Unveiling surface dynamics: in situ oxidation of defective WS₂

Area of Science:

• Materials Science
• Surface Science
• Nanotechnology

Background:

• Transition-metal dichalcogenides (TMDs) are crucial for advanced applications.
• Defects and oxidation in air significantly impact TMD performance.
• Understanding oxidation dynamics is vital for material stability.

Purpose of the Study:

• To investigate the relationship between oxidation dynamics and oxygen availability in defective WS2.
• To elucidate the role of sulfur vacancies in oxidative degradation.
• To provide insights for protecting TMDs in device applications.

Main Methods:

• Inducing sulfur vacancies in WS2 using Ar+ sputtering.
• Studying oxidation under varying O2 pressures (<10-4 mbar and higher).
• Analyzing changes in tungsten (W) oxidation states using X-ray Photoelectron Spectroscopy (XPS).
• Employing Density Functional Theory (DFT) calculations to model reaction mechanisms.

Main Results:

• Oxidation rate is dependent on O2 availability and defect concentration.
• Slow oxidation observed at low O2 pressures (<10-4 mbar) due to limited O2-vacancy interactions.
• Rapid oxidation occurs at higher O2 pressures, evidenced by W oxidation state changes.
• DFT calculations confirm experimental findings and reveal O2 dissociation mechanisms on S vacancy clusters.

Conclusions:

• Sulfur vacancies significantly enhance WS2 susceptibility to oxidation.
• Oxygen pressure is a critical factor controlling oxidation kinetics.
• Reaction barriers for O2 dissociation are influenced by the coordination of surface W atoms.
• Findings offer guidance for mitigating degradation in TMD-based devices.