Aberration corrected electron optics allows routine acquisition of high spatial resolution spectroscopic images in the scanning transmission electron microscope, which is important when trying to understand the physics of transition-metal oxides such as manganites. The physical properties of these perovskites are intimately related to the occupancies of the partially filled $3d$ bands, which define their oxidation state. In this work, we review procedures to obtain this electronic property in ${\text{La}}_x{\text{Ca}}_{1-x}{\text{MnO}}_3$ from atomic-column-resolved electron energy-loss spectra measured in the aberration corrected scanning transmission electron microscope. In bulk samples, several features of both the average $\text{Mn}{L}_{2,3}$ edge and the $\text{O}K$ edge fine structure change linearly with Mn nominal valence. These linear correlations are extracted and used as a calibration to quantify oxidation states from atomic resolution spectroscopic images. In such images, the same fine-structure features exhibit further changes, commensurate with the underlying atomic lattice. Mn valence values calculated from those images show unexpected oscillations. The combination of experiment with density-functional theory and dynamical scattering simulations allows detailed interpretation of these maps, distinguishing dynamical scattering effects from actual changes in electronic properties related to the local atomic structure. Specifically, in ${\text{LaMnO}}_3$, the two nonequivalent O sites can be distinguished by these methods.

The ability to localize, identify, and measure the electronic environment of individual atoms will provide fundamental insights into many issues in materials science, physics, and nanotechnology. We demonstrate, using an aberration-corrected scanning transmission electron microscope, the spectroscopic imaging of single La atoms inside ${\mathrm{C}\mathrm{a}\mathrm{T}\mathrm{i}\mathrm{O}}_3$. Dynamical simulations confirm that the spectroscopic information is spatially confined around the scattering atom. Furthermore, we show how the depth of the atom within the crystal may be estimated.

When CdTe solar cells are doped with Cl, the grain boundaries no longer act as recombination centers but actively contribute to carrier collection efficiency. The physical origin of this remarkable effect has been determined through a combination of aberration-corrected scanning transmission electron microscopy, electron energy loss spectroscopy, and first-principles theory. Cl substitutes for a large proportion of the Te atoms within a few unit cells of the grain boundaries. Density functional calculations reveal the mechanism, and further indicate the grain boundaries are inverted to $n$ type, establishing local $p\text{$-${}}n$ junctions which assist electron-hole pair separation. The mechanism is electrostatic, and hence independent of the geometry of the boundary, thereby explaining the universally high collection efficiency of Cl-doped CdTe solar cells.