Nanofabrication of flat optic silica gratings conformally layered with two-dimensional (2D) MoS 2 is demonstrated over large area (cm 2 ), achieving a strong amplification of the photon absorption in the active 2D layer. The anisotropic subwavelength silica gratings induce a highly ordered periodic modulation of the MoS 2 layer, promoting the excitation of Guided Mode Anomalies (GMA) at the interfaces of the 2D layer. We show the capability to achieve a broadband tuning of these lattice modes from the visible (VIS) to the near-infrared (NIR) by simply tailoring the illumination conditions and/or the period of the lattice. Remarkably, we demonstrate the possibility to strongly confine resonant and nonresonant light into the 2D MoS 2 layers via GMA excitation, leading to a strong absorption enhancement as high as 240% relative to a flat continuous MoS 2 film. Due to their broadband and tunable photon harvesting capabilities, these large area 2D MoS 2 metastructures represent an ideal scalable platform for new generation devices in nanophotonics, photo- detection and -conversion, and quantum technologies.

Flat optics photon harvesting, based on cm-scale MoS2 nanostripe arrays, induces an ultra-broadband enhancement (≈400%) of optical absorption.

Two-dimensional layered materials offer the possibility to create artificial vertically stacked structures possessing an additional degree of freedom—theinterlayertwist. We present a comprehensive optical study of artificially stacked bilayers (BLs) MoS$$_2$$ 2 encapsulated in hexagonal BN with interlayer twist angle ranging from 0$$^{\circ }$$ ∘ to 60$$^{\circ }$$ ∘ using Raman scattering and photoluminescence spectroscopies. It is found that the strength of the interlayer coupling in the studied BLs can be estimated using the energy dependence of indirect emission versus the A$$_\text {1g}$$ 1g –E$$_\text {2g}^1$$ 2g 1 energy separation. Due to the hybridization of electronic states in the valence band, the emission line related to the interlayer exciton is apparent in both the natural (2H) and artificial (62$$^\circ $$ ∘ ) MoS$$_2$$ 2 BLs, while it is absent in the structures with other twist angles. The interlayer coupling energy is estimated to be of about 50 meV. The effect of temperature on energies and intensities of the direct and indirect emission lines in MoS$$_2$$ 2 BLs is also quantified.

A cost effective method to tailor the optical response of large‐area nanosheets of 2D materials is described. A reduced effective metalayer model is introduced to capture the key‐role of the out‐of‐plane component of the dielectric tensor. Such a model indicates that the optical extinction of 2D materials can be strongly altered by controlling the geometry at the local (i.e., subwavelength) scale. In particular, a giant linear optical dichroism at normal incidence is demonstrated, with major features around the excitonic peaks, that can be tailored by acting on the average curvature and slope of the nanosheets. The approach is experimentally demonstrated in few‐layer MoS2 grown by chemical vapor deposition on cm‐scale anisotropic nanopatterned substrates prepared by a self‐assembling technique, based on defocused ion beam sputtering. Major variations in the photoluminescence spectrum as a function of the average curvature and slope are also revealed. A full‐vectorial numerical study beyond the effective metalayer model and comprising strain effects induced by the geometry turns out to be consistent with such a complex scenario. The results demonstrate that the extrinsic geometrical engineering definitely opens viable way to tailor the optical properties and modulate bandgap of low dimensional materials.

Generalized ellipsometry is used to extract the dielectric functions of self-aligned silver nanoparticles on silicon ripple patterns which account for the anisotropic Localized Surface Plasmon Resonance shown by such nanostructures. The biaxial nature of dielectric functions shows its presence through the modified in-plane plasmonic behaviour as compared to the case of random nanoparticles. The nature of in-plane optical coupling and out of plane metallic behavior is further investigated by tuning the interparticle gap along the ripple direction and also varying the ripple periodicity. Thus, we propose that generalized ellipsometry may be used as an effective process monitoring technique to develop anisotropic plasmonic substrates with potential applications in photovoltaic systems as a plasmonic back reflector.

The temperature evolution of the resonant Raman scattering from high-quality bilayer 2H-MoS$$_{2}$$ 2 encapsulated in hexagonal BN flakes is presented. The observed resonant Raman scattering spectrum as initiated by the laser energy of 1.96 eV, close to the A excitonic resonance, shows rich and distinct vibrational features that are otherwise not observed in non-resonant scattering. The appearance of 1st and 2nd order phonon modes is unambiguously observed in a broad range of temperatures from 5 to 320 K. The spectrum includes the Raman-active modes, i.e. E$$_{\text {1g}}^{2}$$ 1g 2 ($$\Gamma$$ Γ ) and A$$_{\text {1g}}$$ 1g ($$\Gamma$$ Γ ) along with their Davydov-split counterparts, i.e. E$$_{\text {1u}}$$ 1u ($$\Gamma$$ Γ ) and B$$_{\text {1u}}$$ 1u ($$\Gamma$$ Γ ). The temperature evolution of the Raman scattering spectrum brings forward key observations, as the integrated intensity profiles of different phonon modes show diverse trends. The Raman-active A$$_{\text {1g}}$$ 1g ($$\Gamma$$ Γ ) mode, which dominates the Raman scattering spectrum at T = 5 K quenches with increasing temperature. Surprisingly, at room temperature the B$$_{\text {1u}}$$ 1u ($$\Gamma$$ Γ ) mode, which is infrared-active in the bilayer, is substantially stronger than its nominally Raman-active A$$_{\text {1g}}$$ 1g ($$\Gamma$$ Γ ) counterpart.

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