Liquid crystal behaviors of micron and submicron-sized black phosphorus nanosheets

Abstract

In this study, liquid crystal behaviors of black phosphorus (BP) nanosheets were investigated. A birefringence of approximately 10−4 was achieved for BP owing to its anisotropy, compared to that of 10−5 for graphene oxide. The submicron-sized BP nanosheets (S-BPNS) showed larger birefringence than the micron-sized BP nanosheets (M-BPNS) in blue–green light. The birefringence of both types increased with the incident wavelength; however, that of the S-BPNS remained a constant of approximately 3.8 × 10−4 near 672 nm, whereas that of the M-BPNS reached 4.8 × 10−4 before 753 nm. This inversion in red–yellow light was caused by the layer-dependent bandgap of BP. The anisotropy and tunable bandgap endow BP unique two-dimensional liquid crystal behaviors.