Lirong Sun1,2, Guo Chen3, Partha P. Banerjee3, Jonathan E. Slagle1, Dean R. Evans1, Mariacristina Rumi1, Peter R. Stevenson1
1Air Force Research Laboratory, Wright-Paterson Air Force Base, OH
2Azimuth Corporation, Beavercreek, OH
3University of Dayton, Dayton, OH
Multilayer metamaterial structures offer performance advantages in a wide range of optical applications such as induced transmission filters, superlenses, tunable filters, sensors, and spatial light modulators. In this work, multilayer metallo-dielectric (MD) induced transmission filters composed of alternating layers of dielectric silicon nitride (Si3N4) and metal (M = Ag, Au, or Al) films were designed using dispersion relations for infinite multilayer metallo-dielectric structures according to the formulation: Si3N4) (d1/2)[M(d2)| Si3N4) (d1)]3M(d2)| Si3N4) (d1/2), where d1 represents the thickness of the internal dielectric layer. The 9-layer MD stacks were fabricated on 2-inch diameter fused silica substrates via pulsed DC magnetron sputtering (PDCMS) in Ar for M film growth and reactive PDCMS in an Ar/N2 mixture for Si3N4) film growth. The optical constants and layer thicknesses of thin film Ag, Au, Al, and Si3N4) were monitored in real time during the PDCMS processes using in situ spectroscopic ellipsometry. In our MD designs, Si3N4 was selected (over conventional low-index dielectric oxides) to protect the deposited metal layers from uncontrolled oxidation or oxidative diffusion during reactive PDCMS and upon subsequent ambient air exposure. Thorough analysis of the optical and structural characteristics of Si3N4) films, metal films, and 9-layer Si3N4) /M multilayer stacks is presented from ex situ spectroscopic ellipsometry, UV-Vis-NIR spectrophotometry, X-ray diffraction (XRD), and X-ray reflectivity (XRR) techniques. The optical transmission spectra of the multilayer MD stacks were also modeled using a 2x2 anisotropic transfer matrix method (TMM), developed to analyze optical propagation through uniaxial stacks and are in close agreement with the experimental transmission spectra measured from UV-Vis-NIR spectrophotometry.