Capturing the Hidden Short-Range Order in Amorphous Oxide Interfaces That Directs Quasi-Epitaxial Thin-Film Growth

Abstract As solid-state device architectures become increasingly complex, buried interfaces play a critical role in determining thin-film texture, morphology, and defect formation. However, resolving the structural features that control growth on nominally amorphous interlayers remains challenging because it requires three-dimensional sensitivity at high spatial resolution. Here, we combine four-dimensional scanning transmission electron microscopy, fluctuation electron microscopy, and multislice electron ptychography to investigate ruthenium (Ru) thin films grown on an underlying amorphous Ta2O5 layer, a material stack relevant for next-generation electronic and spintronic devices. Although the Ta2O5 layer appears amorphous in conventional imaging, diffraction and depth-resolved ptychographic reconstructions reveal nanoscale β-Ta2O5-like ordered motifs near the Ru/Ta2O5 interface. These locally ordered motifs, together with the interfacial morphology, guide the orientation of the Ru layer and produce a textured, quasi-epitaxial film. The curved and atomically rough interface further induces depth-dependent strain gradients and promotes planar defect formation within the Ru layer. Collectively, these results demonstrate that hidden short-range order within nominally amorphous oxides can direct the growth of metallic thin films, providing a framework for engineering buried interfaces in advanced electronic and spintronic material stacks.