Double-walled Carbon Nanotube Films Research Articles

Absorption‐Dominant Electromagnetic Interference (EMI) Shielding across Multiple mmWave Bands Using Conductive Patterned Magnetic Composite and Double‐Walled Carbon Nanotube Film

AbstractThe revolution of millimeter‐wave (mmWave) technologies is prompting a need for absorption‐dominant EMI shielding materials. While conventional shielding materials struggle in the mmWave spectrum due to their reflective nature, this study introduces a novel EMI shielding film with ultralow reflection (<0.05 dB or 1.5%), ultrahigh absorption (>70 dB or 98.5%), and superior shielding (>70 dB or 99.99999%) across triple mmWave frequency bands with a thickness of 400 µm. By integrating a magnetic composite layer (MCL), a conductive patterned grid (CPG), and a double‐walled carbon nanotube film (DWCNTF), specific resonant frequencies of electromagnetic waves are transmitted into the film with minimized reflection, and trapped and dissipated between the CPG and the DWCNTF. The design factors for resonant frequencies, such as the CPG geometry and the MCL refractive index, are systematically investigated based on electromagnetic wave propagation theories. This innovative approach presents a promising solution for effective mmWave EMI shielding materials, with implications for mobile communication, radar systems, and wireless gigabit communication.

Preparing a liquid crystalline dispersion of carbon nanotubes with high aspect ratio.

We successfully prepared a surfactant-assisted carbon nanotube (CNT) liquid crystal (LC) dispersion with double-walled CNTs (DWCNTs) having a high aspect ratio (≈1378). Compared to dispersions of single-walled CNTs (SWCNTs) with lower aspect ratio, the transition concentrations from isotropic phase to biphasic state, and from biphasic state to nematic phase are lowered, which is consistent with the predictions of the Onsager theory. An aligned DWCNT film was prepared from the DWCNT dispersion by a simple bar-coating method. Regardless of the higher aspect ratio, the order parameter obtained from the film is comparable to that from SWCNTs with lower aspect ratios. This finding implies that precise control of the film formation process, including a proper selection of substrate and deposition/drying steps, is crucial to maximize the CNT-LC utilization.

Enhanced Joule heating performance of flexible transparent conductive double-walled carbon nanotube films on sparked Ag nanoparticles

A hybrid flexible and transparent heater based on double-walled carbon nanotubes (DWCNTs) and silver nanoparticles (AgNPs) is fabricated on a polyethylene terephthalate substrate via facile spray-coating and spark-depositing techniques, respectively. The AgNPs are simply prepared by electrically sparking pure Ag wires in ambient environment with no vacuum system required. The optical, electrical and electrothermal properties of the hybrid AgNP/DWCNT and simple DWCNT film devices are investigated. The results show that the hybrid film heaters exhibit superior electrothermal performances to the DWCNT film heaters, as having higher maximum temperatures at the same applied voltages, as well as faster thermal heating and cooling responses. The simple DWCNT heater with optical transmittance of 72.7% at a wavelength of 550 nm reaches the maximum temperature of 95.0 °C, whereas the hybrid AgNP/DWCNT heater with optical transmittance of 64.0% reaches higher maximum temperature of 118.6 °C, as electrically supplied at 8 V. Furthermore, the mechanical flexibility of the hybrid and DWCNT film heaters is studied with different folding directions, and a little deviation in their electronic conduction is observed, while still performing good heating temperature after a bending test. This simple hybrid film heater demonstrates the efficient electrothermal performances, which can be utilized as a flexible and transparent heating device in various practical applications.

Controlled Removal of Surfactants from Double-Walled Carbon Nanotubes for Stronger p-Doping Effect and Its Demonstration in Perovskite Solar Cells.

Double-walled carbon nanotubes (DWNTs) have shown potential as promising alternatives to conventional transparent electrodes owing to their solution processability as well as high conductivity and transparency. However, their DC to optical conductivity ratio is limited by the surrounding surfactants that prevent the p-doping of the DWNTs. To maximize the doping effectiveness, the surfactants are removed from the DWNTs, with negligible damage to the nanotubes, by calcination in an Ar atmosphere. The effective removal of the surfactants is characterized by various analyses, and the results show that the optimal calcination temperature is 400°C. The conductivity of the DWNTs films improves when doped by triflic acid. While the conductivity increase of the surfactants-wrapped DWNT films is 31.9%, the conductivity increase of the surfactants-removed DWNT is found to be 59.7%. Using the surfactants-removed, p-doped, solution-processed transparent electrodes, inverted-type perovskite solar cells are fabricated, resulting in a power conversion efficiency of 17.7% without hysteresis. This work advances the application of DWNTs in transparent conductors, as the efficiency obtained is the highest value achieved to date for carbon nanotube electrode-based perovskite solar cells and solution-processable transparent electrode-based solar cells.

Double-walled carbon nanotube film as the active electrode in an electro-optical modulator for the mid-infrared and terahertz regions

The lack of efficient optical components operating with terahertz (THz) radiation is a limiting step in the ongoing large-scale development of this technology in fields such as telecommunication and imaging. In this work, we propose the use of double-walled carbon nanotube (DWCNT) films as the active electrode in THz modulation devices. Using six bounces in an internal total reflection configuration in a silicon waveguide prism, we achieved high attenuation from a 5 nm thin film, reaching up to −ΔT/T=6% at 50 THz, albeit with a slow speed of modulation on the order of minutes. Moreover, this attenuation −ΔT/T attains a value of 20% at 30 THz using a thicker 20 nm DWCNT film. As a consequence of doping, the modulation of a phonon-related Fano resonance is also observed in the mid-infrared, which could be used as a modulable narrow-band optoelectronic filter. Our study provides a sense of the capabilities unlocked by exploiting the optical and electronic properties of carbon nanotubes in the terahertz and infrared regimes.

Facile fabrication of flexible and conductive cellulose paper from aqueous carbon nanotube/hemicellulose compound

A highly conductive paper is demonstrated using double-walled carbon nanotubes (DWCNTs) simply coated on cellulose fibers by filtration technique from an aqueous suspension. The DWCNT material in this work was non-covalently functionalized by hemicellulose, which enabled them to form as a compound and increased their dispersibility in water. The electronic properties of DWCNT network on cellulose paper were investigated. The measurements show relatively good electrical conduction of the as-prepared samples with the lowest sheet resistance of about 178 Ω/□. Moreover, the flexibility of the DWCNT paper while bending at different conditions was examined and their relative conductivity was observed with a little deviation, indicating of great foldable properties. The results demonstrate that hemicellulose works well as a water-based dispersant without significant effect on the electrical properties of the DWCNT films on cellulose paper and can be further improved toward green and flexible paper-based electronic applications.

Improved interaction between semiconducting polymer and carbon nanotubes in thermoelectric composites through covalent grafting

We developed an unconventional route to produce uniform and intimately interfaced nanocomposite films for their potential application in thermoelectric (TE) devices. Here, amino-terminated poly(3-hexylthiophene-2,5-diyl) (P3HT) was chemically adhered onto the surface of a functionalized double-walled carbon nanotube (DWCNT), via an amidation reaction, to form P3HT-grafted DWCNT (P3HT-g-DWCNT). As the P3HT chains are intimately and permanently tethered on the DWCNT surface, a well-defined P3HT/DWCNT interface prevents the DWCNT from aggregating by promoting the solubility of P3HT-g-DWCNT nanocomposites in organic solvent. Such characteristic changes in DWCNT by polymer grafting can improve the thermoelectric properties of DWCNT films. The covalently grafted P3HT-g-DWCNT film exhibits a significantly enhanced Seebeck coefficient of 116. 6 μV K−1, as compared to a physically mixed P3HT/DWCNT composite (69.2 μV K−1), in conjunction with a high power output in TE modules. This facile approach would open a new way to synthesize intimately connected nanocomposites made up of conductive polymers and carbon materials for high performance thermoelectrics.

A carbon nanotubes photoconductive detector for middle and far infrared regions based on porous silicon and a polyamide nylon polymer

Sensitive and good response photoconductive detectors working in the middle and far infrared regions were fabricated. These detectors were fabricated based on multi and double walled carbon nanotube films and works at room temperature. The films were deposited on a porous silicon (PSi) nanosurface. The surfaces were functionalized by a thin layer of polyamide nylon polymer to improve the photoresponsivity of the fabricated detectors. The response time of the fabricated MWCNTs-PSi detectors were 30 and 0.22 ms for the middle and far IR region respectively. The functionalisation of the MWCNTs-PSi film surface by the polyamide nylon polymer improved the photoconductive gain, photoresponsivity, and specific conductivity in both MWCNTs-PSi and DWCNTs-PSi detectors. The designed carbon nanotube (CNT) based photodetector has low cost, high sensitivity and reasonable speed for the middle and far IR spectral range without cooling.

Field electron emission characteristics of plasma treated carbon nanotubes

This paper reports the effect of hydrogen ( H 2) plasma treatment on field emission property of double walled carbon nanotubes (DWCNTs) synthesized by using chemical vapor deposition method. The hydrogen plasma treatment was carried out for various duration. The DWCNTs films were characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The results showed that the field emission properties of DWCNTs were influenced with increasing plasma treatment duration. The Raman spectra of samples clearly show structural defects after hydrogen plasma treatment. It is observed that the change in the field emission characteristics of DWCNTs is attributed to the structural defects due to the H 2 plasma and depends on the plasma treatment duration.

Preparation of Transparent and Conductive Double-Walled Carbon Nanotube Films

Preparation of Transparent and Conductive Double-Walled Carbon Nanotube Films

Fabrication of flexible transparent conductive films from long double-walled carbon nanotubes

The fabrication of flexible transparent conducting films (TCFs) is important for the development of the next-generation flexible devices. In this study, we used double-walled carbon nanotubes (DWCNTs) as the starting material and described a fabrication method of flexible TCFs. We have determined in a quantitative way that the key factors are the length and the dispersion states of the DWCNTs as well as the weight-ratios of dispersant polymer/DWCNTs. By controlling such factors, we have readily fabricated a flexible highly transparent (94% transmittance) and conductive (surface resistivity = 320 Ω sq−1) DWCNT film without adding any chemical doping that is often used to reduce the surface resistivity. By applying a wet coating, we have succeeded in the fabrication of large-scale conducting transparent DWCNT films based on the role-to-role method.

Significantly enhanced photoresponse in carbon nanotube film/TiO2 nanotube array heterojunctions by pre-electroforming

Traditional TiO2 based photodetectors (PDs) suffer from high dark resistance, which increases loss of photoexcited charge carriers. Here, we report a new and simple way to improve the performance of PDs based on double-walled carbon nanotube (DWCNT)/TiO2 nanotube heterojunctions. Highly ordered TiO2 nanotube arrays were fabricated using a two-step anodic oxidation method, and coated with a DWCNT film, which functioned as a semitransparent electrode and a photoactive layer. Via pre-electroforming, the device was switched from a high resistance state (HRS) to a low resistance state (LRS). At an applied bias of 1 V, the dark resistance was reduced from 926 to 0.67 kΩ, as a result of the formation of oxygen vacancy related conducting filaments. The photoresponse (ΔI = Ip − Id, where Ip and Id represents photocurrent and dark current, respectively) of the PD in LRS reached 816.76 μA W−1 under 532 nm laser illumination and 802.89 μA W−1 under 1064 nm laser irradiation, which is 965 and 3980 times higher, respectively, than those obtained from the HRS device under the same conditions. This strategy for enhancing the photoresponse of TiO2 based PDs may have applications in further improving the power conversion efficiency of dye-sensitized solar cells.

Field Emission Properties of the Graphene Double-Walled Carbon Nanotube Hybrid Films Prepared by Vacuum Filtration and Screen Printing

The graphene double-walled carbon nanotube (DWCNT) hybrid films were prepared by vacuum filtration and screen printing. Their electron field emission properties have been studied systematically. The electron emission properties of the hybrid films are much better than those of pure DWCNT films and pure graphene films. Comparing with the screen printed films, the vacuum filtered films have many advantages, such as lower turn-on field, higher emission current density, better uniformity, better long-term stability, and stronger adhesive strength with conductive substrates. The optimized hybrid films with 20% weight ratio of graphene, which were fabricated by vacuum filtration, show the best electron emission performances with a low turn-on field of 0.50 Vμm−1(at 1 μAcm−2) and a high field enhancement factorβof 27000.

Stabilization of carbon nanotubes by filling with inner tubes: An optical spectroscopy study on double-walled carbon nanotubes under hydrostatic pressure

The stabilization of carbon nanotubes via the filling with inner tubes is demonstrated by probing the optical transitions in double-walled carbon nanotube bundles under hydrostatic pressure with optical spectroscopy. Double-walled carbon nanotube films were prepared from fullerene peapods and characterized by high-resolution transmission electron microscopy and optical spectroscopy. In comparison to single-walled carbon nanotubes, the pressure-induced redshifts of the optical transitions in the outer tubes are significantly smaller below $\ensuremath{\sim}$10 GPa, demonstrating the enhanced mechanical stability due to the inner tube already at low pressures. Anomalies at the critical pressure $P$${}_{d}\ensuremath{\approx}12$ GPa signal the onset of the pressure-induced deformation of the tubular cross sections. The value of $P$${}_{d}$ is in very good agreement with theoretical predictions of the pressure-induced structural transitions in double-walled carbon nanotube bundles with similar average diameters.

Negative and positive photoconductivity modulated by light wavelengths in carbon nanotube film

We explore the photoconductive properties of double-walled carbon nanotube film under laser illumination at different wavelengths in both ambient air and vacuum. In our experimental measurements, the photoconductivity of the film shows a strong dependence on the wavelength of light and can be changed from negative to positive by fully removing oxygen. We propose that competition among photoexcitation, photodesorption, and surface plasmon polaritons is responsible for these interesting phenomena. Our results are expected to provide potential applications in the field of nano-optoelectronic sensors based on carbon nanotubes.

Field Emission Property of Double-walled Carbon Nanotubes Related to Purification and Transmittance

Double-walled carbon nanotubes (DWCNTs) with high purity were produced by the catalytic decomposition of tetrahydrofuran (THF) using a Fe-Mo/MgO catalyst at 800°C. The as-synthesized DWCNTs typically have catalytic impurities and amorphous carbon, which were removed by a two-step purification process consisting of acid treatment and oxidation. In the acid treatment, metallic catalysts were removed in HCl at room temperature for 5 hr with magnetic stirring. Subsequently, the oxidation, using air at 380°C for 5 hr in the a vertical-type furnace, was used to remove the amorphous carbon particles. The DWCNT suspension was prepared by dispersing the purified DWCNTs in the aqueous sodium dodecyl sulfate solution with horn-type sonication. This was then air-sprayed on ITO glass to fabricate DWCNT field emitters. The field emission properties of DWCNT films related to transmittance were studied. This study provides the possibility of the application of large-area transparent CNT field emission cathodes. (Received October 8, 2010)

One-step fabrication of high quality double-walled carbon nanotube thin films by a chemical vapor deposition process

High-quality double-walled carbon nanotubes (DWCNTs) thin-films have been fabricated in one-step by the catalytic chemical vapor deposition gas-flow reaction process with acetone as a carbon source in an argon flow. The DWCNTs film is formed through the self-assembly of the DWCNTs in the gas flow, which is achieved by controlling the gas rates in the synthesis reaction. The DWCNT film is self-supported and consists of preferentially aligned high-quality DWCNT bundles. Raman spectral analysis shows a low intensity ratio of the D band and the G band with I D/ I G being 0.025 indicating a high-quality of DWCNTs at a macroscopic scale. Property measurements show that the DWCNT film is mechanically robust and highly electrically conductive. The formation of high-quality DWCNTs can be attributed to the reaction in the argon environment that is inert and does not attack the DWCNTs at the high synthesis temperature (1170 °C). This one-step fabrication process is feasible for large-scale productions of high-quality DWCNTs films with promising structural and functional applications.

Enhanced field emission properties of screen-printed doubled-walled carbon nanotubes by polydimethylsiloxane elastomer

Field emission (FE) properties of double-walled carbon nanotubes (DWCNTs) treated by polydimethylsiloxane (PDMS) elastomer with different heating temperature have been systematically studied. The current density of treated DWCNT films decreases with the increase of heating temperature. The screen-printed DWCNTs treated by PDMS elastomer with drying temperature 150 °C for 20 min have the best FE performance with a marvelous field enhancement factor ( β = 20194). The optimized FE performance is attributed to the morphological change of DWCNT films after PDMS elastomer treatment and the change of separation energy for the CNT-substrate interface. It is proved that the PDMS treatment is a facile and effective method for field emission display (FED) application, especially for low-temperature FED preparation.

Synthesis of double-walled carbon nanotube films and their field emission properties

Continuous double-walled carbon nanotube (DWCNT) films were synthesized using an Fe–Mo catalyst by the arc discharge method. This new catalyst has dramatically improved the purity and selectivity of DWCNT product. High-resolution transmission electron microscopy indicates that the outer and inner diameter of DWCNT are 1.9–4.7nm and 1.2–3.8nm, respectively. The field emission properties of DWCNT films have been studied. The directly grown film was transferred onto quartz substrates and used as emission cathodes, and has demonstrated a quite good emission performance. Moreover, the emissions of DWCNT films have been further improved by heat treatment. The film after 400°C oxidation shows excellent field emission property with a low turn-on (Eto=0.6V/μm) and threshold field (Eth=0.9V/μm) corresponding to the emission current density of 1μA/cm2 and 1mA/cm2, respectively.

Preparation of large-area double-walled carbon nanotube films and application as film heater

Large-area (larger than 30×30 cm 2) double-walled carbon nanotube (DWCNT) films are prepared and application as a heating element for film heaters is demonstrated. A high heating efficiency is observed. Measurements indicate that the use of the DWCNT film heater would save energy consumption up to 20–30% when compared with a commercial film-like metal-based heater. Morphological analysis reveals that the special surface structure, appropriate electric and high thermal conductivities of the film formed by the network of entangled nanotube bundles may lead to the high heating performance. Considering large-area, shape flexibility, negligible weight and easy manipulation, the film exhibits promising potential applications as a film heater for thermal control in aircrafts, medical equipment, home appliances and other industrial fields at low temperature (below 400 °C).