Revealing buried layers in oxide heterostructures with scanning transmission electron microscopy using integrated differential phase contrast (STEM‐iDPC) imaging

Atomic‐scale characterisation of thin buried layers in oxide heterostructures is often limited by the reduced sensitivity of conventional Z ‐contrast high‐angle annular dark‐field (HAADF) imaging to light elements and low‐density regions. Here, a Sc 2 O 3 /Er 2 O 3 /Si heterostructure was investigated using aberration‐corrected scanning transmission electron microscope (STEM) with simultaneous HAADF and integrated differential phase contrast (iDPC) imaging, with site‐specific cross‐sectional specimens prepared by scanning electron microscope‐plasma focused ion beam (SEM‐PFIB) using a Xe‐ion beam under identical acquisition conditions to enable direct contrast comparison. Although HAADF clearly resolves the heavy rare‐earth oxide layers and reveals a broad interfacial region with contrast variations indicative of structural complexity, simultaneous STEM‐iDPC imaging resolves a distinct ∼3 nm buried interfacial layer with substantially greater clarity. Additional high‐resolution transmission electron microscopy (HRTEM) and electron energy‐loss spectroscopy (EELS) analyses reveal oxygen enrichment and local structural ordering within this region, indicating that it is chemically and structurally distinct from both crystalline Si and bulk Er 2 O 3 . The combined observations are consistent with an oxygen‐rich Er–Si–O transition layer. These results demonstrate the capability of STEM‐iDPC to reveal buried interfacial structure and highlight the value of combining HAADF, iDPC, HRTEM and spectroscopy for comprehensive characterisation of oxide heterostructures.