Search results for "defects"
showing 10 items of 339 documents
Extrinsic Effects on the Optical Properties of Surface Color Defects Generated in Hexagonal Boron Nitride Nanosheets
2021
Hexagonal boron nitride (hBN) is a wide-band gap van der Waals material able to host light-emitting centers behaving as single photon sources. Here, we report the generation of color defects in hBN nanosheets dispersed on different kinds of substrates by thermal treatment processes. The optical properties of these defects have been studied using microspectroscopy techniques and far-field simulations of their light emission. Using these techniques, we have found that subsequent ozone treatments of the deposited hBN nanosheets improve the optical emission properties of created defects, as revealed by their zero-phonon linewidth narrowing and reduction of background emission. Microlocalized co…
Neutron-induced defects in optical fibers
2014
We present a study on 0.8 MeV neutron-induced defects up to fluences of 1017 n/cm2 in fluorine doped optical fibers by using electron paramagnetic resonance, optical absorption and confocal micro-luminescence techniques. Our results allow to address the microscopic mechanisms leading to the generation of Silica-related point-defects such as E', H(I), POR and NBOH Centers.
centers induced by γ irradiation in sol–gel synthesized oxygen deficient amorphous silicon dioxide
2007
The effects of room temperature γ-ray irradiation up to a dose of ∼1300 kGy are investigated by Electron paramagnetic resonance (EPR) measurements in amorphous silicon dioxide (a-SiO2) produced by a sol-gel synthesis method that introduces O{triple bond, long}Si{single bond}Si{triple bond, long}O oxygen deficiency. We have found that exposure to radiation generates the Eγ′ center with the same spectral features found in high purity commercial a-SiO2. The maximum concentration of defects induced in this sol-gel material indicates that its resistance to radiation is comparable to that of synthetic fused a-SiO2. The concentration of Eγ′ center increases with irradiation, featuring a sublinear …
Variability of the Si-O-Si angle in amorphous-SiO2 probed by electron paramagnetic resonance and Raman spectroscopy
2009
We report an experimental investigation by electron paramagnetic resonance (EPR) and Raman spectroscopy on a variety of amorphous silicon dioxide materials. Our study by EPR have permitted us to point out that the splitting of the primary hyperfine doublet of the Eγ′ center shows a relevant sample-to-sample variability, changing from ∼41.8 to ∼42.6 mT in the set of materials we considered. The parallel study by Raman spectroscopy has enabled us to state that this variability is attributable to the different Si-O-Si angle characterizing the matrices of the different materials. © 2009 Elsevier B.V. All rights reserved.
Structural modifications induced by electron irradiation in SiO2 glass: Local densification measurements
2009
We report a study on the structural modifications induced in amorphous silicon dioxide (a-SiO2) by electron irradiation in the dose range from 1.2?103 to 5?106?kGy. This study has been performed by investigating the properties of the 29Si hyperfine structure of the E '? center by electron paramagnetic resonance (EPR) spectroscopy. Our data suggest that the structural modifications induced by irradiation take place through the nucleation of confined high-defective and densified regions statistically dispersed into the whole volume of the material. In addition, we have estimated that in the high dose limit (D?105?kGy) the degree of densification associated to the local (within the defective r…
Pulmonary hypertension in pediatrics. a feasible approach to bridge the gap between real world and guidelines
2019
Pulmonary hypertension (PH) is quite infrequent in pediatric age and its most common etiologies include idiopathic pulmonary arterial hypertension, PH related to congenital heart diseases, bronchopulmonary dysplasia (chronic lung disease), persistence of pulmonary hypertension of the newborn, and congenital diaphragmatic hernia. The developed for adult patients PH classification shows limitations when applied to pediatric subjects since the underlying causes are markedly different between the two ages. In 2011, the Pulmonary Vascular Research Institute Panama Task Force outlined the first specific pediatric pulmonary hypertensive vascular disease diagnostic classification, including 10 main…
A novel Usher protein network at the periciliary reloading point between molecular transport machineries in vertebrate photoreceptor cells.
2008
Contains fulltext : 69178.pdf (Publisher’s version ) (Closed access) The human Usher syndrome (USH) is the most frequent cause of combined deaf-blindness. USH is genetically heterogeneous with at least 12 chromosomal loci assigned to three clinical types, USH1-3. Although these USH types exhibit similar phenotypes in human, the corresponding gene products belong to very different protein classes and families. The scaffold protein harmonin (USH1C) was shown to integrate all identified USH1 and USH2 molecules into protein networks. Here, we analyzed a protein network organized in the absence of harmonin by the scaffold proteins SANS (USH1G) and whirlin (USH2D). Immunoelectron microscopic anal…
MPP1 links the Usher protein network and the Crumbs protein complex in the retina.
2007
Contains fulltext : 53571.pdf (Publisher’s version ) (Closed access) The highly ordered distribution of neurons is an essential feature of a functional mammalian retina. Disruptions in the apico-basal polarity complexes at the outer limiting membrane (OLM) of the retina are associated with retinal patterning defects in vertebrates. We have analyzed the binding repertoire of MPP5/Pals1, a key member of the apico-basal Crumbs polarity complex, that has functionally conserved counterparts in zebrafish (nagie oko) and Drosophila (Stardust). We show that MPP5 interacts with its MAGUK family member MPP1/p55 at the OLM. Mechanistically, this interaction involves heterodimerization of both MAGUK mo…
Field-induced tip–sample oxygen transfer in scanning tunneling microscopy on TiO2(110) (1 1).
2008
International audience; A study on the field-induced tip–surface oxygen transfer at room temperature and its influence on the tunneling conditions for stable STM imaging of the TiO2(110) (1 1) surface is reported. A simple model of field-induced transfer is applied to tungsten and platinum–iridium tips. The oxygen transition rates from the sample to the tip or from the tip to the sample depend on the oxygen desorption barriers formed at tunneling distance. For stable imaging the applied bias voltage has to balance the oxygen transfer probabilities in both directions. In the case of Pt/Ir tips, the tunneling conditions for images with clear evidence of bridging oxygen point defects have been…
A computational study of point defects and diffusion in enstatite
2009
In order to contribute to the understanding of diffusion processes in enstatite (Mg2Si2O6), we have used atomistic simulation techniques to study point defects in this mineral. We present results for a variety of Scottky and Frenkel defects of all atomic species present in it. We have furthermore calculated the activation energy for magnesium diffusion. We break diffusion down into a succession of hops between neighboring sites. Each hop is associated with a migration energy barrier. By making a series of hops, the diffusing ion may cross the unit cell. The maximum migration energy necessary to attain movement in a direction is the activation energy for diffusion in that direction. The defe…