Evidence of ⟨a + c⟩ dislocations in synthetic quartz single crystals compressed along the c axis

Domains visible by transmission electron microscopy, believed to be Dauphiné inversion twins, were found in some specimens of synthetic quartz heated to 680°C and cooled to room temperature. With the electron beam close to parallel to the [0001] direction the domain boundaries appeared as straight lines normal to <100> and <410> or <510> directions. In the selected area diffraction mode, a shift of the Kikuchi lines was observed when the electron beam was made to traverse the specimen across a boundary. This shift indicates a change in orientation which accounts for the visibility of the domain by diffraction contrast when the specimen is tilted. Upon exposure to a 100 KV electron beam with a flux of 5x 1018 electrons/cm2sec the boundaries are rapidly decorated by radiation damage centers appearing as black spots. Similar crystallographio boundaries were sometimes found in unannealed (0001) quartz damaged by electrons.

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The Microstructure of Shock-Synthesized Diamond

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010006163x ◽

1967 ◽

Vol 25 ◽

pp. 324-325

Author(s):

Lucien F. Trueb

Keyword(s):

Single Crystals ◽

Preferred Orientation ◽

High Magnification ◽

Texture Pattern ◽

Shock Process ◽

New Type ◽

Diffraction Diagram

A new type of synthetic industrial diamond formed by an explosive shock process has been recently developed by the Du Pont Company. This material consists of a mixture of two basically different forms, as shown in Figure 1: relatively flat and compact aggregates of acicular crystallites, and single crystals in the form of irregular polyhedra with straight edges.Figure 2 is a high magnification micrograph typical for the fibrous aggregates; it shows that they are composed of bundles of crystallites 0.05-0.3 μ long and 0.02 μ. wide. The selected area diffraction diagram (insert in Figure 2) consists of a weak polycrystalline ring pattern and a strong texture pattern with arc reflections. The latter results from crystals having preferred orientation, which shows that in a given particle most fibrils have a similar orientation.

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A New Defect in Polyethylene Single Crystals

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100070795 ◽

1973 ◽

Vol 31 ◽

pp. 70-71

Author(s):

E. L. Thomas ◽

S. L. Sass

Keyword(s):

Single Crystals ◽

Screw Dislocation ◽

Small Distance ◽

Dipole Model ◽

Dislocation Dipole ◽

Chain Folding ◽

Black And White ◽

Polymer Crystal ◽

Different Types

In polyethylene single crystals pairs of black and white lines spaced 700-3,000Å apart, parallel to the [100] and [010] directions, have been identified as microsector boundaries. A microsector is formed when the plane of chain folding changes over a small distance within a polymer crystal. In order for the different types of folds to accommodate at the boundary between the 2 fold domains, a staggering along the chain direction and a rotation of the chains in the plane of the boundary occurs. The black-white contrast from a microsector boundary can be explained in terms of these chain rotations. We demonstrate that microsectors can terminate within the crystal and interpret the observed terminal strain contrast in terms of a screw dislocation dipole model.

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Preferential Sputtering of Ni3Al Single Crystals Studied Using Atom-Probe Field-Ion Microscopy and XPS

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100096813 ◽

1981 ◽

Vol 39 ◽

pp. 16-17

Author(s):

M.P. Thomas ◽

A.R. Waugh ◽

M.J. Southon ◽

Brian Ralph

Keyword(s):

Single Crystals ◽

Photoelectron Spectroscopy ◽

Surface Composition ◽

Depth Profiling ◽

Analytical Techniques ◽

Atom Probe ◽

Probe Field ◽

Preferential Sputtering ◽

Argon Ion Bombardment ◽

Argon Ion

It is well known that ion-induced sputtering from numerous multicomponent targets results in marked changes in surface composition (1). Preferential removal of one component results in surface enrichment in the less easily removed species. In this investigation, a time-of-flight atom-probe field-ion microscope A.P. together with X-ray photoelectron spectroscopy XPS have been used to monitor alterations in surface composition of Ni3Al single crystals under argon ion bombardment. The A.P. has been chosen for this investigation because of its ability using field evaporation to depth profile through a sputtered surface without the need for further ion sputtering. Incident ion energy and ion dose have been selected to reflect conditions widely used in surface analytical techniques for cleaning and depth-profiling of samples, typically 3keV and 1018 - 1020 ion m-2.

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Dislocation structures around SiO2 Particles in aged Cu-Cr-SiO2

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100110118 ◽

1978 ◽

Vol 36 (1) ◽

pp. 594-595

Author(s):

N.J. Long ◽

M.H. Loretto ◽

C.H. Lloyd

Keyword(s):

Flow Stress ◽

Single Crystals ◽

Room Temperature ◽

Thin Foil ◽

Age Hardening ◽

Dispersion Strengthening ◽

Accurate Picture ◽

The Matrix ◽

Very High ◽

Good Agreement

IntroductionThere have been several t.e.m. studies (1,2,3,4) of the dislocation arrangements in the matrix and around the particles in dispersion strengthened single crystals deformed in single slip. Good agreement has been obtained in general between the observed structures and the various theories for the flow stress and work hardening of this class of alloy. There has been though some difficulty in obtaining an accurate picture of these arrangements in the case when the obstacles are large (of the order of several 1000's Å). This is due to both the physical loss of dislocations from the thin foil in its preparation and to rearrangement of the structure on unloading and standing at room temperature under the influence of the very high localised stresses in the vicinity of the particles (2,3).This contribution presents part of a study of the Cu-Cr-SiO2 system where age hardening from the Cu-Cr and dispersion strengthening from Cu-Sio2 is combined.

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