Current collapse and reliability of III‐N heterostructure field effect transistors

Measurements of GaN HFET lifetime as a function of temperature show that different degradation mechanisms are involved at low temperatures (close to room temperature) and high temperatures (above 150 °C). The degradation at low temperatures is linked to the trap generation and can be explained using the current collapse model. At higher tempe‐ ratures, other degradation mechanisms become important or even dominant. The current collapse related degradation can be diminished by using improved device design, which will greatly increase the overall lifetime (up to long lifetimes obtained by extrapolating high temperature data to room temperature). (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Polarization switching in heterophase nanostructures: PLZT relaxor ceramics

The polarization switching is experimentally investigated in hot-pressed PLZT-x/65/35 ceramics with a lanthanum content from 5 to 12 at. %. The specific features in the temperature dependence of the polarization switching in a heterophase state are interpreted by analyzing the change in the switched charge measured over wide ranges of fields and temperatures. Particular emphasis is placed on the role of depolarization fields induced by interphase boundaries. A model of the evolution of polydomain nanostructures with a change in the temperature and in the response to an external field is considered. It is assumed that the low-temperature dielectric anomaly and the temperature hysteresis are associated with the loss of stability of a large-scale domain structure and its transformation into a nanodomain state.     

Quasi-Feller Extensions of Markov Chains and Existence of Dual Chains

The author presents a revised and detailed version of his theorem on the existence of Feller's extensions of Markov chains; to this end the broader notion of quasi-Feller extension is used. The existence of Markov chains dual to the chains with Borel space of states is derived from this result. Chains irreducible in the Orey sense are studied in most detail. For example, we prove that for such chains the quasi-Feller extension can be chosen recurrent or Liouville if the original chains possess these properties.     

Barkhausen jumps in the motion of a single ferroelectric domain wall

It is shown that the motion of a domain wall in the improper ferroelectric-ferroelastic gadolinium molybdate Gd₂(MoO₄)₃ demonstrates a self-organized critical behavior under polarization reversal. Barkhausen pulses are measured experimentally during the jumpwise motion of a single plane domain wall in monocrystalline plates with artificial pinning centers of the “field inhomogeneity” type.     

Coordination chemistry of anticrowns. An unusual complex of perfluorinated three-mercury anticrown (o-C6F4Hg)3 with p-bromotoluene and 1,2-dichloroethane

Russian Chemical Bulletin -     

Optical properties of antimicrobial barrier layers based on polyethylene terephthalate with a nanostructured surface

The optical properties of nanostructured barrier layers based on polyethylene terephthalate formed by ion technology and their resistance to biodegradation are discussed. The influence of the surface energy and relief parameters on the antimicrobial activity of nanostructured barrier layers is established. The study of reflection spectra demonstrates the fine structure of spectral lines apparently connected with the scattering of electromagnetic radiation by charged centers. These centers are formed on a nanostructured polymer surface after ion-plasma treatment as well as upon the deposition of α-C:H films which are known as electrets with a large number of broken bonds.     

Modeling the Interaction of a Vortex Pair with the Ground

The results of a numerical investigation of the interaction between an aircraft vortex wake (vortex pair) and the ground during the takeoff and landing phases are presented. The calculations were performed within the framework of the time-dependent two-dimensional Reynolds-averaged Navier-Stokes equations using the Spalart-Shur turbulence model generalizing the turbulent viscosity transport model of Spalart and Allmaras to the case of the flows with curved streamlines and rotation. Similar calculations were carried out on the basis of the original Spalart-Allmaras model and the k- model of Menter. Some new qualitative and quantitative data on the distinctive features of the phenomenon under consideration are obtained.