The pressure effect on the crystallization of the Al89La6Ni5 amorphous alloy has been investigated by in situ high-pressure and high-temperature x-ray powder diffraction using synchrotron radiation. The amorphous alloy crystallizes in two steps in the pressure range studied (0–4 GPa). The first process, corresponding to simultaneous precipitation of fcc-Al crystals and the metastable bcc-(AlNi)11La3-like phase, is governed by a eutectic reaction. The second process corresponds to the transformation of a residual amorphous alloy into fcc-Al, Al11La3, Al3Ni, and as yet unidentified phase(s). The applied pressure strongly affects the crystallization processes of the amorphous alloy. Both temperatures first decrease with pressure in the pressure range of 0–1 GPa and then increase with pressure up to 4 GPa. The results are discussed with reference to competing processes between the thermodynamic potential barrier and the diffusion activation energy under pressure.
A photonic crystal waveguide splitter that exhibits ultralow-loss 3-dB splitting for TE-polarized light is fabricated in silicon-on-insulator material by use of deep UV lithography. The high performance is achieved by use of a Y junction, which is designed to ensure single-mode operation, and low-loss 60 degrees bends. Zero-loss 3-dB output is experimentally obtained in the range 1560-1585 nm. Results from three-dimensional finite-difference time-domain modeling with no adjustable parameters are found to be in excellent agreement with the experimental results.
The effect of pressure on the formation of quasicrystals and the amorphous-to-quasicrystalline phase transformation kinetics in the supercooled liquid region for a Zr 65 Al 7.5 Ni 10 Cu 7.5 Ag 10 metallic glass have been investigated by in situ high-pressure and high-temperature nonisothermal and isothermal x-ray powder diffraction measurements using synchrotron radiation, respectively. It is found that with increasing pressure, the onset temperature for the formation of quasicrystals increases with a slope of 9.4 K/GPa while the temperature interval of the stability and the average grain size of quasicrystals decrease. Atomic mobility is important for the formation of quasicrystals from the metallic glass whereas the relationship of the crystallization temperature vs pressure for the transition from the quasicrystalline state to intermetallic compounds may mainly depend on the thermodynamic potential energy barrier. To study the amorphous-to-quasicrystalline phase transformation kinetics in the metallic glass, relative volume fractions of the transferred quasicrystalline phase as a function of annealing time, obtained at 663, 673, 683, and 693 K, have been analyzed in details using 14 nucleation and growth models together with the Johnson-Mehl-Avrami model. The Avrami exponent was found to be near 1 at all four temperatures, also indicating that atomic diffusion might involve in the amorphous-toquasicrystalline phase transformation for the Zr 65 Cu 7.5 Al 7.5 Ni 10 Ag 10 metallic glass. It is found that the timedependent transient nucleation is essential for the transformation and different nucleation and growth models have been critically assessed.
We have investigated the properties of TM polarized light in planar photonic crystal waveguide structures, which exhibit photonic band gaps for TE polarized light. Straight and bent photonic crystal waveguides and couplers have been fabricated in silicon-on-insulator material and modelled using a 3D finite-difference-time-domain method. The simulated spectra are in excellent agreement with the experimental results, which show a propagation loss as low as 2.5+/-4 dB/mm around 1525 nm and bend losses at 2.9+/-0.2 dB for TM polarized light. We demonstrate a high coupling for TM polarized light in a simple photonic crystal coupler with a size of ~ 20 m x 20 m. These promising features may open for the realization of ultra-compact photonic crystal components, which are easily integrated in optical communication networks.
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