Single-walled Carbon Nanotube Films Research Articles

Highly Sensitive MoS2 Photodetectors Enabled with a Dry-Transferred Transparent Carbon Nanotube Electrode.

Fabricating electronic and optoelectronic devices by transferring pre-deposited metal electrodes has attracted considerable attention, owing to the improved device performance. However, the pre-deposited metal electrode typically involves complex fabrication procedures. Here, we introduce our facile electrode fabrication process which is free of lithography, lift-off, and reactive ion etching by directly press-transferring a single-walled carbon nanotube (SWCNT) film. We fabricated Schottky diodes for photodetector applications using dry-transferred SWCNT films as the transparent electrode to increase light absorption in photoactive MoS2 channels. The MoS2 flake vertically stacked with an SWCNT electrode can exhibit excellent photodetection performance with a responsivity of ∼2.01 × 103 A/W and a detectivity of ∼3.2 × 1012 Jones. Additionally, we carried out temperature-dependent current-voltage measurement and Fowler-Nordheim (FN) plot analysis to explore the dominant charge transport mechanism. The enhanced photodetection in the vertical configuration is found to be attributed to the FN tunneling and internal photoemission of charge carriers excited from indium tin oxide across the MoS2 layer. Our study provides a novel concept of using a photoactive MoS2 layer as a tunneling layer itself with a dry-transferred transparent SWCNT electrode for high-performance and energy-efficient optoelectronic devices.

Highly efficient oxidation of single-walled carbon nanotubes in liquid crystalline phase and dispersion for applications in Li-ion batteries

Single-walled carbon nanotubes (SWCNTs), which have high electrical conductivity, are promising candidates for enhancing the energy storage capability of lithium-ion batteries (LIBs). However, their usage in energy storage devices is limited due to the large bundle size and difficulties in dispersion. Here, we implement the debundling and mild oxidation of SWCNTs in the liquid crystalline phase paste (2 wt% solid content) with strong acid and co-intercalant (NaNO3). The thermal treatment successfully introduced carboxylic acid groups without requiring other oxidizing agents. The pretreated SWCNTs were dispersed in organic solvents such as N-methyl pyrrolidone (NMP) without dispersant molecules and were utilized as conductive additives for LIBs. Raman spectroscopy analysis showed that the D/G ratio of the SWCNT film changed from 0.012 to 0.023, implying that the oxidation method proposed herein is less defective and efficient. The filtrated 15 μm film of the SWCNTs exhibited a high electrical conductivity of 2384 S/cm. SWCNT dispersion in NMP was utilized to fabricate LIB cathode electrodes. Compared to the carbon black-applied electrodes, the SWCNT-applied LiNi0.8Co0.1Mn0.1O2 (NCM811) electrodes exhibited enhanced dispersity of conductive additive/binder networks, leading to improved electrode integrity. The capacity retention after 100 cycles for cells with SWCNTs was approximately 23.3 % better than that of the cells without SWCNTs.

Tunable THz flat zone plate based on stretchable single-walled carbon nanotube thin film

Tunable optoelectronics have attracted a lot of attention in recent years because of their variety of applications in next-generation devices. Among the potential uses for tuning optical elements, those allowing consistent parameter control stand out. We present an approach for the creation of mechanically tunable zone plate lenses in the THz range. Our devices comprise single-walled carbon nanotube (SWCNT) thin films of predetermined design integrated with stretchable polymer films. These offer high-performance and in situ tunability of focal length up to 50%. We studied the focusing properties of our lenses using the backward-wave oscillator THz imaging technique, supported by numerical simulations based on the finite element frequency domain method. Our approach may further enable the integration of SWCNT films into photonic and optoelectronic applications and could be of use for the creation of a variety of flexible and stretchable THz optical elements.

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.

Narrow band absorption and sensing properties of the THz metasurface based on single-walled carbon nanotubes

Due to their excellent electrical and optical properties, carbon nanotubes have broad application prospects in the field of optoelectronics. In this work the vacuum filtration method is used to obtain an isotropic single-walled carbon nanotube film by the dispersion of single-walled carbon nanotube powder through vacuum filtration; on the basis of extracting the dielectric parameters of the thin film in a range from 0.4 to 2.0 THz, a novel terahertz metasurface narrowband absorber based on single-walled carbon nanotube films is designed and prepared. This metasurface absorber is composed of square and I-shaped narrow slot resonators. The experimental and simulation results show that the proposed terahertz metasurface absorber exhibits four distinct resonance absorption peaks at 0.65, 0.85, 1.16, and 1.31 THz, respectively, achieving a perfect absorption of up to 90%. The absorption mechanism of this novel multi band terahertz metasurface is elucidated by using the theory of multiple reflection interference. By covering dielectric layers with different refractive indices on the surface of metasurface device, the sensing performance of metasurface acting as refractive index sensor is studied in depth. The research results indicate that this new type of metasurface absorber has high sensitivity for refractive index sensing, providing new ideas and solutions for further developing carbon-based new terahertz metasurface absorbers.

Tuning humidity sensing properties via grafting fluorine and nitrogen-containing species on single-walled carbon nanotubes.

The effect of humidity on the electrical conductivity of single-walled carbon nanotube (SWCNT) films depends on both the conductivity of individual nanotubes and the electrical contacts between them. Here, we study these factors by comparing the sensor response of nanotubes with fluorine- and nitrogen-containing groups attached to the sidewalls. Experiments carried out in a wide range of relative humidity (RH) at room and elevated temperatures showed that the conductivity of non-functionalized SWCNTs and contacts between them decreases upon the adsorption of water molecules. Covalent fluorination reduces the conductivity of SWCNTs and significantly increases the sensitivity of the film to low concentrations of water vapor. The response at high RH decreases due to the large number of water molecules adsorbed on the conductive regions of the nanotubes. As a result of substitutional reactions of fluorinated SWCNTs with dimethylformamide and ethylenediamine, nitrogen-containing groups are added, the amount of which, however, is much less than the amount of fluorine. This modification of the SWCNTs improves intertube contacts in the film and increases the surface area for water adsorption. Our results show that an increase in the number of functional groups on the SWCNT surface enhances the sensitivity of the sensor to low water concentrations and worsens the response at high RH. SWCNTs modified with ethylenediamine have the highest sensitivity over the entire range of RH.

High-performance diodes based on black phosphorus/carbon nanomaterial heterostructures.

The performance of diodes, which are the basic building blocks in integrated circuits, highly depends on the materials used. Black phosphorus (BP) and carbon nanomaterials with unique structures and excellent properties can form heterostructures with favorable band matching to fully utilize their respective advantages and thus achieve high diode performance. Here, high-performance Schottky junction diodes based on a two-dimensional (2D) BP/single-walled carbon nanotube (SWCNT) film heterostructure and a BP nanoribbon (PNR) film/graphene heterostructure were investigated for the first time. The fabricated Schottky diode based on the heterostructure with the 10 nm-thick 2D BP stacked on the SWCNT film had a rectification ratio of 2978 and a low ideal factor of 1.5. The Schottky diode based on the heterostructure with the PNR film stacked on the graphene exhibited a high rectification ratio of 4455 and an ideal factor of 1.9. The high rectification ratios for both devices were attributed to the large Schottky barriers formed between the BP and carbon materials, thus leading to a small reverse current. We found that the thickness of the 2D BP in the 2D BP/SWCNT film Schottky diode and the stacking order of the heterostructure in the PNR film/graphene Schottky diode had a significant effect on the rectification ratio. Furthermore, the rectification ratio and breakdown voltage of the resulting PNR film/graphene Schottky diode were larger than those of the 2D BP/SWCNT film Schottky diode, which was attributed to the larger bandgap of the PNRs compared to the 2D BP. This study demonstrates that high-performance diodes can be achieved via the collaborative application of BP and carbon nanomaterials.

High-quality single-walled carbon nanotube films as current collectors for flexible supercapacitors

High-quality single-walled carbon nanotube films are promising current collectors for flexible supercapacitors.

Ultra-long air-stability of n-type carbon nanotube films with low thermal conductivity and all-carbon thermoelectric generators

This report presents n-type single-walled carbon nanotubes (SWCNT) films with ultra-long air stability using a cationic surfactant and demonstrates that the n-type Seebeck coefficient can be maintained for more than two years, which is the highest stability reported thus far to the best of our knowledge. Furthermore, the SWCNT films exhibit an extremely low thermal conductivity of 0.62 ± 0.08 W/(m·K) in the in-plane direction, which is very useful for thin-film TEGs. We fabricated all-carbon-nanotube TEGs, which use p-type SWCNT films and the n-type SWCNT films developed, and their air-stability was investigated. The TEGs did not degrade for 160 days and exhibited an output voltage of 24 mV, with a maximum power of 0.4 µW at a temperature difference of 60 K. These results open a pathway to enable the widespread use of carbon nanotube TEGs as power sources in IoT sensors.

Elastic single-walled carbon nanotubes pixel matrix electrodes for flexible optoelectronics

This paper demonstrates an elastic (i.e., both flexible and stretchable) pixel matrix based on the patterned films of single-walled carbon nanotubes, which were obtained using optical lithography and plasma etching. The proposed elastic electrodes maintain their initial resistivity at 10% stretching. We also demonstrate an application of the elastic pixel matrix to an array of III–V semiconductor nanowires encapsulated into the elastic polymer matrix, which paves the way for highly deformable inorganic light-emitting or photodetector devices.

Attachment of DNA-Wrapped Single-Walled Carbon Nanotubes (SWNTs) for a Micron-Sized Biosensor.

We fabricated a micron-sized biodevice based on the near-infrared photoluminescence (PL) response of single-walled carbon nanotubes (SWNTs). Various biosensors using the unique optical responses of SWNTs have been proposed by many research groups. Most of these employed either colloidal suspensions of dispersed SWNTs or SWNT films on flat surfaces, such as electrodes. In this study, we attached DNA-wrapped SWNTs (DNA-SWNTs) to frustule (micron-sized nanoporous biosilica) surfaces, which were purified from cultured isolated diatoms. After the injection of an oxidant and a reductant, the SWNTs on the frustules showed prominent PL responses. This suggests that the biodevice functions as a micron-sized redox sensor. Frustules can be easily suspended in aqueous solutions because of their porous structures and can easily be collected as pellets by low-speed centrifugation. Thus, the removal of unbound SWNTs and the recovery of the fabricated DNA-SWNT frustules for reuse were achieved by gentle centrifugation. Our proposal for micron-sized SWNT biodevices would be helpful for various biological applications.

Enhancement Effect of the C60 Derivative on the Thermoelectric Properties of n-Type Single-Walled Carbon Nanotube-Based Films.

Obtaining air-stable and high-performance flexible n-type single-walled carbon nanotube (SWCNT)-based thermoelectric films used in wearable electronic devices is a challenge. In this work, the microstructure and thermoelectric properties of n-type SWCNT-based films have been optimized via doping C60 and its derivative into polyethylenimine/single-walled carbon nanotube (PEI/SWCNT) films. The result demonstrated that the dispersity of triethylene glycol-modified C60 (TEG-C60) was better in PEI/SWCNT films than that of pure C60. Among the prepared composite films, TEG-C60-doped PEI/SWCNT (TEG-C60/PEI/SWCNT) films exhibited the highest TE performance, achieving a peak electrical conductivity of 923 S cm-1 with a Seebeck coefficient of -42 μV K-1 at a TEG-C60/SWCNT mass ratio of 1:100. Compared to that of PEI/SWCNT, the power factor was increased significantly from 40 to 162 μW m-1 K-2 after the addition of TEG-C60, which was higher than that of films after the addition of C60. In addition, the n-type doped SWCNT films had good air stability at high temperatures, and the Seebeck coefficients of C60/PEI/SWCNT and TEG-C60/PEI/SWCNT at 120 °C were still negative and remained at 92% and 85%, respectively, after 20 days. Furthermore, a flexible TE device consisting of five pairs of p-n junctions was assembled using the optimum hybrid film, which generated a maximum output power of 3.6 μW at a temperature gradient of 50.2 K. Therefore, this study provides a facile way to enhance the thermoelectric properties of n-type carbon nanotube-based materials, which have potential application in flexible power generators.

Dispersion-Managed Tm-Ho Co-Doped Ultrashort Pulse Fiber Laser Using Single-Walled Carbon Nanotube and Spectral Filter

In this paper, we have demonstrated a dispersion-managed, high-power, Tm-Ho co-doped ultrashort pulse fiber laser using a single walled carbon nanotube (SWNT) dispersed in polyimide film. An in-line type spectral filter was developed to control the output pulse spectra. Two SWNT films with different modulation depths were examined as a mode-locker. Normal dispersion fiber was used in the fiber laser oscillator, and dependence on net cavity dispersion was investigated. Passive mode-locking was achieved in a wide dispersion range, from −0.319 to +0.101 ps2. Stable soliton mode-locking operation and dissipative soliton mode-locking operations were observed. The pumping efficiency was ~3 times higher than that in a Tm-doped fiber laser with a similar configuration. The developed fiber laser showed self-start and stable operations, and this laser is useful for practical applications.

A self-powered flexible gas-sensing system based on single-wall carbon nanotube films

Flexible self-powered sensors are attracting increasing research interest with the emergence and rapid development of the Internet of Things. However, inefficient power supplies and difficulties in device assembly have largely limited their applications. Here, we report an integrated gas-sensing system using a single-walled carbon nanotube film with good flexibility and large surface area to detect a target gas. A single-walled carbon nanotube/silicon heterojunction solar cell capable of stably providing a voltage of ∼0.5 V under the illumination of a standard solar intensity powers the sensor. Our self-powered sensing system shows an ideal rectangle-shaped nitrogen dioxide detection curve and demonstrates higher sensitivity and faster response time than one driven by external power at room temperature. We attribute this better activity to the increased carrier concentration originating from single-walled carbon nanotubes in both sensing and powering components. Finally, wireless communication between the system and a phone is demonstrated with a Bluetooth Low Energy module.

A solvent-compatible filter-transfer method of semi-transparent carbon-nanotube electrodes stacked with silver nanowires

ABSTRACT Low-density films of single-walled carbon nanotubes (SWNTs) can be used as a semi-transparent top electrode for all-solution-processed film devices; however, their semiconductor characteristics vary depending on the experimental factors in their dispersion into solvents, and the sublayers are damaged as a result of solvent incompatibility. In this study, we report a solvent-compatible filter-transfer method for SWNT films stacked with silver nanowires (AgNWs), and evaluate the semiconductor characteristics through the p/n heterojunction with a Si wafer (SWNT/Si). AgNWs and SWNTs were successively filtered through their aqueous dispersion solutions using a membrane filter. The stacked semi-transparent films (AgNW/SWNT films with controlled densities) were successfully transferred onto glass plates and Si wafers. The transmittance at 550 nm revealed a window between 60% and 80% with a narrow sheet resistance range between 11 and 23 Ω □−1. The power conversion efficiency (PCE) of SWNT/Si was improved to 11.2% in a junction area of 0.031 cm2 through the use of spin-coated Nafion resins; however, the accumulated resistance of SWNTs drastically reduced the PCE to 2% as the area increased to ≥0.5 cm2. AgNWs maintained the PCE within a range of 10.7% to 8.6% for an area ranging from 0.031 cm2 to 1.13 cm2. All of the photovoltaic parameters were dependent on the junction areas, suggesting that AgNWs function as an effective current-collector layer on the semiconductor layer of SWNTs without direct contact of AgNWs with the Si surface. In addition, we report a solvent-compatible experiment for transferring AgNW/SWNT films onto a solvent-sensitive perovskite material (CH3NH3PbI3).

Solvent-optimized monolithic SWCNT-based thermoelectric generator for efficient electricity harvesting from body heat and sunlight

A lightweight and flexible thermoelectric generator (TEG) based on monolithic designed single-walled carbon nanotubes (SWCNT) is successfully developed, which can effectively harvest electricity from hybrid sources of body heat and solar light with high energy output. By properly selecting SWCNT dispersion solvents, SWCNT films with an optimal p-type power factor of 526 μW m−1 K−2, and n-type power factor of 489 μW m−1 K−2 are achieved, among the highest reported power factors for solution-processed CNT-based films. Monolithic TEG based on the optimized SWCNT films leads to exceptionally high device performance both under constant heat and sunlight. The 8-leg TEG exhibits output power density over 110.2 μW cm−2 and 25.3 μW g−1 with a temperature gradient of 28 K, which is among the best energy-harvesting performance of CNT-based TEG. In addition, a large temperature gradient over 22.1 K is generated under AM1.5 1 sun illumination, owing to the SWCNT films act not only as TE modules but also solar-light absorber, and the TEG yields a record-high output power density of 66.0 μW cm−2 and 15.1 μW g−1 under 1 sun. Our TEG design based on SWCNT shows great potential in powering flexible micro-watt electronics by effectively harvesting electricity from both body heat and sunlight.

SWCNT Network-FET Device for Human Serum Albumin Detection.

A thin film of single-walled carbon nanotube (SWCNT) network field-effect transistor (FET) was fabricated by a simple, fast, and reliable deposition method for electronic applications. This study aims to develop a method for fabricating a thin film of random SWCNTs to be used as a transducer to detect human serum albumin (HSA) in biosensor applications. The random SWCNT network was deposited using the airbrush technique. The morphology of the CNT network was examined by utilising atomic force microscopy (AFM) and field-emission scanning electron microscopy (FESEM), while electrical characteristics were analysed using three-terminal IV measurements. The thin film (SWCNT network) was applied as a transducer to detect human serum albumin (HSA) based on its covalent interaction with antibodies. HSA plays a significant part in the physiological functions of the human body. The surface alteration of the SWCNTs was verified using Fourier transform infrared (FTIR) spectroscopy. Electrical current-voltage measurements validated the surface binding and HSA detection. The biosensor linearly recorded a 0.47 fg/mL limit of detection (LOD) and a high sensitivity of 3.44 μA (g/mL)-1 between 1 fg/mL and 10 pg/mL. This device can also be used to identify a genuine HSA despite interference from other biomolecules (i.e., bovine serum albumin (BSA)), thus demonstrating the random SWCNT-FET immunosensor ability to quantify HSA in a complex biological environment.

Highly efficient SWCNT/GaAs van der Waals heterojunction solar cells enhanced by Nafion doping

The atomic-level interface and strong interfacial interaction enable van der Waals (vdW) heterostructures to fabricate innovative photovoltaic devices by combing single-walled carbon nanotubes (SWCNTs) with bulk semiconductors, in which the device performance can be enhanced significantly using outstanding photoelectric property of SWCNTs. Herein, we reported a facile method to fabricate SWCNT/GaAs vdW heterojunction solar cell by transferring p-type (6,5)-enriched SWCNT film onto the n-type GaAs substrate, a power conversion efficiency (PCE) of 7.23 % has been achieved without any other treatment. Furthermore, the PCE value can be enhanced to 11.24 % by introducing Nafion as a highly effective dopant with a short-circuit current density of 24.70 mA/cm2, an open-circuit voltage of 0.64 V and a fill factor of 0.71. Our results reveal that the introduction of Nafion not only induces a stronger and closer contact at the interface between SWCNTs and GaAs, but also shows strong p-doping effect due to the existence of sulfonic acid functional groups. This p-doping effect of Nafion increases the work function of SWCNTs and subsequently enlarges the barrier height at the heterojunction for more efficient carrier separation. In addition, Nafion can also serve as an antireflection and passivation layer, reducing the incident light loss and the carrier recombination rate. These findings suggest that Nafion could be used to improve the performance of SWCNT-based vdW heterojunction devices.

A Flexible NO2 Gas Sensor Based on Single-Wall Carbon Nanotube Films Doped with a High Level of Nitrogen.

Carbon nanotubes (CNTs) are considered a promising candidate for the detection of toxic gases because of their high specific surface area and excellent electrical and mechanical properties. However, the detecting performance of CNT-based detectors needs to be improved because covalently bonded CNTs are usually chemically inert. We prepared a nitrogen-doped single-wall CNT (SWCNT) film by means of gas-phase fluorination followed by thermal annealing in NH3. The doped nitrogen content could be changed in the range of 2.9–9.9 at%. The N-doped SWCNT films were directly used to construct flexible and transparent gas sensors, which can work at a low voltage of 0.01 V. It was found that their NO2 detection performance was closely related to their nitrogen content. With an optimum nitrogen content of 9.8 at%, a flexible sensor had a detection limit of 500 ppb at room temperature with good cycling ability and stability during bending.

Pore structure changes in free-standing single-wall carbon nanotube film on vacuum high-temperature annealing

• Highly pure and crystalline free-standing SWCNT films were fabricated. • Impurities can be removed completely by vacuum high-temperature annealing. • Vacuum annealing can improve crystallinity of SWCNT film. • Vacuum annealing eliminates nanowindows and other defects from SWCNT film. The fabrication of free-standing single-wall carbon nanotube (SWCNT) film is promising for better understanding of SWCNT and many applications. Here we fabricated highly pure and crystalline free-standing SWCNT film using vacuum high-temperature annealing. Impurities can be removed thoroughly by vacuum annealing at 2073 K and 10 −1 Pa for 3 h. Also, the vacuum annealing was quite efficient for removing nanowindows and improving crystallinity of the SWCNT film. The transmission electron microscopic observation and X-ray diffraction confirmed almost no change in the average tube diameter and bundle structure of SWCNT. The vacuum high-temperature annealing decreases the N 2 adsorption amount at 77 K by more than half, supporting closing nanowindows on graphene wall of SWCNT by the vacuum annealing. Our free-standing SWCNT film is expected to promote a fundamental understanding of electrochemical energy issues by the application these films as the well-characterized electrodes.