Dielectrophoresis‐Assisted Integration of 1024 Carbon Nanotube Sensors into a CMOS Microsystem

Carbon‐nanotube (CNT)‐based sensors offer the potential to detect single‐molecule events and picomolar analyte concentrations. An important step toward applications of such nanosensors is their integration in large arrays. The availability of large arrays would enable multiplexed and parallel sensing, and the simultaneously obtained sensor signals would facilitate statistical analysis. A reliable method to fabricate an array of 1024 CNT‐based sensors on a fully processed complementary‐metal‐oxide‐semiconductor microsystem is presented. A high‐yield process for the deposition of CNTs from a suspension by means of liquid‐coupled floating‐electrode dielectrophoresis (DEP), which yielded 80% of the sensor devices featuring between one and five CNTs, is developed. The mechanism of floating‐electrode DEP on full arrays and individual devices to understand its self‐limiting behavior is studied. The resistance distributions across the array of CNT devices with respect to different DEP parameters are characterized. The CNT devices are then operated as liquid‐gated CNT field‐effect‐transistors (LG‐CNTFET) in liquid environment. Current dependency to the gate voltage of up to two orders of magnitude is recorded. Finally, the sensors are validated by studying the pH dependency of the LG‐CNTFET conductance and it is demonstrated that 73% of the CNT sensors of a given microsystem show a resistance decrease upon increasing the pH value.     

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.     

Nanoenvelopes: Wrapping a Single‐Walled Carbon Nanotube with Graphene using an Atomic Force Microscope

Engineering the morphology and structure of low‐dimensional carbon nanomaterials is important to study their mechanical and electrical properties and even superconductivity. Herein, first the techniques that are used to engineer carbon nanotubes, including manipulation, morphology modification, and fabrication of complex nanostructures, are reviewed. This is followed by a summary of the methods applied to fabricate graphene nanostructures, such as heterostructures and nanoenvelopes of graphene. Lastly, an insight into the applications of low‐dimensional‐carbon‐based electronics is given, such as carbon nanotube (CNT) transistors, graphene‐based nanoenvelopes, and graphene‐contacted CNT field‐effect transistors (FETs), which are promising components in future electronics.     

Anti‐Ambipolar Transport with Large Electrical Modulation in 2D Heterostructured Devices

Van der Waals materials and their heterostructures provide a versatile platform to explore new device architectures and functionalities beyond conventional semiconductors. Of particular interest is anti‐ambipolar behavior, which holds potentials for various digital electronic applications. However, most of the previously conducted studies are focused on hetero‐ or homo‐ p–n junctions, which suffer from a weak electrical modulation. Here, the anti‐ambipolar transport behavior and negative transconductance of MoTe₂ transistors are reported using a graphene/h‐BN floating‐gate structure to dynamically modulate the conduction polarity. Due to the asymmetric electrical field regulating effect on the recombination and diffusion currents, the anti‐ambipolar transport and negative transconductance feature can be systematically controlled. Consequently, the device shows an unprecedented peak resistance modulation factor (≈5 × 10³), and effective photoexcitation modulation with distinct threshold voltage shift and large photo on/off ratio (≈10⁴). Utilizing this large modulation effect, the voltage‐transfer characteristics of an inverter circuit variant are further studied and its applications in Schmitt triggers and multivalue output are further explored. These properties, in addition to their proven nonvolatile storage, suggest that such 2D heterostructured devices display promising perspectives toward future logic applications.     

Effects of temperature and torsion speed on torsional properties of single-walled carbon nanotubes

Carbon nanotubes (CNTs) are excellent candidates for torsional elements used in nanoelectro-mechanical systems (NEMS). Simulations show that after being twisted to a certain angle, they buckle and lose their mechanical strength. In this paper, classical molecular dynamics simulations are performed on single-walled carbon nanotubes (CNTs) to investigate the effects of torsion speed and temperature on CNT torsional properties. The AIREBO potential is employed to describe the bonded interactions between carbon atoms. The MD simulations clearly show that the buckling of CNTs in torsion is a reversible process, in which by unloading the buckled CNT in opposite direction, it returns to its original configuration. In addition, the numerical results reveal that the torsional shear modulus of CNTs increases by increasing the temperature and decreasing the torsion speed. Furthermore, the buckling torsion angle of CNTs increases by increasing the torsion speed and decreasing the temperature. Finally, it is observed that torsional properties of CNTs are highly affected by speed of twist and temperature of the nanotubes.     

Wafer‐Scale Fabrication of Suspended Single‐Walled Carbon Nanotube Arrays by Silver Liquid Dynamics

Suspended single‐walled carbon nanotubes (SWNTs) have advantages in mechanical resonators and highly sensitive sensors. Large‐scale fabrication of suspended SWNTs array devices and uniformity among SWNTs devices remain a great challenge. This study demonstrates an effective, fast, and wafer‐scale technique to fabricate suspended SWNT arrays, which is based on a dynamic motion of silver liquid to suspend and align the SWNTs between the prefabricated palladium electrodes in high temperature annealing treatment. Suspended, strained, and aligned SWNTs are synthesized on a 2 × 2 cm² substrate with an average density of 10 tubes per micrometer. Under the optimal conditions, almost all SWNTs become suspended. A promising formation model of suspended SWNTs is established. The Kelvin four‐terminal resistance measurement shows that these SWNT array devices have extreme low contact resistance. Meanwhile, the suspended SWNT array field effect transistors are fabricated by selective etching of metallic SWNTs using electrical breakdown. This method of large‐scale fabrication of suspended architectures pushes the study of nanoscale materials into a new stage related to the electrical physics and industrial applications.     

Anisotropic Magneto‐Coulomb Properties of 2D–0D Heterostructure Single Electron Device

Fabrication and spintronics properties of 2D–0D heterostructures are reported. Devices based on graphene (“Gr”)–aluminium nanoclusters heterostructures show robust and reproducible single‐electron transport features, in addition to spin‐dependent functionality when using a top magnetic electrode. The magnetic orientation of this single ferromagnetic electrode enables the modulation of the environmental charge experienced by the aluminium nanoclusters. This anisotropic magneto‐Coulomb effect, originating from spin–orbit coupling within the ferromagnetic electrode, provides tunable spin valve‐like magnetoresistance signatures without the requirement of spin coherent charge tunneling. These results extend the capability of Gr to act both as electrode and as a platform for the growth of 2D–0D mixed‐dimensional van der Waals heterostructures, providing magnetic functionalities in the Coulomb blockade regime on scalable spintronic devices. These heterostructures pave the way towards novel device architectures at the crossroads of 2D material physics and spin electronics.     

Nanomanufacturing of RGO‐CNT Hybrid Film for Flexible Aqueous Al‐Ion Batteries

A highly electrically conductive film‐type current collector is an essential part of batteries. Apart from the metal‐based current collectors, lightweight and highly conductive carbon materials such as reduced graphene oxide (RGO) and carbon nanotubes (CNTs) show great potential as current collectors. However, traditional RGO manufacturing usually requires a long time and high energy, which decreases the product yielding rate and manufacturing efficiency. Moreover, the performance of the manufactured RGO needs to be further improved. In this work, CNT and GO are evenly mixed into GO‐CNT, which can be directly reduced into RGO‐CNT by Joule heating at 2936 K within less than 1 min. The fabricated RGO‐CNT achieves a high electrical conductivity of 2750 S cm^?1, and realizes a 10⁶‐fold increase. The assembled flexible aqueous Al‐ion battery with RGO‐CNT as the current collector exhibits impressive electrochemical performance in terms of superior cycling stability and exceptional rate capability, and excellent mechanical ability regarding the tolerance to mechanical damage such as bending, folding, piercing, and cutting without detrimental consequences.     

Bioinspired,Spine‐Like,Flexible, Rechargeable Lithium‐Ion Batteries with High Energy Density

The rapid development of flexible and wearable electronics proposes the persistent requirements of high‐performance flexible batteries. Much progress has been achieved recently, but how to obtain remarkable flexibility and high energy density simultaneously remains a great challenge. Here, a facile and scalable approach to fabricate spine‐like flexible lithium‐ion batteries is reported. A thick, rigid segment to store energy through winding the electrodes corresponds to the vertebra of animals, while a thin, unwound, and flexible part acts as marrow to interconnect all vertebra‐like stacks together, providing excellent flexibility for the whole battery. As the volume of the rigid electrode part is significantly larger than the flexible interconnection, the energy density of such a flexible battery can be over 85% of that in conventional packing. A nonoptimized flexible cell with an energy density of 242 Wh L^?1 is demonstrated with packaging considered, which is 86.1% of a standard prismatic cell using the same components. The cell also successfully survives a harsh dynamic mechanical load test due to this rational bioinspired design. Mechanical simulation results uncover the underlying mechanism: the maximum strain in the reported design (≈0.08%) is markedly smaller than traditional stacked cells (≈1.1%). This new approach offers great promise for applications in flexible devices.     

Edge‐Epitaxial Growth of 2D NbS2‐WS2 Lateral Metal‐Semiconductor Heterostructures

2D metal‐semiconductor heterostructures based on transition metal dichalcogenides (TMDs) are considered as intriguing building blocks for various fields, such as contact engineering and high‐frequency devices. Although, a series of p–n junctions utilizing semiconducting TMDs have been constructed hitherto, the realization of such a scheme using 2D metallic analogs has not been reported. Here, the synthesis of uniform monolayer metallic NbS₂ on sapphire substrate with domain size reaching to a millimeter scale via a facile chemical vapor deposition (CVD) route is demonstrated. More importantly, the epitaxial growth of NbS₂‐WS₂ lateral metal‐semiconductor heterostructures via a “two‐step” CVD method is realized. Both the lateral and vertical NbS₂‐WS₂ heterostructures are achieved here. Transmission electron microscopy studies reveal a clear chemical modulation with distinct interfaces. Raman and photoluminescence maps confirm the precisely controlled spatial modulation of the as‐grown NbS₂‐WS₂ heterostructures. The existence of the NbS₂‐WS₂ heterostructures is further manifested by electrical transport measurements. This work broadens the horizon of the in situ synthesis of TMD‐based heterostructures and enlightens the possibility of applications based on 2D metal‐semiconductor heterostructures.     

State of the Art of Carbon Nanotube Fibers: Opportunities and Challenges

The superb mechanical and physical properties of individual carbon nanotubes (CNTs) have provided the impetus for researchers in developing high‐performance continuous fibers based upon CNTs. The reported high specific strength, specific stiffness and electrical conductivity of CNT fibers demonstrate the potential of their wide application in many fields. In this review paper, we assess the state of the art advances in CNT‐based continuous fibers in terms of their fabrication methods, characterization and modeling of mechanical and physical properties, and applications. The opportunities and challenges in CNT fiber research are also discussed.     

Healable,Transparent, Room‐Temperature Electronic Sensors Based on Carbon Nanotube Network‐Coated Polyelectrolyte Multilayers

Transparent and conductive film based electronics have attracted substantial research interest in various wearable and integrated display devices in recent years. The breakdown of transparent electronics prompts the development of transparent electronics integrated with healability. A healable transparent chemical gas sensor device is assembled from layer‐by‐layer‐assembled transparent healable polyelectrolyte multilayer films by developing effective methods to cast transparent carbon nanotube (CNT) networks on healable substrates. The healable CNT network‐containing film with transparency and superior network structures on self‐healing substrate is obtained by the lateral movement of the underlying self‐healing layer to bring the separated areas of the CNT layer back into contact. The as‐prepared healable transparent film is assembled into healable transparent chemical gas sensor device for flexible, healable gas sensing at room temperature, due to the 1D confined network structure, relatively high carrier mobility, and large surface‐to‐volume ratio. The healable transparent chemical gas sensor demonstrates excellent sensing performance, robust healability, reliable flexibility, and good transparency, providing promising opportunities for developing flexible, healable transparent optoelectronic devices with the reduced raw material consumption, decreased maintenance costs, improved lifetime, and robust functional reliability.     

25th Anniversary Article: Carbon Nanotube‐ and Graphene‐Based Transparent Conductive Films for Optoelectronic Devices

Carbon nanotube (CNT)‐ and graphene (G)‐based transparent conductive films (TCFs) are two promising alternatives for commonly‐used indium tin oxide‐based TCFs for future flexible optoelectronic devices. This review comprehensively summarizes recent progress in the fabrication, properties, modification, patterning, and integration of CNT‐ and G‐TCFs into optoelectronic devices. Their potential applications and challenges in optoelectronic devices, such as organic photovoltaic cells, organic light emitting diodes and touch panels, are discussed in detail. More importantly, their key characteristics and advantages for use in these devices are compared. Despite many challenges, CNT‐ and G‐TCFs have demonstrated great potential in various optoelectronic devices and have already been used for some products like touch panels of smartphones. This illustrates the significant opportunities for the industrial use of CNTs and graphene, and hence pushes nanoscience and nanotechnology one step towards practical applications.     

Recent Advances in Research on Carbon Nanotube–Polymer Composites

Carbon nanotubes (CNTs) demonstrate remarkable electrical, thermal, and mechanical properties, which allow a number of exciting potential applications. In this article, we review the most recent progress in research on the development of CNT–polymer composites, with particular attention to their mechanical and electrical (conductive) properties. Various functionalization and fabrication approaches and their role in the preparation of CNT–polymer composites with improved mechanical and electrical properties are discussed. We tabulate the most recent values of Young's modulus and electrical conductivities for various CNT–polymer composites and compare the effectiveness of different processing techniques. Finally, we give a future outlook for the development of CNT–polymer composites as potential alternative materials for various applications, including flexible electrodes in displays, electronic paper, antistatic coatings, bullet‐proof vests, protective clothing, and high‐performance composites for aircraft and automotive industries.     

Aligning Solution‐Derived Carbon Nanotube Film with Full Surface Coverage for High‐Performance Electronics Applications

The main challenge for application of solution‐derived carbon nanotubes (CNTs) in high performance field‐effect transistor (FET) is how to align CNTs into an array with high density and full surface coverage. A directional shrinking transfer method is developed to realize high density aligned array based on randomly orientated CNT network film. Through transferring a solution‐derived CNT network film onto a stretched retractable film followed by a shrinking process, alignment degree and density of CNT film increase with the shrinking multiple. The quadruply shrunk CNT films present well alignment, which is identified by the polarized Raman spectroscopy and electrical transport measurements. Based on the high quality and high density aligned CNT array, the fabricated FETs with channel length of 300 nm present ultrahigh performance including on‐state current I_on of 290 µA µm^?1 (V_ds = ?1.5 V and V_gs = ?2 V) and peak transconductance g_m of 150 µS µm^?1, which are, respectively, among the highest corresponding values in the reported CNT array FETs. High quality and high semiconducting purity CNT arrays with high density and full coverage obtained through this method promote the development of high performance CNT‐based electronics.     

All‐Solution‐Processed Metal‐Oxide‐Free Flexible Organic Solar Cells with Over 10% Efficiency

All‐solution‐processing at low temperatures is important and desirable for making printed photovoltaic devices and also offers the possibility of a safe and cost‐effective fabrication environment for the devices. Herein, an all‐solution‐processed flexible organic solar cell (OSC) using poly(3,4‐ethylenedioxythiophene):poly‐(styrenesulfonate) electrodes is reported. The all‐solution‐processed flexible devices yield the highest power conversion efficiency of 10.12% with high fill factor of over 70%, which is the highest value for metal‐oxide‐free flexible OSCs reported so far. The enhanced performance is attributed to the newly developed gentle acid treatment at room temperature that enables a high‐performance PEDOT:PSS/plastic underlying substrate with a matched work function (≈4.91 eV), and the interface engineering that endows the devices with better interface contacts and improved hole mobility. Furthermore, the flexible devices exhibit an excellent mechanical flexibility, as indicated by a high retention (≈94%) of the initial efficiency after 1000 bending cycles. This work provides a simple route to fabricate high‐performance all‐solution‐processed flexible OSCs, which is important for the development of printing, blading, and roll‐to‐roll technologies.     

Micrometer‐ and Nanometer‐Sized Organic Single‐Crystalline Transistors

The use of micrometer and nanometer‐sized organic single crystals to fabricate devices can retain all the advantages of single crystals, avoid the difficulties of growing large crystals, and provide a way to characterize organic semiconductors more efficiently. Moreover, the effective use of such “small” crystals will be beneficial to nanoelectronics. Here we review the recent progress of organic single‐crystalline transistors based on micro‐/nanometer‐sized structures, namely fabrication methods and related technical issues, device properties, and current challenges.     

Thread‐like Supercapacitors Based on One‐Step Spun Nanocomposite Yarns

Thread‐like electronic devices have attracted great interest because of their potential applications in wearable electronics. To produce high‐performance, thread‐like supercapacitors, a mixture of stable dispersions of single‐walled carbon nanotubes and conducting polyaniline nanowires are prepared. Then, the mixture is spun into flexible yarns with a polyvinyl alcohol outer sheath by a one‐step spinning process. The composite yarns show excellent mechanical properties and high electrical conductivities after sufficient washing to remove surfactants. After applying a further coating layer of gel electrolyte, two flexible yarns are twisted together to form a thread‐like supercapacitor. The supercapacitor based on these two yarns (SWCNTs and PAniNWs) possesses a much higher specific capacitance than that based only on pure SWCNTs yarns, making it an ideal energy‐storage device for wearable electronics.     

A Phase‐Separation Route to Synthesize Porous CNTs with Excellent Stability for Na+ Storage

Porous carbon nanotubes (CNTs) are obtained by removing MoO₂ nanoparticles from MoO₂@C core@shell nanofibers which are synthesized by phase‐segregation via a single‐needle electrospinning method. The specific surface area of porous CNTs is 502.9 m² g^?1, and many oxygen‐containing functional groups (C? OH, C?O) are present. As anodes for sodium‐ion batteries, the porous CNT electrode displays excellent rate performance and cycling stability (110 mA h g^?1 after 1200 cycles at 5 A g^?1). Those high properties can be attributed to the porous structure and surface modification to steadily store Na⁺ with high capacity. The work provides a facile and broadly applicable way to fabricate the porous CNTs and their composites for batteries, catalysts, and fuel cells.     

Non‐Volatile ReRAM Devices Based on Self‐Assembled Multilayers of Modified Graphene Oxide 2D Nanosheets

2D nanomaterials have been actively utilized in non‐volatile resistive switching random access memory (ReRAM) devices due to their high flexibility, 3D‐stacking capability, simple structure, transparency, easy fabrication, and low cost. Herein, it demonstrates re‐writable, bistable, transparent, and flexible solution‐processed crossbar ReRAM devices utilizing graphene oxide (GO) based multilayers as active dielectric layers. The devices employ single‐ or multi‐component‐based multilayers composed of positively charged GO (N‐GO(+) or NS‐GO(+)) with/without negatively charged GO(‐) using layer‐by‐layer assembly method, sandwiched between Al bottom and Au top electrodes. The device based on the multi‐component active layer Au/[N‐GO(+)/GO(‐)]_n/Al/PES shows higher ON/OFF ratio of ≈10⁵ with switching voltage of ?1.9 V and higher retention stability (≈10⁴ s), whereas the device based on single component (Au/[N‐GO(+)]_n/Al/PES) shows ≈10³ ON/OFF ratio at ±3.5 V switching voltage. The superior ReRAM properties of the multi‐component‐based device are attributed to a higher coating surface roughness. The Au/[N‐GO(+)/GO(–)]_n/Al/PES device prepared from lower GO concentration (0.01%) exhibits higher ON/OFF ratio (≈10⁹) at switching voltage of ±2.0 V. However, better stability is achieved by increasing the concentration from 0.01% to 0.05% of all GO‐based solutions. It is found that the devices containing MnO₂ in the dielectric layer do not improve the ReRAM performance.