Fabrication and characterization of thin films of single-walled carbon nanotube bundles on flexible plastic substrates

A convenient method to obtain patterns of films of single-walled carbon nanotubes (SWNT) bundles on flexible plastic is described. Using the Line Patterning method SWNT films of thickness ranging from approximately 300-1500 nm can be obtained from aqueous surfactant-supported dispersions of chemically purified SWNT bundles synthesized by the pulsed-laser ablation method. These films are strongly adherent and are competitive in performance with commercially available films of indium-tin-oxide (ITO) on plastics. For example, an approximately 1500 thick film of SWNT on poly(ethylene terephthalate) (PET) shows a surface resisitvity of approximately 80 Omega/sq, optical transparency >80%, and robust flexibility. Unlike ITO/PET, films of SWNT/PET can be folded and bent to a crease without cracking. The simple techniques involoved in obtaining these films (i.e., those without requiring lithography or ink-jet printing) could help facilitate the rapid fabrication of transparent, flexible electronic devices, heralding what promises to be a new approach towards the development of next-generation optoelectronic devices.     

Structurally programmed capillary folding of carbon nanotube assemblies

We demonstrate the fabrication of horizontally aligned carbon nanotube (HA-CNT) networks by spatially programmable folding, which is induced by self-directed liquid infiltration of vertical CNTs. Folding is caused by a capillary buckling instability and is predicted by the elastocapillary buckling height, which scales with the wall thickness as t(3/2). The folding direction is controlled by incorporating folding initiators at the ends of the CNT walls, and the initiators cause a tilt during densification which precedes buckling. By patterning these initiators and specifying the wall geometry, we control the dimensions of HA-CNT patches over 2 orders of magnitude and realize multilayered and multidirectional assemblies. Multidirectional HA-CNT patterns are building blocks for custom design of nanotextured surfaces and flexible circuits.     

Fabrication of porous carbon nanotube network

We used the spin-coating method combined with ultrasonic atomization as a continuous, one-step process to generate a two-dimensional honeycomb network that was constructed from pure multi-walled carbon nanotubes.     

Direct fabrication of single-walled carbon nanotube macro-films on flexible substrates

We employed a floating chemical vapor deposition technique and applied a liquid (solution)-free precursor system for the fabrication of single-walled carbon nanotube macro-films on various flexible substrates from metallic foils to polymer films.     

Fabrication and electroactive responsive behavior of shape–memory nanocomposite incorporated with self‐assembled multiwalled carbon nanotube nanopaper

A novel shape–memory nanocomposite that exhibits electrical actuation capabilities was fabricated by incorporating a conductive multiwalled carbon nanotube (MWCNT) nanopaper into shape–memory polymer matrix. The self‐assembled MWCNT nanopaper was made on hydrophilic polycarbonate membrane. This process was based on well‐defined dispersion of the nanosized individual MWCNT and controlled traditional pressure vacuum deposition procedure. The self‐assembled MWCNTs in the nanopaper provided a percolating conductive network with a large interfacial area. It not only offered a high electrical conductivity but also simultaneously enhanced recovery speed by electrically resistive heating, with increasing the content of MWCNT nanopaper in nanocomposite. Copyright © 2011 John Wiley & Sons, Ltd.     

Creation of hierarchical carbon nanotube assemblies through alternative packing of complementary semi-artificial beta-1,3-glucan/carbon nanotube composites

Much attention has been focused on exploiting novel strategies for the creation of hierarchical polymer assemblies by the control of the assembling number or the relative location among neighboring polymers. We here propose a novel strategy toward the creation of "hierarchical" single-walled carbon nanotube (SWNT) architectures by utilizing SWNT composites with cationic or anionic complementary semi-artificial beta-1,3-glucans as "building blocks". These beta-1,3-glucans are known to wrap SWNTs helically, to create one-dimensional superstructural composites. If the cationic composite is neutralized by an anionic composite, a well ordered SWNT-based sheet structure was created. Transmission electron microscopy (TEM) observation revealed that this sheet structure is composed of highly-ordered fibrous assemblies of SWNTs. This suggests that the cationic and anionic composites are tightly packed through electrostatic interactions. Moreover, both of the final assembly structures are readily tunable by adjusting the cation/anion ratio. The self-assembling modulation of functional polymers is associated with the progress in ultimate nanotechnologies, thus enabling us to create numerous functional nanomaterials. We believe, therefore, that the present system will extend the frontier of SWNT research to assembly chemistry including "hierarchical" superstructures.     

Electrochemical genosensing properties of gold nanoparticle–carbon nanotube hybrid

We have investigated the electrochemical genosensing properties of gold nanoparticle–carbon nanotube hybrid. Thiolated oligonucleotide probes and mercaptohexanol were self-assembled onto the Au–CNT hybrid. The hybridization events of target oligonucleotides are monitored using electrochemical impedance spectroscopy, cyclic voltammetry and a.c. voltammetry techniques. A redox-active mediator is used to detect the oxidation of guanine residues. The as-fabricated genosensor is able to differentiate between complementary and mismatched hybridizations, relying on the oxidation current of the guanine residues mediated via .     

Templated synthesis of single-walled carbon nanotube and metal nanoparticle assemblies in solution

Carbon nanotube (CNT) and metal nanoparticle (NP) assemblies are conjugated nanosystems with potential applications in catalysis, sensing, and light harvesting. Due to poor solubility of CNTs, previously reported synthetic approaches are limited to large multi-walled CNTs, bundles of single-walled CNTs (SWNTs), or surface-bound CNTs. Here we report a solution-phase synthesis of SWNT-metal NP assemblies that is generally applicable to common metal elements. Key to the process is the poly(styrene-alt-maleic acid) surfactant which disperses SWNTs in aqueous solutions and acts as templates for the binding of metal ions and metal NPs.     

Direct amperometric detection of glucose on a multiple-branching carbon nanotube forest

We show here that a re-structured carbon nanotube (CNT) forest can be used 'as-received' for high selectivity, non-enzymatic glucose detection without the need to incorporate catalytic metal nanoparticles or an exclusion polymeric membrane. Direct amperometric sensing of glucose has been achieved by using multiply-branched CNTs prepared by growing secondary or tertiary 'offshoot' CNTs on top of the existing CNT layer. The increased roughness factor on these re-structured CNTs enhances the amperometric detection sensitivity for glucose by a factor of 20x over that of interfering species like ascorbic acid or uric acid. A sensitivity of 60 microA mM(-1) cm(-2) and a detection limit of 1 microM, with a linear detection range of 1-11 mM (R(2) = 0.999), could be attained on the re-grown CNTs. When the re-grown CNTs were subjected to further anodization in acid to introduce a highly-charged interface, the sensitivity to glucose was enhanced to 157 microA mM(-1) cm(-2).     

Fabrication of carbon nanotube sheets and their bilirubin adsorption capacity

Bilirubin adsorption on carbon nanotube surfaces has been studied to develop a new adsorbent in the plasma apheresis. Powder-like carbon nanotubes were first examined under various adsorption conditions such as temperatures and initial concentrations of bilirubin solutions. The adsorption capacity was measured from the residual concentrations of bilirubin in the solution after the adsorption process using a visible absorption spectroscopy. We found that multi-walled carbon nanotubes (MWCNTs) exhibit greater adsorption capacity for bilirubin molecules than that of single-walled carbon nanotubes (SWCNTs). To guarantee the safety of the adsorbents, we fabricated carbon nanotube sheets in which leakage of CNTs to the plasma is suppressed. Since SWCNTs are more suitable for robust sheets, a complex sheet consisting of SWCNTs as the scaffolds and MWCNTs as the efficient adsorbents. CNT/polyaniline complex sheets were also fabricated. Bilirubin adsorption capacity of CNTs has been found to be much larger than that of the conventional materials because of their large surface areas and large adsorption capability for polycyclic compound molecules due to their surface structure similar to graphite.     

Chiral-selective etching effects on carbon nanotube growth at edge carbon atoms

Chemical vapor deposition (CVD) utilizing metal cluster nanoparticle catalysts is commonly used to synthesize carbon nanotubes (CNT), with oxygen-containing species such as water or alcohol included in the feedstock for enhanced yield. However, the etching effect of these additives on the growth mechanism has rarely been investigated, despite evidence suggesting that etching potentially affects the chirality distribution of product CNTs. We used quantum chemical methods to study how water-based etchant radicals (OH and H) may enhance the chiral selectivity during CVD growth using CNT cap models. Chemical reactivities of the caps with the etchant radicals were evaluated using density functional theory (DFT). It was found that the reactivities on the cap edges correlate with the chirality of the caps. These results suggest that proper selection of etchant species can provide opportunities for selective chirality control of the product CNTs. © 2018 Wiley Periodicals, Inc.     

Quasi-continuous growth of ultralong carbon nanotube arrays

We report the growth of ultralong (>10 cm) multi-walled and single-walled carbon nanotubes such that the length is limited by the size of the furnace rather than by the termination of growth. The disturbance of microscale laminar flows results in disordered or shorter growth of carbon nanotubes. By downsizing reaction pipes, reaction gas flows are stabilized with low Reynolds numbers. In this way, the catalyst nanoparticles at the end of growing carbon nanotubes can travel a longer distance to grow ultralong nanotubes.     

Selective matching of catalyst element and carbon source in single-walled carbon nanotube synthesis on silicon substrates

We have studied the compatibility of various catalysts for ethylene and ethanol chemical vapor deposition (CVD) syntheses of single-walled carbon nanotubes (SWNTs) on Si substrates. A strong selectivity between the catalyst elemental species and carbon source was found; SWNT yield for Fe (Co) catalysts was much higher for ethylene (ethanol) CVD than for ethanol (ethylene) CVD. This strong and completely opposite selectivity implies significantly different SWNT growth mechanisms for ethanol and ethylene CVD on Si substrates.     

Role of subsurface diffusion and Ostwald ripening in catalyst formation for single-walled carbon nanotube forest growth

Here we show that essentially any Fe compounds spanning Fe salts, nanoparticles, and buckyferrocene could serve as catalysts for single-walled carbon nanotube (SWNT) forest growth when supported on AlO(x) and annealed in hydrogen. This observation was explained by subsurface diffusion of Fe atoms into the AlO(x) support induced by hydrogen annealing where most of the deposited Fe left the surface and the remaining Fe atoms reconfigured into small nanoparticles suitable for SWNT growth. Interestingly, the average diameters of the SWNTs grown from all iron compounds studied were nearly identical (2.8-3.1 nm). We interpret that the offsetting effects of Ostwald ripening and subsurface diffusion resulted in the ability to grow SWNT forests with similar average diameters regardless of the initial Fe catalyst.     

Temperature dependence of the Breit–Wigner–Fano Raman line in single-wall carbon nanotube bundles

The G band in Raman spectra of single-wall carbon nanotube (SWNT) bundles is studied between 3 and 500 K. The G band is best fit with five Lorentzian lines and one Breit–Wigner–Fano (BWF) line, indicating coupling of phonons to the electronic continuum of metallic SWNTs. It is found that the line width of the BWF line decreases with increasing temperature. This temperature-dependent behavior is contrary to that of the Lorentzian lines, where the line width increases with increasing temperature. The coupling constant 1/q of the BWF line is also found to decrease with increasing temperature. These temperature-dependent behaviors of BWF line provide evidence that it is the bundling effect of SWNTs that greatly enhances the BWF coupling.     

Fabrication of double-walled carbon nanotube counter electrodes for dye-sensitized solar sells

Double-walled carbon nanotubes (DWCNTs) have been studied for counter-electrode application in dye-sensitized solar cells (DSCs). Mesoporous TiO2 films are prepared from the commercial TiO2 nanopowders by screen-printing technique on optically transparent-conducting glasses. A metal-free organic dye (indoline dye D102) is used as a sensitizer. DWCNTs are applied to substitute for platinum as counter-electrode materials. Morphological and electrochemical properties of the formed counter electrodes are investigated by scanning electronic microscopy and electrochemical impedance spectroscopy, respectively. The electronic and ionic processes in platinum and DWCNT-based DSCs are analyzed and discussed. The catalytic activity and DSC performance of DWCNTs and Pt are compared. A conversion efficiency of 6.07% has been obtained for DWCNT counter-electrode DSCs. This efficiency is comparable to that of platinum counter-electrode-based devices.     

Effect of Cu in electroless Ni–Cu–P coating on passivation process

Electroless Ni–P and Ni–Cu–P coatings were passivated by chromate conversion treatment respectively. The anticorrosive performances of passivated coatings were investigated by potentiodynamic polarization and electrochemical impedance spectroscopy measurements. The passivated Ni–Cu–P coating exhibited a high corrosion resistance with the i_corr of 0.236 μA/cm,² while the value of passivated Ni–P coating was only 1.030 μA/cm,² indicating the passive film could improve the corrosion resistance of Ni–Cu–P coating to a significant extent. High‐resolution X‐ray photoelectron spectroscopy was used to determine the chemical states of elements detected in the passive film. Compared with passivated Ni–P coating, the passive film on Ni–Cu–P coating exhibited a higher ratio of Cr₂O₃ to Cr(OH)₃ with the value of 72:28, which was the main factor for passivated Ni–Cu–P coating showing excellent corrosion resistance. The effect of Cu in electroless Ni–Cu–P coating on passivation process was discussed by the contrast experiment. Copyright © 2016 John Wiley & Sons, Ltd.     

Controlled growth of single-walled carbon nanotubes on patterned substrates

Single-walled carbon nanotubes (SWCNTs) have attracted great interest in the last two decades because of their unique electrical, optical, thermal, mechanical properties, etc. One major research field of SWCNTs is the controlled growth of them from the patterned catalysts on substrates, since the integration of SWCNTs into nanoelectronics and other devices requires well-organized SWCNT arrays. This tutorial review describes the commonly used lithographic techniques to pattern catalysts used for controlled growth of SWCNTs, specifically confined to the horizontal direction. Advantages and disadvantages of each method will be briefly discussed. Applications of the SWCNT arrays grown from the catalyst patterns will also be introduced.     

Fabrication of metal nanoparticles–carbon nanotubes composite materials in solution

A new solution-phase method for synthesis of metal nanoparticles–carbon nanotubes (CNTs) assemblies is described. By injection of CNTs solution into the diethyl ether/aqueous solution of metal salt biphasic mixture, metal (Ag, Au, Pd, and Pt) nanoparticles–decorated CNTs composite materials can be prepared. Metal nanoparticles have spontaneously and selectively formed on the sidewalls of CNTs through redox reaction between CNTs and metal ions. This phenomenon has been probed by transmission electron microscopy, scanning electron microscopy, energy dispersive X-ray analysis, and Raman spectroscopy.