Infrared fingerprints of few-layer black phosphorus

TL;DR

This study provides a comprehensive infrared spectral characterization of few-layer black phosphorus, revealing unique thickness-dependent fingerprints and strain-tunable electronic properties, advancing its potential in infrared photonics and optoelectronics.

Contribution

It offers the first systematic infrared spectral analysis of few-layer black phosphorus, identifying unique fingerprints and demonstrating strain-induced electronic tuning.

Findings

Thickness-dependent infrared absorption spectra identified.

Unexpected absorption features linked to forbidden transitions.

Uniaxial strain effectively tunes electronic structure.

Abstract

Black phosphorus is an infrared layered material. Its bandgap complements other widely studied two-dimensional materials: zero-gap graphene and visible/near-infrared gap transition metal dichalcogenides. Though highly desirable, a comprehensive infrared characterization is still lacking. Here we report a systematic infrared study of mechanically exfoliated few-layer black phosphorus, with thickness ranging from 2 to 15 layers and photon energy spanning from 0.25 to 1.36 eV. Each few-layer black phosphorus exhibits a thickness-dependent unique infrared spectrum with a series of absorption resonances, which reveals the underlying electronic structure evolution and serves as its IR fingerprints. Surprisingly, unexpected absorption features, which are associated with the forbidden optical transitions, have been observed. Furthermore, we unambiguously demonstrate that controllable uniaxial strain can be used as a convenient and effective approach to tune the electronic structure of few-layer black phosphorus. Our study paves the way for black phosphorus applications in infrared photonics and optoelectronics.