Simplification of selective imaging of dislocation loops: diffraction-selected on-zone STEM

ABSTRACT

Contrary to the conventional belief that, in transmission electron microscopy (TEM), selective and sharp imaging of dislocation loops can be realized only by accurate tilting of a specimen from the condition that the symmetrical axis of incident electron beam distribution is parallel to a zone axis of the TEM specimen (on-zone condition), we demonstrate that selective dark-field (DF) imaging of dislocation loops at on-zone condition is possible with a scanning TEM (STEM) mode that uses an objective lens aperture to select a diffraction disk of interest. Diffraction-selected on-zone STEM (DsoZ-STEM) has been applied to selective DF imaging of dislocation loops with a short axis length of <2 nm in a single-crystal aluminum irradiated by argon ions and an electron beam at room temperature. It was found that a Kikuchi line enhances the contrast among the dislocation loops and the matrix of DsoZ-STEM images. DsoZ-STEM obeyed g·b invisibility criterion and showed good agreement with a typical visibility change of a dislocation line and a loop in conventional DF images with a specific pair of $\pm$g. In addition, dislocation loops always showed much higher brightness in the inner side compared to the outer side in DsoZ-STEM images, simplifying the distinction of dislocation loops with apparently the same long-axis direction but different b. Thus, DsoZ-STEM can simplify the selective DF imaging for the determination of the number and the character of dislocation loops.

GRAPHICAL ABSTRACT

KEYWORDS:

• STEM
• dislocation loops
• diffraction contrast
• irradiation damage

Acknowledgements

The authors thank Mr Sho Tamaru and Mr Ryota Kinoshita of Kobe Material Testing Laboratory Co., Ltd for technical support of the electropolishing process for TEM specimen preparation.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Energy Transformation Research Laboratory, Central Research Institute of Electric Power Industry.

Notes on contributors

Masaya Kozuka

Masaya Kozuka is a research scientist of microscopy (especially APT and TEM) and neutron irradiation embrittlement at Central Research Institute of Electric Power Industry (CRIEPI). His work focuses recently on the relationship between dislocation loop formation and embrittlement of the reactor pressure vessel steels. His favourite is running along the coast near his home.

Yuichi Miyahara

Yuichi Miyahara is a research scientist of microstructural analysis (EBSD, TEM, APT) and characterization of environmental degradation of structural materials (Stress Corrosion Cracking, Irradiation hardening and embrittlement) at CRIEPI. His work focuses recently on microstructural evolution of irradiated stainless steels and reactor pressure vessel steels