Chemical termination and interfacial redox behavior of freestanding SrTiO₃

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 Ti[Formula: 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.