Suppressing material loss in the visible and near-infrared range for functional nanophotonics using bandgap engineering

Abstract

All-dielectric nanostructures have recently opened exciting opportunities for functional nanophotonics, owing to their strong optical resonances along with low material loss in the near-infrared range. Pushing these concepts to the visible range is hindered by their larger absorption coefficient, thus encouraging the search for alternative dielectrics for nanophotonics. Here, we employ bandgap engineering to synthesize hydrogenated amorphous Si nanoparticles (a-Si:H NPs) offering ideal features for functional nanophotonics. We observe significant material loss suppression in a-Si:H NPs in the visible range caused by hydrogenation-induced bandgap renormalization, producing strong higher-order resonant modes in single NPs with Q factors up to ~100 in the visible and near-IR range. We also realize highly tunable all-dielectric meta-atoms by coupling a-Si:H NPs to photochromic spiropyran molecules. ~70% reversible all-optical tuning of light scattering at the higher-order resonant mode under a low incident light intensity is demonstrated. Our results promote the development of high-efficiency visible nanophotonic devices.

Revealing Structural Disorder in Hydrogenated Amorphous Silicon for a Low‐Loss Photonic Platform at Visible Frequencies

“…Although, the low‐loss a‐Si:H films are over 50% thicker (73 nm) than the conventional a‐Si:H films (48 nm), they are much more transparent (Figure 2g–i). Contrary to previously reported low‐loss a‐Si:H particles, [ 39 ] here wafer‐scale low‐loss a‐Si:H films can be fabricated with commercial PECVD processes (Figure 2h,i). This facilitates the integration with conventional top‐down fabrication methods including electron‐beam lithography, nanoimprinting, and focused‐ion beam, allowing functional photonic devices with complex geometric nanostructures.…”

“…Previously reported low‐loss a‐Si:H particles [ 39 ] demonstrated with bottom‐up synthesis processes [ 47 ] are suitable for realizing perfect spherical shapes, whereas our low‐loss wafer‐scale a‐Si:H films are highly compatible with conventional fabrication methods including nanoimprinting, electron beam lithography, and focused ion‐beam. This allows the realization of complex geometric structures with low‐loss a‐Si:H. Furthermore, the PECVD is done at relatively lower temperatures (≈200 °C) than conventional synthesis methods (400–500 °C), [ 47 ] enabling the use of poly(dimethylsiloxane) (PDMS) and polyethylene terephthalate substrates for flexible metasurfaces.…”

Decoding Optical Data with Machine Learning

“…[ 104 ] For example, ellipsometry is an optical technique for investigating the dielectric properties of thin films. [ 105 ] However, it is challenging to measure dielectric properties of colloidal particles [ 106 ] or materials of other types of structures using ellipsometry. [ 107 ] Existing theoretical methods such as effective medium theories give us a solution but are often limited to specific scenarios.…”

Individual Si Nanospheres Wrapped in a Suspended Monolayer WS2 for Electromechanically Controlled Mie‐Type Nanopixels

“…All‐dielectric nanostructures have emerged as modern building blocks in nanophotonics, which help to overcome the high level of Joule losses in metallic plasmonic nanostructures. [ 1,2 ] From the intense magnetic dipole resonances based on the Mie theory [ 3–5 ] to the toroidal mode [ 6 ] and anapole mode, [ 7,8 ] the unique resonant modes of all‐dielectric nanostructures offer a variety of intriguing optical effects. Moreover, the capability of the far‐field directional manipulation presents innovative solutions for practical applications.…”

“…All-dielectric nanostructures have emerged as modern building blocks in nanophotonics, which help to overcome the high level of Joule losses in metallic plasmonic nanostructures. [1,2] From the intense magnetic dipole resonances based on the Mie theory [3][4][5] to the toroidal mode [6] and anapole mode, [7,8] the unique resonant modes of all-dielectric nanostructures offer a applying voltages, the electrostatic attraction causes the suspended part of the WS 2 monolayers to deform and approach the surface of Si NS, which resembles a closed umbrella. The parabola cone structures of the suspended WS 2 monolayers effectively overlap with the near-field distributions on the surfaces of Si NSs.…”