Broadband Optical Properties of Atomically Thin PtS 2 and PtSe 2 .

Noble transition metal dichalcogenides (TMDCs) such as PtS 2 and PtSe 2 show significant potential in a wide range of optoelectronic and photonic applications. Noble TMDCs, unlike standard TMDCs such as MoS 2 and WS 2 , operate in the ultrawide spectral range from ultraviolet to mid-infrared wavelengths; however, their properties remain largely unexplored. Here, we measured the broadband (245-3300 nm) optical constants of ultrathin PtS 2 and PtSe 2 films to eliminate this gap and provide a foundation for optoelectronic device simulation. We discovered their broadband absorption and high refractive index both theoretically and experimentally. Based on first-principle calculations, we also predicted their giant out-of-plane optical anisotropy for monocrystals. As a practical illustration of the obtained optical properties, we demonstrated surface plasmon resonance biosensors with PtS 2 or PtSe 2 functional layers, which dramatically improves sensor sensitivity by 60 and 30%, respectively.