Bloch-wave interpretations of Gjønnes-Moodie lines in convergent-beam electron diffraction for non-symmorphic space-group crystals.

The contrast of Gjønnes-Moodie (GM) lines which appear in convergent-beam electron diffraction patterns for non-symmorphic space-group crystals is explained using Bloch waves. In the two-dimensional space groups p2mg and pg the Bloch waves for electron diffraction are described. In both space groups along the Δ line, Bloch waves are arranged as two different types, and it is shown that the two types of Bloch waves do not contribute to the intensity of forbidden reflections. Along the position where the forbidden reflection satisfies the Bragg condition, degeneracies of two Bloch waves are found and it is shown that the degenerated pair of Bloch waves do not contribute to the intensity. These Bloch-wave results provide a new perspective in the understanding of the contrast mechanism of GM lines previously described using scattering polynomials. They also advance the understanding of Bloch-wave behaviour in high-energy electron diffraction.

Surface defects generated by intrinsic origins on 4H-SiC epitaxial wafers observed by scanning electron microscopy.

Surface defects with intrinsic origins in an epitaxial layer on 4H-SiC wafers were observed by scanning electron microscopy. Commercially available 4H-SiC epitaxial wafers with 4° or 8° off-axis angles from the [0001] direction toward the [112¯0] direction were used in this experiment. Various types of defects, including micropipes, pits, carrots, stacking faults and wide terrace and high step structures, were observed and clearly identified. The defects are presented as a catalog that can be used in the identification of surface defects.

Surface defects generated by extrinsic origins on 4H-SiC epitaxial-wafers observed by scanning electron microscopy.

Surface defects on 4H-SiC wafers with an epitaxial layer grown by chemical vapor deposition (CVD) were observed using scanning electron microscopy (SEM). Commercially available epitaxial-wafers with four or eight deg-off surface from the [0001] toward the [112¯0] directions were used for this experiment. 3C-SiC particles, triangular-defects, comets, obtuse-triangular-shaped-defects and micro-holes were identified in the SEM images. This paper can be considered as a catalog of SEM images and descriptions of various surface defects for 4H-SiC wafers with a CVD-grown epilayer.

Reference sample for the evaluation of SEM image resolution at a high magnification--nanometer-scale Au particles on an HOPG substrate.

A new sample preparation technique is proposed for evaluating image resolution in a high magnification range of SEM. The proposed reference samples are uniformly distributed nanometer-scale Au particles on HOPG substrate. The samples are fabricated using the conventional ion sputter coater. The grain size and granularity are controlled by reducing the sputter-induced damage in the top layers of HOPG. The sample heating prior to SEM imaging is essential to suppress beam induced contamination. The heating time and temperature are selected to inhibit large increases in the grain sizes of Au particles. The sputter coated Au particles on the freshly cleaved HOPG substrate are superior in the deviations of particle sizes to the vacuum evaporated Au particles on the plasma etched substrates. The granularity and homogeneous distribution of Au particles on HOPG are demonstrated at a magnification range of x180k to x800k. The average grain size of 3.2 nm and the standard deviation of 1.3 nm are obtained under the condition of an annealing temperature of 180 degrees C for 7 min after sputter coating an average thickness of 0.7 nm.

Behaviors of surfactant atoms on Si(001) surface.

The behaviors of surfactant atoms for thin film growth on the Si(001) surface formed by molecular beam epitaxy were observed. At first, heterointerfaces on Si/Ge and Ge/Si without surfactant effect were investigated and are discussed on the basis of thermodynamics of surfaces and surface diffusion. The mechanism of island formation as a later stage of Stranski-Krastanov growth mode is also discussed. Surfactant effects of Bi atoms on the heteroepitaxial structures were investigated experimentally. Behavior of Sb as a surfactant was also observed and compared with the results of Bi. Mechanisms for improvements in the abruptness at heterointerfaces of Si/Ge/Si as well as suppression of island formation are discussed. The formation of atomic-scale wires of Bi was observed. The structure of Bi wires at high temperatures is described.