Changing vacancy balance in ZnO by tuning synthesis between zinc/oxygen lean conditions

The nature of intrinsic defects in ZnO films grown by metal organic vapor phase epitaxy was studied by positron annihilation and photoluminescence spectroscopy techniques. The supply of Zn and O during the film synthesis was varied by applying different growth temperatures (325–485 °C), affecting decomposition of the metal organic precursors. The microscopic identification of vacancy complexes was derived from a systematic variation in the defect balance in accordance with Zn/O supply trends.Peer reviewe

Two vicious circles contributing to a diagnostic delay for tuberculosis patients in Arkhangelsk

Setting: Delay in tuberculosis (TB) diagnosis increases the infectious pool in the community and the risk of development of resistance of mycobacteria, which results in an increased number of deaths. Objective: To describe patients’ and doctors’ perceptions of diagnostic delay in TB patients in the Arkhangelsk region and to develop a substantive model to better understand the mechanisms of how these delays are linked to each other. Design: A grounded theory approach was used to study the phenomenon of diagnostic delay. Patients with TB diagnostic delay and doctors–phthisiatricians were interviewed. Results: A model named ‘sickness trajectory in health-seeking behaviour among tuberculosis patients’ was developed and included two core categories describing two vicious circles of diagnostic delay in patients with TB: ‘limited awareness of the importance to contact the health system’ and ‘limited resources of the health system’ and the categories: ‘factors influencing health-seeking behaviour’ and ‘factors influencing the health system effectiveness’. Men were more likely to report patient delay, while women were more likely to report health system delay. Conclusions: To involve people in early medical examinations, it is necessary to increase alertness on TB among patients and to improve health systems in the districts

Le Kouri : race bovine du lac Tchad. I. Introduction générale à son étude zootechnique et biochimique : origines et écologie de la race

Les auteurs présentent de façon détaillée la race des taurins Kouris, bovins du lac Tchad. Cette première étude est l'introduction pour l'ensemble des travaux qui visent à éclairer les divers aspects zootechniques et biochimiques de cette race, connue depuis longtemps déjà et qui est étroitement liée au milieu aquatique du lac Tchad. Le but poursuivi est de ne pas laisser disparaître un maillon, sans doute essentiel, dans la phylogénie des races bovines et de tirer profit rapidement des propriétés les plus intéressantes de la race : production laitière, production de viande de qualité et propriétés des métis de 1re ou de 2e génération. Après l'étude écologique de l'aire géographique, le type caractéristique est décrit ainsi que ses propriétés économiques. Le mode d'élevage et la pathologie sont largement détaillés. De nombreuses raisons plaident actuellement pour le maintien et la sélection des bovins Kouris purs. (Résumé d'auteur

Testing ZnO based photoanodes for PEC applications

AbstractWe report on multi layered ZnCdO photoanode structures synthesized on c-A12O3 substrates using metal organic vapor phase epitaxy and covered with a thin TiO2 protective film using atomic layer deposition and pulsed laser deposition techniques. Structural, optical and photoelectrochemical properties of the multilayers were investigated systematically in connection with their potential application in the photolysis of water. X-ray diffraction and Rutherford backscattering techniques confirmed staggered arrangement and graded Cd content of the multilayers. Temperature-dependant photoluminescence revealed excitonic nature of a broad emission band representing combined band-edge emissions from the individual layers. The photocurrent was found to increase with decreasing thickness of the TiO2 protective layer

Cross-Sectional Carrier Lifetime Profiling and Deep Level Monitoring in Silicon Carbide Films Exhibiting Variable Carbon Vacancy Concentrations

The carrier lifetime control over 150 μm thick 4H-SiC epitaxial layers via thermal generation and annihilation of carbon vacancy (VC) related Z1/2 lifetime killer sites is reported. The defect developments upon typical SiC processing steps, such as high- and moderate-temperature anneals in the presence of a carbon cap, are monitored by combining electrical characterization techniques capable of VC depth-profiling, capacitance–voltage (CV) and deep-level transient spectroscopy (DLTS), with a novel all-optical approach of cross-sectional carrier lifetime profiling across 4H-SiC epilayer/substrate based on imaging time-resolved photoluminescence (TRPL) spectroscopy in orthogonal pump-probe geometry, which readily exposes in-depth efficacy of defect reduction and surface recombination effects. The lifetime control is realized by initial high-temperature treatment (1800 °C) to increase VC concentration to ≈1013 cm−3 level followed by a moderate-temperature (1500 °C) post-annealing of variable duration under C-rich thermodynamic equilibrium conditions. The post-annealing carried out for 5 h in effect eliminates VC throughout the entire ultra-thick epilayer. The reduction of VC-related Z1/2 sites is proven by a significant lifetime increase from 0.8 to 2.5 μs. The upper limit of lifetimes in terms of carrier surface leakage and the presence of other nonradiative recombination centers besides Z1/2, possibly related to residual impurities such as boron are discussed.publishedVersio

Vacancy clustering and acceptor activation in nitrogen-implanted ZnO

The role of vacancy clustering and acceptor activation on resistivity evolution in N ion-implanted n-type hydrothermally grown bulk ZnO has been investigated by positron annihilation spectroscopy, resistivity measurements, and chemical profiling. Room temperature 220 keV N implantation using doses in the low 10 exp 15 cm exp −2 range induces small and big vacancy clusters containing at least 2 and 3–4 Zn vacancies, respectively. The small clusters are present already in as-implanted samples and remain stable up to 1000°C with no significant effect on the resistivity evolution. In contrast, formation of the big clusters at 600°C is associated with a significant increase in the free electron concentration attributed to gettering of amphoteric Li impurities by these clusters. Further annealing at 800°C results in a dramatic decrease in the free electron concentration correlated with activation of 10 exp 16–10 exp 17cm exp −3 acceptors likely to be N and/or Li related. The samples remain n type, however, and further annealing at 1000°C results in passivation of the acceptor states while the big clusters dissociate.Peer reviewe

Back-illuminated Si photocathode:a combined experimental and theoretical study for photocatalytic hydrogen evolution

We present the first experimental demonstration of c-Si based photocathode for hydrogen production under back-illumination with theoretical model study.</p

Universal radiation tolerant semiconductor

Radiation tolerance is determined as the ability of crystalline materials to withstand the accumulation of the radiation induced disorder. Nevertheless, for sufficiently high fluences, in all by far known semiconductors it ends up with either very high disorder levels or amorphization. Here we show that gamma/beta double polymorph Ga2O3 structures exhibit remarkably high radiation tolerance. Specifically, for room temperature experiments, they tolerate a disorder equivalent to hundreds of displacements per atom, without severe degradations of crystallinity; in comparison with, e.g., Si amorphizable already with the lattice atoms displaced just once. We explain this behavior by an interesting combination of the Ga- and O- sublattice properties in gamma-Ga2O3. In particular, O-sublattice exhibits a strong recrystallization trend to recover the face-centered-cubic stacking despite the stronger displacement of O atoms compared to Ga during the active periods of cascades. Notably, we also explained the origin of the beta-to-gamma Ga2O3 transformation, as a function of the increased disorder in beta-Ga2O3 and studied the phenomena as a function of the chemical nature of the implanted atoms. As a result, we conclude that gamma/beta double polymorph Ga2O3 structures, in terms of their radiation tolerance properties, benchmark a class of universal radiation tolerant semiconductors