Edge Raman enhancement at layered PbI₂ platelets induced by laser waveguide effect

Abstract

As a two-dimensional (2D) layered semiconductor, lead iodide (PbI2) has been widely used in optoelectronics owing to its unique crystal structure and distinctive optical and electrical properties. A comprehensive understanding of its optical performance is essential for further application and progress. Here, we synthesized regularly shaped PbI2 platelets using the chemical vapor deposition method. Raman scattering spectroscopy of PbI2 platelets was predominantly enhanced when the laser radiated at the edge according to Raman mapping spectroscopy. Combining the outcome of polarized Raman scattering spectroscopy and finite-difference time domain simulation analysis, the Raman enhancement was proven to be the consequence of the enhancement effects inherent to the high refractive index contrast waveguide, which is naturally formed in well-defined PbI2 platelets. Because of the enlarged excited area determined by the increased propagation length of the laser in the PbI2 platelet formed waveguide, the total Raman enhancements are acquired rather than a localized point enhancement. Finally, the Raman enhancement factor is directly related to the thickness of the PbI2 platelet, which further confirms the waveguide-enhanced edge Raman. Our investigation of the optical properties of PbI2 platelets offers reference for potential 2D layered-related optoelectronic applications.