Phase Instability in van der Waals In₂ Se₃ Determined by Surface Coordination

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Two-dimensional (2D) van der Waals In2Se3 exhibits room-temperature ferroelectricity/antiferroelectricity, even at monolayer thickness.
• The stability and degradation pathways of 2D In2Se3 remain insufficiently understood, hindering device applications.

Purpose of the Study:

• To investigate the phase instability and degradation mechanisms of 2D In2Se3.
• To elucidate the role of environmental factors and intrinsic material properties in In2Se3 stability.

Main Methods:

• Combined experimental and theoretical approaches were employed.
• Analysis focused on the octahedral coordination and edge structures of In2Se3.
• Investigated oxidation processes in air under various conditions (moisture, oxygen, light).

Main Results:

• Phase instability in both α- and β'-In2Se3 is linked to unstable octahedral coordination and broken bonds at edge steps.
• Moisture and oxygen facilitate the oxidation of In2Se3 in air, forming amorphous In2Se3-3xO3x layers and Se particles.
• Oxidation is promoted by light and self-passivates to a few nanometer thickness due to the In2Se3-3xO3x layer.

Conclusions:

• The inherent instability of In2Se3, particularly its coordination and edge structure, contributes to its degradation.
• Environmental factors like moisture, oxygen, and light accelerate oxidation, but a self-passivation mechanism limits the extent of degradation.
• Understanding these mechanisms is crucial for optimizing 2D In2Se3 for future electronic and spintronic device applications.