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

Abstract

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.