippage under repetitive stretching. The enhanced interfacial bonding enables the conductor both high electrical conductivity (>132 S m⁻¹) and high stretchability (>150% strain) while ensuring long-term stability (1000 stretching-releasing cycles under 60% tensile strain). To demonstrate the outstanding flexibility and electrical stability, a flexible and stretchable light-emitting diode circuit with stable performance during stretching, bending, twisting, and pressing conditions is further fabricated. The unique welding mechanism can be easily extended to other material systems to broaden the application of stretchable conductors to a myriad of new applications.     

A carbon nanotube-based sensing element

A carbon nanotube-based(CNT) sensing element is presented, which consists of substrate, insulating layer, electrodes, carbon nanotube and measuring circuit. The sensing components are a single or array of CNTs, which are located on the two electrodes. The CNT-based sensing element is fabricated by CVD (chemical vapor deposition)-direct-growth on micro- electrodes. The sensing model and measurement method of electromechanical property are also presented. Finally, the voltage-current characteristics are measured, which show that the CNT-based sensing element has good electrical properties.     

Noninvasive Assessment of Human Gastric Motor Function

A noninvasive technique to monitor gastric electrical activity (GEA) and mechanical activity as an aid in assessing gastric motor function is presented. The GEA is measured with ordinary ECG electrodes located on the torso in the region above the stomach. The mechanical activity is recorded through an electrical impedance monitoring device. A study of a mathematical model of the electrically active antral part of the stomach in the body revealed that the waveform of the extracorporeally measured signals can be related to the direction of propagation of the GEA. This feature was confirmed experimentally.     

薄膜衬底电极CNT阴极制备及场发射性能研究

采用电泳沉积(EPD,electrophoretic deposition)法在不同薄膜衬底电极上制备碳纳米管(CNT,carbon nanotube)场发射阴极.采用场发射扫描电子显微镜(FESEM)对其进行表面形貌表征,结果表明,EPD可以制得CNT均匀分布的场发射阴极.场发射测试结果表明衬底电极对CNT阴极的场发...     

High Electromechanical Response of Ionic Polymer Actuators with Controlled‐Morphology Aligned Carbon Nanotube/Nafion Nanocomposite Electrodes

Recent advances in fabricating controlled‐morphology vertically aligned carbon nanotubes (VA‐CNTs) with ultrahigh volume fraction create unique opportunities for markedly improving the electromechanical performance of ionic polymer conductor network composite (IPCNC) actuators. Continuous paths through inter‐VA‐CNT channels allow fast ion transport, and high electrical conduction of the aligned CNTs in the composite electrodes lead to fast device actuation speed (>10% strain/second). One critical issue in developing advanced actuator materials is how to suppress the strain that does not contribute to the actuation (unwanted strain) thereby reducing actuation efficiency. Here, experiments demonstrate that the VA‐CNTs give an anisotropic elastic response in the composite electrodes, which suppresses the unwanted strain and markedly enhances the actuation strain (>8% strain under 4 V). The results reported here suggest pathways for optimizing the electrode morphology in IPCNCs using ultrahigh volume fraction VA‐CNTs to further enhanced performance.     

Carbon Nanotubes: High Electromechanical Response of Ionic Polymer Actuators with Controlled‐Morphology Aligned Carbon Nanotube/Nafion Nanocomposite Electrodes (Adv. Funct. Mater. 19/2010)

Recent advances in fabricating controlled‐morphology vertically aligned carbon nanotubes (VA‐CNTs) with ultrahigh volume fraction create unique opportunities for markedly improving the electromechanical performance of ionic polymer conductor network composite (IPCNC) actuators. Continuous paths through inter‐VA‐CNT channels allow fast ion transport, and high electrical conduction of the aligned CNTs in the composite electrodes lead to fast device actuation speed (>10% strain/second). One critical issue in developing advanced actuator materials is how to suppress the strain that does not contribute to the actuation (unwanted strain) thereby reducing actuation efficiency. Here, experiments demonstrate that the VA‐CNTs give an anisotropic elastic response in the composite electrodes, which suppresses the unwanted strain and markedly enhances the actuation strain (>8% strain under 4 V). The results reported here suggest pathways for optimizing the electrode morphology in IPCNCs using ultrahigh volume fraction VA‐CNTs to further enhanced performance.     

Reducing Motion Artifacts and Interference in Biopotential Recording

The application of engineering principles and techniques to biopotential recording has resulted in a continual improvement both in the type and the quality of recorded signals. Physical placement of electrodes has enabled improved discrimination of the biopotential of interest (such as the ECG) from unwanted biopotentials (such as the EMG). Understanding that the major motion artifact in ECG recording arises from the skin and not the electrode has resulted in techniques that reduce this artifact, such as skin abrasion and mechanical stabilization. However, skin abrasion makes the skin more subject to irritation, so mild gels are required. The development of the floating silver/silver chloride electrode has eliminated motion artifact and noise caused by the electrode. The development of the driven-right-leg circuit has greatly reduced interference due to power lines. Adaptive filters have reduced the difficult-to-eliminate interference due to spark-gap electrosurgical units.     

Ground-Free ECG Recording with Two Electrodes

ECG recordings normally use three electrodes?two for the differential inputs of the ECG amplifier and the third for ground. We analyze those situations where the ground electrode can be eliminated. We propose a model for the source of electrical interference and determine various parameter values. Making use of experimentally obtained data for the model parameters we suggest optimal design for a two-electrode amplifier. The two-electrode design is useful for biotelemetry, portable Holter monitors, and portable arrhythmia monitors. Under certain circumstances it may be useful for grounded monitoring equipment. The two-electrode technique has the advantage that it improves patient safety by eliminating the ground electrode. Fewer electrodes make patient attachment easier and lower electrode costs.     

Ultrahigh Electrical Resistance of Poly(cyclohexyl methacrylate)/Carbon Nanotube Composites Prepared Using Surface‐Initiated Polymerization

Multiwalled carbon nanotubes on which poly(cyclohexyl methacrylate)s are densely grafted (PCHMA‐CNTs), are synthesized using a modified surface‐initiated atom transfer radical polymerization technique. The electrical resistance of PCHMA‐CNT is systematically characterized under direct current (DC) and alternating current and compared to that of conventional nanocomposites prepared by blending PCHMA with the CNT (PCHMA/CNT). At a comparable volume fraction of CNT, DC volume resistivity of PCHMA‐CNT is 14 orders of magnitude higher than that of PCHMA/CNT. This is because the grafted polymer with a combination of the high molecular weight and the high grafting density isolates individual CNTs at a long distance in the PCHMA‐CNT system. In addition, impedance analysis reveals that the highly insulated PCHMA‐CNT has the same electrical nature as neat PCHMA, i.e., it is a dielectric. Furthermore, dynamic mechanical analysis shows PCHMA‐CNT has a good mechanical properties as well as ultrahigh electrical resistance.     

Electrically Addressable Hybrid Architectures of Zinc Oxide Nanowires Grown on Aligned Carbon Nanotubes

The fabrication and characterization of hybrid architectures of ZnO nanowires (ZNWs) grown on organized carbon nanotubes (CNTs), by a two‐step chemical vapor deposition (CVD) process involving CNT growth from a hydrocarbon source followed by ZNW growth using a Zn metal source, is reported. The ZNWs grow uniformly and radially from individual CNTs and CNT bundles, and the aligned morphology of the CNTs is not disturbed by the ZNW growth process. The nucleation and growth of ZnO crystals on CNTs are analyzed in relation to the classical vapor–solid mechanism. Importantly, the CNTs make uniform and distributed electrical contact to the ZNWs, with up to a 1000‐fold yield advantage over conventional ZNW growth on a flat substrate. Hybrid ZNW/CNT sheets are fabricated by scalable CVD, rolling, and printing methods; and their electrical properties, which are governed by transport through the anisotropic CNT network, are characterized. Functional interaction between the ZNWs and CNTs is demonstrated by photoconductive behavior and photocurrent generation of the hybrid material under UV illumination. There is significant future opportunity to extend these processing methods to fabricate other functional oxides on CNTs, and to build devices that harness the attractive properties of ZNWs and CNTs with high volumetric efficiency over large areas.     

Biocompatible and Biodegradable Organic Transistors Using a Solid‐State Electrolyte Incorporated with Choline‐Based Ionic Liquid and Polysaccharide

Biocompatible, biodegradable, and solid‐state electrolyte‐based organic transistors are demonstrated. As the electrolyte is composed of all edible materials, which are levan polysaccharide and choline‐based ionic liquid, the organic transistor fabricated on the electrolyte can be biocompatible and biodegrable. Compared to the other ion gel based electrolytes, it has superior electrical and mechanical properties, large specific capacitance (≈40 µF cm^?2), non‐volatility, flexibility, and high transparency. Thus, it shows mechanical reliability by maintaining electrical performances under up to 1.11% of effective bending strain, 5% of stretching, and have low operation voltage range when it is utilized in organic transistors. Moreover, the biodegradable electrolyte‐based organic transistors can be applied to bio‐integrated devices, such as electrocardiogram (ECG) recordings on human skin and the heart of a rat. The measured ECG signals from the transistors, compared to signals from electrode‐based sensors, has a superior signal‐to‐noise ratio. The biocompatible and biodegradable materials and devices can contribute to the development of many bioelectronics.     

A Wearable ECG Acquisition System With Compact Planar-Fashionable Circuit Board-Based Shirt

A wearable electrocardiogram (ECG) acquisition system implemented with planar-fashionable circuit board (P-FCB)-based shirt is presented. The proposed system removes cumbersome wires from conventional Holter monitor system for convenience. Dry electrodes screen-printed directly on fabric enables long-term monitoring without skin irritation. The ECG monitoring shirt exploits a monitoring chip with a group of electrodes around the body, and both the electrodes and the interconnection are implemented using P-FCB to enhance wearability and to lower production cost. The characteristics of P-FCB electrode are shown, and the prototype hardware is implemented to successfully verify the proposed concept.      

Carbon nanotubes for nanoscale low temperature flip chip connections

In this work we demonstrate a new approach for ultra fine flip chip interconnections based on carbon nanotubes as a wiring material. In contrast to other works we show patterned growth of multi walled CNTs on substrates with pre-structured bond pads including a complete metallization system for electrical characterization. Furthermore, we succeeded achieving a reliable flip chip connection between CNT-covered contact pads and metal pads at temperatures lower than 200 °C. Our goal is a reversible electrical and mechanical chip assembly with CNT bumps.For bonding experiments and electrical characterization a test structure with a damascene metallization including a layer stack of TiN/Cu/TiN was prepared. For CNT growth a thin nickel catalyst layer was selectively deposited with sputtering and a lift-off technique on the contact pads. The CNTs were grown by thermal CVD with ethylene as carbon source. CNT growth parameters like catalyst thickness, gas composition, growth time and temperature were optimized to get dense CNT growth. The metal bumps of the counter chip consist of electroless deposited Ni. With the selected layout we can obtain daisy chain and four-point measurements for lossless determination of single contact resistance. We have obtained reliable electrical contacts with relatively small resistance reaching values as low as 2.2 Ω. As CNT-quality is strongly dependent on the growth temperature we observed a strong change in resistivity of the flip chip connection as the growth temperature was varied. Reliability tests showed long time stability under thermal stress proving a reliable electrical contact between the contact pads. There is an appropriate potential for further optimization of the CNT bump resistance and applying this technology for IC-devices.