Catalytic Metasurfaces Empowered by Bound States in the Continuum

Abstract

Photocatalytic platforms based on ultrathin reactive materials facilitate carrier transport and extraction but are typically restricted to a narrow set of materials and spectral operating ranges due to limited absorption and poor energy-tuning possibilities. Metasurfaces, a class of 2D artificial materials based on the electromagnetic design of nanophotonic resonators, allow optical absorption engineering for a wide range of materials. Moreover, tailored resonances in nanostructured materials enable strong absorption enhancement and thus carrier multiplication. Here, we develop an ultrathin catalytic metasurface platform that leverages the combination of loss-engineered substoichiometric titanium oxide (TiO2–x ) and the emerging physical concept of optical bound states in the continuum (BICs) to boost photocatalytic activity and provide broad spectral tunability. We demonstrate that our platform reaches the condition of critical light coupling in a TiO2–x BIC metasurface, thus providing a general framework for maximizing light–matter interactions in diverse photocatalytic materials. This approach can avoid the long-standing drawbacks of many naturally occurring semiconductor-based ultrathin films applied in photocatalysis, such as poor spectral tunability and limited absorption manipulation. Our results are broadly applicable to fields beyond photocatalysis, including photovoltaics and photodetectors.

Designing Metasurfaces for Efficient Solar Energy Conversion

“…In a follow-up study, the extinction coefficient and the geometry of ellipsoidal nanoresonators of TiO 2 metasurfaces were engineered to excite quasi -BICs (see also section ). Contrary to the previous example, TiO 2 metasurfaces with the lowest defect concentration exhibited the highest photocatalytic activity (also in this case measured by the photodeposition of Ag NPs) thanks to the electric field enhancement produced by quasi -BICs, leading to resonant absorption (Figure d).…”

“…(d) Photocatalysis for the formation of silver NPs from TiO 2– x BIC metasurfaces. Adapted with permission from ref . Copyright 2022 Author(s), licensed under a CC-BY-NC-ND Creative Commons Attribution 4.0 License.…”

Improved In Situ Characterization of Electrochemical Interfaces Using Metasurface‐Driven Surface‐Enhanced IR Absorption Spectroscopy

“…The value of the highest field enhancement of the system was evaluated within the volume of the numerical model. To extract the Q-factor and coupling ratio γ e /γ i , the simulated resonance was fitted in reflectance (Figure 1d, blue curve) using temporal coupled mode theory according to Hu et al [70] Metasurface Fabrication: CaF 2 was selected as the substrate due to its transparent nature in the mid-IR spectral range, low solubility, and high chemical stability. The measurements shown in Figures 3 and 4 used metasurface arrays with at least 2200 by 2700 unit cells resulting in a pattern area of approximately 13.3 mm 2 , which ensured that there are more than enough unit cells for the measured resonance to correspond to the mode of the infinite periodic array used for the numerical simulations.…”

Optimizing Hot Electron Harvesting at Planar Metal–Semiconductor Interfaces with Titanium Oxynitride Thin Films

“…As a first step, we investigate the hot electron reduction of silver ions − from a 1 mol/L solution of AgNO 3 in degassed DI water by a TiON film (Figure a) and a sputtered TiO 2 control (Figure b). Silver reduction is a well-known reaction on metal oxide semiconductors in the presence of water, , and it also has the advantage that Ag deposition can be clearly visualized by dark-field microscopy (as shown in Figure a). The TiO 2 sample was illuminated at 7 mW with a 785 nm CW laser for over 1 min with no formation of Ag on the surface.…”