Toru Kuzumaki

Processing of Carbon Nanotube Reinforced Aluminum Composite

Carbon nanotube reinforced aluminum (Al) composites were produced by hot-press and hot-extrusion methods. The interfacial structure between the carbon nanotube and Al was examined using a transmission electron microscope (TEM), and the mechanical properties were measured by a tensile test. TEM observations have shown that the nanotubes in the composites are not damaged during the composite preparation and that no reaction products at the nanotube/Al interface are visible after annealing for 24 h at 983 K. The strength of the composites is only slightly affected by the annealing time at 873 K, while that of the pure Al produced in a similar powder metallurgy process significantly decreases with time. These studies are considered to yield experimental information valuable for producing high performance composites.

Mechanical characteristics and preparation of carbon nanotube fiber-reinforced Ti composite

Carbon nanotubes, a kind of high order fullerenes, offers remarkable electronic as well as mechanical properties, e.g., an extremely high Young’s modulus of TPa order has been reported. This suggests the suitability of carbon nanotubes as novel fiber materials for metal matrix composites. The authors demonstrate that Ti/ nanotube composites show a large increase in hardness and Young’s modulus as compared to pure Ti. This makes the composite an attractive advanced material for future applications.

Measurement of Young’s modulus of carbon nanotubes by nanoprobe manipulation in a transmission electron microscope

A method for quantifying the nanomechanics of nanomaterials was developed using a nanoprobe manipulator fitted into a transmission electron microscope. Apparent Young’s moduli of various carbon nanotubes (CNTs) were measured using this method. The apparent Young’s modulus of an arc-grown CNT is as large as approximately 3.3TPa, which is close to the theoretical Young’s modulus (5.5TPa) of the single-walled CNT simulated using molecular dynamics. The relationship between the apparent Young’s modulus and the crystallinity of CNTs is demonstrated using the crystallinity parameter ID∕IG derived by Raman spectroscopic analysis. The apparent Young’s modulus is higher for better crystallinity of CNT.

Structural change at the carbon-nanotube tip by field emission

Carbon-nanotube tips are plastically deformed during field emission. High-resolution transmission electron microscopy and structural simulations suggest that the deformed structure of the closed nanotube is explained by heterogeneous nucleation of the pentagonal and heptagonal carbon ring pairs, and that of the opened one is represented by sp3-like line defects in the hexagonal carbon network. It is considered that the changing of the inclination of the Fowler–Nordheim plots corresponds to the structural change in which a tip becomes sharp. The field ion microscope image and the corresponding field-emission pattern suggest that the electron emission from a closed nanotube is not necessarily from pentagonal carbon rings, but from the protrudent carbon network sites on the tip.

In-situ observed deformation of carbon nanotubes

Abstract Carbon nanotubes have a whisker-like structure so an extremely high strength and lack of plasticity are generally predicted. In-situ observations made by transmission electron microscopy, however, prove that carbon nanotubes bend plastically at room temperature. The bending process at the atomic level is suggested by a molecular mechanics calculation: a nanotube deforms elastically until certain critical curvature is attained; then the atomic bonding in the stressed side changes from a graphite-like bonding state to a diamond-like state.

Dynamic measurement of electrical conductivity of carbon nanotubes during mechanical deformation by nanoprobe manipulation in transmission electron microscopy

The effect of mechanical deformation on the electrical characteristics of individual multiwall carbon nanotubes (MWCNTs) was investigated by a nanoprobe manipulation technique in a transmission electron microscope (TEM). The electrical conductivity was measured during the deformation of the MWCNT in TEM. The electrical conductivity of the MWCNTs was sensitive to structural variation. The electromechanical characteristics were reversible within the elastic limit. However, when lattice defects were formed due to deformation, the electrical conductivity was not restored to the original state, even when the applied stress was released.

Nanoscale Mechanics of Carbon Nanotube Evaluated by Nanoprobe Manipulation in Transmission Electron Microscope

We investigated the nanoscale mechanics of individual multiwalled carbon nanotubes (MWCNTs) by a nanoprobe manipulation technique in a transmission electron microscope (TEM). The force applied to individual MWCNTs was measured using a commercially available Si cantilever installed in a manipulator. It was clearly observed that this force is released by buckling like deformation. The average Youngs modulus of the MWCNTs estimated using a conventional mechanical theory was approximately 1.1 TPa. Although the MWCNTs exhibited a high flexibility, the deformation of the MWCNTs above the elastic limit led to structural defects, which resulted in a local plastic deformation. Nanomechanics measurements in the TEM revealed that the structural defects cause stiffness deterioration.

Selective processing of individual carbon nanotubes using dual-nanomanipulator installed in transmission electron microscope

Nanoscale processings such as deformation, cutting off, and bonding of individual carbon nanotubes (NTs) have been selectively performed using a dual-nanomanipulation system installed in a high-resolution transmission electron microscope. These processes are directly observed in situ at a lattice resolution of 0.1 nm. At high applied electric field between the NT tip and Au tip, we have found a carbon monolayer extending out from the carbon cluster which was deposited on the NT tip. The cutting off and bonding of individual NT tips can be performed by contacting the NT tips and the opposite nanometer-sized tips at an applied bias voltage. The threshold voltage of the processing is approximately 2 V.

Atomic level analysis of carbon and silicon by a scanning atom probe

Carbon nanotubes, chemical vapor deposition (CVD) diamond, high-temperature-high-pressure (HPHT) diamond, vitreous carbon, graphite and silicon are analyzed by a scanning atom probe (SAP). All specimens contain a large amount of hydrogen. The CVD diamond grown in hydrogen exhibits the highest hydrogen concentration with a ratio of hydrogen to carbon atoms (H/C) of 2.02, and vitreous carbon has the lowest hydrogen concentration with a H/C ratio of 0.25. Significant difference is noticed in the hydrogen desorption energy among analyzed CNTs. The [111]-oriented silicon wafers are chemically etched by HF and NH4F. Although a few analyzed areas are hydrogen-covered and stay clean even when exposed to air, most areas are contaminated with hydrogen, oxygen and carbon. The carbon concentration in the HF-treated silicon is found to be slightly higher than that in the NH4F-treated silicon. An unexpected finding is the shift of the most abundant Si-H clusters from Si4H+ to Si2H+ with the depth of the analyzed area of the NH4F-treated silicon.

In-situ atomistic observation of carbon nanotubes during field emission

The structural variation in the tip of carbon-nanotube during field emission was in-situ observed at an atomic scale by high-resolution transmission electron microscopy equipped with newly designed two specimen holders system. The nanotubes which were sticking out of the rod specimen were fixed in a specimen holder. In another specimen holder, a gold coated silicon tip was fixed as an opposite electrode. Dynamic in-situ observation revealed that the graphene layers of the tip protruded along the electric field direction. The protrusion then recovered during the field emission. A semi-empirical molecular orbital calculation suggested that the protrusion structure resulted from the exchanges of several hexagonal carbon rings for pentagonal-heptagonal carbon rings pairs at the tip.