Layered Structure

In this paper, the characteristics of layered structures (photonic or electromagnetic bandgaps), including chiral media, are studied by means of two different numerical methods, one in the time domain (finite differences in the time domain, FDTD) and the other in the frequency domain (coupled-mode method, CMM). The results (reflection and transmission coefficients for a plane wave normally incident over a layered structure) obtained by means of both well different techniques are practically identical. Copyright © 2009 John Wiley & Sons, Ltd.

The effect of layer structure (GaN versus AlGaN cap) and cleaning procedure prior to Sc2O3 or MgO deposition at 100° C were examined for their effects on the long-term bias-stress stability of AlGaN/GaN high electron mobility transistors (HEMTs). Surface cleaning by ...

We report highly efficient red phosphorescent organic light-emitting diodes with a triplet p-i-n single quantum well (QW) structure. This p-i-n single QW structure is realized using p-doped and n-doped wide band-gap hole and electron injection and transporting layers with narrow band-gap host and dopant materials. The maximum current and power efficiencies of 11.1 cd/A and 14.4 lm/W, respectively, are demonstrated by a good carrier confinement effect of QW. Very low driving voltage characteristics of 3.7 ∼ 3.9 V at 1000 cd/m2 are realized by almost no injection barrier with high conductivity configuration in our p-i-n structure.

A method was developed to chemically functionalize graphene sheets by silylation. The graphene oxide sheets were silanized with N-(trimethoxysilylpropyl) ethylenediamine triacetic acid. Then the silanized graphene oxide sheets were reduced to produce water-soluble graphene derivatives (EDTA–graphenes). Fourier transform infrared spectroscopy, scanning electron microscopy and X-ray photoelectron spectroscopy were employed to characterize the structures and properties of the EDTA–graphenes and to

In this study Cu was reacted with pure liquid Sn and liquid Sn saturated with Cu at 240,250, and 275 °C. Different microstructures were observed for different liquid Sn baths. For reaction in the Sn bath saturated with Cu, Cu6Sn5 and Cu3Sn with the layered structure formed. This microstructure is very similar to that formed in reaction between Cu and pure solid Sn. The growth follows the parabolic kinetics, suggesting diffusion-controlled kinetics. The activation energy for the parabolic growth constant is also quite similar to that for the reaction between Cu and pure solid Sn. For reaction in pure Sn, the reaction produced a very thin and irregular Cu3Sn layer and a thicker Cu6Sn5 layer with long protrusions into the Sn region. In addition to the diffusional reaction, Cu dissolved very rapidly into the pure liquid Sn bath. It is proposed that the non-planar structure formed in reaction with pure liquid Sn bath is due to the different dissolution and crystallization rates of Cu6Sn5 in liquid Sn along different crystallography directions.

A modified synthesis process was developed based on co-precipitation method followed by spray drying process. In this process, a spherical shaped (Co 1/3 Ni 1/3 Mn 1/3 )(OH) 2 precursor was synthesized by co-precipitation and pre-heated at 500 °C to form a high structural stability ...

High values of proton conductivity have been observed in a class of hydrated metal oxide pyrochlores, HMOâ.xHâO (M = Sb, Nb, Ta). Two new polymorphs of HSbOâ.xHâO have been synthesized and are also found to be good proton conductors. One polymorph has a layer structure and is derived from KSbOâ with the ilmenite structure. The other new HSbOâ.xHâO polymorph has

We have considered a wide array of scenarios for Europa's chemical evolution in an attempt to explain the presence of ice and hydrated materials on its surface and to understand the physical and chemical nature of any ocean that may lie below. We postulate that, following formation of the jovian system, the europan evolutionary sequence has as its major links: (a) initial carbonaceous chondrite rock, (b) global primordial aqueous differentiation and formation of an impure primordial hydrous crust, (c) brine evolution and intracrustal differentiation, (d) degassing of Europa's mantle and gas venting, (e) hydrothermal processes, and (f) chemical surface alteration. Our models were developed in the context of constraints provided by Galileo imaging, near infrared reflectance spectroscopy, and gravity and magnetometer data. Low-temperature aqueous differentiation from a carbonaceous CI or CM chondrite precursor, without further chemical processing, would result in a crust/ocean enriched in magnesium sulfate and sodium sulfate, consistent with Galileo spectroscopy. Within the bounds of this simple model, a wide range of possible layered structures may result; the final state depends on the details of intracrustal differentiation. Devolatilization of the rocky mantle and hydrothermal brine reactions could have produced very different ocean/crust compositions, e.g., an ocean/crust of sodium carbonate or sulfuric acid, or a crust containing abundant clathrate hydrates. Realistic chemical-physical evolution scenarios differ greatly in detailed predictions, but they generally call for a highly impure and chemically layered crust. Some of these models could lead also to lateral chemical heterogeneities by diapiric upwellings and/or cryovolcanism. We describe some plausible geological consequences of the physical-chemical structures predicted from these scenarios. These predicted consequences and observed aspects of Europa's geology may serve as a basis for further analys is and discrimination among several alternative scenarios. Most chemical pathways could support viable ecosystems based on analogy with the metabolic and physiological versatility of terrestrial microorganisms.

AlxGayIn1−x−yAs/InP strained-layer multiple-quantum-well lasers emitting at 1.3 µm have been grown by solid source molecular beam epitaxy, and the performance characteristics have been studied. The lasers contain 4, 5, or 6 compressively strained quantum wells in the active region. They exhibit low transparency current densities, high gain coefficients, and high characteristic temperatures compared to conventional GaInAsP/InP quantum well lasers. The results show that desired lasing features can be achieved with relatively simple layer structures if the doping profiles and waveguide structures are properly designed and the material is grown to high structural perfection.