Contamination-free and damage-free patterning of single-walled carbon nanotube transparent conductive films on flexible substrates

High quality patterning of single-walled carbon nanotube (SWCNT) transparent conductive films is achieved by a lift-off aluminum interlayer method, which has the advantage of resulting in contamination-free and damage-free SWCNTs. The obtained patterns preserve the electrical properties of the SWCNT films and show promising applications in flexible high frequency electronic and display devices.     

The production of a flexible electroluminescent device on polyethylene terephthalate films using transparent conducting carbon nanotube electrode

An inorganic electroluminescent (EL) device on a flexible polyethylene terephthalate (PET) substrate and its properties were investigated. The transparent conducting film (TCF) made from carbon nanotubes (CNTs) (CNT-TCF) was employed in the flexible EL device. CNT-TCF was formed by filtration of CNT solution and was transferred to the PET film. It was found that the brightness of the inorganic EL device was strongly dependent on the quality of the CNT composite films. After a 3-aminopropyltriethoxysilane treatment of the PET substrate, CNTs uniformly were dispersed and showed a good adhesion to the substrate, and the resulting EL device showed better performance. The flexible EL device showed the brightness of 96.8 cd/m² at 28 kHz and 50 V.     

The production of graphene nanosheets decorated with silver nanoparticles for use in transparent, conductive films

Aggregation and restacking of graphene nanosheets (GNS) can be efficiently inhibited by decorating the silver nanoparticles on the surface of GNS to form GNS/silver (GNS-Ag) composites, which can construct high transparent and electrically conductive thin films. Silver nanoparticles act as a useful nanospacer and conductor, which not only increase the interlayer distance but also improve the electrical conductivity between layers. A two-step reduction process using sodium borohydride and ethylene glycol was also demonstrated reducing graphene oxide to GNS efficiently. The GNS-Ag composite films showed a maximum sheet resistance of 93 Ω□⁻¹, while maintaining up to 78% light transmittance, which was two order of magnitude lower than that of GNS (8.2 × 10³ Ω□⁻¹, 81%), and the value of DC conductivity to optical conductivity ratio was 13.5 instead of 0.25.     

Fabrication of transparent and conductive carbon nanotube/polyvinyl butyral films by a facile solution surface dip coating method

We present a simple solution surface dip coating method for fabricating transparent and conductive carbon nanotube/polyvinyl butyral (CNT/PVB) composite films. This fabrication process is simple to scale production and requires only ethanol and water as solvents, which is green and environment friendly.     

Spectroscopic studies and electrical properties of transparent conductive films fabricated by using surfactant-stabilized single-walled carbon nanotube suspensions

This study evaluates the effect of anionic and cationic surfactants on the dispersion of purified SWCNTs in water in terms of dispersibility and on electrical conductivity of TCFs and electronic band structures of SWCNTs. The dispersibility of surfactants in an aqueous SWCNT suspension is assessed with the amount of SWCNTs dispersed, the content of surfactants required to suspend SWCNTs, and the long-term stability of dispersion. Sodium dodecylbenzene sulfonate (SDBS) shows better dispersibility and electrical conductivity of SWCNTs than sodium dodecyl sulfate, sodium cholate, and cetyltrimethyl ammonium bromide. Electronic band structures of SWCNTs vary with surfactants and nitric acid treatment, investigated by using UV–Vis–NIR and Raman spectroscopy. Metallic and semiconducting SWCNTs and surfactants make electrostatic charge interactions between them, which occur in different manners according to the electronic types of tubes and the natures of surfactants. TCFs are fabricated by using the SWCNT suspension dispersed with SDBS, which reveal a low percolation threshold with the two dimensional percolation behavior. The highest ratio of dc to optical conductivity (σ_dc/σ_op) is observed to be ∼23.1, corresponding to sheet resistance of 69 Ω/sq at the 550-nm optical transmission of 80%, upon nitric acid treatment of the SWCNT films.     

Direct reduction of graphene oxide films into highly conductive and flexible graphene films by hydrohalic acids

We report a simple but highly-effective hydrohalic acid reducing method to reduce graphene oxide (GO) films into highly conductive graphene films without destroying their integrity and flexibility at low temperature based on the nucleophilic substitution reaction. GO films reduced for 1 h at 100 °C in 55% hydroiodic (HI) acid have an electrical conductivity as high as 298 S/cm and a C/O ratio above 12, both of which are much higher than films reduced by other chemical methods. The reduction maintains good integrity and flexibility, and even improves the strength and ductility, of the original GO films. Based on this reducing method, a flexible graphene-based transparent conductive film with a sheet resistance of 1.6 kΩ/sq and 85% transparency was obtained, further verifying the advantage of HI acid reduction.     

High performance of carbon nanotubes/silver nanowires-PET hybrid flexible transparent conductive films via facile pressing-transfer technique

To obtain low sheet resistance, high optical transmittance, small open spaces in conductive networks, and enhanced adhesion of flexible transparent conductive films, a carbon nanotube (CNT)/silver nanowire (AgNW)-PET hybrid film was fabricated by mechanical pressing-transfer process at room temperature. The morphology and structure were characterized by scanning electron microscope (SEM) and atomic force microscope (AFM), the optical transmittance and sheet resistance were tested by ultraviolet-visible spectroscopy (UV-vis) spectrophotometer and four-point probe technique, and the adhesion was also measured by 3M sticky tape. The results indicate that in this hybrid nanostructure, AgNWs form the main conductive networks and CNTs as assistant conductive networks are filled in the open spaces of AgNWs networks. The sheet resistance of the hybrid films can reach approximately 20.9 to 53.9 Ω/□ with the optical transmittance of approximately 84% to 91%. The second mechanical pressing step can greatly reduce the surface roughness of the hybrid film and enhance the adhesion force between CNTs, AgNWs, and PET substrate. This process is hopeful for large-scale production of high-end flexible transparent conductive films.     

A scalable fabrication of highly transparent and conductive thin films using fluorosurfactant-assisted single-walled carbon nanotube dispersions

A single-walled carbon nanotube (SWCNT)/sodium dodecylbenzenesulfonate (NaDDBS) dispersion containing a fluorosurfactant was bar-coated in order to produce a highly transparent and conductive thin film (TCF) for large-area application. The addition of a small amount of fluorosurfactant greatly reduced the surface tension of the CNT-dispersed solution, which produced a uniform film of CNTs by preventing agglomeration of CNTs during the drying process, and, furthermore, rendered bar-coating as the most practical large-area coating technique for a CNT solution. This particular fluorosurfactant addition maintained a CNT dispersion in the solution, which led to a dramatic improvement in the wettability of the CNT dispersion on the substrate towards high-performance TCF films. The thickness of the CNT films was controlled simply by adjusting the amount of CNTs in the solution. Moreover, the addition of a waterborne polymethyl methacrylate (PMMA) binder to the CNT dispersion improved the adhesion of the CNT films on a glass substrate.     

Preparation and characterization of highly conductive transparent films with single-walled carbon nanotubes for flexible display applications

Dense, aligned single-walled carbon nanotubes (SWCNTs) were obtained by nitric acid treatment and the subsequent removal of metal impurities by HCl. The highly purified SWCNTs were dispersed with sodium dodecyl sulfate in order to obtain a stabilized suspension for spray coating on flexible polyethylene terephthalate (PET) substrate. The low sheet resistance of the resulting thin conductive film on the PET substrate was due to the interconnecting networks of highly purified SWCNT bundles. These bundles formed strong crisscross networks of nanotubes clustered together with well defined channels, thus improving the electrical and optical properties of the film. Its sheet resistance varied from 956 to 472 Ω/square with 85% optical transmittance at a wavelength of 550 nm. The films may be potential candidates for flexible display applications.     

Highly flexible and thermal conductive films of graphene/poly(naphthylamine) and applications in thermal management of LED devices

In 5G era, integration and miniaturization of electronic components lead to increasing challenges in thermal management. Materials with high thermal conductivity and flexibility are strongly desired for dissipating heat locally generated in such devices. Due to its extraordinary thermal conducting performance, graphene has been exhibiting great potential in thermal management. In this work, composite films based on graphene oxide and poly-naphthylamine (gGO/PNA) with enhanced thermal conducting performance have been achieved by employing poly (naphthylamine) (PNA) as repairing additives to restore topological defects of graphene oxide (GO). Specifically, gGO/PNA films are prepared with a facile operation of vacuum filtration followed by an elevated temperature treatment. The optimal thermal conductivity (κ) of gGO/PNA reaches to 1016.03 W m⁻¹ K⁻¹, 31.3% enhancement over that of the pristine graphene one. The thermal conducting performance test demonstrates the film an efficient heat-dissipation ability from a heat-generating LED bulb. Furthermore, the film exhibits excellent flexibility, making it survival from a 1000-cycle bending test. This finding may promote the development of heat-spreading materials and their applications in thermal management of highly integrated electronics.     

Solution casting of transparent and conductive carbon nanotubes/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) films under a magnetic field

Transparent and conductive composite films of carboxyl functionalized single-walled carbon nanotubes and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) were deposited on various substrates under the influence of a magnetic field. It was demonstrated that the sample dewetting under the magnetic field enhances the conductivity of the dried films. Highly transparent films (∼88%) were obtained with a low sheet resistivity of ∼90 Ω/sq. The magnetic field assisted deposition method proposed here suggests scalable production of flexible and cost-effective transparent electronics.     

Fabrication of a large-area,flexible and color-neutral single-wall carbon nanotube:sodium dodecylbenzene sulfonate/poly-(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) transparent conductive film having a new conduction mechanism

Flexible transparent conductive films (TCFs) are vital to promote the development of flexible and foldable devices including touch panels, displays, organic solar cells, etc. We have prepared a large-area, flexible, and color-neutral single-wall carbon nanotube:sodium dodecylbenzene sulfonate/poly-(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (SWCNT:SDBS/PEDOT:PSS) composite TCF on a poly(ethylene terephthalate) substrate by a spray coating method. The TCF has a sheet resistance of 178 Ω sq⁻¹ with 85% transmittance at 550 nm. The light transmission characteristics of the films can be tuned by changing the mass fraction of SWCNTs. When the mass fraction of SWCNTs is higher than 4 wt.%, the original blue tint of the TCFs has disappeared. More importantly, we find that SDBS may play a more important role than the SWCNT network in improving the electrical conductivity of the films by acting as a secondary dopant of PEDOT:PSS, which is different from the traditional understanding and existing explanation about the conduction mechanism of PEDOT:PSS-based composite films.     

Preparation of transparent and conducting carbon nanotube/N-hydroxymethyl acrylamide composite thin films by in situ polymerization

The preparation of optically transparent and electrically conductive composite thin films composed of multi-walled carbon nanotube (MWCNT) and poly N-hydroxymethyl acrylamide were fabricated by a simple in situ polymerization technique. The film displays conductivities up to 10³ S/m depending on the MWCNT loading and a sheet resistance as low as 53 Ω/□ for an optical transparency greater than 95% at 550 nm. The dispersability characteristics of the suspension were determined by measuring specific surface charge, rheological behavior and UV–vis spectra.     

Fabrication of super-stretchable and electrical conductive membrane of spandex/multi-wall carbon nanotube/reduced graphene oxide composite

Hybrid conductive fillers (hybrids) are prepared through simultaneous chemical reduction of the graphene oxide and acid-treated multi-wall carbon nanotube in the presence of hydrazine. Subsequently, the thermoplastic spandex-based composite membranes with different hybrids contents are fabricated by solution casting method. At 20 wt% loading of hybrids, the membrane displays both super-stretchability (387% of elongation at break) and good electrical conductivity (49.5 S cm^?1). Further investigations of the electromechanical behaviour show that the strain sensitivity is dependent on hybrids content. Therefore, the as-prepared spandex/hybrids composite membranes are promising materials for the fabrication of wearable electronics and stretchable energy storage/conversion devices.     

Frictional dependence of graphene and carbon nanotube in diamond-like carbon/ionic liquids hybrid films in vacuum

The use of graphene and multi-walled carbon nanotubes (MWCNTs) additives as lubricants has received considerable interest because of their excellent mechanical and frictional properties. Given their structural differences, both carbon nano-additives are expected to have different synergistic effects at various conditions (from boundary to mixed lubrication). For applications in space, the tribological properties of graphene and MWCNTs additives in diamond-like carbon/ionic liquids hybrid films in different lubricating states at high vacuum were compared. The wear surfaces, transfer films, wear debris, and microstructures of the hybrid films were analyzed via Raman spectroscopy, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The results showed that MWCNTs and graphene present the different nano-scale tribological mechanisms and produce different lubricating effect on the hybrid films at different lubricating states.     

Preparation of transparent and conductive thin films of carbon nanotubes using a spreading/coating technique

This study demonstrates large-scale purification of single-walled carbon nanotubes (SWCNTs) and preparation of transparent and conductive thin films of carbon nanotubes using a spreading/coating technique. Wire-bar, which wraps a stainless steel wire around a shaft, is useful equipment to spread inks on flexible materials. Coating of purified SWCNT film thickness was tunable depending not only on the wire-bar thickness but also on the SWCNT concentration in dispersion. The SWCNT concentration in the dispersion increased concomitantly with the increase of the C₆₀(OH)_n concentration. These two factors, wire-bar thickness and SWCNT concentration in dispersion, control the film’s conductivity and transparency.     

Microstructure and tribological properties of in-situ TiC-C/Cu nanocomposites synthesized using different carbon sources (graphite,carbon nanotube and graphene) in the Cu-Ti-C system

For the first time, TiC-C/Cu nanocomposites were fabricated from a mixture of Cu, Ti and C powders by the use of different carbon sources (graphite, carbon nanotube (CNT) and graphene) through two-step high energy mechanical milling and in-situ synthesis by annealing, to study the effect of carbon source on phases formation and tribological properties. The results showed the presence of Cu as the matrix, TiC and unreacted carbon phases in the microstructure of sintered samples, and relatively uniform distribution of the reinforcement phase in the copper matrix was obtained. With the decrease of carbon source size, the density of sintered nanocomposites was reduced. It was revealed that using the CNT and graphene as carbon sources results in finer TiC nanoparticles, which considerably improves the tribological properties of the nanocomposite. Using CNT and graphene as carbon sources led to 15% and 49% reduction in wear volume loss and 16% and 6% decrease in friction coefficient respectively, in compassion to using graphite.     

The strain sensing and thermal–mechanical behavior of flexible multi-walled carbon nanotube/polystyrene composite films

The strain sensing and thermal–mechanical behaviors of well dispersed multi-walled carbon nanotube/polystyrene (MWCNT/PS) composite films with different wt.% of carbon nanotubes were analyzed. The thermal–mechanical properties are studied using a dynamical mechanical analyzer and the results give their storage modulus (E′) and loss modulus (E″) as a function of temperature. We found an increase in E′ of up to 122% at 80 °C for a 6 wt.% MWCNT/PS composite compared to PS. The glass transition temperature increased significantly with an increase in MWCNTs concentration. The strain sensing behavior of the films is measured by applying an axial load over film which is attached to a brass specimen. The composite films exhibit excellent strain sensing behavior for different MWCNT contents. The result shows that an electromechanical response of the composite films varies linearly with applied strain even at high strains.     

Field emission properties of Cu/multiwalled carbon nanotube composite films fabricated by an electrodeposition technique

Composite films of Cu and multiwalled carbon nanotubes (MWCNTs) were fabricated by an electrodeposition technique, and their field emission properties were examined. Commercially available MWCNTs with various diameters (60–150 nm) were used. The microstructure of the composite films was analyzed by scanning electron microscopy and the field emission properties were measured using a diode-type system. Cu/MWCNT composite films with homogeneous dispersion of MWCNTs were fabricated using each type of MWCNT. Bare MWCNTs were present on the surface of the composite films and the ends of the protruding tips were fixed by the deposited copper matrix. The composite films produced clear emission currents and the corresponding Fowler–Nordheim (F–N) plots showed that these were field emission currents. The turn-on electric field tended to decrease with decreasing MWCNT diameter. A light-emitting device incorporating the Cu/MWCNT composite film as a field emitter was fabricated, and its light-emitting properties were investigated. Light emission with a brightness of around 100 cd m^?2 was observed for approximately 100 h.