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Among transition-metal nitrides, the mononitride γ-MoN with a rock-salt structure has drawn particular attention because it has been predicted to possess excellent mechanical and electronic properties, especially the high superconducting temperature around 30 K. However, synthesis of bulk γ-MoNx with the nitrogen concentration, x, more than 0.5 is still challenging, leading to contradictions on its phase stability and properties. In this work, we formulated a high-pressure synthesis reaction for the formation of single-crystal γ-MoNx with a remarkably high nitrogen concentration value of x ≈ 0.67. This nitride possesses a high asymptotic hardness of ∼24 GPa, which is so far the second hardest among metal nitrides. Impressively, the expected superconductivity is absent in the as-synthesized product. We further performed density functional theory calculations to clarify the structural stability and the absence of superconductivity in stoichiometric γ-MoN. We find that the ground state of γ-MoN is theoretically explored to be a Mott insulator with an antiferromagnetic phase, while a paramagnetic configuration is adopted at the ambient conditions. Such magnetic properties would explain the structural stability and the absence of superconductivity in the as-synthesized γ-MoNx with a high nitrogen concentration.

A kind of three dimensional, sub-diffraction grating with converging-diverging channel working at terahertz regime has been developed on doped silicon wafers by wet etching. By introducing a geometric asymmetry to the vertical direction of the 3D grating, an anti-resonance is observed near the resonant wavelength of the surface plasmon polariton mode. Numerical simulations reveal that the surface waves propagating on the top and bottom surfaces are decoupled due to the symmetry breaking, which results in the destructive interference of electromagnetic field and thus the anti-resonance in the spectrum. It was also found that the bulk sensitivity of the 3D structure as a terahertz sensor can reach a value up to 8818%/RIU and a figure of merit up to 50.

We report a kind of subwavelength, compound hole arrays formed by two nested sub-lattices used to modulate the Fano resonance of spoof surface plasmons (SSPs). Experiments complemented with numerical simulations show that the asymmetry parameter (q) of the Fano line shape can be tuned artificially and continuously: the q value experiences a sign reversal and varies linearly with the variation of hole size. The coupling between different SSP modes of sub-lattices is suggested to be responsible for the tunability of Fano resonance in the compound hole arrays.