Hideki Ichinose

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.

Observation of [110) tilt boundary structures in gold by high resolution HVEM

Abstract Tilt boundaries in evaporated gold foils with a [110] rotation axis perpendicular to the foil surface have been examined by a multi-beam lattice imaging technique in a JEM 1250 kV transmission electron microscope and various boundary structures, small-angle, twin, coincidence-related and near-coincidence tilt boundaries, analysed.

Determination of the Burgers vector of a dislocation by weak-beam imaging in a HVEM

Abstract Both the magnitude and the sense of the Burgers vector have been determined exactly from the number of the terminating thickness fringes at the exit of a dislocation from a wedge-shaped foil. Thickness fringes in foils of A1-Mg or Fe-Mn alloys were examined under weak-beam conditions in a 1 MV electron microscope for diffractions up to 211 in the former crystals and 220 in the latter. If the Burgers vector is limited to basic ones, the identification can be made with little tilting of the specimen. The smallness of the tilt angle and the narrowness of the dislocation image allow one to analyse relatively dense dislocation structures. The present technique is recommended as a standard method of determining the Burgers vector in metals and alloys.

GAAS/GE/GAAS SUBLATTICE REVERSAL EPITAXY ON GAAS (100) AND (111) SUBSTRATES FOR NONLINEAR OPTICAL DEVICES

Sublattice reversal epitaxy is demonstrated in lattice-matched GaAs/Ge/GaAs (100) and (111) systems using molecular beam epitaxy, and confirmed by reflection high energy electron diffraction and preferential etching. In the GaAs/Ge/GaAs (100) system, the sublattice reversal is assisted by self-annihilation of the antiphase domains generated at the GaAs/Ge interface. In the GaAs/Ge/GaAs (111) system, the sublattice reversal results from the unique structure of the As-terminated Ge (111) surfaces. The quality of the sublattice-reversed GaAs crystal is investigated using cross-sectional transmission electron microscopy. A method to fabricate a periodically domain-inverted structure using sublattice reversal epitaxy is demonstrated for the GaAs/Ge/GaAs (100) system.

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.

Sublattice Reversal in GaAs/Si/GaAs (100) Heterostructures by Molecular Beam Epitaxy

Sublattice reversal in III-V compound semiconductors grown on group-IV epitaxial layers on III-V substrates has been proposed for fabricating nonlinear optical devices with domain-inverted compound semiconductor structures. Sublattice reversal epitaxy is demonstrated in the GaAs/Si/GaAs (100) system and confirmed by reflection high energy electron diffraction, cross-sectional transmission electron microscopy, anisotropic etching, and optical second-harmonic generation measurements. The present sublattice reversal seems to be assisted by self annihilation of antiphase domains generated at GaAs/Si interfaces.

Structure and hardness of nanocrystalline silver

Nanocrystalline silver (Ag) was prepared by in situ compacting of ultra-fine silver particles. The structures of as-compacted and annealed specimens were analysed by high-resolution transmission electron microscopy and scanning electron microscopy. Vickers microhardness was measured on the specimens. The ultra-fine particles aggregate before compaction. It is found that the nanocrystalline specimens are obtained by the compaction of the aggregates. Microstructure inside the aggregates does not change as the compacting pressure increases from 0.25 to 2.00 GPa. The compacting pressure affects on the structure and density of the boundaries between the aggregates, i.e. the formation of the crack-type defects of about 1 μm at the boundaries. Thermal stability of nanocrystalline Ag is significantly low; grain coarsening starts below 200 °C. However, a nanometre-sized layered structure forms in local regions upon annealing and is stable up to 800 °C. Vickers microhardness of as-compacted specimens increases with increasing compacting pressure. The increase is attributed to the decrease of the number of crack-type defects. Vickers microhardness of nanocrystalline Ag begins to decrease due to grain coarsening upon annealing around 200 °C. The microhardness of nanocrystalline Ag deviates from the HalI–Petch relation.

Lattice imaging analysis of Σ3 coincidence-site-lattice boundaries in gold

Abstract High-resolution transmission electron microscope images of Σ3 coincidence-site-lattice boundaries in gold have been observed, and analysed in terms of structure models. In particular (112) A/B and (111) A/B boundaries, having different degrees of misorientation and amounts of relaxation, have been observed. The maximum amount of misorientation correlates well with Brandons θ=15/Σ1/2 criterion. Relaxation of the atoms near the boundary is explained in terms of simple atomic repulsions.