Self-Assembled, Ultrahigh Refractive Index Pseudo-Periodic Sn Nanostructures for Broad-Band Infrared Photon Management in Single Layer Graphene

Graphene is a two-dimensional material with intriguing electrical and optical properties for infrared photonic devices. However, single layer graphene (SLG) suffers from a very low optical absorption of ∼1–2% depending on the substrate, which significantly limits its efficiency as photonic devices. In this Letter, we address this challenge by coating SLG with self-assembled, pseudoperiodic ultrahigh refractive index (n = 8–9 at λ = 1600–5000 nm) semimetal Sn nanostructures for highly effective, broad-band infrared photon management in SLG, offering a new approach for light trapping beyond plasmonics and high refractive index dielectric photonics. The infrared absorption in SLG on fused quartz (SiO2) is greatly increased from 15% in a very broad spectral range of λ = 900–2000 nm due to the near-field electromagnetic interactions between the ultrahigh refractive index Sn nanostructures and SLG, a significant advantage over relatively narrow-band plasmonic resonances for photon management in SLG. The optical absorption enhancement in SLG has also been confirmed by field-enhanced Raman peaks from SLG and supported by higher photoconductivities both at an infrared wavelength of λ = 1550 nm and at a visible wavelength of λ = 650 nm. This work also opens the door to the investigations of ultrahigh refractive index semimetal nanostructures for nanoscale photon management