Single-walled Carbon Nanotube Networks Research Articles

Affordable paper-based SWNTs field-effect transistor biosensors for nucleic acid amplification-free and label-free detection of micro RNAs

Micro RNAs (miRNAs) are 19–23 nucleotides-long non-coding RNA which have been identified as important biomarkers for many diseases, including cancers. Here, we report an ultrasensitive, highly specific, label-free, and without nucleic acid amplification (NAA) detection of miRNAs using paper-based single-walled carbon nanotubes (SWNTs) field-effect transistor (FET) biosensors. The strategy involved a two-step protocol starting with direct hybridization of the target miRNA with a specific RNA probe immobilized on SWNTs networks deposited on the paper substrate to generate the first response, followed by the recognition of the resulting RNA/miRNA duplexes with the Carnation Italian ringspot virus p19 protein (p19) in a size-dependent manner, giving the second electrical response that magnified the biosensor sensitivity. As a demonstration, we detected the miRNA-122a, a promising biomarker for the diagnosis of early-stage hepatocellular carcinoma (HCC) in various sample matrices, including phosphate buffers, human serum, and synthetic saliva. We achieved the lowest detection of 0.1 aM and a wide dynamic range of 0.1 aM–1 fM, that demonstrated its potential for rapid, facile, low-cost, and point-of-care detection of miRNAs for early cancer diagnosis.

Tuning counterion chemistry to reduce carrier localization in doped semiconducting carbon nanotube networks

Understanding and controlling the impact that electrostatic interactions have on the transport of injected charge carriers is important for the utilization of pi-conjugated semiconductors in opto-electronic applications. Here, we explore the impact of dopant chemical and electronic structure on the doping efficacy and charge carrier transport in semiconducting single-walled carbon nanotube (s-SWCNT) networks using molecular charge-transfer dopants based on functionalized icosahedral dodecaborane (DDB) clusters. Calculations indicate that localization of electron density on the DDB core reduces the coulombic interactions that contribute to hole localization in the s-SWCNTs, thereby improving charge carrier transport. The enhanced delocalization produces an increase in the electrical conductivity and thermopower at lower charge carrier densities, yielding enhanced thermoelectric transport and a thermoelectric power factor that surpasses the previous best in class for enriched s-SWCNT thin-film networks. This strategy can be applied broadly across pi-conjugated semiconductors to tune and enhance performance in a variety of energy harvesting devices.

Integrated Low‐Dimensional Semiconductors for Scalable Low‐power CMOS Logic

AbstractScalable nanoelectronics with energy‐efficient logic technology is crucial for next‐generation edge devices. Low‐dimensional semiconductors, such as transition metal dichalcogenides and single‐walled carbon nanotubes (SWCNTs), have tunable properties with reduced short‐channel effects. The unique properties of each material can be utilized owing to the heterogeneous integration of multiple semiconducting channels to form complementary metal‐oxide‐semiconductor (CMOS) logic. However, the integration remains challenging. This study reveals the realization of low static power hetero‐CMOS inverters by the integration of n‐type monolayer MoS2 and p‐type SWCNT networks. The balanced inverter exhibits a large peak gain of ≈67 at a supply voltage of 2 V with the customized design of the wafer‐scale synthetic process and channel integration. An ultralow standby power consumption of ≈5 pW and a practical peak gain of ≈7 at a reduced supply voltage of 0.25 V are achieved. A high noise margin (>70%) validates the circuit's tolerance to external noises and the dynamic analysis of the inverting amplifier in push–pull configuration exhibits a large AC gain. This work paves the way toward the wafer‐scale integration of low‐dimensional materials for low‐power nanoelectronics.

An integrated oxygen electrode derived from a flexible single-walled carbon nanotube film for rechargeable Zn-air batteries produced by electropolymerization

The development of low-cost, high-activity, and durable integrated bifunctional flexible air electrodes for use in Zn-air batteries is both challenging and important. We report a simple and scalable electropolymerization method used to prepare an electrode material comprising heavily N-doped carbon covering single-walled carbon nanotube (N/C-SWCNT) networks. The resulting core/shell structure of the hybrid electrode enabled the flexibility, mechanics, and three-dimensional interconnected porous structure of SWCNT films while containing abundant pyridinic N, which provided excellent catalytic activity for both the oxygen reduction and evolution reactions (overpotential gap = 0.76 V). A binder-free Zn-air battery using the N/C-SWCNT film as an oxygen electrode was assembled and showed a high peak power density of 181 mW/cm2, a high specific capacity of 810 mAh/g and stable discharge‒charge cycling performance. We also constructed a flexible solid-state Zn-air battery featuring not only a high power density of 22 mW/cm2 but also good flexibility and stability.

Selective Purity Modulation of Semiconducting Single-Walled Carbon Nanotube Networks for High-Performance Thin-Film Transistors

Single-walled carbon nanotube (SWCNT) random networks have become strong candidates for next-generation electronics due to their exceptional mechanical, electrical, and optical properties. However, metallic nanotubes in networks generally incur a trade-off between the charge carrier mobility and on/off ratio, limiting the performance of SWCNT-based devices. Therefore, various methods to increase the purity of semiconducting nanotubes in entire random networks have been reported, but this direction has faced other issues, such as nanotube shortening, higher cost, and higher energy. Here, we introduce SWCNT random network-based thin-film transistors (SWCNT TFTs) with a varying purity profile of semiconducting SWCNTs across the channel, exploiting the superior mobility of metallic SWCNTs by partially tuning the semiconducting SWCNT purity and developing a novel perspective on metallic nanotubes in semiconductor channels. Based on the high-precision drop-on-demand capability of inkjet printing and various concentrations of semiconducting SWCNT ink, we form selectively patterned channel regions with different semiconducting SWCNT purities. The metallic nanotube-dominant region drastically increases the carrier density with a minimized Schottky barrier, while high-purity semiconducting regions at the channel boundaries effectively block off-state leakage through carrier depletion. As a result, the SWCNT TFTs with selectively patterned metallic nanotube regions show superior carrier mobility (75.50 cm2 V–1 s–1) and channel width normalized on-current (34.33 nA μm–1) without compromising the on/off ratio (1.62 × 107). To show the feasibility of our device in high-performance electronics, we demonstrate all-inkjet-printed flexible display driving circuits with two transistors that enable low-power, high-performance operation in display applications.

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.

Mid-Infrared Electrochromics Enabled by Intraband Modulation in Carbon Nanotube Networks.

Tuneable infrared properties, such as transparency and emissivity, are highly desirable for a range of applications, including thermal windows and emissive cooling. Here, we demonstrate the use of carbon nanotube networks spray-deposited onto an ionic liquid-infused membrane to fabricate devices with electrochromic modulation in the mid-infrared spectrum, facilitating control of emissivity and apparent temperature. Such modulation is enabled by intraband transitions in unsorted single-walled carbon nanotube networks, allowing the use of scalable nanotube inks for printed devices. These devices are optimized by varying film thickness and sheet resistance, demonstrating the emissivity modulation (from ∼0.5 to ∼0.2). These devices and the understanding thereof open the door to selection criteria for infrared electrochromic materials based on the relationship between band structure, electrochemistry, and optothermal properties to enable the development of solution-processable large-area coatings for widespread thermal management applications.

Highly Electrical Conductive PEDOT:PSS/SWCNT Flexible Thermoelectric Films Fabricated by a High-Velocity Non-solvent Turbulent Secondary Doping Approach.

Materials based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) can be potentially employed as flexible thermoelectric generators (TEGs) to capture waste heat and generate electrical energy. Among various methods, secondary doping is an effective way to modulate its thermoelectric (TE) performance. Different from conventional measures such as dropping, soaking, and steam fumigation, strong shear is integrated with the doping process and termed high-velocity non-solvent turbulent secondary doping (HNTD). We systematically investigate the transformation of PEDOT:PSS during this procedure and the formation mechanism of its highly conductive pathway. It is illustrated that PEDOT:PSS experiences PSS swelling, the phase separation of PEDOT from PSS, the removal of isolated PSS, and the evolution of PEDOT to a linear conformation. These evolutions contribute to the substantial elevation of electrical conductivity (σ). Furthermore, by employing continuous single-walled carbon nanotube (SWCNT) networks as structural units, highly conductive flexible PEDOT:PSS/SWCNT TE thin films could be prepared without sacrificing the Seebeck coefficient (S). Additionally, the effect of HNTD and direct addition method on TE properties of composite films is also compared. Finally, the PEDOT:PSS composite film with 40 wt % SWCNTs by the HNTD method exhibits the maximized power factor (PF) of 501.31 ± 19.23 μW m-1 K-2 with σ of 4717.8 ± 41.51 S cm-1 and S of 32.6 ± 0.13 μV K-1 at room temperature. It is worth mentioning that the σ value 4717.8 ± 41.51 S cm-1 is the highest among the composites based on commercial carbon fillers and organic semiconductors. Finally, a 6-leg TEGs prototype is assembled and illustrates an output power of 4.416 μW under a temperature difference (ΔT) of 58 K. It is thought that such a strategy may provide some guidelines for manufacturing PEDOT:PSS-based functional materials.

High-performance infrared photodetector based on single-wall carbon nanotube films

Bolometric photodetectors based on single-wall carbon nanotubes (SWCNTs) have shown advantages of an ultrawide absorption spectrum, high charge carrier mobility, good processability, and high mechanical flexibility. However, their detection performance needs to be improved to meet the requirements of real applications. A flexible infrared photodetector was fabricated based on high quality SWCNT films. The device showed an ultrahigh detectivity up to 1.35 × 108 Jones under a bias voltage of 0.2 V, and a short response time of 70 ms in air. In addition, we found that the photocurrent response of the detector was closely related to the structure of the SWCNT network. A negative photocurrent was measured using photodetectors constructed from highly-crystalline SWCNTs owing to dominant phonon scattering transfer, while a positive photocurrent was detected from those fabricated using defect-rich SWCNTs due to dominant electron hopping transfer. Our results shed light on the construction of high-performance SWCNT film-based infrared photodetectors.

Impact of Dielectric Environment on Trion Emission from Single-Walled Carbon Nanotube Networks.

Trions are charged excitons that form upon optical or electrical excitation of low-dimensional semiconductors in the presence of charge carriers (holes or electrons). Trion emission from semiconducting single-walled carbon nanotubes (SWCNTs) occurs in the near-infrared and at lower energies compared to the respective exciton. It can be used as an indicator for the presence of excess charge carriers in SWCNT samples and devices. Both excitons and trions are highly sensitive to the surrounding dielectric medium of the nanotubes, having an impact on their application in optoelectronic devices. Here, the influence of different dielectric materials on exciton and trion emission from electrostatically doped networks of polymer-sorted (6,5) SWCNTs in top-gate field-effect transistors is investigated. The observed differences of trion and exciton emission energies and intensities for hole and electron accumulation cannot be explained with the polarizability or screening characteristics of the different dielectric materials, but they show a clear dependence on the charge trapping properties of the dielectrics. Charge localization (trapping of holes or electrons by the dielectric) reduces exciton quenching, emission blue-shift and trion formation. Based on the observed carrier type and dielectric material dependent variations, the ratio of trion to exciton emission and the exciton blue-shift are not suitable as quantitative metrics for doping levels of carbon nanotubes.

Robust Single‐Walled Carbon Nanotube‐Infiltrated Carbon Fiber Electrodes for Structural Supercapacitors: from Reductive Dissolution to High Performance Devices

AbstractMultifunctional electrodes for structural supercapacitors are prepared by vacuum infiltration of single‐walled carbon nanotubes (SWCNTs) into woven carbon fibers (CFs); the use of reductive charging chemistry to form nanotubide solutions ensured a high degree of individualization. The route is highly versatile, as shown by comparing four different commercial nanotube feedstocks. In film form, the pure nanotubide networks (“buckypapers”) are highly conductive (up to 2000 S cm−1) with high surface area (>1000 m2 g−1) and great electrochemical performance (capacitance of 101 F g−1, energy density of 27.5 Wh kg−1 and power density of 135 kW kg−1). Uniformly integrating these SWCNT networks throughout the CF fabrics significantly increased electrical conductivity (up to 318 S cm−1), surface area (up to 196 m2 g−1), and in‐plane shear properties, all simultaneously. The CNT‐infiltrated CFs electrodes exhibited intrinsically high specific energy (2.6–4.2 Wh kg−1) and power (6.0–8.7 kW kg−1) densities in pure 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM TFSI) electrolyte. Multifunctional structural supercapacitors based on CNT‐coated CFs offer a substantial increase in capacitive performance while maintaining the tensile mechanical properties of the as‐received CF‐based composite. This non‐damaging approach to modify CFs with highly graphitic, high surface area nanocarbons provides a new route to structural energy storage systems.

The role of branched alkylthio side chain on dispersion and thermoelectric properties of regioregular polythiophene/carbon nanotubes nanocomposites

Herein, poly(3-alkylthiophene)s (P3ATs) and poly[(3-alkylthio)thiophene]s (P3ATTs) are respectively synthesized using poly(thiophene)s with linear/branched alkyl groups and branched alkylthio moieties with short/long side chain lengths for dispersing single-walled carbon nanotubes (SWCNTs), and the resulting composites are solution-processed for use as p-type thin film thermoelectric devices. With an additional sulfur atom on the side chain, a well-dispersed P3ATTs/SWCNTs nanocomposite is obtained by polymer-wrapping at the SWCNTs surfaces driven by S − π and π − π interactions between the alkylthio side chain substituents and π-conjugated backbones of the P3ATTs and SWCNTs, thereby contributing to greatly improved thermoelectric performance relative to the P3ATs/SWCNTs nanocomposite without the added sulfur. The poly[3-(2-hexyldecylthio)thiophene] (P3HDTT) nanocomposite with the longest alkylthio side chain exhibits the strongest interaction with the SWCNTs, yielding the highest power factor (PF) of 307.7 μW m−1 K−2. The ability of this spray-coated nanocomposite film to generate power is demonstrated with a prototype flexible thermoelectric generator (TEG) that produces 888.1 μW m−2. Thus, the introduction of debundled SWCNTs networks wrapped by P3ATTs with alkylthio side chains suggests a feasible strategy for the design of high-performance thermoelectric materials and opens up new opportunities for capturing waste heat in wearable electronics.

Ultrafast Optomechanical Terahertz Modulators Based on Stretchable Carbon Nanotube Thin Films

For terahertz wave applications, tunable and rapid modulation is highly required. When studied by means of optical pump–terahertz probe spectroscopy, single-walled carbon nanotube (SWCNT) thin films demonstrated ultrafast carrier recombination lifetimes with a high relative change in the signal under optical excitation, making them promising candidates for high-speed modulators. Here, combination of SWCNT thin films and stretchable substrates facilitated studies of the SWCNT mechanical properties under strain and enabled the development of a new type of an optomechanical modulator. By applying a certain strain to the SWCNT films, the effective sheet conductance and therefore modulation depth can be fine-tuned to optimize the designed modulator. Modulators exhibited a photoconductivity change of approximately 2 times of magnitude under the strain because of the structural modification in the SWCNT network. Stretching was used to control the terahertz signal with a modulation depth of around 100% without strain and 65% at a high strain operation of 40%. The sensitivity of modulators to beam polarization is also shown, which might also come in handy for the design of a stretchable polarizer. Our results give a fundamental grounding for the design of high-sensitivity stretchable devices based on SWCNT films.

Visualization of deformation-induced changes in carbon nanotube networks in rubber composites using lock-in thermography.

In this study, we used the lock-in thermography technique (LIT) to successfully visualize the single-walled carbon nanotube (CNT) networks during the tensile deformation of CNT/fluoro-rubber (FKM) composites. The LIT images revealed that the CNT network modes in CNT/FKM during strain-loading and unloading can be classified into four sites: (i) disconnection, (ii) recovery after disconnection, (iii) undestroyable, and (iv) no network. Quantitative analysis of the heat intensity of the LIT also indicated that the change in resistance during strain-loading and unloading plays a role in the balance of disconnection and reconstruction of the conductive network. We demonstrated the ability of LIT to effectively visualize and quantify the network state of the composite under deformation, and the LIT results were found to be strongly correlated with the composite properties. These results highlighted the potential of LIT as a valuable tool for composite characterization and material design.

Photogating interfacial effects in carbon nanotube-based transistors on a Si/SiO2 substrate toward highly sensitive photodetection.

Single-walled carbon nanotubes (SWCNTs) are considered to be promising material platforms for various photodetectors (including phototransistors) due to their unique optoelectrical properties (e.g., high mobility and a wide variety of bandgap values). Herein, we present highly sensitive phototransistors which utilised sparse networks of SWCNTs on a silicon/silica substrate and operated by means of the photogating effect. The response of SWCNTs to photo-induced electrostatic charges (photogating effect) was highly dependent on the conductivity type of the channel, which was "metallic" or "semiconducting", depending on the SWCNT density. We determined the performance of these transistors depending on the characteristics of the substrate and conductivity type of the SWCNT channel. The optimized configuration of phototransistors with a channel comprising a sparse network of SWCNTs permitted improvement in the specific detectivity and relative response compared with previously reported photodetectors based on graphene and carbon nanotubes. We demonstrated an absolute responsivity of ∼60 A W-1 at an incident light power of ∼2 nW, specific detectivity of 7.8 × 1011 cm·Hz1/2 W-1, and response time of 300 μs. These data revealed the high potential of photogating-based SWCNTs detectors for extremely weak signals with a high signal-to-noise ratio.

Single-Walled Carbon Nanotubes with Red Phosphorus in Lithium-Ion Batteries: Effect of Surface and Encapsulated Phosphorus.

Single-walled carbon nanotubes (SWCNTs) with their high surface area, electrical conductivity, mechanical strength and elasticity are an ideal component for the development of composite electrode materials for batteries. Red phosphorus has a very high theoretical capacity with respect to lithium, but has poor conductivity and expends considerably as a result of the reaction with lithium ions. In this work, we compare the electrochemical performance of commercial SWCNTs with red phosphorus deposited on the outer surface of nanotubes and/or encapsulated in internal channels of nanotubes in lithium-ion batteries. External phosphorus, condensed from vapors, is easily oxidized upon contact with the environment and only the un-oxidized phosphorus cores participate in electrochemical reactions. The support of the SWCNT network ensures a stable long-term cycling for these phosphorus particles. The tubular space inside the SWCNTs stimulate the formation of chain phosphorus structures. The chains reversibly interact with lithium ions and provide a specific capacity of 1545 mAh·g-1 (calculated on the mass of phosphorus in the sample) at a current density of 0.1 A·g-1. As compared to the sample containing external phosphorus, SWCNTs with encapsulated phosphorus demonstrate higher reaction rates and a slight loss of initial capacity (~7%) on the 1000th cycle at 5 A·g-1.

Three-in-one organic-inorganic heterostructures: From scalable ball-milling synthesis to freestanding cathodes with high areal capacity for aqueous zinc-ion batteries

Aqueous Zn-ion batteries (AZIBs) have great potential in large-scale energy storage, however, developing suitable cathodes with high energy/power densities remains highly challenging. Herein, a unique organic-inorganic heterostructures (denoted as Ov-PVO/G) of poly(3,4-ethylenedioxythiophene) intercalated V2O5 nanocrystals anchored on few-layer graphene by a simple and scalable ball-milling approach are demonstrated for high areal-capacity AZIBs cathodes, in which, adjusted interlayer spacing, abundant oxygen vacancies and robust heterointerfaces can be simultaneously constructed. Moreover, the feature of being well dispersed in different polar solvents (H2O, NMP, etc.) enable facile incorporation of the Ov-PVO/G heterostructures into conductive networks of single-walled carbon nanotubes to fabricate freestanding composite cathodes. Electrochemical measurement and first-principles calculations indicate that such “Three-in-One” heterostructure can significantly enhance Zn2+ adsorption/desorption, electrical conductivity and charge transfer due to strong synergy, thereby exhibiting high-capacity and accelerated reaction kinetics during cycling. Specifically, at a practical mass loading of 12.0 mg/cm2, the freestanding Ov-PVO/G cathodes show a high areal-capacity of 6.1 mAh/cm2 at 2.4 mA/cm2 and works stable with an area-capacity of 1.63 mAh/cm2 at 120 mA/cm2 after 500 cycles. More importantly, flexible soft-packaged AZIBs based on 3×3 cm2 high mass-loading Ov-PVO/G cathodes deliver record-high and stable electric energy beyond 21.5 mAh at different bending states. This work paves a more promising way to practical application of high-performance AZIBs.

Bio-inspired electronic fingerprint PUF device with single-walled carbon nanotube network surface mediated by M13 bacteriophage template

Human fingerprints are randomly created during fetal activity in the womb, resulting in unique and physically irreproducible fingerprint patterns that are applicable as a biological cryptographic primitive. Similarly, stochastically knitted single-walled carbon nanotube (SWNT) network surfaces exhibit inherently random and unique electrical characteristics that can be exploited as a physical unclonable function (PUF) in the authentication. In this study, filamentous M13 bacteriophages are used as a biological gluing template to create a random SWNT network surface with mechanical flexibility, with electrical properties determined by random variation during fabrication. The resistance profile between two adjacent electrodes was mapped for these M13-mediated SWNT network surfaces, with the results demonstrating a unique resistance profile for each M13-SWNT device, similar to that of human fingerprints. Randomness and uniqueness measures were evaluated as respectively 50.5% and 50% using generated challenge–response pairs. Min-entropy for unpredictability evaluation of the M13-SWNT based PUFs resulted in 0.98. Our results showed that M13-SWNT random network exhibits cryptographic characteristics when used in a bio-inspired PUF device.

Conductivity inversion of methyl viologen-modified random networks of single-walled carbon nanotubes

One of the challenges of using carbon nanotubes electronics is achieving precise control of the conductivity type. It is particularly difficult to obtain the n-type conductive nanotubes. One of the most common methods of CNTs modification allowing to change their conductivity type is chemical functionalization. This paper describes the results of studies on non-covalent modification of randomly oriented single-walled carbon nanotubes (SWCNT) layers with methyl viologen (MV), which allows for the change of the conductivity of SWCNT from p- to n-type. The properties of pristine and MV-modified SWCNT have been compared using Scanning Electron Microscopy, Raman spectroscopy, and X-ray Photoelectron Spectroscopy. The SWCNT conductivity type change was confirmed by photo-conductance under ultraviolet illumination and measurements in the field effect transistor configuration.

Diameter-Dependent Semiconducting Carbon Nanotube Network Transistor Performance

Single-walled carbon nanotube (SWCNT) network based devices show application potentials due to their extraordinary electric and optical properties, and the device performance is largely determined by the network morphology and tube–tube junction interactions. In this work, five SWCNT samples with narrow bandgap distributions covering a wide diameter range of 0.7–1.6 nm were purified by the conjugated polymer extraction (CPE) process. Both chirality distribution and semiconducting purity of these samples were systematically characterized by optical methods. Uniform high density network based thin film transistors (TFTs) were fabricated, and their performance can be related to tube bandgap/diameter and defects density or tube length. The diameter-dependent tube–tube junction resistance, the most important parameter for nanowire network devices, was extracted using a network predictive model. It was found that junction resistance inversely scales with tube diameter and is about 2 orders of magnitude higher than tube intrinsic resistance. The impacts of network morphology, tube diameter, and length on their network TFT performance were further discussed. We hope these results can provide some guideline to address various application challenges for SWCNT network based devices.