Bottom-up fabrication of nanostructured silicon-based materials with unprecedented optical properties

Project Information

SCATTER

Grant agreement ID: 948319

DOI

10.3030/948319

EC signature date 4 September 2020

Start date 1 January 2021

End date 31 December 2026

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 499 403,00

EU contribution

€ 1 499 403,00

Coordinated by

CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE CNRS
France

Periodic Reporting for period 3 - SCATTER (Bottom-up fabrication of nanostructured silicon-based materials with unprecedented optical properties)

Reporting period: 2024-01-01 to 2025-06-30

Summary of the context and overall objectives of the project

Controlling the crystallinity, form, dimensions and porosity of nano-objects produces remarkable and unique physical properties. Silica (SiO2) is among the most studied nanomaterial, where its morphology can be controlled precisely. The reduced form, silicon (Si), has exceptional properties of interest to batteries, semi-conductors, electronics and optics. If it were possible to control the physical characteristics of silicon nano-objects, a host of applications would become possible in new domains of optics. Hence a major current challenge is the creation of synthetic routes to optically resonant silicon particles and their assembly into metamaterials.

The aim of Scatter is to revolutionize silicon synthesis, producing nano-objects that are currently inaccessible, and achieving silicon-based materials with fantastic light manipulation. To obtain an efficient metamaterial, responsive to light across the visible spectrum, the intensity and frequency of the electric and magnetic resonances should overlap. Creating materials with electric and magnetic resonances at the same frequency requires the development of novel synthesis techniques for silicon nano-objects.

Four strategies, guided by optical models, will be pursued to coalesce the electric and magnetic resonance in silicon objects: controlled porosity in spheres, synthesis of anisotropic objects, fabrication of clusters of 13 kissing spheres, and the assembly of spheres with two differing diameters. The silicon nano-objects will be self-assembled into diverse materials and their optical properties assessed using advanced optical measurements.

Properties that may result from the realization of silicon-based materials include zero and negative refractive index, total light transmission or total absorption, and low-loss light confinement below the diffraction limit. Mastering the fabrication of silicon building blocks will enable many new systems, including real examples of metamaterials in the form of planar lenses, monoliths, fibers, inks, films and surfaces.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

In the first 36 months of the project, we have worked on low-temperature, solution based methods to create silicon spheres having the right dimensions to support optical resonance. We have tested the synthesis of different silicon coordination complexes as precursors that can be reduced to elemental silicon in solution. We have also attempted silicon decomposition from hydrogen silsesquioxane under supercritical conditions, and have eliminated this technique as a synthetic method, thanks to in depth in situ mechanistic studies. These results will appear in Chemistry of Materials in late 2023.

In order to coallesce the electric and magnetic dipole resonances of silicon nanoparticles, we have worked to grow a shell of silica around the silicon core using thermal oxidation. Although the shell can be grown using this technique, the synthesis is not very controllable and led to particle-particle sintering. We are pursuing solution syntheses to achieve these materials.

We have synthesized silicon particles surrounded by a thin layer of silica using a supercritical synthesis technique and a custom-made silicon coordination complex combined with trisilane. These resonant silicon particles are active in the near infrared. We have assembled these particles into monolayer metasurfaces and are currently exploring their optical properties.

The assembly of spherical particles using dip-coating has been explored as a way to create metamaterials. We have explored the effects of viscosity, surface tension and evaporation rate, finding that in order to create homogeneous monolayers, a dispersant phase with low surface tension and high viscosity should be used. These results will appear in a publication in Langmuir in early 2023.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

We have prepared a metamaterial prepared using bottom-up techniques of Mie resonant silicon particles. The synthesis could be commercialized and prepared on a large scale. Via this real example of a metamaterial, we are able to study the difference between collective and individual resonances.

We are in parallel developing a synthetic route to similar silicon@silica core-shell particles, this time active in the visible spectrum rather than the near infrared. We expect to have assemblies of these materials within the timeframe of the project.

We are currently developing silicon@gold core-shell particles with an ultra thin and homogenous shell. Such particles show forward-scattering and could be used for a host of applications from theranostics to energy harvesting.

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