Broadband, Angle- and Polarization-Invariant Antireflective and Absorbing Films by a Scalable Synthesis of Monodisperse Silicon Nanoparticles

Abstract

Optically induced magnetic resonances (OMRs) are highly tunable scattering states that cannot be reproduced in systems that only support electric resonances, such as in metals, lossy, or low-index materials. Despite offering unique scattering and coupling behavior, the study of OMRs in thin films has been limited by synthesis and simulation constraints. We report on the absorption and scattering response of OMR-based thin films composed of monodisperse crystalline silicon nanoparticles synthesized using a scalable nonthermal plasma growth technique and tractable simulation framework. The synthesis is solvent and ligand free, ensuring minimal contamination, and crystalline particles form with high yield and a narrow size distribution at close to room temperature. Using a scalable high-throughput deposition method, we deposit random particle films, without the need of a solid host matrix, showing near complete blackbody absorption at the collective OMR. This is achieved using 70% less material than an optimized antireflective-coated crystalline silicon thin film. The film exhibits strongly directional forward scattering with very low reflectivity, thus giving rise to angle- and polarization-insensitive antireflection properties across the visible spectrum. We find that, while commonly used effective medium models cannot capture the optical response, a modified effective medium accounting for multipole resonances and interparticle coupling shows excellent agreement with experiment. The effective permittivity and permeability are written in a mode and cluster resolved form, providing useful insight into how individual resonances and nanoparticle clusters affect the overall film response. Electric and magnetic-mode coupling show dramatically different behavior, resulting in uniquely different spectral broadening.

A Single-Step Bottom-up Approach for Synthesis of Highly Uniform Mie-Resonant Crystalline Semiconductor Particles at Visible Wavelengths

“…Bapat et al 61 expanded this limit to c-Si NPs of 35 nm by operating the plasma in a regime in which NPs were temporarily trapped inside the reactor. Recently, Wray et al 62 improved this process by optimizing the plasma conditions, pushing the average particle diameter to 82 nm with a standard deviation of 1.2 nm. In this study, we expand on the previous work on nonthermal plasmas that use trapping to extend the particle residence time in the reactor showing that this approach can produce monolithic c-Si NPs in a wide range of diameters exhibiting strong scattering resonance with extinction peaks covering the entire visible range.…”

Monolayer of Mie-Resonant Silicon Nanospheres for Structural Coloration

“…The crucial issue of this approach is the production of high-quality inks, in which Si NPs with a uniform size and shape are dispersed without agglomeration. Si NP inks satisfying these requirements had been hard to be produced by conventional processes such as plasma synthesis, − chemical vapor deposition, , laser ablation, ,,− and mechanical milling. , In previous work, ,,− we developed a process to produce suspensions of almost perfectly spherical Si NPs [Si nanospheres (Si NSs)] with very narrow size distributions. The suspension exhibited size-dependent vivid structural color due to the Mie resonance. ,, By mixing the suspension with an optically transparent binder such as polyvinylpyrrolidone, we produced the structural color inks and demonstrated coloration of a base material such as a PET film by painting …”

Understanding the Formation Mechanisms of Silicon Particles from the Thermal Disproportionation of Hydrogen Silsesquioxane

“…Applications of resonant Si particles include anticounterfeit labels, nonlinear nanophotonics, and enhanced Raman scattering, , among others. Optimizing a bottom-up synthesis method to easily obtain resonant units with the desired characteristics could open pathways toward large-scale fabrication of highly efficient metamaterials. , One of the most promising fabrication methods currently available is the thermal disproportionation of silicon-rich oxide compounds, in particular hydrogen silsesquioxane (HSQ), [HSiO 3/2 ] n , producing objects that fully possess the desired criteria for resonant silicon particles. − The main drawbacks of this synthesis are that the synthesis occurs at very high temperatures, and thus is energy-intensive, and that the particles produced are polydisperse in size, and thus need to undergo a size separation process in order to obtain a monodisperse sample. ,, Perhaps by understanding the particle formation mechanism, it would be possible either to decrease the polydispersity or to decrease the energy requirements of this synthetic approach.…”