Abstract
Intense electric fields developed during gating at the interface between an ionic liquid and an oxide layer have been shown to lead to significant structural and electronic phase transitions in the entire oxide layer. An archetypical example is the reversible transformation between the brownmillerite SrCoO2.5 and the perovskite SrCoO3 engendered by ionic liquid gating. Here we show using in situ atomic force microscopy studies with photothermal excitation detection, that allows for high quality measurements in the viscous environment of the ionic liquid that the edges of atomically smooth terraces at the surface of SrCoO2.5 films are significantly modified by ionic liquid gating but that the terraces themselves remain smooth. The edges develop ridges that we show, using complementary X-ray photoemission spectroscopy studies, result from the adsorption of hydroxyl groups. Our findings exhibit a way of electrically controlled surface modifications in emergent ionitronic applications.
Highlights
Intense electric fields developed during gating at the interface between an ionic liquid and an oxide layer have been shown to lead to significant structural and electronic phase transitions in the entire oxide layer
Transistor devices that use ionic liquids (ILs) allow for the development of intense electric fields within an ultrathin electric double layer (EDL) that is formed at the interface between the IL and a thin film channel.[2−5] It has been shown that these fields can lead to ion migration into and out of the film that results in structural changes or phase transformations.[6−13] These changes have potential for applications in spintronic,[14,15] sensing,[16] bioinspired,[17] and neuromorphic[18] devices
With the help of X-ray photoemission spectroscopy (XPS), we show that subnanoscale ridge structures (RSs) that emerge at the terrace edges result from reaction with hydroxyl (OH−) groups dissolved in the ionic liquid
Summary
Intense electric fields developed during gating at the interface between an ionic liquid and an oxide layer have been shown to lead to significant structural and electronic phase transitions in the entire oxide layer. The IL gating induced migration of ions can take place over very long distances up to microns, resulting in changes in physical properties of the entire bulk of a thin film.[19−21] the modification of the thin film surface itself has been little studied,[22,23] even though small changes in the state of the surface can strongly influence the electrochemical reactions that can take place in IL gating.[24,25] The existence of the viscous IL hinders the application of many surface sensitive characterization techniques.[26,27] There has been preliminary work investigating the ordering, dynamics, and interactions of ions in ILs at neutral and electrified solid/liquid interfaces using conventional atomic force microscopy (AFM).[28−30] Here, using photothermal excitation[31,32] we employ in situ. Firstprinciples density functional calculations show that the terrace edges are more reactive than the terraces themselves, consistent with our experiments
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