Annular dark-field scanning transmission electron microscopy (ADF-STEM) imaging is often called as the Z-contrast, where the element with a higher atomic number gives rise to the brighter contrast. ADF-STEM imaging on the self-assembled (Ti,V)O2 heterostructure, exhibiting the alternating V-rich and Ti-rich layers, unexpectedly reveals the higher contrast in V-rich layers in spite of the nearly identical atomic numbers of Ti (Z = 22) and V (Z = 23). Our analyses of local strain mapping and electron energy loss spectroscopy (EELS) confirm that oxygen vacancies are formed dominantly in the V-rich and thus the higher contrast in the V-rich layers is attributable to the accumulation of oxygen vacancies facilitated by the inherent 001 channel pathways of the rutile structure. Our results highlight the critical role of crystallographic pathways in guiding oxygen vacancy diffusion within rutile-based heterostructures.
Sim et al. (Mon,) studied this question.