Influence of Y-doped induced defects on the optical and magnetic properties of ZnO nanorod arrays prepared by low-temperature hydrothermal process

One-dimensional pure zinc oxide (ZnO) and Y-doped ZnO nanorod arrays have been successfully fabricated on the silicon substrate for comparison by a simple hydrothermal process at the low temperature of 90°C. The Y-doped nanorods exhibit the same c-axis-oriented wurtzite hexagonal structure as pure ZnO nanorods. Based on the results of photoluminescence, an enhancement of defect-induced green-yellow visible emission is observed for the Y-doped ZnO nanorods. The decrease of E2(H) mode intensity and increase of E1(LO) mode intensity examined by the Raman spectrum also indicate the increase of defects for the Y-doped ZnO nanorods. As compared to pure ZnO nanorods, Y-doped ZnO nanorods show a remarked increase of saturation magnetization. The combination of visible photoluminescence and ferromagnetism measurement results indicates the increase of oxygen defects due to the Y doping which plays a crucial role in the optical and magnetic performances of the ZnO nanorods.

Tunable optical properties of a two-dimensional square-lattice superconductor-dielectric Bragg reflector

We numerically analyze the optical properties of a two-dimensional (2D) superconducting Bragg reflector (SBR) using the finite element method in conjunction with a two-fluid model. It is found that the wavelength-dependent reflectance spectra of the proposed 2D SBR are strongly dependent on the polarizations of incident light and can be parametrically tuned by the system temperature and the geometric parameters of embedded dielectric rods. Taking advantage of the dispersive superconductor with its zero-refractive index characteristic and the structural periodicity of the proposed superconducting structure, narrow passband filters can be generated near the threshold wavelength. Furthermore, the narrow passband features of the 2D SBR are found to be sustained up to a very large angle of incidence. The extraordinary optical properties imply that the proposed 2D SBR may be applied to the design of an omnidirectional narrowband transmission filter.

Temperature dependent pinning phenomenon in superconducting Nb films with triangular and honeycomb pinning arrays

The pinning phenomena in superconducting Nb films with triangular and honeycomb pinning arrays were explored. Special temperature dependent phenomena were found for both films. For the film with a triangular pinning array, the pronounced matching peaks in the critical currents as a function of magnetic field reduce from six to three within a narrow temperature range. This temperature dependent matching effect is explained by considering the dramatic change of coherent length with temperature when the temperature is close to T(c). In order to compare with the film with a triangular pinning array, we fabricated a film with a honeycomb pinning array with similar pinning site spacing and pinning size. Special prominent matching peaks at H = 3.5H(1) were found for this film. Molecular dynamic simulations were made to study this phenomenon. The ground state distribution of vortices obtained from simulations reasonably explains the prominent matching peaks. Pronounced temperature dependent matching effects were also found for the film with a honeycomb pinning array.