Quantum Effects and Phase Tuning in Epitaxial Hexagonal and Monoclinic MoTe₂ Monolayers

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Monolayer transition-metal dichalcogenides (TMDs) exhibit distinct structural phases, notably hexagonal (2H) and monoclinic (1T").
• These phases possess fundamentally different electronic properties, with 2H-MoTe2 being semiconducting and 1Test-MoTe2 being semimetallic.
• The small formation energy difference between 2H- and 1Test-MoTe2 suggests potential for phase tuning and applications in phase-change electronics.

Purpose of the Study:

• To achieve controlled growth of both 2H- and 1Test-MoTe2 monolayer (ML) structures.
• To investigate the tunability of MoTe2 ML phases via molecular-beam epitaxy (MBE) conditions.
• To characterize the atomic structures, electronic properties, and quantum effects in different MoTe2 phases and at domain boundaries.

Main Methods:

• Growth of 2H- and 1Test-MoTe2 MLs using molecular-beam epitaxy (MBE).
• Systematic variation of MBE growth conditions to tune the phase formation.
• Utilizing scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) for atomic and electronic characterization.

Main Results:

• Successful growth of both 2H- and 1Test-MoTe2 MLs.
• Demonstration of phase tunability by altering MBE conditions, attributed to Te adsorption effects.
• Atomic and electronic structures of both phases were resolved by STM/STS.
• Observation of quantum confinement in 2H-MoTe2 domains and quantum interference in 1Test-MoTe2 domains, influenced by domain boundaries.

Conclusions:

• MBE is a viable technique for growing both 2H- and 1Test-MoTe2 MLs with tunable phase formation.
• Te adsorption plays a crucial role in controlling the phase of MoTe2 MLs.
• The distinct electronic properties and quantum phenomena in each phase, as well as at their interfaces, offer opportunities for novel electronic device applications.