Contrast Investigation of Annular Bright-Field Imaging in Scanning Transmission Electron Microscopy of LiFePO4
Light elements, such as lithium, are difficult to detect using high-angle annular dark-field imaging (HAADF) in STEM because of their weak atomic scattering. Recently, a novel imaging mode in aberration-corrected STEM was presented that uses an annular detector spanning an angular range mainly within the illumination cone of the focused electron beam . It was shown that due to the smaller dependence on atomic number Z, approximately Z1/3 compared to Z2 in HAADF, the resulting images enable one to visualize the light element columns . This imaging mode has been called annular bright-field (ABF) imaging.
We study the contrast in ABF imaging in STEM on LiFePO4, correlating results of experiments from the newly installed probe-aberration-corrected JEM-ARM 200CF and simulations using the STEMsim program . Previous work briefly demonstrated the possibility of acquiring direct images of LiFePO4 and partially de-lithiated LiFePO4 at atomic resolution . Experimental comparisons have been made of the visualization of lithium in LiFePO4 with HAADF and ABF (see figure). We aim to present a more detailed description of the contrast dynamics of ABF imaging of LiFePO4 with a view to its interpretation, and optimization. Thickness, defocus, angular range, and possible contamination introduced by sample preparation are taken into account to understand the image contrast. In particular, the probe and detector configurations in the microscope are taken into consideration to step from qualitative to quantitative contrast evaluation.
 Okunishi, E., Ishikawa, I., Sawada, H., Hosokawa, F., Hori, M., Kondo, Y., Microsc Microanal., 15 (2009) 164-165
 Findlay, S. D., Shibata, N., Sawada, H., Okunishi, E., Kondo, Y., Ikuhara, Y., Ultramicroscopy, 110 (2010) 903-923
 Rosenauer, A., Schowalter, M., Springer Proc. Phys., 120 (2008) 169-172
 Gu, L., Zhu, C.B., Li, H., Yu, Y., Li, C.L., Tsukimoto, S., Maier, J., Ikuhara, Y., J. Am. Chem. Soc., 133 (2011) 4661-4663
This research has received funding from the European Union Seventh Framework Programme [FP7/2007-2013] under grant agreement no. 312483 (ESTEEM2). Researchers from Dept. Maier collaborate in this project.