Investigation of changes in the order parameters near antiphase boundaries in the Cu3Au alloy

ABSTRACTA procedure similar to that of Gehlen and Cohen and Williams is used to simulate atomic configurations of short range ordered Ni3Fe. The short range order parameters were previously measured after different heat treatments. Probabilities of different clusters are computed from those models : triangles, tetrahedrons, clusters as defined by Clapp.These probabilities vary with the enhancement of short range order. It is shown that most of the clusters the probabilities of which increase with short range order, are directly related with the L12 ordered structure: either they have the L12 structure, or the L12 structure modified by one or two antiphase boundaries. Such clusters are identified in the model in order to display perfectly ordered domains.

Download Full-text

Exsolution and inversion in pigeonite from the Whin Sill, Northern England

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100109513 ◽

1978 ◽

Vol 36 (1) ◽

pp. 474-475

Author(s):

P.P.K. Smith

Keyword(s):

High Temperature ◽

Low Temperature ◽

Homogeneous Nucleation ◽

Silicate Mineral ◽

Antiphase Boundaries ◽

Two Phase ◽

Primitive Form ◽

The Core ◽

Nucleation Mechanisms ◽

And Inversion

Grains of pigeonite, a calcium-poor silicate mineral of the pyroxene group, from the Whin Sill dolerite have been ion-thinned and examined by TEM. The pigeonite is strongly zoned chemically from the composition Wo8En64FS28 in the core to Wo13En34FS53 at the rim. Two phase transformations have occurred during the cooling of this pigeonite:- exsolution of augite, a more calcic pyroxene, and inversion of the pigeonite from the high- temperature C face-centred form to the low-temperature primitive form, with the formation of antiphase boundaries (APB's). Different sequences of these exsolution and inversion reactions, together with different nucleation mechanisms of the augite, have created three distinct microstructures depending on the position in the grain.In the core of the grains small platelets of augite about 0.02μm thick have farmed parallel to the (001) plane (Fig. 1). These are thought to have exsolved by homogeneous nucleation. Subsequently the inversion of the pigeonite has led to the creation of APB's.

Download Full-text

Faceted antiphase boundaries in GaAs grown on Ge

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010012638x ◽

1987 ◽

Vol 45 ◽

pp. 314-315

Author(s):

N.-H. Cho ◽

S. McKernan ◽

C.B. Carter ◽

K. Wagner

Keyword(s):

Cross Section ◽

Atomic Resolution ◽

Face Centered Cubic ◽

Electrical Behavior ◽

Sphalerite Structure ◽

Antiphase Boundaries ◽

Transmission Electron ◽

Face Centered ◽

Quality Material ◽

Simulated Images

Interest has recently increased in the possibility of growing III-V compounds epitactically on non-polar substrates to produce device quality material. Antiphase boundaries (APBs) may then develop in the GaAs epilayer because it has sphalerite structure (face-centered cubic with a two-atom basis). This planar defect may then influence the electrical behavior of the GaAs epilayer. The orientation of APBs and their propagation into GaAs epilayers have been investigated experimentally using both flat-on and cross-section transmission electron microscope techniques. APBs parallel to (110) plane have been viewed at the atomic resolution and compared to simulated images.Antiphase boundaries were observed in GaAs epilayers grown on (001) Ge substrates. In the image shown in Fig.1, which was obtained from a flat-on sample, the (110) APB planes can be seen end-on; the faceted APB is visible because of the stacking fault-like fringes arising from a lattice translation at this interface.

Download Full-text

Diffraction from arrays of antiphase boundaries in ordered III-V alloys

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100126378 ◽

1987 ◽

Vol 45 ◽

pp. 312-313

Author(s):

T. S. Kuan

Keyword(s):

High Surface ◽

Growth Conditions ◽

Ternary Alloys ◽

Local Growth ◽

Antiphase Boundaries ◽

Surface Mobility ◽

Ordered Phases ◽

Diffraction Patterns ◽

Atomically Flat ◽

Degree Of Order

Recent electron diffraction studies have found ordered phases in AlxGa1-xAs, GaAsxSb1-x, and InxGa1-xAs alloy systems, and these ordered phases are likely to be found in many other III-V ternary alloys as well. The presence of ordered phases in these alloys was detected in the diffraction patterns through the appearance of superstructure reflections between the Bragg peaks (Fig. 1). The ordered phase observed in the AlxGa1-xAs and InxGa1-xAs systems is of the CuAu-I type, whereas in GaAsxSb1-x this phase and a chalcopyrite type ordered phase can be present simultaneously. The degree of order in these alloys is strongly dependent on the growth conditions, and during the growth of these alloys, high surface mobility of the depositing species is essential for the onset of ordering. Thus, the growth on atomically flat (110) surfaces usually produces much stronger ordering than the growth on (100) surfaces. The degree of order is also affected by the presence of antiphase boundaries (APBs) in the ordered phase. As shown in Fig. 2(a), a perfectly ordered In0.5Ga0.5As structure grown along the <110> direction consists of alternating InAs and GaAs monolayers, but due to local growth fluctuations, two types of APBs can occur: one involves two consecutive InAs monolayers and the other involves two consecutive GaAs monolayers.

Download Full-text