The determination of the geometry and nature of small Frank loops using the weak‐beam method

Abstract

Theoretical and experimental investigations have been carried out to determine under which conditions weak-beam images can give useful information on the geometry, size and nature of small Frank loops. Suitable experimental conditions for obtaining such information were deduced from computed weakbeam images of Frank loops under various selected loop and foil orientations and diffraction vectors. Experiments to check these deductions were performed in silicon damaged by irradiation with phosphorus ions. It was found that the geometry and size of loops of diameter 2 8 nm (80 A) viewed normal to their habit plane was well defined by weak-beam images taken in (220) reflections lying in the loop plane for which g.b = 0 and g.b x u # 0. By imaging in reflections with g vectors not in the loop plane the enclosed stacking faults were imaged (thus confirming the loops to be Frank loops) and the sense of the Burgers vector fi.e. the loop nature) was determined.

Observation and analysis of defect cluster production and interactions with dislocations

“…Prior to their studies, weak beam microscopy was routinely used by only a few radiation effects researchers [16,17]. The standard electron microscopy method for imaging small defect clusters from the 1960s until the 1980s was based on dynamical two-beam bright field imaging [18][19][20][21][22].…”

On the application of the weak-beam technique to the determination of the sizes of small point-defect clusters in ion-irradiated copper

“…This presents considerable difficulty, especirdly for defects placed throughout foils of thickness 20-80 nm. It has long been known that the weak-beam dark-field technique has advantages over conventional strong-beam methods for imaging small clusters, for example in imaging and sizing loops of diameter> 5nrn [1] or gaining itiormation on the morphology of complex clusters such as partially-dissociated Frank loops [2]. However, the technique has certain drawbacks when the defect sizes are ve~small (see section 2.1 below).…”

Dislocation Loops in Pressureless‐Sintered Undoped BaTiO3 Ceramics

“…In contrast to the crystallographic shear (CS) structure and unstable loops reported 1 for acceptor‐doped compositions sintered in reducing atmospheres, we have observed in undoped BaTiO 3 ceramics, prepared by pressureless sintering of TiO 2 excess powder, ubiquitous dislocation loops that have survived irradiation by an electron beam at 300 keV. Such loops are characterized for the Burgers vectors ( b ), the habit plane normal ( n ), and its nature of vacancy or interstitial by the g·b =0 (effective) invisibility criteria, and the inside–outside contrast technique, 13–18 together with high‐resolution imaging, 1,4 are reported here. Atomic models that probably represent the dislocation loops are proposed.…”