Study Of The Birefriengence Of Black Phosphorus By Picosecond Interferometry

Abstract

This thesis presents a modified picosecond interferometry method to study the optical properties of bulk black phosphorus (BP). BP is an emerging two-dimensional material which exhibits great potential for use in future nano-photonic and nano-electronic devices. BP differentiates itself from other two-dimensional materials such as graphene in that it possesses anisotropy in in-plane direction. It has zigzag and armchair in-plane crystalline direction, which gives its unique optical and electrical properties along these two directions, and the interlayers are under Van der Waals interactions. BP has direct band gap which is tunable via controlling the number of layers, strain and the applied electric field, making it a versatile material for use in semi-conductor industry. Currently, BP has been used as few-layer materials for devices such as photodetector and field effect transistor. However, the studies on the bulk optical properties of BP are still lacking, partially due to its tendency to degrade when exposed to air. This work focused on presenting picosecond interferometry as a new method for indirectly measuring the optical properties of BP and discuss the extended application of picosecond interferometry for studying other two-dimensional materials. Picosecond interferometry is a modified pump-probe method. It observes Brillouin scattering in a crystalline system to measure the optical and acoustic properties of the crystalline system. In this study, I modified the pump-probe system in our laboratory into a polarization-sensitive picosecond interferometry setup. I studied BP’s birefringent optical properties at several different wavelengths using picosecond interferometry. The Brillouin scattering signals was modelled by exponential decaying function. The polarization-resolved optical properties of BP were extracted by fitting the exponential decaying function. The thermal backgrounds of the measurement is analyzed with computational simulation.