Structural Transition Analysis of Bilayer Black Phosphorus under High Pressure via Ultralow-Frequency Raman...

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Black phosphorus (BP) is a 2D material with unique anisotropic electron-photon and electron-phonon interactions.
• Anisotropic properties of BP can be tuned by thickness, stacking, pressure, and strain.
• Pressure effects on bilayer BP, unlike multilayer or bulk, remain underexplored.

Purpose of the Study:

• To investigate the high-pressure response (0-20 GPa) of bilayer black phosphorus (BP).
• To identify structural phase transitions and stacking sequence variations in bilayer BP.
• To analyze pressure effects on different bilayer BP stacking sequences (AA, AB, AC).

Main Methods:

• Experimental exploration of bilayer BP under high hydrostatic pressure (0-20 GPa).
• Utilized extreme low Raman shift spectroscopy (5-150 cm^-1).
• Employed angular-resolved polarized Raman spectroscopy (ARPR) to analyze stacking sequences.

Main Results:

• Observed phase transitions at ~7 GPa (orthorhombic to rhombohedral) and ~14-16 GPa (to simple cubic).
• Demonstrated reversibility of structural phase transitions across all stacking sequences.
• First-time detection of pressure-induced stacking sequence alterations, with AA and AC relaxing to AB.

Conclusions:

• Bilayer BP undergoes reversible structural phase transitions under high pressure.
• Pressure significantly modifies stacking sequences, impacting anisotropic properties.
• Bilayer BP shows promise for pressure-sensitive optoelectronic nanodevices and offers insights into 2D material interactions.