Ion-gel-gating-induced oxygen vacancy formation in epitaxial La0.5Sr0.5CoO3−δ films from in operando x-ray and neutron scattering

Jeff Walter, Guichuan Yu, Biqiong Yu, Alexander Grutter, Brian Kirby, Julie Borchers, Zhan Zhang, Hua Zhou, Turan Birol, Martin Greven, Chris Leighton

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31 Scopus citations

Abstract

Ionic-liquid/gel-based transistors have emerged as a potentially ideal means to accumulate high charge-carrier densities at the surfaces of materials such as oxides, enabling control over electronic phase transitions. Substantial gaps remain in the understanding of gating mechanisms, however, particularly with respect to charge carrier vs oxygen defect creation, one contributing factor being the dearth of experimental probes beyond electronic transport. Here we demonstrate the use of synchrotron hard x-ray diffraction and polarized neutron reflectometry as in operando probes of ion-gel transistors based on ferromagnetic La0.5Sr0.5CoO3−δ. An asymmetric gate-bias response is confirmed to derive from electrostatic hole accumulation at negative gate bias vs oxygen vacancy formation at positive bias. The latter is detected via a large gate-induced lattice expansion (up to 1%), complementary bulk measurements and density functional calculations enabling quantification of the bias-dependent oxygen vacancy density. Remarkably, the gate-induced oxygen vacancies proliferate through the entire thickness of 30–40-unit-cell-thick films, quantitatively accounting for changes in the magnetization depth profile. These results directly elucidate the issue of electrostatic vs redox-based response in electrolyte-gated oxides, also demonstrating powerful approaches to their in operando investigation.
Original languageEnglish (US)
Article number071403
JournalPhysical Review Materials
Volume1
Issue number7
DOIs
StatePublished - Dec 19 2017

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