Atomic-Level Imaging and Quantification of Dopants in a Semiconducting Complex Oxide

Functional oxide materials exhibit unique electronic and ionic properties that can readily be tuned via compositional variations and local defect chemistry. Adding small amounts of dopant atoms is a classical approach for tuning the conductivity. The impact of doping, however, can go way beyond changes in conductivity, driving completely new physical phenomena such as insulator-metal transitions, interfacial magnetism and superconductivity. Despite this substantial influence on the material properties, atomic scale 3D imaging and quantification of the dopant atoms that are responsible for the emergent phenomena remain major challenges.<br/><br/>Here, we apply atom probe tomography (APT) to overcome this issue, gaining experimental insight into the 3D distribution of solute Ti atoms in the narrow band gap semiconductor Er(Mn,Ti)O₃. Using APT, we quantify local doping levels, here Ti concentration of just 0.04 at.%, with nanoscale spatial precision and study key characteristics, such as density fluctuations, gradient effects, and dopant clustering. Most importantly, we manage to resolve the 3D position of individual Ti atoms within the crystal lattice, showing that the dopant atoms occupy Mn lattice sites.<br/><br/>Our results establish a new pathway for atomic-scale 3D imaging of individual dopants in functional oxides, bringing us an important step closer to understanding their complex atomic-scale physics and control their lattice, charge and spin degrees of freedom at the local scale.