We investigated the wavelength dependence of the focusing properties of a germanium-cylinder-based two-dimensional (2D) decagonal Penrose-type photonic quasicrystal (PQC) flat lens for the first time, to the best of our knowledge. We found that near the second bandgap and in the high-frequency side (between the bandgap boundary and the first light intensity peak) of the pass band, the flat lens can exhibit a focusing effect for a point light source and that the focusing wavelengths can directly be drawn from the photonic band structure. For all the focusing wavelengths, the summation of the object distance and the image distance is less than the thickness of the flat lens when the object distance is half the thickness of the flat lens. As the wavelength increases, the image distance, the image quality, and the effective refractive index of the flat lens increase, whereas the image power of the point light source decreases. The effective refractive index of the flat lens is less than -1.

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This paper deals with the plasma nitriding of the nanocrystallized 18Ni maraging steel at lower temperature for different time. The microstructures and the mechanical properties of the nitrided layer were detected. The electronic structure and elastic properties of nitriding phase formed in nanocrystallized surface were calculated based on first principles. GIXRD results show that the layer is composed of the mono phase FeN 0 076 formed during plasma nitriding at 360 C for 8∼24 h and the hardness and elastic modulus of the mono phase are above 13 GPa and 220 GPa. The calculated results indicate that the FeN 0 076 crystal cell is stable, and N and Fe atoms forms the strong covalent bond. The calculated bulk modulus B, shear modulus G and elastic modulus E are 341.6 GPa, 113.6 GPa and 306.8 GPa, respectively. The results mentioned above offer a novel approach for achieving a nitrided layer with preferred property on elastic alloy.