Optical properties and surface-enhanced Raman scattering of hybrid structures with Ag nanoparticles and graphene

Two kinds of surface-enhanced Raman scattering (SERS) substrates structured with hybrid of Ag nanoparticles (AgNPs) and graphene (GE) were synthesized, namely GE underneath AgNPs (AgNPs-GE) and GE covered AgNPs (GE-AgNPs). They provide a platform to make a comparative study on the optical properties and SERS effects of the hybrid structures as well as on the interactions between AgNPs and GE. The localized surface plasmon resonance (LSPR) of AgNPs exhibits a ∼24/∼16 nm red-shift and a ∼24/∼17 nm broadening at the presence of GE underneath/covered AgNPs. The Raman intensity of GE underneath (covered) AgNPs is enhanced by 7.15/4.76 folds at G peak due to the SERS effects and plasmonic coupling, and the position of G peak is upshifted by 5.69/5.21 cm−1, 2D peak is upshifted/downshifted by 2.33/9.75 cm−1, which is caused by strain and doping effects. A “vector decomposition method” was used to decompose the total values of position into the variations induced by strain and doping. Through experiments and analyses, we demonstrated that for AgNPs-GE, compressive strain is the primary cause and the secondary is n-type doping. For GE-AgNPs, n-type doping is the primary cause and the secondary is tensile strain.