Quantitative Nanoscale Absorption Mapping: A Novel Technique to Probe Optical Absorption of Two-Dimensional Materials

wo-dimensional semiconductors, in particulartransition metal dichalcogenides and related heterostructures,have gained increasing interest as they constitute potential newbuilding blocks for the next generation of electronic andoptoelectronic applications. In this work, we develop a novelnondestructive and noncontact technique for mapping theabsorption properties of 2D materials, by taking advantage ofthe underlying substrate cathodoluminescence emission. We mapthe quantitative absorption of MoS2and MoSe2monolayers,obtained on sapphire and oxidized silicon, with nanoscaleresolution. We extend our technique to the characterization ofthe absorption properties of MoS2/MoSe2van der Waalsheterostructures. We demonstrate that interlayer excitonic phenomena enhance the absorption in the UV range. Ourtechnique also highlights the presence of defects such as grain boundaries and ad-layers. We provide measurements on theabsorption of grain boundaries in monolayer MoS2at different merging angles. We observe a higher absorption yield ofrandomly oriented monolayers with respect to 60°rotated monolayers. This work opens up a new possibility for characterizingthe functional properties two-dimensional semiconductors at the nanoscale.