Journal
JOURNAL OF ELECTRON MICROSCOPY
Volume 61, Issue 6, Pages 393-400Publisher
OXFORD UNIV PRESS
DOI: 10.1093/jmicro/dfs065
Keywords
He bubbles; Fresnel contrast; multislice simulation; RAFM steels
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Funding
- U.S. Department of Energy, Office of Fusion Energy Sciences [DE-AC06-76RLO1830]
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Formation of nanoscale helium (He) bubbles in reduced activation ferritic/martensitic steels may lead to degradation of mechanical properties of materials. Transmission electron microscopy (TEM) has commonly been used to image the Fresnel contrast of He bubbles, using an underfocus of 0.5-1 mu m. This paper presents our study of multislice simulation of the size correlation between imaged Fresnel rings and the actual He bubbles. It was found that for bubbles equal to or > 3 nm in diameter, the imaged bubble size, represented by its inner diameter of the first dark Fresnel ring (D-in) in underfocused imaging conditions, increases with increasing electron-beam incoherency, but decreases with increasing underfocus. The electron-beam accelerating voltage, bubble size, bubble position and TEM sample thickness were found to have no significant influence on the deviation of D-in from the actual bubble size (D-0). However, for bubbles equal to or < 2 nm, D-in/D-0 increases dramatically with increasing underfocus when it is above a threshold limit (e.g. delta f = -1 mu m for a 2-nm bubble). The results of this study also suggested that He bubbles can be differentiated from argon (Ar) bubbles by contrast differences.
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