  A small percentage of dopant atoms can completely change the physical
properties of the host material. For example, chemical doping controls the
electronic transport behavior of semiconductors and gives rise to a wide range
of emergent electric and magnetic phenomena in oxides. Imaging of individual
dopant atoms in lightly doped systems, however, remains a major challenge,
hindering characterization of the site-specific effects and local dopant
concentrations that determine the atomic-scale physics. Here, we apply
atom-probe tomography (APT) to resolve individual Ti atoms in the narrow band
gap semiconductor ErMnO3 with a nominal proportion of 0.04 atomic percent. Our
3D imaging measures the Ti concentration at the unit cell level, providing
quantitative information about the dopant distribution within the ErMnO3
crystal lattice. High-resolution APT maps reveal the 3D lattice position of
individual Ti atoms, showing that they are located within the Mn layers with no
signs of clustering or other chemical inhomogeneities. The 3D atomic-scale
visualization of individual dopant atoms provides new opportunities for the
study of local structure-property relations in complex oxides, representing an
important step toward controlling dopant-driven quantum phenomena in
next-generation oxide electronics.
