Chiral visible light metasurface patterned in monocrystalline silicon by focused ion beam

Abstract

High refractive index makes silicon the optimal platform for dielectric metasurfaces capable of versatile control of light. Among various silicon modifications, its monocrystalline form has the weakest visible light absorption but requires a careful choice of the fabrication technique to avoid damage, contamination or amorphization. Presently prevailing chemical etching can shape thin silicon layers into two-dimensional patterns consisting of strips and posts with vertical walls and equal height. Here, the possibility to create silicon nanostructure of truly tree-dimensional shape by means of the focused ion beam lithography is explored, and a 300 nm thin film of monocrystalline epitaxial silicon on sapphire is patterned with a chiral nanoscale relief. It is demonstrated that exposing silicon to the ion beam causes a substantial drop of the visible transparency, which, however, is completely restored by annealing with oxidation of the damaged surface layer. As a result, the fabricated chiral metasurface combines high (50–80%) transmittance with the circular dichroism of up to 0.5 and the optical activity of up to 20° in the visible range. Being also remarkably durable, it possesses crystal-grade hardness, heat resistance up to 1000 °C and the inertness of glass.

High‐QChiroptical Resonances by Quasi‐Bound States in the Continuum in Dielectric Metasurfaces with Simultaneously Broken In‐Plane Inversion and Mirror Symmetries

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Most of preceding works for quasi-BICs in all-dielectric metasurfaces dealt with in-plane inversion symmetry-broken photonic systems (see, e.g., refs. [8,14]) rather than mirror symmetry-broken ones.Chiral metamaterials [17][18][19] and metasurfaces, [20][21][22][23][24][25][26][27][28][29] which are characterized by broken mirror symmetry, [30][31][32] have found broad photonic applications for circular dichroic nonlinear generations, [33][34][35][36] spinselective wavefront shaping and manipulating, [37][38][39] and biosensing. [40][41][42] Up to date, a number of results for chiral metasurfaces and metamaterials have been reported, while they dealt with wide bandwidth circular dichroism.

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A Review on Metasurface: From Principle to Smart Metadevices

“…Photolithography, electron-beam lithography, and focused-ionbeam lithography are the most commonly used lithography for patterning nanostructures over the metasurfaces [49,140,174]. The resonance pattern over a flexible substrate can be accomplished with electron beam lithography [176], focused ion beam lithography [40,113], plasmonic lithography [101], probe scanning lithography [62], laser writing lithography [44,186] and plasmonic lithography [101]. Nanostencil lithography [105,149] has enabled nanopatterning on a wider range of flexible nonplanar substrates with a simple fabrication process.…”

Chiroptical Metasurfaces: Principles, Classification, and Applications

“…Figure 2 d shows an example of chiral structures that are fabricated using focused-ion beam lithography [ 93 ]. The monocrystalline silicon layer was epitaxially grown on a sapphire substrate, and an oxide glass-like coating was obtained through high-temperature annealing ( Figure 2 d(i)).…”