Defects and Surface Structural Stability of MoTe₂ Under Vacuum Annealing

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Transition-metal dichalcogenides (TMDs) require structural stability assessments to prevent surface and interface degradation.
• Molybdenum ditelluride (MoTe2) is a key TMD with potential applications, necessitating an understanding of its thermal behavior.

Purpose of the Study:

• To investigate the structural stability of 2H-MoTe2 under thermal treatments up to 500 °C.
• To explore defect formation mechanisms and identify strategies for enhancing MoTe2 thermal stability.

Main Methods:

• Utilized scanning tunneling microscopy (STM) and scanning transmission electron microscopy (STEM) to analyze MoTe2 structure.
• Employed scanning tunneling spectroscopy (STS) to identify electronic states within MoTe2.
• Investigated the effect of monolayer graphene passivation on MoTe2 structural integrity.

Main Results:

• Observed subsurface donors from excess Te atoms at room temperature.
• Detected surface decomposition, Te vacancies, and cluster defects starting at 200 °C, increasing with temperature.
• Identified 60° inversion domain boundaries forming a 'wagon wheel' morphology after annealing at 400 °C.
• Graphene passivation effectively prevented Te loss and structural defects up to 500 °C.

Conclusions:

• Thermal treatments induce significant structural instability and defect formation in 2H-MoTe2.
• Graphene passivation is a viable strategy to greatly enhance the thermal stability of MoTe2.
• Passivated MoTe2 maintains structural integrity at temperatures up to 500 °C, enabling advanced applications.