Fumio Nagata

Composition dependence of equal thickness fringes in an electron microscope image of GaAs/AlxGa1−xAs multilayer structure

A new method is presented for the composition analysis of GaAs/AlxGa1-xAs multilayer structure using transmission electron microscopy. It is found that the position of equal thickness fringe observed at the edge of a cleaved chip is closely related to the composition. Change in Al composition in GaAs/AlxGa1-xAs superstructure is observed as a shift of the equal thickness fringe. Compositional abruptness at the heterointerface and compositional fluctuation in the thin layer can be estimated in the electron microscope image.

Simulation studies of a composition analysis by Thickness-fringe (CAT) in an electron microscope image of GaAs/AlxGa1−xAs superstructure

The intensity distribution of thickness fringes, observed at the edge of a cleaved chip of GaAs/AlxGa1-xAs superstructure using a transmission electron microscope, was computer-simulated by means of the dynamical theory of electron diffraction. It was theoretically verified that the distance of a thickness fringe from the edge of a chip systematically changes, depending on the Al composition (experimentally found by the present authors (H. Kakibayashi and F. Nagata: Jpn. J. Appl. Phys. 24 (1985) L905)). The precise composition profile in the heterointerface and the most suitable observation condition for a composition analysis were studied using the simulation technique.

222 Electron Reflection from Aluminium and Systematic Interaction

Energy dependence of electron diffraction from a bent wedge crystal of Al was investigated experimentally at energies from 100 KeV to 1 MeV as well as theoretically with particular interest in the systematic interaction. The (222) intensity at the crystal orientation for this reflection is remarkably reduced under observation at some 600 KeV where two dispersion sheets cross each other; furthermore the measured energy-dependence of a fine fringe appearing in the extinction contours agrees fairly well with our theoretical prediction. Around the orientation for (111) reflection the observed profile of (222) image-intensity includes a fringe synchronous to that in the (111) intensity, correspondingly to Vingsbos observation for an MgO crystal (Proc. 6th International Congress for Electron Microscopy, Kyoto (1966), Vol. I 109.). As for (111) extinction distance, the present theoretical estimation gives a fringe-period shorter by 9% and 16% at 100 KeV and 1 MeV respectively than the simple two-ray approximation does.

Structure Analysis of Oval Defect on Molecular Beam Epitaxial GaAs Layer by Cross-Sectional Transmission Electron Microscopy Observation

The fine structure of a surface defect on GaAs grown by molecular beam epitaxy (MBE) is analyzed by transmission electron microscopy (TEM) observing cross-sectional views of the specimen. The defect has a pyramid structure consisting of four {111} stacking fault planes whose Burgers vectors are a0/6 , a0/6 , a0/6 and a0/6 . Because a defect of this type always starts at the GaAs substrate surface, the origin is thought to be a point defect or atomic contamination on the surface.

Observation of Fine Compositional Fluctuation in GaAs/AIxGa1-xAs Superstructure Using Composition Analysis by Thickness-Fringe (CAT) Method

The fine compositional fluctuation in a GaAs/AlxGa1-xAs superstructure grown by metal-organic chemical vapor deposition (MOCVD) was evaluated by using the composition analysis by thickness-fringe (CAT) method. A sinusoidally oscillating Al composition in the growth direction was observed to have a period of 1~4 nm and in the range x=0.15 to 0.5. The CAT method was successfully applied to measure such fine compositional fluctuations with a high spacial resolution.

Observation of Wet Biological Materials in a High Voltage Electron Microscope

Studies are made to investigate the possibility of observing living organs in an electron microscope. An environmental cell is developed, which can be put on an ordinary specimen stage. Microorganisms in pond water are introduced into the environmental cell with water, and observed with a high voltage electron microscope operated at 750 kV. Dynamical image recording is made with a TV system besides stationary film recording. In the environmental cell, the image contrast of the specimen is fairly good, and the image resolution is better than 0.1 µm. Dim images are observed and interpreted as the surface linings of individual cells. The effect of electron irradiation is found to besevere. Future problems for and possibilities with direct observation of living organs are discussed.

Electron microscopic characterization of cubic BN prepared by water solvent

Abstract Cubic BN crystallites prepared by water solvent under various high pressure and temperature conditions were examined by high resolution electron microscopy. The crystallites, obtained at 800°C and 60 kb, are 100 A or smaller and the size increases with increasing temperatures up to 0.4 μm at 1500°C. The crystal shape of cubic BN is based on a tetrahedron defined by slightly distorted (111) crystallographic surfaces.

Depth Profiling of Superstructures by µ-AES Utilizing Angle-Lapped Specimens

Line scanning of an angle-lapped specimen by microprobe Auger electron spectroscopy ( µ-AES) is proposed for depth profiling of superstructures. A multilayer structure enlarged several hundred times is exposed on an angle-lapped surface, and depth profiling is carried out using electron beam scanning. This method makes it possible to measure the compositional depth profiles of a large depth region that is over several thousand A within only several minutes. The composition profile of Ga in a GaAs/AlxGa1-xAs superstructure is measured with the depth resolution of 80 A. The thinnest detectable GaAs layer is 15 A.