For most acoustic metamaterials, once they have been fabricated, their operating frequencies and functions cannot be adjusted, which is an intrinsic barrier for development of realistic applications. The study to overcome this limit has become an urgent issue at the heart of acoustic metamaterial engineering. Although with the advance of metamaterials in the past two decades, a series of methods such as electric or magnetic control have been proposed, most of them can only work in the condition of no fluid passage. Some metamaterials with large transmission losses have been proposed, but the sounds are essentially reflected rather than absorbed. Here, to overcome this intrinsic difficulty, we propose a ventilated sound absorber that can be manually tuned in a large range after being manufactured. During the tuning which is 2 achieved through an intricately designed slider, high-performance absorption and ventilation are both ensured. The tunable ventilated sound absorber is demonstrated experimentally and the effective model of coupled lossy oscillators can be employed to understand its mechanism. The manually tunable ventilated metamaterial has the potential application values in various complicated pipe systems that require frequency adjustment and it also establishes the foundation for future development of active tunable ventilated acoustic metamaterials.

Single crystal Zn 3 N 2 films with (100) orientation have been grown by plasma-assisted molecular beam epitaxy on MgO and A-plane sapphire substrates with in situ optical reflectance monitoring of the growth. The optical bandgap was found to be 1.25-1.28 eV and an electron Hall mobility as high as 395 cm 2 V −1 s −1 was measured. The films were n-type with carrier concentrations in the 10 18 -10 19 cm −3 range.

Epitaxial Mg3N2 films with a (100) orientation have been grown by plasma-assisted molecular beam epitaxy on single crystal MgO substrates. The growth was monitored in situ by both reflection high-energy electron diffraction and optical reflectivity. The growth rate was determined from the optical reflectivity during growth. The index of refraction of Mg3N2 was measured by spectroscopic ellipsometry and found to be in good agreement with the in situ reflectivity. The optical bandgap was found to be ∼2.5 eV from transmission measurements.

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Ammonia (NH 3 ) is a key component in fertilizers, plastics, medicine, and many other chemical products. [1] Since 1908, the dominant method of industrial large-scale ammonia synthesis has been the Haber-Bosch process, which requires extreme conditions (temperature: 400-500 °C, pressure: 200-300 atm) and consumes a tremendous amount of energy (1% of total worldwide power consumption [2] ). Greenhouse gas emissions, the ineffective conversion rate of raw material, and complex and costly equipment maintenance have meant the unsustainability of the Haber-Bosch process. [2,3] Even high-efficiency ammonia production that was using potassium-hydride-intercalated graphite [4] at 250-400 °C and 1 MPa in a home-built, fixed-bed reactor also consumes considerable power. The clean-energy-driven ENRR is a potential candidate to replace Ammonia is a key chemical feedstock worldwide. Compared with the wellknown Haber-Bosch method, electrocatalytic nitrogen reduction reaction (ENRR) can eventually consume less energy and have less CO 2 emission. In this study, a plasma-enhanced chemical vapor deposition method is used to anchor transition metal element onto 2D conductive material. Among all attempts, Ru single-atom and Ru-cluster-embedded perovskite oxide are discovered with promising electrocatalysis performance for ENRR (NH 3 yield rate of up to 137.5 ± 5.8 µg h −1 mg cat −1 and Faradaic efficiency of unexpected 56.9 ± 4.1%), reaching the top record of Ru-based catalysts reported so far. In situ experiments and density functional theory calculations confirm that the existence of Ru clusters can regulate the electronic structure of Ru single atoms and decrease the energy barrier of the first hydrogenation step (*NN to *NNH). Anchoring Ru onto various 2D perovskite oxides (LaMO-Ru, MCr, Mn, Co, or Ni) also show boosted ENRR performance. Not only this study provides an unique strategy toward transition-metal-anchored new 2D conductive materials, but also paves the way for fundamental understanding the correlation between cluster-involved single-atom sites and catalytic performance.

Magnetic nanostructures with conical shape are highly desired for pursuing extraordinary magnetic properties and microwave absorption. However, the fabrication of such nanostructures with controlled shape and size uniformities and alignment is not yet realized. Accordingly, the magnetic properties and their application as microwave absorber are not well understood. Here, we report on the first demonstration of controlled fabrication of soft magnetic nickel nanocone arrays with sharp geometry, large aspect ratio, uniform size, and parallel alignment. The imaginary part of the relative complex permeability shows multiband absorption in the 2−17 GHz range. Such an exceptional microwave absorption results from the uniform conical shape and size and the parallel alignment. The absorption mechanisms are discussed under the framework of natural resonance and exchange resonance. The natural resonance is dependent on the shape anisotropy and facilitated by the conical geometry. The exchange resonance is well explained by the observation of the bulk spin waves with exchange coupling at the tip of nanocones using the inelastic light scattering and is consistent with exchange theory predictions for the quantization of bulk spin waves. We expect that our work will shed light on the physical insights into the magnetic properties of nanocones and find great potential in applications of microwave absorption.

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