Localized Surface Plasmon of Ag Nanoparticles Dispersed in β-FeSi₂ Matrix for Enhancing Infrared Refractive Index

Abstract

Composite films, comprising Ag nanoparticles dispersed within a β-FeSi 2 matrix, are fabricated using sputtering deposition and thermal treatment to attain a high refractive index (n) and low extinction coefficient (k) within the infrared spectrum. In addition to the arrangement and thicknesses of the deposited β-FeSi 2 and Ag multilayers, the temperature applied during subsequent heating significantly influences the size, morphology, dispersibility, and volume fraction of Ag nanoparticles. During the β-FeSi 2 crystallization, the agglomeration of the Ag layers into distinct particles is significantly influenced by the Si/Fe ratio within the matrix phase. Si deficiency leads to ε-FeSi phase formation, segregating sizable Ag particles along the grain boundaries of β-FeSi 2 . In contrast, excess Si causes Ag to cluster within β-FeSi 2+x grains, inducing nonuniform growth of larger Ag particles. Consequently, the stoichiometric β-FeSi 2 is critical in ensuring the uniform dispersion of fine Ag nanoparticles and enhancing the plasmon resonance effect. Because of the huge plasmon resonance at 1,500 nm in wavelength, the n exceeds 8.0, while the k approaches nearly zero above the resonance point.