Spatial resolution assessment in confocal Raman microscopy using two-dimensional materials and the underlying Si substrate

Confocal Raman microscopy is a powerful tool for micro/nano-scale characterization, yet a systematic and quantitative method to assess its spatial resolution — encompassing both lateral (LSR) and axial (ASR) dimensions — remains a critical challenge, particularly in understanding how atomically thin materials compare to bulk substrates as reference standards. Here we present a comprehensive methodology integrating Gaussian beam modeling with experimental cross-edge and z-axial Raman scans on graphene and MoS_2 flakes deposited on SiO_2/Si substrates. By quantitatively analyzing the Raman intensity profiles of the two-dimensional materials and the underlying Si substrate, we elucidate the distinct influences of the substrate's optical penetration depth and the two-dimensional nature of the flakes on LSR and ASR measurements. Our findings reveal a critical distinction between the two materials: graphene flakes (monolayer and multilayer) serve as a universal LSR calibration standard, whereas MoS_2's suitability is confined to monolayer and bilayer forms, as thicker flakes are compromised by edge-induced Raman enhancement. The Si substrate yields larger LSR values but ASR values comparable to those from two-dimensional flakes. This work establishes a robust framework for spatial resolution assessment, clarifies the role of pinhole size, and provides critical insights for optimizing the performance of confocal Raman microscopy.