Enhanced stability of plasmonic metal thin films by CVD grown graphene transfer

One of the major problems to practical application of plasmonic devices is the chemical instability of the metal-dielectric interfaces, which easily oxidize and degrade in time, influencing the performances of the optical devices. Here we use AFM microscopy and angle interrogation scheme of Surface Plasmon Resonance (SPR) spectroscopy to study the stability in air of plasmonic devices constituted by gold (Au) and silver (Ag) thin films deposited on glass slides functionalized with (3-mercaptopropyl) trimethoxysilane (MPTS). We find that the stability of the SPR response is enhanced when protection against the environment is obtained by typical OLEDs encapsulation technique or by the transfer of CVD grown graphene over the metal thin films. AFM results confirm that the instability of the SPR response is associated to the degradation of the Metal/SiO2 interface with possible delamination of the metal deposition. We observed a shift in the SPR angle of about 0.0050 for Ag/graphene and Au/graphene samples after 4 h of observation, comparable to the zero angle indetermination in SPR spectroscopy. The presented research put a limit to the time useful for dielectric thin film characterization by SPR spectroscopy in air and confirms the unique permeation properties of graphene.