Local field enhancement factor of spheroidal core–shell nanocomposites with passive and active dielectric cores

Abstract

We studied the effects of depolarization factor ( L ), metal fraction ( p ), and dielectric function of host matrix ( ε _h ) on the local field enhancement factor (LFEF) of spheroidal core–shell nanocomposites (NCs) with passive and active dielectric cores. Solving Laplace’s equations in the quasi-static limit, we obtained expressions of electric potentials for spheroidal core–shell NCs. Then, by introducing L and the Drude-Sommerfeld model into these expressions, we derived the equation of LFEF in the core of spheroidal core–shell NCs. The results show that whether L , p , and/or ε _h vary or kept constant, LFEF of the spheroidal core–shell NCs possesses two sets of peaks with passive dielectric core, whereas only a set of peak is observed with active dielectric core. In NCs with passive dielectric core, an increase in any of these parameters resulted in a more pronounced LFEF peaks in the first set of resonances. With both passive and active dielectric cores, increasing L increases the peaks of LFEF of spheroidal core–shell NCs, whereas increasing p shows decreasing tendency on the peaks of LFEF of the same material with active dielectric core. Moreover, the highest peak of LFEF is obtained by increasing L than p or ε _h indicating that change in the geometry of spheroidal core–shell NCs has the highest effect on the LFEF than the metal concentration and host dielectric function. With the same increase in ε _h , intensities of LFEF of the spheroidal core–shell NCs decrease when the dielectric core is passive and increase when the dielectric core is active. Briefly, the number and intensities of peaks of LFEF of spheroidal core–shell NCs vary greatly when its core is made either passive or active dielectric. Furthermore, by changing parameters like L , p , and ε _h , adjustable LFEF could be obtained and used for applications in optical sensing, nonlinear optics, and quantum optics.

Keywords

• local field enhancement factor
• active dielectric
• passive dielectric
• depolarization factor
• metal fraction
• dielectric function