<p>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 <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41598_2025_15902_Article_IEq3.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="52" /> </InlineMediaObject> <EquationSource Format="TEX">\(\hbox {SrTiO}_3\)</EquationSource> </InlineEquation> membranes with high crystallinity and defined surface morphology. To study the interfacial redox-behavior of the singly <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41598_2025_15902_Article_IEq4.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="36" /> </InlineMediaObject> <EquationSource Format="TEX">\(\hbox {TiO}_2\)</EquationSource> </InlineEquation>-terminated, annealed membrane, we employ the formation of oxygen vacancies in <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41598_2025_15902_Article_IEq3.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="52" /> </InlineMediaObject> <EquationSource Format="TEX">\(\hbox {SrTiO}_3\)</EquationSource> </InlineEquation>, triggered by the low-pressure deposition of a thin <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41598_2025_15902_Article_IEq6.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="55" /> </InlineMediaObject> <EquationSource Format="TEX">\(\hbox {LaAlO}_3\)</EquationSource> </InlineEquation> layer epitaxially grown on the transferred <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41598_2025_15902_Article_IEq3.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="52" /> </InlineMediaObject> <EquationSource Format="TEX">\(\hbox {SrTiO}_3\)</EquationSource> </InlineEquation> layer. A mixed Ti<InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41598_2025_15902_Article_IEq8.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="37" /> </InlineMediaObject> <EquationSource Format="TEX">\(^{3+/4+}\)</EquationSource> </InlineEquation> valence state is indicative of the induced transfer of oxygen ions from the confined <InlineEquation ID="IEq9"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41598_2025_15902_Article_IEq3.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="52" /> </InlineMediaObject> <EquationSource Format="TEX">\(\hbox {SrTiO}_3\)</EquationSource> </InlineEquation> membrane into the <InlineEquation ID="IEq10"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41598_2025_15902_Article_IEq6.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="55" /> </InlineMediaObject> <EquationSource Format="TEX">\(\hbox {LaAlO}_3\)</EquationSource> </InlineEquation> overlayer, resulting in an oxygen vacancy concentration of around <InlineEquation ID="IEq11"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41598_2025_15902_Article_IEq11.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="71" /> </InlineMediaObject> <EquationSource Format="TEX">\(10^{21}~{\hbox {cm}^{-3}}\)</EquationSource> </InlineEquation> in the confined <InlineEquation ID="IEq12"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41598_2025_15902_Article_IEq3.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="52" /> </InlineMediaObject> <EquationSource Format="TEX">\(\hbox {SrTiO}_3\)</EquationSource> </InlineEquation> membrane. Our results highlight that interfacial redox-reactions can be induced in <InlineEquation ID="IEq13"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41598_2025_15902_Article_IEq3.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="52" /> </InlineMediaObject> <EquationSource Format="TEX">\(\hbox {SrTiO}_3\)</EquationSource> </InlineEquation> membranes, which enables the ionic engineering of confined oxide heterointerfaces based on the freestanding oxide approach.</p>

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Chemical termination and interfacial redox behavior of freestanding SrTiO3

  • M. A. Wohlgemuth,
  • K. Nayak,
  • A. Kaus,
  • L. Heymann,
  • L.-K. Huang,
  • A. Sarantopoulos,
  • J. D. Thomsen,
  • R. E. Dunin-Borkowski,
  • V. Rouco,
  • J. Santamaría,
  • R. Dittmann,
  • F. Gunkel

摘要

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.