Exciton photoluminescence from ZnO layers produced by laser-induced gas breakdown processing

The plasma of optically-excited gas breakdown has been used to treat a Zn target in atmospheric pressure gases (air, O₂, N₂, Ar). The breakdown is produced near the target by a pulsed CO₂ laser radiation, yielding to a local erosion of the target under the irradiation spot and the formation of a porous nanostructured layer, consisting of ZnO nanoscale spheres. We show that the produced nanostructured layers exhibit an intense exciton emission band in the ultraviolet range (380–385 nm), while defect-related photoluminescent bands were weak and could be completely removed by varying the fabrication parameters. Properties of the produced layers were found to be very promising for the development of optoelectronic devices. PACS 81.16.Mk; 81.05.-t     

Electron and hole μτ-products in a-Si:H/a-SiNχ:H multilayers

In this work the influence of the interface defect density on the a-Si:H/a-SiN_χ:H multilayers is investigated through photoconductivity, ambipolar diffusion length, dark conductivity activation energy, and defect density measurements. The results show a strong asymmetric dependence of (μτ)_e and μτ)_h on the interface defect density: As the thickness of the well decreases, (μτ)_e decreases strongly, whereas (μτ)_h remains constant. The asymmetry is consistently explained by a simple model, in which recombination of free carriers occurs via midgap defect states (in the bulk and at interfaces) and via trapping of electrons (holes) into their respective deep tail states below (above) their respective demarcation levels. Since the samples are slightly n-type and due to the asymmetric density-of-state distribution we can show analytically that (μτ)_h is indeed insensitive to the midgap defect density. Finally, when fitting the measured mobility-lifetime products to an exponentially decaying defect density profile we can conclude that the interface region is about 5 Åwide.     

Mass singularities at finite temperature in a scalar field theory

Using as a model the φ³ field theory in space-time dimensionD=6, we show the validity of the Kinoshita-Lee-Nauenberg theorem at finite temperature to first order in the coupling constant.     

Biocompatibility of some materials used in dental implantology: histological study

This study deals with bioreactive materials for potential applications as endosseus dental implants. Currently used dental implants are made of dental alloys but due to cytotoxic problems, high strength ceramic materials appear as an interesting alternative to these alloys. In order to combine good mechanical properties and promotion of the osteointegration process, a ceramic composite material composed of 10 wt.% tricalcium phosphate (TCP) mixed with partially stabilized zirconia has been elaborated. Such a ceramic has been implanted into albino rats, the sites of implantation being the adrenal gland for the toxicity evaluation and the sphenoid bone to estimate the osteogenesis potential. These results have been compared to those obtained with implants made of alumina (Al₂O₃), zirconia (ZrO₂) or poly(ethylene terephthalate) (Dacron®). In all cases no rejection effect was observed. The histological study indicated that ZrO₂-TCP ceramics induced a marginal and subjacent cell disorganization. However, the existence of an irregular cellular band indicated a cellular colonization process on the TCP particles. The microscopy study of the implants after removal confirmed the bioresorption of TCP.     

Vacuum arc deposition of carbon thin films in a low pressure ofhydrogen

Results on the vacuum arc deposition (VAD) of thin carbon films on silicon, tungsten, and nickel are presented for different hydrogen pressures in the arc chamber. Raman and Auger electron spectroscopy and SEM analysis show that a large variety of film structures can be obtained. Highly oriented pyrolytic graphite is formed at high hydrogen pressure and low substrate temperature. Vacuum deposition resulted in a diamondlike structure. Evidence of the presence of multicrystalline spheres of diamond in some films is also presented     

New chromogenic reagents for labelling amino groups in peptides. Chromatographic and preparatives aspects

Summary A new type of chromogenic reagent for labelling the amino groups of peptides or amino acids, 5-substituted 2,4-dinitrofluorobenzenes, is presented. These reagents are characterized by a polarity determined by the function included in the substituent in the 5-position and by the nature of this substituent. Preparation and chromatographic behaviour of these reagents, of eventual by-products of reactions and of some N-(2,4-dinitro-5-diethylaminophenyl)-peptides or amino acids are described.Proportions in solvent mixtures are v/v except otherwise indicated. Abbreviations: lit=literature, TLC=thin-layer chromatography, TLE=TL electrophoresis, see also: Figs. 2, 3, 5.