A global trend towards miniaturization and multiwavelength performance of nanophotonics drives research on novel phenomena as well as surveys for high-refractive index and strongly anisotropic materials and metasurfaces, where hBN has a central role.

The growing family of two-dimensional crystals has been recognized as a promising platform for investigation of rich low-dimension physics and production of a variety of devices. Of particular interest are recently reported atomic sheets of non-van der Waals materials, which reshape our understanding of chemical bonds and enable heterostructures with novel functionality. Here, we study the structural and optical properties of ultrathin non-van der Waals InGaS3 sheets produced by standard mechanical cleavage. Our ab initio calculations reveal weak out-of-plane covalent bonds, responsible for the layered structure of the material. The energy required for isolation of a single layer is as low as ~50 meVÅ–2, which is comparable with the conventional van der Waals material’s monolayer isolation energies of 20–60 meVÅ–2. A comprehensive study of the structural, vibrational, and optical properties of the material reveals its wide bandgap (2.73 eV), high refractive index (>2.5) and negligible losses in the visible and infrared spectral ranges. These properties make it a perfect candidate for visible-range all-dielectric nanophotonics.

Graphene/hBN heterostructures can be considered as one of the basic building blocks for the next-generation optoelectronics mostly owing to the record-high electron mobilities. However, currently, the studies of the intrinsic optical properties of graphene are limited to the standard substrates (SiO2/Si, glass, quartz) despite the growing interest in graphene/hBN heterostructures. This can be attributed to a challenging task of the determination of hBN’s strongly anisotropic dielectric tensor in the total optical response. In this study, we overcome this issue through imaging spectroscopic ellipsometry utilizing simultaneous analysis of hBN’s optical response with and without graphene monolayers. Our technique allowed us to retrieve the optical constants of graphene from graphene/hBN heterostructures in a broad spectral range of 250–950 nm. Our results suggest that graphene’s absorption on hBN may exceed the one of graphene on SiO2/Si by about 60%.