Islands Size-Controlled Phase Transition in MBE-Grown Two-Dimensional NbSe₂

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Single-layer Niobium Diselenide (NbSe2) exhibits unique phase-dependent electronic properties.
• Controlling the crystalline phase (1T vs. 2H) is essential for its applications.
• Existing methods for phase control in NbSe2, like substrate temperature in MBE, have limitations.

Purpose of the Study:

• To investigate alternative methods for phase control in single-layer NbSe2.
• To understand the underlying mechanism of phase transitions.
• To achieve large, phase-pure 2H-phase NbSe2 islands.

Main Methods:

• Utilized molecular beam epitaxy (MBE) for NbSe2 growth.
• Controlled the island size during MBE growth as a key parameter.
• Employed scanning tunneling spectroscopy (STS) to analyze island morphology and phase.
• Performed statistical analysis and theoretical calculations to elucidate the mechanism.

Main Results:

• Demonstrated phase transition from 1T to 2H phase by controlling island size.
• Observed distinct growth stages: 1T nucleation, coalescence with transition, and 2H formation.
• Identified edge energy-controlled size effect as the mechanism for phase transition.
• Successfully produced large, compact 2H-phase NbSe2 islands.

Conclusions:

• Island size control in MBE offers a viable route for phase engineering in single-layer NbSe2.
• The size-effect mechanism provides fundamental insights into phase transitions in 2D materials.
• This approach can potentially be extended to other transition metal dichalcogenides (TMDs).