Accurate Optical Metrology of van der Waals Monolayers and Heterostructures from the Interference of Interface Polariton Waves

New two-dimensional (2D) van der Waals materials are emerging, and their optical parameters urgently need to be acquired experimentally. Most of the reported results come from traditional metrologies used in the past for bulk materials. This unavoidably causes controversy regarding the correctness and accuracy of results, as well as the physical model. Surface/interface plasmon polariton waves are sub-diffraction-limited and very sensitive to surroundings. Here, 2D van der Waals materials with metal embodied are presented. Surface/interface exciton-plasmon polaritons come into being with excitons in 2D transition-metal dichalcogenides (TMDCs), which are physically taken as the boundary conditions with complex optical conductivities at the interfaces. Complex optical conductivities of 2D TMDCs are measured by means of interference behavior of surface/interface polariton waves. The size requirement of 2D van der Waals materials becomes relaxed, and complex optical conductivities can be measured for single-crystalline WS2 and MoS2 monolayers with small sizes. Furthermore, a remarkable capability is manifested by yielding complex optical conductivity of van der Waals heterostructures. The proposed metrology can apply to other newly developed materials with modified underlying physical models, as well as various types of 2D van der Waals materials. When the heterostructure constructed by two-dimensional materials is laid on a single-crystalline Ag surface, surface/interface interlayer exciton-plasmon polariton waves can be generated and interfere in the presence of a cavity, from which the optical conductivity of the heterostructure can be extracted.image