Oxygen orders differently under graphene: new superstructures on Ir(111).

Area of Science:

• Surface Science
• Materials Science
• Nanotechnology

Background:

• Oxygen adsorption on metal surfaces is crucial for catalysis and electronics.
• Understanding adsorbate superstructures on iridium(111) is key, but previous findings on specific structures were uncertain.
• The role of graphene as an interfacial layer in modifying surface chemistry is an active research area.

Purpose of the Study:

• To identify and compare oxygen adsorbate superstructures on bare Ir(111) versus those formed by intercalation under graphene on Ir(111).
• To clarify the existence and stability of oxygen structures on bare Ir(111).
• To investigate novel oxygen intercalation structures formed between graphene and Ir(111) and their formation conditions.

Main Methods:

• Scanning tunneling microscopy (STM) was employed to image oxygen adsorbate superstructures.
• Oxygen exposure under varying conditions (pressure, temperature, duration) was performed.
• Density functional theory (DFT) calculations, including dispersive forces, were used for comparison.

Main Results:

• On bare Ir(111), O-(2 × 2) and O-(2 × 1) superstructures were observed, confirming their existence.
• Under graphene on Ir(111), several oxygen intercalation superstructures were imaged, including O-(2 × 2), O-(√3×√3)-R30°, O-(2 × 1), and O-(2√3 × 2√3)-R30°.
• Two unique structures, O-(√3×√3)-R30° and O-(2√3 × 2√3)-R30°, were exclusively observed when the graphene layer was present.
• Phase coexistence and formation conditions of these intercalation structures were analyzed.

Conclusions:

• The presence of a graphene layer significantly alters oxygen adsorption behavior on Ir(111), enabling new intercalation structures.
• Graphene modifies the adsorbate-substrate interaction, leading to the formation of phases not observed on bare Ir(111).
• These findings provide fundamental insights into the role of 2D materials in controlling surface chemistry and designing novel interfaces.