A New Mechanism for the Alpha to Omega Martensitic Transformation in Pure Titanium

We propose a new direct mechanism for the pressure driven alpha to omega martensitic transformation in pure titanium. A systematic algorithm enumerates all possible mechanisms whose energy barriers are evaluated. A new, homogeneous mechanism emerges with a barrier at least four times lower than other mechanisms. This mechanism remains favorable in a simple nucleation model.Comment: 4 pages, 4 figure

Depth and thermal stability of dry etch damage in GaN Schottky diodes

GaN Schottky diodes were exposed to N2 or H2 Inductively Coupled Plasmas prior to deposition of the rectifying contact. Subsequent annealing, wet photochemical etching or (NH4)2S surface passivation treatments were examined for their effect on diode current- voltage characteristics. We found that either annealing at 750 °C under N2, or removal of ~500-600 Å of the surface essentially restored the initial I-V characteristics. There was no measurable improvement in the plasma-exposed diode behavior with (NH4)2S treatments

ФОТОЭЛЕКТРИЧЕСКИЕ ПРЕОБРАЗОВАТЕЛИ В СИСТЕМЕ СО СПЕКТРАЛЬНЫМ РАСЩЕПЛЕНИЕМСОЛНЕЧНОЙ ЭНЕРГИИ

This paper presents results on the simulation of photo converters in a spectral splitting system where solar radiation is separated into three spectral ranges (∆λ1<500 nm, ∆λ2 = 500−725 nm and ∆λ3>725 nm) by means of dichroic filters and then converted to electrical energy by photoconverters based on InGaN/GaN, GaAs/AlGaAs single−junction heterostructures and monocrystalline silicon c−Si. Special attention is paid to the absorption spectrum spreading due to more efficient conversion of the ultraviolet part of the spectrum. The total efficiency of the system varies from 21% to 37% depending on the design of heterostructures.Представлены результаты моделирования фотоэлектрических преобразователей в системе со спектральным расщеплением солнечной энергии, в которой солнечное излучение разделяется с помощью дихроичных фильтров на три спектральных диапазона (∆λ1 < 500 нм, ∆λ2 = 500÷725 нм, ∆λ3 > 725 нм) и затем преобразуется в электроэнергию фотоэлектрическими преобразователями на основе однопереходных гетероструктур InGaN/GaN, GaAs/AlGaAs и монокристаллического кремния c−Si. Особое внимание уделено исследованию расширения спектрального диапазона поглощения системы за счет более эффективного преобразования ультрафиолетовой части спектра. Суммарный КПД системы на всем спектре варьируется от 21 до 37 % в зависимости от дизайна гетероструктур однопереходных фотоэлектрических пре-образователей и вариантов оптических систем

Структурные, электрические и люминесцентные характеристики ультрафиолетовых светодиодов, выращенных методом хлорид–гидридной эпитаксии

Electrical and luminescent properties of near−UV light emitting diode structures (LEDs) prepared by hydride vapor phase epitaxy (HVPE) were studied. Variations in photoluminescence and electroluminescence efficiency observed for LEDs grown under nominally similar conditions could be attributed to the difference in the structural quality (dislocation density, density of dislocations agglomerates) of the GaN active layers, to the difference in strain relaxation achieved by growth of AlGaN/AlGaN superlattice and to the presence of current leakage channels in current confining AlGaN layers of the double heterostructure.Изучены электрические и люминесцентные характеристики светодиодных структур (СД), излучающих в ближней ультрафиолетовой (УФ) области и выращенных методом хлорид−гидридной эпитаксии. Обнаружены различия в характеристиках УФ СД, выращенных в номинально одинаковых условиях, которые приписывают различиям в структурном совершенстве (плотности дислокаций и дислокационных агломератов) в активных слоях GaN, разнице в степени релаксации напряжений, достигаемой с помощью сверхрешеток AlGaN/AlGaN, а также существованию каналов токовых утечек в слоях AlGaN, ограничивающих заряд в двойной гетероструктуре.

THE PART OF PATHOMORPHOLOGIC STUDY IN SURGICAL TREATMENT PLANNING AT METASTATIC BONE TUMORS

The pathomorphologic study is the key examination in the therapy planning of patients with metastatic bone tumors. Since 1994 till 2009 424 patients with this pathology were treated in RRITO n.a. R. Vreden. The authors give clinical example showing the influence of pathomorphologic study results on the sequence of stages of complex treatment of patients with malignant tumors

Atomic and electrostatic force microscopy observations on gallium nitride

International audienceThe aim of this paper is to precise the interest of scanning force microscopy (SFM) observations on gallium nitride films. These observations concern the atomic force microscopy (AFM) and, more especially, the electrostatic force microscopy (EFM) and electrical force gradient microscopy (EFGM). First of all, the EFM and EFGM method are recalled and situated one versus the other. Secondly, a rapid review of the literature results is made, in order to precise which observations could be expected. Finally, on various gallium nitride films, we show: (i) the obtained performances in terms of spatial resolution and voltage sensitivity and (ii) observations using the EFM and EFGM methods and their interpretation

STUDY OF MECHANISMS RESPONSIBLE FOR THE EFFICIENCY DEGRADATION OF THE III-NITRIDES LIGHT EMITTING DIODES

The results for external quantum efficiency degradation of two types of light emitting diodes based on III-nitrides: blue and ultraviolet ones are presented. Existing mechanisms proposed for the degradation are considered briefly. Applying several techniques for studying the light emitting diodes at various stages of the aging test gives the possibility to reveal a new mechanism of defects formations with a help of multi-phonon recombination of carriers in an extended defects system and in local regions of random alloy fluctuations. These techniques include analysis of current voltage characteristics evolution at V<2V, the low frequency noise methods, and infrared microscopy. The multi-phonon recombination of carriers is accomplished by generation of native defects, in particular, In- or Ga-atoms and their migration. These processes lead to modification of the extended defects system properties and local composition of InGaN alloys in several regions that result in decreasing of the carriers participating in a radiative recombination and degradation of the external quantum efficiency. It was demonstrated that this mechanism of the defects formation can be responsible for the degradation of the blue and ultraviolet light emitting diodes. The mechanism can explain non monotonic dependence of the degradation process during the aging test, catastrophic failures of the light emitting diodes and low lifetime of the ultraviolet light emitting diodes

Quality Assessment of Processed Graphene Chips for Biosensor Application

The quality of graphene intended for use in biosensors was assessed on manufactured chips using a set of methods including atomic force microscopy (AFM), Raman spectroscopy, and low-frequency noise investigation. It is shown that local areas of residues on the graphene surface, formed as a result of the interaction of graphene with a photoresist at the initial stage of chip development, led to a spread of chip resistance (R) in the range of 1–10 kOhm and to an increase in the root mean square (RMS) roughness up to 10 times, which can significantly worsen the reproducibility of the parameters of graphene chips for biosensor applications. It was observed that the control of the photoresist residues after photolithography (PLG) using AFM and subsequent additional cleaning reduced the spread of R values in chips to 1–1.6 kOhm and obtained an RMS roughness similar to the roughness in the graphene film before PLG. Monitoring of the spectral density of low-frequency voltage fluctuation (SU), which provides integral information about the system of defects and quality of the material, makes it possible to identify chips with low graphene quality and with inhomogeneously distributed areas of compressive stresses by the type of frequency dependence SU(f)