Edge phonons in black phosphorus

TL;DR

This study investigates the atomic structure and phonon behavior at black phosphorus edges using Raman spectroscopy and density functional theory, revealing edge-specific phonon modes linked to atomic edge configurations.

Contribution

It provides the first combined experimental and theoretical analysis of edge phonons in black phosphorus, highlighting the dependence on edge atomic structure.

Findings

New edge-specific phonon modes observed in Raman spectra

Edge phonon modes originate from lattice termination rearrangements

Spectra depend on zigzag or armchair edge configurations

Abstract

Exfoliated black phosphorus has recently emerged as a new two-dimensional crystal that, due to its peculiar and anisotropic crystalline and electronic band structures, may have potentially important applications in electronics, optoelectronics and photonics. Despite the fact that the edges of layered crystals host a range of singular properties whose characterization and exploitation are of utmost importance for device development, the edges of black phosphorus remain poorly characterized. In this work, the atomic structure and the behavior of phonons near different black phosphorus edges are experimentally and theoretically studied using Raman spectroscopy and density functional theory calculations. Polarized Raman results show the appearance of new modes at the edges of the sample, and their spectra depend on the atomic structure of the edges (zigzag or armchair). Theoretical simulations confirm that the new modes are due to edge phonon states that are forbidden in the bulk, and originated from the lattice termination rearrangements.