Yoku Inoue

Shizuoka University · Department of Electronics and Materials Science

Ultrasonication is a simple way to cut carbon nanotubes in suspension. The length of fragmented carbon nanotubes is made shorter by iterating ultrasonication but approaches a critical aspect ratio. The critical aspect ratio is determined by the tensile strength of the carbon nanotube, the viscosity of the solvent, and physical properties of the cav...

Carbon nanotubes (CNTs) are thought to have higher elastic modulus and strength than carbon fibers. The recent development of spinnable multi-walled carbon nanotubes (MWNTs) enables us to produce unidirectional MWNT reinforced polymer-based composites with a higher volume fraction of CNTs. The results of tensile tests of spinnable MWNTs in scanning...

An interesting technique for modifying carbon fiber-reinforced polymer matrix composites is through hybridization with carbon nanotubes (CNTs). Carbon nanotubes sheets/carbon fibers offer potential benefits of nanoscale reinforcement to the well-established fibrous composites by creating multiscale hybrid micro-nano composites. In this study, the t...

A GaN crystal comprises two polar structures along the c-axis direction, and functions as a quasi-phase-matching (QPM) crystal by fabricating a periodic inversion structure. We fabricated GaN-QPM crystals to design rib-waveguide-type devices for achieving highly efficient wavelength conversion. The QPM period required for wavelength conversion was...

In carbon nanotube (CNT) growth, the role of catalytic nanoparticles involves complex processes of feedstock gas decomposition, carbon feedstock transport, and CNT crystal precipitation. We report on the improvement of the catalytic activity by chlorine addition during the CNT forest growth process. The addition of Cl2 enhanced the diffusion rate o...

Composites of long carbon nanotube (CNT) yarns, which are lightweight and have high mechanical properties, and copper, which has high electrical conductivity, are expected to exhibit high material properties. However, research and development have not progressed much. In this study, we developed a copper plating method for CNT yarns loaded with cop...

Carbon nanotube (CNT) is tubular nanofibers made of cylindrical graphene sheets. CNT is thought to have higher tensile strength and elastic modulus than those of conventional carbon fibers. Its ideal mechanical properties are estimated to be about 1 TPa for Young's modulus and 10 GPa or more for tensile strength. However, intrinsic excellent mechan...

The fabrication of ultra-violet (UV) second-harmonic generation (SHG) (UV-SHG) devices requires GaN quasi-phase matching (GaN-QPM) crystals with periodically arranged polar GaN. For fabricating GaN-QPM crystals, the double polarity selective area growth (DP-SAG) using carbon mask technique is employed. However, the growth of narrow (2–4 [Formula: s...

In this study, vertical-type thick BGaN PIN diodes were successfully fabricated to improve the neutron capture rate of BGaN diodes by improving the BGaN epitaxial growth technique. In this technique, 5-μm-thick epitaxial growth was achieved using trimethylboron as a B metal-organic source, which suppressed the gas-phase reaction. The α-particle ene...

Spinnable carbon nanotubes enable us to produce carbon nanotube assemblies such as yarn and sheet without binder. Untwisted carbon nanotube yarn is one of the assemblies. Untwisted carbon nanotube yarns are composed of unidirectionally aligned carbon nanotubes along with the yarn axis, and thus untwisted carbon nanotube yarns are an ideal preform f...

We investigated the growth enhancement effects of chlorine on carbon nanotube (CNT) grown by a chemical vapor deposition method in which FeCl 2 is used as a catalyst precursor. Cross-sectional observation of the CNT forest revealed that the FeCl 2 -originated catalyst showed a liquid-like behavior, and it caused metallic catalyst incorporation into...

A carbon nanotube forest with a length of 14 cm grew with an average growth rate of 1.5 μm s⁻¹ and a growth lifetime of 26 h. Several key factors to realize this unprecedented long growth such as catalyst conditions, growth conditions in chemical vapor deposition, and reactor system were clarified. It was found that the combination of the catalyst...

The mechanical and electrical properties of multiwalled carbon nanotube (MWCNT) yarns with a wide variety of MWCNT diameters were studied to understand the relationship between the microscopic structures of MWCNTs and the load/charge transport properties of macroscopic MWCNT assemblies. The MWCNT diameters were varied from 14.6 nm to 41.6 nm by var...

Spinnable carbon nanotubes enable us to produce carbon nanotube assemblies such as yarn and sheet without binder. Untwisted carbon nanotube yarn is one of the assemblies. Untwisted carbon nanotube yarns are composed of unidirectionally aligned carbon nanotubes along with the yarn axis, and thus untwisted carbon nanotube yarns are an ideal preform f...

In this study, we demonstrated a novel method to grow carbon nanotubes (CNTs) by chloride-mediated chemical vapor deposition with hydride vapor-phase nucleated catalyst (HVPN). In the HVPN method, FeCl 2 as a catalyst precursor was produced by an in situ chemical reaction between Fe powder and HCl gas. After the synthesis of FeCl 2 , CNTs were grow...

In this study, we synthesized oriented multiwalled carbon nanotube (CNT)/polyethylene (PE) composite films and investigated their electromagnetic interference (EMI) shielding properties. The oriented CNT sheet structure was prepared by stacking CNT webs produced by a dry spinning technique with a CNT forest. In a near-field EMI attenuation measurem...

Carbon nanotubes (CNTs) are nanofibers with excellent mechanical properties and low specific gravity. In recent years, spinnable CNTs have been developed that can be spun into yarns. Research has been conducted on CNT composites using spun yarns as preform. However, excellent mechanical properties of CNTs have not been fully utilized due to defects...

Carbon nanotube (CNT) yarns comprise few-walled CNTs (FWCNTs), mainly consisting of double- and triple-walled CNTs, and have several properties which are beneficial for practical bulk-scale carbon devices. These features include high tensile strength, electrical conductivity, thermal conductivity, chemical stability, and environmental tolerance. Ho...

Aligned multi-walled carbon nanotube (MWCNT) sheets were thermally annealed at high temperatures of 1800°C, 2200°C, and 2600°C. Pristine and thermally annealed MWCNT/epoxy composites were fabricated using hot-melt prepreg processing. Effects of thermal annealing on properties of aligned MWCNT sheets and their composites were examined. Transmission...

Carbon nanotube (CNT) yarns were exposed to the space environment on the international space station (ISS) at low Earth orbit (LEO) of around 400 km altitude. Ground-based comparison tests, including irradiation of atomic oxygen (AO), electron beam (EB) and ultraviolet (UV) individually for different sets of samples, were performed. Significant det...

Untwisted multi-walled carbon nanotube (CNT) yarn was spun from vertically aligned CNT arrays by solid-state drawing CNT webs through a ceramic die. CNT yarn-reinforced epoxy composites were developed using a resin drop method. Waviness and poor packing of CNTs in the untwisted spun yarns have limited the mechanical properties of the yarns and thei...

Multiwall carbon nanotubes (MWCNTs) fabricated by chemical vapor deposition contain magnetic nanoparticles. While increasing frequency of electromagnetic field (EMF) exposure (up to <10 kHz) of MWCNTs resulted in slight induced magnetization decrease due to skin effect of the conducting carbon, we discovered that higher frequencies (>10 kHz) contai...

Carbon nanotube (CNT) forest with very low concentration of metallic impurity particle was grown by a two-step floating-catalyst chemical vapor deposition (CVD) method. Fe catalyst nanoparticles were uniformly formed on the substrate by flowing ferrocene/ethanol mist generated by an ultrasonic nebulizer. Then, the growth of the CNT forest was follo...

High heat resistance composites based on thermoplastic polyimide resin and aligned multi-walled carbon nanotube sheets have been developed using hot-melt processing method with a vacuum-assisted system. The horizontally aligned carbon nanotube sheets were produced from vertically aligned carbon nanotube arrays using drawing and press-winding techni...

By using aligned multi-walled carbon nanotube (MWCNT) reinforced epoxy composites possessing a negative coefficient of thermal expansion (CTE) as well as high Young's modulus and aluminum foils, novel electrothermal bimorph actuators are fabricated. U-shaped bimorph actuators are formed by cutting out the middle part of the composite/aluminum lamin...

Horizontally aligned 100-ply multi-walled carbon nanotube (MWCNT) sheets were produced from vertically aligned MWCNT arrays using drawing and press-winding techniques. Composites based on thermoplastic polyimide (TPI) resin and the aligned MWCNT sheets have been fabricated using hotmelt processing method. Effects of processing temperature and hot s...

GaN films are prepared via double‐polarity selective‐area growth (DP‐SAG) using metal‐organic vapor‐phase epitaxy. Here, we demonstrate an improved DP‐SAG process using a carbon mask and an initial Ga‐polar GaN layer to fabricate a GaN film consisting of periodic Ga‐polar and N‐polar domains. The GaN films with periodically poled structures (altern...

In this study, the nominal tensile strength, Young's modulus and Weibull scale and shape parameter of the nominal tensile strength distribution of the MWCNTs synthesized by a thermal chemical vapor deposition (CVD) method were investigated by conducting uniaxial tensile tests. In addition, the structural defects which induced the failure of the MWC...

In this study, we report the relationship between the mechanical properties and structural defects of multi-walled carbon nanotubes (MWCNTs) synthesized by a chemical vapor deposition (CVD) method. The tensile strength, Young's modulus and Weibull modulus of the individual MWCNTs were determined by conducting uniaxial tensile tests using a manipula...

Feasibility of using multi-walled carbon nanotubes (MWCNTs) for the control of coefficients of thermal expansion (CTEs) of composite materials was evaluated, based on experimental data of CTEs and Young’s modulus newly obtained using a combined testing procedure. The axial CTE of the MWCNTs were evaluated over the temperature range -5˚C to 85˚C by...

In this study, to evaluate the temperature dependence of the coefficient of thermal expansion (CTE) of multi-walled carbon nanotubes (MWCNTs) in the axial direction, the CTEs of aligned MWCNT reinforced epoxy composites are measured, and the axial CTEs of the MWCNTs are computed using the rule of mixtures. The mean diameters of the MWCNTs used in t...

This study examined the processing and mechanical properties of cross-ply and quasi-isotropic composite laminates processed using aligned multi-walled carbon nanotube/epoxy prepreg sheets. Three kinds of CNT/epoxy laminates, ([0°/90°]s, [60°/0°/−60°]s, [0°/45°/90°/−45°]s) were successfully fabricated using aligned CNT/epoxy prepreg sheets. The CNT...

We studied the use of carbon nanotube (CNT)-based strain sensors as components of a textile-based, wearable sensing system for real-time motion detection. In the stretchable sensor, millimeter-long multi-walled CNTs (MWCNTs) are uni-directionally aligned and sandwiched between elastomer layers. We synthesized urethane resin to make the elastomer, w...

Recently, GaN, which has remarkable properties as a material for optical devices and high-power electron devices, has also attracted attention as a material for radiation detectors. We previously suggested the use of BGaN as a neutron detector material. However, the radiation detection characteristics of GaN itself are not yet adequately understood...

The fabrication of quasi-phase-matching (QPM) crystals by selective-area growth on the two asymmetrically polar surfaces of GaN is examined. We attempted the fabrication of GaN-QPM crystals by one-time growth using a carbon mask. For GaN double-polarity selective-area growth (DP-SAG), we investigated the effect of varied nitriding times of the Al2O...

Researchers expect the material BGaN to be useful in neutron detectors and ultraviolet (UV) light-emitting devices. In this study, we investigate the effect of the substrate offcut angle and polarity upon BGaN growth. In particular, BGaN is grown on top of GaN upon Al2O3 substrates with various offcut angles. In the case of Ga-polar BGaN growth, th...

This study investigated the stress recovery of aligned multi-walled carbon nanotubes (MWCNTs) embedded in epoxy using Raman spectroscopy, and evaluated interfacial shear stress between MWCNTs and epoxy using shear-lag analysis. To this end, ultralong aligned MWCNTs (3.8 mm long) were embedded in epoxy to obtain Raman spectra at multiple points alon...

Aligned multi-walled carbon nanotube (CNT) sheets produced from aligned CNT arrays were used to develop high volume fraction CNT/epoxy composites. Stretching and pressing techniques were applied during CNT sheet processing to straighten the wavy CNTs and to enhance the dense packing of CNTs in the sheets. Raman spectra measurements showed better CN...

By using an aligned multi-walled carbon nanotube (MWCNT) reinforced epoxy composite, an electrothermal bimorph actuator was fabricated and its load and deformation capacities were investigated. The composite has a negative coefficient of thermal expansion (CTE) as well as large Young’s modulus. To evaluate the actuator property, a composite/aluminu...

Due to their superior material properties, carbon nanotubes (CNTs) have many potential applications such as actuators, composites and electronic components. These CNT-based devices may experience high temperature during manufacture and operation. This leads to thermal expansion and residual stress in devices, and affects the device reliability. The...

Drawing, winding, and pressing techniques were used to produce horizontally aligned carbon nanotube (CNT) sheets from free-standing vertically aligned CNT arrays. The aligned CNT sheets were used to develop aligned CNT/epoxy composites through hot-melt prepreg processing with a vacuum-assisted system. Effects of CNT diameter change on the mechanica...

We study a novel method to modify carbon nanotubes (CNT) surfaces using hydrogen and develop a composite with epoxy resin. This method is effective for functionalization of CNT surfaces and for chemical and physical interactions with other materials. The C = C/C–C ratio increased until 20 min and decreased thereafter. In addition, the C–O peak decr...

Silicon can store Li(+) at a capacity 10 times that of graphite anodes. However, to harness this remarkable potential for electrical energy storage, one has to address the multifaceted challenge of volume change inherent to high capacity electrode materials. Here, we show that, solely by chemical tailoring of Si-carbon interface with atomic oxygen,...

Stress transfer efficiency for 60 walls multi-walled carbon nanotube (MWNT) was calculated by the shear-lag theory. The results indicated that stress transfer between walls is insufficient at several tens of nanometer from the end; however stress converged to the same value for adequate length. Effective young’s modulus was also calculated and indi...

This paper presents effects of carbon nanotube (CNT) orientation angle distribution on elastic moduli of aligned CNT/epoxy composites that were fabricated with various volume fractions using hot-melt prepreg method. Tensile testing was conducted to evaluate the composites’ mechanical properties. The composites’ Young’s moduli increased with increas...

This study has investigated the possible applications of ultra thin fiber reinforced plastics based on uni-directionally aligned carbon nanotube (CNT) sheet for the low thermal deformation structures like high accuracy satellite parts, antennas or optical benches. The aligned multi-walled CNT arrays with mean CNT diameters of 30 and 50 nm were grow...

A solid-state drawing and winding process was done to create thin aligned carbon nanotube (CNT) sheets from CNT arrays. However, waviness and poor packing of CNTs in the sheets are two main weaknesses restricting their reinforcing efficiency in composites. This report proposes a simple press-drawing technique to reduce wavy CNTs and to enhance dens...

Two types of epoxy composites reinforced with an aligned multi-walled carbon nanotube (MWCNT) sheet and its thermal annealed analog were prepared and the effects of thermal annealing on the mechanical properties of the composites were investigated by conducting uniaxial tensile tests. The MWCNTs with lengths exceeding 1 mm were vertically grown on...

In order to achieve a sufficiently high volume fraction and the preferred alignment of long carbon nanotubes (CNTs), CNT spun yarns were used as preforms for fabricating epoxy-based composite materials with excellent mechanical properties using the pultrusion technique. Epoxy resin was well impregnated into the preforms, resulting in better load tr...

Composites based on epoxy resin and differently aligned multi-walled carbon nanotube (MWCNT) sheets have been developed using hot-melt prepreg processing. Aligned MWCNT sheets were produced from MWCNT arrays using the drawing and winding technique. Wavy MWCNTs in the sheets have limited reinforcement efficiency in the composites. Therefore, mechani...

In this study, we developed a new neutron-detection device using a boron gallium nitride (BGaN) semiconductor in which the B atom acts as a neutron converter. BGaN and gallium nitride (GaN) samples were grown by metal organic vapor phase epitaxy, and their radiation detection properties were evaluated. GaN exhibited good sensitivity to α-rays but p...

The tensile properties of carbon fiber (CF) reinforced polymer matrix composites incorporating carbon nanotubes (CNT) sheet (CNT sheet/CF epoxy hybrid composites) and CNT-grafted CF (CNT-grafted CF polyimide hybrid composites) were investigated. For the CNT sheet/CF epoxy hybrid composites, the tensile modulus of hybrid composites was higher than t...

Here we present a simple way of preparing an alumina ceramic material that contains aligned multi-walled carbon nanotube (MWCNT) layers, i.e., aligned MWCNT sheet/alumina laminated ceramics are prepared for the first time by using a filtration technique and spark plasma sintering (SPS) method. It is demonstrated that the introduction of the aligned...

The objective of this study is evaluating the effect of stretching on the angular orientation of carbon nanotubes (CNT) and the mechanical properties of aligned CNT/epoxy composites. Stretching tests were conducted by tensile testing after fabricating prepregs with stretch ratios of 0%, 2%, 5%, 10% and 18%, respectively. Microscopic observations by...

This study examined the nanoscopic damage progression of aligned multi-walled carbon nanotubes (CNT)/epoxy composites under tensile loading using transmission electron microscopy (TEM). Aligned CNT/epoxy composite films (30 mu m thickness) were processed using a forest-drawn aligned CNT sheet and hot-melt prepreg method. Four film specimens, respec...

Ultralong multiwalled carbon nanotube arrays (forests) were grown by chloride-mediated chemical vapor deposition, in which iron chloride was used as a catalyst precursor. Highly spinnable millimeter-long arrays were grown with a very rapid growth rate of 100 μm/min. By stacking long-lasting carbon nanotube (CNT) webs, unidirectionally aligned CNT s...

For nonlinear optical applications using gallium nitride (GaN), periodic inversion of crystallographic orientation (polarity) is required for quasi-phase matching. We developed a novel procedure for designing polarity patterns in GaN using metal organic vapor phase epitaxy (MOVPE), and we used this to fabricate periodic polarity-inverted GaN films....

In this paper, we investigate the effect of chlorine as a growth promoter in the synthesis of multiwalled carbon nanotubes (MWCNTs). We find that the addition of chlorine gas to the chemical vapor deposition process reduces the amount of amorphous carbon deposited on the MWCNT surfaces and results in a longer catalyst lifetime. By using optimum gro...

This study examined the mechanical properties of aligned multi-walled carbon nanotube (CNT)/epoxy composites processed using a hot-melt prepreg method. Vertically aligned ultra-long CNT arrays (forest) were synthesized using chemical vapor deposition with high growth rate, and were converted to horizontally aligned CNT sheets by pulling them out. A...

Carbon nanotube (CNT) yarns have been fabricated by dry spinning from vertically aligned millimeter-long multi-walled carbon nanotube (MWCNT) arrays and their mechanical properties have been studied. By using 2-mm long CNTs and densely packing of CNT yarns we achieved a tensile strength of 1068 MPa and Young’s modulus of 55 GPa. Our CNT yarns have...