Probing the local dielectric function of WS2 on an Au substrate by near field optical microscopy operating in the visible spectral range

The optoelectronic properties of nanoscale systems such as carbon nanotubes (CNTs), graphene nanoribbons and transition metal dichalcogenides (TMDCs) are determined by their dielectric function. This complex, frequency dependent function is affected excitonic resonances, charge transfer effects, doping, sample stress strain, surface roughness. Knowledge the grants access to a material’s transmissive absorptive characteristics. Here we use dual scanning near field optical microscope (dual s-SNOM) for imaging local variations extracting values using pre-established mathematical inversion method. To demonstrate our approach, studied monolayer WS2 on bulk Au identified two areas with differing levels transfer. experiments highlight further advantage technique: contaminated samples can be measured, dirty easily excluded calculation, being important especially exfoliated 2D materials (Rodriguez et al., 2021). Our measurements corroborated atomic force microscopy (AFM), Kelvin probe (KPFM), photoluminescence (PL) intensity mapping, tip enhanced (TEPL). We extracted from s-SNOM images confirmed reliability obtained spectroscopic ellipsometry (SIE) measurements.