Abstract
Metal-dielectric multilayers are versatile optical devices that can be designed to combine the visible transmittance of dielectrics with the electronic properties of metals for plasmonic and meta-material applications. However, their performances are limited by an interfacial optical absorption often attributed entirely to the metal surface roughness. Here, we show that during deposition of AlN/Ag/AlN and SiNx/Ag/SiNx multilayers, significant diffusion of Ag into the top dielectric layer form Ag nanoparticles which excite localized surface plasmon resonances that are primarily responsible for the interfacial optical absorption. Based on experimental depth profiles, we model the multilayer’s silver concentration profile as two complementary error functions: one for the diffused Ag nanoparticles and one for the interface roughness. We apply the Maxwell-Garnett and Bruggeman effective medium theories to determine that diffusion characteristics dominate the experimental absorption spectra. The newfound metal nanoparticle diffusion phenomenon effectively creates a hybrid structure characteristic of both metal-dielectric multilayer and metal-dielectric composite.
Highlights
Metal-dielectrics are fundamental material platforms for photonic and electronic devices
We begin by first focusing on aluminium nitride (AlN) as the dielectric that forms an interface with Ag, in a later section we generalize these results by demonstrating their applicability to SiNx
With the existence of Ag nanoparticles confirmed via several types of characterization, we can contemplate its formation mechanism
Summary
Metal-dielectrics are fundamental material platforms for photonic and electronic devices. Many studies in the literature[7,8,9,10] identify this interfacial absorption as the surface plasmon resonances (SPR) associated with the surface roughness of the metal film. The multilayer is effectively a hybrid metal-dielectric multilayer-composite structure and can potentially serve as the basis for a novel synthesis method for nanostructures[18] that exploit in-situ Ag diffusion and nanoparticle formation for applications such as optical switching[19,20] and memristor devices[21,22], or applications that combine[23] SPR and LSPR such as ultra sensitive immunoassays[24], DNA detection[25], and enhanced surface plasmon-coupled emission[26]
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