Facile large-area autofocusing Raman mapping system for 2D material characterization.

Two-dimensional (2D) materials have attracted tremendous research interests due to their intriguing properties and promising applications. As one of the most typical 2D material characterization methods, however, the conventional Raman mapping only works within few-hundreds micrometers range at a time due to the focus depth constraint and the non-ideal level of the substrate. To implement wafer-scale Raman scanning, large-area autofocusing Raman mapping (LARM) is highly desirable. Here, we present a modified centroid method to build a facile LARM system in which the Raman excitation laser is employed as the focus laser, reducing the system cost and complexity. Based on identifying the shape of the semicircle laser reflection image, a self-written autofocusing algorithm allows a real-time adjusting the focus position during the large-scale scanning. As a state-of-the-art demonstration, the thickness distribution of both few layer WS triangle domains sparsely located in sub-millimeter range and polycrystalline continuous MoS film up to 2-inch scale can be well-revealed. Our results may shed light on wafer-scale nondestructive optical characterization of 2D materials.