Optical properties and electron characteristics of noble-metal-dielectric oxide nanostructures with covered graphene layer

Abstract

A comparative study of surface plasmon resonances (SPR) and optical properties of metal/dielectric/graphene multilayer films based on high conductive Ag and Cu metals is presented. For measurements of the generation of surface plasmon polaritons under the resonant condition, we involved the total internal reflection ellipsometry and direct spectroscopic ellipsometry for determining optical properties. SPR was studied in graphene/HfO2/Ag(Cu)/Cr/substrate nano-hetero-structures which contain an additional graphene surface layer for enhancement of their sensing performance. The plasmonic performance of each hybrid nano-hetero-structure is evaluated based on quality factors and propagation length of surface plasmon polaritons. The SPR in the graphene/HfO2/Ag(Cu)/Cr/substrate hybrid nano-hetero-structures demonstrate a strong correlation with the measured macroscopic optical characteristics such as the effective real dielectric function ε1(λ) and optical conductivity σ(λ) and extracted from them effective microscopic parameters: the plasma and relaxation frequencies of free electrons ωP and γ. Our results on graphene/HfO2/Ag(Cu)/Cr/substrate hybrid nano-hetero-structures indicate that the real part of the effective dielectric function ε1(λ) and optical conductivity σ(λ) generally follows effective medium approach and the stronger SPR occurs at higher values of ε1(λSPR), and the ratio of ωP2/γ and lower ones of σ (λSPR). Going forward, it appears that graphene/HfO2/Ag(Cu)/Cr/substrate hybrid nano-hetero-structure designs are more suitable for surface plasmon biomedical sensor applications because they could provide both tunability and low optical loss due to specific electronic properties of graphene.