Enhanced H2 Evolution at Patterned MoSx-Modified Si-Based Photocathodes by Incorporating the Interfacial 3D Nanostructure of Ag.

Photoelectrochemical cells represent one of the promising ways to renewably produce hydrogen (H2) as a future chemical fuel. The design of a catalyst/semiconductor junction for the hydrogen evolution reaction (HER) requires various factors for high performance. In catalytic materials, an intrinsic activity with fast charge-transfer kinetics is important. Additionally, their thermodynamic property and physical adhesion should be compatible with the underlying semiconductor for favorable band alignment and stability during vigorous H2 bubble formation. Moreover, catalysts, especially non-noble materials that demand a large amount of loading, should be adequately dispersed on the semiconductor surface to allow sufficient light absorption to generate excitons. One of the methods to simultaneously satisfy these conditions is to adopt an interfacial layer between the semiconductor and active materials in HER. The interfacial layer efficiently extracts the electrons from the semiconductor and conveys those to the catalytically active surface. We demonstrate Ag as a 3D interfacial nanostructure of patterned MoSx catalysts for photoelectrochemical HER. The nanostructured porous Ag layer was introduced by a simple chemical process, followed by photoelectrochemical deposition of MoSx to form MoSx/Ag nanostructures in cross-shaped catalyst pattern arrays. Ag modulated the surface electronic property of MoSx to improve the reaction kinetics as well as helped a charge transport at the Ag|p-Si(100) junction. The physically stable adhesion of catalysts was also achieved despite the ∼40 nm thick catalysts owing to the interfacial Ag nanostructure. This work contributes to further understand the complex multistep HER from light absorption to charge transfer to protons, helping to develop cost-effective and efficient photocathodes.

Cathodic electroorganic reaction on silicon oxide dielectric electrode.

The faradaic reaction at the insulator is counterintuitive. For this reason, electroorganic reactions at the dielectric layer have been scarcely investigated despite their interesting aspects and opportunities. In particular, the cathodic reaction at a silicon oxide surface under a negative potential bias remains unexplored. In this study, we utilize defective 200-nm-thick n+-Si/SiO2 as a dielectric electrode for electrolysis in an H-type divided cell to demonstrate the cathodic electroorganic reaction of anthracene and its derivatives. Intriguingly, the oxidized products are generated at the cathode The experiments under various conditions provide consistent evidence supporting that the electrochemically generated hydrogen species, supposedly the hydrogen atom, is responsible for this phenomenon. The electrogenerated hydrogen species at the dielectric layer suggests a synthetic strategy for organic molecules.

Vertical beaming of incoherent quantum emitters via the near-field coupling of Fano resonance.

We report highly collimated radiation from incoherent quantum emitters coupled to photonic dispersion-engineered structures. Two-dimensional free-standing photonic crystal slabs sustained an extremely high density of states for vertically leaky light at discrete frequencies, which results from the constructive interference between directly reflected light and quasi-bound guided modes, referred to as Fano resonance. Electromagnetic simulations showed that an electric dipole that is excited near a photonic crystal slab generates vertically directional radiation at every Fano resonance frequency. The radiation distribution of an electric dipole is strongly correlated with the angular reflectance of a coupled photonic crystal slab. The strategy developed herein will be useful to achieve a vertical beam from quantum emitters such as transition metal dichalcogenide monolayers, facilitating the delivery of light into other external optics.

Recent advances in electrochemical non-enzymatic glucose sensors - A review.

This review encompasses the mechanisms of electrochemical glucose detection and recent advances in non-enzymatic glucose sensors based on a variety of materials ranging from platinum, gold, metal alloys/adatom, non-precious transition metal/metal oxides to glucose-specific organic materials. It shows that the discovery of new materials based on unique nanostructures have not only provided the detailed insight into non-enzymatic glucose oxidation, but also demonstrated the possibility of direct detection in whole blood or interstitial fluids. We critically evaluate various aspects of non-enzymatic electrochemical glucose sensors in terms of significance as well as performance. Beyond laboratory tests, the prospect of commercialization of non-enzymatic glucose sensors is discussed.

Polarization-sensitive beam steering from quantum emitters coupled with birefringent metamaterials.

One-dimensional metal/dielectric subwavelength periodic patterns have dielectric or metallic material dispersions depending on the polarization of incident light. This feature enables the development of artificial, ultrathin, birefringent films. In this study, we report polarization-sensitive beam steering from quantum emitters coupled with one-dimensional metal/dielectric metamaterial films. Electromagnetic simulations show that an Al/ITO metamaterial film functioning as a quarter-wave plate leads to vertically directed radiation for one polarization and a saddle-shaped, diverging radiation pattern for the orthogonal polarization. The strategy studied herein is extended to achieve polarized, vertically directed emission from organic light-emitting diodes. A tailored Al/ITO metamaterial mirror yields an approximately 30-fold improvement in polarization ratio, in conjunction with polarization-dependent Purcell factor enhancement.