Exploiting plasmons in 2D metals for refractive index sensing: Simulation study

Ultrathin and two-dimensional (2D) metals can support strong plasmons, with concomitant tight field confinement and large field enhancement. Accordingly, 2D-metal nanostructures exhibiting plasmonic resonances are highly sensitive to the environment and intrinsically suitable for optical sensing. Here, based on a proof-of-concept numerical study, nano-engineered ultrathin 2D-metal films that support infrared plasmons are demonstrated to enable highly responsive refractive index (RI) sensing. For 3 nm-Au nanoribbons exhibiting plasmonic resonances at wavelengths around 1600 nm, a RI sensitivity of SRI > 650 nm per refractive index unit (RIU) is observed for a 100 nm-thick analyte layer. A parametric study of the 2D-Au system indicates the strong dependence of the RI sensitivity on the 2D-metal thickness. Furthermore, for an analyte layer as thin as 1 nm, a RI sensitivity up to 110 (90 nm/RIU) is observed in atomically thin 2D-In (2D-Ga) nanoribbons exhibiting highly localized plasmonic resonances at mid-infrared wavelengths. Our results not only reveal the extraordinary sensing characteristics of 2D-metal systems but also provide insight into the development of 2D-metal-based plasmonic devices for enhanced IR detection.