Interplay between Thermal Stress and Interface Binding on Fracture of WS₂ Monolayer with Triangular Voids

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Defect engineering in 2D materials like tungsten disulfide (WS₂) is key for tuning properties.
• Controlling structural defects is vital for preventing premature device failure in atomically thin materials.
• Understanding substrate interactions and thermal mismatch is essential for WS₂ monolayer reliability.

Purpose of the Study:

• To investigate the interplay between structural defects, thermal mismatch stress, and fracture behavior in WS₂ monolayers.
• To correlate microscopic and spectroscopic observations with theoretical simulations to understand failure mechanisms.
• To elucidate the role of different substrates (Silicon and sapphire) on WS₂ monolayer stability.

Main Methods:

• Microscopic imaging (STEM-HAADF) to observe structural defects and strain localization.
• Raman and Photoluminescence (PL) spectroscopy to analyze material properties and stress.
• Density Functional Theory (DFT) for calculating interfacial binding energies.
• Finite Element Method (FEM) simulations for stress distribution analysis.

Main Results:

• A direct correlation was found between thermal mismatch stress and crack patterns originating from faceted voids in WS₂.
• Tensile strain was observed to localize around the corners of faceted voids.
• WS₂ on Silicon exhibited a binding energy 20 times higher than on sapphire, increasing substrate-aided thermal stress.
• FEM simulations showed maximum stress concentration at the void tips in the WS₂ monolayer.

Conclusions:

• Substrate-aided thermal mismatch stress, exacerbated by strong interfacial interaction (e.g., WS₂/Si), is a primary cause of fracture in WS₂ monolayers.
• Faceted voids act as initiation sites for cracks due to localized strain, leading to premature failure.
• Precise control over defects and substrate selection is critical for robust WS₂-based devices.