Multiwalled Carbon Nanotube Thin Films Research Articles

Carbon-based thin films as a suitable alternative to metallized films for the preparation of radioactive sources

A new method for radionuclide labeling by the use of graphene thin films was previously presented. In this work, a comparison among low energy radioactive sources supported on carbonaceous thin films on polyvinyl chloride-polyvinyl acetate copolymer (VYNS), based on the use of aqueous solutions is investigated as a feasible alternative to the traditional metallized films avoiding the downside of the loss of many broken films. Graphene-based materials were prepared by both oxidation-exfoliation-reduction and direct graphite exfoliation routes. In addition, multiwalled carbon nanotubes (MWCNTs) thin films were also evaluated. The stability of both carbonaceous materials aqueous dispersions were studied by using ionic and non-ionic surfactants. Solid carbon-based materials were characterized by X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) whereas the colloidal nature of the aqueous dispersions was verified by the measurement of Tyndall effect and the morphology of thin films was evaluated by Scanning Electron Microscopy (SEM). 55Fe solutions were used to prepare the radioactive sources on the thin films by quantitative drop deposition. The quality of spectra was measured in a pressurized proportional counter. Results showed a resolution higher than 0.9 keV for all the tested sources. However, MWCNT-based along with non-surfactant sources presented non-adequate escape peaks and low energy tails. On the contrary, all the graphene-based sources prepared using surfactants to stabilize aqueous solutions presented an energy resolution comparable to that of the metallized source while offering notable advantages in terms of cost efficiency and reliability of the as-prepared supports.

THz near-field intensity distribution imaging in the 0.3 THz band using a highly sensitive polarization CMOS image sensor using a 0.35 μm CMOS process

In this paper, we propose a low-disturbance and fast terahertz (THz) near-field intensity distribution imaging method. The THz detector is fabricated using an oriented multiwalled carbon nanotube (CNT) thin film and a LiNbO3(LN) crystal to the thin film is attached. The CNT absorbs and converts THz waves into heat, and the birefringence change of the LN crystal owing to the heat is used. The birefringence change was measured with high sensitivity using a dual-polarizer configuration of a uniform polarizer and a polarization CMOS image sensor. The fabricated THz detector is a low-disturbance method because it does not use metal, and it can measure the THz distribution in the plane all at once, which is faster than the antenna scanning method. Using the proposed method, we have successfully imaged the THz near-field intensity distribution emitted from an impact avalanche and transit time diode oscillating at 0.278 THz.

Direct formation of carbon nanotube wiring with controlled electrical resistance on plastic films

We have developed a simple method to fabricate multi-walled carbon nanotube (MWNT) wiring on a plastic film at room temperature under atmosphere pressure. By irradiating a MWNT thin film coated on a polypropylene (PP) film with a laser, a conductive wiring made of a composite of MWNT and PP can be directly fabricated on the PP film. The resistance of MWNT wiring fabricated using this method were ranging from 0.789 to 114 kΩ/cm. By changing the scanning speed of laser, we could fabricate various regions with different resistances per unit length even within a single wiring. The formation mechanism of the MWNT wiring with tunable resistance was discussed from both experimental results, such as microscopic structural observation using cross-sectional scanning electron microscopy and microscopic Raman imaging, and simulation results, such as heat conduction in the film during local laser heating. The results suggest that the MWNT wiring was formed by PP diffusion in MWNT at high temperature. We also demonstrated that excess MWNTs that were not used for wiring could be recovered and used to fabricate new wirings. This method could be utilized to realize all-carbon devices such as light-weight flexible sensors, energy conversion devices, and energy storage devices.

Feasibility of wear reduction for soft nanostructured thin film through enhanced elastic recoverability and contact stress relief

This work shows that a soft, thin film comprising randomly aligned carbon nanotubes (CNTs) can reduce surface wear more effectively than a homogeneous thin film because of enhanced elastic recoverability and contact stress relief originating from its mesh structure. To investigate the wear characteristics of the mesh structure compared to those of the homogeneous thin film, multi-walled CNTs (MWCNTs) and diamond-like carbon (DLC) thin films were prepared to conduct nanoscale tribological experiments using the atomic force microscopy (AFM). The MWCNT thin film showed unmeasurably low wear compared with the DLC thin film under a certain range of normal load. To demonstrate the wear reduction mechanism of the MWCNT thin film, its indentation and frictional behaviors were assessed. The indentation behavior of the MWCNT thin film revealed repetitive elastic deformation with a wide strain range and a significantly lower elastic modulus than that of the DLC thin film. The permanent deformation of the MWCNT thin film was observed through frictional experiments under relatively high normal load conditions. These results are expected to provide insights into the design of highly wear-resistant surfaces using nanostructures.

Investigating the Impact of Doping Ratios on the Optical Features of Poly (Methyl Methacrylate)

Using spin-coating method, the poly (methyl methacrylate) (PMMA)/multi-walled carbon nanotubes (MWCNTs) thin films are prepared. The optical features from the band gap, refractive index and optical connectivity are studied. The gap was calculated from the UV-Vis spectra. The superficial structure is examined through the use of the atomic force microscope (AFM) to investigate the dispersion of MWCNT within the polymer matrix.

The influence of zinc phthalocyanine on the formation and properties of multiwalled carbon nanotubes thin films on the air–solid and air–water interface

The influence of zinc phthalocyanine (PC) on the formation and properties of multiwalled carbon nanotube (MWCNT) Langmuir films was studied. The mixtures of PC and MWCNT at different concentrations were prepared and used to obtain films on the air–solid and air–water interface. The excess Gibbs energy, excess areas and the area fraction covered by the mixtures components were determined for mixed systems at various surface pressures. For the mass fractions of MWCNT lower than 0.9, the interactions between the mixture components were attractive, while for the MWCNT mass fractions higher than 0.9, they were repulsive. Analysis of the area fractions and fluorescence images revealed three stages of filling the MWCNT films with PC. In the first stage, the PC filled the area between the MWCNT and started to form inclusions in the MWCNT film structure. In the second stage, gradual increase in the PC inclusion size with increasing PC concentration was observed. In the third stage, continuous PC films were formed. These observations were further confirmed by the calculation of electrical percolation threshold.

Generation of stable mode-locked fiber laser based MWCNTs in 1.5-µm waveband

Pulses fiber laser had been successfully generated by using multi-wall carbon nanotubes thin film saturable absorber at room temperature. The saturable absorber is incorporated into a ring laser cavity. A stable Kelly sidebands mode-locked pulse spectrum with 1561.3 nm wavelength at the pump power of 86.8 mW. The repetition rate and pulse width of 12.3 MHz and 0.51 picosecond, respectively. A stable operation is observed for an hour at room temperature. These simple and reliable system features offer interesting research study especially in mode-locked pulse generation at 1.5 μm waveband.

In situ crack mapping of large-scale self-sensing concrete pavements using electrical resistance tomography

This study aims to validate the large-scale application of self-sensing concrete in airport runway pavements and to use electrical resistance tomography (ERT) for characterizing spatially distributed damage during accelerated pavement testing. This self-sensing concrete not only retains the expected mechanical properties of typical airport pavements, but it can also sense deformation and strain. First, sensing properties were encoded in concrete pavements by modifying the cement-aggregate interface with multi-walled carbon nanotube (MWCNT) thin films. MWCNT thin films were spray-coated onto dried fine and coarse aggregates, and the film-coated aggregates were directly used for concrete casting. Second, an ERT algorithm was implemented for spatial conductivity mapping of self-sensing concrete pavements. Extensive laboratory tests were conducted on different sized specimens for characterizing their spatial damage detection performance. Last, a full-scale concrete airport pavement slab was cast with self-sensing concrete patches at locations where damage was expected. A heavy vehicle simulator was employed for accelerated pavement testing to induce cracks, while ERT measurements were collected at periodic intervals during testing. The results confirmed that the severities, locations, and patterns of cracks could be identified from the reconstructed ERT conductivity maps. Furthermore, subsurface damage features were identified prior to these cracks propagated and became visible on the surface.

The effect of different multiwall carbon nanotubes concentration on morphology, optical, and electrical properties used as flexible anode

Spin coating technique has been used to deposit various concentration of Multi-wall carbon nanotube (MWCNTs) thin films on flexible substrate of polyethylene terephthalate (PET) as electrode, the study shows the effect of (1, 2, 3 mg/ml) concentration of (MWCNTs) thin films, by AFM, optical and electrical measurements which is indicate that the best concentration is2 mg/ml according to (2, 3D) images, which shown widespread and regular spread of CNTs, low absorption of wavelengths (400, 550, 700 nm) at low concentrations, and compatible increase of responsivity with increased current for PET-MWCNTs/MEH-PPV:MWCNTs/AL as photodetector device.

The Effect of Multi-walled Carbon Nanotubes and Reduced Graphene Oxide Doping on the Optical and Photovoltaic Performance of Ag2BiI5-Based Solar Cells

Due to the nontoxic and air-stable nature of bismuth-based photovoltaic materials, they are suitable materials to replace lead-based perovskite ones. In this research, the influence of doping with multi-walled carbon nanotubes (MWCNTs) and reduced graphene oxide (RGO) on the structural, morphological, and optical properties of silver bismuth iodide (SBI) compounds was investigated. Structural characterizations revealed the formation of the hexagonal structure in SBI thin films, and also showed improvement in the surface morphology in the MWCNT and RGO-doped thin films. All absorber layers had a relatively high absorption coefficient above 104 cm−1 in the visible range, and the bandgap values varied between ∼ 1.83 eV and 2.04 eV. Also, we fabricated SBI-based solar cells, and their photovoltaic performance was studied. For the solar cell employing pure silver bismuth iodide, a photo conversion efficiency (PCE) of 0.44% was achieved. The inclusion of MWCNTs and RGO dopants in the SBI thin film PCE increased the device performance, and the highest PCE of 1.61% and 1.32% was obtained, respectively. The stability of the solar cells was also investigated under the environmental conditions. Results show that after 30 days, devices preserved about 90% of their efficiency.

Determination of arsenic (V) in cannabis oil by adsorption on multiwall carbon nanotubes thin film using XRF technique

Many heavy metals, such as arsenic, mercury, and lead, can be introduced into the cannabis plant—and therefore the flowers—through cultivation in contaminated soil. We report a novel and selective method for the preconcentration and determination of As(V) in cannabis oil through their adsorption on a tertiary amine, ALIQUAT 336- Multiwalled carbon nanotubes, determinations were made directly on the solid by X-Ray Fluorescence spectrometry, which reduces the number of reagents used and minimizes the sample handling. The method here in described combines the advantages of solid phase extraction with the benefits of any X-Ray Fluorescence method associated to the large areas held by the carbon nanotubes, which make them a promising solid sorbent for preconcentration procedures.A high preconcentration factor was achieved for a very low volume of sample. The enrichment factor was calculated after considering that the thin film obtained from the 5 mL solution of 1 mg L-1 of As(V) has a real thickness of 0.04 mm and a final diameter of 16.7 mm, so that the volume deposited on the pellet was 0.0088 cm3 and the preconcentration factor can be calculated to be 104.

Convective self-assembled processed multiwall carbon nanotube thin films for semi-transparent microelectronic applications

A self-assembled convective setup was utilized to manufacture multiwall carbon nanotube (MWCNTs) thin films at room temperature on glass substrates. The extracted X-ray diffraction patterns revealed that the manufactured MWCNTs films have a crystal structure with observed peaks at 2θ = 26.61°, 43.45°, and 53.1°, and are related to the (002), (101) and (004) planes, respectively, confined to graphite of a hexagonal structure. The Raman spectroscopic behavior of the samples was investigated, and the intensity of the D:G band ratio was utilized to estimate the crystallinity degree of carbon in the MWCNTs samples (~ 0.81). The SEM images of the films showed that the topographical properties of the films are retained and densely packed, confirming a network distribution. Briefly, the films are significantly influenced to have a rod-like shape of the MWCNTs. The analyzed HR-TEM images of the films have a uniform structure with cylindrical-shaped MWCNTs. When the energy of the probe waves was ~ 3.95 eV, the reflected and transmitted probe wave vanished. The fabricated MWCNTs films may play an essential role as a real absorber with an absorption coefficient α(hυ = 3.5 eV) ≈ 5.36 × 105 cm−1. The manufactured MWCNTs films are found to support the interpretation of a direct bandgap; the evaluated energy gap is $${E}_{g}^{OPT}$$ =3.748 eV as a result of the carbon atoms impurities; and a direct transition at low energy is estimated by $${E}_{g}^{Onset}=0.59 \mathrm{e}\mathrm{V}$$ . The performance of the fabricated films is predicted and analyzed by the complex parameters: dispersion, n*, optical dielectric, e*, and optical conductivity, σ*. The manufactured MWCNTs provide a pathway to fabricate a broadband stable behavioral absorptive layer for photovoltaic devices and optical switching optoelectronics (at low reflectance and transmittance with high absorbance).

Self-heating and electrical performance of carbon nanotube-enhanced cement composites

This work hypothesizes that mixing carbon nanotubes with cement improves the thermal and electrical properties of bulk cement composites. To test this, two different methods of combining cement and dispersed multi-walled carbon nanotubes (MWCNTs) were considered. In the first method, cement composites were produced by adding a dispersion of MWCNTs to cement. In the second, MWCNT-based thin films were spray-coated and integrated with cement to produce cement composites. A third group of specimens was produced using both MWCNT dispersions and MWCNT thin films. The experimental parameters considered were the mixing method, MWCNT concentrations, number of curing days, and voltages applied. Furthermore, field emission scanning electron microscopy revealed that the MWCNTs were evenly dispersed within the composites and formed a percolated network. In addition, X-ray diffraction analysis confirmed that the products formed during hydration of the composites (i.e., C-H and C-S-H) were the same as those generated using ordinary mortar. Upon testing these mortar-based specimens, it was found that the cement composites formed using a combination of MWCNT dispersions and MWCNT-based films exhibited the highest heating performance and lowest electrical resistance. Finally, thermal imaging showed that increased MWCNT concentrations during specimen casting led to a corresponding increase in their surface temperature upon voltage application.

Environment-friendly paper-based flexible pressure sensors with carbon nanotubes and liquid metal

We have proposed and fabricated resistive-type flexible pressure sensors composed of multi-walled carbon nanotube thin films, liquid metal droplets, sponge rubber, and paper. The pressure sensor detects external pressure in the range of tens of kilopascals. The resistance change was found to be approximately 70% when a pressure of 100 kPa was applied. The sensor operation showed good reproducibility under cyclic applied pressure. The simple sensor structure and environment-friendly materials allow the sensor to be easily disassembled into its components, which are reusable and combustible.

Percolation-amplified infrared sensitivity in titanium oxide-multi-walled carbon nanotube composite films

Titanium dioxide (TiO2)-multi-walled carbon nanotube (MWCNT) thin films were prepared and studied systematically for the effects of the concentration of MWCNTs on the electro-optical properties. Result shows that the addition of MWCNTs not only improves the optical absorption and electrical conductivity, but also reduces the 1/f noise of the films. Percolation phenomenon is observed at MWCNT concentrations of 0.20–0.25 wt%. In this concentration range, the composite films exhibit an abrupt rise of the temperature coefficient of resistance value (−2.93% K−1) and large general thermal parameter, both of which are desirable for applications in uncooled infrared detectors.

Deposition of Pd nanoparticles on MWCNTs: Green approach and application to hydrogen sensing

A facile and green method is proposed for the deposition of palladium nanoparticles (NPs) on multiwalled carbon nanotube (MWCNT) thin films. Reduction and deposition of Pd NPs are achieved via oxidation of methanol on CNT supports under UV light irradiation. The proposed process yields uniformly distributed and highly crystalline Pd NPs on MWCNTs. When Pd-MWCNT thin films are exposed to hydrogen gas, H2 is adsorbed onto the Pd surface and spills over, followed by stable C–H bond formation via chemisorption of H atoms on the MWCNTs, resulting in increased electrical resistance due to widening of the band gap. As an electrical sensor, Pd-MWCNTs can detect H2 gas within a concentration range of 0.0004–80% in air at room temperature with a rapid response and quick recovery. Importantly, the proposed photochemical method can be extended to deposition of Pd NPs on thin films of other materials.

MWCNTs patterning by thermally enhanced and confined evaporation for transparent and conductive thin film

Conductive and transparent thin film structures are useful in flexible electronics. In this paper, we report multi-walled carbon nanotubes (MWCNTs) patterning into gradient regular patterns with large area of about several square centimeters on silicon or wafer glass slide via thermally enhanced evaporative self-assembly under wedge-shaped geometric confinement. The morphologies, electrical and optical properties of the MWCNTs thin film were characterized. The findings reveal that the conductance would increase with depositing times, meanwhile the transparency would decrease. The resistance of the grid patterning films of MWCNTs has a nearly linear relation to the transmittance in a relatively large range. The MWCNTs can be easily transferred to flexible substrate such as PET films or an adhesive tape. In comparison, SWCNTs could hardly be deposited into stripes or grid patterns, but the continuous thick films and discontinuous thin films could demonstrate better electrical and mechanical performance.

Unusual conductivity temperature dependence of multiwalled carbon nanotube thin film

The Multiwalled carbon nanotube (MWCNT) thin films has been formed on PVC substrate using Langmuir-Blodgett technique as highly promising material for optoelectronics. The layers were annealed at 367 K which has led to significant electrical resistance decrease. The resistance of the obtained layer was investigated in wide temperature range showing the dependence significantly different from that observed for the layers created using CNTs of smaller diameter. The reason of the unusual conductivity temperature dependence is most probably the difference in thermal expansion coefficients of MWCNTs and the polymer combined with relatively high stiffness of the nanotubes with such large diameter.

Printable low-cost and flexible carbon nanotube buckypaper motion sensors

Wearable technology, which features affordable and flexible sensors integrated into fabrics and garments to detect both deliberate and subtle body movements, will reshape the way we approach self-rehabilitation, physical training, and many high-dexterity tasks by harvesting data about the wearer's activity. Metallic and semi-conductor sensors are currently the most commercially viable sensors. Metallic sensors designs are low profile and flexible; however, they are limited by low sensitivity and complex manufacturing. Semi-conductor sensor designs are highly sensitive but limited by their rigidity and brittle nature. Wearable sensors that are low profile, flexible, and sensitive to micro-strains are highly desired. We have developed a printable and low profile strain sensor using multi-wall carbon nanotube thin films called buckypaper (MWCNT-BP). Our tests indicate that the buckypaper sensors are 77% more sensitive than similar sensor designs. This paper explains the low-cost printing technology and displays the sensors' performance after integration into a fabric glove.

Rapid fabrication and photovoltaic performance of Pt-free carbon nanotube counter electrodes of dye-sensitized solar cells

We fabricated uniform multiwalled carbon nanotube (MWCNT) thin films on fluorine-doped tin oxide (FTO) glass substrates with controlled thickness by an easy and versatile spin-coating process (SCP). Aqueous dispersions of MWCNTs were dropped on the FTO glass substrates and spin-coated to form uniform MWCNT thin films, which were then used as the catalytic medium on the counter electrodes (CEs) of dye-sensitized solar cells (DSCs). For the DSC with an optimized MWCNT-thin-film thickness coated on the CE, the short circuit current density (Jsc) was more than that of the conventional Pt-based DSC (10.97±0.13mAcm−2 vs 9.58±0.17mAcm−2), while its power conversion efficiency (PCE) was comparable to that of conventional DSC (∼4.41±0.14% and ∼4.69±0.22%, respectively). This suggests that the accumulation of MWCNTs on the CE increases the interfacial contact area between the MWCNTs and liquid electrolyte in the DSC, allowing the rapid reduction of I3−. Simultaneously, it decreases the charge transfer resistance owing to rapid electron transport through the MWCNT medium with its relatively high electrical conductivity. Thus, the precisely controlled rapid accumulation of MWCNT thin films by the SCP on the CEs of DSCs is a very promising approach for replacing the expensive Pt metal that is currently used in DSC applications.