Quantitative HRTEM and its application in the study of oxide materials

On the basis of a state-of-the-art aberration-corrected transmission electron microscope, the spherical aberration coefficient C_S of the objective lens can be tuned to either a positive or a negative value. The use of a negative value of C_S combined with an overfocus setting of the objective lens leads to the development of the negative C_S imaging (NCSI) technique. Images obtained using the NCSI technique show superior contrast and signal intensity at atomic column positions than the corresponding positive C_S images, especially for weakly scattering oxygen columns that are in close proximity to strongly scattering cation columns in oxides. Based on the images obtained under the NCSI condition, quantification of the image contrast allows measurements of the atom positions with a precision of a few picometers and the local chemistry on atomic scale. In the present review, we discuss firstly the benefits of the NCSI technique in studies of oxide materials, and then show a procedure for quantitative analysis of the image based on the absolute value of contrast. In the last part, examples are given for the application of the quantitative high-resolution transmission electron microscopy (HRTEM) to the study of electric dipoles of oxide ferroelectrics and atomic-scale chemistry of interfaces.