Structure Evolution of Graphitic Surface upon Oxidation: Insights by Scanning Tunneling Microscopy

Area of Science:

• Materials Science
• Surface Science
• Nanotechnology

Background:

• Oxidation of graphitic materials is crucial for synthesizing advanced materials like graphene oxide.
• Understanding early oxidation stages is limited due to experimental challenges with reactive epoxy groups and gasification during imaging.

Purpose of the Study:

• To experimentally validate theoretical predictions of early-stage oxidation structures in graphitic materials.
• To elucidate the formation and evolution of epoxy clusters and associated vacancy defects.

Main Methods:

• Utilized low-temperature scanning tunneling microscopy (LT-STM) at 4 K for atomic-resolution imaging of oxidized graphitic surfaces.
• Employed van der Waals density functional theory for quantitative verification of experimental data.

Main Results:

• Identified three distinct nanostructures of epoxy clusters, representing stages of vacancy defect evolution.
• Observed cyclic epoxy trimers, validating their energetic stability and cyclic structure.
• Demonstrated that vacancy defects form in larger clusters (2-3 nm) due to lattice strain and that epoxy groups can be reversibly removed upon heating.

Conclusions:

• Provided the first experimental validation of theoretical predictions regarding epoxy trimers in oxidized graphitic materials.
• Revealed the structural evolution of epoxy clusters and the role of lattice strain in vacancy defect formation.
• Indicated reversible functionalization of epoxy groups in graphitic materials.