Conductive Carbon Nanotube Films Research Articles

Study on the law and mechanism of anisotropic conductivity of carbon nanotubes film prepared by floating catalytic chemical vapor deposition method

Carbon nanotubes (CNTs) film has attracted extensive attention in the field of electronics, sensors, and other potential applications due to their excellent electrical conductivity. The conductivity of CNTs film is one of the most important aspects of engineering applications. This study investigates the conductivity of CNTs film with varying areal density, prepared using the floating catalyst chemical vapor deposition (FCCVD) method and densified by rolling. The square resistance of pre- and post-rolling films was measured to characterize the electrical properties. Experimental results indicate that square resistance decreases with increasing areal density and stabilizes eventually. A mathematical formula was derived to explain the relationship between areal density and square resistance, incorporating volume and areal density formulas. Experimental data curves of pre- and post-rolling films were fitted, yielding mathematical relations consistent with the derived formulas. The electrical conductivity of post-rolling CNTs film was superior to pre-rolling in experiment and calculation. The charge carrier transport mechanism in CNTs film was studied by analyzing its internal structure and electrical properties. Surface conductivity was over 1000 times higher than volume conductivity, attributed to the distribution of CNTs bundles in collection and thickness directions. Charge carrier transport capacity decreased with increasing layers in thickness direction due to contact resistance and large resistance at tube–tube junctions. Layers of CNTs near the current application surface significantly contribute to charge carrier transport at high areal density levels.

Rapid Production of Carbon Nanotube Film for Bioelectronic Applications.

Flexible electronics have enormous potential for applications that are not achievable in standard electronics. In particular, important technological advances have been made in terms of their performance characteristics and potential range of applications, ranging from medical care, packaging, lighting and signage, consumer electronics, and alternative energy. In this study, we develop a novel method for fabricating flexible conductive carbon nanotube (CNT) films on various substrates. The fabricated conductive CNT films exhibited satisfactory conductivity, flexibility, and durability. The conductivity of the conductive CNT film was maintained at the same level of sheet resistance after bending cycles. The fabrication process is dry, solution-free, and convenient for mass production. Scanning electron microscopy revealed that CNTs were uniformly dispersed over the substrate. The prepared conductive CNT film was applied to collect an electrocardiogram (ECG) signal, which showed good performance compared to traditional electrodes. The conductive CNT film determined the long-term stability of the electrodes under bending or other mechanical stresses. The well-demonstrated fabrication process for flexible conductive CNT films has great potential in the field of bioelectronics.

Mechanochromic Photonic Vitrimer Thermal Management Device Based on Dynamic Covalent Bond

AbstractFlexible self‐healing thermal management devices are increasingly in demand due to their high flexibility, low driving voltage, and excellent stability of thermal property. In this paper, the design of mechanochromic self‐healing thermal management devices is reported based on photonic vitrimer through self‐healing dynamic covalent bond. A series of new photonic vitrimers i first prepared by dynamic disulfide covalent bond and PS@SiO2 photonic crystals. The resulting photonic vitrimer exhibits bright structural colors, large tensile strain (>1000%), high mechanical strength (>10 MPa) and self‐healing ability (>95% efficiency). More importantly, the structural color remains constant after 10000 stretching/releasing cycles, demonstrating excellent mechanical stability, creep‐resistance, and durability. Taking advantage of the above features, a novel mechanochromic flexible wireless thermal management (MFW) device is developed by semi‐embedding the photonic vitrimer in a thermally conductive carbon nanotube film and then integrating it with a Bluetooth module and a control chip. Interestingly, the MFW device exhibits mechanochromic property, fast thermal response, low driving voltage (103 °C, at 3 V), and precise temperature control. Notably, the device even remains electrothermal performance (105 °C) after self‐healing. This work provides new insight into the self‐healing photonic materials, and the device shows promising applications in wearable electronics, vitro physiotherapy, and personal heating.

Effects of Different Factors on the Heat Conduction Properties of Carbon Films and Fibers

The increasing popularity of carbon nanotubes has created a demand for greater scientific understanding of the characteristics of thermal transport in nanostructured materials. However, the effects of impurities, misalignments, and structure factors on the thermal conductivity of carbon nanotube films and fibers are still poorly understood. Carbon nanotube films and fibers were produced, and the parallel thermal conductance technique was employed to determine the thermal conductivity. The effects of carbon nanotube structure, purity, and alignment on the thermal conductivity of carbon films and fibers were investigated to understand the characteristics of thermal transport in the nanostructured material. The importance of bulk density and cross-sectional area was determined experimentally. The results indicated that the prepared carbon nanotube films and fibers are very efficient at conducting heat. The structure, purity, and alignment of carbon nanotubes play a fundamentally important role in determining the heat conduction properties of carbon films and fibers. Single-walled carbon nanotube films and fibers generally have high thermal conductivity. The presence of non-carbonaceous impurities degrades the thermal performance due to the low degree of bundle contact. The thermal conductivity may present power law dependence with temperature. The specific thermal conductivity decreases with increasing bulk density. At room temperature, a maximum specific thermal conductivity is obtained but Umklapp scattering occurs. The specific thermal conductivity of carbon nanotube fibers is significantly higher than that of carbon nanotube films due to the increased degree of bundle alignment.

Karbon nanotüplerin ve fiberlerin ısı iletim özellikleri üzerine yapı, saflık ve hizalamanın etkileri

The increasing popularity of carbon nanotubes has created a demand for greater scientific understanding of the characteristics of thermal transport in nanostructured materials. However, the effects of impurities, misalignments, and structure factors on the thermal conductivity of carbon nanotube films and fibers are still poorly understood. Carbon nanotube films and fibers were produced, and the parallel thermal conductance technique was employed to determine the thermal conductivity. The effects of carbon nanotube structure, purity, and alignment on the thermal conductivity of carbon films and fibers were investigated to understand the characteristics of thermal transport in the nanostructured material. The importance of bulk density and cross-sectional area was determined experimentally. The results indicated that the prepared carbon nanotube films and fibers are very efficient at conducting heat. The structure, purity, and alignment of carbon nanotubes play a fundamentally important role in determining the heat conduction properties of carbon films and fibers. Single-walled carbon nanotube films and fibers generally have high thermal conductivity. The presence of non-carbonaceous impurities degrades the thermal performance due to the low degree of bundle contact. The thermal conductivity may present power law dependence with temperature. The specific thermal conductivity decreases with increasing bulk density. At room temperature, a maximum specific thermal conductivity is obtained but Umklapp scattering occurs. The specific thermal conductivity of carbon nanotube fibers is significantly higher than that of carbon nanotube films due to the increased degree of bundle alignment.

Single-Walled Carbon Nanotube-Germanium Heterojunction for High-Performance Near-Infrared Photodetector.

In this research, we report on a high-performance near-infrared (near-IR) photodetector based on single-walled carbon nanotube-germanium (SWCNT-Ge) heterojunction by assembling SWCNT films onto n-type Ge substrate with ozone treatment. The ozone doping enhances the conductivity of carbon nanotube films and the formed interfacial oxide layer (GeOx) suppresses the leakage current and carriers’ recombination. The responsivity and detectivity in the near-IR region are estimated to be 362 mA W−1 and 7.22 × 1011 cm Hz1/2 W−1, respectively, which are three times the value of the untreated device. Moreover, a rapid response time of ~11 μs is obtained simultaneously. These results suggest that the simple SWCNT-Ge structure and ozone treatment method might be utilized to fabricate high-performance and low-cost near-IR photodetectors.

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.

Effects of Carbon Nanotube Structure, Purity, and Alignment on the Heat Conduction Properties of Carbon Films and Fibers

The increasing popularity of carbon nanotubes has created a demand for greater scientific understanding of the characteristics of thermal transport in nanostructured materials. However, the effects of impurities, misalignments, and structure factors on the thermal conductivity of carbon nanotube films and fibers are still poorly understood. Carbon nanotube films and fibers were produced, and the parallel thermal conductance technique was employed to determine the thermal conductivity. The effects of carbon nanotube structure, purity, and alignment on the thermal conductivity of carbon films and fibers were investigated to understand the characteristics of thermal transport in the nanostructured material. The importance of bulk density and cross-sectional area was determined experimentally. The results indicated that the prepared carbon nanotube films and fibers are very efficient at conducting heat. The structure, purity, and alignment of carbon nanotubes play a fundamentally important role in determining the heat conduction properties of carbon films and fibers. Single-walled carbon nanotube films and fibers generally have high thermal conductivity. The presence of non-carbonaceous impurities degrades the thermal performance due to the low degree of bundle contact. The thermal conductivity may present power law dependence with temperature. The specific thermal conductivity decreases with increasing bulk density. At room temperature, a maximum specific thermal conductivity is obtained but Umklapp scattering occurs. The specific thermal conductivity of carbon nanotube fibers is significantly higher than that of carbon nanotube films due to the increased degree of bundle alignment.

Ultra low friction of conductive carbon nanotube films and their structural evolution during sliding

Solid lubricating coatings with high conductivity are widely used in aerospace, tram and micro mechanical systems. In this study, a solid lubricating film with ultralow friction coefficient and good electrical conductivity was prepared using hydroxylated CNTs through electrophoretic deposition, and the structural evolutions when the CNT films act as lubricants are investigated in-depth. It was found that the electric resistance reduced significantly with the increase of the deposited CNT film thickness, and then it reached a saturation value of approximately 40 Ω at the film thickness of 0.7 ± 0.10 μm deposited at 50 V. Moreover, the friction coefficient was reduced by 71% at the deposition voltage of 40 V compare to the single crystal silicon. It is worth noting that the original carbon nanotubes transformed into nano-scrolls under the action of friction shearing and heating. At the same time, this work provided new insights for the structure evolution of carbon nanotube films during the rubbing process.

Bio-inspired Janus structural color films as visually flexible electronics

Multifunctional composite flexible sensors are essential components in flexible and stretchable electronics. In this paper, we present novel mussel-inspired Janus structural color films as visually flexible electronics. The Janus composite film with a three-layer structure, which is compozed of a conductive carbon nanotube (CNT) layer, a supporting polydimethylsiloxane (PDMS) layer and a structural color layer formed by two-dimensional colloidal crystals (2D-CCs), is prepared by a hierarchical assembly strategy. The manufactured multi-layer CNT films and the 2D-CCs are integrated on both sides of the supporting PDMS layer, respectively by the self-assembly process and the adhesion of polydopamine (PDA) to provide corresponding excellent conductivity, flexibility and visual optical sensing for the Janus composite film. It is demonstrated that the CNT films could not only increaze the contrast of structural color of the 2D-CC array as their light absorption characteristics in the broadband frequency field, but also impart the composite film with photothermal response characteristics. In addition, because of the outstanding electrical properties, visualized structural color and photothermal response, the resulting Janus structural color films show stable electrical sensing and visualized color-sensing under deformations arose by human motions and near-infrared (NIR) illumination, which could play essential roles in flexible and stretchable electronics.

Stamp-Perforation-Inspired Micronotch for Selectively Tearing Fiber-Bridged Carbon Nanotube Thin Films and Its Applications for Strain Classification.

Cracks typically deteriorate the structural and electrical properties of materials when not properly controlled. A few papers recently reported the controlling methods of crack formation in the brittle materials utilizing the lateral V-notch structure. For ductile materials, however, there have been few papers reporting cracking phenomenon, but full cracking control including predesigned initiation, propagation, and termination has not been reported yet. Therefore, we report a predesigned full cracking control in ductile conductive carbon nanotube (CNT) films by introducing inkjet-printed L-shape micronotch (LMN) structures inspired by directional stamp perforation marks. In spite of the high fracture toughness of CNT films, the LMNs determine locations of initial crack formation and guide crack propagation in a predesigned way. Selective connection of isolated cracks in the CNT film increases its resistance monotonically under tensile strain and thus tremendously well maintains high linearity (adj. R2 value > 0.99) in resistance change over record large strain ranges of 0.01-100%, which enables us to quantitatively classify strain values accurately for previously reported practical body signals for the first time. We believe that our facile printing-based crack control strategy not only provides a comprehensive solution to various stretchable sensor applications but also builds a new milestone for cracking mechanism studies in fracture mechanics.

Highly flexible and stretchable strain sensors based on conductive whisker carbon nanotube films

We fabricated a conductive whisker carbon nanotube (CNT) film by a simplified Langmuir−Blodgett method in which loose whisker CNTs (WCNTs) were densified via a capillary-induced compression assisted by a porous sponge. After this densification treatment, WCNTs formed conductive networks. The deformation of WCNT networks can cause a significant resistance change. The electric resistance of conductive WCNT network is highly sensitive to external mechanical stimuli. We developed a flexible and stretchable WCNT-based strain sensor using WCNT film sandwiched between two pieces of elastic polydimethylsiloxane films. This WCNT-based sensor exhibits an extremely high sensitivity (up to a gauge factor of 4839) over a wide strain range, fast response (60 ms), the good stability of mechanical cycling (1000 cycles), and extremely wide response window (it can detect strains as low as 0.05% and up to 420%). The WCNT-based sensing devices are able to monitor human muscle activity ranging from vital signs to high-strain human joint motions due to their high sensitivity and wide strain sensing range.

Direct Patterning of Carbon Nanotube via Stamp Contact Printing Process for Stretchable and Sensitive Sensing Devices

HighlightsA dry transfer method for the mass production of transparent conductive carbon nanotube (CNT) films inspired by typography has been proposed.The strain sensors based on the CNT films have high stretchability and repeatability (gauge factor up to 9960 at 85% strain).These ultrathin strain sensors can detect human motion, sound, and pulse, suggesting promising application prospects in wearable devices.

Highly conducting, durable and large area carbon nanotube thick films for stretchable and flexible electrodes

We demonstrated a straightforward strategy to fabricate highly conductive carbon nanotube (CNT) films by introducing polyacrylic acid (PAA) as a dispersant and a dopant. A dispersion process was developed to fabricate highly concentrated and viscous aqueous suspensions, which enabled an easy deposition of uniform micrometer-thick CNT films on a large scale. The CNT-PAA hybrid film exhibited a ten fold increase in the conductivity as compared with the nondoped film. Furthermore, a mild acid-treatment was utilized to modify the CNTs before dispersion, resulting in a high density of small-bundle CNTs without clear structural damage and a further two fold increase in the conductivity. The CNT-PAA hybrid film with a thickness of around 5.1 μm exhibited a sheet resistance of 0.1 Ω/sq with a surprisingly high electrical conductivity of 19 600 ± 4000 S/cm. The conductivity of the hybrid film remained almost constant after aging tests under the conditions of 85 °C and 85% relative humidity for more than 1000 h, suggesting its outstanding long-term stability. Furthermore, HNO3 doping increased the conductivity to 35 000 ± 5000 S/cm.

Free-standing CuS–ZnS decorated carbon nanotube films as immobilized photocatalysts for hydrogen production

Free-standing carbon nanotube films (CNTF) with entangled carbon nanotubes (CNT) were used as conductive supports for the preparation of CuS–ZnS/CNTF composite as immobilized photocatalysts for H2 production. The surface morphology, crystalline property, surface chemistry, and optical properties of the CuS–ZnS/CNTF photocatalysts were investigated. The effects of forming CuS–ZnS heterojunction and conductive CNTF on the separation of photogenerated charges and photocatalytic hydrogen production activity of CuS–ZnS/CNTF photocatalysts were evaluated by the photocatalytic hydrogen production tests. Conductive CNT films can prevent the recombination of photogenerated electron–hole pairs. The deposition of CuS nanoparticles on the ZnS/CNTF leads to higher photocatalytic activity which can be attributed to the effective electron–hole separation. Introducing ZnS and CuS makes the photocatalyst surface more hydrophilic. The porous structure contributed to the effective contact between the sacrificing agents and the photocatalysts, leading to enhanced H2 production activity.

Stable iodide doping induced by photonic curing for carbon nanotube transparent conductive films

Doping has become crucial for achieving stable and high-performance conductive transparent carbon nanotube (CNT) films. In this study, we systematically investigate the doping effects of a few materials including alkali metal iodides, nonmetal iodide, and metals. We demonstrate that photonic curing can enhance the doping effects, and correspondingly improve the conductivity of CNT films, and that such iodides have better doping effects than metals. In particular, doping with a nonmetal compound (NH4I) shows the largest potential to improve the conductivity of CNT films. Typically, doping with metal iodides reduces the sheet resistance (RS) of CNT films with 70–80% optical transmittances at λ = 550 nm from 600–2400 to 250–440 Ω/square, whereas doping with NH4I reduces RS to 57 and 84 Ω/square at 74 and 84% optical transmittances, respectively. Interestingly, such a doped CNT film exhibits only a slight increase in sheet resistance under an extreme environment of high temperature (85 °C) and high relative humidity (85%) for 350 h. The results suggest that photonic-curing-induced iodide doping is a promising approach to producing high-performance conductive transparent CNT films.

Highly conductive and high-strength carbon nanotube film reinforced silicon carbide composites

Abstract Film formed by carbon nanotubes is usually called carbon nanotube film (CNTf). In the present study, CNTf fabricated by floating catalyst method was used to prepare CNTf/SiC ceramic matrix composites by chemical vapor infiltration (CVI). Mechanical and electrical properties of the resulting CNTf/SiC composites with different CVI cycles were investigated and discussed, and the results revealed that the CNTf has a good adaptability to CVI method. Tensile test demonstrated an excellent mechanical performance of the composites with highest tensile strength of 646 MPa after 2 CVI cycles, and the strength has a decline after 3 CVI cycles for an excessively dense matrix. While, the elastic modulus of the composite increased with the CVI cycles and reached 301 GPa after 3 CVI cycles. Tensile fracture morphologies of the composites were analyzed by scanning electron microscope to study the performance change laws with the CVI cycles. With SiC ceramic matrix infiltrated into the CNTf, enhanced electrical conductivity of the CNTf/SiC composite compared to pure CNTf was also obtained, from 368 S/cm to 588 S/cm. Conductivity of the SiC matrix with free carbon forming in the CVI process was considered as the reason.

Highly conductive and transparent single-walled carbon nanotube thin films from ethanol by floating catalyst chemical vapor deposition.

Single-walled carbon nanotube (SWCNT) films have great potential to replace indium tin oxide films for applications in transparent and conductive electronics. Here we report a high yield production of SWCNT transparent conducting films (TCFs) by the floating catalyst chemical vapor deposition method using ethanol as the carbon source. To the best of our knowledge, this is the first report regarding SWCNT TCFs using ethanol as the carbon source. The fabricated uniform SWCNT TCFs exhibit a competitive sheet resistance of 95 Ω sq-1 at 90% transmittance after doping with AuCl3. The SWCNT TCFs possess high quality and the mean length of SWCNT bundles is approximately 27.4 μm. Furthermore, the concentration of semiconducting SWCNTs is 75-77%. Additionally, the chirality maps obtained from electron diffraction analysis demonstrate that our SWCNTs are biased towards the armchair type.

High thermal conductivities of carbon nanotube films and micro-fibres and their dependence on morphology

Thermal conductivity of carbon nanotube (CNT) films and micro-fibres synthesised by floating catalyst chemical vapour deposition was measured by the parallel thermal conductance method. CNT films showed in-plane thermal conductivities of 110 W m−1 K−1. Online condensation into a micro-fibre morphology – a two-dimensional reduction in the transverse plane, including some axial stretching during solvent evaporation – resulted in room-temperature thermal conductivity values as high as 770 ± 10 W m−1 K−1, which is the highest thermal conductivity reported for CNT bulk materials to date. In specific terms, this matches the maximum thermal conductivity of heat-treated carbon fibre, but with a higher onset temperature for Umklapp scattering processes (300 K rather than 150 K). We selected four sample types to investigate effects of alignment, purity, and single- or multi-wall character on their thermal conductivity. For both the electrical and thermal conductivity of as-spun material, i.e. without any post-synthesis treatment, we show that the density and quality of CNT bundle alignment are still the predominant factors affecting these properties, outweighing the influence of single- or multi-walled character of the nanotubes. This raises the promise that, with optimal alignment and junction points, even higher values of thermal conductivity are achievable for macroscopic CNT fibres.

A highly flexible solid-state supercapacitor based on the carbon nanotube doped graphene oxide/polypyrrole composites with superior electrochemical performances

Flexible electrodes of ternary composites, in which highly conductive carbon nanotube films (CNFs) are coated with carbon nanotube-doped graphene oxide/polypyrrole (CNT-GO/PPy), have been fabricated via facile electrochemical synthesis. Long and short CNTs are separately doped into the composites (lCNT-GO/PPy and sCNT-GO/PPy) and their electrochemical performances are compared. Electrochemical measurements indicate that the doping of CNTs in the composites significantly improves the electrochemical behaviors of the GO/PPy electrodes. Notably, the lCNT-GO/PPy electrodes show superior electrochemical properties with respect to the sCNT-GO/PPy electrodes, which is related to the introduction of abundant CNTs in the former electrodes and their special microstructures. Two symmetric electrodes with the lCNT-GO/PPy composites coated on CNFs are assembled to fabricate a solid-state supercapacitor device, which features lightweight, ultrathinness, and high flexibility. The device achieves a high areal and volumetric specific capacitance of 70.0 mF cm−2 at 10 mV s−1 and 6.3 F cm−3 at 0.043 A cm−3, respectively. It also shows superior rate performance and cycle stability, with a capacitance retention rate of 87.7% for 10,000 cycles. The supercapacitor device fabricated is promising for the use in lightweight and flexible integrated electronics.