Surface Plasmon Characterization in Ag Nanotriangles for Evaluation of Fano Resonance Conditions

Surface plasmon polariton (SPP) is a collective oscillation of electrons and light at the metal -dielectric interface excited by the incident radiation on metal surface through the momentum matching conditions. The properties of SPPs and the resonance conditions are highly dependent on the confining materials and geometry of the confining nanostructure. The sensitivity of the surface plasmon resonance to the property of the confining materials made Surface plasmon resonance (SPR) sensors a central tool for biosensing. However, the frequency resolution of SPR sensors is typically limited by the broad resonance of the SPR mode. The resolution can be enhanced through the Fano resonance which yields a sharp resonance peak. In this work, SPPs are excited in a triangular Ag nanoplate deposited on a planar ITO waveguide by the incident femtosecond laser beam. The interference pattern created by the excitation radiation and the SPPs are imaged using photoemission electron microscopy (PEEM) which are studied for surface plasmon characterization through mode analysis. Finally, by numerical calculations using Finite Element Analysis (FEA) the conditions for Fano resonance through the coupling of SPP mode within the Ag nanotriangle and the waveguide mode were evaluated to achieve quantitative understanding of the sharp Fano resonance.