Atomic-scale characterization of oxide thin films gated by ionic liquid

Area of Science:

• Materials Science
• Electrochemistry
• Surface Science

Background:

• Ionic liquids (ILs) are increasingly used for electrostatic gating in complex oxide systems.
• Understanding the IL/oxide interface and potential degradation is crucial for interpreting transport phenomena.

Purpose of the Study:

• To investigate the integrity of the 1-ethyl-3-methylimidazolium hexafluorophosphate (IL) and La1/3Sr2/3FeO3 (LSF) interface under various biasing conditions.
• To identify and characterize any bias-induced electrochemical degradation at the IL/oxide interface.

Main Methods:

• Analytical transmission electron microscopy (TEM) was employed to examine the IL/oxide interface.
• Electron energy loss spectroscopy (EELS) was used to analyze elemental migration and secondary phase formation.

Main Results:

• An irreversible chemical reaction and film degradation were observed at the IL/LSF interface, irrespective of the applied bias.
• An intermixing region of 4-6 nm formed at the interface.
• La and Fe migration into the IL occurred under negative bias, leading to secondary phase formation.

Conclusions:

• The IL/LSF interface is susceptible to irreversible electrochemical degradation, forming an intermixing layer and causing element migration.
• This degradation impacts the reliability of electrostatic gating devices based on IL/oxide systems.
• The methodology can be applied to other IL/oxide systems to determine their electrochemical stability windows.