Chemical termination and interfacial redox behavior of freestanding SrTiO3

Abstract

Abstract 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 $$\hbox {SrTiO}_3$$ membranes with high crystallinity and defined surface morphology. To study the interfacial redox-behavior of the singly $$\hbox {TiO}_2$$ -terminated, annealed membrane, we employ the formation of oxygen vacancies in $$\hbox {SrTiO}_3$$ , triggered by the low-pressure deposition of a thin $$\hbox {LaAlO}_3$$ layer epitaxially grown on the transferred $$\hbox {SrTiO}_3$$ layer. A mixed Ti $$^{3+/4+}$$ valence state is indicative of the induced transfer of oxygen ions from the confined $$\hbox {SrTiO}_3$$ membrane into the $$\hbox {LaAlO}_3$$ overlayer, resulting in an oxygen vacancy concentration of around $$10^{21}~{\hbox {cm}^{-3}}$$ in the confined $$\hbox {SrTiO}_3$$ membrane. Our results highlight that interfacial redox-reactions can be induced in $$\hbox {SrTiO}_3$$ membranes, which enables the ionic engineering of confined oxide heterointerfaces based on the freestanding oxide approach.