Single-walled Carbon Nanotube Network Films Research Articles

Infrared Light-Emitting Diodes Based on Chirality-Sorted Carbon Nanotube Films.

An important goal in carbon nanotube optoelectronics is to achieve a high-performance near-infrared light source. But there are still many challenges such as the purity of single-walled carbon nanotube (SWCNT) chirality, nonradiative defects, thin-film quality, and device structure design. Here, we realize infrared light-emitting diodes (LEDs) based on chirality-sorted (10, 5) SWCNT network films, which operate at a low bias voltage and emit at a telecom O band of 1290 nm. Asymmetric palladium (Pd) and hafnium (Hf) contacts are used as electrodes for hole and electron injection, respectively. However, the large Schottky barrier at the interface of the SWCNTs and the Hf electrode, primarily resulting from the polymer wrapped on the nanotube surface during the sorting process, leads to inefficient electron injection and thus a low electroluminescence efficiency. We find that the efficiency of electron injection can be improved by the local doping of the nanotubes with dielectric layers of YOX-HfO2, which reduces the Schottky barrier at the SWCNT/Hf interface. Accordingly, the (10, 5) SWCNT film-based LED achieves an external quantum efficiency of larger than 0.05% without any optical coupling structure. With further improvement, we expect that such an infrared light source will have great application potential in the carbon nanotube monolithic optoelectronic integrated system and on-chip optical interconnection, especially in the field of short-distance optical fiber communications and data center.

Ionic Dopant-Encapsulating Single-Walled Carbon Nanotube Films with Metal-Like Electrical Conductivity.

Heavy doping is inevitable for utilizing single-walled carbon nanotubes for wiring. However, the electrical conductivity of their films is currently as low as one tenth of the films made from typical metal pastes. Herein we report on metal-comparable electrical conductivity from single-walled carbon nanotube network films. We use ionic liquids and crown ether complexes for p-type and n-type doping, respectively. The encapsulation of counterions into carbon nanotubes promotes the conductivities in the range of 7000 S cm-1 , approximately ten times larger than those of undoped films.

Effects of Tube Diameter and Length on Transparent Conductivity of Single-Walled Carbon Nanotube Network Films

The effects of single-walled carbon nanotube (SWCNT) structures on the transparent conductivity of their network films have been investigated. SWCNTs with different average tube diameters of 1.3 nm, 1.7 nm, and 2.0 nm were processed at the same conditions. Then unit structure characterization was performed by determining the tube diameter, length, bundle thickness, and so on, before the fabrication of SWCNT network films by the filtration and transfer method using the dispersions. The result of the transparent conductivity measurements clearly showed better performance with a decrease in the tube diameter: that is, narrower SWCNTs form narrow bundles, and their dense network results in an increase in the total length of conduction pathways in the SWCNT network films with high transparency. Furthermore, the figure of merit and the percolation exponent for the transparent conductivity obtained by using the data fitting of the percolation model were also discussed in terms of the tube diameter and length.

Evaluation of Surface Cleaning Procedures in Terms of Gas Sensing Properties of Spray-Deposited CNT Film: Thermal- and O₂ Plasma Treatments.

The effect of cleaning the surface of single-walled carbon nanotube (SWNT) networks by thermal and the O2 plasma treatments is presented in terms of NH3 gas sensing characteristics. The goal of this work is to determine the relationship between the physicochemical properties of the cleaned surface (including the chemical composition, crystal structure, hydrophilicity, and impurity content) and the sensitivity of the SWNT network films to NH3 gas. The SWNT networks are spray-deposited on pre-patterned Pt electrodes, and are further functionalized by heating on a programmable hot plate or by O2 plasma treatment in a laboratory-prepared plasma chamber. Cyclic voltammetry was employed to semi-quantitatively evaluate each surface state of various plasma-treated SWNT-based electrodes. The results show that O2 plasma treatment can more effectively modify the SWNT network surface than thermal cleaning, and can provide a better conductive network surface due to the larger number of carbonyl/carboxyl groups, enabling a faster electron transfer rate, even though both the thermal cleaning and the O2 plasma cleaning methods can eliminate the organic solvent residues from the network surface. The NH3 sensors based on the O2 plasma-treated SWNT network exhibit higher sensitivity, shorter response time, and better recovery of the initial resistance than those prepared employing the thermally-cleaned SWNT networks.

High Conductivity and Ultraviolet Band Transparency of Single-Walled Carbon Nanotube Films Bridged with Gold Nanoparticles

We report the fabrication of single-walled carbon nanotube (SWNT) films bridged with gold nanoparticles (Au NPs) that exhibit high conductivity and transparency in the ultraviolet (UV) region. The film was obtained by annealing the Au films deposited onto quartz substrate by e-beam evaporation, followed by dip coating in SWNT-dispersed solution under different dipping cycles. The optical tranmittance spectrum of the film thus obtained shows a transmittance between 80.2 and 85% in the wavelength range of 350-600 nm. In addition, the SWNT film bridged with Au NPs shows an electrical conductivity of 1.72 mA at 5 V, which is about six-times higher than that of the SWNT film without Au NPs (0.29 mA). These results confirm that the Au NPs enhance the electrical conductivity of the SWNT network films, without compromising the optical transmittance.

Ultrafast Separation of Emulsified Oil/Water Mixtures by Ultrathin Free‐Standing Single‐Walled Carbon Nanotube Network Films

As an alternative to polymer membranes, ultrathin free-standing single-walled carbon-nanotube network films are used to realize oil/water separation with ultrahigh flux. The films with tunable thickness of the tens of nanometer scale can effectively separate both micrometer and nanometer-sized surfactant-free and surfactant-stabilized water-in-oil emulsions with a flux 2-3 orders of magnitude higher than commercial filtration membranes with similar separation performance.

High-performance biosensors based on enzyme precipitate coating in gold nanoparticle-conjugated single-walled carbon nanotube network films

Single-walled carbon nanotube (SWCNT) network films with high network density were prepared by vacuum-filtering a suspension of SWCNTs, and used as a host of enzyme precipitate coating of glucose oxidase (EPC-GOx). EPC-GOx was fabricated into the SWCNT network films in a two-step process of enzyme precipitation and crosslinking. High GOx loading in a form of EPC expedited the generation of electrons while the good connectivity of conductive SWCNTs in the network structure increased the electron transfer rate. According to amperometric measurements, the sensitivities of GOx/SWCNT electrodes, governed by both generation and transfer of electrons, were significantly enhanced by filling up the open pores of SWCNT films with the EPC-GOx when compared to the approaches of covalent-attachment (CA) and enzyme coating (EC) with no step of enzyme precipitation. For example, the sensitivities of CA, EC and EPC-GOx were 0.039, 0.140, and 5.72 μA mM −1, respectively. High sensitivity of EPC-GOx was maintained under iterative uses for 10 days. The deposition of gold nanoparticles into SWCNT films has resulted in high-performance glucose sensors with a remarkable sensitivity of 24.5 μA mM −1, which can be explained by further expedited electron transfer due to deposited gold nanoparticles.

Modulating Conductivity, Environmental Stability of Transparent Conducting Nanotube Films on Flexible Substrates by Interfacial Engineering

We have characterized the previously undescribed parameters for engineering the electrical properties of single-walled carbon nanotube (SWCNT) films for technological applications. First, the interfacial tension between bare SWCNT network films and a top coating passivation material was shown to dictate the variability of the films' sheet resistance (R(s)) after application of the top coating. Second, the electrical stability of the coated SWCNT films was affected by the mismatch between the CTE of the supporting substrate and the SWCNT network film. An upshift in the Raman G-band spectrum of SWCNTs on bare PET suggested that compressive strain was induced by the CTE mismatch after heating and cooling. These findings provide important guidelines for the choice of substrate and passivation coating materials that promote environmental stability in SWCNT-based transparent conductive films.

Effect of Au Doping and Defects on the Conductivity of Single-Walled Carbon Nanotube Transparent Conducting Network Films

We examined the electrical conductivity and transmittance of six types of SWNT network films, developed for potential use in transparent conductive films, to investigate the effect of Au doping on single-walled carbon nanotube (SWNT) defects: (i) SWNT network films without Au doping (as-produced (AP-SWNTs), purified (P-SWNTs), and cut (C-SWNTs)) and (ii) Au-doped films of AP-SWNTs (Au/AP SWNTs), P-SWNTs (Au/P-SWNTs), and C-SWNTs (Au/C-SWNTs). The density of SWNT network films was varied systematically by controlling the SWNT concentration and mediating defect formation. The electrical conductivity of each SWNT film was found to be significantly enhanced upon Au doping, with a negligible loss of optical transmittance. The effects of Au doping differed depending on the type of nanotube network present: the electrical conductivity of Au/C-SWNTs was found to be similar to that of Au/AP-SWNTs for a given transmittance, whereas the conductivity of C-SWNTs is much lower than that of the AP-SWNTs prior to Au dopi...