High contrast STEM imaging for light elements by an annular segmented detector

•Detector geometries for observing ultra-light elements in annular bright-field (ABF) STEM is considered.•To predict image characteristics of annular detectors, a phase contrast transfer function (PCTF) including effects of finite specimen thickness is calculated.•The predictions agree well with mul...

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Bibliographic Details
Published in:Ultramicroscopy 2019-07, Vol.202, p.148-155
Main Authors: Ooe, Kousuke, Seki, Takehito, Ikuhara, Yuichi, Shibata, Naoya
Format: Article
Language:English
Subjects:
Annular bright-field
Lithium-rich cathode
Phase contrast
Scanning transmission electron microscopy (STEM)
Segmented detector
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Summary:•Detector geometries for observing ultra-light elements in annular bright-field (ABF) STEM is considered.•To predict image characteristics of annular detectors, a phase contrast transfer function (PCTF) including effects of finite specimen thickness is calculated.•The predictions agree well with multi-slice simulations and experiments, and a better detector geometry for observing lithium atomic columns is established.•The optimal inner angle of the ABF detector is determined to vary from 0.79 α to 0.9 α (α denoting the convergence semi-angle). Annular bright-field scanning transmission electron microscopy (ABF STEM) has been actively used to directly observe the light element atoms inside materials and devices. However, the detector angle condition for conventional ABF STEM has been empirically selected and thus is not always optimized for observing ultra-light element atoms such as hydrogen and lithium atoms. In this study, the detector conditions for ABF STEM were reexamined by calculating a new type of phase contrast transfer function (PCTF) for an annularly segmented detector to maximize the image contrast of ultra-light element atoms such as lithium. Using this new PCTF, an improved detector geometry for observing lithium atoms is demonstrated, which is confirmed by the image simulations and experiments in several types of lithium cathode materials.
ISSN:0304-3991
1879-2723
DOI:10.1016/j.ultramic.2019.04.011