Michio Hibino

Defect structure in selective area growth GaN pyramid on (111)Si substrate

A GaN pyramid grown selectively on a (111)Si substrate with a patterned dot structure of a SiO2 mask, by metalorganic vapor phase epitaxy using AlGaN as an intermediate layer, was characterized by transmission electron microscopy. The dot pattern has an array of 5.0-μm-diameter window openings with a 10 μm period. The density of threading dislocations observed in the window region decreased gradually with increasing distance from the interface. This was mainly due to the dislocation reaction and bending of threading dislocations for the first 2 μm region from the interface and for the upper region, respectively. Dominantly observed defects in the lateral-growth part were dislocations parallel to the interface. An amorphous layer was formed at the interface in the window region. Nitride particles were observed at the interface in the mask region.

Structural characterization of GaN laterally overgrown on a (111)Si substrate

Using transmission electron microscopy, we have characterized defect structures in laterally overgrown GaN crystals, grown directly on SiO2 stripe-patterned (111)Si substrates by metalorganic vapor phase epitaxy using AlGaN as an intermediate layer. The width and the period of the stripe windows were nominally 1 and 2 μm, respectively. The average threading dislocation density for a completely coalesced 2-μm-thick GaN crystal obtained on the [112]-oriented stripe-patterned substrate was ∼2×109 cm−2. The reduction in threading dislocation density is a consequence of the lateral growth and dislocation reactions at the coalesced front of the mask. On the other hand, valleys and pits tend to remain on the mask during the growth on the [110]-oriented stripe-patterned substrate. Cracks were present in both crystals.

Hologram simulation for off-axis electron holography

Hologram simulation for electron holography using an electron biprism is described. An electron hologram is superimposed by Fresnel fringes originating from the electron biprism, which affects both the amplitude and the phase of the object wave and the reference wave. In this simulation, we consider the effects of Fresnel diffraction as well as the electron-wave phase shift due to the electromagnetic field produced by the specimen. We also take into account the phase shift due to the inner potential of the specimen, the amplitude modulation due to the absorption of the incident electrons by the specimen, reference-wave distortion caused by the electromagnetic fields, coherency of the electron wave, and quantum noise of the detected electrons. Simulated and experimentally obtained holograms and reconstructed images are compared for the cases of a charged latex spherical particle and a single magnetic-domain spherical particle placed on a carbon film.

Improvement of Light Collection Efficiency of Lens-Coupled YAG Screen TV System for a High-Voltage Electron Microscope

A new lens coupling television (TV) system using a YAG (Yttrium Aluminum Garnet: Y3Al5O12 : Ce3+) single crystal screen has been developed for a high‐voltage electron microscope (HVEM), and its performance is examined. The system, using a combination of YAG and lenses, is less damaged by high‐energy electron irradiation and reduces the influence of X‐rays on the image. YAG screens have not been used for lens‐coupling systems, because the high refractive index (n = 1.84) of YAG results in a low light collection efficiency for emitted light. This disadvantage is overcome by combining a thin YAG disk screen (thickness; 100 μm) with a glass hemisphere whose refractive index is 1.81. We found that the light intensity is almost the same as that obtained with a conventional P22 powder screen and lenses system. The resolution is about 55 μm on the YAG screen, and this value is 1.3 times higher than that measured by the conventional system. Shading and distortion do not affect TV observation. Detection quantum efficiency, obtained after correction of the channel mixing effect, is about 0.1. Microsc. Res. Tech. 49:596–604, 2000.

Self-assembling of hot carbon nanoparticles observed by short pulse-arc-discharge

Abstract Little is known about the behavior of carbon nanoparticles produced by arc-discharge in which they are so hot that atoms are mobile. Such hot carbon nanoparticles were produced by short pulse-arc-discharge. Under a condition of reducing coalescence due to gas-convection flow, we found confidently that nanoparticles of 5–10 nm in diameter were self-assembled into a tree-like structure, and could study the growth process. Individual nanoproducts with the tree-like structure were deposited uniformly as a monolayer over a macroscopic area of the cathode. Occasionally self-assembling of nanoparticles resulted in the formation of a linear structure which was as long as 500 nm.

Computational Fresnel Images of Magnetic Nanoparticles

Lorentz microscopy is applied to observe the magnetic structures of Fe fine particles in granular films. Observed particles, 20–60 nm in diameter, are prepared by precipitation in an Fe–Mo amorphous thin film. In order to understand accurately the observed Lorentz micrographs, image contrast is simulated mimetically. Some analyses for single-magnetic-domain particles are shown in comparison with experimental data. The minimum size of the observable Fe particle is thought to be about 10 nm in diameter.

Correction of the spherical aberration of the CTEM objective lens using a foil lens

Abstract A foil lens has been applied to the objective lens of a conventional transmission electron microscope and its characteristics in correcting the spherical aberration have been investigated experimentally. Special polepieces of the objective lens were designed so that the foil lens can easily be inserted into them. The spherical aberration of a compound lens consisting of the objective lens and the foil lens was measured from the displacement of the {200} dark field image of a magnesium oxide crystal from its bright field image for various voltages of the foil lens. The experiment has shown that the spherical aberration of the objective lens, being excited at NI √V = 19.6 A V −1 2 at 100 kV, is reduced and becomes negative as the foil lens voltage is increased. The experimental result is in good agreement with calculations involving the third- and fifth-order spherical aberrations.

Measurement of axial geometrical aberrations of the probe-forming lens by means of the shadow image of fine particles

Abstract A method using a shadow image of fine particles, proposed for the stigmation and the measurement of spherical aberration of the probe-forming lens, was further developed for the accurate measurement of spherical aberration and of non-rotationally symmetrical axial aberrations. From the radii of the rings of infinite magnification in a pair of shadow images, the coefficient of two- or three-fold astigmatism or axial coma can be measured together with the spherical aberration coefficient. A theoretical evaluation and an experiment carried out with a probe-forming lens of 1.5 nm resolution showed that the error of measurement is within several percent for the spherical aberration coefficient and is less than 30 nm for the coefficient of two-fold astigmatism. The three-fold astigmatism remaining after the correction of spherical aberration was also measured and was found to be of considerable importance in limiting the performance of the spherically corrected lens.

Brief communication:XTEM sample preparation technique for n-type compound semiconductors using photochemical etching

A sample preparation technique based on photochemical etching (PCE) is described for cross‐sectional transmission electron microscopy (XTEM) of n‐type compound semiconductors. XTEM samples of an InGaAsP/InP single‐layer structure, prepared by using a moderately focused laser beam and Br2‐methanol solution, gave high quality, damage‐free XTEM images. The PCE technique is applicable to other n‐type compound semiconductors.

Transmission electron microscopy study of InGaAsPInGaP thin-layer structure grown by liquid phase epitaxy

Abstract Cross-sectional transmission electron microscopy observations were carried out for InGaAsP InGaP thin layers grown on (111)A GaAs by liquid phase epitaxy. Fine-scale periodic contrast modulation along the surface was observed in epilayers irrespective of the composition. The period is 20–30 nm. The heterointerfaces were found to be abrupt down to the atomic scale (i.e., ∼ 1.2 nm).