Large Frequency Change with Thickness in Interlayer Breathing Mode--Significant Interlayer Interactions in Few Layer...

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Few-layer black phosphorus (BP) is a promising channel material for next-generation electronics.
• Understanding its physical properties, particularly phonon behavior, is essential for its application.
• Interlayer interactions in layered materials significantly impact their electronic and vibrational properties.

Purpose of the Study:

• To investigate the phonon properties of few-layer black phosphorus (BP) in the low-frequency regime.
• To analyze the thickness dependence of interlayer vibrational modes.
• To elucidate the nature and strength of interlayer interactions in BP.

Main Methods:

• Theoretical calculations of phonon properties.
• Experimental measurements of vibrational modes in few-layer BP.
• Comparison of experimental and theoretical results for interlayer breathing modes.

Main Results:

• The interlayer breathing mode A(3)g exhibits a significant redshift with increasing layer thickness.
• BP's thickness dependence is twice that of MoS2 and WSe2 due to a larger interlayer force constant and smaller atomic mass.
• The derived interlayer out-of-plane force constant is ~50% larger than in graphene and MoS2.

Conclusions:

• Interlayer interactions in BP are strong and possess a sizable covalent character, not merely van der Waals forces.
• These strong interactions explain BP's surface reactivity and are vital for phenomena like electric-field induced Dirac cones.
• The unique phonon properties of few-layer BP offer new avenues for advanced electronic applications.