The exploitation of the stable and earth-abundant electrocatalyst with high catalytic activity remains a significant challenge for hydrogen evolution reaction. Being different from complex nanostructuring, this work focuses on a simple and feasible way to improve hydrogen evolution reaction performance via manipulation of intrinsic physical properties of the material. Herein, we present an interesting semiconductor-metal transition in ultrathin troilite FeS nanosheets triggered by near infrared radiation at near room temperature for the first time. The photogenerated metal-phase FeS nanosheets demonstrate intrinsically high catalytic activity and fast carrier transfer for hydrogen evolution reaction, leading to an overpotential of 142 mV at 10 mA cm−2 and a lower Tafel slope of 36.9 mV per decade. Our findings provide new inspirations for the steering of electron transfer and designing new-type catalysts.

Fully reflective deep ultraviolet to near infrared spectrometer and entrance optics for resonance Raman spectroscopy Rev. Sci. Instrum. 76, 073107 (2005);Variable reflectance of a self-supported Si grating mirror is reported. A grating suspended in air consisted of an array of 300 nm wide, 300 nm thick, and 20 m long beams. The period of the grating was varied with an electrostatic microactuator from 600 to 720 nm. A broadband reflection in the wavelength longer than the grating period was observed, which was caused by a resonant interference of the light wave propagating along the grating similar to the guided-mode resonant gratings. Increasing the period of the grating with a microactuator, the reflection spectrum changed. The results were explained by the theoretical calculations based on rigorous coupled-wave analysis.

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Column-crystallized InGaN∕GaN quantum-well flower structure was deposited on pillared Si (111) substrate. Dotted GaN nuclei grew along the direction of the coming Ga and N atoms, forming arrays of InGaN∕GaN quantum-well flower structure. Raman spectra measurement demonstrated that these crystals were fully relaxed. Photoluminescence measurement showed a room temperature peak position of 556nm and two peak positions of 400 and 549nm at low temperature. Hg lamp excited photoluminescence demonstrated a clear fluorescence distribution from the low to the top part of the flower structure and much stronger emission compared with the quantum-well crystals on the flat Si substrate.

It's of significant interest to combine freestanding nanostructure with active gallium nitride (GaN) material for surface-emitting optoelectronic application. By utilizing bulk micromachining of silicon, we demonstrate here a promising way to fabricate freestanding GaN nanostructures using a GaN-on-silicon system. The well-defined nanoscale circular GaN gratings are realized by fast-atom beam (FAB) etching, and the freestanding GaN gratings are obtained by removing silicon substrate using deep reactive ion etching (DRIE). The freestanding GaN slab is thinned from the backside by FAB etching to reduce the confined modes inside the GaN slab. The measured microphotoluminescence (micro-PL) spectra experimentally demonstrate significant enhancements in peak intensity and integrated intensity by introducing freestanding circular grating. This work represents an important step in combining GaN-based active material with freestanding nanostructures for further increasing light-extraction efficiency.