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

• Published in: ACS applied optical materials 2024-08, Vol.2 (8), p.1600-1609
• Main Authors: Okuhara, Yoshiki, Kamide, Ryusei, Yokoe, Daisaku, Kuroyama, Tomohiro
• Format: Article
• Language: English
• ISSN: 2771-9855; 2771-9855
• DOI: 10.1021/acsaom.4c00216

Composite films, comprising Ag nanoparticles dispersed within a β-FeSi2 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-FeSi2 and Ag multilayers, the temperature applied during subsequent heating significantly influences the size, morphology, dispersibility, and volume fraction of Ag nanoparticles. During the β-FeSi2 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-FeSi2. In contrast, excess Si causes Ag to cluster within β-FeSi2+x grains, inducing nonuniform growth of larger Ag particles. Consequently, the stoichiometric β-FeSi2 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.