Terahertz Non-Drude Conductivity of Mirror Twin Boundary Networks on Monolayer MoS2 Bicrystals

Mirror twin boundaries (MTBs) in monolayer MoS₂ bicrystals─the one-dimensional (1D) line defects between adjacent single-crystalline grains with 60° in-plane rotations─can host delocalized metallic states, forming continuous 1D network pathways within otherwise semiconducting monolayers upon large-area epitaxial growth. In this study, we investigated terahertz time-domain spectroscopy (THz-TDS) on epitaxially grown MoS₂ bicrystal films, where the density of imbedded MTBs─and thus the percolative MTB network connection─was tuned during the metal–organic chemical vapor deposition. Our measurements reveal that the MTB networks generate characteristic low-energy attenuation, which becomes more substantial with increasing MTB densities and decreasing temperature. Using thin-film sheet conductivity calculations, we find that the conductivity spectra exhibit a distinct non-Drude response, described by partially localized Drude–Smith scattering features. Our findings suggest that the epitaxial manipulation of the MTB-imbedded MoS₂ bicrystal films can serve as an atomically thin THz attenuator for electromagnetic shielding applications.