Direct Investigation of the Birefringent Optical Properties of Black Phosphorus with Picosecond Interferometry

TL;DR

This study directly measures the birefringent optical constants of black phosphorus using picosecond interferometry, overcoming degradation issues and providing accurate, polarization-dependent optical data crucial for nanoelectronic and nanophotonic applications.

Contribution

It introduces a novel ps-interferometry method with a protective platinum layer to accurately quantify BP's birefringent optical properties, addressing previous measurement challenges.

Findings

Successfully measured birefringent constants of BP from 780 to 890 nm.

Demonstrated the method's reliability and high sensitivity.

Provided polarization-dependent optical data for BP.

Abstract

Black phosphorus (BP) is an emerging two-dimensional semiconducting material with great potential for nanoelectronic and nanophotonic applications, especially owing to its unique anisotropic electrical and optical properties. Many theoretical studies have predicted the anisotropic optical properties of BP, but the direct experimental quantification remains challenging. The difficulties stem from the ease of BP's degradation when exposed to air in ambient conditions, and from the indirect nature of conventional approaches that are subject to large measurement uncertainties. This work reports a direct investigation of the birefringent optical constants of micrometer-thick BP samples with picosecond (ps) interferometry, over the wavelength range from 780 to 890 nm. In this ps-interferometry approach, an ultrathin (5 nm) platinum layer for launching acoustic waves naturally protects the BP flake from degradation. The birefringent optical constants of BP for light polarization along the two primary crystalline orientations, zigzag and armchair, are directly obtained via fitting the attenuated Brillouin scattering signals. A bi-exponential model is further proposed to analyze the BS signals for a random incident light polarization. The BP experimental results and the associated measurement sensitivity analysis demonstrate the reliability and accuracy of the ps-interferometry approach for capturing the polarization-dependent optical properties of birefringent materials.