Hunting for Monolayer Black Phosphorus with Photoluminescence Microscopy

Monolayer black phosphorus (BP) holds great promise for naturally hyperbolic polaritons and correlated states in rectangular moiré superlattices. However, preparing and identifying high-quality monolayer BP are challenging due to its instability and high transparency, which limits extensive studies. In this study, we developed a method for rapidly and nondestructively identifying monolayer BP and its crystal orientation simultaneously using modified photoluminescence (PL) microscopy. The optical contrast of monolayer BP has been significantly increased by at least twenty times compared to previous reports, making it visible even on a transparent substrate. The polarization dependence of optical contrast also allows for the in situ determination of crystal orientation. Our study facilitates the identification of monolayer BP, expediting more extensive research on and potential industrial applications of this material.