Multiwalled Carbon Nanotube Thin Films Research Articles

Exploiting the hierarchical morphology of single-walled and multi-walled carbon nanotube films for highly hydrophobic coatings.

Self-assembled hierarchical solid surfaces are very interesting for wetting phenomena, as observed in a variety of natural and artificial surfaces. Here, we report single-walled (SWCNT) and multi-walled carbon nanotube (MWCNT) thin films realized by a simple, rapid, reproducible, and inexpensive filtration process from an aqueous dispersion, that was deposited at room temperature by a dry-transfer printing method on glass. Furthermore, the investigation of carbon nanotube films through scanning electron microscopy (SEM) reveals the multi-scale hierarchical morphology of the self-assembled carbon nanotube random networks. Moreover, contact angle measurements show that hierarchical SWCNT/MWCNT composite surfaces exhibit a higher hydrophobicity (contact angles of up to 137°) than bare SWCNT (110°) and MWCNT (97°) coatings, thereby confirming the enhancement produced by the surface hierarchical morphology.

Multiwalled carbon nanotube thin films prepared by aerosol deposition process for use as highly efficient Pt-free counter electrodes of dye-sensitized solar cells

In this study, transparent and catalytic multiwalled carbon nanotube (MWCNT) thin films with controlled thickness were fabricated using a simple and conventional multiple nozzle-based aerosol deposition process (ADP). MWCNTs were homogeneously dispersed in deionized water via surfactant treatment, and the MWCNT-dispersed aqueous solution was then aerosolized and deposited on fluorine-doped tin oxide glass substrates to form MWCNT thin films. The characteristics of MWCNTs, degree of MWCNT dispersion stability in the aqueous solution, and morphology and light transmittance of the prepared MWCNT thin films were systematically examined. Finally, the prepared MWCNT thin films were used as the counter electrodes (CEs) of dye-sensitized solar cells (DSSCs). For comparison purposes, the photovoltaic performance of DSSCs composed of MWCNT thin-film CEs was compared to that of reference DSSCs composed of conventional Pt thin-film CEs. The results showed that the power conversion efficiency of DSSCs composed of critical amount of MWCNTs coated on CEs was almost equal or slightly higher than that of conventional Pt-based DSSCs. Thus, it can be concluded that the ADP-assisted precisely controlled accumulation of transparent and catalytic MWCNT thin films on the CEs of DSSCs is a very promising approach for replacing the expensive Pt metal that is currently used in DSSC industries.

Optical properties of carbon nanotube thin films in subterahertz frequency regime

Multiwalled carbon nanotube (MWCNT) thin films deposited on fused quartz substrates are characterized by continuous wave subterahertz free space technique using a vector network analyzer (VNA). The scattering (S) parameters are measured by a VNA in the frequency range of 220–325 GHz (G-band) and 325–500 GHz (Y-band). The complex refractive index is extracted with the help of Nicholson–Ross–Weir method. The transmission and absorption of the thin films are also studied. VNA offers a good spectral resolution and a dynamic range of 60–70 dB around 500 GHz. The experimental technique and material parameter extraction procedures are described. The refractive index, transmission and absorption coefficient obtained for MWCNT thin films are plotted and the results are discussed. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1895–1898, 2014

Ag Ion Irradiation of Multi-Walled Carbon Nanotubes Modified ITO Induces Electrocatalytic Effects

Energetic ion irradiation has been used as a tool to improve the electrocatalytic activity of multi-walled carbon nano tubes (MWCNTs) modified indium tin oxide (ITO). A thin film of MWCNTs was irradiated with Ag ions having energy of 120 MeV with fluences of 1x1012, 3x1012 and 1x1013 ions/cm2, using a palleteron accelerator. The structural differences between un-irradiated and irradiated thin films were characterized by SEM observation and energy dispersive x-ray analysis. The change in MWCNTs due to ion beam irradiation was determined by Raman spectroscopy. The effect of irradiation on the electrocatalytic activity was examined by voltammetric measurements on epinephrine and it was found that irradiation improved peak current response. The anodic peak current for epinephrine increased by ~10 times in the pH range 2.0 -10.0 over that for the original MWCNTs and the peak potential shifted to less positive values. The detection limit (3<sigma>/slope) and sensitivity for epinephrine for the pristine material were found to be 100 nM and 0.1086 <mu>A/<mu>M as compared to 2 nM and 0.998 <mu>A/<mu>M for the Ag ion beam irradiated MWCNT.

Tunable Carbon Nanotube Mesh Fabricated Via Surfactant Assisted Direct Deposition for High Performance Transparent Electrodes

This study involved the deposition of multi-walled carbon nanotubes (MWCNTs) onto plastic, polyethylene terephalate (PET), substrates. The MWCNTs were suspended in an aqueous solution via the assistance of an ionic surfactant, sodium dodecyl sulfate (SDS). The SDS/MWCNT complexes in solution were attracted to the PET substrate because of electrostatic forces that were demonstrated by contrasting poor coverage on glass substrates. The solutions were deposited onto the PET films and allowed to interact for different amounts of time resulting in films that had decreasing resistivity and transparency because of increasing thicknesses.The ratio of SDS to MWCNT to solvent, water in this case, was from an optimized MWCNT colloid study.1 The ratio used was 10:1:1000 respectively by weight. The excess surfactant was removed at different times using the spin coating technique. Films were then rinsed in water to remove excess surfactant caught in-between the nanotubes in the mesh and then dried in an oven.The best thin film had an average resistivity of 110 Ω/sq at 81% transmittance at 550 nm and a thickness of ± 2 um. Their performance is similar to indium tin oxide thin films as cathodes. The MWCNT and SDS composite thin films will be tested in optoelectronic applications such as solar cells and liquid crystal displays.References 1 Rastogi, R.; Kaushal, R.; Tripathi, S.; Sharma, A.; Kaur, I.; Bharadwaj, L. Comparative study of carbon nanotube dispersion using surfactants. 2008, J. Colloid Interface Sci. 328, 421-428. 2 Jo, J.; Jung, J.; Lee, J.; Jo, W. Fabrication of Highly Conductive and Transparent Thin Films from Single Walled Carbon Nanotubes Using a New Non-ionic Surfactant via Spin. 2010, ACS Nano. 4 (9), 5382-5388.

Sub‐THz characterisation of multi‐walled carbon nanotube thin films using vector network analyser

A vector network analyser is used to study the electrical properties of multi-walled carbon nanotube (MWCNT) thin films deposited on a fused quartz substrate in the sub-terahertz (THz) frequency ranges of 220-325 GHz (WR3.4) and 325-500 GHz (WR2.2). The experiment is performed in free space. The complex permittivity of the MWCNT thin films is extracted using the Nicholson-Ross-Weir method. The refractive index and conductivity are then determined from the extracted permittivity. The method is validated by comparison with values obtained using THz time-domain spectroscopy.

Conducting nano films based on multi-walled carbon nanotubes and poly(3,4-ethylene dioxy thiophene-poly(styrene sulfonate) for organic light-emitting diode

It is well known that multi-walled carbon nanotubes (MWCNTs) are an excellent nanomaterial. In this paper, the nanocomposite ultra-thin films were fabricated consisting of MWCNTs and poly (3,4-ethylene dioxy thiophene-poly(styrene sulfonate) (PEDOT-PSS) for organic light-emitting diode (OLED). The field-emission scanning electron microscopy (FESEM) images of MWCNTs thin films show that the diameter of MWCNTs are 10–30 nm and their length is 300–500 nm. Electrical and optical properties of the films are investigated and the sheet resistance can reach minimum value at 36.5 Ω sq−1 and the transparency of the film is about 80%. The current density–voltage (J–V) characteristics of the devices were also studied.

Terahertz electrical conductivity and optical characterization of composite nonaligned single- and multiwalled carbon nanotubes

We employed noncontact terahertz time-domain spectroscopy to investigate and com- pare the electrical/optical properties of nonaligned single-walled carbon nanotube and non- aligned multiwalled carbon nanotube thin films. Using Drude-Lorentz model together with the Maxwell Garnett effective medium theory, we determined the electrical conductivities from the extracted data of differential complex terahertz analysis in the frequency range of 0.1 to 2 THz. The results demonstrate that the conductivity of isotropic single-walled carbon nanotube thin film is almost two times larger compared to isotropic multiwalled carbon nanotube thin film due to the increased number of surface defects and the availability of mobile carriers. By using Drude-Lorentz model, the broadening optical density and conductivity can be studied at higher frequencies. © 2014 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.JNP.8

High-performance all-solid-state flexible micro-supercapacitor arrays with layer-by-layer assembled MWNT/MnO(x) nanocomposite electrodes.

In this study, we report on the fabrication of high performance planar-type flexible micro-supercapacitor (MSC) arrays using Au electrodes coated with a functionalized multi-walled carbon nanotube (MWNT) film and a layer of MWNT-COOH/MnOx nanoparticle (NP) composite on top. The MWNT thin film was formed via layer-by-layer (LbL) assembly of MWNTs functionalized with amine groups and MWNTs with carboxylic acid groups in water. The hydrothermally synthesized composite of MWNT-COOH/MnOx NPs was coated on top of the MWNT film (LbL-MWNT). The addition of MWNT-COOH/MnOx NP composite as a top layer enhanced the performance of the MSCs dramatically, resulting in a volumetric capacitance of 50 F cm(-3) at a scan rate of 10 mV s(-1) and a coulombic efficiency of ∼100%. By contrast, a volumetric capacitance of 3.6 F cm(-3) was obtained when using only the LbL-MWNT film. After repetitive operation up to ∼10(4) times, the capacitance remained at ∼88.3% of the original value. With a deliberate circuit design consisting of serially connected MSC arrays, various light-emitting diodes operating at different bias voltages could be lit. The MSC circuit fabricated on a polyethylene terephthalate (PET) film showed stable electrochemical properties upon 1000 cycles of bending deformation.

Transparent and conductive multi walled carbon nanotubes flexible electrodes for optoelectronic applications

Regarding their flexibility, transparency and their ability to conduct, the carbon nanotubes thin films has been a growing interest for applications in optoelectronics. This paper illustrates a process of fabrication for multiwalled carbon nanotubes (MWCNT) thin films on PET (polyethylene terephthalate) substrates to obtain flexible conductive electrodes. Actually, there are several processes to elaborate a flexible conductive electrode using carbon nanotubes, such as: (i) Direct deposition using spin coating, spraying, or incubation produces films, or (ii) deposition by vacuum filtration. In our experiments, we had adopted the deposition by vacuum filtration method to prepare our flexible electrodes using the PET substrate. The optimum result was achieved with a concentration of 1.2mg/ml, corresponding to a sheet resistance (Rs) of 180Ωcm−2 with optical transparence about 81% at 550nm. We will also demonstrate the usage of elaborated flexible conductive electrodes to fabricate organic diodes having the following structure: PET–MWCNTs/P3HT: PC70BM/Al.

Oxygen Plasma Functionalized Multiwalled Carbon Nanotube Thin Film as A pH Sensing Membrane of Extended-Gate Field-Effect Transistor

High-performance pH sening membranes of extended-gate field-effect transistors (EGFETs) composed only of oxygen-plasma-functionalized carbon nanotube thin films (CNTFs) are demonstrated. A large number of oxygen-containing functional groups are decorated on the sidewalls of carbon nanotubes (CNTs) after the oxygen plasma treatment. These functional groups act as the sensing sites and accurately respond to the ions of interest in different pH levels. Therefore, these functionalized CNTFs as the pH-EGFET sensing membranes can achieve a high voltage sensitivity of 56.8 mV/pH, a large voltage linearity of 0.9995, and a wide sensing range of pH 1-13. In addition, the oxygen-plasma-functionalized CNTFs also exhibit superior reliability with a small hysteresis voltage of 4.98 mV.

A high effect polymer-free covalent layer by layer self-assemble carboxylated MWCNTs films modified GCE for the detection of paracetamol

This work presents an excellent strategy to assemble a new carboxylic acid functionalized multi-wall carbon nanotubes (CMWCNTs) thin film via layer by layer (LBL) covalent bond by using ethylenediamine as an arm linker. Scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy were used to characterize the assembly process. Electrochemical studies indicated that the modified electrode possesses a remarkably electrocatalytic activity toward paracetamol at a lower potential compared with the bare glass carbon electrode (GCE), and without the need for redox mediators. The thickness of the film assembled CMWCNTs is easily controlled by changing the numbers of the cycles in the LBL assembly process, which also effectively tuned the electrocatalytic activity of the film toward paracetamol. The experiments result display that the six layers film performs the best electrocatalytic activity to paracetomol. The constructed electrode with six layers showed a good sensitivity of 2.293μAM−1cm−2 in the linear range of 1–200μM, and a detection limit of 0.092μM (S/N=3). Furthermore, the CMWCNTs film also showed good selectivity and excellent stability for the determination of paracetamol.

Electrophoretic deposition of graphene, carbon nanotubes and composite films using methyl violet dye as a dispersing agent

Cathodic electrophoretic deposition (EPD) of methyl violet (MV) was performed from aqueous solutions. The film microstructure and deposition mechanism were studied using scanning electron microscopy (SEM) and cyclic voltammetry (CV). MV allowed efficient dispersion of multiwalled carbon nanotubes (MWCNT) and graphene in aqueous suspensions. Thin films of MWCNT and graphene were obtained by cathodic EPD using MV as a charging, dispersing and film forming agent. The deposition yield was varied by variation of MV concentration in the suspensions and deposition voltage. The possibility to deposit both MWCNT and graphene using MV as a dispersing and charging agent allowed the fabrication of MWCNT–graphene composites by EPD. The film microstructures and advantages of cathodic EPD were discussed. The films were investigated for application in electrochemical supercapacitors (ES). Electrochemical investigation showed capacitive behavior of the films in 0.5M Na2SO4 electrolyte. The specific capacitance (SC) of ∼130Fg−1 was obtained at a scan rate of 2mVs−1, and the capacitance retention in the range of 2–100mVs−1 was ∼50%. The impedance spectroscopy data were in agreement with simulation results, obtained using equivalent circuit model. The composite films showed improved capacitive behavior compared to the films of individual components.

The effect of substrate pore size on the network interconnectivity and electrical properties of dropcasted multiwalled carbon nanotube thin films

Abstract

Detection of spatially distributed damage in fiber-reinforced polymer composites

This work describes a novel method of embedded damage detection within glass fiber–reinforced polymer composites. Damage detection is achieved by monitoring the spatially distributed electrical conductivity of a strain-sensitive multiwalled carbon nanotube thin film. First, thin films were spray-deposited directly upon glass fiber mats. Second, using electrical impedance tomography, the spatial conductivity distribution of the thin film was determined before and after damage-inducing events. The resolution of the sensor was determined by drilling progressively larger holes in the center of the composite specimens, and the corresponding electrical impedance tomography response was measured by recording the current–voltage data at the periphery of the monitored composite sample. In addition, the sensitivity to damage occurring at different locations in the composite was also investigated by comparing electrical impedance tomography spatial conductivity maps obtained for specimens with sets of holes drilled at different locations in the sensing area. Finally, the location and severity of damage from low-velocity impact events were detected using the electrical impedance tomography method. The work presented in this study indicates a paradigm shift in the available possibilities for structural health monitoring of fiber-reinforced polymer composites.

Chemically Derived Graphene Sheets Top Assembled Over Multi-Walled Carbon Nanotube Thin Film by Langmuir Blodgett Method for Improved Dual Field Emission

Graphene and carbon nanotubes are very much known as effective field emitter materials. However field emission applications with hybrid carbon nanostructures have mostly remained elusive so far. Here we report, top assembly of very thin layer of reduced graphene oxide (RGO) by Langmuir Blodgett method over a multi-walled carbon nanotubes (MWCNTs) thin film/ITO substrate to investigate the dual field emission property of the hybrid structure. The non-functionalized type of attachment in between the hybrid carbon nanostructures mainly due to van der Waals force of attraction ensured easy fabrication procedure. Evidence of uniform distribution of web like networks of very thin transparent RGO sheets top assembled over densely packed MWCNTs thin film was found from the field emission scanning electron microscopy analysis. The base layer conductivity was enhanced due to the incorporation of MWCNTs bottom layer over ITO and the former also additionally facilitated as emitter site pockets in between RGO planes. Finally, the RGO top assembly resulted in achieving significant improvement in current density and turn-on field in tandem with MWCNTs bottom layer bed making this hybrid system a much feasible candidate for future field emission (FE) based device applications.

Electrically conductive superhydrophobic octadecylamine-functionalized multiwall carbon nanotube films

Electrically conductive, superhydrophobic multiwall carbon nanotube (MWCNT) thin films were prepared by direct amination of MWCNTs with up to 14wt.% of octadecylamine (ODA) by vacuum filtration method. The ODA-functionalized MWCNT films exhibit a high water contact angle of 165° and electrical conductivity of 860S/m. The liquid–air–solid interface is directly observed from above the water droplet using an optical microscope. The observation indicates that the wettability state of the MWCNTs has changed from relatively hydrophilic to superhydrophobic state upon functionalization with ODA. The fundamental mechanisms responsible for the unusual combination of surface superhydrophobicity and high electrical conductivity of the MWCNT films are described and their implications are discussed.

Near-superhydrophobic behavior of multi-walled carbon nanotube thin films

Thin films of multi-walled carbon nanotubes created by standard drop and dry methodology are reported here to give water contact angles of ~138° accessing an intermediate region between smooth, apolar materials and superhydrophobic surfaces. Their near-superhydrophobic nature is attributed to hierarchical nanoscale roughness leading to the formation of Cassie–Baxter interfaces. While complete quantitative determination of surface energy parameters was prevented due to the porous nature of the films, the dispersive component of nanotube surface energy was found to be in the range of 39.1–47.8mJ/m2.

Optically transparent carbon nanowire thin film

Thin films of amorphous carbon nanowire (a-CNW) have been fabricated from crossed multi-walled carbon nanotube (MWCNT) thin film. The fabrication was done by means of ion beam irradiation on various substrates. It is found that the a-CNW thin films show electrical conduction behaviour, and electrical conductivity varies after annealing. In addition, the transmission spectra in the visible range reveal that the film has above 90% optical transmission. It can be ascribed to the fact that the decreased crystallinity of MWCNTs by ion beam irradiation has caused the incremental increase of optical transmission. We also report on a method for cutting or destroying a-CNWs using low-energy focused electron beam from a scanning electron microscope.

Effect of cross-linkable polymer on the morphology and properties of transparent multi-walled carbon nanotube conductive films

In this study, we fabricated optically transparent and electrically conductive multi-walled carbon nanotube (MWCNT) thin films using a spray-coating technique. The transparency and the electrical resistance of thin film are dependent on the nanotube content deposited on the polyethylene terephthalate (PET) substrate. Poly(acrylic acid) (PAA) and poly(N-vinyl pyrrolidone) (PVP) were used as adhesion promoters to improve MWCNT coating more significantly. The cross-linked polymer resulted in a superior bond between the MWCNTs and the substrates. The surface electrical resistance was significantly lower than the original sheet after nitric acid (HNO 3) treatment because of the removed surfactant and the increased interconnecting networks of MWCNT bundles, thus improving the electrical and optical properties of the films. Stronger interaction between the MWCNTs and the substrates resulted in lower decomposition of the polymer chain and less amounts of MWCNTs separated into the HNO 3 solution. The lower sheet electrical resistance of PVP/PAA-g-MWCNT conductive films on the PET substrate was because of a more complete conductive path with the cross-linked polymer than that without. Such an improved sheet of electrical resistance varied from 8.83 × 10 4 Ω/□ to 2.65 × 10 3 Ω/□ with 5.0 wt.% PVP/PAA-g-MWCNT sprayed on the PET after acid treatment.