Luminescence from Si nanocrystals in silica deposited by helicon activated reactive evaporation

An alternative method is investigated for the preparation of Si-rich SiO₂films used for the fabrication of light-emitting Si nanocrystalstructures. The technique, helicon-activated reactive evaporation (HARE), combines e-beam evaporation of silicon with plasma activation of a reactive argon–oxygen atmosphere, and has the advantage of being able to produce thick, H-free films suitable for planar photonic device applications. The nanocrystal-rich films were formed by annealing as-deposited films at 1100 °C for 1 h. Room temperature photoluminescence was then measured and compared with that from ion-implanted samples annealed under similar conditions. The HARE-deposited films exhibited strong visible luminescence for a range of excess Si concentrations, demonstrating their potential for the manufacture of such materials. The films also exhibited a concentration dependence comparable to that of ion-implanted samples: the luminescence intensity initially increased with excess Si concentration up to a maximum before decreasing with increasing concentration thereafter. The cause of the decrease at higher concentrations is briefly discussed

La faune sauvage des chênaies (les Vertébrés terrestres).

Dans un premier temps les deux groupes suivants : mammifères et oiseaux des chênaies sont abordés de manière globale (analyse du peuplement). Dans un second temps, quelques cas d'espèces sont traités (geai des chênes, palombe, sanglier, rongeur)

Les bases biologiques du maintien de la biodiversité : l'exemple des oiseaux de Provence.

La conservation du patrimoine biologique de la Provence, de 55 à 95 % de celui de la France, passe par le maintien des habitats naturels et de tous les éléments qui composent ces écosystèmes

Increased conductivity of a hole transport layer due to oxidation by a molecular nanomagnet

Thin film transistors based on polyarylamine poly(N,N′-diphenyl-N,N′bis(4-hexylphenyl)-[1,1′biphenyl]-4,4′-diamine (pTPD) were fabricated using spin coating in order to measure the mobility of pTPD upon oxidation. Partially oxidized pTPD with a molecular magnetic cluster showed an increase in mobility of over two orders of magnitude. A transition in the mobility of pTPD upon doping could also be observed by the presence of a maximum obtained for a given oxidant ratio and subsequent decrease for a higher ratio. Such result agrees well with a previously reported model based on the combined effect of dipolar broadening of the density of states and transport manifold [email protected] [email protected]

Active planar optical waveguide made from luminescent silicon nanocrystals

We show experimentally that a layer of silicon nanocrystals, prepared by the Si-ion implantation (with the energy of 400 keV) into a synthetic silica slab and exhibiting room-temperature red photoluminescence, can serve simultaneously as a single-mode planar optical waveguide. The waveguide is shown to self-select guided transverse electric and transverse magnetic modes from the broad photoluminescence emission of the nanocrystals resulting in a substantially narrower emission spectrum for these modes. We further report on an investigation of optical gain in a sample implanted to a dose of 4×1017 cm−2. Despite the occurrence of strong waveguiding, results of the variable stripe length method turned out not to be able to give unambiguous evidence for optical gai

Photonic band-gap effects on photoluminescence of silicon nanocrystals embedded in artificial opals

Si nanocrystals were formed in synthetic opals by Si-ion implantation and their optical properties studied using microphotoluminescence and reflection techniques. The properties of areas with high crystalline quality are compared with those of disordered regions of samples. The photoluminescencespectrum from Si nanocrystals embedded in silica spheres is narrowed by the inhibition of emission at wavelengths corresponding to the opalphotonic pseudoband gap (∼690 nm). Measurements of photoluminescencespectra from individual implanted silica spheres is also demonstrated and the number of emitting Si nanocrystals in single brightly emitting spheres is estimated to be of the order of one thousand.This work was supported by GACR (202/03/0789), NATO (PST.CLG.978100), and by the Royal Swedish Academy of Sciences. One of the authors ~J.V.! appreciates financial support from the French government (program Echange)

Sub-wavelength patterning of the optical near-field

We report the sub-wavelength patterning of the optical near-field by total internal reflection illumination of a regular array of resonant gold nano-particles. Under appropriate conditions, the in-plane coupling between Localized Surface Plasmon (LSP) fields gives rise to sub-wavelength light spots between the structures. Measurements performed with an Apertureless Scanning Near-Field Optical Microscope (ASNOM) show a good agreement with theoretical predictions based on the Green dyadic method. This concept might offer a convenient way to elaborate extended optical trap landscapes for manipulation of sub-micrometer systems.Peer ReviewedPostprint (published version

A hybrid light source with integrated inorganic light-emitting diode and organic polymer distributed feedback grating

We report a compact light source that incorporates a semiconductor light-emitting diode, nanostructured distributed feedback (DFB) Bragg grating and spin-coated thin conjugated polymer film. With this hybrid structure, we transferred electrically generated 390 nm ultraviolet light to an organic polymer via optical pumping and out-couple green luminescence to air through a second-order DFB grating. We demonstrate the feasibility of electrically driven, hybrid, compact light-emitting devices and lasers in the visible range. © IOP Publishing Ltd

Optical properties of structurally-relaxed Si/SiO2_2 superlattices: the role of bonding at interfaces

We have constructed microscopic, structurally-relaxed atomistic models of Si/SiO$_2$ superlattices. The structural distortion and oxidation-state characteristics of the interface Si atoms are examined in detail. The role played by the interface Si suboxides in raising the band gap and producing dispersionless energy bands is established. The suboxide atoms are shown to generate an abrupt interface layer about 1.60 \AA thick. Bandstructure and optical-absorption calculations at the Fermi Golden rule level are used to demonstrate that increasing confinement leads to (a) direct bandgaps (b) a blue shift in the spectrum, and (c) an enhancement of the absorption intensity in the threshold-energy region. Some aspects of this behaviour appear not only in the symmetry direction associated with the superlattice axis, but also in the orthogonal plane directions. We conclude that, in contrast to Si/Ge, Si/SiO$_2$ superlattices show clear optical enhancement and a shift of the optical spectrum into the region useful for many opto-electronic applications.Comment: 11 pages, 10 figures (submitted to Phys. Rev. B

Revista de Vertebrados de la Estación Biológica de Doñana

Catálogo descriptivo de los anfibios y reptiles de CubaEvolución estacional de la comunidad de aves en un robledal de Sierra NevadaComposición de la comunidad de aves en pinares del Parque Nacional de Doñana (suroeste de España).Alimentación de la pagaza piconegra (Gelochelidon nilotica) en las marismas del GuadalquivirContaminación xenobiótica del Parque Nacional de Doñana. III. Residuos de insecticidas organoclorados, bifenilos policlorados y metales pesados en ciconiformesAlimentación de la lechuza común Tyto alba en la cuenca del Duero, EspañaEstudio de una población rural de (Mus musculus L.) I. La probabilidad de captura y la estima numéricLa reproducción en Gazella dorcasIncidencia del Nemátodo parásito Skrjabingylus Leuckart, 1842 sobre el Mustela en España.Desplazamientos de ungulados silvestres a través de una zona de ecotono en Doñana.Etograma de la cabra montés (Capra pyrenaica) y comparación con otras especies.Sobre comportamiento agresivo de Triturus marmoratus en época de celoEmbarrancamiento masivo de ejemplares de tortuga lad (Dermochelys coriacea L.) en las costas de Ceuta (España, norte de África)Sobre un ejemplar melánico de Podarcis hispanica (Steindachner, 1870)Nuevos datos sobre la distribución de cuatro especies de reptiles en la provincia de Cádiz.Algunos datos sobre la nidificación de Ciconia nigra L. en sierra Morena (S. España)Observación del halcón de Eleonor (Falco eleonorae) en el centro de EspañaNueva localidad de cría del pájaro moscón (Remiz pendulinus) en la Península IbéricaRegistro de aves en el sur de BoliviaNidificación del paiño de Madeira Oceanodroma castro (Harcourt, 1851) en las Islas Canarias.Observación primaveral de Phalaropus fulicarius L. en el SO de EspañaNuevos datos sobre la presencia del nóctulo gigante Nyctalus lasiopterus (Chiroptera, vespertilionidae) en EspañaNote sur l'alimentation de Martes martes a Menorca (Baleares).Peer reviewe