Ultrahigh-performance transparent conductive films of carbon-welded isolated single-wall carbon nanotubes

A Flexible Long-Wave Infrared Radiation Modulator Integrated with Electrochromic Behavior for Dual-Band Camouflage

Electrochromic devices (ECDs), which are capable of modulating optical properties in the visible and long-wave infrared (LWIR) spectra under applied voltage, are of great significance for military camouflage. However, there are a few materials that can modulate dual frequency bands. In addition, the complex and specialized structural design of dual-band ECDs poses significant challenges. Here, we propose a novel approach for a bendable ECD capable of modulating LWIR radiation and displaying multiple colors. Notably, it eliminates the need for a porous electrode or a grid electrode, thereby improving both the response speed and fabrication feasibility. The device employs multiwalled carbon nanotubes (MWCNTs) as both the transparent electrode and the LWIR modulator, polyaniline (PANI) as the electrochromic layer, and ionic liquids (HMIM[TFSI]) as the electrolyte. The ECD is able to reduce its infrared emissivity (Δε = 0.23) in a short time (resulting in a drop in infrared temperature from 50 to 44 °C) within a mere duration of 0.78 ± 0.07 s while changing its color from green to yellow within 3 s when a positive voltage of 4 V is applied. In addition, it exhibits excellent flexibility, even under bending conditions. This simplified structure provides opportunities for applications such as wearable adaptive camouflage and multispectral displays.

Fabricating Ultrastrong Carbon Nanotube Fibers via a Microwave Welding Interface

Liquid crystal wet-spun carbon nanotube fibers (CNTFs) offer notable advantages, such as precise alignment and scalability. However, these CNTFs usually suffer premature failure through intertube slippage due to the weak interfacial interactions between adjacent shells and bundles. Herein, we present a microwave (MW) welding strategy to enhance intertube interactions by partially carbonizing interstitial heterocyclic aramid polymers. The resulting CNTFs exhibit ultrahigh static tensile strength (6.74 ± 0.34 GPa) and dynamic tensile strength (9.52 ± 1.31 GPa), outperforming other traditional high-performance fibers. This work provides a straightforward yet effective approach to strengthening CNTFs for advanced engineering applications.

Dynamics of growing carbon nanotube interfaces probed by machine learning-enabled molecular simulations

Carbon nanotubes (CNTs), hollow cylinders of carbon, hold great promise for advanced technologies, provided their structure remains uniform throughout their length. Their growth takes place at high temperatures across a tube-catalyst interface. Structural defects formed during growth alter CNT properties. These defects are believed to form and heal at the tube-catalyst interface but an understanding of these mechanisms at the atomic-level is lacking. Here we present DeepCNT-22, a machine learning force field (MLFF) to drive molecular dynamics simulations through which we unveil the mechanisms of CNT formation, from nucleation to growth including defect formation and healing. We find the tube-catalyst interface to be highly dynamic, with large fluctuations in the chiral structure of the CNT-edge. This does not support continuous spiral growth as a general mechanism, instead, at these growth conditions, the growing tube edge exhibits significant configurational entropy. We demonstrate that defects form stochastically at the tube-catalyst interface, but under low growth rates and high temperatures, these heal before becoming incorporated in the tube wall, allowing CNTs to grow defect-free to seemingly unlimited lengths. These insights, not readily available through experiments, demonstrate the remarkable power of MLFF-driven simulations and fill long-standing gaps in our understanding of CNT growth mechanisms.

Large-Area Flexible Carbon Nanofilms with Synergistically Enhanced Transmittance and Conductivity Prepared by Reorganizing Single-Walled Carbon Nanotube Networks

Large-area flexible transparent conductive films (TCFs) are highly desired for future electronic devices. Nanocarbon TCFs are one of the most promising candidates, but some of their properties are mutually restricted. Here, a novel carbon nanotube network reorganization (CNNR) strategy, that is, the facet-driven CNNR (FD-CNNR) technique, is presented to overcome this intractable contradiction. The FD-CNNR technique introduces an interaction between single-walled carbon nanotube (SWNT) and Cu─-O. Based on the unique FD-CNNR mechanism, large-area flexible reorganized carbon nanofilms (RNC-TCFs) are designed and fabricated with A3-size and even meter-length, including reorganized SWNT (RSWNT) films and graphene and RSWNT (G-RSWNT) hybrid films. Synergistic improvement in strength, transmittance, and conductivity of flexible RNC-TCFs is achieved. The G-RSWNT TCF shows sheet resistance as low as 69 Ω sq-1 at 86% transmittance, FOM value of 35, and Young's modulus of ≈45 MPa. The high strength enables RNC-TCFs to be freestanding on water and easily transferred to any target substrate without contamination. A4-size flexible smart window is fabricated, which manifests controllable dimming and fog removal. The FD-CNNR technique can be extended to large-area or even large-scale fabrication of TCFs and can provide new insights into the design of TCFs and other functional films.

Flexible, Transparent and Conductive Metal Mesh Films with Ultra-High FoM for Stretchable Heating and Electromagnetic Interference Shielding

Despite the growing demand for transparent conductive films in smart and wearable electronics for electromagnetic interference (EMI) shielding, achieving a flexible EMI shielding film, while maintaining a high transmittance remains a significant challenge. Herein, a flexible, transparent, and conductive copper (Cu) metal mesh film for EMI shielding is fabricated by self-forming crackle template method and electroplating technique. The Cu mesh film shows an ultra-low sheet resistance (0.18 Ω □-1), high transmittance (85.8%@550 nm), and ultra-high figure of merit (> 13,000). It also has satisfactory stretchability and mechanical stability, with a resistance increases of only 1.3% after 1,000 bending cycles. As a stretchable heater (ε > 30%), the saturation temperature of the film can reach over 110 °C within 60 s at 1.00 V applied voltage. Moreover, the metal mesh film exhibits outstanding average EMI shielding effectiveness of 40.4 dB in the X-band at the thickness of 2.5 μm. As a demonstration, it is used as a transparent window for shielding the wireless communication electromagnetic waves. Therefore, the flexible and transparent conductive Cu mesh film proposed in this work provides a promising candidate for the next-generation EMI shielding applications.

Creating covalent bonds between Cu and C at the interface of metal/open-ended carbon nanotubes

The unique electrical properties of carbon nanotubes (CNTs) are highly desired in many technological applications. Unfortunately, in practice, the electrical conductivity of most CNTs and their assemblies has fallen short of expectations. One reason for this poor performance is that electrical resistance develops at the interface between carbon nanomaterials and metal surfaces when traditional metal-metal type contacts are employed. Here, a method for overcoming this resistance using covalent bond formation between open-ended CNTs and Cu surfaces is investigated experimentally and supported by theoretical calculations. The open-ended CNTs are vertically oriented compared to the substrate and have carboxylic functional groups that react with aminophenyl groups (linkers) grafted on metal surfaces. The covalent bond formation, crosslinking carboxylic and amine, via amide bond formation occurs at 120 °C. The covalent bonding nature of the aminophenyl linker is demonstrated theoretically using (100), (110), and (111) Cu surfaces, and bridge-like bond formation between carbon and two adjacent Cu atoms is revealed. The electrical conductivity calculated for a single intramolecular-type junction supports covalent bond formation between Cu and CNTs. Experimentally, the robustness of the covalent bonding between vertically oriented CNTs is tested by exposing CNTs on Cu to sonication, which reveals that CNTs remain fixed to the Cu supports. Since bonding CNTs to metals was performed at low temperatures, the reported method of covalent bond formation is expected to facilitate the application of CNTs in multiple fields, including electronics.

Molecular Doping Modulation and Applications of Structure-Sorted Single-Walled Carbon Nanotubes: A Review

Single-walled carbon nanotubes (SWCNTs) that have a reproducible distribution of chiralities or single chirality are among the most competitive materials for realizing post-silicon electronics. Molecular doping, with its non-destructive and fine-tunable characteristics, is emerging as the primary doping approach for the structure-controlled SWCNTs, enabling their eventual use in various functional devices. This review provides an overview of important advances in the area of molecular doping of structure-controlled SWCNTs and their applications. The first part introduces the underlying physical process of molecular doping, followed by a comprehensive survey of the commonly used dopants for SWCNTs to date. Then, it highlights how the convergence of molecular doping and structure-sorting strategies leads to significantly improved functionality of SWCNT-based field-effect transistor arrays, transparent electrodes in optoelectronics, thermoelectrics, and many emerging devices. At last, several challenges and opportunities in this field are discussed, with the hope of shedding light on promoting the practical application of SWCNTs in future electronics.

Synthesis, Properties, and Application of Ultrathin and Flexible Tellurium Nanorope Films: Beyond Conventional 2D Materials

Nanomaterials that can be easily processed into thin films are highly desirable for their wide range of applicability in electrical and optical devices. Currently, Te-based 2D materials are of interest because of their superior electrical properties compared to transition metal dichalcogenide materials. However, the large-scale manufacturing of these materials is challenging, impeding their commercialization. This paper reports on ultrathin, large-scale, and highly flexible Te and Te-metal nanorope films grown via low-power radiofrequency sputtering for a short period at 25 °C. Additionally, the feasibility of such films as transistor channels and flexible transparent conductive electrodes is discussed. A 20 nm thick Te-Ni-nanorope-channel-based transistor exhibits a high mobility (≈450 cm2 V-1 s-1 ) and on/off ratio (105 ), while 7 nm thick Te-W nanorope electrodes exhibit an extremely low haze (1.7%) and sheet resistance (30 Ω sq-1 ), and high transmittance (86.4%), work function (≈4.9 eV), and flexibility. Blue organic light-emitting diodes with 7 nm Te-W anodes exhibit significantly higher external quantum efficiencies (15.7%), lower turn-on voltages (3.2 V), and higher and more uniform viewing angles than indium-tin-oxide-based devices. The excellent mechanical flexibility and easy coating capability offered by Te nanoropes demonstrate their superiority over conventional nanomaterials and provide an effective outlet for multifunctional devices.

Flexible Carbon Nanotube-Epitaxially Grown Nanocrystals for Micro-Thermoelectric Modules

Flexible thermoelectric materials have attracted increasing interest because of their potential use in thermal energy harvesting and high-spatial-resolution thermal management. However, a high-performance flexible micro-thermoelectric device (TED) compatible with the microelectronics fabrication process has not yet been developed. Here a universal epitaxial growth strategy is reported guided by 1D van der Waals-coupling, to fabricate freestanding and flexible hybrids comprised of single-wall carbon nanotubes and ordered (Bi,Sb)2 Te3 nanocrystals. High power factors ranging from ≈1680 to ≈1020 µW m-1 K-2 in the temperature range of 300-480 K, combined with a low thermal conductivity yield a high average figure of merit of ≈0.81. The fabricated flexible micro-TED module consisting of two p-n couples of freestanding thermoelectric hybrids has an unprecedented open circuit voltage of ≈22.7 mV and a power density of ≈0.36 W cm-2 under ≈30 K temperature difference, and a net cooling temperature of ≈22.4 K and a heat absorption density of ≈92.5 W cm-2 .

Carrier Transport Regulation of Pixel Graphene Transparent Electrodes for Active-Matrix Organic Light-Emitting Diode Display

Integrating a graphene transparent electrode (TE) matrix with driving circuits is essential for the practical use of graphene in optoelectronics such as active-matrix organic light-emitting diode (OLED) display, however it is disabled by the transport of carriers between graphene pixels after deposition of a semiconductor functional layer caused by the atomic thickness of graphene. Here, the carrier transport regulation of a graphene TE matrix by using an insulating polyethyleneimine (PEIE) layer is reported. The PEIE forms an ultrathin uniform film (≤10 nm) to fill the gap of the graphene matrix, blocking horizontal electron transport between graphene pixels. Meanwhile, it can reduce the work function of graphene, improving the vertical electron injection through electron tunneling. This enables the fabrication of inverted OLED pixels with record high current and power efficiencies of 90.7 cd A-1 and 89.1 lm W-1 , respectively. By integrating these inverted OLED pixels with a carbon nanotube-based thin-film transistor (CNT-TFT)-driven circuit, an inch-size flexible active-matrix OLED display is demonstrated, in which all OLED pixels are independently controlled by CNT-TFTs. This research paves a way for the application of graphene-like atomically thin TE pixels in flexible optoelectronics such as displays, smart wearables, and free-form surface lighting.

Stretchable, Electrochemically-Stable Electrochromic Devices Based on Semi-Embedded Ag@Au Nanowire Network

Stretchable electrochromic (EC) devices that can adapt the irregular and dynamic human surfaces show promising applications in wearable display, adaptive camouflage, and visual sensation. However, challenges exist in lacking transparent conductive electrodes with both tensile and electrochemical stability to assemble the complex device structure and endure harsh electrochemical redox reactions. Herein, a wrinkled, semi-embedded Ag@Au nanowire (NW) networks are constructed on elastomer substrates to fabricate stretchable, electrochemically-stable conductive electrodes. The stretchable EC devices are then fabricated by sandwiching a viologen-based gel electrolyte between two conductive electrodes with the semi-embedded Ag@Au NW network. Because the inert Au layer inhibits the oxidation of Ag NWs, the EC device exhibits much more stable color changes between yellow and green than those with pure Ag NW networks. In addition, since the wrinkled semi-embedded structure is deformable and reversibly stretched without serious fractures, the EC devices still maintain excellent color-changing stability under 40% stretching/releasing cycles.

Interfacial Chemical Bridging Constructed by Multifunctional Lewis Acid for Carbon Nanotube/Silicon Heterojunction Solar Cells with an Efficiency Approaching 17.7

Single-wall carbon nanotube/silicon (SWCNT/Si) heterojunction shows appealing potential for use in photovoltaic devices. However, the relatively low conductivity of SWCNT network and interfacial recombination of carriers have limited their photovoltaic performance. Herein, a multifunctional Lewis acid (p-toluenesulfonic acid, TsOH) is used to significantly reduce the energy loss in SWCNT/Si solar cells. Owing to the charge transfer doping effect of TsOH, the conductivity and work function of SWCNT films are optimized and tuned. More importantly, a chemical bridge is constructed at the interface of SWCNT/Si heterojunction. Experimental studies indicate that the phenyl group of TsOH can interact with SWCNTs through π-π interaction, meanwhile, the oxygen in the sulfonic functional group of the TsOH molecule can graft on the dangling bonds of the Si surface. The chemical bridge structure effectively suppresses the recombination of photogenerated carriers. The TsOH coating also works as an antireflection layer, leading to a 19% increment of the photocurrent. As a result, a champion power conversion efficiency of 17.7% is achieved for the TsOH-SWCNT/Si device, and it also exhibits an excellent stability, retaining more than 96% of the initial efficiency in the ambient air after 1 month.

A Microwave-Assisted, Solvent-Free Approach for the Versatile Functionalization of Carbon Nanotubes

While the functionalization of carbon nanotubes (CNTs) has attracted extensive interest for a wide range of applications, a facial and versatile strategy remains in demand. Here, we report a microwave-assisted, solvent-free approach to directly functionalize CNTs both in raw form and in arbitrary macroscopic assemblies. Rapid microwave irradiation was applied to generate active sites on the CNTs while not inducing excessive damage to the graphitic network, and a gas-phase deposition afforded controllable grafting for thorough or regioselective functionalization. Using methyl methacrylate (MMA) as a model functional group and a CNT sponge as a model assembly, homogeneous grafting was exhibited by the increased robust hydrophobicity (contact angle increase from 30 to 140°) and improved structural stability (compressive modulus increased by 135%). Therefore, when our MMA-functionalized CNTs served as a solar absorber for saline distillation, high operating stability with a superior water evaporation rate of ∼2.6 kg m^-2 h^-1 was observed. Finally, to highlight the efficacy and versatility of this functionalization approach, we fabricated asymmetrically hydrophobic CNT sponges by regioselective functionalization to serve as a moisture-driven generator, which demonstrated a stable open-circuit voltage of 0.6 mV. This versatile, solvent-free approach can complement conventional solution-based techniques in the design and fabrication of multifunctional nanocarbon-based materials.

Defect-Induced Efficient Heteroepitaxial Growth of Single-Wall Carbon Nanotubes @ Hexagonal Boron Nitride Films

Carbon nanotube-based derivatives have attracted considerable research interest due to their unique structure and fascinating physicochemical properties. However, the controlled growth mechanism of these derivatives remains unclear, and the synthesis efficiency is low. Herein, we proposed a defect-induced strategy for the efficient heteroepitaxial growth of single-wall carbon nanotubes (SWCNTs)@hexagonal boron nitride (h-BN) films. Air plasma treatment was first performed to generate defects on the wall of SWCNTs. Then, atmospheric pressure chemical vapor deposition was conducted to grow h-BN on the surface of SWCNTs. Controlled experiments combined with first-principles calculations revealed that the induced defects on the wall of SWCNTs function as nucleation sites for the efficient heteroepitaxial growth of h-BN.

Multilayer Ultrathin MXene@AgNW@MoS2 Composite Film for High-Efficiency Electromagnetic Shielding

Structure and material composition is crucial in realizing high electromagnetic interference (EMI) shielding effectiveness (SE). Herein, an ultrathin MXene@AgNW@MoS₂ (MAM) composite film that resembles the structure of a pork belly and exhibits superior EMI shielding performance was fabricated via the vacuum-assisted suction filtration process and atomic layer deposition (ALD). The staggered AgNWs form skeletons and intersperse in MXene sheets to build a doped layer with three-dimensional network structures, which improves the electrical conductivity of the film. Based on the optimal dispersion concentration of Ag in doped and single layers, the MXene/AgNW doped layer and AgNW single layer are alternately vacuum-assisted-filtered to obtain laminated structures with multiple heterogeneous interfaces. These interfaces generate interface polarization and increase multiple reflection and scattering, resulting in the increased electromagnetic (EM) wave losses. On the other hand, MoS₂ outer nanolayers fabricated precisely by ALD effectively increases the absorption proportion of electromagnetic waves, reduces the secondary reflection, and improves the stability of EMI shielding properties. Ultimately, an ultrathin MAM film (a thickness of 0.03 mm) with five alternating internal layers and MoS₂ outer layers exhibits an excellent EMI SE of 86.3 dB in the X-band.

Synthesis of Ultralong Carbon Nanotubes with Ultrahigh Yields

Ultralong carbon nanotubes (CNTs) are in huge demand in many cutting-edge fields due to their macroscale lengths, perfect structures, and extraordinary properties, while their practical application is limited by the difficulties in their mass production. Herein, we report the synthesis of ultralong CNTs with a dramatically increased yield by a simple but efficient substrate interception and direction strategy (SIDS), which couples the advantages of floating-catalyst chemical vapor deposition with the flying-kite-like growth mechanism of ultralong CNTs. The SIDS-assisted approach prominently improves the catalyst utilization and significantly increases the yield. The areal density of the ultralong CNT arrays with length of over 1 cm reached a record-breaking value of ∼6700 CNTs mm^-1, which is 2-3 orders of magnitude higher than the previously reported values obtained by traditional methods. The SIDS provides a solution for synthesizing high-quality ultralong CNTs with high yields, laying the foundation for their mass production.

Efficient Fabrication of High-Quality Single-Walled Carbon Nanotubes and Their Macroscopic Conductive Fibers

High-purity and well-graphitized single-walled carbon nanotubes (SWCNTs) with excellent physiochemical properties are ideal building blocks for the assembly of various CNT macrostructures for a wide range of applications. We report the preparation of high-quality SWCNTs on a large scale using a floating catalyst chemical vapor deposition (FCCVD) method. Under the optimum conditions, the conversion rate of the carbon source to SWCNTs reached 28.8%, and 20.4% of the metal nanoparticles were active for SWCNT growth, which are 15% and ∼400 times higher than those previously reported for FCCVD synthesis, respectively. As a result, the prepared SWCNTs have a very low residual catalyst content of ∼1.9 wt % and a high rapid oxidation temperature of 717 °C. Using these high-quality SWCNTs, we spun macroscopic SWCNT fibers by a wet-spinning process. The resulting fibers had a high electrical conductivity of 6.67 MS/m, which is 32% higher than the best value previously reported for SWCNT fibers.

Embedded ultra-high stability flexible transparent conductive films based on exfoliated graphene-silver nanowires-colorless polyimide

Transparent conductive films with high stability were prepared by embedding silver nanowires in colorless polyimide and adding a protective layer of exfoliated graphene. The films exhibit great light transmission and conductivity with a sheet resistance of 22 Ω sq^-1at transmittance of 83%. Due to its special embedded structure, the conductive layer can withstand several peeling experiments without falling off. In addition, the most outstanding advantage is the ultra-high stability of the films, including high mechanical robustness, strong chemical corrosion resistance and high operating voltage capacity. The organic light-emitting diode devices prepared based on this transparent conductive electrode exhibit comparable efficiency to indium tin oxide (ITO) based devices, withC.E._max= 2.78 cd A^-1,P^-1.E._max= 1.89 lm W^-1,EQE_max= 0.89%. Moreover, the efficiencies were even higher than that of ITO devices when the operating voltage of the device exceeds 5 V. The above performances show that the transparent conductive electrode based on this structure has high potential for application in organic electronic devices.

Spatially modulated femtosecond laser direct ablation-based preparation of ultra-flexible multifunctional copper mesh electrodes and its application

Multifunctional electrodes possess superior properties such as high photoelectric properties and high stability. Laser manufacturing process is one of the widely used method for electrode fabrication. However, the current multifunctional electrode laser manufacturing process suffers from low fabrication speed. Here, we report a high-efficiency laser digital patterning process to fabricate copper-based flexible transparent conducting electrodes. By using a spatially modulated, one single laser spot is modulated into an array of spots with equal intensity, and the fabrication speed can be improved by more than 20 times over the traditional single pulse processing. In addition, copper mesh electrodes with a high photoelectric property have been fabricated. A transparent touch screen panel and multifunctional windows are fabricated with transparent electrodes to demonstrate their use in vehicle defogging, portable heating, and wearable devices.

Study on Ultrathin Silver Film Transparent Electrodes Based on Aluminum Seed Layers with Different Structures

Ag has the lowest electrical resistivity among all metals, and at the same time, the best optical properties in the visible and near-IR spectral range; it is therefore the most widely employed material for thin-metal-film-based transparent conductors. In this work, an ultra-thin transparent silver film electrode with aluminum as seed layer was prepared by a resistive thermal evaporation technique. Using a range of electrical, optical and surface morphology techniques, it can be noted that the presence of the thin layer of aluminum changes the growth kinetics (nucleation and evolution) of the thermal evaporation of Ag, leading to silver films with smooth surface morphology and high electrical conductivity, and the threshold thickness of the silver film is reduced. It is inferred that the aluminum layer showed a good infiltration effect on the ultra-thin silver film, by analyzing the transmittance spectrum, sheet resistance and surface morphology. Moreover, the average transmittance of silver film with 10 nm is 40% in the 400-2500 nm band, whereas the sheet resistance is 13 Ωsq ^-1. A series of experiments show that the introduction of Al seed layer has certain effect on improving the properties of transparent conductive silver films. Then, a new method for deposition of 1 nm Al seed layer was proposed; that is, the 1 nm aluminum infiltrated layer is divided into two or more layers, and the average transmittance of silver film with 5 nm is 60% in the 400-2500 nm band, whereas the sheet resistance does not exceed 100 Ω sq^-1.

Gas Sensors Based on Single-Wall Carbon Nanotubes

Single-wall carbon nanotubes (SWCNTs) have a high aspect ratio, large surface area, good stability and unique metallic or semiconducting electrical conductivity, they are therefore considered a promising candidate for the fabrication of flexible gas sensors that are expected to be used in the Internet of Things and various portable and wearable electronics. In this review, we first introduce the sensing mechanism of SWCNTs and the typical structure and key parameters of SWCNT-based gas sensors. We then summarize research progress on the design, fabrication, and performance of SWCNT-based gas sensors. Finally, the principles and possible approaches to further improving the performance of SWCNT-based gas sensors are discussed.

Selected-Area Fabrication of a Single-Walled Carbon Nanotube Schottky Junction with Tunable Gate Rectification

Single-walled carbon nanotube (SWNT)-based devices are expected to play an important role in the next generation of electronic integrated circuits. As an important structural unit for SWNT-based electronics, the Schottky junction has a series of functions such as rectification, photoelectric detection, switching, etc. Here, we demonstrate a well-controlled localized radical reaction method to prepare an intramolecular SWNT Schottky junction with a closed edge. This junction exhibits strong gate-dependent rectifying behavior and a high rectification ratio of 962. Furthermore, the semiconducting part on the junction side could be effectively tuned from p-type doping to n-type doping, resulting in reversible rectifying behavior. Our work paves a new avenue for the design and synthesis of an SWNT Schottky junction, which is very important to future applications for carbon-based nanoelectronic devices.

Nanoparticle-based single molecule fluorescent probes

Single molecule fluorescent probes have attracted considerable attention duet to their ultimate sensitivity, fast response, low sample consumption, and high signal-to-noise ratio. Nanoparticles with outstanding optical properties make them perfect candidates for probes in application of single molecule detection. In this review, we focus on various kinds of nanoparticles acting as single molecule fluorescent probes, including quantum dots, upconverting fluorescent nanoparticles, carbon dots, single-wall carbon nanotubes, fluorescent nanodiamonds, polymeric nanoparticles, nanoclusters, and metallic nanoparticles. Optical properties of various nanoparticles and their recent application in single molecule fluorescent probes are explored. How nanoparticles boost the sensitivity of detection is emphasized in combination with different sensing strategies. Future trends of nanoparticles in single molecule detection are also discussed. We hope this review can provide practical guidance for researchers who work on nanoparticle-based single molecule fluorescent probes.

Transparent Conducting Films Based on Carbon Nanotubes: Rational Design toward the Theoretical Limit

Electrically conductive thin-film materials possessing high transparency are essential components for many optoelectronic devices. The advancement in the transparent conductor applications requires a replacement of indium tin oxide (ITO), one of the key materials in electronics. ITO and other transparent conductive metal oxides have several drawbacks, including poor flexibility, high refractive index and haze, limited chemical stability, and depleted raw material supply. Single-walled carbon nanotubes (SWCNTs) are a promising alternative for transparent conducting films (TCFs) because of their unique and excellent chemical and physical properties. Here, the latest achievements in the optoelectronic performance of TCFs based on SWCNTs are analyzed. Various approaches to evaluate the performance of transparent electrodes are briefly reviewed. A roadmap for further research and development of the transparent conductors using "rational design," which breaks the deadlock for obtaining the TCFs with a performance close to the theoretical limit, is also described.

Electrochemical Redox In-Situ Welding of Silver Nanowire Films with High Transparency and Conductivity

Silver nanowire (AgNW) networks with high transparency and conductivity are crucial to developing transparent conductive films (TCFs) for flexible optoelectronic devices. However, AgNW-based TCFs still suffer from the high contact resistance of AgNW junctions with both the in-plane and out-of-plane charge transport barrier. Herein, we report a rapid and green electrochemical redox strategy to in-situ weld AgNW networks for the enhanced conductivity and mechanical durability of TCFs with constant transparency. The welded TCFs show a marked decrease of the sheet resistance (reduced to 45.5% of initial values on average) with high transmittance of 97.02% at 550 nm (deducting the background of substrates). The electrochemical welding treatment enables the removal of the residual polyvinylpyrrolidone layer and the in-situ formation of Ag solder in the oxidation and reduction processes, respectively. Furthermore, local conductivity studies confirm the improvement of both the in-plane and the out-of-plane charge transport by conductive atomic force microscopy. This proposed electrochemical redox method provides new insights on the welding of AgNW-based TCFs with high transparency and low resistance for the development of next-generation flexible optoelectronic devices. Furthermore, such conductive films based on the interconnected AgNW networks can be acted as an ideal supporter to construct heterogeneous structures with other functional materials for wide applications in photocatalysis and electrocatalysis.

Flexible and Transparent Electrode of Hybrid Ti3C2TX MXene-Silver Nanowires for High-Performance Quantum Dot Light-Emitting Diodes

The development of electrodes with high conductivity, optical transparency, and reliable mechanical flexibility and stability is important for numerous solution-processed photoelectronic applications. Although transparent Ti₃C₂T_X MXene electrodes with high conductivity are promising, their suitability for displays remains limited because of the high sheet resistance, which is caused by undesirable flake junctions and surface roughness. Herein, a flexible and transparent electrode has been fabricated that is suitable for a full-solution-processed quantum dot light-emitting diode (QLED). An MXene-silver nanowire (AgNW) hybrid electrode (MXAg) consists of a highly conductive AgNW network mixed with solution-processed MXene flakes. Efficient welding of wire-to-wire junctions with MXene flakes yields an electrode with a low sheet resistance and a high transparency of approximately 13.9 Ω sq^-1 and 83.8%, respectively. By employing a thin polymer buffer layer of poly(methyl methacrylate) (PMMA), followed by mild thermal treatment, a hybrid PMMA-based MXene-AgNW (MXAg@PMMA) electrode in which the work function of an MXAg hybrid FTE physically embedded in PMMA (MXAg@PMMA) can be tuned by controlling the amount of MXene in the hybrid film facilitates the development of a high-performance solution-processed QLED that exhibits maximum external quantum and current efficiencies of approximately 9.88% and 25.8 cd/A, respectively, with excellent bending stability. This work function-tunable flexible transparent electrode based on solution-processed nanoconductors provides a way to develop emerging high-performance, wearable, cost-effective, and soft electroluminescent devices.

Freestanding 3D Metallic Micromesh for High-Performance Flexible Transparent Solid-State Zinc Batteries

Flexible transparent energy supplies are extremely essential to the fast-growing flexible electronic systems. However, the general developed flexible transparent energy storage devices are severely limited by the challenges of low energy density, safety issues, and/or poor compatibility. In this work, a freestanding 3D hierarchical metallic micromesh with remarkble optoelectronic properties (T = 89.59% and R_s = 0.23 Ω sq^-1 ) and super-flexibility is designed and manufactured for flexible transparent alkaline zinc batteries. The 3D Ni micromesh supported Cu(OH)₂ @NiCo bimetallic hydroxide flexible transparent electrode (3D NM@Cu(OH)₂ @NiCo BH) is obtained by a combination of photolithography, chemical etching, and electrodeposition. The negative electrode is constructed by electrodeposition of electrochemically active zinc on the surface of Ni@Cu micromesh (Ni@Cu@Zn MM). The metallic micromesh with 3D hierarchical nanoarchitecture can not only ensure low sheet resistance, but also realize high mass loading of active materials and short electron/ion transmission path, which can guarantee high energy density and high-rate capability of the transparent devices. The flexible transparent 3D NM@Cu(OH)₂ @NiCo BH electrode realizes a specific capacity of 66.03 μAh cm^-2 at 1 mA cm^-2 with a transmittance of 63%. Furthermore, the assembled solid-state NiCo-Zn alkaline battery exhibits a desirable energy density/power density of 35.89 μWh cm^-2 /2000.26 μW cm^-2 with a transmittance of 54.34%.

Ultrasensitive Airflow Sensors Based on Suspended Carbon Nanotube Networks

High-performance airflow sensors are in great demand in numerous fields but still face many challenges, such as slow response speed, low sensitivity, large detection threshold, and narrow sensing range. Carbon nanotubes (CNTs) exhibit many advantages in fabricating airflow sensors due to their nanoscale diameters, excellent mechanical and electrical properties, and so on. However, the intrinsic extraordinary properties of CNTs are not fully exhibited in previously reported CNT-based airflow sensors due to the mixed structures of macroscale CNT assemblies. Herein, this article presents suspended CNT networks (SCNTNs) as high-performance airflow sensors, which are self-assembled by ultralong CNTs and short CNTs in a one-step floating catalyst chemical vapor deposition process. The SCNTN-based airflow sensors achieved a record-breaking short response time of 0.021 s, a high sensitivity of 0.0124 s m^-1 , a small detection threshold of 0.11 m s^-1 , and a wide detection range of ≈0.11-5.51 m s^-1 , superior to most of the state-of-the-art airflow sensors. To reveal the sensing mechanism, an acoustic response testing system and a mathematical model are developed. It is found that the airflow-caused intertube stress change resulted in the resistance variation of SCNTNs.

Nanosphere Lithography: A Versatile Approach to Develop Transparent Conductive Films for Optoelectronic Applications

Transparent conductive films (TCFs) are irreplaceable components in most optoelectronic applications such as solar cells, organic light-emitting diodes, sensors, smart windows, and bioelectronics. The shortcomings of existing traditional transparent conductors demand the development of new material systems that are both transparent and electrically conductive, with variable functionality to meet the requirements of new generation optoelectronic devices. In this respect, TCFs with periodic or irregular nanomesh structures have recently emerged as promising candidates, which possess superior mechanical properties in comparison with conventional metal oxide TCFs. Among the methods for nanomesh TCFs fabrication, nanosphere lithography (NSL) has proven to be a versatile platform, with which a wide range of morphologically distinct nanomesh TCFs have been demonstrated. These materials are not only functionally diverse, but also have advantages in terms of device compatibility. This review provides a comprehensive description of the NSL process and its most relevant derivatives to fabricate nanomesh TCFs. The structure-property relationships of these materials are elaborated and an overview of their application in different technologies across disciplines related to optoelectronics is given. It is concluded with a perspective on current shortcomings and future directions to further advance the field.

Directly Printed Embedded Metal Mesh for Flexible Transparent Electrode via Liquid Substrate Electric-Field-Driven Jet

Flexible transparent electrodes (FTEs) with embedded metal meshes play an indispensable role in many optoelectronic devices due to their excellent mechanical stability and environmental adaptability. However, low-cost, simple, efficient, and environmental friendly integrated manufacturing of high-performance embedded metal meshes remains a huge challenge. Here, a facile and novel fabrication method is proposed for FTEs with an embedded metal mesh via liquid substrateelectric-field-driven microscale 3D printing process. This direct printing strategy avoids tedious processes and offers low-cost and high-volume production, enabling the fabrication of high-resolution, high-aspect ratio embedded metal meshes without sacrificing transparency. The final manufactured FTEs with 80 mm × 80 mm embedded metal mesh offers excellent optoelectronic performance with a sheet resistance (R_s ) of 6 Ω sq^-1 and a transmittance (T) of 85.79%. The embedded metal structure still has excellent mechanical stability and good environmental suitability under different harsh working conditions. The practical feasibility of the FTEs is successfully demonstrated with a thermally driven 4D printing structure and a resistive transparent strain sensor. This method can be used to manufacture large areas with facile, high-efficiency, low-cost, and high-performance FTEs.

Versatile acid solvents for pristine carbon nanotube assembly

Chlorosulfonic acid and oleum are ideal solvents for enabling the transformation of disordered carbon nanotubes (CNTs) into precise and highly functional morphologies. Currently, processing these solvents using extrusion techniques presents complications due to chemical compatibility, which constrain equipment and substrate material options. Here, we present a novel acid solvent system based on methanesulfonic or p-toluenesulfonic acids with low corrosivity, which form true solutions of CNTs at concentrations as high as 10 g/liter (≈0.7 volume %). The versatility of this solvent system is demonstrated by drop-in application to conventional manufacturing processes such as slot die coating, solution spinning continuous fibers, and 3D printing aerogels. Through continuous slot coating, we achieve state-of-the-art optoelectronic performance (83.6 %T and 14 ohm/sq) at industrially relevant production speeds. This work establishes practical and efficient means for scalable processing of CNT into advanced materials with properties suitable for a wide range of applications.

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.

Stable Doping of Single-Walled Carbon Nanotubes for Flexible Transparent Conductive Films

Possessing excellent electronic and mechanical properties and great stability, single-walled carbon nanotubes (SWCNTs) are exceptionally attractive in fabricating flexible transparent conductive films. Doping is a key step to further enhance the conductivity of the SWCNT films and the reliable doping is highly needed. We developed a feasible strategy that uses solid acids such as phosphotungstic acid (PTA) to dope the SWCNT films stably relying on the nonvolatility of the dopants. The sheet resistance of the films was reduced to around a half of the original value meanwhile with no obvious change in transmittance. The doping effect maintained during a 700 days' observation. The excellent flexibility of the PTA-doped films was demonstrated by a bending test of 1000 cycles, during which the sheet resistance and transmittance was basically unaffected. The blue shifts of G band in the Raman spectra and the increase of work function measured by the Kelvin probe force microscopy both reveal the p-type doping of the films by PTA. The strong acidity of PTA plays a key role in the doping effect by increasing the redox potential of the ambient O₂ and thus the Fermi level of the SWCNTs is brought down. The great feasibility and robustness of our doping strategy are desirable in the practical application of SWCNT-based flexible transparent conductive films. This strategy can be extended to the p-type doping of various CNT-based assemblies (such as sponges and forests) as well as other material families, expanding the application spectrum of polyacids.

Conductivity and Stability Enhancement of PEDOT:PSS Electrodes via Facile Doping of Sodium 3-Methylsalicylate for Highly Efficient Flexible Organic Light-Emitting Diodes

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is one of the most prospering transparent conductive materials for flexible optoelectronic devices, which arises from its nonpareil features of low-cost solution processability, tunable conductivity, high transparency, and superior mechanical flexibility. However, acidity and hygroscopicity of PSS chains cause a decrease in conductivity, substrate corrosion, and device degradation. This work proposes a facile and effective direct doping strategy of sodium 3-methylsalicylate to enhance the conductivity, alleviate the acidity, and improve the stability of PEDOT:PSS electrodes, simultaneously. Owing to the formation of weaker acid and PSS-Na, PSS chains are disentangled from the coiled PEDOT:PSS complexes, leading to the phase separation of PEDOT:PSS and the formation of fibril-like PEDOT domains. Eventually, the sodium 3-methylsalicylate-modified PEDOT:PSS electrode is employed in flexible organic light-emitting diodes with an outstanding external quantum efficiency of up to 25%. The improved performance is attributed to the more matched work function and the as-formed interfacial dipole. The sodium 3-methylsalicylate-modified PEDOT:PSS electrode with high conductivity and transmittance, superior stability in the air as well as good mechanical flexibility has the potential to be the most promising transparent conductive material for flexible optoelectronic device applications.

Semiconductor nanochannels in metallic carbon nanotubes by thermomechanical chirality alteration

[Figure: see text].

Quantitative Evidence for the Dependence of Highly Crystalline Single Wall Carbon Nanotube Synthesis on the Growth Method

We present a study quantitatively demonstrating that the method of synthesis (gas phase, fixed bed, non-fixed bed) represents a determining factor in the level of crystallinity in growing single wall carbon nanotubes (SWCNTs). Using far infrared spectroscopy, the "effective length" (associated with the level of crystallinity) was estimated for CNTs grown using various synthetic methods (lab-produced and supplemented by commercially purchased SWCNTs) as a metric for crystallinity (i.e., defect density). Analysis of the observed "effective lengths" showed that the SWCNTs fell into two general groups: long and short (high and low crystallinity) synthesized by gas-phase methods and all other supported catalyst methods, respectively. Importantly, the "long" group exhibited effective lengths in the range of 700-2200 nm, which was greater than double that of the typical values representing the "short" group (110-490 nm). These results highlight the significant difference in crystallinity. We interpret that the difference in the crystallinity stemmed from stress concentration at the nanotube-catalyst interface during the growth process, which originated from various sources of mismatch in growth rates (e.g., vertically aligned array) as well as impact stress from contact with other substrates during fluidization or rotation. These results are consistent with well-accepted belief, but now are demonstrated quantitatively.

Impedance Analysis and Noise Measurements on Multi Walled Carbon Nanotube Networks

The electrical impedance characteristics of multi-walled carbon nanotube (MWCNTs) networks were studied as a function of CNT concentrations in the frequency range of 1 kHz–1 MHz. The novelty of this study is that the MWCNTs were not embedded in any polymer matrix and so the response of the device to electrical measurements are attributed to the CNTs in the network without any contribution from a polymer host matrix. Devices with low MWCNT packing density (0.31–0.85 µg/cm²) exhibit a frequency independent plateau in the low-frequency regime. At higher frequencies, the AC conductivity of these devices increases following a power law, characteristic of the universal dynamic response (UDR) phenomenon. On the other hand, devices with high MWCNT concentrations (>1.0 µg/cm²) exhibit frequency independent conductivity over the entire frequency range (up to 1 MHz), indicating that conduction in these devices is due to direct contact between the CNTs in the network. A simple single-relaxation time electrical equivalent circuit with an effective resistance and capacitance is used to describe the device performance. The electrical noise measurements on devices with different MWCNT packing densities exhibit bias-dependent low-frequency 1/f noise, attributed to resistance fluctuations.

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.

Safe-by-Design part II: A strategy for balancing safety and functionality in the different stages of the innovation process

Manufactured nanomaterials have the potential to impact an exceedingly wide number of industries and markets ranging from energy storage, electronic and optical devices, light-weight construction to innovative medical approaches for diagnostics and therapy. In order to foster the development of safer nanomaterial-containing products, two main aspects are of major interest: their functional performance as well as their safety towards human health and the environment. In this paper a first proposal for a strategy is presented to link the functionality of nanomaterials with safety aspects. This strategy first combines information on the functionality and safety early during the innovation process and onwards, and then identifies Safe-by-Design (SbD) actions that allow for optimisation of both aspects throughout the innovation process. The strategy encompasses suggestions for the type of information needed to balance functionality and safety to support decision making in the innovation process. The applicability of the strategy is illustrated using a literature-based case study on carbon nanotube-based transparent conductive films. This is a first attempt to identify information that can be used for balancing functionality and safety in a structured way during innovation processes.

One-dimensional van der Waals heterostructures: Growth mechanism and handedness correlation revealed by nondestructive TEM

We recently synthesized one-dimensional (1D) van der Waals heterostructures in which different atomic layers (e.g., boron nitride or molybdenum disulfide) seamlessly wrap around a single-walled carbon nanotube (SWCNT) and form a coaxial, crystalized heteronanotube. The growth process of 1D heterostructure is unconventional-different crystals need to nucleate on a highly curved surface and extend nanotubes shell by shell-so understanding the formation mechanism is of fundamental research interest. In this work, we perform a follow-up and comprehensive study on the structural details and formation mechanism of chemical vapor deposition (CVD)-synthesized 1D heterostructures. Edge structures, nucleation sites, and crystal epitaxial relationships are clearly revealed using transmission electron microscopy (TEM). This is achieved by the direct synthesis of heteronanotubes on a CVD-compatible Si/SiO₂ TEM grid, which enabled a transfer-free and nondestructive access to many intrinsic structural details. In particular, we have distinguished different-shaped boron nitride nanotube (BNNT) edges, which are confirmed by electron diffraction at the same location to be strictly associated with its own chiral angle and polarity. We also demonstrate the importance of surface cleanness and isolation for the formation of perfect 1D heterostructures. Furthermore, we elucidate the handedness correlation between the SWCNT template and BNNT crystals. This work not only provides an in-depth understanding of this 1D heterostructure material group but also, in a more general perspective, serves as an interesting investigation on crystal growth on highly curved (radius of a couple of nanometers) atomic substrates.

High-Performance Flexible Transparent Electrodes Fabricated via Laser Nano-Welding of Silver Nanowires

Silver nanowires (Ag-NWs), which possess a high aspect ratio with superior electrical conductivity and transmittance, show great promise as flexible transparent electrodes (FTEs) for future electronics. Unfortunately, the fabrication of Ag-NW conductive networks with low conductivity and high transmittance is a major challenge due to the ohmic contact resistance between Ag-NWs. Here we report a facile method of fabricating high-performance Ag-NW electrodes on flexible substrates. A 532 nm nanosecond pulsed laser is employed to nano-weld the Ag-NW junctions through the energy confinement caused by localized surface plasmon resonance, reducing the sheet resistance and connecting the junctions with the substrate. Additionally, the thermal effect of the pulsed laser on organic substrates can be ignored due to the low energy input and high transparency of the substrate. The fabricated FTEs demonstrate a high transmittance (up to 85.9%) in the visible band, a low sheet resistance of 11.3 Ω/sq, high flexibility and strong durability. The applications of FTEs to 2D materials and LEDs are also explored. The present work points toward a promising new method for fabricating high-performance FTEs for future wearable electronic and optoelectronic devices.

In Silico Study of the Influence of Various Substrates on the Electronic Properties and Electrical Conductivity of Mono- and Bilayer Films of Armchair Single-Walled Carbon Nanotubes

We investigate electronic and electro-physical properties of mono- and bilayer armchair single-walled carbon nanotube (SWCNT) films located on substrates of different types, including substrates in the form of crystalline silicon dioxide (SiO2) films with P42/mnm and P3121 space symmetry groups. The SWCNT films interact with substrate only by van der Waals forces. The densities of electronic states (DOS) and the electron transmission functions are calculated for SWCNT films with various substrates. The electrical conductivity of SWCNT films is calculated based on the electron transmission function. It is found that the substrate plays an important role in the formation of DOS of the SWCNT films, and the surface topology determines the degree and nature of the mutual influence of the nanotube and the substrate. It is shown that the substrate affects the electronic properties of monolayer films, changing the electrical resistance value from 2% to 17%. However, the substrate has practically no effect on the electrical conductivity and resistance of the bilayer film in both directions of current transfer. In this case, the values of the resistances of the bilayer film in both directions of current transfer approach the value of ~6.4 kΩ, which is the lowest for individual SWCNT.

Recent progress in post treatment of silver nanowire electrodes for optoelectronic device applications

Owing to the economical and practical solution synthesis and coating strategies, silver nanowires (AgNWs) have been considered as one of the most suitable alternative materials to replace commercial indium tin oxide (ITO) transparent electrodes. The primitive AgNW electrode cannot meet the requirements for preparing high performance optoelectronic devices due to its high contact resistance, large surface roughness and poor stability. Thus, various post-treatments for AgNW film optimization are needed before its actual applications, such as welding treatment to decrease contact resistance and passivation to increase film stability. This review investigates recent progress on the preparation and optimization of AgNWs. Moreover, some unique fabrication strategies to produce highly oriented AgNW films with unique anisotropic properties have also been carried out with detailed analysis. The representative devices based on the AgNW electrode have been summarized and discussed at the end of this review.

Electrically Conductive Networks from Hybrids of Carbon Nanotubes and Graphene Created by Laser Radiation

A technology for the formation of electrically conductive nanostructures from single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), and their hybrids with reduced graphene oxide (rGO) on Si substrate has been developed. Under the action of single pulses of laser irradiation, nanowelding of SWCNT and MWCNT nanotubes with graphene sheets was obtained. Dependences of electromagnetic wave absorption by films of short and long nanotubes with subnanometer and nanometer diameters on wavelength are calculated. It was determined from dependences that absorption maxima of various types of nanotubes are in the wavelength region of about 266 nm. It was found that contact between nanotube and graphene was formed in time up to 400 fs. Formation of networks of SWCNT/MWCNT and their hybrids with rGO at threshold energy densities of 0.3/0.5 J/cm² is shown. With an increase in energy density above the threshold value, formation of amorphous carbon nanoinclusions on the surface of nanotubes was demonstrated. For all films, except the MWCNT film, an increase in defectiveness after laser irradiation was obtained, which is associated with appearance of C–C bonds with neighboring nanotubes or graphene sheets. CNTs played the role of bridges connecting graphene sheets. Laser-synthesized hybrid nanostructures demonstrated the highest hardness compared to pure nanotubes. Maximum hardness (52.7 GPa) was obtained for MWCNT/rGO topology. Regularity of an increase in electrical conductivity of nanostructures after laser irradiation has been established for films made of all nanomaterials. Hybrid structures of nanotubes and graphene sheets have the highest electrical conductivity compared to networks of pure nanotubes. Maximum electrical conductivity was obtained for MWCNT/rGO hybrid structure (~22.6 kS/m). Networks of nanotubes and CNT/rGO hybrids can be used to form strong electrically conductive interconnections in nanoelectronics, as well as to create components for flexible electronics and bioelectronics, including intelligent wearable devices (IWDs).

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.

Critical challenges and advances in the carbon nanotube-metal interface for next-generation electronics

Next-generation electronics can no longer solely rely on conventional materials; miniaturization of portable electronics is pushing Si-based semiconductors and metallic conductors to their operational limits, flexible displays will make common conductive metal oxide materials obsolete, and weight reduction requirement in the aerospace industry demands scientists to seek reliable low-density conductors. Excellent electrical and mechanical properties, coupled with low density, make carbon nanotubes (CNTs) attractive candidates for future electronics. However, translating these remarkable properties into commercial macroscale applications has been disappointing. To fully realize their great potential, CNTs need to be seamlessly incorporated into metallic structures or have to synergistically work alongside them which is still challenging. Here, we review the major challenges in CNT-metal systems that impede their application in electronic devices and highlight significant breakthroughs. A few key applications that can capitalize on CNT-metal structures are also discussed. We specifically focus on the interfacial interaction and materials science aspects of CNT-metal structures.

Optimization of Optoelectronic Properties of Patterned Single-Walled Carbon Nanotube Films

We propose a novel strategy to enhance optoelectrical properties of single-walled carbon nanotube (SWCNT) films for transparent electrode applications by film patterning. First, we theoretically considered the effect of the conducting pattern geometry on the film quality factor and then experimentally examined the calculated structures. We extend these results to show that the best characteristics of patterned SWCNT films can be achieved using the combination of initial film properties: low transmittance and high conductivity. The proposed strategy allows the patterned layers of SWCNTs to outperform the widely used indium-tin-oxide electrodes on both flexible and rigid substrates.

Pushing the conductance and transparency limit of monolayer graphene electrodes for flexible organic light-emitting diodes

Graphene has emerged as an attractive candidate for flexible transparent electrode (FTE) for a new generation of flexible optoelectronics. Despite tremendous potential and broad earlier interest, the promise of graphene FTE has been plagued by the intrinsic trade-off between electrical conductance and transparency with a figure of merit (σDC/σOp) considerably lower than that of the state-of-the-art ITO electrodes (σDC/σOp <123 for graphene vs. ∼240 for ITO). Here we report a synergistic electrical/optical modulation strategy to simultaneously boost the conductance and transparency. We show that a tetrakis(pentafluorophenyl)boric acid (HTB) coating can function as highly effective hole doping layer to increase the conductance of monolayer graphene by sevenfold and at the same time as an anti-reflective layer to boost the visible transmittance to 98.8%. Such simultaneous improvement in conductance and transparency breaks previous limit in graphene FTEs and yields an unprecedented figure of merit (σDC/σOp ∼323) that rivals the best commercial ITO electrode. Using the tailored monolayer graphene as the flexible anode, we further demonstrate high-performance green organic light-emitting diodes (OLEDs) with the maximum current, power and external quantum efficiencies (111.4 cd A-1, 124.9 lm W-1 and 29.7%) outperforming all comparable flexible OLEDs and surpassing that with standard rigid ITO by 43%. This study defines a straightforward pathway to tailor optoelectronic properties of monolayer graphene and to fully capture their potential as a generational FTE for flexible optoelectronics.

Transparent and Freestanding Single-Walled Carbon Nanotube Films Synthesized Directly and Continuously via a Blown Aerosol Technique

Single-walled carbon nanotube (SWCNT) films are promising materials as flexible transparent conductive films (TCFs). Here, inspired by the extrusion blown plastic film technique and the SWCNT synthesis approach by floating catalyst chemical vapor deposition (FCCVD), a novel blown aerosol chemical vapor deposition (BACVD) method is reported to directly and continuously produce freestanding SWCNT TCFs at several hundred meters per hour. The synthesis mechanism, involving blowing a stable aerosol bubble and transforming the bubble into an aerogel, is investigated, and a general phase diagram is established for this method. For the SWCNT TCFs via BACVD, both carbon conversion efficiency and SWCNT TCF yield can reach three orders of magnitude higher than those with the conventional FCCVD. The film displays a sheet resistance of 40 ohm sq^-1 at 90% transmittance after being doped, representing the record performance based on large-scale SWCNT films. Transparent, flexible, and stretchable electrodes based on BACVD films are demonstrated. Moreover, this high-throughput method of producing SWCNT TCFs can be compatible with the roll-to-roll process for mass production of flexible displays, touch screens, solar cells, and solid-state lighting, and is expected to have a broad and long-term impact on many fields from consumer electronics to energy conversion and generation.