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Tailoring oxide heterointerfaces has sparked the search for electronic and ionic phenomena in low-dimensional, confined systems. The fabrication of freestanding oxide membranes has further expanded the possible fields of application. Based on the structural vulnerability and physical confinement of such membranes, it remains a great challenge to achieve atomically defined and single-terminated surfaces by the typical chemical treatments and to induce interfacial redox-reactions in these nanoscopic transition metal oxides. To address this, we use the sacrificial layer exfoliation route, involving an all-perovskite epitaxial layer structure to fabricate freestanding Formula: see text membranes with high crystallinity and defined surface morphology. To study the interfacial redox-behavior of the singly Formula: see text-terminated, annealed membrane, we employ the formation of oxygen vacancies in Formula: see text, triggered by the low-pressure deposition of a thin Formula: see text layer epitaxially grown on the transferred Formula: see text layer. A mixed TiFormula: see text valence state is indicative of the induced transfer of oxygen ions from the confined Formula: see text membrane into the Formula: see text overlayer, resulting in an oxygen vacancy concentration of around Formula: see text in the confined Formula: see text membrane. Our results highlight that interfacial redox-reactions can be induced in Formula: see text membranes, which enables the ionic engineering of confined oxide heterointerfaces based on the freestanding oxide approach.
Wohlgemuth et al. (Thu,) studied this question.