Single-walled Carbon Nanotube Thin Films Research Articles

High-quality parallel patterning of carbon nanotube thin films by a pulsed laser beam

Single-walled carbon nanotube thin films solution-deposited on the glass substrate were directly patterned by a spatially-modulated pulsed laser beam (wavelength=355nm, pulse width=5ns) incident from the backside of the substrate. This method utilizes a ultrashort pulse-induced strong thermo-elastic force exerting on the film which plays a role to detach it from the substrate. The threshold energy density required for patterning was as low as 90mJ/cm2, making it possible to pattern over a few square centimeters by a single pulse with maximum energy of 180mJ. The irradiated regions of the film were clearly photoetched without leaving any residual nanotubes. High-fidelity patterns could be fabricated with a feature size of 35μm.

Effect of Ag ion irradiation on the performance of single-walled carbon nanotubes thin film modified Indium tin oxide sensor

Effect of Ag ion irradiation on the performance of single-walled carbon nanotubes thin film modified Indium tin oxide sensor

Metal/metal sulfide functionalized single-walled carbon nanotubes: FTO-free counter electrodes for dye sensitized solar cells

The use of single-walled carbon nanotubes (CNT) thin films to replace conventional fluorine-doped tin oxide (FTO) and both FTO and platinum (Pt) as the counter electrode in dye sensitized solar cells (DSSC) requires surface modification due to high sheet resistance and charge transfer resistance. In this paper, we report a simple, solution-based method of preparing FTO-free counter electrodes based on metal (Pt) or metal sulfide (Co(8.4)S(8), Ni(3)S(2)) nanoparticles/CNT composite films to improve device performance. Based on electrochemical studies, the relative catalytic activity of the composite films was Pt > Co(8.4)S(8) > Ni(3)S(2). We achieved a maximum efficiency of 3.76% for the device with an FTO-free counter electrode (Pt/CNT). The device with an FTO- and Pt-free (CoS/CNT) counter electrode gives 3.13% efficiency.

Optical gas sensing with dip-coated carbon nanotubes through the modulation of photoluminescence and optical absorption

Photoluminescence (PL) and optical absorption (OA) of single-wall carbon nanotube (CNT) thin films are shown to substantially change after exposure to NO2 or NH3 gas. These films prepared by dip-coating in surfactant-aided CNT dispersions consist of unbundled and well-exposed tubes; the former property enables the detection of PL, a task difficult for bundled CNTs, while the latter enlarges the effective surface area available for gas adsorption. The observed changes correspond well to those in electrical resistance, which are consistently explained by charge transfer between the CNTs and the gas molecules. Highly resolved spectral peaks in two-dimensional PL excitation contour maps and their changes induced by the gas exposure revealed that wider tubes are more sensitive to gas adsorption.

Solid‐state Bis‐hexahapto‐metal complexation of single‐walled carbon nanotubes

We report the effect of transition metal deposition on the conductivity of single‐walled carbon nanotube (SWNT) networks. The slow evaporation of small amounts of highly mobile transition metal atoms significantly reduces the resistance of SWNT thin films; we suggest that Cr, Fe, and Ti atoms form bis‐hexahapto complexes at the SWNT sidewalls, thereby bridging adjacent carbon nanotubes and reducing the inter‐nanotube junction resistance. Copyright © 2012 John Wiley & Sons, Ltd.

Carbon nanotube thin film pH electrode for potentiometric enzymatic acetylcholine biosensing

Carboxylated single-walled carbon nanotube thin-film (SWCNT-TF) is demonstrated as a pH electrode and a platform for enzymatic potentiometric acetylcholine biosensors. SWCNT is layer-by-layer assembled with a positively charged polyelectrolyte on the metal electrode. The open circuit potential on SWCNT-TF electrode is measured with reference to an Ag/AgCl electrode in various pH buffers. With the aid of acetylcholinesterase (AchE), acetylcholine (Ach) is successfully detected using the SWCNT-TF pH electrode that demonstrates Nernst potential of −43 mV/pH. AchE-modified electrode has a sensing resolution of 10 μM of Ach and sensitivity of 19 mV/decade. The SWCNT-TF pH electrode fabricated by layer-by-layer self-assembly may play an important role in micro/nanoscale electrochemical sensors.

Terahertz Characterization of Single-Walled Carbon Nanotube and Graphene On-Substrate Thin Films

In this paper, single-walled carbon nanotube (SWNT) thin films with thicknesses on the order of hundreds nanometers on glass substrates and a graphene thin film (2-3 layers) on a glass substrate are characterized via terahertz time-domain spectroscopy. The substrate permittivity is first characterized. The thin film is then treated as a surface boundary condition between the substrate and air. Using the uniform field approximation, the surface conductivities of these films are extracted. To improve accuracy, precise thickness of the sample substrate is calculated through an iteration process in both dielectric constant extraction and surface conductivity extraction. Uncertainty analysis of the measured thin-film properties is performed. The SWNT results show consistent surface conductivities for samples on different substrates and with different film thicknesses. The measured graphene terahertz conductivity is comparable to the values reported in the literature at dc and optical frequency. This characterization method has been successfully applied as a means to evaluate metallic content of SWNT samples to verify a metallic SWNT removing process using high-power microwave irradiation.

Ion Beam Bombardment Effect on Contacts in Solution-Processed Single-Walled Carbon Nanotube Thin Film Transistor

Effect of argon ion bombardment (AIB) on performance of solution-processed single-walled carbon nanotube (SWCNT) thin film transistor (TFT) has been investigated. AIB was applied to the source/drain contacts to reduce contact resistance. It was found that AIB enhances on-state current of TFT. Over 5 decades' on/off ratio is obtained by applying AIB. Results of transmission line method using metallic SWCNT clearly indicate that contact resistance between CNT network and Au electrode is reduced by the application of AIB.

Ion Beam Bombardment Effect on Contacts in Solution-Processed Single-Walled Carbon Nanotube Thin Film Transistor

Ion Beam Bombardment Effect on Contacts in Solution-Processed Single-Walled Carbon Nanotube Thin Film Transistor

Absorption spectra of high purity metallic and semiconducting single-walled carbon nanotube thin films in a wide energy region

Absorption spectra of high purity metallic and semiconducting single-walled carbon nanotubes separated by the density-gradient ultracentrifugation method have been measured in the wide energy region from 1 meV to 5 eV. In the high purity metallic nanotube sample, a strong and broad absorption band has been observed at 0.06 eV. This observation suggests that the optical properties of even high purity metallic nanotube bundles cannot be explained by the simple Drude conduction model. We discuss the origin of these absorption bands for metallic and semiconducting nanotube samples by considering the existence of a small energy gap in metallic nanotube bundles and plasmon resonance.

Transport Characterization of Chemically-Functionalized Single-Walled Carbon Nanotube Thin Film Transistor

The electronic transport properties of the thin film transistor (TFT) devices consisting of carboxyl-modified single-walled carbon nanotube (c-SWCNT) network are studied. This work is focused on the analysis of the effect of chemical treatment on the electronic transport properties from these devices. The c-SWCNT thin film transistor (c-SWCNT TFT) devices were fabricated by a directed assembly method based on electrostatic interaction between amino-functionalized substrate and c-SWCNTs. The electrical characteristics of c-SWCNT TFTs were measured at room temperature. From the Raman results and the transport characteristics of c-SWCNT TFT devices, the transport mechanism in these devices can be accounted that the deep levels arising from vacancy-adatom complex induced the changes in the electronic band structure of SWCNTs.

Single-Walled Carbon Nanotube Thin Film Transistor Fabricated Using Solution Prepared with 9,9-Dioctyfluorenyl-2,7-diyl–Bipyridine Copolymer

Single-Walled Carbon Nanotube Thin Film Transistor Fabricated Using Solution Prepared with 9,9-Dioctyfluorenyl-2,7-diyl–Bipyridine Copolymer

Single-Walled Carbon Nanotube Thin Film Transistor Fabricated Using Solution Prepared with 9,9-Dioctyfluorenyl-2,7-diyl–Bipyridine Copolymer

Performance of thin film transistor (TFT) whose channel is fabricated by using a solution process of single-walled carbon nanotube (SWCNT) has been studied. SWCNT solution is prepared by using 9,9-dioctyfluorenyl-2,7-diyl–bipyridine (PFO–BPy) copolymer as solubilizer. Over 4 decades' on/off ratio is obtained by using drop-coating at room temperature without any further optimization. Other solubilizers are chosen as control groups to measure the on/off ratio of SWCNT TFT to investigate effects of the use of PFO–BPy. Results suggest that thick SWCNT network should be uniformly established at the channel region and the channel is required to be formed with well-separated SWCNTs.

Anti-scratch and transparency properties of transparent conductive carbon nanotube films improved by incorporating polyethoxysiloxane

Transparent conductive films of single-walled carbon nanotubes (SWCNTs) were fabricated by a simple method to significantly enhance anti-scratch and transparency properties by the incorporation of polyethoxysiloxane (PES). The reasons for changes in the mechanical properties and transmittance were investigated through the reflection property and morphology of thin films. With the incorporation of PES, the sheet resistance of the SWCNT thin film remained unchanged after the anti-scratch test. It was found that the transmittance of the thin films suddenly increased when the thickness of the PES layer was ca 100 nm. Although the PES incorporation resulted in a slight increase in the sheet resistance, the experimental results revealed that the sheet resistance of the SWCNT thin films with PES was lower than that of films without PES for the same transmittance due to the increase of the transmittance caused by the PES incorporation. We have demonstrated that the sheet resistance was halved at a transmittance of ∼86% due to PES incorporation. SWCNT thin films with PES showed better electrical properties than those without PES after a bend test.

Ink-jet printed thin-film transistors with carbon nanotube channels shaped in long strips

The present work reports on the development of a class of sophisticated thin-film transistors (TFTs) based on ink-jet printing of pristine single-walled carbon nanotubes (SWCNTs) for the channel formation. The transistors are manufactured on oxidized silicon wafers and flexible plastic substrates at ambient conditions. For this purpose, ink-jet printing techniques are developed with the aim of high-throughput production of SWCNT thin-film channels shaped in long strips. Stable SWCNT inks with proper fluidic characteristics are formulated by polymer addition. The present work unveils, through Monte Carlo simulations and in light of heterogeneous percolation, the underlying physics of the superiority of long-strip channels for SWCNT TFTs. It further predicts the compatibility of such a channel structure with ink-jet printing, taking into account the minimum dimensions achievable by commercially available printers. The printed devices exhibit improved electrical performance and scalability as compared to previously reported ink-jet printed SWCNT TFTs. The present work demonstrates that ink-jet printed SWCNT TFTs of long-strip channels are promising building blocks for flexible electronics.

High-performance local back gate thin-film field-effect transistors using sorted carbon nanotubes on an amino-silane treated hafnium oxide surface

Wafer-scale fabrication and characterization of local back gate semiconducting nanotube thin-film transistors (SN-TFTs) are reported in this paper. The local back gate voltage of the corresponding SN-TFT controls the individual transistor switching. In order to achieve high performance, a high-k dielectric material is employed as a gate oxide and this helped to achieve low-voltage operations, much steeper sub-threshold voltage swings and higher transconductance values. A simple procedure to deposit a high-density single-walled carbon nanotube thin film on an amino-silane-treated hafnium oxide (HfOX) surface is suggested such that a good density of nanotubes is realized without degrading the device on–off current ratio and mobility values. The density of the nanotubes achieved on the silanized HfOX surface is about 40–45 nanotubes µm−2. SN-TFTs exhibit an excellent p-type output characteristic with distinct linear and saturation regions. Local back gate SN-TFTs exhibit an on–off current ratio exceeding 104 and a steep sub-threshold slope of 400 mV/decade. SN-TFTs achieve a maximum current density of 13 μA µm−1, an average threshold voltage of −0.5 V, a maximum normalized transconductance of 18.5 μS µm−1 and exhibit a maximum carrier mobility of 60.6 cm2(Vs)−1.

Patterned Single-Wall Carbon Nanotube Transparent Conducting Films for Liquid Crystal Switching Electrodes

We have fabricated transparent and electrically conductive single-wall carbon nanotube (SWCNT) thin films for liquid crystal switching electrodes. The SWCNT film had a sheet resistance of 91.02 Ω/□ and a transmittance of 92.33% at 550 nm. Our CNT-based transparent conducting film (TCF) patterning technique is a combination of photolithography and O2 plasma etching. We were able to pattern CNT-TCFs with a high resolution, and as small as 4 µm, and to fabricate them with various shapes and patterns. Our CNT-TCFs were used to successfully switch liquid crystal cells with 100 µm and 15 mm line widths.

Layer-by-Layer Self-Assembly of Single-Walled Carbon Nanotubes with Amine-Functionalized Weak Polyelectrolytes for Electrochemically Tunable pH Sensitivity

The layer-by-layer (LbL) assembly of carboxylated single-walled carbon nanotubes (SWCNT) is demonstrated to tune the electrochemical pH sensitivity of thin-film devices. The positively charged amine containing weak polyelectrolyte (wPE) is used as a counter species to control the proximal ions. The LbL assembly process is monitored by the quartz crystal microbalance, which results in the linear growth of a multilayer. The amount adsorbed is strongly dependent on the surface charge of previously deposited species. However, the thickness of the multilayer is determined by both the amount adsorbed and the coiling of polyelectrolyte chains. Indeed, electrical and structural characteristics of the (wPE/SWCNT) multilayer thin film are obtained according to the acid dissociation constants of amino groups in wPE. The electrochemical pH sensitivity in the physiological range demonstrates the effects of both charge carrier doping/trapping and proximal ions on the conductance of the SWCNT multilayer. Although doping/trapping shows the decreasing conductance, the proximal ion effect reveals the increasing conductance with pH in the basic region as a result of the p-type semiconducting nature of SWCNTs and the ability of wPE to capture hydrogen ions. This work sheds light on the applicability of nanostructured and/or engineered functional thin films of SWCNTs as chemical and biological sensors.

A pure single-walled carbon nanotube thin film based three-terminal microelectromechanical switch

The electrical and physical properties of pure single-walled carbon nanotube thin films deposited through a layer-by-layer-self-assembly process are discussed. The film thickness was proportional to the number of dipping cycles. The film resistivity was estimated as 2.19×10−3 Ω cm after thermal treatment processes were performed. The estimated specific contact resistance to gold electrodes was 6.33×10−9 Ω m2 from contact chain measurements. The fabricated three-terminal microelectromechanical switch using these films functioned as a beam for multiple switching cycles with a 4.5 V pull-in voltage. This switch is believed to be a promising device for low power digital logic applications.

Single-Walled Carbon Nanotube Thin Film Gas Sensors Controlled by Diffusion

The electrical and gas sensing properties of mat-type thin films fabricated by the packing of single-walled carbon nanotubes are investigated. The responses of the sensors with various thicknesses or resistances are measured, and the behavior is explained by a diffusion model. The successful explanation of the sensor response using the diffusion model suggests that the mat-type structure of compacted carbon nanotubes can be treated as a porous medium for gas sensor applications.