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Naoto Takanashi, Takehito Seki, Eiji Abe, B11-P-07
Phase-contrast characteristics of annular bright-field imaging in STEM , Microscopy, Volume 64, Issue suppl_1, November 2015, Page i81, https://doi.org/10.1093/jmicro/dfv211Close - Share Icon Share
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Recently, annular-bright-filed (ABF) imaging in scanning transmission electron microscopy (STEM) has attarcted increasing attentions, since it is extremely sensitive to detect light atom positions such as lithium and hydrogen. High-sensitivity of ABF imaging is effectively explained by its phase-contrast nature; i.e., accroding to reciprocity, ABF imaging is shown to be equivalent to the hollow-cone illumination (HCI) imaging in TEM [ 1 ]. Generally, the phase-contrast in conventional high-resolution TEM reveals complicated behaviors, as the image appearance varies strognly depending on the defocus values and specimen thickness. For the ABF -STEM images, these complexities seem to be significantly supressed [ 2 ], but its phase-contrast characteristics are not fully understood yet. In the present paper, we attempt to interpret the ABF-STEM imaging based on the unique contrast-transfer-function (CTF) [ 3 ].
Although ABF-STEM is believed to be significantly robust to the contrast reversal of typical phase-contrast characteristics, it indeed occurs as demonstrated by simulations of the cubic boron-nitride (c-BN) crystal (Fig. 1 ). The contrast reverses systematically depend on the defocus values from 0 nm to 10nm. This focus-dependence behavior of ABF-STEM cannot be simply interpreted by the conventional HCI-related CTF [ 2 ]. Alternatively, we find that such behaviors can be reasonably interpreted according to “integrated CTF” concept [ 3 ].
