Probe- and Substrate-Dependent Visibility of Mie Resonances in Silicon Nanospheres

TL;DR

This study reveals how different substrates influence the optical Mie resonances of silicon nanospheres, affecting their spectral signatures and implications for device design.

Contribution

It provides a systematic analysis of substrate effects on silicon nanosphere resonances using experiments and simulations, highlighting environment-dependent spectral modifications.

Findings

Substrate type significantly alters resonance spectra.

Probe-specific effects can suppress or enhance certain modes.

Guidelines for designing substrate-supported dielectric resonators.

Abstract

Silicon nanospheres are high-quality optical resonators and promising building blocks for Mie-tronic devices. While the Mie resonances of an isolated sphere are well understood, practical implementations require substrates that inevitably modify the measured optical response. Here, we investigate how substrates alter the observable spectrum of individual nanospheres, focusing on three fundamentally different cases: a thin silicon nitride membrane, that emulates a free-standing particle, bulk silicon, which is common in experiments, and gold, where mirror charges lead to hybrid optical modes. Cathodoluminescence and dark-field spectroscopy, combined with electrodynamic simulations, show that the measured resonances are not intrinsic to the particle but depend strongly on the environment and the excitation mechanism. We find that substrate-induced effects and probe-specific selection rules can suppress, enhance, or even invert the spectral signatures of electric and magnetic modes. These results provide practical guidelines for interpreting and designing substrate-supported dielectric resonators for Mie-tronic applications.