Atomic scale microstructure and properties of Se-deficient two-dimensional MoSe2

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Nonstoichiometric transition metal dichalcogenides exhibit unique properties.
• Molybdenum diselenide (MoSe2) is a key 2D material with potential applications.
• Controlling defects is crucial for tuning material performance.

Purpose of the Study:

• Investigate the atomic-scale microstructure of Se-deficient MoSe2 (MoSe2-x).
• Determine the role of Se-deficit in forming structural defects.
• Understand the electronic properties associated with these defects.

Main Methods:

• Aberration-corrected high-resolution transmission electron microscopy (HRTEM) for microstructure analysis.
• Density functional theory (DFT) calculations for thermodynamic stability.
• Electronic transport calculations to assess charge carrier behavior.

Main Results:

• Se-deficit in MoSe2 leads to a dense network of thermodynamically stable mirror-twin-boundaries (MTBs).
• MTBs create localized states near the valence band minimum, enhancing conductance along the boundaries.
• Hole charge carrier transmission across MTBs is significantly suppressed due to band bending.
• MTBs form in situ due to Se atom removal, not grain coalescence.
• High Se-deficit can induce transformation of 2D sheets into nanowires.

Conclusions:

• Mirror-twin-boundaries are stable defects in Se-deficient MoSe2.
• While MTBs conduct electricity along their length, they act as barriers to charge carrier transport across them.
• Deviations from stoichiometry offer a pathway to engineer the electronic and structural properties of 2D transition metal dichalcogenides.