Enrichment of high-purity large-diameter semiconducting single-walled carbon nanotubes

Semiconducting single-walled carbon nanotubes SWCNTs (s-SWCNTs) are considered one of the most promising alternatives to traditional silicon-based semiconductors. In particular, large-diameter s-SWCNTs (>1.2 nm) exhibit more advantages over small-diameter ones in high-performance electronic applications because of their higher charge carrier mobility and reduced Schottky barrier height. Great efforts have been made to enriching large-diameter s-SWCNTs from mass-produced raw CNTs that contain both metallic SWCNTs and s-SWCNTs. Among separation technologies, the effective and scalable ones are conjugated polymer wrapping (CPW), gel permeation chromatography (GC), aqueous two-phase extraction (ATPE), and density gradient ultracentrifugation (DGU). In this review, we survey recent progress on enriching large-diameter s-SWCNTs using those methods and outline the strategies and challenges in the separation according to the electronic type and chirality of SWCNTs. Finally, we highlight some applications of the enriched large-diameter s-SWCNTs and outlook for the future of SWCNT-based electronic devices.

Selective separation of single-walled carbon nanotubes in aqueous solution by assembling redox nanoclusters

The selective separation of soluble and individual single-walled carbon nanotubes (SWCNTs) in aqueous solution is a key step for harnessing the extraordinary properties of these materials. Manipulating the strong van der Waals intertube interactions between the SWCNT bundles is very important in selective separation, which is a long-standing challenge. Here we reported the ability of redox polyoxometalate clusters to modulate the intertube π-π stacking interaction through electron transfer and achieved the diameter-selective separation of SWCNTs in a surfactant aqueous solution. The large-diameter SWCNTs concentrated at ∼1.3-1.4 nm were selectively separated when ∼1 nm clusters encapsulated within the tube cavity, and the dispersion of subnanometer ∼0.7-0.9 nm SWCNTs was boosted when clusters were adsorbed on the outer surface of small-diameter nanotubes. The mechanism of diameter-selective separation of SWCNTs associated with the size-dependent interaction between cluster-tubes and the steric hindrance effect of clusters was revealed by optical absorption and Raman spectroscopy. This simple method thus enables the selective separation of individual high-quality SWCNTs in aqueous solutions without harsh sonication with the potential for other separation applications.

Dip-Coating Self-Assembly Fabrication and Polarization Sensitive Photoresponse of Aligned Single-Walled Carbon Nanotube Film

It is challenging to obtain wafer-scaled aligned films for completely exploiting the promising properties of semiconducting single-walled carbon nanotubes (s-SWCNTs). Aligned s-SWCNTs with a large area can be obtained by combining water evaporation and slow withdrawal-induced self-assembly in a dip-coating process. Moreover, the tunability of deposition morphology parameters such as stripe width and spacing is examined. The polarized Raman results show that s-SWCNTs can be aligned in ±8.6°. The derived two terminal photodetector shows both a high negative responsivity of 41 A/W at 520 nm and high polarization sensitivity. Our results indicate that aligned films with a large area may be useful to electronics- and optoelectronics-related applications.

Regio- and Steric Effects on Single Molecule Conductance of Phenanthrenes

Here, six phenanthrene (the smallest arm-chair graphene nanoribbon) derivatives with dithiomethyl substitutions at different positions as the anchoring groups were synthesized. Scanning tunneling microscopy break junction technique was used to measure their single molecule conductances between gold electrodes, which showed a difference as much as 20-fold in the range of ∼10^-2.82 G₀ to ∼10^-4.09 G₀ following the trend of G_2,7 > G_3,6 > G_2,6 > G_1,7 > G_1,6 > G_1,8. DFT calculations agree well with this measured trend and indicate that the single molecule conductances are a combination of energy alignment, electronic coupling, and quantum effects. This significant regio- and steric effect on the single molecule conductance of phenanthrene model molecules shows the complexity in the practice of graphene nanoribbons as building blocks for future carbon-based electronics in one hand but also provides good conductance tunability on the other hand.

Elastomeric Nanodielectrics for Soft and Hysteresis-Free Electronics

Elastomeric dielectrics are crucial for reliably governing the carrier densities in semiconducting channels during deformation in soft/stretchable field-effect transistors (FETs). Uncontrolled stacking of polymeric chains renders elastomeric dielectrics poorly insulated at nanoscale thicknesses, thereby thick films are usually required, leading to high voltage or power consumption for on/off operations of FETs. Here, layer-by-layer assembly is exploited to build 15-nm-thick elastomeric nanodielectrics through alternative adsorption of oppositely charged polyurethanes (PUs) for soft and hysteresis-free FETs. After mild thermal annealing to heal pinholes, such PU multilayers offer high areal capacitances of 237 nF cm^-2 and low leakage current densities of 3.2 × 10^-8 A cm^-2 at 2 V. Owing to the intrinsic ductility of the elastomeric PUs, the nanofilms possess excellent dielectric properties at a strain of 5% or a bending radius of 1.5 mm, while the wrinkled counterparts show mechanical stability with negligible changes of leakage currents after repeated stretching to a strain of 50%. Besides, these nanodielectrics are immune to high humidity and conserve their properties when immersed into water, despite their assembly occurs aqueously. Furthermore, the PU dielectrics are implemented in carbon nanotube FETs, demonstrating low-voltage operations (< 1.5 V) and negligible hysteresis without any encapsulations.

Carbon Nanotube-Based Field-Effect Transistor-Type Sensor with a Sensing Gate for Ppb-Level Formaldehyde Detection

The detection of harmful trace gases, such as formaldehyde (HCHO), is a technical challenge in the current gas sensor field. The weak electrical signal caused by trace amounts of gases is difficult to be detected and susceptible to other gases. Based on the amplification effect of a field-effect transistor (FET), a carbon-based FET-type gas sensor with a gas-sensing gate is proposed for HCHO detection at the ppb level. Semiconducting carbon nanotubes (s-CNTs) and a catalytic metal are chosen as channel and gate materials, respectively, for the FET-type gas sensor, which makes full use of the respective advantages of the channel transport layer and the sensitive gate layer. The as-prepared carbon-based FET-type gas sensor exhibits a low detection limit toward HCHO up to 20 ppb under room temperature (RT), which can be improved to 10 ppb by a further heating strategy. It also exhibits a remarkable elevated recovery rate from 80 to 97% with almost no baseline drift (2%) compared to the RT condition, revealing excellent reproducibility, stability, and recovery. The role of sensitive function in the FET-type gas sensor is performed by means of an independent gas-sensing gate, that is, the independence of the sensitive gate and the electron transmission channel is the main reason for its high sensitivity detection. We hope our work can provide an instructive approach for designing high-performance formaldehyde sensor chips with on-chip integration potential.

Functionalized Carbon Materials in Syngas Conversion

Functionalized carbon materials are widely used in heterogeneous catalysis due to their unique properties such as adjustable surface properties, excellent thermal conductivity, high surface areas, tunable porosity, and moderate interactions with guest metals. The transformation of syngas into hydrocarbons (known as the Fischer-Tropsch synthesis) or oxygenates is an exothermic reaction and is typically catalyzed by transition metals dispersed on functionalized supports. Various carbon materials have been employed in syngas conversions not only for improving the performance or decreasing the dosage of expensive active metals but also for building model catalysts for fundamental research. This article provides a critical review on recent advances in the utilization of carbon materials, in particular the recently developed functionalized nanocarbon materials, for syngas conversions to either hydrocarbons or oxygenates. The unique features of carbon materials in dispersing metal nanoparticles, heteroatom doping, surface modification, and building special nanoarchitectures are highlighted. The key factors that control the reaction course and the reaction mechanism are discussed to gain insights for the rational design of efficient carbon-supported catalysts for syngas conversions. The challenges and future opportunities in developing functionalized carbon materials for syngas conversions are briefly analyzed.

Advances and Frontiers in Single-Walled Carbon Nanotube Electronics

Single-walled carbon nanotubes (SWCNTs) have been considered as one of the most promising electronic materials for the next-generation electronics in the more Moore era. Sub-10 nm SWCNT-field effect transistors (FETs) have been realized with several performances exceeding those of Si-based FETs at the same feature size. Several industrial initiatives have attempted to implement SWCNT electronics in integrated circuit (IC) chips. Here, the recent advances in SWCNT electronics are reviewed from in-depth understanding of the fundamental electronic structures, the carrier transport mechanisms, and the metal/SWCNT contact properties. In particular, the subthreshold switching properties are highlighted for low-power, energy-efficient device operations. State-of-the-art low-power SWCNT-based electronics and the key strategies to realize low-voltage and low-power operations are outlined. Finally, the essential challenges and prospects from the material preparation, device fabrication, and large-scale ICs integration for future SWCNT-based electronics are foregrounded.

BN-Embedded Perylenes

Transition metal catalyzed coupling reaction strategy has been utilized in the synthesis of two novel BN-perylenes starting from halogenated BN-naphthalene derivatives. The molecular structures and packing modes of BN-perylenes were confirmed by NMR spectroscopy and X-ray single-crystal diffraction experiments. Their photophysical properties were further investigated using UV-vis and fluorescence spectroscopy and DFT calculations. Interestingly, the isosteric BN-insertion in perylene system resulted in stronger π-π stacking interaction both in solid and solution phases. The synthesized BN-perylenes are proved to be highly stable and thus provide a new valuable platform for novel organic materials applications which is otherwise inaccessible to date.

Building a Bridge for Carbon Nanotubes from Nanoscale Structure to Macroscopic Application

Through 30 years of research, researchers have gained a deep understanding of the synthesis, characteristics, and applications of carbon nanotubes (CNTs). However, up to now, there are still few industries using CNT as the leading material. The difficulty of CNTs to be applied in industry is the gap between the properties of CNT-based aggregates and those of a single carbon nanotube. Therefore, how to maintain the intrinsic properties of CNTs when they are assembled into aggregates is of great significance. Herein, we summarize and analyze the research status of CNT materials applied in different fields from proven techniques to potential industries, including energy storage, electronics, mechanical and other applications. For each application, the intrinsic properties of CNTs and the real performances of their aggregates are compared to figure out the key problems in CNT synthesis. Finally, we give an outlook for building a bridge for CNTs from nanoscale structure to macroscopic application, giving inspiration to researchers making efforts toward the real application of carbon nanotubes.

Beyond Color: The New Carbon Ink

For thousands of years, carbon ink has been used as a black color pigment for writing and painting purposes. However, recent discoveries of nanocarbon materials, including fullerenes, carbon nanotubes, graphene, and their various derivative forms, together with the advances in large-scale synthesis, are enabling a whole new generation of carbon inks that can serve as an intrinsically programmable materials platform for developing advanced functionalities far beyond color. The marriage between these multifunctional nanocarbon inks with modern printing technologies is facilitating and even transforming many applications, including flexible electronics, wearable and implantable sensors, actuators, and autonomous robotics. This review examines recent progress in the reborn field of carbon inks, highlighting their programmability and multifunctionality for applications in flexible electronics and stimuli-responsive devices. Current challenges and opportunities will also be discussed from a materials science perspective towards the advancement of carbon ink for new applications beyond color.

Confined Fe Catalysts for High-Density SWNT Arrays Growth: a New Territory for Catalyst-Substrate Interaction Engineering

Great efforts have been devoted to searching for efficient catalytic systems to produce ultra-high density single-walled carbon nanotube (SWNT) arrays, which lay the foundation for future electronic devices. However, one major obstacle for realizing high-density surface-aligned SWNT arrays is the poor stability of metal nanoparticles in chemical vapor deposition catalytic processes. Recently, Trojan catalyst has been reported to yield unprecedented high-density SWNT arrays with 130 SWNTs per µm on the a-plane (11-20) of the sapphire substrate. Herein, a concept of catalyst confinement effect is put forward to revealing the secret of remarkable growth efficiency of SWNT arrays by Trojan catalyst. Combined experimental and theoretical studies indicate that confinement of catalyst nanoparticles on discrete a-plane strips plays a key role in stabilizing the small nanoparticles. The highly dispersive and active states of catalysts are maintained, which promote the growth of super-dense SWNT arrays. By rationally designing the substrate reconstruction process, large areas of dense SWNT arrays (130 SWNTs per µm) covering the entire substrate are obtained. This approach may provide novel ideas for the synthesis of various high-density 1D nanomaterials.

Mechanomaterials: A Rational Deployment of Forces and Geometries in Programming Functional Materials

The knowledge of mechanics of materials has been extensively implemented in developing functional materials, giving rise to recent advances in soft actuators, flexible electronics, mechanical metamaterials, tunable mechanochromics, regenerative mechanomedicine, etc. While conventional mechanics of materials offers passive access to mechanical properties of materials in existing forms, a paradigm shift is emerging toward proactive programming of materials' functionality by leveraging the force-geometry-property relationships. Here, such a rising field is coined as "mechanomaterials". To profile the concept, the design principles in this field at four scales is first outlined, namely the atomic scale, the molecular scale, the manipulation of nanoscale materials, and the microscale design of structural materials. A variety of techniques have been recruited to deliver the multiscale programming of functional mechanomaterials, such as strain engineering, capillary assembly, topological interlocking, kirigami, origami, to name a few. Engineering optical and biological functionalities have also been achieved by implementing the fundamentals of mechanochemistry and mechanobiology. Nonetheless, the field of mechanomaterials is still in its infancy, with many open challenges and opportunities that need to be addressed. The authors hope this review can serve as a modest spur to attract more researchers to further advance this field.

Toward an Intelligent Synthesis: Monitoring and Intervening in the Catalytic Growth of Carbon Nanotubes

The bottom-up approach to directly synthesizing low-dimensional materials with outstanding performance has extended the material basis for the next generation integrated circuit industry. All the low-dimensional semiconductors, metals, dielectrics, and their heterojunctions are very promising bricks to build faster and more efficient chips because of their atomically smooth surface and interfaces. The greatest challenge in the synthesis of nanomaterials is how to precisely control the structure, crystalline orientation, defects, dimensions, etc. In past decades, both the methodology and the mechanism of synthesis have been systematically investigated to improve the controllability. However, few studies focused on sensing the synthesis processes in situ and responding to the synthesis immediately. Here, we propose the concept of intelligent synthesis in which the final product can be automatically fine-controlled by a closed loop including in situ monitoring and real-time interventions. As a model system, a high-temperature-tolerant circuit is fabricated on the single-walled carbon nanotube (SWCNT) growth substrate for sensing and responding to the synthesis processes. As a result, either highly pure semiconducting (s-) SWCNT arrays or metallic-semiconducting (m-s) junction arrays with different junction positions is simply synthesized by programming the responding signal. The intelligent synthesis shows much higher efficiency and controllability compared to conventional methods and will lead to the next leap in nanotechnology.

Poly(ionic liquid)-Based Efficient and Robust Antiseptic Spray

Exploring efficient and robust antibacterial materials is crucially important for human health and ecological security. Compared with intrinsically antibacterial materials, materials modified with antibacterial agents either by chemical or physical modification can simultaneously maintain basic functions and antibacterial properties. In particular, physical modification with antiseptic sprays is quite suitable for large-size objects in our daily life but restricted by high volatility of the antibacterial agents or poor adhesion strength between the antibacterial agents and the targeted objects. In this paper, we report a poly(ionic liquid) (PIL-Cn)-based efficient and robust antiseptic spray that exhibits long-term antibacterial properties against both Gram-positive and Gram-negative bacteria on diverse substrates, including glass, PE, and cotton. It is believed that this work will provide an alternative for current antiseptic sprays for usage in our daily life and hospitals.

Applications of Carbon Nanotubes in the Internet of Things Era

The post-Moore's era has boosted the progress in carbon nanotube-based transistors. Indeed, the 5G communication and cloud computing stimulate the research in applications of carbon nanotubes in electronic devices. In this perspective, we deliver the readers with the latest trends in carbon nanotube research, including high-frequency transistors, biomedical sensors and actuators, brain-machine interfaces, and flexible logic devices and energy storages. Future opportunities are given for calling on scientists and engineers into the emerging topics.

Aligned 2D carbon nanotube liquid crystals for wafer-scale electronics

Semiconducting carbon nanotubes promise faster performance and lower power consumption than Si in field-effect transistors (FETs) if they can be aligned in dense arrays. Here, we demonstrate that nanotubes collected at a liquid/liquid interface self-organize to form two-dimensional (2D) nematic liquid crystals that globally align with flow. The 2D liquid crystals are transferred onto substrates in a continuous process generating dense arrays of nanotubes aligned within ±6°, ideal for electronics. Nanotube ordering improves with increasing concentration and decreasing temperature due to the underlying liquid crystal phenomena. The excellent alignment and uniformity of the transferred assemblies enable FETs with exceptional on-state current density averaging 520 μA μm⁻¹at only −0.6 V, and variation of only 19%. FETs with ion gel top gates demonstrate subthreshold swing as low as 60 mV decade⁻¹. Deposition across a 10-cm substrate is achieved, evidencing the promise of 2D nanotube liquid crystals for commercial semiconductor electronics.

Tuning Electrostatic Gating of Semiconducting Carbon Nanotubes by Controlling Protein Orientation in Biosensing Devices

The ability to detect proteins through gating conductance by their unique surface electrostatic signature holds great potential for improving biosensing sensitivity and precision. Two challenges are: (1) defining the electrostatic surface of the incoming ligand protein presented to the conductive surface; (2) bridging the Debye gap to generate a measurable response. Herein, we report the construction of nanoscale protein-based sensing devices designed to present proteins in defined orientations; this allowed us to control the local electrostatic surface presented within the Debye length, and thus modulate the conductance gating effect upon binding incoming protein targets. Using a β-lactamase binding protein (BLIP2) as the capture protein attached to carbon nanotube field effect transistors in different defined orientations. Device conductance had influence on binding TEM-1, an important β-lactamase involved in antimicrobial resistance (AMR). Conductance increased or decreased depending on TEM-1 presenting either negative or positive local charge patches, demonstrating that local electrostatic properties, as opposed to protein net charge, act as the key driving force for electrostatic gating. This, in turn can, improve our ability to tune the gating of electrical biosensors toward optimized detection, including for AMR as outlined herein.

Tuning Electrostatic Gating of Semiconducting Carbon Nanotubes by Controlling Protein Orientation in Biosensing Devices

The ability to detect proteins through gating conductance by their unique surface electrostatic signature holds great potential for improving biosensing sensitivity and precision. Two challenges are: (1) defining the electrostatic surface of the incoming ligand protein presented to the conductive surface; (2) bridging the Debye gap to generate a measurable response. Herein, we report the construction of nanoscale protein-based sensing devices designed to present proteins in defined orientations; this allowed us to control the local electrostatic surface presented within the Debye length, and thus modulate the conductance gating effect upon binding incoming protein targets. Using a β-lactamase binding protein (BLIP2) as the capture protein attached to carbon nanotube field effect transistors in different defined orientations. Device conductance had influence on binding TEM-1, an important β-lactamase involved in antimicrobial resistance (AMR). Conductance increased or decreased depending on TEM-1 presenting either negative or positive local charge patches, demonstrating that local electrostatic properties, as opposed to protein net charge, act as the key driving force for electrostatic gating. This, in turn can, improve our ability to tune the gating of electrical biosensors toward optimized detection, including for AMR as outlined herein.

Designing artificial two-dimensional landscapes via atomic-layer substitution

Technology advancements in history have often been propelled by material innovations. In recent years, two-dimensional (2D) materials have attracted substantial interest as an ideal platform to construct atomic-level material architectures. In this work, we design a reaction pathway steered in a very different energy landscape, in contrast to typical thermal chemical vapor deposition method in high temperature, to enable room-temperature atomic-layer substitution (RT-ALS). First-principle calculations elucidate how the RT-ALS process is overall exothermic in energy and only has a small reaction barrier, facilitating the reaction to occur at room temperature. As a result, a variety of Janus monolayer transition metal dichalcogenides with vertical dipole could be universally realized. In particular, the RT-ALS strategy can be combined with lithography and flip-transfer to enable programmable in-plane multiheterostructures with different out-of-plane crystal symmetry and electric polarization. Various characterizations have confirmed the fidelity of the precise single atomic layer conversion. Our approach for designing an artificial 2D landscape at selective locations of a single layer of atoms can lead to unique electronic, photonic, and mechanical properties previously not found in nature. This opens a new paradigm for future material design, enabling structures and properties for unexplored territories.

Can Carbon Nanotube Transistors Be Scaled Down to the Sub-5 nm Gate Length?

Single-walled carbon nanotubes (CNTs) have been considered as a promising semiconductor to construct transistors and integrated circuits in the future owing to their ultrathin channel thickness and ultrahigh injection velocity. Although a 5 nm gate-length CNT field-effect transistor (FET) has already been experimentally fabricated and demonstrates excellent device performance, the potential or constraint factors on performance have not been explored or revealed. Based on the benchmark of the device performance between the experimental and simulated 5 nm gate-length CNT FETs, we use the first-principles quantum transport approach to explore the performance limit of CNT FETs based on the gate-all-around (GAA) device geometry for the first time. It is found that the GAA CNT FETs can fulfill the ITRS 2028 high-performance target in the 2 nm gate-length node in terms of the on-state current, delay time, and power consumption. We also find that the energy-delay product of the CNT FETs is superior to those of the high-performance 2D materials and Si Fin FETs at the sub-5 nm gate length due to its unique electrical property. Though theoretically the gate length of CNT FETs can be potentially scaled to 2 nm, considering the tradeoff between the performance and power consumption, 5 nm is the ultimate scaled limit.

Host-Guest Molecular Interaction Enabled Separation of Large-Diameter Semiconducting Single-Walled Carbon Nanotubes

Semiconducting single-walled carbon nanotubes (s-SWCNTs) with a diameter of around 1.0-1.5 nm, which present bandgaps comparable to silicon, are highly desired for electronic applications. Therefore, the preparation of s-SWCNTs of such diameters has been attracting great attention. The inner surface of SWCNTs has a suitable curvature and large contacting area, which is attractive in host-guest chemistry triggered by electron transfer. Here we reported a strategy of host-guest molecular interaction between SWCNTs and inner clusters with designed size, thus selectively separating s-SWCNTs of expected diameters. When polyoxometalate clusters of ∼1 nm in size were filled in the inner cavities of SWCNTs, s-SWCNTs with diameters concentrated at ∼1.3-1.4 nm were selectively extracted with the purity of ∼98% by a commercially available polyfluorene derivative. The field-effect transistors built from the sorted s-SWCNTs showed a typical behavior of semiconductors. The sorting mechanisms associated with size-dependent electron transfer from nanotubes to inner polyoxometalate were revealed by the spectroscopic and in situ electron microscopic evidence as well as the theoretical calculation. The polyoxometalates with designable size and redox property enable the flexible regulation of interaction between the nanotubes and the clusters, thus tuning the diameter of sorted s-SWCNTs. The present sorting strategy is simple and should be generally feasible in other SWCNT sorting techniques, bringing both great easiness in dispersant design and improved selectivity.

Atomically precise graphene nanoribbons: interplay of structural and electronic properties

Graphene nanoribbons hold great promise for future applications in nanoelectronic devices, as they may combine the excellent electronic properties of graphene with the opening of an electronic band gap - not present in graphene but required for transistor applications. With a two-step on-surface synthesis process, graphene nanoribbons can be fabricated with atomic precision, allowing precise control over width and edge structure. Meanwhile, a decade of research has resulted in a plethora of graphene nanoribbons having various structural and electronic properties. This article reviews not only the on-surface synthesis of atomically precise graphene nanoribbons but also how their electronic properties are ultimately linked to their structure. Current knowledge and considerations with respect to precursor design, which eventually determines the final (electronic) structure, are summarized. Special attention is dedicated to the electronic properties of graphene nanoribbons, also in dependence on their width and edge structure. It is exactly this possibility of precisely changing their properties by fine-tuning the precursor design - offering tunability over a wide range - which has generated this vast research interest, also in view of future applications. Thus, selected device prototypes are presented as well.

Application-Driven Carbon Nanotube Functional Materials

Carbon nanotube functional materials (CNTFMs) represent an important research field in transforming nanoscience and nanotechnology into practical applications, with potential impact in a wide realm of science, technology, and engineering. In this review, we combine the state-of-the-art research activities of CNTFMs with the application prospect, to highlight critical issues and identify future challenges. We focus on macroscopic long fibers, thin films, and bulk sponges which are typical CNTFMs in different dimensions with distinct characteristics, and also cover a variety of derived composite/hierarchical materials. Critical issues related to their structures, properties, and applications as robust conductive skeletons or high-performance flexible electrodes in mechanical and electronic devices, advanced energy conversion and storage systems, and environmental areas have been discussed specifically. Finally, possible solutions and directions are proposed for overcoming current obstacles and promoting future efforts in the field.

Synaptic transistors and neuromorphic systems based on carbon nano-materials

Carbon-based materials possessing a nanometer size and unique electrical properties perfectly address the two critical issues of transistors, the low power consumption and scalability, and are considered as a promising material in next-generation synaptic devices. In this review, carbon-based synaptic transistors were systematically summarized. In the carbon nanotube section, the synthesis of carbon nanotubes, purification of carbon nanotubes, the effect of architecture on the device performance and related carbon nanotube-based devices for neuromorphic computing were discussed. In the graphene section, the synthesis of graphene and its derivative, as well as graphene-based devices for neuromorphic computing, was systematically studied. Finally, the current challenges for carbon-based synaptic transistors were discussed.

Growth of Homogeneous High-Density Horizontal SWNT Arrays on Sapphire through a Magnesium-Assisted Catalyst Anchoring Strategy

In-situ growth of high-density single-walled carbon nanotube (SWNT) arrays with homogeneity is highly desirable for integrated circuits. However, disastrous migration and aggregation of catalyst nanoparticles on substrate has greatly limited the area of as-grown SWNT arrays. Herein, we develop a magnesium-assisted catalyst anchoring strategy to restrain catalyst nanoparticles sintering on substrate. Magnesium modification ameliorates sapphire surface by high temperature solid reaction and thus provides a stronger metal-support interaction (SMSI). Hereby, we realize the direct growth of high-density SWNT arrays that fully cover an entire 10×10 mm² substrate with the local highest density of ≈110 tubes μm^-1 using iron as catalyst. This strategy was also proven universal when employing solid carbide catalysts.

Low-Loss Broadband Transverse Electric Pass Hybrid Plasmonic Fiber Polarizers Using Metallic Nanomaterials

Metals were for decades perceived as devoid of interesting optical properties that could be harnessed for optical components and devices. However, with the development of accurate nanofabrication techniques and precise control over architectural parameters, metals can be structured and characterized on the nanoscale. Metallic plasmonic nanomaterials exhibit a number of unique structural and optical properties, which offer the potential for developing new types of plasmonic devices. Here, we demonstrate a low-loss broadband polarizer based on a hybrid plasmonic fiber structure using metals as polarization-selective absorption materials. The polarization mechanism, design, fabrication, and characteristics of the plasmonic polarizers are investigated theoretically, numerically, and experimentally. The theoretical analysis predicts that the polarization-selective absorption with insensitivity to wavelength enables hybrid plasmonic fibers to function as broadband polarizers. Numerical simulations give the comparison of the polarization-selective absorption of various metallic nanomaterials (Ag, Au, In, Al, Cr) and show that aluminum is regarded as the optimum absorption material for the plasmonic polarizer. Experimental results show that through precise control over geometrical parameters, this device is capable of offering a high polarization extinction ratio (PER) of over 40 dB and a low insertion loss (IL) of less than 1.3 dB in the wavelength region of 810.1-870.0 nm. Compared with commercial birefringent-crystal-fiber polarizers, the plasmonic fiber polarizer has a better PER and IL bandwidth. These merits, combined with a compact and robust configuration, enable the plasmonic polarizer to have great potential in a broad range of applications.

Carbon Nanotube Films for Energy Applications

This perspective article describes the application opportunities of carbon nanotube (CNT) films for the energy sector. Up to date progress in this regard is illustrated with representative examples of a wide range of energy management and transformation studies employing CNT ensembles. Firstly, this paper features an overview of how such macroscopic networks from nanocarbon can be produced. Then, the capabilities for their application in specific energy-related scenarios are described. Among the highlighted cases are conductive coatings, charge storage devices, thermal interface materials, and actuators. The selected examples demonstrate how electrical, thermal, radiant, and mechanical energy can be converted from one form to another using such formulations based on CNTs. The article is concluded with a future outlook, which anticipates the next steps which the research community will take to bring these concepts closer to implementation.

Superstretching MXene Composite Hydrogel as a Bidirectional Stress Response Thixotropic Sensor

The arrival of the era of artificial intelligence is constantly advancing the development of flexible electronic materials. However, low mechanical properties, nonflexible signal transmission, and insensitive signal output have restricted their development as sensors. In this study, a superstretching MXene composite conductive hydrogel was developed with a tensile strain of more than 1800%. The hydrogel was used as a flexible wearable sensor to detect human motion signals in real time. High sensitivity was achieved using the sensor to discern multidirectional human motions, such as bending of human joints, throat vocalization, swallowing, and pulse beat. In addition, rapid resilience was observed for the MXene composite hydrogel after unloading reverse compressive stress, which can quickly cause a specific current response in the micropressure area without leaving any traces. This thixotropic sensor achieves a rapid response to bidirectional stress and has huge application prospects in the field of human body motion detection and national defense information encryption.

Materials Science Challenges to Graphene Nanoribbon Electronics

Graphene nanoribbons (GNRs) have recently emerged as promising candidates for channel materials in future nanoelectronic devices due to their exceptional electronic, thermal, and mechanical properties and chemical inertness. However, the adoption of GNRs in commercial technologies is currently hampered by materials science and integration challenges pertaining to synthesis and devices. In this Review, we present an overview of the current status of challenges, recent breakthroughs toward overcoming these challenges, and possible future directions for the field of GNR electronics. We motivate the need for exploration of scalable synthetic techniques that yield atomically precise, placed, registered, and oriented GNRs on CMOS-compatible substrates and stimulate ideas for contact and dielectric engineering to realize experimental performance close to theoretically predicted metrics. We also briefly discuss unconventional device architectures that could be experimentally investigated to harness the maximum potential of GNRs in future spintronic and quantum information technologies.

Chemical and topographical patterns combined with solution shear for selective-area deposition of highly-aligned semiconducting carbon nanotubes

Selective deposition of semiconducting carbon nanotubes (s-CNTs) into densely packed, aligned arrays of individualized s-CNTs is necessary to realize their potential in semiconductor electronics. We report the combination of chemical contrast patterns, topography, and pre-alignment of s-CNTs via shear to achieve selective-area deposition of aligned arrays of s-CNTs. Alternate stripes of surfaces favorable and unfavorable to s-CNT adsorption were patterned with widths varying from 2000 nm down to 100 nm. Addition of topography to the chemical contrast patterns combined with shear enabled the selective-area deposition of arrays of quasi-aligned s-CNTs (∼14°) even in patterns that are wider than the length of individual nanotubes (>500 nm). When the width of the chemical and topographical contrast patterns is less than the length of individual nanotubes (<500 nm), confinement effects become dominant enabling the selective-area deposition of much more tightly aligned s-CNTs (∼7°). At a trench width of 100 nm, we demonstrate the lowest standard deviation in alignment degree of 7.6 ± 0.3° at a deposition shear rate of 4600 s^-1, while maintaining an individualized s-CNT density greater than 30 CNTs μm^-1. Chemical contrast alone enables selective-area deposition, but chemical contrast in addition to topography enables more effective selective-area deposition and stronger confinement effects, with the advantage of removal of nanotubes deposited in spurious areas via selective lift-off of the topographical features. These findings provide a methodology that is inherently scalable, and a means to deposit spatially selective, aligned s-CNT arrays for next-generation semiconducting devices.

Selective Chemistry-Based Separation of Semiconducting Single-Walled Carbon Nanotubes and Alignment of the Nanotube Array Network under Electric Field for Field-Effect Transistor Applications

Semiconducting single-walled carbon nanotubes (s-SWCNTs) are considered as a replacement for silicon in field-effect transistors (FETs), solar cells, logic circuits, and so forth, because of their outstanding electronic, optical, and mechanical properties. Herein, we have studied the reaction of pristine SWCNTs dispersed in a pluronic F-68 (PF-68) polymer solution with para-amino diphenylamine diazonium sulfate (PADDS) to separate nanotubes based on their metallicity. The preferential selectivity of the reactions was monitored by changes in the semiconducting (S22 and S33) and metallic (M11) bands by ultraviolet-visible-near infrared spectroscopy. Metallic selectivity depended on the concentrations of PADDS, reaction time, and the solution pH. Furthermore, separation of pure s-SWCNTs was confirmed by Raman spectroscopy and Fourier-transform infrared spectroscopy. After the removal of metallic SWCNTs, direct current electric field was applied to the pure s-SWCNT solution, which effectively directed the nanotubes to align in one direction as nanotube arrays with a longer length and high density. After that, electrically aligned s-SWCNT solution was cast on a silicon substrate, and the length of the nanotube arrays was measured as ∼2 to ∼14 μm with an areal density of ∼2 to ∼20 tubes/μm of s-SWCNTs. Next, electrically aligned s-SWCNT arrays were deposited on the channel of the FET device by drop-casting. Field-emission scanning electron microscopy and electrical measurements have been carried out to test the performance of the aligned s-SWCNTs/FETs. The fabricated FETs with a channel length of 10 μm showed stable electrical properties with a field-effect mobility of 30.4 cm2/Vs and a log10 (I on/I off) current ratio of 3.96. We envisage that this new chemical-based separation method and electric field-assisted alignment could be useful to obtain a high-purity and aligned s-SWCNT array network for the fabrication of high-performance FETs to use in digital and analog electronics.

Small organic molecules act as a trigger in an "unzippering" mechanism to facilitate carbon nanotube dispersion

In binary dispersing agents system, the contribution and roles of different sized molecules to carbon nanotubes (CNTs) dispersion remain unclear, which hinders the understanding of the environmental behaviour and risks of CNTs. This study compared the dispersion of CNTs by m-nitrobenzoic acid (NBA), trans-cinnamic acid (TCA), tannic acid (TA), and their mixtures. The dispersion efficiency of CNTs significantly reduced with the increased solid-phase concentration (Q_e) of TA due to the adsorption of TA on newly exposed CNTs surfaces. However, the CNTs dispersion efficiency by NBA or TCA was independent of Q_e because the dispersed CNTs surface was completely occupied by NBA or TCA without new exposed sites available for subsequent adsorption. The mixture of NBA or TCA with TA significantly enhanced the dispersion efficiency of CNTs, indicating a synergistic effect of CNTs dispersion. The addition of NBA or TCA decreased the hydrodynamic diameter of CNTs dispersed by TA, which indicated that NBA or TCA facilitated TA wedging into CNTs bundles for more complete separation of CNTs. This study highlighted the triggering effect of small molecules in the "unzippering" mechanism for improving the dispersing efficiency of CNTs by large molecules.

Submilligram-scale separation of near-zigzag single-chirality carbon nanotubes by temperature controlling a binary surfactant system

Mass production of zigzag and near-zigzag single-wall carbon nanotubes (SWCNTs), whether by growth or separation, remains a challenge, which hinders the disclosure of their previously unknown property and practical applications. Here, we report a method to separate SWCNTs by chiral angle through temperature control of a binary surfactant system of sodium cholate (SC) and SDS in gel chromatography. Eleven types of single-chirality SWCNT species with chiral angle less than 20° were efficiently separated including multiple zigzag and near-zigzag species. Among them, (7, 3), (8, 3), (8, 4), (9, 1), (9, 2), (10, 2), and (11, 1), were produced on the submilligram scale. The spectral detection results indicate that lowering the temperature induced selective adsorption and reorganization of the SC/SDS cosurfactants on SWCNTs with different chiral angles, amplifying their interaction difference with gel. We believe that this work is an important step toward industrial separation of single-chirality zigzag and near-zigzag SWCNTs.

Graphene oxide-supported cobalt tungstate as catalyst precursor for selective growth of single-walled carbon nanotubes

Graphene oxide-supported uniform cobalt tungstate nanoparticles (CoWO₄/GO) were prepared, which can be used as catalyst precursors for the diameter-controlled growth of single-walled carbon nanotubes (SWCNTs).

Electronic Raman Scattering in Suspended Semiconducting Carbon Nanotube

The electronic Raman scattering (ERS) features of single-walled carbon nanotubes (SWNTs) can reveal a wealth of information about their electronic structures. Previously, the ERS processes have been exclusively reported in metallic SWNTs (M-SWNTs) and attributed to the inelastic scattering of photoexcited excitons by a continuum of low-energy electron-hole pairs near the Fermi level. Therefore, the ERS features have been thought to appear exclusively in M-SWNTs but not in semiconducting SWNTs (S-SWNTs), which are more desired in many application fields such as nanoelectronics and bioimaging. In this work, the experimental observation of the ERS features in suspended S-SWNTs is reported, the processes of which are accomplished via the available high-energy electron-hole pairs. The excitonic transition energies with an uncertainty in the order of ±1 meV can be directly obtained via the ERS spectra, compared to a typical uncertainty of ±10 meV in conventional electronic spectroscopies. The ERS features can facilitate further systematic studies on the properties of SWNT, both metallic and semiconducting, with defined chirality.

Single-nanostructure bandgap engineering enabled by magnetic-pulling thermal evaporation growth

Realizing the substantial potential of bottom-up 1D semiconductor nanostructures in developing functional nanodevices calls for dedicated single-nanostructure bandgap engineering by various growth approaches. Although thermal evaporation has been advised as a facile approach for most semiconductors to form 1D nanostructures from bottom-up, its capability of achieving single-nanostructure bandgap engineering was considered a challenge. In 2011, we succeeded in the direct growth of composition-graded CdS1-x Se x (0 ≤ x ≤ 1) nanowires by upgrading the thermal-evaporation tube furnace with a home-made magnetic-pulling module. This report aims to provide a comprehensive review of the latest advances in the single-nanostructure bandgap engineering enabled by the magnetic-pulling thermal evaporation growth. The report begins with the description of different magnetic-pulling thermal evaporation strategies associated with diverse examples of composition-engineered 1D nanostructures. Following is an elaboration on their optoelectronic applications based on the resulting single-nanostructure bandgap engineering, including monolithic white-light sources, proof-of-concept asymmetric light propagation and wavelength splitters, monolithic multi-color and white-light lasers, broadband-response photodetectors, high-performance transistors, and recently the most exciting single-nanowire spectrometer. In the end, this report concludes with some personal perspectives on the directions toward which future research might be advanced.

Comprehensive Performance Quasi-Non-Volatile Memory Compatible with Large-Scale Preparation by Chemical Vapor Deposition

Two-dimensional materials with atomic thickness have become candidates for wearable electronic devices in the future. Graphene and transition metal sulfides have received extensive attention in logic computing and sensing applications due to their lower power dissipation, so that their processes have been relatively mature for large-scale preparation. However, there are a few applications of two-dimensional materials in storage, which is not in line with the development trend of integration of storage and computing. Here, a charge storage quasi-non-volatile memory with a lanthanum incorporation high-k dielectric for next-generation memory devices is proposed. Thanks to the excellent electron capture capability of LaAlO₃, the MoS₂ memory exhibits a very comprehensive information storage capability, including robust endurance and ultra-fast write speed of 1 ms approximately. It is worth mentioning that it exhibits a long-term stable charge storage capacity (refresh time is about 1000 s), which is 10⁵ times that of the dynamic random access memory (refresh time is on a milliseconds timescale) so that the unnecessary power dissipation greatly reduces caused by frequent refresh. In addition, its simple manufacturing process makes it compatible with various current two-dimensional electronic devices, which will greatly promote the integration of two-dimensional electronic computing.

Separation of Semiconducting Carbon Nanotubes Using Conjugated Polymer Wrapping

In the past two decades, single-walled carbon nanotubes (SWNTs) have been explored for electronic applications because of their high charge carrier mobility, low-temperature solution processability and mechanical flexibility. Semiconducting SWNTs (s-SWNTs) are also considered an alternative to traditional silicon-based semiconductors. However, large-scale, as-produced SWNTs have poor solubility, and they are mixtures of metallic SWNTs (m-SWNTs) and s-SWNTs, which limits their practical applications. Conjugated polymer wrapping is a promising method to disperse and separate s-SWNTs, due to its high selectivity, high separation yield and simplicity of operation. In this review, we summarize the recent progress of the conjugated polymer wrapping method, and discuss possible separation mechanisms for s-SWNTs. We also discuss various parameters that may affect the selectivity and sorting yield. Finally, some electronic applications of polymer-sorted s-SWNTs are introduced. The aim of this review is to provide polymer chemist a basic concept of polymer based SWNT separation, as well as some polymer design strategies, influential factors and potential applications.