The last three decades have seen a growing trend towards studying the interfacial phenomena in complex oxide heterostructures. Of particular concern is the charge distribution at interfaces, which is a crucial factor in controlling the interface transport behavior. However, the study of the charge distribution is very challenging due to its small length scale and the intricate structure and chemistry at interfaces. Here, by a combination of aberration-corrected scanning transmission electron microscopy (STEM) and spectroscopy techniques, we identify the charge accumulation in the SrMnO₃ (SMO) side of SrMnO₃ /SrTiO₃ hetero-interfaces, and find that the charge density attains the maximum of 0.13±0.07 e^- /unit cell (uc) at the first SMO monolayer. Based on quantitative atomic-scale STEM analyses and first-principle calculations, we explore the origin of interfacial charge accumulation in terms of epitaxial strain-favored oxygen vacancies, cationic interdiffusion, interfacial charge transfer, and space-charge effects. This study, therefore, provides a comprehensive description of the charge distribution and related mechanisms at the SMO/STO hetero-interfaces, which is beneficial for the functionality manipulation viacharge engineering at interfaces.

We present the fabrication and exploration of arrays of nanodots of SrRuO₃ with dot sizes between 500 nm and 15 nm. Down to the smallest dot size explored, the samples were found to be magnetic with a maximum of the Curie temperature T_C achieved by dots of 30 nm diameter. This peak in T_C is associated with a dot-size-induced relief of the epitaxial strain, as evidenced by scanning transmission electron microscopy.