Volume 91, Issue 7, 01 April 2002
Index of content:
91(2002); http://dx.doi.org/10.1063/1.1456240View Description Hide Description
The preparation of solid solutions 0.25, 0.5, 0.75, and 1.0) was attempted to control their energy gap and band edge emission energy. X-ray diffraction analysis revealed that the lattice constant of increased linearly with increasing x, indicating the formation of a complete solid solution in the LaCuOS–LaCuOSe system. The energy gap estimated from the diffuse reflectance spectra varied continuously from ∼3.1 eV for to ∼2.8 eV for The sharp emission near the absorption edge was observed in all samples at room temperature under ultraviolet lightirradiation.p-type electrical conduction in these materials was confirmed by Seebeck measurements, and the conductivity was enhanced by substitution of Sr for La. These results demonstrated that the formation of the solid solutions enabled band gapengineering in oxychalcogenides keeping their band edge emission feature and p-type conductivity.
Demultiplexer using directly resonant tunneling between point defects and waveguides in a photonic crystal91(2002); http://dx.doi.org/10.1063/1.1456956View Description Hide Description
We propose a frequency selective demultiplexer that is realized by the directly resonant tunneling between waveguides and point defects in a two-dimensional photonic crystal. The multiple scattering method is used to simulate the behavior of the demultiplexer. Results show that the demultiplexing efficiency is very high when the point defects are symmetrically arranged at both sides of the central line of the inlet waveguide. The selective frequency is only determined by the defect mode of the corresponding point defect in the photonic crystal and is not affected by the other point defects. A microwave experiment results agree well with the simulation. This structure may be valuable for the design of all-optical integrated circuits.
91(2002); http://dx.doi.org/10.1063/1.1459621View Description Hide Description
We report on a surface-bulk hybrid acoustic mode, which exists within a limited frequency interval in some piezoelectric substrates within a periodic metalgrating. These hybrid modes result from the coupling between a bulk wave and a counter-propagating surface (or leaky) wave. An example of such a hybrid mode, which propagates in 36°-YX cut of lithiumtantalate, is described. The hybrid mode gives rise to an additional branch of dispersion relation. The Bragg reflection stop band occurs due to phase match between surface and bulk waves. The lower edge of this stop band manifests itself by a resonance of harmonic admittance, being a reason of undesired resonances in resonator filters.
Lateral stress and shear strength measurements in polycrystalline potassium chloride, above and below the B1/B2 phase transition during shock loading91(2002); http://dx.doi.org/10.1063/1.1459623View Description Hide Description
Manganin stress gauges have been placed in potassium chloride plates, in such orientation that they are sensitive to the lateral component of stress during shock loading. At ∼2 GPa, this material undergoes a dynamic phase change from the B1, NaCl structure under ambient conditions to the B2 CsCl structure. Impact conditions were chosen such that measurements were made both above and below this stress. In combination with known longitudinal stresses, the shear strengths were determined and plotted as a function of impact stress. In the low pressure phase, it would appear that shear strength is constant or only increases marginally, while at higher stresses, strengthening is clearly observed. Both observations are discussed in terms of dislocation motion, generation, and storage.