Super-aligned Carbon Nanotube Research Articles

Super-aligned carbon nanotubes patterned sapphire substrate to improve quantum efficiency of InGaN/GaN light-emitting diodes.

In this paper, the high performance GaN-based light-emitting diodes (LEDs) on carbon-nanotube-patterned sapphire substrate (CNPSS) by metal-organic chemical vapor deposition (MOCVD) are demonstrated. By studying the mechanism of nucleation, we analyze the reasons of the crystal quality improvement induced by carbon nanotubes (CNTs) in different growth process. Combining with low temperatures photoluminescence (PL) measurements and two-dimensional (2D) finite difference time-domain (FDTD) simulation results, we conclude that the improvement of optical properties and electrical properties of CNPSS mainly originates from the improvement of the internal quantum efficiency (IQE) due to decreased dislocation density during nano-epitaxial growth on CNPSS. Additionally, in order to reduce the light absorption characteristics of CNTs, different time annealing under the oxygen environment is carried out to remove part of CNTs. Under 350 mA current injections, the light output power (LOP) of CNPSS-LED annealed 2 h and 10 h exhibit 11% and 6% enhancement, respectively, compared to that of the CNPSS-LED without annealing. Therefore, high temperature annealing can effectively remove parts of CNTs and further increase the LOP, while overlong annealing time has caused degradation of the quantum well resulting in the attenuation of optical power.

Geometrically constrained self-assembly and crystal packing of flattened and aligned carbon nanotubes

While the mechanical properties of highly aligned carbon nanotube (CNT) thin films and their nanocomposites have been widely studied, the load transfer mechanisms and failure modes of aligned CNT composites have not been sufficiently explored and understood. In this research, super-aligned CNT thin films with a measured alignment fraction of up to 0.93 are fabricated by mechanical stretching. High concentration (50–60wt% CNT) CNT reinforced bismaleimide (CNT/BMI) nanocomposites are fabricated from the aligned network to study mechanical properties and microstructures. Atomic resolution transmission electron microscopy (TEM) analysis reveal unusual CNT crystal packing and permit the observation of interesting structural features of the CNTs and their assemblages, including collapse, flattened packing, preferred stacking, folding and twisting phenomena, as well as CNT pullouts from bundles and the resin matrix. The large surface-to-surface contact areas between aligned and flattened nanotubes, driven by van der Waals interactions, give rise to a high density packing of the flattened CNTs in the nanocomposite, resembling a graphitic material. Molecular dynamics (MD) simulations are performed to model the packing structure and understand the dependence of density on the relative content of flattened nanotube and void space. The modeling results support the conclusions drawn from the experimental observations.

Study of Carbon Nanotubes as Etching Masks and Related Applications in the Surface Modification of GaAs-based Light-Emitting Diodes.

The surface modification of LEDs based on GaAs is realized by super-aligned multiwalled carbon nanotube (SACNT) networks as etching masks. The surface morphology of SACNT networks is transferred to the GaAs. It is found that the light output power of LEDs based on GaAs with a nanostructured surface morphology is greatly enhanced with the electrical power unchanged.

Stacking dependent electronic properties of the nanofilms composing of super-aligned single-walled carbon nanotubes

Films composed of super-aligned single-walled carbon nanotubes (SWCNTs) have been widely used in electronic devices. Using first-principles calculations, we investigate the energetically most favorable stacking patterns and the electronic structures of SWCNT monolayers and bilayers formed by super-aligned (5, 5) and (7, 0) SWCNTs. It is found that the (5, 5) SWCNT monolayer prefers a ‘face-by-face’ stacking pattern with the binding energy of 13.90 meV/atom, whereas the (7, 0) SWCNT monolayer favors an ‘edge-by-edge’ pattern with the binding energy of 10.82 meV/atom. The (5, 5) SWCNT arrays are semiconducting with a band gap up to 114 meV for the bilayer, while the (7, 0) SWCNT arrays are metallic with a tiny overlap between valence and conduction bands, in sharp contrast to the cases of isolated (5, 5) and (7, 0) SWCNTs. This implies that weak van der Waals interactions between SWCNTs play an important role in applications of SWCNT films in electronic devices.

Design and Simulation of a Bending Actuator Based on Super-Aligned Carbon Nanotube/Polymer Composites

Super-aligned carbon nanotube films are carbon nanotube macrostructures which have excellent orientations. The bending actuator based on super-aligned carbon nanotube/polymer composites can make a significant controllable bending deformation under a very low DC voltage (< 700 V/m). In this paper, we explored how to make the thermal induced actuator reach maximal deformation. By theoretical modeling and simulation through Mathematica software, the relationship between free-end displacement of the actuator and actuator length, thickness (or thickness ratio) of two layers, difference of coefficient of thermal expansion between two layers, temperature variation and other parameters were studied. Simulation results showed that the deformation is greatly influenced by the thickness ratio of the two layers of the actuator. The deformation displacement reaches a maximum value with a specified thickness ratio. This study may provide valuable theoretical references for the experimental design of carbon nanotube composite actuators.

Ice-assisted transfer of carbon nanotube arrays.

Decoupling the growth and the application of nanomaterials by transfer is an important issue in nanotechnology. Here, we developed an efficient transfer technique for carbon nanotube (CNT) arrays by using ice as a binder to temporarily bond the CNT array and the target substrate. Ice makes it an ultraclean transfer because the evaporation of ice ensures that no contaminants are introduced. The transferred superaligned carbon nanotube (SACNT) arrays not only keep their original appearance and initial alignment but also inherit their spinnability, which is the most desirable feature. The transfer-then-spin strategy can be employed to fabricate patterned CNT arrays, which can act as 3-dimensional electrodes in CNT thermoacoustic chips. Besides, the flip-chipped CNTs are promising field electron emitters. Furthermore, the ice-assisted transfer technique provides a cost-effective solution for mass production of SACNTs, giving CNT technologies a competitive edge, and this method may inspire new ways to transfer other nanomaterials.

Large area nanoscale metal meshes for use as transparent conductive layers.

We report on the experimental realization of using super-aligned carbon nanotubes (SACNTs) as etching masks for the fabrication of large area nanoscale metal meshes. This method can easily be extended to different metals on both rigid and flexible substrates. The as-fabricated metal meshes, including the ones made of gold, copper, and aluminum, are suitable for use as transparent conductive layers (TCLs). The metal meshes, which are similar to the SACNT networks in their dimensional features of tens of nanometers, exhibit compatible performance in terms of optical transmittance and sheet resistance. Moreover, because the metal meshes are fabricated as an integrated material, there is no junction resistance between the interconnected metal nanostructures, which markedly lowers their sheet resistance at high temperatures. The fabrication of such an effective etching mask involves a simple drawing process of the SACNT networks prepared and a common deposition process. This approach should be easy to extend to various research fields and has broad prospects in commercial applications.

Ultra-stretchable conductors based on buckled super-aligned carbon nanotube films.

Ultra-stretchable conductors are fabricated by coating super-aligned carbon nanotube (SACNT) films on pre-strained polydimethylsiloxane (PDMS) substrates and forming buckled SACNT structures on PDMS after release of the pre-strain. The parallel SACNT/PDMS conductors demonstrate excellent stability with normalized resistance changes of only 4.1% under an applied strain as high as 200%. The SACNT/PDMS conductors prepared with cross-stacked SACNT films show even lower resistance variation. The parallel SACNT/PDMS conductors exhibit high durability with a resistance increase of less than 5% after 10,000 cycles at 150% strain. In situ microscopic observations demonstrate that the buckled SACNT structures are straightened during the stretching process with reversible morphology evolution and thus the continuous SACNT conductive network can be protected from fracture. Due to the excellent electrical and mechanical properties of SACNT films and the formation of the buckled structure, SACNT/PDMS films exhibit high stretchability and durability, possessing great potential for use as ultra-stretchable conductors for wearable electronics, sensors, and energy storage devices.

High-performance flexural fatigue of carbon nanotube yarns

Carbon nanotube yarns (CNTY) possess good specific strength and specific conductivity. As such, their potential for commercial applications is significant. Fatigue performance is a significant consideration in yarn/wire applications. In this study, the flexural fatigue performance of CNTY spun from super-aligned carbon nanotube arrays was investigated using a reversed bending test. The results showed that CNTY exhibited excellent resistance to pure flexural fatigue, significantly outperforming stainless steel wire; CNTY failed where a combination of flexural fatigue and tension–tension fatigue had special hollow fracture morphology, and CNTY resistance remained fundamentally unchanged in the combination fatigue process.

Carbon Nanotube Thin Film-Supported Fibroblast and Pluripotent Stem Cell Growth

In this study, we functionalized superaligned carbon nanotube (CNT) thin film and performed detailed analysis to characterize the surface modifications. Our results demonstrated that chemical and biochemical modification of CNT thin films significantly altered the level of hydrophilicity. We also showed that the growth of mammalian fibroblasts and pluripotent stem cells on functionalized CNT thin films were better than that on untreated CNT films. Moreover, extracellular matrix protein-conjugated CNT thin film can support pluripotent stem cell growth without feeder cells. These results suggest that once properly functionalized, CNT thin film can be a suitable scaffolding material for a broad range of mammalian cell culture. Our work provided basis for future cell/tissue engineering with this material.

Sulfur nanocrystals confined in carbon nanotube network as a binder-free electrode for high-performance lithium sulfur batteries.

A binder-free nano sulfur-carbon nanotube composite material featured by clusters of sulfur nanocrystals anchored across the superaligned carbon nanotube (SACNT) matrix is fabricated via a facile solution-based method. The conductive SACNT matrix not only avoids self-aggregation and ensures dispersive distribution of the sulfur nanocrystals but also offers three-dimensional continuous electron pathway, provides sufficient porosity in the matrix to benefit electrolyte infiltration, confines the sulfur/polysulfides, and accommodates the volume variations of sulfur during cycling. The nanosized sulfur particles shorten lithium ion diffusion path, and the confinement of sulfur particles in the SACNT network guarantees the stability of structure and electrochemical performance of the composite. The nano S-SACNT composite cathode delivers an initial discharge capacity of 1071 mAh g(-1), a peak capacity of 1088 mAh g(-1), and capacity retention of 85% after 100 cycles with high Coulombic efficiency (∼100%) at 1 C. Moreover, at high current rates the nano S-SACNT composite displays impressive capacities of 1006 mAh g(-1) at 2 C, 960 mAh g(-1) at 5 C, and 879 mAh g(-1) at 10 C.

AlGaInP light-emitting diodes with SACNTs as current-spreading layer

Transparent conductive current-spreading layer is important for quantum efficiency and thermal performance of light-emitting diodes (LEDs). The increasing demand for tin-doped indium oxide (ITO) caused the price to greatly increase. Super-aligned carbon nanotubes (SACNTs) and Au-coated SACNTs as current-spreading layer were applied on AlGaInP LEDs. The LEDs with Au-coated SACNTs showed good current spreading effect. The voltage bias at 20 mA dropped about 0.15 V, and the optical power increased about 10% compared with the LEDs without SACNTs.

Improvement of sound absorption characteristics under low frequency for micro-perforated panel absorbers using super-aligned carbon nanotube arrays

Super-aligned carbon nanotube (SACNT) arrays are grown on the surface of micro perforated panel (MPP) in the hope of improving the acoustic performance of MPP absorbers by virtue of their unique properties. Scanning electron microscopy reveals that SACNT arrays did not block the perforations of MPPs or changed the perforation diameter due to their “super-aligned” nature, although MPPs are thickened. The absorption effect of SACNT arrays which are of the same and different lengths with different incident side on MPP absorbers are investigated, and standing wave tube method is used to determine the normal sound absorption coefficient. Results show that both of the lengths of SACNT arrays and the incident side have effects on the sound absorption performance of MPP absorbers. And generally SACNT arrays help to improve the sound absorption capacity of MPP absorbers in low-frequency regions only when the SACNT arrays surface is the incident side. SACNT arrays decrease absorption performance of MPP absorbers when the MPP surface is used as the incident side. Moreover, SACNT arrays are found to increase the acoustic ability of MPP absorbers with the same structure parameters monotonically at lengths up to 600μm in the condition that the SACNT arrays surface is used as the incident side.

Synthesis and failure behavior of super-aligned carbon nanotube film wrapped graphene fibers

Significant progress has been made in recent years in research on wet spinning and hydrothermal synthesis of graphene fibers. In this paper, we report the relationship between the mechanical performance of graphene oxide (GO) fibers and their processing parameters in wet spinning. With super-aligned carbon nanotube (CNT) film wrapping, the specific strength and electrical conductivity of reduced GO (rGO) fibers were simultaneously enhanced by 22% and 49%, respectively. Thicker CNT film wrapping of the rGO fiber induces a core–sheath structure; the resulting interfacial debonding and slippage under fiber axial loading were examined. The findings of this study provide guidelines for optimization of high-performance graphene/CNT hybrid fibers.

Facile oxidation of superaligned carbon nanotube films for primary cell culture and genetic engineering.

A material that can simultaneously support mammalian cell growth and preserve their physiological function is highly desirable in biomedical research. To meet this need, we fabricated superaligned carbon nanotube (SACNT) thin films and modified their surface using a convenient oxidization method. Our analysis demonstrated that the physical properties of oxidized SACNT films became more biocompatible. It supported the attachment and growth of primary mouse fibroblast cells as well as neonatal rat cardiomyocytes. Moreover, when cultured on oxidized SACNT films, neonatal rat cardiomyocytes spread normally and displayed calcium influx. Finally, we showed that, as oxidized SACNT films retained their electrical conductivity, attached cells can be electrotransfected in situ on them. Strong and prolonged expression of green fluorescence proteins (GFPs) or red fluorescence proteins (RFPs) was observed upon cell electroporation on oxidized SACNT films. In summary, our results provide evidence that simple oxidation greatly improved the biocompatibility of carbon nanotube films, which becomes more suitable for future applications in cell and genetic engineering.

Cycle and rate performance of chemically modified super-aligned carbon nanotube electrodes for lithium ion batteries

Super-aligned multi-walled carbon nanotubes (MWCNTs), which had been produced in large-scale, were oxidized by H2O2 and HNO3. The surface defects and oxygen-containing functional groups introduced during the oxidizing process were characterized by Raman spectroscopy and X-ray photoelectron spectroscopy. The surface modification of MWCNTs improved the electrochemical properties. As a result, H2O2-treated and HNO3-treated MWCNTs displayed reversible capacities of 364mAh/g and 391mAh/g, respectively, after 80 galvanostatic cycles, corresponding to 143% and 154% improvements compared with pristine MWCNTs. The rate capability was also increased. At a current density of 3500mA/g, H2O2-treated and HNO3-treated MWCNTs exhibited reversible capacities of 66mAh/g and 156mAh/g, respectively. In contrast, pristine MWCNTs were only able to deliver 27mAh/g at this current density.

Influence of Nitrogen Doping Concentration on Morphology and Microstructure of Nitrogen Doped Super-Aligned Carbon Nanotube Forest

Influence of Nitrogen Doping Concentration on Morphology and Microstructure of Nitrogen Doped Super-Aligned Carbon Nanotube Forest

Mn3O4 nanoparticles anchored on continuous carbon nanotube network as superior anodes for lithium ion batteries

Mn3O4 nanoparticles anchored on continuous super-aligned carbon nanotube (SACNT) films are synthesized by decomposition of Mn(NO3)2. In the Mn3O4/SACNT composite electrodes, SACNT film is capable of serving as both the conductive pathway and structural scaffold, therefore no binder, extra conductive agent, or current collector is needed. The electrochemical performance of the Mn3O4/SACNT composite electrode is significantly affected by the particle size of Mn3O4. With smaller particle size, the electrode displays smaller voltage hysteresis and much improved reversibility and rate capability. The Mn3O4/SACNT electrodes with particle size of Mn3O4 less than 10 nm show a capacity retention of 95% after 100 cycles at 1 C and a high rate capacity of 342 mAh g−1 at 10 C (based on the total mass of the electrode), suggesting their advantages over the commercial graphite anode and potential in practical applications.

Field Emission Behavior of Carbon Nanotube Yarn for Micro-Resolution X-Ray Tube Cathode

Carbon nanotube (CNT) has excellent electrical and thermal conductivity and high aspect ratio for X-ray tube cathode. However, CNT field emission cathode has been shown unstable field emission and short life time due to field evaporation by high current density and detachment by electrostatic force. An alternative approach in this direction is the introduction of CNT yarn, which is a one dimensional assembly of individual carbon nanotubes bonded by the Van der Waals force. Because CNT yarn is composed with many CNTs, CNT yarns are expected to increase current density and life time for X-ray tube applications. In this research, CNT yarn was fabricated by spinning of a super-aligned CNT forest and was characterized for application to an X-ray tube cathode. CNT yarn showed a high field emission current density and a long lifetime of over 450 hours. Applying the CNT yarn field emitter to the X-ray tube cathode, it was possible to obtain micro-scale resolution images. The relationship between the field emission properties and the microstructure evolution was investigated and the unraveling effect of the CNT yarn was discussed.

Excitation of Surface Plasmon Resonance in Composite Structures Based on Single-Layer Superaligned Carbon Nanotube Films

Surface-enhanced Raman scattering (SERS) provides valuable information on the vibrational modes of molecules and the physical mechanism of surface plasmon resonance (SPR). In this paper we study th...