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A study was conducted to analyze thin Si/SiO2 nanocomposite films determined by magnetron co-sputtering. The layers were prepared with different values of deposition temperature and sputtered silicon area. Results indicated the effectiveness of the spectroscopic ellipsometry method in determining estimates of the thickness, the silicon content of the silica layers and the dielectric role of silicon nanograms.

Nanocrystalline silicon (nc-Si) thin films have potential for solar cells and thin film transistors. Detailed structural analyses of nc-Ci layers are presented, achieved through thermal annealing of sputtered films containing various hydrogen concentrations. Infrared (IR) spectroscopy, x-ray diffraction, Raman scattering and high resolution microscopy were used to investigate the as-deposited and thermally nanocrystallized layers, and the impact of prior presence of hydrogen on the microstructure and properties of thermally nanocrystallized silicon films.

The nature of NiSi2 plates grown in the grain boundary (GB) region of nickel silicides is associated with the electrical characteristics of the silicides at the boundary of silicon bicrystals. The electrical characteristics also depend on the temperature at which heat treatment of these crystals is performed. The study reveals that the movement of interface levels toward the band edge is cause by an increase in annealing temperature.

Deep-level transient spectroscopic analysis of silicon bicrystal reveals continuous energy level distributions between minus 0.20 and minus 0.38 eV. The bicrystals contaminated with Cu or Ni reveal interface trap characteristics of quenched Cu precipitates at minus 0.54 eV. Introduction of Ni in 'copper-free' bicrystals causes a discrete energy level at minus 0.50 eV.

This experiment was conducted to study the effect of long term selection for breast circumference (BC) of Gimmizah (GM) chickens on some body measurements of males at 12, 25 and 45 weeks of age such as body weight (BW), BC, shank length (SL), and secondary sexual characters as comb length (CL) and wattle length (WL), besides fertility with hatchability and their genetic parameters. Two hundred and twenty GM hens with twenty males were randomly chosen and considered as base population (G0). Chicks produced from G0 were selected for BC at 12-wk of age and selected through additional five generations. The results revealed that selection for BC significantly increased BW at 12-wk of age for selected line compared to control one among 4 and 5th generations. Comb length for selected lines had significantly increased compared to control lines for CL12 in G4 and G5. Wattle lengths for selected lines were increased (p˂0.05) in the last three generations compared to the rest ones among all the experimental ages. There were a significant improvement of fertility and hatchability of fertile eggs percentages among the subsequent selected generations. Most of heritability ( estimates for CL and WL were considered high and ranged between 0.50 and 0.78. Low estimates of were recorded for which ranged between 0.02 to 0.14 and for hatchability of fertile eggs between 0.02 and 0.05. Furthermore, CL represented high genetic correlation with fertility among the bird's ages and generations. In conclusion, body circumference could be used as selection tool for improving body weight and secondary sexual characters without detrimental effect on fertility, besides suggesting other body measurements as shank, comb and wattle lengths could be included in selection index. [ABSTRACT FROM AUTHOR]

The present experiment was carried out for evaluation the influence of body weight selection at 12 –wk of age for Gimmizah chickens on hatching traits besides same genetic and phenotypic parameters related to it. The obtained results are summarized as follows: fertility percentage was numerically increased for first generation after selection of body weight compared with those for base population also, hatchability percentages were significantly decreased for the first generation compared with those for the base one population, while late and total embryonic mortalities were significantly increased for the first generation comparable to base one. Values of heritability for all studied parameters of fertility, hatchability and embryonic mortalities were low. Also, there are no obvious changes for heritability between base and 1st generations with respect to all studied hatching traits. Moreover, most values of additive gene for fertility, hatchability and embryonic mortalities were low with relatively marked decrease for hatchability of total eggs among the base population and first generation. Highly positive significant phenotypic correlation was detected between fertility and hatchability of fertile eggs. While, all stages of embryonic mortalities represented highly negative significant phenotypic correlations with hatchability of fertile eggs. Moreover, hatchability of fertile eggs is genetically highly positive correlated with fertility. In conclusion fertility, hatchability and embryonic mortality could be considered in designing the program of improving body weight for Gimmizah chickens and this criteria should be involved in the selection index. [ABSTRACT FROM AUTHOR]

This work is dedicated to figuring out robust epoxy/magnetite/boron carbide (EP/Mag/B4C) composite for radiation attenuation at multiple applications related to nuclear installations, as well as restoration mortar for cracking developed in concrete biological shields. The mechanical properties (flexural, compressive, and impact strengths) and the physical properties (water absorption, porosity, and dry bulk density), each, have been performed to label the composite integrity for practical application. In practice, attenuation properties have been performed by using a collimated beam emitted from spontaneous fission 252Cf (100 μg) neutron source and neutron gamma spectrometer with stilbene scintillator. The pulse shape discrimination technique which would come of the zero cross over method was used to measure the fast neutron and gamma-ray spectra. Thermal neutron fluxes have been measured by using the thermal neutron detection system and the BF-3 detector. The attenuation parameters: precisely, macroscopic effective removal cross-sections ΣR (cm-1), macroscopic cross-sections Σ (cm-1), and total attenuation coefficients μ (cm-1) of fast and thermal neutrons and total gammarays respectively were evaluated using the attenuation relations. Also, the MCNP5 code and MERCSF-N program have been used to compute the parameters theoretically. When applicable, measured and calculated results were compared, and it tells us a comprehensive agreement. [ABSTRACT FROM AUTHOR]

We report a spectroscopic study about the energy transfer mechanism among silicon nanoparticles (Si-np), both amorphous and crystalline, and Er ions in a silicon dioxide matrix. From infrared spectroscopic analysis, we have determined that the physics of the transfer mechanism does not depend on the Si-np nature, finding a fast (<200 ns) energy transfer in both cases, while the amorphous nanoclusters reveal a larger transfer efficiency than the nanocrystals. Moreover, the detailed spectroscopic results in the visible range here reported are essential to understand the physics behind the sensitization effect, whose knowledge assumes a crucial role to enhance the transfer rate and possibly employing the material in optical amplifier devices. Joining the experimental data, performed with pulsed and continuous-wave excitation, we develop a model in which the internal intraband recombination within Si-np is competitive with the transfer process via an Auger electron-'recycling' effect. Posing a different light on some detrimental mechanism such as Auger processes, our findings clearly recast the role of Si-np in the sensitization scheme, where they are able to excite very efficiently ions in close proximity to their surface. [ABSTRACT FROM AUTHOR]

Optical properties of directly excited erbium (Er3+) ions have been studied in silicon rich silicon oxide materials codoped with Er3+. The spectral dependence of the direct excitation cross section (σdir) of the Er3+ atomic 4I15/2→4I11/2 transition (around 0.98 μm) has been measured by time resolved μ-photoluminescence measurements. We have determined that σdir is 9.0±1.5×10-21 cm2 at 983 nm, at least twice larger than the value determined on a stoichiometric SiO2 matrix. This result, in combination with a measurement of the population of excited Er3+ as a function of the pumping flux, has allowed quantifying accurately the amount of optically active Er3+. This concentration is, in the best of the cases, 26% of the total Er population measured by secondary ion mass spectrometry, which means that only this percentage could provide optical gain in an eventual optical amplifier based on this material. [ABSTRACT FROM AUTHOR]

We have studied the current transport and electroluminescence properties of metal oxide semiconductor (MOS) devices in which the oxide layer, which is codoped with silicon nanoclusters and erbium ions, is made by magnetron sputtering. Electrical measurements have allowed us to identify a Poole–Frenkel conduction mechanism. We observe an important contribution of the Si nanoclusters to the conduction in silicon oxide films, and no evidence of Fowler–Nordheim tunneling. The results suggest that the electroluminescence of the erbium ions in these layers is generated by energy transfer from the Si nanoparticles. Finally, we report an electroluminescence power efficiency above 10-3%. [ABSTRACT FROM AUTHOR]

The energy transfer process between amorphous silicon nanoparticles and erbium ions in Er-doped silicon-rich silicon oxide is investigated by fluorescence dynamics measurements. A fast decay is observed in the wavelength range of the radiative relaxation of erbium excited ions at 1.53 μm. Alternatively to a previous interpretation, we assign this fast decay to emission of deep traps induced by Si-based sensitizers of Er3+ ions, which emit in the visible and the infrared region. [ABSTRACT FROM AUTHOR]

Series of Er-doped Si-rich silicon oxide layers were studied with the aim of optimizing the coupling between Er ions and the Si-based sensitizers. The layers were grown at substrate temperature between 400 and 600 °C by the cosputtering of three confocal targets: Si, SiO2, and Er2O3. The influence of Si excess (5–15 at. %) and annealing temperature (500–1100 °C) was examined for two concentrations of Er ions (3.5×1020 and ∼1021 cm-3). We report the first observation of significant Er photoluminescence (PL) from as-grown samples excited by a nonresonant 476 nm line, with a lifetime in the range of 1.3–4 ms. This suggests the occurrence of an indirect excitation of Er through Si-based entities formed during the deposition. A notable improvement was observed for both Er PL intensity and lifetime after annealing at 600 °C. This temperature is lower than that required for phase separation, suggesting the formation of “atomic scale” sensitizers (Si agglomerates, for example) considered in recent work. For high Er doping (∼1021 cm-3), an optimum Er PL was obtained for the sample grown at 500 °C, annealed at 600 °C, and containing ∼13 at. % of Si excess. This high PL should correspond to an optimum fraction of coupled Er for this series, which was roughly estimated to about 11% of the total Er content for an excitation photon flux of few 1019 ph cm-2 s-1. For the moderately Er-doped series (3.5×1020 cm-3) grown at 500 °C, the optimum Er PL was found for the samples containing about 9 at. % silicon and annealed in the 600–900 °C range. The time decay reached a value as high as 9 ms for low Si excess (<6 at. %) and 6–7.5 ms for high values of Si excess. The fraction of Er ions coupled to sensitizers was similarly estimated for the best sample of this series and found to be as high as 22% of the total Er content. [ABSTRACT FROM AUTHOR]

Hydrogenated nanocrystalline silicon carbide were grown at various deposition temperatures Td from 200 to 600 °C by means of reactive magnetron sputtering in a plasma of 80% H2 and 20% Ar mixture. A detailed investigation of the structural, compositional, phase nature, and morphology was carried out by complementary sophisticated techniques, such as Fourier transform infrared spectroscopy, x-ray diffraction (XRD), Rutherford backscattering, nuclear reaction, and elastic recoil detection analysis techniques, in addition to conventional and high-resolution transmission electron microscopy (HRTEM) observations. A crystallization onset with a fraction of 35% was observed for Td=300 °C, which improved to 80% for Td=600 °C, reflected by an increasing density of the SiC nanocrystals which kept an average size of about 5 nm. The observed fiber textures present <102> and <11ℓ> texture components, with ℓ larger than 2, while SiC nanocrystals elongated along the [111] direction are also evidenced. These latter are supported by the careful analyses of the HRTEM images which show evidence of faulted growing cubic SiC, as the origin of the very close hexagonal 6H–SiC structure taken into account in the XRD refinement. These various features were found quite consistent with the optical properties of the layers, and, in particular, the evolutions of both optical gap and static refractive index. [ABSTRACT FROM AUTHOR]

The complex refractive index of SiO2 layers containing Si nanoclusters (Si-nc) has been measured by spectroscopic ellipsometry in the range from 1.5 to 5.0 eV. It has been correlated with the amount of Si excess accurately measured by x-ray photoelectron spectroscopy and the nanocluster size determined by energy-filtered transmission electron microscopy. The Si-nc embedded in SiO2 have been produced by a fourfold Si+ ion implantation, providing uniform Si excess aimed at a reliable ellipsometric modeling. The complex refractive index of the Si-nc phase has been calculated by the application of the Bruggeman effective-medium approximation to the composite media. The characteristic resonances of the refractive index and extinction coefficient of bulk Si vanish out in Si-nc. In agreement with theoretical simulations, a significant reduction of the refractive index of Si-nc is observed, in comparison with bulk and amorphous silicon. The knowledge of the optical properties of these composite layers is crucial for the realization of Si-based waveguides and light-emitting devices. [ABSTRACT FROM AUTHOR]

Textured silicon thin films are deposited by reactive magnetron sputtering in hydrogen-rich plasma on (100)-Si and amorphous SiO2 substrates. We quantitatively determine, combining x-ray texture analysis, x-ray reflectivity, transmission electron microscopy, atomic force microscopy measurements, and Raman and Fourier transform infrared spectroscopy analyses, the structure (cell parameter and mean electron density) and microstructure (crystalline fraction, preferred orientations, anisotropic crystallite sizes, thicknesses, etc.) of these films. For both kinds of substrates, no perfect <111> orientation is observed whereas a systematic elongation of the anisotropic Si crystallites along one [111] direction is present. A small elongation of the Si cell parameter of the nanocrystals is found without internal stress. With the substrate to target distance, the crystalline fraction and mean electron density show an opposite behavior to that of the film porosity. The former increases and the latter decreases, and are correlated to the texture evolution. Preferred orientations are observed with texture strengths around two to three times a random distribution, with a tendency to achieve lower strengths for films grown on SiO2 substrates. The texture components are evolving with the substrate to target distance, with <110> and (ℓ larger than 2) orientations favored for smaller and larger distances, respectively. All these microstructural properties are correlated with their optical properties and more particularly to their refractive index and their optical band gap. [ABSTRACT FROM AUTHOR]

The present article deals with the optimized processing conditions leading to the highest density of Si nanoclusters which play the role of sensitizing centers for the nearby Er ions within a silica matrix. The layers were obtained by reactive magnetron sputtering under a plasma of Ar mixed to different rates of hydrogen, and were subsequently annealed at various temperatures. The increase of the dilution degree of the Ar plasma with hydrogen was found to multiply the nucleation sites whose density foreshadows that of the Si nanoclusters formed upon annealing. Both hydrogen content and annealing temperature govern the growth of the clusters. The maximum density of efficient sensitizing centers was obtained for hydrogen rate in the plasma of 50% and annealing at 900 °C. This has directly led to the enhancement of the coupling rate between the Si nanoclusters and the Er ions, as reflected by the ten times increase of the proportion of optically active ions, compared to that for standard conditions. In parallel, the lifetime emission of the active Er ions was found to continuously improve with the annealing temperature and has reached values exceeding 7 ms. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Reports on erbium-doped silicon (Si)-rich silica layers obtained by reactive magnetron sputtering and both structural and room-temperature photoluminescence properties. Finding that the controlled introduction of hydrogen in the plasma plays a role in the microstructure and distribution of the Si nanograins formed after annealing.