Wafer-scale monodomain films of spontaneously aligned single-walled carbon nanotubes

Efficient Emission of Highly Polarized Thermal Radiation from a Suspended Aligned Carbon Nanotube Film

A polarized light source covering a wide wavelength range is required in applications across diverse fields, including optical communication, photonics, spectroscopy, and imaging. For practical applications, high degrees of polarization and thermal performance are needed to ensure the stability of the radiation intensity and low energy consumption. Here, we achieved efficient emission of highly polarized and broadband thermal radiation from a suspended aligned carbon nanotube film. The anisotropic nature of the film, combined with the suspension, led to a high degree of linear polarization (∼0.9) and great thermal performance. Furthermore, we performed time-resolved measurements of thermal emission from the film, revealing a fast time response of approximately a few microseconds. We also obtained visible light emission from the device and analyzed the film's mechanical breakdown behavior to improve the emission intensity. Finally, we demonstrated that suspended devices with a constriction geometry can enhance the heating performance. These results show that carbon nanotube film-based devices, as electrically driven thermal emitters of polarized radiation, can play an important role for future development in optoelectronics and spectroscopy.

Upscaling Thermoelectrics: Micron-Thick, Half-a-Meter-Long Carbon Nanotube Films with Monolithic Integration of p- and n-Legs

In order for organic thermoelectrics to successfully establish their own niche as energy-harvesting materials, they must reach several crucial milestones, including high performance, long-term stability, and scalability. Performance and stability are currently being actively studied, whereas demonstrations of large-scale compatibility are far more limited and for carbon nanotubes (CNTs) are still missing. The scalability challenge includes material-related economic considerations as well as the availability of fast deposition methods that produce large-scale films that simultaneously satisfy the thickness constraints required for thermoelectric modules. Here we report on true solutions of CNTs that form gels upon air exposure, which can then be dried into micron-thick films. The CNT ink can be extruded using a slot-shaped nozzle into a continuous film (more than half a meter in the present paper) and patterned into alternating n- and p-type components, which are then folded to obtain the finished thermoelectric module. Starting from a given n-type film, differentiation between the n and p components is achieved by a simple postprocessing step that involves a partial oxidation reaction and neutralization of the dopant. The presented method allows the thermoelectric legs to seamlessly interconnect along the continuous film, thus avoiding the need for metal electrodes, and, most importantly, it is compatible with large-scale printing processes. The resulting thermoelectric legs retain 80% of their power factor after 100 days in air and about 30% after 300 days. Using the proposed methodology, we fabricate two thermoelectric modules of 4 and 10 legs that can produce maximum power outputs of 1 and 2.4 μW, respectively, at a temperature difference ΔT of 46 K.

Guidelines derived from biomineralized tissues for design and construction of high-performance biomimetic materials: from weak to strong

Living organisms in nature have undergone continuous evolution over billions of years, resulting in the formation of high-performance fracture-resistant biomineralized tissues such as bones and teeth to fulfill mechanical and biological functions, despite the fact that most inorganic biominerals that constitute biomineralized tissues are weak and brittle. During the long-period evolution process, nature has evolved a number of highly effective and smart strategies to design chemical compositions and structures of biomineralized tissues to enable superior properties and to adapt to surrounding environments. Most biomineralized tissues have hierarchically ordered structures consisting of very small building blocks on the nanometer scale (nanoparticles, nanofibers or nanoflakes) to reduce the inherent weaknesses and brittleness of corresponding inorganic biominerals, to prevent crack initiation and propagation, and to allow high defect tolerance. The bioinspired principles derived from biomineralized tissues are indispensable for designing and constructing high-performance biomimetic materials. In recent years, a large number of high-performance biomimetic materials have been prepared based on these bioinspired principles with a large volume of literature covering this topic. Therefore, a timely and comprehensive review on this hot topic is highly important and contributes to the future development of this rapidly evolving research field. This review article aims to be comprehensive, authoritative, and critical with wide general interest to the science community, summarizing recent advances in revealing the formation processes, composition, and structures of biomineralized tissues, providing in-depth insights into guidelines derived from biomineralized tissues for the design and construction of high-performance biomimetic materials, and discussing recent progress, current research trends, key problems, future main research directions and challenges, and future perspectives in this exciting and rapidly evolving research field.

Biomimetic wafer-scale alignment of tellurium nanowires for high-mobility flexible and stretchable electronics

Flexible and stretchable thin-film transistors (TFTs) are crucial in skin-like electronics for wearable and implantable applications. Such electronics are usually constrained in performance owing to a lack of high-mobility and stretchable semiconducting channels. Tellurium, a rising semiconductor with superior charge carrier mobilities, has been limited by its intrinsic brittleness and anisotropy. Here, we achieve highly oriented arrays of tellurium nanowires (TeNWs) on various substrates with wafer-scale scalability by a facile lock-and-shear strategy. Such an assembly approach mimics the alignment process of the trailing tentacles of a swimming jellyfish. We further apply these TeNW arrays in high-mobility TFTs and logic gates with improved flexibility and stretchability. More specifically, mobilities over 100 square centimeters per volt per second and on/off ratios of ~104 are achieved in TeNW-TFTs. The TeNW-TFTs on polyethylene terephthalate can sustain an omnidirectional bending strain of 1.3% for more than 1000 cycles. Furthermore, TeNW-TFTs on an elastomeric substrate can withstand a unidirectional strain of 40% with no performance degradation.

Assembly and Alignment of High Packing Density Carbon Nanotube Arrays Using Lithographically Defined Microscopic Water Features

High packing density aligned arrays of semiconducting carbon nanotubes (CNTs) are required for many electronics applications. Past work has shown that the accumulation of CNTs at a water-solvent interface can drive array self-assembly. Previously, the confining interface was a large-area, macroscopic feature. Here, we report on the CNT assembly on microscopic water features. Water microdroplets are formed on 10-100 μm wide hydrophilic stripes patterned on a substrate. Exposure to CNTs dispersed in solvent accumulates CNTs at the microdroplet-solvent interface, driving their alignment and deposition at the microdroplet-solvent-substrate contact line. Compared with macroscopic methods in which the contact line uncontrollably moves across the substrate as it is pulled out of the liquids, the hydrophilic patterns and microdroplets allow pinning of the contact line. As CNTs deposit, the contact line self-translates, allowing for dense CNT packing. We realize monolayer CNT arrays aligned within ±3.9° at density of 250 μm-1 and field effect transistors with a high current density of 1.9 mA μm-1 and transconductance of 1.2 mS μm-1 at -0.6 V drain bias and 60 nm channel length.

New Carbon Materials for Multifunctional Soft Electronics

Soft electronics are garnering significant attention due to their wide-ranging applications in artificial skin, health monitoring, human-machine interaction, artificial intelligence, and the Internet of Things. Various soft physical sensors such as mechanical sensors, temperature sensors, and humidity sensors are the fundamental building blocks for soft electronics. While the fast growth and widespread utilization of electronic devices have elevated life quality, the consequential electromagnetic interference (EMI) and radiation pose potential threats to device precision and human health. Another substantial concern pertains to overheating issues that occur during prolonged operation. Therefore, the design of multifunctional soft electronics exhibiting excellent capabilities in sensing, EMI shielding, and thermal management is of paramount importance. Because of the prominent advantages in chemical stability, electrical and thermal conductivity, and easy functionalization, new carbon materials including carbon nanotubes, graphene and its derivatives, graphdiyne, and sustainable natural-biomass-derived carbon are particularly promising candidates for multifunctional soft electronics. This review summarizes the latest advancements in multifunctional soft electronics based on new carbon materials across a range of performance aspects, mainly focusing on the structure or composite design, and fabrication method on the physical signals monitoring, EMI shielding, and thermal management. Furthermore, the device integration strategies and corresponding intriguing applications are highlighted. Finally, this review presents prospects aimed at overcoming current barriers and advancing the development of state-of-the-art multifunctional soft electronics.

Machine Learning-Assisted Exploration and Identification of Aqueous Dispersants in the Vast Diversity of Organic Chemicals

Dispersion represents a central processing method in the organization of nanomaterials; however, the strong interparticle interaction represents a significant obstacle to fabricating homogeneous and stable dispersions. While dispersants can greatly assist in overcoming this obstacle, the appropriate type is dependent on such factors as nanomaterial, solvent, experimental conditions, etc., and there is no general guide to assist in the selection from the vast number of possibilities. We report a strategy and successful demonstration of the machine-learning-based "Dispersant Explorer", which surveys and identifies suitable dispersants from open databases. Through the combined use of experimental and molecular descriptors derived from SMILES databases, the model showed exceptional predictive accuracy in surveying about ∼1000 chemical compounds and identifying those that could be applied as dispersants. Furthermore, fabrication of transparent conducting films using the predicted and previously unknown dispersant exhibited the highest sheet resistance and transmittance compared with those of other reported undoped films. This result highlights that, in addition to opening new avenues for novel dispersant discovery, machine learning has a potential to elucidate the chemical structures essential for optimal dispersion performance to assist in the advancement of the complex topic of nanomaterial processing.

Highly selective chiral molecules detection by terahertz SWNT-based metamaterials

The selectively effective behavior of chiral molecules may have deleterious consequences on nontarget organisms and the surrounding ecosystem. Therefore, detecting enantiomers in minute concentrations is essential to prevent undesired side effects. The majority of approaches, including chiral coupling in the shortwave band with sophisticated fabrication and eluting molecules based on the time signal, are incapable of achieving rapid chiral detection. In this study, we use chemically modified single-wall carbon nanotubes (SWNT) as metamaterials to increase sensitivity in the THz region while using it as the chiral stationary phase to selectively bundle one of two enantiomers. We identify chiral molecules by detecting the optical response of chemically modified SWNT-based metamaterials. The measured spectra, in particular, show very selective indications in the spectral region directly associated with distinct chiral responses, which is caused by the difference in binding forces between chemically modified SWNTs and chiral molecules. In addition, we demonstrated that the desired resonance for aqueous sensing was enveloped resonance as opposed to that with a high quality factor, which was sought for drip-dry detection. Our findings provide a simple platform for highly selectively sensing chiral compounds.

Cobalt ferrite/semiconducting single-walled carbon nanotubes based field-effect transistor for determination of carbamate pesticides

Carbaryl and carbofuran are the carbamate pesticides which have been widely used worldwide to control insects in crops and house. If the pesticides entered in to the food products and drinking water, they could cause serious health effects in humans. Therefore, the development of a rapid, simple, sensitive and selective analytical device for on-site detection of carbamates is crucial to evaluate food and environmental samples. Recently, semiconducting single-walled carbon nanotube-based field effect transistors (s-SWCNT/FETs) have shown several advantages such as high carrier mobility, good on/off ratio, quasi ballistic electron transport, label-free detection and real-time response. Herein, cobalt ferrite (CFO) nanoparticles decorated s-SWCNTs have been prepared and used to bridge the source and drain electrodes. As-prepared CFO/s-SWCNT/FET had been used for the non-enzymatic detection of carbaryl and carbofuran. When used as a sensing platform, the CFO/s-SWCNT hybrid film exhibited high sensitivity, and selectivity with a wide linear range of detection from 10 to 100 fMand the lowest limit of detections for carbaryl (0.11 fM) and carbofuran (0.07 fM) were estimated. This sensor was also used to detect carbaryl in tomato and cabbage samples, which confirmed its practical acceptance. Such performance may be attributed to the oxidation of carbamates by potent catalytic activity of CFO, which led to the changes in the charge transfer reaction on the s-SWCNTs/FET conduction channel. This work presents a novel CFO/s-SWCNT based sensing system which could be used to quantify pesticide residues in food samples.

Engineering chirality at wafer scale with ordered carbon nanotube architectures

Creating artificial matter with controllable chirality in a simple and scalable manner brings new opportunities to diverse areas. Here we show two such methods based on controlled vacuum filtration - twist stacking and mechanical rotation - for fabricating wafer-scale chiral architectures of ordered carbon nanotubes (CNTs) with tunable and large circular dichroism (CD). By controlling the stacking angle and handedness in the twist-stacking approach, we maximize the CD response and achieve a high deep-ultraviolet ellipticity of 40 ± 1 mdeg nm-1. Our theoretical simulations using the transfer matrix method reproduce the experimentally observed CD spectra and further predict that an optimized film of twist-stacked CNTs can exhibit an ellipticity as high as 150 mdeg nm-1, corresponding to a g factor of 0.22. Furthermore, the mechanical rotation method not only accelerates the fabrication of twisted structures but also produces both chiralities simultaneously in a single sample, in a single run, and in a controllable manner. The created wafer-scale objects represent an alternative type of synthetic chiral matter consisting of ordered quantum wires whose macroscopic properties are governed by nanoscopic electronic signatures and can be used to explore chiral phenomena and develop chiral photonic and optoelectronic devices.

High-Speed Modulation of Polarized Thermal Radiation from an On-Chip Aligned Carbon Nanotube Film

Spectroscopic analysis with polarized light has been widely used to investigate molecular structure and material behavior. A broadband polarized light source that can be switched on and off at a high speed is indispensable for reading faint signals, but such a source has not been developed. Here, using aligned carbon nanotube (CNT) films, we have developed broadband thermal emitters of polarized infrared radiation with switching speeds of ≲20 MHz. We found that the switching speed depends on whether the electrical current is parallel or perpendicular to the CNT alignment direction with a significantly higher speed achieved in the parallel case. Together with detailed theoretical simulations, our experimental results demonstrate that the contact thermal conductance to the substrate and the conductance to the electrodes are important factors that determine the switching speed. These emitters can lead to advanced spectroscopic analysis techniques with polarized radiation.

Confinement-induced nonlocality and casimir force in transdimensional systems

We study within the framework of the Lifshitz theory the long-range Casimir force for in-plane isotropic and anisotropic free-standing transdimensional material slabs. In the former case, we show that the confinement-induced nonlocality not only weakens the attraction of ultrathin slabs but also changes the distance dependence of the material-dependent correction to the Casimir force to go as contrary to the ∼1/l dependence of that of the local Lifshitz force. In the latter case, we use closely packed array of parallel aligned single-wall carbon nanotubes in a dielectric layer of finite thickness to demonstrate strong orientational anisotropy and crossover behavior for the inter-slab attractive force in addition to its reduction with decreasing slab thickness. We give physical insight as to why such a pair of ultrathin slabs prefers to stick together in the perpendicularly oriented manner, rather than in the parallel relative orientation as one would customarily expect.

Parameters Affecting Interfacial Assembly and Alignment of Nanotubes

Tangential flow interfacial self-assembly (TaFISA) is a promising scalable technique enabling uniformly aligned carbon nanotubes for high-performance semiconductor electronics. In this process, flow is utilized to induce global alignment in two-dimensional nematic carbon nanotube assemblies trapped at a liquid/liquid interface, and these assemblies are subsequently deposited on target substrates. Here, we present an observational study of experimental parameters that affect the interfacial assembly and subsequent aligned nanotube deposition. We specifically study the water contact angle (WCA) of the substrate, nanotube ink composition, and water subphase and examine their effects on liquid crystal defects, overall and local alignment, and nanotube bunching or crowding. By varying the substrate chemical functionalization, we determine that highly aligned, densely packed, individualized nanotubes deposit only at relatively small WCA between 35 and 65°. At WCA (< 10°), high nanotube bunching or crowding occurs, and the film is nonuniform, while aligned deposition ceases to occur at higher WCA (>65°). We find that the best alignment, with minimal liquid crystal defects, occurs when the polymer-wrapped nanotubes are dispersed in chloroform at a low (0.6:1) wrapper polymer to nanotube ratio. We also demonstrate that modifying the water subphase through the addition of glycerol not only improves overall alignment and reduces liquid crystal defects but also increases local nanotube bunching. These observations provide important guidance for the implementation of TaFISA and its use toward creating technologies based on aligned semiconducting carbon nanotubes.

Chiral photonic crystals from sphere packing

Inspired by recent developments in self-assembled chiral nanostructures, we have explored the possibility of using spherical particles packed in cylinders as building blocks for chiral photonic crystals. In particular, we focused on an array of parallel cylinders arranged in a perfect triangular lattice, each containing an identical densest sphere packing structure. Despite the non-chirality of both the spheres and cylinders, the self-assembled system can exhibit chirality due to spontaneous symmetry breaking during the assembly process. We have investigated the circular dichroism effects of the system and have found that, for both perfect electric conductor and dielectric spheres, the system can display dual-polarization photonic band gaps for circularly polarized light at normal incidence along the axis of the helix. We have also examined how the polarization band gap size depends on the dielectric constant of the spheres and the packing fraction of the cylinders. Furthermore, we have explored the effects of non-ideality and found that the polarization gap persists even in the presence of imperfections and heterogeneity. Our study suggests that a cluster formed by spheres self-assembling inside parallel cylinders with appropriate material parameters can be a promising approach to creating chiral photonic crystals.

Biotemplated precise assembly approach toward ultra-scaled high-performance electronics

Structural DNA nanotechnology can be programmed into complex designer structures with molecular precision for directing a wide range of inorganic and biological materials. However, the use of DNA-templated approaches for the fabrication and performance requirements of ultra-scaled semiconductor electronics is limited by its assembly disorder and destructive interface composition. In this protocol, using carbon nanotubes (CNTs) as model semiconductors, we provide a stepwise process to build ultra-scaled, high-performance field-effect transistors (FETs) from micron-scale three-dimensional DNA templates. We apply the approach to assemble CNT arrays with uniform pitches scaled between 24.1 and 10.4 nm with yields of more than 95%, which exceeds the resolution limits of conventional lithography. To achieve highly clean CNT interfaces, we detail a rinsing-after-fixing step to remove residual DNA template and salt contaminations present around the contact and the channel regions, without modifying the alignment of the CNT arrays. The DNA-templated CNT FETs display both high on-state current (4-15 μA per CNT) and small subthreshold swing (60-100 mV per decade), which are superior to previous examples of biotemplated electronics and match the performance metrics of high-performance, silicon-based electronics. The scalable assembly of defect-free three-dimensional DNA templates requires 1 week and the CNT arrays can be synthesized within half a day. The interface engineering requires 1-2 d, while the fabrication of high-performance FET and logic gate circuits requires 2-4 d. The structural and performance characterizations of molecular-precise DNA self-assembly and high-performance electronics requires 1-2 d. The protocol is suited for users with expertise in DNA nanotechnology and semiconductor electronics.

Extreme Polarization Anisotropy in Resonant Third-Harmonic Generation from Aligned Carbon Nanotube Films

Carbon nanotubes (CNTs) possess extremely anisotropic electronic, thermal, and optical properties owing to their 1D character. While their linear optical properties have been extensively studied, nonlinear optical processes, such as harmonic generation for frequency conversion, remain largely unexplored in CNTs, particularly in macroscopic CNT assemblies. In this work, macroscopic films of aligned and type-separated (semiconducting and metallic) CNTs are synthesized and polarization-dependent third-harmonic generation (THG) from the films with fundamental wavelengths ranging from 1.5 to 2.5 µm is studied. Both films exhibited strongly wavelength-dependent, intense THG signals, enhanced through exciton resonances, and third-order nonlinear optical susceptibilities of 2.50 × 10-19  m2  V-2 (semiconducting CNTs) and 1.23 × 10-19  m2  V-2 (metallic CNTs), respectively are found, for 1.8 µm excitation. Further, through systematic polarization-dependent THG measurements, the values of all elements of the susceptibility tensor are determined, verifying the macroscopically 1D nature of the films. Finally, polarized THG imaging is performed to demonstrate the nonlinear anisotropy in the large-size CNT film with good alignment. These findings promise applications of aligned CNT films in mid-infrared frequency conversion, nonlinear optical switching, polarized pulsed lasers, polarized long-wave detection, and high-performance anisotropic nonlinear photonic devices.

Multifunctional Perovskite Photodetectors: From Molecular-Scale Crystal Structure Design to Micro/Nano-scale Morphology Manipulation

Multifunctional photodetectors boost the development of traditional optical communication technology and emerging artificial intelligence fields, such as robotics and autonomous driving. However, the current implementation of multifunctional detectors is based on the physical combination of optical lenses, gratings, and multiple photodetectors, the large size and its complex structure hinder the miniaturization, lightweight, and integration of devices. In contrast, perovskite materials have achieved remarkable progress in the field of multifunctional photodetectors due to their diverse crystal structures, simple morphology manipulation, and excellent optoelectronic properties. In this review, we first overview the crystal structures and morphology manipulation techniques of perovskite materials and then summarize the working mechanism and performance parameters of multifunctional photodetectors. Furthermore, the fabrication strategies of multifunctional perovskite photodetectors and their advancements are highlighted, including polarized light detection, spectral detection, angle-sensing detection, and self-powered detection. Finally, the existing problems of multifunctional detectors and the perspectives of their future development are presented.

Metal Contact Induced Unconventional Field Effect in Metallic Carbon Nanotubes

One-dimensional carbon nanotubes (CNTs) are promising for future nanoelectronics and optoelectronics, and an understanding of electrical contacts is essential for developing these technologies. Although significant efforts have been made in this direction, the quantitative behavior of electrical contacts remains poorly understood. Here, we investigate the effect of metal deformations on the gate voltage dependence of the conductance of metallic armchair and zigzag CNT field effect transistors (FETs). We employ density functional theory calculations of deformed CNTs under metal contacts to demonstrate that the current-voltage characteristics of the FET devices are qualitatively different from those expected for metallic CNT. We predict that, in the case of armchair CNT, the gate-voltage dependence of the conductance shows an ON/OFF ratio of about a factor of two, nearly independent of temperature. We attribute the simulated behavior to modification of the band structure under the metals caused by deformation. Our comprehensive model predicts a distinct feature of conductance modulation in armchair CNTFETs induced by the deformation of the CNT band structure. At the same time, the deformation in zigzag metallic CNTs leads to a band crossing but not to a bandgap opening.

Transition from Diffusive to Superdiffusive Transport in Carbon Nanotube Networks via Nematic Order Control

The one-dimensional confinement of quasiparticles in individual carbon nanotubes (CNTs) leads to extremely anisotropic electronic and optical properties. In a macroscopic ensemble of randomly oriented CNTs, this anisotropy disappears together with other properties that make them attractive for certain device applications. The question however remains if not only anisotropy but also other types of behaviors are suppressed by disorder. Here, we compare the dynamics of quasiparticles under strong electric fields in aligned and random CNT networks using a combination of terahertz emission and photocurrent experiments and out-of-equilibrium numerical simulations. We find that the degree of alignment strongly influences the excited quasiparticles' dynamics, rerouting the thermalization pathways. This is, in particular, evidenced in the high-energy, high-momentum electronic population (probed through the formation of low energy excitons via exciton impact ionization) and the transport regime evolving from diffusive to superdiffusive.

Radial Alignment of Carbon Nanotubes via Dead-End Filtration

Dead-end filtration is a facile method to globally align single wall carbon nanotubes (SWCNTs) in large area films with a 2D order parameter, S_2D , approaching unity. Uniaxial alignment has been achieved using pristine and hot-embossed membranes but more sophisticated geometries have yet to be investigated. In this work, three different patterns with radial symmetry and an area of 3.8 cm² are created. Two of these patterns are replicated by the filtered SWCNTs and S_2D values of ≈0.85 are obtained. Each of the radially aligned SWCNT films is characterized by scanning cross-polarized microscopy in reflectance and laser imaging in transmittance with linear, radial, and azimuthal polarized light fields. The former is used to define a novel indicator akin to the 2D order parameter using Malu's law, yielding 0.82 for the respective film. The films are then transferred to a flexible printed circuit board and terminal two-probe electrical measurements are conducted to explore the potential of those new alignment geometries.

Dielectrophoretic alignment of carbon nanotubes: theory, applications, and future

Carbon nanotubes (CNTs) are nominated to be the successor of several semiconductors and metals due to their unique physical and chemical properties. It has been concerning that the anisotropic and low controllability of CNTs impedes their adoption in commercial applications. Dielectrophoresis (DEP) is known as the electrokinetics motion of polarizable nanoparticles under the influence of nonuniform electric fields. The uniqueness of this phenomenon allows DEP to be employed as a novel method to align, assemble, separate, and manipulate CNTs suspended in liquid mediums. This article begins with a brief overview of CNT structure and production, with the emphasize on their electrical properties and response to electric fields. The DEP phenomenon as a CNT alignment method is demonstrated and graphically discussed, along with its theory, procedure, and parameters. We also discussed the side forces that arise in DEP systems and how they negatively or positively affect the CNT alignment. The article concludes with a brief review of CNT-based devices fabricated using DEP, as well as the method's limitations and future prospects.

High-Performance Shortwave Infrared Detector Based on Multilayer Carbon Nanotube Films

Carbon nanotube (CNT) is an ideal candidate material for shortwave infrared (SWIR) detectors due to its large band gap tunability, strong infrared light absorption, and high mobility. Furthermore, the photodetectors based on CNT can be prepared on any substrate using a low-temperature process, which is conducive to three-dimensional (3D) integration. However, owing to the absorption limitation (<2%) of a single-layer network CNT film with low density, the photodetectors of CNT film show low photocurrent responsivity and detectivity. In this paper, we optimize the thickness of the high-purity semiconducting network CNT films to increase the photocurrent responsivity of the photodetectors. When the thickness of network CNT film is about 5 nm, the responsivity of the zero-bias voltage can reach 32 mA/W at 1800 nm wavelength. Then, using stacked CNT films and contact electrode design, the photodetectors exhibit a maximum responsivity of 120 mA/W at 1800 nm wavelength. The photodetectors with stacked CNT films and local n-type channel doping demonstrated a wide response spectral range of 1200-2100 nm, a peak detectivity of 3.94 × 10⁹ Jones at room temperature, and a linear dynamic range over 118 dB. Moreover, the peak detectivity is over 2.27 × 10¹¹ Jones when the temperature is 180 K. Our work demonstrates the potential of the CNT film for future SWIR imaging at a low cost.

The Impact of Carbon Nanotube Length and Diameter on their Global Alignment by Dead-End Filtration

Dead-end filtration has proven to effectively prepare macroscopically (3.8 cm² ) aligned thin films from solutionbased single-wall carbon nanotubes (SWCNTs). However, to make this technique broadly applicable, the role of SWCNT length and diameter must be understood. To date, most groups report the alignment of unsorted, large diameter (≈1.4 nm) SWCNTs, but systematic studies on their small diameter are rare (≈0.78 nm). In this work, films with an area of A = 3.81 cm² and a thickness of ≈40 nm are prepared from length-sorted fractions comprising of small and large diameter SWCNTs, respectively. The alignment is characterized by cross-polarized microscopy, scanning electron microscopy, absorption and Raman spectroscopy. For the longest fractions (L_avg = 952 nm ± 431 nm, Δ = 1.58 and L_avg = 667 nm ± 246 nm, Δ = 1.55), the 2D order parameter, S2D, values of ≈0.6 and ≈0.76 are reported for the small and large diameter SWCNTs over an area of A = 625 µm² , respectively. A comparison of Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory calculations with the aligned domain size is then used to propose a law identifying the required length of a carbon nanotube with a given diameter and zeta potential.

Room Temperature Lasing from Semiconducting Single-Walled Carbon Nanotubes

Miniaturized near-infrared semiconductor lasers that are able to generate coherent light with low energy consumption have widespread applications in fields such as optical interconnects, neuromorphic computing, and deep-tissue optogenetics. With optical transitions at near-infrared wavelengths, diameter-tunable electronic structures, and superlative optoelectronic properties, semiconducting single-walled carbon nanotubes (SWCNTs) are promising candidates for nanolaser applications. However, despite significant efforts in this direction and recent progress toward enhancing spontaneous emission from SWCNTs through Purcell effects, SWCNT-based excitonic lasers have not yet been demonstrated. Leveraging an optimized cavity-emitter integration scheme enabled by a self-assembly process, here we couple SWCNT emission to the whispering gallery modes supported by polymer microspheres, resulting in room temperature excitonic lasing with an average lasing threshold of 4.5 kW/cm². The high photostability of SWCNTs allows stable lasing for prolonged duration with minimal degradation. This experimental realization of excitonic lasing from SWCNTs, combined with their versatile electronic and optical properties that can be further controlled by chemical modification, offers far-reaching opportunities for tunable near-infrared nanolasers that are applicable for optical signal processing, in vivo biosensing, and optoelectronic devices.

Anomalous phase behavior of quasi-one-dimensional attractive hard rods

We study a two-state model of attractive hard rods using the transfer matrix method, where the centers of the particles are confined to a straight line, but the orientations of the rods can be parallel or perpendicular to the confining line. The rods are modeled as hard rectangles with length L and width D and decorated with attractive sites at both ends of the rectangles. We find that the particles align parallel to the line and form long chains at low densities, while they turn out of the line and form a Tonks gas at high densities. With increasing the stickiness between the rods, the structural change between parallel and perpendicular states becomes stronger and the pressure vs density curve becomes almost a horizontal line at the transition pressure. We show that such a behavior is reminiscent of the first-order phase transition. This manifests in the validity of the lever rule of the phase transitions for very sticky cases.

Parallel Field-Effect Nanosensors Detect Trace Biomarkers Rapidly at Physiological High-Ionic-Strength Conditions

Sensitivity and speed of detection are contradicting demands that profoundly impact the electrical sensing of molecular biomarkers. Although single-molecule sensitivity can now be achieved with single-nanotube field-effect transistors, these tiny sensors, with a diameter less than 1 nm, may take hours to days to capture the molecular target at trace concentrations. Here, we show that this sensitivity-speed challenge can be addressed using covalently functionalized double-wall CNTs that form many individualized, parallel pathways between two electrodes. Each carrier that travels across the electrodes is forced to take one of these pathways that are fully gated chemically by the target-probe binding events. This sensor design allows us to electrically detect Lyme disease oligonucleotide biomarkers directly at the physiological high-salt concentrations, simultaneously achieving both ultrahigh sensitivity (as low as 1 fM) and detection speed (<15 s). This unexpectedly simple strategy may open opportunities for sensor designs to broadly achieve instant detection of trace biomarkers and real-time probing of biomolecular functions directly at their physiological states.

Electrically Driven Hyperbolic Nanophotonic Resonators as High Speed, Spectrally Selective Thermal Radiators

We introduce and experimentally demonstrate electrically driven, spectrally selective thermal emitters based on globally aligned carbon nanotube metamaterials. The self-assembled metamaterial supports a high degree of nanotube ordering, enabling nanoscale ribbons patterned in the metamaterial to function both as Joule-heated incandescent filaments and as infrared hyperbolic resonators imparting spectral selectivity to the thermal radiation. Devices batch-fabricated on a single chip emit polarized thermal radiation with peak wavelengths dictated by their hyperbolic resonances, and their nanoscale heated dimensions yield modulation rates as high as 1 MHz. As a proof of concept, we show that two sets of thermal emitters on the same chip, operating with different peak wavelengths and modulation rates, can be used to sense carbon dioxide with one detector. We anticipate that the combination of batch fabrication, modulation bandwidth, and spectral tuning with chip-based nanotube thermal emitters will enable new modalities in multiplexed infrared sources.

The influence of laser-induced alignment on Z-scan properties of 2D carbon nanomaterials suspension dependent on polarization

The Z-scan technique uses a single beam that can be used for observing the nonlinear or optical limiting properties of materials. For the first time, the Z-scan properties dependent on the polarization of 2D carbon nanomaterial suspension were experimentally investigated using optical Z-scan technology. The Z-scan curves of graphene and graphene oxide (GO) in N-methyl-2-pyrrolidinone suspensions exhibited strong polarization-dependent characteristics. In paper, a reverse saturated absorption (RSA) dip surrounded the lens focus when the horizontal polarized beam was focused in the suspension, and two saturated absorption (SA) peaks appeared adjacent to the dip. However, for the vertical polarized beam, only one RSA dip surrounded the lens focus, and the threshold was higher than the SA for a horizontally polarized beam. The transmission of RSA for the GO suspension was evidently lower than that of the graphene suspension. The polarization-dependent characteristic can be ascribed to the laser-induced alignment in case the suspension is moved in or out of the beam focal point. Furthermore, the polarization-dependent 2D carbon nanomaterial suspension can be applied in several practical purposes such as 2D material-based optical and opto-fludic devices.

Dependence of Single-Wall Carbon Nanotube Alignment on the Filter Membrane Interface in Slow Vacuum Filtration

The recent introduction of slow vacuum filtration (SVF) technology has shown great promise for reproducibly creating high-quality, large-area aligned films of single-wall carbon nanotubes (SWCNTs) from solution-based dispersions. Despite clear advantages over other SWCNT alignment techniques, SVF remains in the developmental stages due to a lack of an agreed-upon alignment mechanism, a hurdle which hinders SVF optimization. In this work, the filter membrane surface is modified to show how the resulting SWCNT nematic order can be significantly enhanced. It is observed that directional mechanical grooving on filter membranes does not play a significant role in SWCNT alignment, despite the tendency for nanotubes to follow the groove direction. Chemical treatments to the filter membrane are shown to increase SWCNT alignment by nearly 1/3. These findings suggest that membrane surface structure acts to create a directional flow along the filter membrane surface that can produce global SWCNT alignment during SVF, rather serving as an alignment template.

Soft-lock drawing of super-aligned carbon nanotube bundles for nanometre electrical contacts

The assembly of single-walled carbon nanotubes (CNTs) into high-density horizontal arrays is strongly desired for practical applications, but challenges remain despite myriads of research efforts. Herein, we developed a non-destructive soft-lock drawing method to achieve ultraclean single-walled CNT arrays with a very high degree of alignment (angle standard deviation of ~0.03°). These arrays contained a large portion of nanometre-sized CNT bundles, yielding a high packing density (~400 µm^-1) and high current carrying capacity (∼1.8 × 10⁸ A cm^-2). This alignment strategy can be generally extended to diverse substrates or sources of raw single-walled CNTs. Significantly, the assembled CNT bundles were used as nanometre electrical contacts of high-density monolayer molybdenum disulfide (MoS₂) transistors, exhibiting high current density (~38 µA µm^-1), low contact resistance (~1.6 kΩ µm), excellent device-to-device uniformity and highly reduced device areas (0.06 µm² per device), demonstrating their potential for future electronic devices and advanced integration technologies.

Carbon Nanotube Devices for Quantum Technology

Carbon nanotubes, quintessentially one-dimensional quantum objects, possess a variety of electrical, optical, and mechanical properties that are suited for developing devices that operate on quantum mechanical principles. The states of one-dimensional electrons, excitons, and phonons in carbon nanotubes with exceptionally large quantization energies are promising for high-operating-temperature quantum devices. Here, we discuss recent progress in the development of carbon-nanotube-based devices for quantum technology, i.e., quantum mechanical strategies for revolutionizing computation, sensing, and communication. We cover fundamental properties of carbon nanotubes, their growth and purification methods, and methodologies for assembling them into architectures of ordered nanotubes that manifest macroscopic quantum properties. Most importantly, recent developments and proposals for quantum information processing devices based on individual and assembled nanotubes are reviewed.

One-Dimensional van der Waals Heterostructures: A Perspective

As a new frontier in low-dimensional material research, van der Waals (vdW) heterostructures, represented by 2D heterostructures, have attracted tremendous attention due to their unique properties and potential applications. The emerging 1D heterostructures open new possibilities for the field with expectant unconventional properties and yet more challenging preparation pathways. This Perspective aims to give an overall understanding of the state-of-the-art growth strategies and fantastic properties of the 1D heterostructures and provide an outlook for further development based on the controlled preparation, which will bring up a variety of applications in high-performance electronic, optoelectronic, magnetic, and energy storage devices. A quick rise of the fundamentals and application study of 1D heterostructures is anticipated.

Magnetic Manipulation of Nanowires for Engineered Stretchable Electronics

Nanowires are often key ingredients of high-tech composite materials. The properties and performance of devices created using these, depend heavily on the structure and density of the embedded nanowires. Despite significant efforts, a process that can be adapted to different materials, compatible with current nanowire deposition methods, and that is able to control both variables simultaneously has not been achieved yet. In this work, we show that we can use low magnetic fields (80 mT) to manipulate nanowires by electrostatically coating them with superparamagnetic iron oxide nanoparticles in an aqueous solution. Monolayers, multilayers, and hierarchical structures of oriented nanowires were achieved in a highly ordered manner using vacuum filtration for two types of nanowires: silver and gold-coated titanium dioxide nanowires. The produced films were embedded in an elastomer, and the strain-dependent electrical properties of the resulting composites were investigated. The orientation of the assembly with respect to the tensile strain heavily impacts the performance of the composites. Composites containing nanowires perpendicular to the strain direction exhibit an extremely low gauge factor. On the other hand, when nanowires are arranged parallel to the strain direction, the composites have a high gauge factor. The possibility to orient nanowires during the processing steps is not only interesting for the shown strain sensing application but also expected to be useful in many other areas of material science.

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.

Stretchable Energy Storage Devices Based on Carbon Materials

Stretchable energy storage devices are essential for developing stretchable electronics and have thus attracted extensive attention in a variety of fields including wearable devices and bioelectronics. Carbon materials, e.g., carbon nanotube and graphene, are widely investigated as electrode materials for energy storage devices due to their large specific surface areas and combined remarkable electrical and electrochemical properties. They can also be effectively composited with many other functional materials or designed into different microstructures for fabricating stretchable energy storage devices. This review summarizes recent advances toward the development of carbon-material-based stretchable energy storage devices. An overview of common carbon materials' fundamental properties and general strategies to enable the stretchability of carbon-material-based electrodes are presented. The performances of the as-fabricated stretchable energy storage devices including supercapacitors, lithium-ion batteries, metal-air batteries, and other batteries are then carefully discussed. Challenges and perspectives in this emerging field are finally highlighted for future studies.

Integrated polarization-sensitive amplification system for digital information transmission

Polarized light can provide significant information about objects, and can be used as information carrier in communication systems through artificial modulation. However, traditional polarized light detection systems integrate polarizers and various functional circuits in addition to detectors, and are supplemented by complex encoding and decoding algorithms. Although the in-plane anisotropy of low-dimensional materials can be utilized to manufacture polarization-sensitive photodetectors without polarizers, the low anisotropic photocurrent ratio makes it impossible to realize digital output of polarized information. In this study, we propose an integrated polarization-sensitive amplification system by introducing a nanowire polarized photodetector and organic semiconductor transistors, which can boost the polarization sensitivity from 1.24 to 375. Especially, integrated systems are universal in that the systems can increase the anisotropic photocurrent ratio of any low-dimensional material corresponding to the polarized light. Consequently, a simple digital polarized light communication system can be realized based on this integrated system, which achieves certain information disguising and confidentiality effects.

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.

Laser-induced dynamic alignment and nonlinear-like optical transmission in liquid suspensions of 2D atomically thin nanomaterials

Nonlinear optical property of atomically thin materials suspended in liquid has attracted a lot of attention recently due to the rapid development of liquid exfoliation methods. Here we report laser-induced dynamic orientational alignment and nonlinear-like optical response of the suspensions as a result of their intrinsic anisotropic properties and thermal convection of solvents. Graphene and graphene oxide suspensions are used as examples, and the transition to ordered states from initial optically isotropic suspensions is revealed by birefringence imaging. Computational fluid dynamics is performed to simulate the velocity evolution of convection flow and understand alignment-induced birefringence patterns. The optical transmission of these suspensions exhibits nonlinear-like saturable or reverse saturable absorptions in Z-scan measurements with both nanosecond and continuous-wave lasers. Our findings not only demonstrate a non-contact controlling of macroscopic orientation and collective optical properties of nanomaterial suspensions by laser but also pave the way for further explorations of optical properties and novel device applications of low-dimensional nanomaterials.

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.

A Meta-Analysis of Conductive and Strong Carbon Nanotube Materials

A study of 1304 data points collated over 266 papers statistically evaluates the relationships between carbon nanotube (CNT) material characteristics, including: electrical, mechanical, and thermal properties; ampacity; density; purity; microstructure alignment; molecular dimensions and graphitic perfection; and doping. Compared to conductive polymers and graphitic intercalation compounds, which have exceeded the electrical conductivity of copper, CNT materials are currently one-sixth of copper's conductivity, mechanically on-par with synthetic or carbon fibers, and exceed all the other materials in terms of a multifunctional metric. Doped, aligned few-wall CNTs (FWCNTs) are the most superior CNT category; from this, the acid-spun fiber subset are the most conductive, and the subset of fibers directly spun from floating catalyst chemical vapor deposition are strongest on a weight basis. The thermal conductivity of multiwall CNT material rivals that of FWCNT materials. Ampacity follows a diameter-dependent power-law from nanometer to millimeter scales. Undoped, aligned FWCNT material reaches the intrinsic conductivity of CNT bundles and single-crystal graphite, illustrating an intrinsic limit requiring doping for copper-level conductivities. Comparing an assembly of CNTs (forming mesoscopic bundles, then macroscopic material) to an assembly of graphene (forming single-crystal graphite crystallites, then carbon fiber), the ≈1 µm room-temperature, phonon-limited mean-free-path shared between graphene, metallic CNTs, and activated semiconducting CNTs is highlighted, deemphasizing all metallic helicities for CNT power transmission applications.

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.

Sensing Organophosphorus Compounds with SWCNT Films

Promising electrical properties of single-walled carbon nanotubes (SWCNTs) open a spectrum of applications for this material. As the SWCNT electronic characteristics respond well to the presence of various analytes, this makes them highly sensitive sensors. In this contribution, selected organophosphorus compounds were detected by studying their impact on the electronic properties of the nanocarbon network. The goal was to untangle the n-doping mechanism behind the beneficial effect of organic phosphine derivatives on the electrical conductivity of SWCNT networks. The highest sensitivity was obtained in the case of the application of 1,6-Bis(diphenylphoshpino)hexane. Consequently, free-standing SWCNT films experienced a four-fold improvement to the electrical conductivity from 272 ± 21 to 1010 ± 44 S/cm and an order of magnitude increase in the power factor. This was ascribed to the beneficial action of electron-rich phenyl moieties linked with a long alkyl chain, making the dopant interact well with SWCNTs.

Unexpected Dependence of Photonic Band Gap Size on Randomness in Self-Assembled Colloidal Crystals

Using computer simulations, we explore how thermal noise-induced randomness in a self-assembled photonic crystal affects its photonic band gaps (PBGs). We consider a two-dimensional photonic crystal composed of a self-assembled array of parallel dielectric hard rods of infinite length with circular or square cross section. We find that PBGs can exist over a large range of intermediate packing densities and the largest band gap does not always appear at the highest packing density studied. Remarkably, for rods with square cross section at intermediate packing densities, the transverse magnetic (TM) band gap of the self-assembled (i.e., thermal) system can be larger than that of identical rods arranged in a perfect square lattice. By considering hollow rods, we find the band gap of transverse electric modes can be substantially increased while that of TM modes show no obvious improvement over solid rods. Our study suggests that particle shape and internal structure can be used to engineer the PBG of a self-assembled system despite the positional and orientational randomness arising from thermal noise.

Chiral 2D-Perovskite Nanowires for Stokes Photodetectors

Structural engineering in multiple scales permits the integration of exotic properties into a single material, which boosts the development of ultracompact multifunctional devices. Layered perovskites are capable of cross-linking efficient carrier transport originating from few-layer perovskite frameworks with extended functionalities contributed by designable bulky organic cations and nanostructures, thus providing a platform for multiscale material engineering. Herein, high-performance Stokes-parameter photodetectors for arbitrary polarized light detection are realized on the basis of solution-processed chiral-perovskite nanowire arrays. The chiral ammonium cations intercalated between the perovskite layers are responsive to circularly polarized light with a maximum anisotropy factor of 0.15, while the strictly aligned nanowires with the anisotropic dielectric function result in a large polarized ratio of 1.6 to linearly polarized light. Single crystallinity and pure crystallographic orientation permit efficient in-plane carrier transport along the nanowires, yielding a responsivity of 47.1 A W_^-1 and a detectivity of 1.24 × 10¹³ Jones. By synergy of linear- and circular-polarization response with high optoelectronic performance for providing sufficient photocurrent contrasts, Stokes-parameter photodetection is demonstrated on these nanowires. Our Stokes-parameter photodetectors with a small footprint and high performances present promising applications toward polarization imaging.

Label-free terahertz microfluidic biosensor for sensitive DNA detection using graphene-metasurface hybrid structures

Metasurface assisted terahertz (THz) real-time and label-free biosensors have attracted intense attention. However, it is still challenging for specific detection of highly absorptive liquid samples with high sensitivity in the THz range. Here, we incorporated graphene with THz metasurface into a microfluidic cell for sensitive biosensing. The proposed THz graphene-metasurface microfluidic platform can effectively reduce the volume of the sample solution and boost the interaction between biomolecules and THz waves, thus enhancing the sensitivity. As a proof of concept, comparative experiments using other three kinds of microfluidic cells (pure microfluidic cell, metasurface-based microfluidic cell and graphene-based microfluidic cell) were conducted to explore and verify the sensing mechanism, which evidences the high sensitivity of delicate sensing based on the hybrid graphene-metasurface THz microfluidic device. Furthermore, to perform biosensing applications on that basis, specific aptamers were modified on the graphene-metasurface, enabling DNA sequences of foodborne pathogen Escherichia coli O157:H7 to be recognized. Based on the THz microfluidic biosensor, 100 nM DNA short sequences can be successfully detected. The sensing results of antibiotics and DNA based on the graphene-metasurface microfluidic biosensor confirm the superiority of the proposed design and considerable promise in THz biosensing. The novel sensing platform provides the merits of enabling highly sensitive, label-free, low-cost, easy to use, reusable, and real-time biosensing, which opens an exciting prospect for nanomaterial-metasurface hybrid structure assisted THz label-free biosensing in liquid environment.

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.

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.