Ellipsometry of hybrid noble metal-dielectric nanostructures

Abstract

Angular ellipsometric measurements of thin Ag and Cu films covered by a HfO₂ protective layer were performed. The ellipsometric parameters ψ and ∆ were measured in θ = 43°…85° light incidence angle range, where ψ is the azimuth of restored linear polarization, ∆ and is the phase shift between p- and s-components of reflected light. For comparison, a thin Au film (traditional sensor for surface plasmon resonance (SPR)) was examined as well. The curve ∆(θ) for all the samples investigated falls down with increasing angle of light incidence, while ψ(θ) changes relatively weakly. It has been ascertained that the increase in the thickness of the HfO₂ layer affects the tan(ψ) value, while tan(ψ) deviation is mainly determined by the type of metallic film. With the growth of the HfO₂ layer, the minimum position of tan(ψ) shifts to smaller angles. From these angular dependences, one could choose the appropriate SPR-compatible structure due to the maximal deviation of tan(ψ). To optimize layer thickness for a high SPR-response, spectral measurements and additional calculations are required.