Aligned Carbon Nanotube Thin Films Research Articles

A flexible, multifunctional, active terahertz modulator with an ultra-low triggering threshold

Flexible, multifunctional, active THz modulators with ultra-low triggering threshold were developed by aligned carbon nanotube thin films coated with VO2. These active THz modulators find applications in THz communication and THz imaging.

Effect of constructive rehybridization on transverse conductivity of aligned single-walled carbon nanotube films

Alignment of densely packed single-walled carbon nanotubes (SWNTs) largely preserves the extraordinary electronic properties of individual SWNTs in the alignment direction, while in transverse direction the films are very resistive due to large energy barriers for tunneling between adjacent SWNTs. We demonstrate that chromium atoms inserted between the sidewalls of parallel SWNTs effectively coordinate to the benzene rings of the nanotubes via hexahapto bonds that preserve the nanotube-conjugated electronic structure and serve as a conduit for electron transfer. The atomically interconnected aligned SWNTs exhibit enhanced transverse conductivity, which increases by ∼2100% as a result of the photoactivated organometallic functionalization with Cr. The hexahapto mode of bonding the graphitic surfaces of carbon nanotubes with transition metal atoms offers an attractive route to the reversible chemical engineering of the transport properties of aligned carbon nanotube thin films. We demonstrate that a device fabricated with aligned SWNTs can be reversibly switched between a state of high electrical conductivity (ON) by light and low electrical conductivity (OFF) by applied potential. This study provides a route to the design of novel nanomaterials for applications in electrical atomic switches, optoelectronic and spintronic devices.

Multi-property enhancement of aligned carbon nanotube thin films from floating catalyst method

The carbon nanotube (CNT) thin film synthesized by the floating catalyst method has attracted increasing attention because of the easy fabrication process and promising mass production at low cost. However, the limited morphology-controlled structure and the loose CNT arrangement make CNT films show relatively low mechanical and electrical properties. In this work, highly dense CNT films with controllable density have been successfully fabricated by a fast two-step post treatment technique combining mechanical condensation and acid treatment. Multiple fracture mechanisms have been identified and analyzed to explain the mechanical performance of these CNT films, including the load transfer efficiency between CNTs, alignment and waviness of CNT films, as well as the effects of CNT qualities. Benefited from the stronger intertube interaction and better CNT quality, the combined post treatment method is found to have dramatically enhanced the mechanical and electrical properties of the CNT films, with tensile strength up to 243±16MPa (by 101%), modulus up to 2.5±0.1GPa (by 32%) and electrical conductivity up to 4990±636S/cm (by 254%) compared to the as-prepared ones. This work proposes a route to fabricate high-quality CNT films on a large scale as promising multifunctional engineering materials.

Aligned Carbon Nanotube Thin Films from Liquid Crystal Polyelectrolyte Inks.

Single walled carbon nanotube thin films are fabricated by solution shearing from high concentration sodium nanotubide polyelectrolyte inks. The solutions are produced by simple stirring of the nanotubes with elemental sodium in dimethylacetamide, and the nanotubes are thus not subject to any sonication-induced damage. At such elevated concentrations (∼4 mg mL(-1)), the solutions exist in the liquid crystal phase and during deposition this order is transferred to the films, which are well aligned in the direction of shear with a 2D nematic order parameter of ∼0.7 determined by polarized absorption measurements. Compared to similarly formed films made from superacids, the polyelectrolyte films contain smaller bundles and a much narrower distribution of bundle diameters. After p-doping with an organic oxidizer, the films exhibit a very high DC electrical to optical conductivity ratio of σ(DC)/σ(OP) ∼ 35, corresponding to a calculated DC conductivity of over 7000 S cm(-1). When very thin (T550 ∼ 96%), smooth (RMS roughness, R(q) ∼ 2.2 nm), and highly aligned films made via this new route are used as the front electrodes of carbon nanotube-silicon solar cells, the power conversion efficiency is almost an order of magnitude greater than that obtained when using the much rougher (R(q) ∼ 20-30 nm) and less conductive (peak σ(DC)/σ(OP) ∼ 2.5) films formed by common vacuum filtration of the same starting material, and having the same transmittance.

Effect of oxygen plasma treatment on horizontally aligned carbon nanotube thin film as pH-sensing membrane of extended-gate field-effect transistor

The high-performance pH-sensing membrane of extended-gate field-effect transistors (EGFET) composed of high-conductivity horizontally aligned carbon nanotube thin films (HACNTFs) after oxygen plasma treatment is successfully demonstrated. The 10-µm-wide catalytic metal lines with 60 µm interspace produced CNT vertical plates, and the plates were mechanically pulled down and densified to form HACNTFs. A large amount of oxygen-containing functional groups are decorated on the CNTs after the oxygen plasma treatment. These functional groups act as the sensing sites and respond to the H+ or OH− ions in solutions with different pH values. Therefore, these functionalized HACNTFs as pH-EGFET-sensing membranes can achieve a high voltage sensitivity of 40 mV/pH and high current sensitivity of 0.78 µA1/2/pH. Moreover, large linearity of 0.998 is measured in a wide sensing range from pH 1 to 13. These results reveal that the oxygen plasma treatment is an effective way to improve the CNT-sensing characteristics in pH-EGFET sensors.

Growth of primary motor neurons on horizontally aligned carbon nanotube thin films and striped patterns

Objective. Carbon nanotubes (CNTs) are attractive for use in peripheral nerve interfaces because of their unique combination of strength, flexibility, electrical conductivity and nanoscale surface texture. Here we investigated the growth of motor neurons on thin films of horizontally aligned CNTs (HACNTs). Approach. We cultured primary embryonic rat motor neurons on HACNTs and performed statistical analysis of the length and orientation of neurites. We next presented motor neurons with substrates of alternating stripes of HACNTs and SiO2. Main results. The neurons survived on HACNT substrates for up to eight days, which was the full duration of our experiments. Statistical analysis of the length and orientation of neurites indicated that the longest neurites on HACNTs tended to align with the CNT direction, although the average neurite length was similar between HACNTs and glass control substrates. We observed that when motor neurons were presented with alternating stripes of HACNTs and SiO2, the proportion of neurons on HACNTs increases over time, suggesting that neurons selectively migrate toward and adhere to the HACNT surface. Significance. The behavior of motor neurons on CNTs has not been previously investigated, and we show that aligned CNTs could provide a viable interface material to motor neurons. Combined with emerging techniques to build complex hierarchical structures of CNTs, our results suggest that organised CNTs could be incorporated into nerve grafts that use physical and electrical cues to guide regenerating axons.

Surface modifications of aligned carbon nanotube thin films by Argon‐ion sputtering

AbstractTo use carbon nanotubes (CNTs) as anode material for the solid‐state thin‐film Li‐ion rechargeable battery, the tubes are preferred to be aligned perpendicular to a substrate and the CNT thin film to have a smooth surface. Using an Ar‐ion sputtering technique, we carried out the surface modifications of the CNT thin film prepared by the SiC surface decomposition method. In order to evaluate the surface modification, the surface and cross section of the modified CNT film were investigated by field‐emission scanning electron microscopy and atomic force microscopy. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Evaluation of aligned carbon nanotube thin film modified by an Argon-ion sputtering method

In order to apply carbon nanotubes (CNTs) as the anode materials of a solid-state Li-ion secondary battery, the surface modifications of the CNT thin film formed by the SiC surface decomposition method were carried out by the Ar-ion sputtering method. Then, we observed the CNT film by field emission scanning electron and measured the Raman scattering spectra of the CNT film in order to evaluate the effect of Ar-ion bombardments on the CNT film.

Fabrication of Directionally Aligned Carbon Nanotube Thin Films on Solid Surfaces Using Chemical Patterns

We propose a simple fabrication process of directionally aligned single-walled carbon nanotube (SWCNT) thin films. This process consists of dropping of a highly dispersed SWCNT suspension followed by its drying. We used a substrate surface on which hydrophilic and hydrophobic patterns are formed by chemical processes. A SWCNT suspension dropped on the hydrophobic areas is transferred to the hydrophilic areas in the early stage of the drying. During the drying, the SWCNTs in the suspension are self-aligned by the surface tension. When the degree of hydrophilicity on the hydrophilic areas is too large, deposition of the SWCNTs on small hydrophilic areas is blocked by the repulsive force owing to hydration between the hydrophilic substrate and the SWCNT surfaces. We demonstrated that narrow line patterns of the SWCNT thin films can be fabricated by controlling the hydrophilicity on the hydrophilic areas on the substrate. [DOI: 10.1380/ejssnt.2010.207]

Aligned carbon nanotube thin films for DNA electrochemical sensing

Carbon nanotubes are interesting materials for DNA electrochemical sensing due to their unique electric properties: high surface area, fast heterogeneous electron transfer, and electrochemical stability. In this work aligned Carbon NanoTube (CNT) thin films were designed and tested as candidate platforms for DNA immobilization and for the development of an electrochemical genosensor. The films were prepared by Chemical Vapor Deposition (CVD) using acetylene and ammonia as precursor gases and nickel particles as catalyst. A preliminary electrochemical characterization was performed using cyclic voltammetry since, so far, these films have been used only for gas sensing. The surfaces were then covalently functionalized with a DNA oligonucleotide probe, complementary to the sequence of the most common inserts in the GMOs: the Promoter 35S. The genosensor format involved the immobilization of the probe onto the sensor surface, the hybridization with the target-sequence and the electrochemical detection of the duplex formation. Careful attention was paid to the probe immobilization conditions in order to minimize the signal due to non-specifically adsorbed sequences. For the detection of the hybridization event both label-free and enzyme-labelled methods were investigated. In case of the enzyme-labelled method a target concentration at nanomolar level can be easily detected, with a linear response from 50 nM to 200 nM, whereas the label-free method showed a linear response between 0.5 μM and 10 μM. The reproducibility was 11% and 20% with the enzyme-labelled method and the label-free method, respectively. The batch-to-batch reproducibility of the different sensors was also evaluated.

A deeper understanding of the photodesorption mechanism of aligned carbon nanotube thin films by impedance spectroscopy

The photoelectrical properties of aligned carbon nanotube (CNT) thin films deposited by pulsed plasma enhanced chemical vapor growth were probed through impedance spectroscopy. We found that photodesorption strongly depends on the polar impurities adsorbed on the CNT surface, the details of which led to a fundamental understanding of how light stimulates molecular desorption on nanotubes. The total film impedance increased dramatically upon illumination under ambient conditions and then slowly recovered after the light was turned off. These results are consistent with the light inducing desorption of molecular oxygen from CNTs. From the Fourier transform infrared (FTIR) transmission spectra of the as-grown nanotubes, large amounts of OH, CH 2 and CH 3 functional groups were detected. The surface structure performed by Raman and FTIR spectroscopy after thermal annealing at 350 °C indicates fewer structural defects and the loss of the OH functional group. With these results and equivalent circuit modelling, the release of the trapped OH polar molecule was confirmed to be a dominant light molecular desorption mechanism.