  Metal-dielectric interfaces of various geometries are fundamental photonic
material platforms for surface plasmons. Surface plasmon polaritons and
localized surface plasmons are two surface plasmon modes that are excited on
planar and curved metal-dielectric interfaces, respectively. Herein, we
demonstrate in-situ formation of silver nanoparticles by diffusion at a planar
interface between sputter-deposited silver and nitride dielectrics. In one
step, we synthesize a nanostructure that exhibits both localized surface
plasmon resonances at silver nanoparticles and surface plasmon resonances at
the planar interface. We develop an accurate optical model describing both
surface plasmon modes by applying effective medium theories to experimental
ToF-SIMS and XPS depth profiles. Our findings provide fundamental material
insights into intrinsic metal-dielectric interfacial defects, along with a new
in-situ nanoparticle synthesis method that seamlessly integrates with
conventional fabrication of planar interfaces. These unique results open the
prospect of promising photonic-plasmonic applications availing the coupling of
both surface plasmon modes.
