Tailoring Metal and Insulator Contributions in Plasmonic Perfect Absorber Metasurfaces

Maximum absorption of light using plasmonic perfect absorbers (PPAs) is highly desired in the field of energy harvesting, sensing, as well as photothermal light sources. We reveal how optical properties of several popular metals (Au, Ag, Cu, Pd) and insulators (SiO2, Si, ZnO) affect performance of PPAs at mid-infrared (IR) wavelengths. At this wavelength range radiation properties of a plasmonic system are also linked to its thermal conductivity; hence, in this work thinner insulator layers around 10 nm in thickness are given special focus. Optical properties of experimentally prepared (by plasma sputtering) structures follow expected scalings; however, departure from the finite-difference time-domain (FDTD) simulations is significant when roughness of the first metal base layer is not taken into account. Electrical conductivity is shown to strongly affect performance of PPAs. Absorbance values above 90% were attained for nanodisc array based PPA structures with a 10 nm thick insulator spacer.