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Published May 25, 2022 | Supplemental Material
Journal Article Open

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


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.

Additional Information

© 2022 American Chemical Society. Received: February 21, 2022; Accepted: April 15, 2022; Published: May 12, 2022. This work is supported by the Army Research Office under MURI project under W911NF-18-1-0240. Portions of this work were conducted in the Minnesota Nano Center, which is supported by the National Science Foundation through the National Nanotechnology Coordinated Infrastructure (NNCI) under Award Number ECCS-2025124. O.I. also acknowledges support from the 3M Foundation through the 3M Non-Tenured Faculty Award grant. Author Contributions. P.R.W. and M.A.E. contributed equally. P.R.W. conceived the idea, designed the experiments, developed the effective medium theory, and performed calculations, analysis, and interpretation of results pertaining to the electromagnetic aspects of the project. M.A.E. designed the nonthermal plasma reactor for nanoparticle synthesis and film deposition, and performed TEM for characterization of particle size, shape, and crystallinity. G.M.N. performed optical measurements of the particle film with oversight by P.R.W. and, with help from M.A.E., performed SEM and density calculations to determine the particle film's fill fraction and structure. H.A.A., U.R.K., and O.I. oversaw the project. All authors contributed to writing and editing the manuscript. The authors declare no competing financial interest.

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August 22, 2023
October 24, 2023