Shigeo Sugawara

Determination of Quasi-Crystallographic Orientations of Al–Pd–Mn Icosahedral Phase by Means of Light Figure Method

The light figure method has been utilized for the determination of quasi-crystallographic orientations of a bulk single quasi-crystal of Al–Pd–Mn icosahedral phase. Prior to the light figure experiment, anodic etching was carried out in a solution of CH3OH+HNO3 (volume ratio 3:1), which revealed the occurrence of well-faceted micropits consisting of etch pits and microvoids on specific surface areas, showing approximately twofold, threefold or fivefold symmetry. The facet planes of the etch pits as well as those of the microvoids, when irradiated by a narrow light beam passing through a hole in the center of a screen, reflected the beam effectively, thus giving rise to a well-defined light figure with a specific symmetry on the screen. It is demonstrated that the light figure method functions effectively for the identification of principal symmetry directions of the quasi-crystal.

Morphological study of micropits formed by anodic etching of an Al-Pd-Mn icosahedral quasicrystal

Faceted micropits obtained by electrochemical etching of a single quasicrystal of an Al-Pd-Mn icosahedral phase have been examined by optical and electron microscopy. Anodic etching of the flat surface of a fivefold plane in a solution composed of CH3OH and HNO3(3:1 in volume ratio) reveals a variety of icosahedrally faceted micropits which originated from pre-existing microvoids and etch pits of pentagonal pyramid shape due to the other origins, probably structural defects inside the specimen. As the dissolution progresses, the micropits make successive changes in their shapes, ending in pentagonal pyramids before they vanish.

Dissolution patterns caused by etching of low-indexed surfaces of Al-Pd-Mn icosahedral and Al-Cu-Co decagonal quasicrystals

Abstract Dissolution patterns caused by anodic etching of an Al–Pd–Mn icosahedral quasicrystal and chemical etching of an Al–Cu–Co decagonal quasicrystal were examined by optical and electron microscopy as well as by atomic force microscopy. Appropriate etching treatments of these quasicrystals, i.e. the anodic etching of the Al–Pd–Mn quasicrystal in a solution of CH 3 OH–HNO 3 , and the chemical etching of the Al–Cu–Co quasicrystal in a solution of HF–HNO 3 –H 2 O resulted in occurrence of dissolution patterns composed of a number of well-facetted micropits (and hillocks for the Al–Cu–Co alloy as well) on low-indexed surfaces of the specimens. The morphological features of these etch-figures are discussed in relation to the internal structural symmetries.

Transmission Electron Microscopy and Atomic Force Microscopy Studies of an Al–Pd–Mn Thin Film Prepared by a Combined Technique of Vacuum Deposition and Thermal Annealing

A thin-film sample of Al–Pd–Mn ternary alloy has been produced by a vacuum deposition technique using dual evaporation sources, followed by thermal annealing. The microstructure of the film has been examined by transmission electron microscopy (TEM) and by atomic force microscopy (AFM). The TEM observations reveal that the film has a granular texture of highly ordered icosahedral phase islands embedded in the matrix consisting mainly of multiple-twinned crystals exhibiting a pseudo-tenfold symmetry. It is shown by AFM that the icosahedral islands form protuberant structures with the average height of approximately 50 nm.

Chemical etching of {111} surfaces of GaAs crystals in H2SO4-H2O2-H2O system

The H2SO4–H2O2–H2O system, typically a solution with five parts H2SO4, one part H2O2 and one part H2O in volume ratio, is currently used for chemical polishing of a GaAs crystal to obtain microscopically smooth surfaces. However, the etching of the (111)Ga surface in this etchant leads to the formation of etch pits. In this study, the etching behavior of the (111)Ga surface in various compositions of the H2SO4–H2O2–H2O system at temperatures of 0–70°C is mainly re-examined. It is found that a microscopically smooth {111} surface can be obtained by etching in the solutions with 78+x parts H2SO4, two parts H2O2 and 20-x parts H2O (x=0–4) at 70°C. In contrast, dark and light pits are formed on the (111)Ga surface etched in a solution with two parts H2SO4, one part H2O2 and seven parts H2O at 0°C. Their origin is predicted on the basis of double-etching test results.

Epitactic growth of a decagonal phase in an Al–Ni–Co alloy film deposited on a (0001) sapphire substrate

Thin films of Al–Ni–Co alloy with an average thickness of 15 nm were produced by means of conventional vacuum deposition technique on (0001) sapphire substrates heated at various test temperatures. The microstructures and textures of the films obtained were thoroughly investigated by atomic force microscopy, X-ray diffraction and transmission electron diffraction and imaging techniques. The diffraction measurements have evidenced that the vacuum deposition of Al72Ni15Co13 alloy on the substrates heated above 400°C allows a homogeneous poly-quasicrystalline film, consisting of the Ni-rich basic decagonal phase to grow. It has been further indicated by in-plane XRD analysis that the film deposited at 550°C contains a considerable amount of the decagonal grains epitaxially grown on the sapphire substrate. Possible epitaxial relations occurring between the deposit and the substrate will be detailed on the basis of results obtained from electron diffraction measurements.

Dissolution patterns caused by chemical etching of Al–Co–Cu and Al–Co–Ni decagonal quasicrystals with a HF–HNO3–H2O solution

Dissolution patterns essential for Al–Co–Cu and Al–Co–Ni decagonal quasicrystals (d-QCs) have been investigated in detail by chemical etching using a HF–HNO3–H2O solution followed by scanning electron microscopy (SEM) observations. The chemical etching of definite surface areas of the samples, which are either normal or parallel to the tenfold axes, using a solution with HF–HNO3–H2O (1 : 5 : 4 in volume ratio; 0°C; 5–10 min), produces a large number of microfacet pits of decagonal prismatic shape. In addition, the same etching test in combination with SEM observations was carried out on a deformed sample of the Al–Co–Ni d-QC, which had been subjected to concentrated mechanical stress at an elevated temperature of 850°C by means of the Vickers indentation technique. The morphological features of the resulting micropits and their possible origins are discussed on the basis of results obtained by SEM observations.

Etch Spirals Formed at Screw-Dislocation Sites on (111) Surface of Cu Crystal by Etching with Marukawa's Solution

Dislocation etch pits were produced by etching of the (111) surface of Cu single crystal for 10-50 s at 280-300 K with Marukawas solution ( FeCl36H2O-HCl-HBr). From electron microscopic observation of their replicas, it was found that spiral terraces often occurred at apices of the etch pits formed at screw-dislocation sites. The spiral terraces tended to occupy somewhat wider regions as etching time and temperature were increased.

Evidence of the climb motion of a Shockley partial during glide at room temperature

A dissociated dislocation introduced by compression at room temperature in a Ag-15at.%Al alloy was studied comprehensively by the weak-beam method. In addition to the two Shockley partials of the dissociated dislocation, faint contrasts were observed near the Shockley partial with pure edge orientation. Contrast experiment was carried out on the faint contrast, and we conclude that this is evidence for the interaction between an edge-orientated Shockley partial moving under the action of an applied stress and vacancies at room temperature.