Simulation of Birefringence and Absorption in InGaAs-GaAs Multiple Quantum Well Acoustooptic Modulators Operating Near 980 nm

This paper presents the simulation of surface acoustic wave (SAW)-induced absorption coefficient and refractive index change in InGaAs-GaAs multiple quantum well (MQW) structures operating near 980 nm. The exciton problem is solved in two dimensional momentum space to include the non-axial effect due to strain induced valance band mixing and nonparabolicity. The optical absorption coefficient and refractive index changes near the band gap in the MQWs are calculated as a function of SAW power.     

Self-organization in granular slurries

We report the existence of self-organization in wet granular media or slurries, mixtures of particles of different sizes dispersed in a lower density liquid. As in the case of dry granular mixtures, axial banding (alternating bands rich in small and large particles in a long rotating cylinder) and radial segregation (in quasi-2D containers) are observed in slurries. However, when compared with the dry counterpart axial segregation is significantly faster and the spectrum of outcomes is richer. Moreover, experiments with suitable fluids reveal, for the first time, the internal structure of axially segregated systems, something that up to now has been accessible only via magnetic resonance imaging experimentation.     

Phase transition behavior of highly (100) textured sol-gel-derived Ba<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript> thin films

We have investigated the relations between microstructure and dielectric properties in order to fabricate sol-gel-derived highly (100) oriented Ba_0.5Sr_0.5TiO₃ (BST 50/50) thin films with properties comparable to those of the bulk material. For the first time, we were able to fabricate BST thin films which exhibited the orthorhombic-to-tetragonal transition in addition to the commonly observed tetragonal-to-cubic transition. We were successful in explaining the commonly observed degradation of the dielectric behavior of BST thin films, when compared to that of the bulk material, in terms of grain size, compositional inhomogeneity (measured in terms of Sr/Ba ratio) between the grain bulk and grain boundary, and mechanical stresses. PACS 77.55.+f; 77.22Gm; 77.80.Bh; 77.80.Dj     

Surface plasma waves over bismuth-vacuum interface

A surface plasma wave (SPW) over bismuth-vacuum interface has a signature of mass anisotropy of free electrons. For SPW propagation along the trigonal axis there is no birefringence. The frequency cutoff of SPW lies in the far infrared region and can be accessed using free electron laser. The damping rate of waves at low temperatures is low. The surface plasma wave may be excited by an electron beam of current ∼100 mA propagating parallel to the interface in its close proximity.     

HfO2/AlGaN/GaN structures with HfO2 deposited at ultra low pressure using an e‐beam

We show that HfO₂/AlGaN/GaN structures with HfO₂ layer deposited using an e‐beam in ultra high vacuum are suitable for field effect transistors. The dielectric constant of the HfO₂ was found ε_HfO > 23–24, which is close to the highest re‐ ported values for this material. The leakage current did not exceed 10^–4 A/cm² at the threshold voltage. The comparison of the losses in the samples with and without HfO₂ indicates low concentration of the interface traps. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)