Electric-Field-Controlled Phase Transformation in WO₃ Thin Films through Hydrogen Evolution.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Electrochemistry

Background:

• Ionic-liquid gating (ILG) offers excellent carrier-density tunability in field-effect transistors.
• The precise role of electrochemical effects in ILG remains a subject of recent debate.

Purpose of the Study:

• To investigate the insulator-to-metal transition in WO3 thin films using ILG.
• To elucidate the underlying mechanisms, particularly the influence of electrochemical effects.

Main Methods:

• Fabrication of WO3 thin films.
• Application of ionic-liquid gating (ILG) to induce electrical and structural changes.
• Secondary-ion mass spectrometry (SIMS) for elemental and chemical state analysis.

Main Results:

• Achieved a field-induced insulator-to-metal transition in WO3 thin films via ILG.
• Observed significant structural transformations accompanying the electrical transition.
• SIMS data confirmed electrochemically driven hydrogen evolution as the dominant mechanism, involving surface absorption and bulk intercalation.

Conclusions:

• Electrochemical hydrogen evolution is the primary driver of the observed insulator-to-metal transition and structural changes in ILG-treated WO3 films.
• The findings clarify the role of electrochemical effects in ILG phenomena.
• This study provides critical insights into the mechanisms governing carrier modulation in transition metal oxides.