Figure 1

Giant optical path lengths (OPLs) from single- and few-layer MoS₂. (a) Optical microscope image of a mechanically exfoliated MoS₂ sample on a SiO₂/Si substrate (275 nm thermal SiO₂). Different contrasts correspond to MoS₂ flakes of different thicknesses. The areas labeled as “1L”, “2L”, “3L,”and “4L” are single-, bi-, triple-, and quadruple-layer MoS₂, respectively. (b) Phase shifting interferometry (PSI) image of the region inside the box indicated by the dashed line in (a). (c) PSI-measured OPL values versus position for 1L, 2L, 3L, and 4L MoS₂ along the dashed line in (b). (d) Statistical data of the OPL values from PSI for 1L, 2L, 3L, and 4L MoS₂ and graphene samples. For each layer number of MoS₂ and graphene, at least five different samples were characterized for the statistical measurements. Inset is the schematic plot showing the PSI-measured phase shifts of the reflected light from the MoS₂ flake and the SiO₂ substrate (${\varphi }_{{\text{SiO}}_2}$). (e) Atomic force microscopy (AFM) image of 1L and 2L MoS₂ from the box enclosed by the dashed line 1 in (b). (f) AFM image of 3L and 4L MoS₂ from box enclosed by the dashed line 2 in (b).