The high-temperature (over 1020 degrees C) polymorph of ZnS, wurtzite ZnS, has been successfully prepared through a low-temperature (180 degrees C) hydrothermal synthesis route in the presence of ethylenediamine (en). The effects of en concentrations, reactant concentrations, reaction temperatures, and reaction times on crystal structures and shapes of ZnS have been investigated. We have demonstrated that the wurtzite ZnS showing rodlike morphology can be kinetically stabilized in the presence of en, especially at a high reactant concentration under appropriate hydrothermal conditions. Besides phase evolution of ZnS from hexagonal to cubic, morphological transformation from nanorods to nanograins has also been observed in the present investigation. Nanograins of phase-pure cubic ZnS, the thermodynamically stable polymorph, are easily prepared, and no hexagonal ZnS nanorods are detected in "pure" water, i.e., in the absence of en molecules. The above investigations indicate that the controlled fabrication of wurtzite ZnS nanorods is due to a mediated generation of the lamellar phase, ZnS.0.5en, a covalent organic-inorganic network based on ZnS slabs, and to its subsequent thermolysis in aqueous solution. The controlled growth of wurtzite ZnS nanorods and sphalerite ZnS nanograins provides us an opportunity to structurally modulate physical properties. These wurtzite ZnS nanorods display narrower and stronger blue emission than sphalerite ZnS nanograins.

A silver film-based superlens, a plasmonic microzone plate, is put forth for the purpose of superfocusing at visible regime. The numerical analysis results reveal that it has unique focusing characteristics of longer focal length and depth of focus with resolving power beyond diffraction limit in comparison to the conventional zone plates. Working at near field, it increases working distance l at near field from l<λ∕10 to l≈λ∼5λ. This feature makes it a promising superlens to be used as a probe for the optical systems with high resolution imaging and detection as well as feedback control system immune for autofocusing.

Metamaterials, which are composed of metallic and dielectric subwavelength structures arranged in periodic array, are artifi cial materials with the permittivity or permeability less than that of vacuum or with negative values unattainable in nature. [1][2][3] Due to their unique electromagnetic properties, metamaterials have been widely used in many applications, such as sensors, superlenses, miniature antennas, and invisible cloaks. [4][5][6][7] Recently, metamaterial-based perfect absorbers have been attracted considerable attentions and various types of terahertz metamaterial absorbers have been reported. For example, Landy et al. presented a polarization-insensitive metamaterial absorber composed of metallic split ring resonators and cutting wires with singe-band absorption. [ 8 ] X.-J. He et al. proposed a dual-band metamaterial absorber made of two stacked metallic cross resonators and a lower metallic ground plane, separated by an isolation material spacer. [ 9 ] Cheng-Wen Cheng presented wide-angle polarization independent infrared dual band absorbers based on metallic multisized disk arrays. [ 10 ] Yanxia Cui proposed a sawtooth anisotropic metamaterial slab absorber for Transverse Magnetic (TM) polarized light with absorptivity higher than 95% covering a waveband ranging from 3 to 5.5 μ m. [ 11 ] However, current metamaterial absorbers suffer from many disadvantages such as narrow operating waveband, sensitivity to the polarization state of the incident light, narrow accepted angles and a fi xed azimuthal angle, which greatly limit their potential applications to spectroscopic detection and phase imaging. [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] Hence, a light absorbing device that is broadband, wide-angle and insensitive to the incident light polarization state is urgently needed for its applications in areas mentioned above. In this letter, we propose a two-dimensional (2D) pyramidal shape metamaterial-based absorber. In comparison with previous designs, this pyramid metamaterial absorber has a very high absorptivity performance that is polarization-insensitive, wide-angle and omni-directional at full infrared waveband.The proposed two-dimensional pyramid absorber is composed of alternating metallic and dielectric thin fi lms as shown in the insets of Figure 1 a. The metal thin fi lm is made of gold with thickness t m = 10 nm; dielectric thin fi lm is made of germanium with thickness t d = 190 nm. The total number of metal/dielectric pairs ( N) is 15. These multiple thin fi lm layers are carved into a pyramid structure for each unite cell. The periods of the unit cell in both x and y directions are 1600 nm. A gold fi lm with a thickness ( t = 100 nm) is added under the pyramid metamaterial absorber to block any incident light transmission. The optimized pyramid absorber structure was obtained through fi nite-difference time-domain (FDTD) simulations (Lumerical Inc.). [ 24 ] The material properties of gold and germanium were chosen from the software database-Gold Palik and Ger...

Four types of plasmonic lenses for the purpose of superfocusing designed on the bases of approximate negative refractive index concept, subwavelength metallic structures, waveguide mode were introduced, and curved chains of nanoparticles, respectively, were introduced. Imaging mechanism, fabrication, and characterization issues were presented. Theoretical analyses of the illumination with different polarization states on focusing performance of the plasmonic lenses were given also. In addition, a hybrid Au-Ag plasmonic lens with chirped slits for the purpose of avoiding oxidation of Ag film was presented.