Interlayer coupling effect in twisted stacked few layer black phosphorus revealed by abnormal blue shifts in Raman spectra

TL;DR

This study investigates the interlayer coupling in twisted black phosphorus heterostructures, revealing abnormal Raman blue shifts caused by non-van der Waals interactions, supported by experimental and theoretical analysis.

Contribution

It demonstrates the significant interlayer coupling effects in twisted black phosphorus, highlighting interactions beyond traditional van der Waals forces through combined experiments and density functional theory.

Findings

Observation of abnormal blue shifts in Raman spectra

Identification of non-van der Waals interlayer interactions

Theoretical explanation of phonon behavior differences

Abstract

Twisted stacked few layer black phosphorus heterostructures were successfully fabricated in this work. Abnormal blue shifts in their Ag1 and Ag2 Raman peaks and unique optical reflections were observed in these samples. The phonon behavior difference can be explained by our density functional theory calculations, which suggest that interlayer coupling has a significant effect in twisted bilayer black phosphorus. According to the calculations, the interlayer interactions are not simply van der Waals interactions. Additional interactions, such as weak valence bonding between the top and bottom flakes, are considered to be the cause of the blue shifts in their Raman spectra.