Deep-level trapping centers in heterostructures for GaN field-effect transistors

Structural and electrophysical properties of heteroepitaxial gallium nitride layers on a sapphire substrate that are grown via the molecular beam epitaxy (MBE) method are studied. The parameters of deep-level trapping centers are determined by the method of the thermostimulated capacitor discharge; the degree of perfection of the film and substrate are determined by the two-crystal X-ray spectrometry method. The following structures are studied: i-GaN (1–2 μm)/GaN 〈Si〉(0.1−0.4 μm) and multilayer structures (Al_0.3Ga_0.7N-GaN-Al_0.3-Ga_0.7N-GaN-Al₂O₃) grown via the MBE method on a sapphire substrate. The effect of reactive ion etching on the energy spectrum of deep-level trapping centers in gallium nitride is studied. The obtained results are used to calculate the energy spectrum of defects in gallium nitride structures. Original Russian Text ? M.S. Andreev, L.E. Velikovskii, T.S. Kitichenko, T.G. Kolesnikova, A.P. Korovin, V.G. Mokerov, S.N. Yakunin, 2007, published in Radiotekhnika i Elektronika, 2007, Vol. 52, No. 7, pp. 880–887.     

Autoemission structures of nanosized carbon with ionic protection. Studying the prospects of reliable control in forming structures

The results of theoretical and experimental study of the criticality of the process of forming nanosized α-carbon blades for autoemission structures with ionic protection are given. It is shown that this technology provides reliable control of the process. A weak dependence of the field strength in the tip area of emitter from the length of the blade visor was found, which promotes a good reproducibility of its parameters.     

On the development of high-throughput and area-efficient multi-mode cryptographic hash designs in FPGAs

In this paper, area-efficient and high-throughput multi-mode architectures for the SHA-1 and SHA-2 hash families are proposed and implemented in several FPGA technologies. Additionally a systematic flow for designing multi-mode architectures (implementing more than one function) of these families is introduced. Compared to the corresponding architectures that are produced by a commercial synthesis tool, the proposed ones are better in terms of both area (at least 40%) and throughput/area (from 32% up to 175%). Finally, the proposed architectures outperform similar existing ones in terms of throughput and throughput/area, from 4.2× up to 279.4× and from 1.2× up to 5.5×, respectively.     

HyperTree: a structural approach to web authoring

The expansion of the World Wide Web (WWW) has created an increasing need for tools capable of supporting WWW authors in composing documents using the HyperText Markup Language (HTML). Currently, most web authors use tools which are basically ordinary text editors and have additional features to facilitate the easy and correct use of HTML tags. This approach places the burden on the web author to design and then create the entire web site in a top-down fashion, without any explicit support for the structural design of the site. In this paper we discuss an alternative structural approach to Web authoring, which is based on the use of the HyperTree hypermedia system as the central authoring tool. The advantages of using HyperTree are two-dimensional. Firstly, web authors can manage a web site as a single complete hypermedia database. For example, HyperTree provides facilities like the automatic creation of indices and the discovery of link inconsistencies. Additionally, it organizes the web pages in an easy to understand hierarchy without using any HTML directly. Secondly, web end-users can benefit from the use of HyperTree, since seeking information in structured web sites is generally less disorientating and develops fewer cognitive overheads. ©1997 John Wiley & Sons, Ltd.     

Pheromone specificity inEriocrania semipurpurella (Stephens) andE. sangii (Wood) (Lepidoptera: Eriocraniidae) based on chirality of semiochemicals

The fifth abdominal segment of femaleEriocrania semipurpurella (Stephens) andE. sangii (Wood) contains a pair of exocrine glands. Hexane extracts of this segment were prepared from both species and analyzed by gas chromatography with simultaneous flame ionization and electroantennographic detection (EAD). For both species, the EAD active peaks were identified as nonan-2-one, (Z)-6-nonen-2-one, and (Z)-6-nonen-2-ol by means of mass spectrometry and comparison of retention indices with those of synthetic standards. Enantiomeric separation of chiral alcohols from the female extracts was achieved by gas chromatographic analysis on a cyclodextrin column. InE. semipurpurella, a mixture of (2S,6Z)-nonen-2-ol and (2R,6Z)-nonen-2-ol (2: I) was found, whereas inE. sangii (2S,6Z)-nonen-2-ol was the predominant enantiomer and only traces of theR enantiomer were indicated by the antennal response. In field tests, a blend of the three compounds was not attractive to conspecific males. A subtractive assay showed that the alcohol in various enantiomeric mixtures was the only attractive compound, whereas addition of (Z)-6-nonen-2-one to the alcohol completely inhibited the attraction of both species. A trapping experiment including a wide range of ratios between theR andS enantiomers showed that baits containing 95–100% of theS enantiomer were attractive to maleE. sangii, whereas males ofE. semipurpurella were attracted to all tested ratios of the enantiomers. However, the response profiles of maleE. semipurpurella differed between populations from southern Sweden, south Finland, and the Kola Peninsula in Russia. In south Sweden males were maximally attracted to a racemic mixture of the alcohols. At the Kola PeninsulaE. semipurpurella was attracted to baits containing 95–100% of theR enantiomer. In south Finland all tested ratios between 0 and 100%R enantiomer trappedE. semipurpurella, but the trap catches appeared to be bimodally distributed with peaks around 15 and 70%R enantiomer. The trapping results suggest the existence of pheromone races or sibling species among the specimens identified asE. semipurpurella.Dedicated to Prof. H. J. Bestmann on the occasion of his 70th birthday.     

Nonlinear magnetization reversal in copper-permalloy composite wires induced by a high-frequency current

The phenomenon of magnetization reversal in copper-permalloy composite wires induced by a high-frequency ac current field was studied. The frequency spectrum of a voltage measured in the probing coil wound on the wire contains only even harmonics in a broad range of amplitudes of the ac excitation current and the bias magnetic field strength. The amplitude of the even harmonics measured is highly sensitive with respect to the bias field. The results can be used to develop weak magnetic field sensors.     

Nature of high reactivity of metal/solid oxidizer nanocomposites prepared by mechanoactivation: a review

In this review, the regularities of formation, structure and high reactivity of two types of energetic metal/solid oxidizer nanocomposites (Al(Mg)/X (X = MoO₃, (–C₂F₄–) _n )) prepared by mechanoactivation are examined. One reason for the high reactivity is an increase in contact surface between the components occurring after mechanoactivation. Two methods for determination of area of contact surface S _C between the components are used, and the values of S _C for all the systems are estimated. Considerable attention is paid to the role of highly reactive defects (grain sizes, dislocations and stacking faults, paramagnetic centers, “weakly bound” oxygen in MoO₃, etc.), formed in the components under mechanical stress. For the Me/MeO₃ systems, the formation of point defects in the oxide is an important factor. It was found that, after mechanoactivation, the evolution of O₂ from MoO₃ occurs at 230–450 °C. It is argued that this process is associated with the thermal destruction of “weak” Mo–O bonds in the “bridge” oxygen. It was suggested that the formation of defect structure in MoO₃ and increasing of the oxygen mobility under heating give rise to a low-temperature peak in DSC curves and initiated self-ignition on the fuel–air mixture. For composites Mg/MoO₃, self-ignition occurs at temperature 100 °C lower than that for Al/MoO₃: The decreasing of temperature can be connected with larger S _C in the first system. In the Mg/(–C₂F₄–) _n system, the reactions of magnesium defects with (–C₂F₄–) _n are accompanied by a weak heat evolution, too low to initiate ignition. In this case, the reaction is initiated by the thermal depolymerization of (–C₂F₄–) _n , while a high values of S _C provide a complete conversion. In the case of shock-wave initiation, defects in the components play only a minor role in the conversion, whereas the value of S _C remains to be highly important.