Diffusive equilibrium properties of O2 in amorphous SiO2 nanoparticles probed via dependence of concentration on size and pressure

An experimental study on the diffusive equilibrium value of interstitial O2 in silica nanoparticles was carried out on samples with average particles diameter 40, 14, and 7 nm. The investigation was performed by measuring the concentration of interstitial O2 by Raman and photoluminescence techniques. The dependence of diffusive equilibrium concentration on pressure and temperature was investigated in the pressure range from 0.2 to 76 bar and in the temperature range from 98 to 244 °C. The equilibrium concentration of interstitial O2 follows Henry’s law at pressures below 13 bar whereas a departure from this model is observed at higher pressures. In particular, O2 concentration saturates abo…

Direct sunlight facility for testing and research in HCPV

A facility for testing different components for HCPV application has been developed in the framework of "Fotovoltaico ad Alta Efficienza" (FAE) project funded by the Sicilian Regional Authority (PO FESR Sicilia 2007/2013 4.1.1.1). The testing facility is equipped with an heliostat providing a wide solar beam inside the lab, an optical bench for mounting and aligning the HCPV components, electronic equipments to characterize the I-V curves of multijunction cells operated up to 2000 suns, a system to circulate a fluid in the heat sink at controlled temperature and flow-rate, a data logging system with sensors to measure temperatures in several locations and fluid pressures at the inlet and ou…

Visible-ultraviolet vibronic emission of silica nanoparticles

We report the study of the visible-ultraviolet emission properties and the structural features of silica nanoparticles prepared through a laboratory sol-gel technique. Atomic force microscopy, Raman and Infrared investigations highlighted the 10 nm size, purity and porosity of the obtained nanoparticles. By using time resolved photoluminescence techniques in air and in a vacuum we were able to single out two contributions in the visible emission: the first, stable in both atmospheres, is a typical fast blue band centered around 2.8 eV; the second, only observed in a vacuum around the 3.0-3.5 eV range, is a vibrational progression with two phonon modes at 1370 cm(-1) and 360 cm(-1). By fully…

Micro-Raman characterization of graphene grown on SiC(000-1)

Graphene (Gr) was grown on the C face of 4H-SiC under optimized conditions (high annealing temperatures ranging from 1850 to 1950°C in Ar ambient at 900 mbar) in order to achieve few layers of Gr coverage. Several microscopy techniques, including optical microscopy (OM), ?Raman spectroscopy, atomic force microscopy (AFM) and atomic resolution scanning transmission electron microscopy (STEM) have been used to extensively characterize the lateral uniformity of the as-grown layers at different temperatures. ?Raman analysis provided information on the variation of the number of layers, of the stacking-type, doping and strain.

Modification of Ce oxidation state by thermal treatments in controlled atmosphere of Ce-Ti-Eu doped SiO2 glasses

29Si Hyperfine structure of the E’_alfa center in amorphous silicon dioxide

We report a study by electron paramagnetic resonance on the E0 point defect in amorphous silicon dioxide (a-SiO2). Our experiments were performed on -ray irradiated oxygen-deficient materials and pointed out that the 29Si hyperfine structure of the E0 consists of a pair of lines split by 49 mT. On the basis of the experimental results, a microscopic model is proposed for the E0 center, consisting of a hole trapped in an oxygen vacancy with the unpaired electron sp3 orbital pointing away from the vacancy in a back-projected configuration and interacting with an extra oxygen atom of the a-SiO2 matrix.

Resonance Raman of oxygen dangling bonds in amorphous silicon dioxide

We investigate the origin of a resonance Raman band induced by ionizing radiation in amorphous silicon dioxide (silica glass), which can be detected under ultraviolet laser excitation. A silica sample, rich of oxygen-excess related defects, was prepared by treating some length of a pure-silica-core multimode fiber in an O2 atmosphere (at high temperature and pressure) and by irradiating it with X-rays at 10 MGy(SiO2) dose. A micro-Raman study revealed a gaussian band peaking at 896 cm−1 with a full width at half maximum of 32 cm−1, which could be detected by exciting the sample with the 325-nm line of a HeCd laser. This spectral feature is absent in the Raman spectra performed with the 442-…

Effect of thermal annealing on the luminescence of defective ZnO nanoparticles synthesized by pulsed laser ablation in water

This work concerns ZnO nanoparticles (NPs), with sizes of tens of nm, produced by ablation with a pulsed Nd:YAG laser of a Zn plate in H2O. TEM images evidence the formation of nanoparticles with sizes of tens of nm. Moreover, HRTEM images and Raman spectra show that the distance between the crystalline planes and the vibrational modes are consistent with ZnO nanocrystal in wurtzite structure. Their optical properties are characterized by two emission bands both excited above the energy gap (3.4 eV): the first at 3.3 eV is associated with excitons recombination, the second at 2.2 eV is proposed to originate from a singly ionized oxygen vacancy. The green emission is independent of water pH,…

Effects of thermal treatments in controlled atmosphere on the Ce oxidation state in Ce-Ti-Eu doped SiO2 sol-gel glasses

We report an experimental study by optical absorption, photoluminescence and Raman spectroscopies of the modifications induced on Ce–Ti-Eu doped SiO2 glasses by thermal treatments in controlled atmosphere. Samples with Ce content varying up to 5,000 part per million by weight (ppm) and with Ti and Eu content fixed at 40 and 300 ppm respectively, have been investigated. The treatments were done in inert atmosphere of He and in O2 atmosphere at 390 C and 100 bar. Our experiments show that only Ce4? ions are affected by He treatments, whereas both Ce4? and Ce3? ions are affected by O2 treatments. The obtained results are interpreted on the basis of microstructural changes induced by the therma…

Properties and Structural Studies of Multi-Wall Carbon Nanotubes-Phosphate Ester Hybrids

Long chain phosphate esters bearing at least one or two aryl groups have been synthesized and used for the preparation of stable multi-walled carbon nanotube (MWCNT) hybrids. The non-covalent interaction ester/MWCNT has been investigated by several techniques (SEM, UV-vis, 31P-NMR, RAMAN). The used phosphate ester derivatives demonstrated the ability to produce an excellent dispersion of MWCNT in CHCl3. The obtained dispersions showed a great stability from one to at least three weeks in the range of concentration considered. Thermal analysis showed an increase in the decomposition temperature for the hybrids with respect to pristine MWCNT.

Luminescent silicon nanocrystals produced by near-infrared nanosecond pulsed laser ablation in water

Abstract We report the investigation of luminescent nanoparticles produced by ns pulsed Nd:YAG laser ablation of silicon in water. Combined characterization by AFM and IR techniques proves that these nanoparticles have a mean size of ∼3 nm and a core–shell structure consisting of a Si-nanocrystal surrounded by an oxide layer. Time resolved luminescence spectra evidence visible and UV emissions; a band around 1.9 eV originates from Si-nanocrystals, while two bands centered at 2.7 eV and 4.4 eV are associated with oxygen deficient centers in the SiO 2 shell.

Ge-doped silica nanoparticles: production and characterisation

Silica nanoparticles were produced from germanosilicate glasses by KrF laser irradiation. The samples were investigated by cathodoluminescence and scanning electron microscopy, providing the presence of nanoparticles with size from tens up to hundreds of nanometers. The emission of the Germanium lone pair center is preserved in the nanoparticles and atomic force microscopy revealed the presence of no spherical particles with a size smaller than ~4 nm. The absorption coefficient enhancement induced by Ge doping is reputed fundamental to facilitate the nanoparticles production. This procedure can be applied to other co-doped silica materials to tune the nanoparticles features.

Tailoring the Emission Color of Carbon Dots through Nitrogen-Induced Changes of Their Crystalline Structure

Nitrogen content in carbon dots (CDs) plays a crucial role both on the structure and on the optical properties. We synthesized two distinct families of CDs which differ both in structure and in optical emission, demonstrating how nitrogen determines the structure and the optical properties of N-CDs in two main cases: low content and high content of nitrogen. While the low-nitrogen-content family is characterized by blue-emitting nanoparticles with a N-doped hexagonal C-graphite crystalline core structure and a complex surface structure, the high-nitrogen-content family is composed of nanoparticles behaving as dual emitters (blue and green) with a hexagonal β-C3N4crystalline core structure a…

Vibronic structures in the visible luminescence of silica nanoparticles

Time resolved photoluminescence investigation in air and in vacuum atmosphere of the visible luminescence related to silica surface defects is here reported. Two contributions can be singled out: one, observed both in air and in vacuum, is the well-known blue band, peaked around 2.8 eV decaying in ∼5 ns; the other, only observed in vacuum, is a structured emission in the violet range characterized by two vibronic progressions spaced 1370 cm−1 and 360 cm−1 decaying in ∼100 ns. In contrast with previous attribution, the well distinguishable spectroscopic properties together with the observation of the effects induced by the interaction with nitrogen allow to state that the emission bands orig…

Optical properties of Ge-oxygen defect center embedded in silica films

The photo-luminescence features of Ge-oxygen defect centers in a 100nm thick Ge-doped silica film on a pure silica substrate were investigated by looking at the emission spectra and time decay detected under synchrotron radiation excitation in the 10-300 K temperature range. This center exhibits two luminescence bands centered at 4.3eV and 3.2eV associated with its de-excitation from singlet (S1) and triplet (T1) states, respectively, that are linked by an intersystem crossing process. The comparison with results obtained from a bulk Ge-doped silica sample evidences that the efficiency of the intersystem crossing rate depends on the properties of the matrix embedding the Ge-oxygen defect ce…

Structure of amorphous SiO 2 nanoparticles probed through the E′ γ centers

We report an experimental investigation by electron paramagnetic resonance (EPR) spectroscopy on the properties of the E′ γ centers induced by β-ray irradiation in nanoparticles of amorphous SiO 2 (fumed silica) with mean diameters from 7 up to 40 nm. We found that the E′ γ centers are induced in all the fumed silica types in the dose range 4-400 kGy. They are characterized by an EPR line shape similar to that observed in common bulk silica materials independently on the particle diameter. Moreover, the E′ γ center concentration decreases on decreasing of the particle size for each given dose. Our findings are interpreted in terms of a shell-like model of nanoparticles in which it is assume…

Two-Dimensional Carbon: A Review of Synthesis Methods, and Electronic, Optical, and Vibrational Properties of Single-Layer Graphene

Graphite has been widely used by humans for a large part of their history. Nevertheless, it has only recently been possible to isolate its basic unit: carbon atoms arranged in a honeycomb structure on a single plane, namely graphene. Since its discovery, many techniques have been developed and improved to properly synthesize graphene and its derivatives which are part of the novel class of two-dimensional materials. These advanced materials have imposed themselves in nanotechnology thanks to some outstanding physical properties due to their reduced dimensions. In the case of graphene, its reduced dimension gives rise to a high electrical mobility, a large thermal conductivity, a high mechan…

Structural and CO [sub] 2 capture properties of ethylenediamine-modified HKUST-1 metal-organic framework

The high structural and compositional flexibility of metal–organic frameworks (MOFs) shows their great potential for CO2 capture and utilization in accordance with the environmental guidelines of low-carbon technology developments. HKUST-1 as one of the most intensively studied representatives of MOFs for such purposes excels because of its simplicity of production and high ability to tune its intrinsic properties by various functionalization processes. In the present work, ethylenediamine functionalization was performed for the first time in order to thoroughly investigate the amine sorption sites’ impact on the CO2 capture performance of HKUST-1. The placement of ethylenediamine moieties …

Structural properties of core and surface of silica nanoparticles investigated by Raman spectroscopy

We studied the experimental Raman spectra of various commercial silica nanoparticles of average diameter from 7 to 40 nm and specific surface from 50 to 380 m^2/g. We found that the peculiarities of the particles Raman spectra systematically depend on their specific surface. In detail, the peak position of the R band at about 440 cm ^-1 shifts towards high wavenumbers following an almost linear dependence on the specific surface. Similarly, the amplitudes of the D1 and D2 bands, at about 495 and 605 cm ^-1, respectively, increase linearly with the same quantity. Our results are interpreted in the frame of the shell model for the nanoparticles clarifying that the network of the core of the n…

Delocalized Nature of theEδ′Center in Amorphous Silicon Dioxide

We report an experimental study by electron paramagnetic resonance (EPR) of E(')(delta) point defect induced by gamma-ray irradiation in amorphous SiO2. We obtained an estimation of the intensity of the 10 mT doublet characterizing the EPR spectrum of such a defect arising from hyperfine interaction of the unpaired electron with a 29Si (I=1/2) nucleus. Moreover, determining the intensity ratio between this hyperfine doublet and the main resonance line of E(')(delta) center, we pointed out that the unpaired electron wave function of this center is actually delocalized over four nearly equivalent silicon atoms.

Structural modifications induced by electron irradiation in SiO2 glass: Local densification measurements

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…

Facile and novel synthesis of Graphene oxide/Silica nanohybrids with tunable properties

Experimental evidence for two different precursors of Eγ′ centers in silica

Abstract Electron paramagnetic resonance measurements of concentration and line shape of E γ ′ centers induced by γ ray irradiation are presented for natural and synthetic commercial silica with different OH contents. Synthetic materials with OH content >200 ppm by weight show one line shape for all investigated doses. In contrast, the other materials show a different line shape at low irradiation doses. Differences are also observed in the concentration growth of the E γ ′ centers in synthetic wet materials and in the other materials. The results are interpreted as evidence of two E γ ′ centers distinguishable by their line shape and having different precursors.

γ-ray-induced bleaching in silica: Conversion from optical to paramagnetic defects

We report experimental results on optical and ESR measurements performed in $\ensuremath{\gamma}$-irradiated natural silica samples having different content of OH groups. A partial bleaching of the optical absorption band ${B}_{2\ensuremath{\beta}}$ at 5.15 eV and the related photoluminescence emissions at 3.1 eV and 4.2 eV is observed together with the growth of an ESR doublet split by 11.8 mT. The kinetics of the two processes as a function of the $\ensuremath{\gamma}$ dose are correlated and depend on the OH content. Our experiments indicate the occurrence of a $\ensuremath{\gamma}$-ray-induced conversion, from optically active centers to paramagnetic ones and vice versa, changing the re…

X-ray irradiation effects on fluorine-doped germanosilicate optical fibers

International audience; We report an experimental investigation on the effects of fluorine codoping on the radiation response of Ge-doped Optical Fibers (OFs) obtained by three different drawing conditions. The OFs were irradiated with 10 keV X-rays up to 300 Mrad and studied by online Radiation-Induced-Attenuation (RIA) measurements. Confocal Micro- Luminescence (CML) and Electron Paramagnetic Resonance (EPR) were also employed to investigate the permanent radiation-induced-defects. The variation of the Germanium-Lone-Pair-Center (GLPC) and Non-Bridging- Oxygen-Hole-Centers (NBOHC) concentration with the radiation dose is investigated by CML, whereas the ones of the induced Ge(1), Ge(2) an…

Modifications of optical absorption band of E'gamma center in silica

We report a study by electron paramagnetic resonance on the E0 point defect in amorphous silicon dioxide (a-SiO2). Our experiments were performed on -ray irradiated oxygen-deficient materials and pointed out that the 29Si hyperfine structure of the E0 consists of a pair of lines split by 49 mT. On the basis of the experimental results, a microscopic model is proposed for the E0 center, consisting of a hole trapped in an oxygen vacancy with the unpaired electron sp3 orbital pointing away from the vacancy in a back-projected configuration and interacting with an extra oxygen atom of the a-SiO2 matrix.

Substrate and atmosphere influence on oxygen p-doped graphene

Abstract The mechanisms responsible for p-type doping of substrate supported monolayer graphene (Gr) by thermal treatments in oxygen ambient have been investigated by micro-Raman spectroscopy, atomic force microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS), considering commonly employed dielectric substrates, such as SiO 2 and Al 2 O 3 thin films grown on Si. While a high p-type doping (∼10 13  cm −2 ) is observed for Gr on SiO 2 , no significant doping is found for Gr samples on the Al 2 O 3 substrate, suggesting a key role of the Gr/SiO 2 interface states in the trapping of oxygen responsible for the Gr p-type doping. Furthermore, we investigated the doping stability of Gr on SiO…

Nanoscale inhomogeneity of the Schottky barrier and resistivity inMoS2multilayers

Conductive atomic force microscopy (CAFM) is employed to investigate the current injection from a nanometric contact (a Pt coated tip) to the surface of ${\text{MoS}}_{2}$ thin films. The analysis of local current-voltage characteristics on a large array of tip positions provides high spatial resolution information on the lateral homogeneity of the $\mathrm{tip}/{\text{MoS}}_{2}$ Schottky barrier ${\mathrm{\ensuremath{\Phi}}}_{B}$ and ideality factor $n$, and on the local resistivity ${\ensuremath{\rho}}_{\text{loc}}$ of the ${\text{MoS}}_{2}$ region under the tip. Here, ${\mathrm{\ensuremath{\Phi}}}_{B}=300\ifmmode\pm\else\textpm\fi{}24\phantom{\rule{0.28em}{0ex}}\text{meV}, n=1.60\ifmmode…

Raman and IR investigation of silica nanoparticles structure

Abstract In the present investigation we report experimental data regarding the Raman and Infra-Red (IR) absorption activities of commercial silica nanoparticles. We compared the data of the nanoparticles with the ones acquired in the same experimental conditions for commercial bulk silica. By this comparison we highlighted that the variability of the spectral features of the matrix related Raman and IR bands in the nanoparticles is above the one observed for the bulk systems before any treatments. Furthermore, by studying nanoparticles with different sizes (diameters from 40 to 7 nm) and applying the shell-model we can suggest that the core network of the nanoparticles is close to the one …

Characterization ofE′δand triplet point defects in oxygen-deficient amorphous silicon dioxide

We report an experimental study by electron paramagnetic resonance (EPR) of $\ensuremath{\gamma}$-ray irradiation induced point defects in oxygen deficient amorphous $\mathrm{Si}{\mathrm{O}}_{2}$ materials. We have found that three intrinsic ($\mathrm{E}^{\ensuremath{'}}{}_{\ensuremath{\gamma}}$, $\mathrm{E}^{\ensuremath{'}}{}_{\ensuremath{\delta}}$, and triplet) and one extrinsic $({[\mathrm{Al}{\mathrm{O}}_{4}]}^{0})$ paramagnetic centers are induced. All the paramagnetic defects but $\mathrm{E}^{\ensuremath{'}}{}_{\ensuremath{\gamma}}$ center are found to reach a concentration limit value for doses above ${10}^{3}\phantom{\rule{0.3em}{0ex}}\mathrm{kGy}$, suggesting a generation process f…

Annealing of radiation induced oxygen deficient point defects in amorphous silicon dioxide: evidence for a distribution of the reaction activation energies

The selective annealing of point defects with different activation energies is studied, by performing sequences of thermal treatments on gamma irradiated silica samples in the temperature range 300-450 °C. Our experiments show that the dependence on time of the concentration of two irradiation induced point defects in silica, named ODC(II) (standing for oxygen deficient centre II) and the E(γ)(') centre, at a given temperature depends on the thermal history of the sample for both of the centres studied; moreover in the long time limit this concentration reaches an asymptotic value that depends on the treatment temperature alone. These results suggest the existence of a distribution of the a…

INTRINSIC PARAMAGNETIC CENTERS INDUCED IN GAMMA RAY IRRADIATED OXYGEN-DEFICIENT SILICA

Plasma Functionalization of Multiwalled Carbon Nanotubes and Their Use in the Preparation of Nylon 6-Based Nanohybrids

The possibility to obtain carbon nanotubes (CNT)/polyamide 6 composites with excellent mechanical properties in a simple, industrially scalable way is investigated. Commercial CNTs are treated by plasma while changing some key parameters (exposure time, plasma power, type of gas) in order to optimize the process and to achieve a sufficient degree of functionalization. The treated samples are characterized by Fourier transform infrared spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The most interesting samples are selected to be used as reinforcing fillers, in different concentrations, in a polyamide 6 matrix. The mechanical tests show a dramatic increase of both tens…

Amorphous hydrogenated carbon (a-C:H) depositions on polyoxymethylene: Substrate influence on the characteristics of the developing coatings

Abstract After oxygen plasma treatment polyoxymethylene (POM) material was exposed to acetylene plasma to progressively deposit two different types of amorphous hydrogenated carbon (a-C:H) films. Radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) was used to generate both plasma processes. The surface morphology of the coated samples has been investigated by atomic force microscopy (AFM) and their chemical composition by Diffusive Reflectance Infrared Fourier Transform (DRIFT) and Raman spectroscopy. Results revealed the absence of a solid interlayer formation between the a-C:H films and POM. The in sequence exposure of oxygen and acetylene plasma on POM substrate prevents…

Electron paramagnetic resonance investigation on the hyperfine structure of the E’_delta center in amorphous silicon dioxide

Synthesis of multi-color luminescent ZnO nanoparticles by ultra-short pulsed laser ablation

Abstract Crystalline ZnO nanoparticles (NPs) are synthesized by ultra-short femtosecond (fs) pulsed laser ablation (PLA) of a zinc plate in deionized water, and are investigated by optical absorption and time resolved luminescence spectra in combination with the morphology and structure analysis. The comparison with previous experiments based on short nanosecond (ns) PLA highlights that pulse duration is a crucial parameter to determine the size and the optical properties of ZnO NPs. While short PLA generates NPs with average size S ‾ of ~ 30 nm, ultrashort PLA allows to achieve much smaller NPs, S ‾ ⩽ 10  nm, that evidence weak quantum confinement effects on both the absorption edge and th…

Oxidation of silicon nanoparticles produced by ns laser ablation in liquids

The investigation of nanoparticles produced by ns pulsed Nd:YAG laser ablation of silicon in liquids is reported. Combined characterization by morphological and structural techniques shows that these nanoparticles have a mean diameter of ~3 nm and a core-shell structure consisting of a Si-nanocrystal surrounded by a layer of oxidized Si. Time resolved luminescence spectra evidence visible and UV emissions: a broad band around 1.9 eV originates from Si-nanocrystals, while two bands centered at 2.7 eV and 4.4 eV are associated with oxygen deficient centers in the SiO2 shell.

Nanoscale structural and electrical properties of graphene grown on AlGaN by catalyst-free chemical vapor deposition

The integration of graphene (Gr) with nitride semiconductors is highly interesting for applications in high-power/high-frequency electronics and optoelectronics. In this work, we demonstrated the direct growth of Gr on Al0.5Ga0.5N/sapphire templates by propane (C3H8) chemical vapor deposition (CVD) at temperature of 1350{\deg}C. After optimization of the C3H8 flow rate, a uniform and conformal Gr coverage was achieved, which proved beneficial to prevent degradation of AlGaN morphology. X-ray photoemission spectroscopy (XPS) revealed Ga loss and partial oxidation of Al in the near-surface AlGaN region. Such chemical modification of a 2 nm thick AlGaN surface region was confirmed by cross-sec…

Evidence of different red emissions in irradiated germanosilicate materials

International audience; This experimental investigation is focused on a radiation induced red emission in Ge doped silica materials, elaborated with different methods and processes. The differently irradiated samples as well as the pristine ones were analyzed with various spectroscopic techniques, such as confocal microscopy luminescence (CML), time resolved luminescence (TRL), photoluminescence excitation (PLE) and electron paramagnetic resonance (EPR). Our data prove that irradiation induces a red luminescence related to the presence of the Ge atoms. Such emission features a photoexcitation spectrum in the UV-blue spectral range and, TRL measurements show that its decrease differs from a …

Effects of Pressure, Temperature, and Particles Size on O2 Diffusion Dynamics in Silica Nanoparticles

The O2 diffusion process in silica nanoparticles is experimentally studied in samples of average radius of primary particles ranging from 3.5 to 20 nm and specific surface ranging from 50 to 380 (m2/g). The investigation is done in the temperature range from 98 to 177 °C at O2 pressure ranging from 0.2 to 66 bar by measuring the interstitial O2 concentration by Raman and photoluminescence techniques. The kinetics of diffusion can be described by the Fick’s equation with an effective diffusion coefficient depending on the temperature, O2 pressure, and particles size. In particular, the dependence of the diffusion coefficient on the pressure and nanoparticles size is more pronounced at lower …

Evolution of Photo-induced defects in Ge-doped fiber/preform: influence of the drawing

International audience; We have studied the generation mechanisms of two different radiation-induced point defects, the Ge(1) and Ge(2) centers, in a germanosilicate fiber and in its original preform. The samples have been investigated before and after X-ray irradiation using the confocal microscopy luminescence and the electron paramagnetic resonance techniques. Our experimental results show the higher radiation sensitivity of the fiber as compared to the perform and suggest a relation between Ge(1) and Ge(2) generation. To explain our data we have used different models, finding that the destruction probability of the Ge(1) and Ge(2) defects is larger in fiber than in preform, whereas the …

Interstitial O2 distribution in amorphous SiO2 nanoparticles determined by Raman an Photoluminescence spectroscopy

The O2 content and emission properties in silica nanoparticles after thermal treatments in oxygen rich atmosphere have been investigated by Raman and photoluminescence measurements. The nanoparticles have different sizes with average diameter ranging from 7 up to 40 nm. It is found that O2 concentration in nanoparticles monotonically increases with nanoparticles size. This finding is independent on the measurement technique and evidences that oxygen molecules are not present in all the nanoparticles volume. This dependence is interpreted on the basis of a structural model for nanoparticles consisting of a core region able to host the oxygen molecules and a surface shell of fixed size and fr…

<title>Study of color centers in optical fibers to be used for ITER plasma diagnostics</title>

ABSTRACT The paper presents a comparative study, by off-line measurements of the irradiation induced optical attenuation in several large diameter (600 µm) optical fibers subjected to gamma-rays and neutron irradiation. The optical fiber samples fall into two categories: optical fibers with an enhanced UV transmission (high OH content core) and solarization resistant optical fibers. The irradiation conditions were as follows: a) gamma irradiation at a 60 Co source, with a dose rate of 0.33 kGy/h +/- 5%, up to the maximum total irradiation dose of 313 kGy; b) neutron irradiation (mean energy 5.2 MeV) using a deuteron beam (13 MeV) and a thick beryllium target, for a total fluence of 6x10 12 …

Experimental evidence of E’_gamma centers generation from oxygen vacancies in a-SiO2

Abstract We report on the thermal treatment effects in a γ-ray irradiated oxygen deficient amorphous silicon dioxide (a-SiO2) containing Al impurities. We observed that by thermal treatments the intensity of the 7.6 eV optical absorption band, associated to an oxygen deficient center, and the EPR signal amplitude of irradiation induced [AlO4]0 centers gradually decrease. During these thermal treatments, the E γ ′ centers concentration is found to increase in a correlated way to the decrease of the 7.6 eV absorption amplitude. These results are interpreted assuming an hole-transfer process from the [AlO4]0 centers to the diamagnetic oxygen vacancies, resulting in the generation of E γ ′ cent…

Electron paramagnetic resonance line shape investigation of the 29Si hyperfine doublet of the E’_gamma center in a-SiO2

Temperature dependence of decay process of luminescence activity in Sn-doped silica.

Bright blue emission of synthesized silica nanoparticles conferred by surface defects

Controlled solution-based fabrication of perovskite thin films directly on conductive substrate

Abstract Organometallic perovskites are one of the most investigated materials for high-efficiency thin-film devices to convert solar energy and supply energy. In particular, methylammonium lead iodide has been used to realize thin-film perovskite solar cells, achieving an efficiency higher than 20%. Different fabrication procedures based on the spin-coating technique have been proposed, which do not ensure homogenous morphologies. In this work, we present a scalable process to fabricate methylammonium lead iodide thin films directly on conductive substrates, consisting of electrodeposition and two subsequent chemical conversions. A thorough investigation of the morphological, structural an…

In-situ monitoring by Raman spectroscopy of the thermal doping of graphene and MoS2 in O-2-controlled atmosphere

The effects of temperature and atmosphere (air and O2) on the doping of monolayers of graphene (Gr) on SiO2 and Si substrates, and on the doping of MoS2 multilayer flakes transferred on the same substrates have been investigated. The investigations were carried out by in situ micro-Raman spectroscopy during thermal treatments up to 430 °C, and by atomic force microscopy (AFM). The spectral positions of the G and 2D Raman bands of Gr undergo only minor changes during treatment, while their amplitude and full width at half maximum (FWHM) vary as a function of the temperature and the used atmosphere. The thermal treatments in oxygen atmosphere show, in addition to a thermal effect, an effect a…

Luminescence properties of III-V multi-junctions solar cells

The recent achievement of multi-junctions solar cells, based on III-V semiconductors, exceeding 43% efficiency, has stimulated a rapid growth of concentration photovoltaic (CPV) technology. The large efficiency of these cells is based on the matching between the semiconductors band gap and the solar spectrum and the capability of working under concentrated illumination, up to ~1000 suns. The research pays, therefore, attention to investigate in detail the mechanisms that affect the conversion efficiency, such as the non radiative losses that increase the cell temperature thus favoring the electron-hole (e-h) recombination. With the aim to clarify the performances of these III-V cells, here …

Near infrared radio-luminescence of O2 loaded radiation hardened silica optical fibers: A candidate dosimeter for harsh environments

We report on an experimental investigation of the infrared Radio-Luminescence (iRL) emission of interstitial O2 molecules loaded in radiation hardened pure-silica-core and fluorine-doped silica-based optical fibers (OFs). The O2 loading treatment successfully dissolved high concentrations of oxygen molecules into the silica matrix. A sharp luminescence at 1272 nm was detected when 2.5 cm of the treated OFs were irradiated with 10 keV X-rays. This emission originates from the radiative decay of the first excited singlet state of the embedded O2 molecules. The dose, dose-rate, and temperature dependencies of the infrared emission are studied through in situ optical measurements. The results s…

Optical and morphological properties of infrared emitting functionalized silica nanoparticles

Abstract The loading process of functionalized silica nanoparticles was investigated in order to obtain nanoparticles having functional groups on their surface and Near-Infrared (NIR) emission properties. The NIR emission induced by O 2 loading was studied in silica nanoparticles, produced by pyrogenic and microemulsion methods, with size ranging from 20 to 120 nm. Loading was carried out by thermal treatments in O 2 atmosphere up to 400 °C and 90 bar. The effects of the thermal treatments on the NIR emission and on the structural properties were studied by luminescence and Raman techniques, whereas the morphological features were investigated by Transmission Electron Microscopy and Atomic …

Fluorescent Carbon Nanodots as Sensors of Toxic Metal Ions and Pesticides

Carbon nanodots (CDs) are a new class of fluorescent carbon-based nanomaterials characterized by a plethora of morphologies and sizes. Among these, we can include two different types of CDs, namely, graphitic and diamond-like. This wide range of structures opens up the possibility to design different CDs, with tunable optical properties accordingly to the synthesis method and precursors used. We prepared two different CDs following a bottom-up approach by thermally induced decomposition of organic precursors (namely, citric acid and urea in different molar ratios), and using purification by Size Exclusion Chromatography (SEC). Obtained CDs were characterized by Raman, absorption and fluores…

Intrinsic defects induced by β-irradiation in silica

We report an electron paramagnetic resonance study of defects induced by β-irradiation in natural and synthetic samples of high purity commercial silica. Data are collected for the E′ centers and a resonance satellite signal split by 1.36 mT. By comparison with the effects of γ-irradiation it is shown that the mechanisms of defect generation are the same for the two irradiation sources and that in the high-dose limit they involve intrinsic defects of the glassy matrix. Moreover, the high concentration of defects generated by β-irradiation modifies the EPR spectrum due to spin–spin interaction.

O2 Diffusion in Amorphous SiO2 Nanoparticles Probed by Outgassing

An experimental study of the O2 diffusion process in nanoparticles of amorphous SiO2 in the temperature range from 98 to 157 °C was carried out by Raman and photoluminescence techniques. We studied O2 diffusion in high purity silica nanoparticles with a mean diameter of 14, 20, and 40 nm detecting the outgassing of molecules trapped during the manufacturing. The kinetics of diffusion is well described for all the investigated nanoparticles by the Fick’s equation proving its applicability to nanoscale systems. The diffusion coefficient features an Arrhenius law temperature dependence in the explored temperature range, and the diffusion coefficient values are in good agreement with extrapolat…

Transient nutations decay: The effect of field-modified dipolar interaction

The anomalous behavior of transient nutations is experimentally investigated in a set of two-level $(S=\frac{1}{2})$ spin systems differing only in spin concentration. Our results show that the non-Bloch power dependence of the decay rate of transient nutations is a concentration-dependent effect, which is more and more pronounced in more and more concentrated samples. The experimental results are interpreted in the framework of the recent theory by Shakhmuratov et al. [Phys. Rev. Lett. 79, 2963 (1997)] and support the hypothesis that the anomalous decay of transient nutations in solids originates from radiation-induced changes of the dipolar field, rather than from residual fluctuations of…

Facile synthesis of a monolith of silicon nanocrystal embedded in silica

Thermally Induced Structural Modification of Silica Nanoparticles Investigated by Raman and Infrared Absorption Spectroscopies

We report an experimental investigation by Raman and infrared (IR) absorption spectroscopies on the structural modifications induced by isochronal thermal treatments on amorphous SiO2 nanoparticles (fumed silica). In particular, three different commercial types of this material, characterized by particle mean diameters of 7, 14, and 40 nm, were subjected to thermal treatments from 100 up to 1000 °C. We found that some properties of fumed silica, such as the SiOSi mean bond angle, ring size distribution, and surface adsorbed water content, are drastically different from those of common bulk silica materials and intimately related to the particles' dimension. The SiOSi mean bond angle, probed…

Gamma ray induced 11.8 mT ESR doublet in natural silica

Abstract We report electron spin resonance (ESR) measurements in natural and synthetic vitreous SiO2 samples irradiated by γ rays. An 11.8 mT doublet, asymmetrically centered on the resonance line of the E′ center, was detected only in natural samples. The intensity of this doublet as a function of γ exposure tends to saturate for doses as low as 0.2 Mrad and is not related to the growth kinetics of the E′ centers. Photoluminescence (PL) measurements on the same samples have shown that two emissions at 3.15 and 4.26 eV bleach with the same kinetics as does the 11.8 mT doublet on increasing the γ ray dose. We tentatively suggest the presence of a conversion mechanism, activated by γ irradiat…

Electrical-optical characterization of multijunction solar cells under 2000X concentration

In the framework of the FAE "Fotovoltaico ad Alta Efficienza" ("High Efficiency Photovoltaic") Research Project (PO FESR Sicilia 2007/2013 4.1.1.1), we have performed electrical and optical characterizations of commercial InGaP/InGaAs/Ge triple-junction solar cells (1 cm2) mounted on a prototype HCPV module, installed in Palermo (Italy). This system uses a reflective optics based on rectangular off-axis parabolic mirror with aperture 45×45 cm2 leading to a geometrical concentration ratio of 2025. In this study, we report the I-V curve measured under incident power of about 700 W/m2 resulting in an electrical power at maximum point (PMP) of 41.4 W. We also investigated the optical properties…

Structural properties of core and surface of silica nanoparticles investigated by Raman spectroscopy

We studied the experimental Raman spectra of various commercial silica nanoparticles of average diameter from 7 to 40 nm and specific surface from 50 to 380 m2/g. We found that the peculiarities of the particles Raman spectra systematically depend on their specific surface. In detail, the peak position of the R band at about 440 cm−1 shifts towards high wavenumbers following an almost linear dependence on the specific surface. Similarly, the amplitudes of the D1 and D2 bands, at about 495 and 605 cm−1, respectively, increase linearly with the same quantity. Our results are interpreted in the frame of the shell model for the nanoparticles clarifying that the network of the core of the nanopa…

In situ observation of UV absorption spectra induced in silica by beta irradiation

Near infrared emitting silica nanoparticles: O2 diffusion properties and excited state relaxation

A rapid and eco-friendly route to synthesize graphene-doped silica nanohybrids

International audience; In the present study, the possibility to synthesize graphene oxide (GO)-based nanohybrids with pure and O2-doped silica nanoparticles by a rapid and easy hydrothermal process has been explored. The nanohybrids were prepared by varying the type of silica nanoparticles (average diameter 7 nm or 40 nm) and the silica/GO weight ratio. All the materials were fully characterized by spectroscopic and morphological techniques.The experimental results revealed that it is possible to tune the characteristics of the obtained nanohybrids, such as morphology and amount of ester/ether linkages upon varying the preparation parameters, together with the nanosilica's typology and the…

Optical properties of GeODC embedded in Ge-doped films on a-SiO2 substrate

Investigation on the ganaration process of HO2• radicals by γ-ray irradiation in O2-loaded fumed silica

Abstract We report an experimental investigation on the effects of γ-ray irradiation in three types of fumed silica previously loaded with O 2 molecules. Our data indicate that the main effect of irradiation in these systems is to generate a very large concentration of HO 2 interstitial radicals (about 10 18  molecules/cm 3 ). Furthermore, the number of generated HO 2 was found to be larger in the samples with higher O 2 contents before irradiation. This correlation suggests that HO 2 radicals are induced by reaction of interstitial O 2 molecules with radiolytic H atoms, as previously suggested for O 2 -loaded bulk amorphous silicon dioxide (a-SiO 2 or silica) samples. However, at variance …

Investigation by raman spectroscopy of the decomposition process of HKUST-1 upon exposure to air

We report an experimental investigation by Raman spectroscopy of the decomposition process of Metal-Organic Framework (MOF) HKUST-1 upon exposure to air moisture (T=300 K, 70% relative humidity). The data collected here are compared with the indications obtained from a model of the process of decomposition of this material proposed in literature. In agreement with that model, the reported Raman measurements indicate that for exposure times longer than 20 days relevant irreversible processes take place, which are related to the occurrence of the hydrolysis of Cu-O bonds. These processes induce small but detectable variations of the peak positions and intensities of the main Raman bands of th…

Optical absorption and electron paramagnetic resonance of the E’_alfa center in amorphous silicon dioxide

We report a combined study by optical absorption OA and electron paramagnetic resonance EPR spectroscopy on the E point defect in amorphous silicon dioxide a-SiO2. This defect has been studied in -ray irradiated and thermally treated oxygen-deficient a-SiO2 materials. Our results have pointed out that the E center is responsible for an OA Gaussian band peaked at 5.8 eV and having a full width at half maximum of 0.6 eV. The estimated oscillator strength of the related electronic transition is 0.14. Furthermore, we have found that this OA band is quite similar to that of the E center induced in the same materials, indicating that the related electronic transitions involve states highly locali…

Si29Hyperfine Structure of theE′αCenter in Amorphous Silicon Dioxide

We report a study by electron paramagnetic resonance on the $E^{\ensuremath{'}}{}_{\ensuremath{\alpha}}$ point defect in amorphous silicon dioxide ($a\mathrm{\text{\ensuremath{-}}}{\mathrm{SiO}}_{2}$). Our experiments were performed on $\ensuremath{\gamma}$-ray irradiated oxygen-deficient materials and pointed out that the $^{29}\mathrm{Si}$ hyperfine structure of the $E^{\ensuremath{'}}{}_{\ensuremath{\alpha}}$ consists of a pair of lines split by $\ensuremath{\sim}49\text{ }\text{ }\mathrm{mT}$. On the basis of the experimental results, a microscopic model is proposed for the $E^{\ensuremath{'}}{}_{\ensuremath{\alpha}}$ center, consisting of a hole trapped in an oxygen vacancy with the un…

Atomic force microscopy and Raman investigation on the sintering process of amorphous SiO2 nanoparticles

We report an experimental investigation on the sintering process induced in fumed silica powders by isochronal thermal treatments at T=1270 K. Three types of fumed silica are considered, consisting of amorphous SiO2 (a-SiO2) particles with mean diameters 7, 14, and 40 nm. The study is performed by atomic force microscopy (AFM), to follow the morphological changes, and by Raman scattering, to obtain information on the concomitant structural modifications. The former method indicates that the sintering process proceeds by aggregation of single particles into larger grains, whose sizes increase with the thermal treatment duration. Furthermore, for each fumed silica type considered, the quantit…

Optical absorption band at 5.8 eV associated with the E’_gamma centers in amorphous silicon dioxide: Optical absorption and EPR measurements

Line shape modifications induced by thermal treatment in the optical absorption and electron paramagnetic resonance EPR signals associated with the E center are experimentally investigated in various types of -irradiated amorphous silicon dioxide a-SiO2. The g values of the EPR main resonance line of the E center show a shift correlated with the peak energy variation of the absorption band at about 5.8 eV associated with this defect. These spectroscopic changes are proposed to originate from structural modifications of the defect environment. The correlation is theoretically explained considering that the spin-orbit interaction couples the g-tensor’s elements and the electronic energy level…

NANO-EMETTITORI NIR A BASE DI SILICE PER APPLICAZIONI IN-VIVO E RELATIVO PROCESSO DI PRODUZIONE

Realizzazione di nano-sonde paramagnetiche e fosforescenti, ottenibili a partire da particelle nanometriche di silice mediante procedure di sintesi e arricchimento di O2 a seguito di opportuni trattamenti termici in ambiente controllato. Le nano-sonde così ottenute presentano emissioni nel vicino infrarosso (NIR), sono eccitabili nel visibile e nel NIR, e sono caratterizzate da un tempo di vita nell’ordine del secondo. Tali nano-sonde presentano un notevole potenziale scientifico e commerciale nel mercato della spettroscopia confocale per bio-imaging e nel mercato delle applicazioni medico-farmaceutiche di drug-labelling e drug-delivery.

Silica Nanoparticles for Near-Infrared Imaging and Photonics Applications

Temperature dependence of O2 singlet photoluminescence in silica nanoparticles

Abstract The near infrared singlet emission and photoluminescence lifetime of O 2 molecules embedded in silica nanoparticles are studied from room temperature down to 10 K. The area of the photoluminescence band under infrared excitation decreases for temperature above 100 K and the lifetime is shortened. These observations provide evidence of a thermally activated relaxation channel with activation energy of about 40 meV. This relaxation mechanism adds to the already known temperature independent electronic-to-vibrational coupling involving high energy vibrational modes of the host matrix or its impurities. The thermally activated process is suggested to consist in the breakage of the O 2 …

O2-Loading Treatment of Ge-Doped Silica Fibers: A Radiation Hardening Process

International audience; The effects of a high-pressure O2-loading treatment on the radiation response of Ge-doped optical fibers (OFs) were investigated. We found that the incorporation of high concentration of interstitial molecular oxygen remarkably enhances the resistance to ionizing radiation of Ge-doped OFs in the UV-Visible domain and, at the same time, improves the transmission of UV light in the unirradiated OF sample. By comparison with previously reported results, the O2-loading treatment turned out to increase the radiation resistance of Ge-doped OFs more efficiently than F or Ce codoping. The understanding of such amelioration relies in basic radiation-induced mechanisms that we…

Generation of oxygen deficient point defects in silica by γ and β irradiation

We report an experimental study of the effects of y and β irradiation on the generation of a point defect known as ODC(II) in various types of commercial silica (a-SiO 2 ). The ODC(II) has been detected by means of photoluminescence (PL) spectroscopy measuring the PL band centered at 4.4 eV and excited at 5.0 eV associated to this defect. Our experiments show that ODC(II) are induced in all the investigated materials after irradiation at doses higher than 5 x 10 2 kGy. A good agreement is observed between the efficiencies of generation of ODC(II) under y and β irradiation, enabling a comprehensive study up to the dose of 5 x 10 6 kGy. Two different growth rates, one in the low and one in th…

Oxidation of silicon nanoparticles produced by nanosecond laser ablation in liquids

We investigated nanoparticles produced by laser ablation of silicon in water by the fundamental harmonic (1064 nm) of a ns pulsed Nd:YAG. The silicon oxidation is evidenced by IR absorption features characteristic of amorphous SiO2 (silica). This oxide is highly defective and manifests a luminescence activity under UV excitation: two emission bands at 2.7 eV and 4.4 eV are associated with the twofold coordinated silicon, =SiO••.

Photoluminescence in gamma-irradiated alpha-quartz investigated by synchrotron radiation

Abstract We report an experimental investigation of the photoluminescence, under excitation by synchrotron radiation within the absorption band at 7.6 eV , induced in γ-irradiated α-quartz. Two emissions centered at 4.9 and 2.7 eV are observed at low temperature: the former decreases above 40 K , whereas the second band exhibits an initial slight increase and its quenching is effective above 100 K . Furthermore, the decay kinetics of both emissions occur in a time scale of nanoseconds: at T=17.5 K we measured a lifetime τ∼1.0 ns for the photoluminescence at 4.9 eV and τ∼3.6 ns for that at 2.7 eV . These results give new insight on the optical properties associated with defects peculiar of c…

IMPROVED STABILITY OF GRAPHENE OXIDE-SILICA NANOHYBRIDS AND RELATED POLYMER-BASED NANOCOMPOSITES

Although its promising properties make the graphene oxide (GO) very interesting as filler for polymer matrices, some problems related to its thermal stability in the region which ranges from 80 to 200 °C, are crucial for the possibility to melt process GO together with practically all the polymers [1,2]. Moreover, above 100 °C GO lamellae were found to become stacked. In this work, two different ways to preserve the GO structure and ensure its dispersion within different polymer matrices have been investigated and schematized in Fig. 1. Exfoliation plays a key-role in the achievement of good mechanical properties since it preserves the GO from both stacking phenomena. The capability of sili…

β-ray irradiation effects on silica nanoparticles

By electron paramagnetic resonance (EPR) measurements, we examine the amplitude of the signal typically due to a combination of NBOHC (Non Bridging Hole Center) and POR (Peroxy Radical) defects induced by β-ray irradiation (from 1.2 to 1200 MGy) in silica nanoparticles with diameter ranging from 7 to 20 nm. Our data indicate that the signal line-shapes recorded at different doses is quite independent from the particles sizes and from the dose. Furthermore, for each considered nanoparticles size, the concentration of defects is also almost constant with respect to dose, and it does not change significantly if measured after 2 or 9 months from the irradiation. By contrast, we observed that th…

EPR on Radiation-Induced Defects in SiO2

Continuous-wave electron paramagnetic resonance (EPR) spectroscopy has been the technique of choice for the studies of radiation-induced defects in silica (SiO2) for 60 years, and has recently been expanded to include more sophisticated techniques such as high-frequency EPR, pulse electron nuclear double resonance (ENDOR), and pulse electron spin echo envelope modulation (ESEEM) spectroscopy. Structural models of radiation-induced defects obtained from single-crystal EPR analyses of crystalline SiO2 (alfa-quartz) are often applicable to their respective analogues in amorphous silica (a-SiO2), although significant differences are common.

Efficiency of concentration photovoltaic cells governed by luminescence processes

The development of multi-junctions III-V semiconductors solar cells, that combine high conversion efficiency (over 40%) and capability of working under high illumination intensity (up to 1000 suns), has stimulated a rapid growth of concentrating photovoltaic (CPV) technology. The performance of these cells is based on the matching between the semiconductors band gap and the solar spectrum so as to optimize the current balancing between the subcells. This requirement is also important in connection with the CPV modules using lenses, mirrors, optical coupling compounds that introduce a wavelength dependent response to the sunlight. Therefore, care must be exercised in designing optimum cells …

Nitrogen-doped carbon dots embedded in a SiO2 monolith for solid-state fluorescent detection of Cu2+ ions

We describe the simple fabrication of SiO2 sol-gel monoliths embedding highly luminescent carbon nanodots (CDs) sensitive to metal ions. The pristine CDs we synthesize display an intense dual emission consisting in two fluorescence bands in the green and violet region, and we demonstrate that this photoluminescence is substantially unchanged when the dots are incorporated in the SiO2 matrix. The emission of these CDs is quenched by interactions with Cu2+ ions, which can be used to detect these ions with a detection limit of 1 μM. The chromophores remain accessible to diffusing Cu2+ ions even after embedding CDs in the sol-gel monolith, where their detection capabilities are preserved. Such …

Diffusion and outgassing of O2 in amorphous SiO2 silica nanoparticles with specific surface properties

Silica nanoparticles with hydrophilic and hydrophobic surface and average diameter of 12 and 40 nm are investigated to study the surface group influence on the diffusion process of molecular oxygen. The O2 diffusion kinetics and molecular solubility are determined by Raman/Photoluminescence measurements. Thermal treatments up to 127°C in controlled atmosphere show that the surface chemistry of nanoparticles is not changed, the equilibrium emission of O2 depends on nanoparticles surface properties, whereas the dynamics of diffusion is surface independent suggesting that surface groups could only affect overall content or detectability of interstitial molecules. The post loading outgassing in…

Influence of O2 loading pre-treatment on the radiation response of pure and fluorine doped silica-based optical fibers

International audience; We investigated the impact of an oxygen pre-loading on pure-silica-core or fluorine-doped-core fiber responses to high irradiation doses (up to 1 MGy(SiO2)). Oxygen enrichment was achieved through a diffusion-based technique and the long term presence of O2 molecules was confirmed by micro-Raman experiments. Online Radiation Induced Attenuation (RIA) experiments were carried out in both the pristine and the O2-loaded optical fibers to investigate the differences induced by this pre-treatment in the UV and visible ranges. Contrary to results recently published on the positive impact of O2 on infrared RIA, our results reveal a RIA increased with O2 presence. Data are a…

Streptomyces coelicolor Vesicles: Many Molecules To Be Delivered

ABSTRACT Streptomyces coelicolor is a model organism for the study of Streptomyces, a genus of Gram-positive bacteria that undergoes a complex life cycle and produces a broad repertoire of bioactive metabolites and extracellular enzymes. This study investigated the production and characterization of membrane vesicles (MVs) in liquid cultures of S. coelicolor M145 from a structural and biochemical point of view; this was achieved by combining microscopic, physical and -omics analyses. Two main populations of MVs, with different sizes and cargos, were isolated and purified. S. coelicolor MV cargo was determined to be complex, containing different kinds of proteins and metabolites. In particul…

Structural and thermal stability of graphene oxide-silica nanoparticles nanocomposites

Abstract The investigation of the thermal stability up to 400 °C of Graphene Oxide (GO) and GO-silica nanoparticles (n-SiO2) composites prepared by direct mixture of GO and n-SiO2 is reported. Using Scanning Electron Microscopy, X-ray Photoelectron Spectroscopy, Energy Dispersive X-ray analysis, Atomic Force Microscopy, Raman and Infrared absorption measurements a thorough characterization of the prepared materials is carried out. By deepening the changes induced in the 2D Raman spectral region of GO at about 2900 cm−1 the comprehension of an interplay, driven by the thermally induced changes of the material, between inter-valley and intra-valley vibrational transitions is elucidated. This …

Creation of paramagnetic defects by gamma irradiation in amorphous silica

An electron spin resonance (ESR) study of the defects induced by γ-rays in various types of natural and synthetic silica is reported. Three main structures were identified: the E′ center and two doublets with field splitting of 7.4 and 11.8 mT, respectively, both centered around the E′ center signal. Another structure partially overlapping the E′ center line was also detected, consisting in three peaks with a maximum field splitting of 1.36 mT. We have investigated the growth kinetics of these centers on increasing the y-ray accumulated dose. In all investigated materials the growth of E′ centers can be interpreted as caused by γ-activated conversion of one or more precursors. The 1.36 mT s…

Effect of oxygen deficiency on the radiation sensitivity of sol-gel Ge-doped amorphous SiO2

We report experimental investigation by electron paramagnetic resonance (EPR) measurements of room temperature γ-ray irradiation effects in sol-gel Ge doped amorphous SiO2. We used materials with Ge content from 10 up to 104 part per million (ppm) mol obtained with different preparations. These latter gave rise to samples characterized by different extents of oxygen deficiency, estimated from the absorption band at ~5.15 eV of the Ge oxygen deficient centers (GeODC(II)). The irradiation at doses up to ~400 kGy induces the E'-Ge, Ge(1) and Ge(2) paramagnetic centers around g ~ 2 with concentrations depending on Ge and on GeODC(II) content. We found correlation between Ge(2) and GeODC(II) con…

Unveiled the Source of the Structural Instability of HKUST-1 Powders upon Mechanical Compaction: Definition of a Fully Preserving Tableting Method

Metal–organic frameworks (MOFs) are getting closer to finally being used in commercial applications. In order to maximize their packing density, mechanical strength, stability in reactive environme...

Photoluminescent and paramagnetic centers in gamma irradiated porous silica

Abstract The photoluminescence and electron spin resonance properties of gamma irradiated (up to 500 kGy) porous silica are reported. By exciting at 5.6 eV a photoluminescence contribution can be detected before irradiation, peaked at about 4.1 eV. Gamma irradiation causes the generation of the E′ centers (about 1 × 1014 defects cm−3) of paramagnetic hole centers and modifies the photoluminescence properties of the sample: the emission amplitude decreases and three contributions can be singled out at about 3.3, 3.8 and 4.4 eV.

Highly Efficient Electron Transfer in a Carbon Dot–Polyoxometalate Nanohybrid

Using solar radiation to fuel catalytic processes is often regarded as the solution to our energy needs. However, developing effective photocatalysts that are active under visible light has proven to be difficult, often due to the toxicity, instability, and high cost of suitable catalysts. We engineered a novel photoactive nanomaterial obtained by the spontaneous electrostatic coupling of carbon nanodots with [P2W18O62]6-, a molecular catalyst belonging to the class of polyoxometalates. While the former are used as photosensitizers, the latter was chosen for its ability to catalyze reductive reactions such as dye decomposition and water splitting. We find the electron transfer within the na…

Direct atomic layer deposition of ultrathin aluminium oxide on monolayer $MoS_2$ exfoliated on gold: the role of the substrate

In this paper we demonstrated the thermal Atomic Layer Deposition (ALD) growth at 250 {\deg}C of highly homogeneous and ultra-thin ($\approx$ 3.6 nm) $Al_2O_3$ films with excellent insulating properties directly onto a monolayer (1L) $MoS_2$ membrane exfoliated on gold. Differently than in the case of 1L $MoS_2$ supported by a common insulating substrate ($Al_2O_3/Si$), a better nucleation process of the high-k film was observed on the 1L $MoS_2/Au$ system since the ALD early stages. Atomic force microscopy analyses showed a $\approx 50\%$ $Al_2O_3$ surface coverage just after 10 ALD cycles, its increasing up to $>90\%$ (after 40 cycles), and an uniform $\approx$ 3.6 nm film, after 80 cycle…

Near-Infrared emission of O2 embedded in amorphous SiO2 nanoparticles

We report an experimental study on the emission properties of O2 molecules loaded by a thermal diffusion process at 200 °C into high-purity silica nanoparticles with mean diameters of 7 and 40 nm. The embedded O2 features a singlet to triplet emission band peaked at 1272 nm in agreement with the band observed for bulk silica materials. The photoluminescence excitation spectra have been determined in the visible and in the infrared range and are characterized by narrow bands peaked at 691, 764,and 1069 nm, respectively. By comparison of the transition energies, the vibrational quanta have been determined for the ground and for both the excited states; the values found are lower than the corr…

Irradiation induced Germanium Lone Pair Centers in Ge-doped Sol-gel SiO2: luminescence lifetime and temperature dependence

We studied the temperature dependence of the emission profile and of the lifetime, measured at 4.3 eV, related to the germanium lone pair centers (GLPC) induced by gamma ray at 5 MGy in a Ge-doped silica sample and in an analogous sample irradiated at 10 MGy, in which by a successive thermal treatment up to 415 °C the induced GLPC has been modified (named residual GLPC in the following). The measurements were recorded in the temperature range 10-300 K using an excitation of ∼5.2 eV. The data show that the energy level scheme of the induced and the residual GLPC is very similar to that of the native defects generated during the synthesis, and the intersystem crossing process (ISC) of the ind…

E’_delta center in amorphous silicon dioxide: a potential probe for embedded silicon nanostructures

Graphene‐SiO2 Interaction from Composites to Doping

An overview of the interaction between monolayer graphene and SiO2 dielectric substrate is reported focusing on the effect this latter has on doping and strain induced by thermal treatments in controlled atmosphere. The disentanglement of strain and doping is highlighted and the comparison with another dielectric substrate of Al2O3 evidences the critical role that the substrate has in the electronic properties of graphene. The reported results pave the way for microelectronic devices based on graphene on dielectrics and for Fermi level tuning in composites of graphene and nanoparticles.

Properties of HO2• radicals induced by γ-ray irradiation in silica nanoparticles

Abstract We report an experimental investigation on the effects of γ -ray irradiation in several types of silica nanoparticles previously loaded with O 2 molecules. They differ in specific surface and average diameter. By electron paramagnetic resonance (EPR) measurements we observe the generation of about 10 18 HO 2 • /cm 3 interstitial radicals. These radicals are induced by reaction of interstitial O 2 molecules with radiolytic H atoms, as previously suggested for O 2 -loaded bulk a-SiO 2 samples. However, at variance with respect to bulk materials, our experimental evidences suggest a different generation process of HO 2 • radical. In fact, by a detailed study of samples exposed to D 2 …

Temperature dependence of luminescence decay in Sn-doped silica

We report an experimental study on the temperature dependence, in the range 18-300 K, of the decay kinetics of the emission at 4.1 eV from the first excited electronic state of oxygen deficient centers in a 2000 ppm Sn-doped sol-gel silica. At low temperature, this luminescence decays exponentially with a lifetime of 8.4 ns, whereas, on increasing the temperature, the time decay decreases and cannot be fitted with an exponential function. These results are expected if there is a competition between the radiative and the thermally activated intersystem-crossing decay channels toward the associated triplet state. The comparison with previous data in pure oxygen-deficient and Ge-doped silica g…

The thin and medium filters of the EPIC camera on-board XMM-Newton: measured performance after more than 15 years of operation

After more than 15 years of operation of the EPIC camera on board the XMM-Newton X-ray observatory, we have reviewed the status of its Thin and Medium filters. We have selected a set of Thin and Medium back-up filters among those still available in the EPIC consortium and have started a program to investigate their status by different laboratory measurements including: UV/VIS transmission, Raman scattering, X-Ray Photoelectron Spectroscopy, and Atomic Force Microscopy. Furthermore, we have investigated the status of the EPIC flight filters by performing an analysis of the optical loading in the PN offset maps to gauge variations in the optical and UV transmission. We both investigated repea…

Current injection from metal to MoS2 probed at nanoscale by conductive atomic force microscopy

Contacts with MoS2 are currently the object of many investigations, since current injection through metal/MoS2 interfaces represents one of the limiting factors to the performance of MoS2 thin film transistors. In this paper, we employed conductive atomic force microscopy (CAFM) to investigate the current injection mechanisms from a nanometric contact (a Pt coated tip) to the surface of MoS2 thin films exfoliated on SiO2. The analysis of local current-voltage (I-V) characteristics on a large array of tip positions provided high spatial resolution information on the lateral homogeneity of the tip/MoS2 Schottky barrier Phi(B) and of the ideality factor n. From the histograms of the measured P…

Electron Irradiation Effects on Single‐Layer MoS 2 Obtained by Gold‐Assisted Exfoliation

International audience; Mechanical exfoliation assisted by gold is applied to obtain good quality large lateral size single-layer MoS2. The effects of 2.5 MeV electron irradiation are investigated at room temperature on structural and electronic features by Raman and microluminescence spectroscopy. The exciton recombination emission in the direct bandgap of single-layer MoS2 is affected during irradiation starting from the minimum explored dose of 1 kGy. At higher doses, Raman bands show no relevant modifications whereas the exciton emission is quenched, suggesting that irradiation-induced point defects affect exciton dynamics.

Effects of Pressure, Thermal Treatment, and O2 Loading in MCM41, MSU-H, and MSU-F Mesoporous Silica Systems Probed by Raman Spectroscopy

We present a Raman study of the effects induced by pressure, thermal treatments, and O2 loading in MCM41, MSU-H, and MSU-F representative mesoporous silica. We compared the starting powders with the mechanically pressed tablets produced applying pressures of ∼0.2 and ∼0.45 GPa. The spectra of the three untreated tablets evidence that the main value of the Si-O-Si angle decreases and that in the MCM41 and the MSU-H Si-O-Si hydrolysis occurs, whereas such a process is absent or much less efficient in the MSU-F. Despite their different networks, the three powders tend to crystallize in cristobalite when treatments are at 1000 °C. The MCM41 and MSU-H tablets exhibit behavior similar to their st…

Effects of high pressure thermal treatments in oxygen and helium atmospheres on amorphous silicon dioxide and its radiation hardness

The effects of thermal treatments at similar to 400 degrees C in oxygen or helium atmospheres at similar to 180 baron the radiation hardness of amorphous SiO(2) are studied. The generation efficiency of several point defects under gamma irradiation is compared to that of the untreated material. All the effects on point defects generation here observed can be explained in terms of changes in the precursor sites. In particular it has been observed that the thermal treatments can change the precursors sites of point defects both through temperature and pressure related processes, not depending on the atmosphere, and through oxygen related processes creating oxygen excess sites. The presence of…

La Scuola Adotta un Esperimento

Influence of <formula formulatype="inline"><tex Notation="TeX">${\hbox{O}}_2$</tex></formula>-Loading Pretreatment on the Radiation Response of Pure and Fluorine-Doped Silica-Based Optical Fibers

We investigated the impact of an oxygen preloading on pure-silica-core or fluorine-doped-core fiber responses to high irradiation doses (up to 1 MGy (SiO 2 )). Oxygen enrichment was achieved through a diffusion-based technique, and the long-term presence of O 2 molecules was confirmed by micro-Raman experiments. Online radiation induced attenuation (RIA) experiments were carried out in both the pristine and the O 2 -loaded optical fibers to investigate the differences induced by this pretreatment in the UV and visible ranges. Contrary to results recently published on the positive impact of O 2 on infrared RIA, our results reveal a RIA increase with O 2 presence. Data are analyzed in order t…

Thermal stability of gamma-irradiation-induced oxygen-deficient centers in silica

The effects of isochronal thermal treatments on three {gamma}-irradiation-induced point defects, named the E{sup '}, ODC(II), and H(I) centers, are investigated in various types of commercial silica (a-SiO{sub 2}). ODC(II) is investigated by means of photoluminescence spectroscopy, and the H(I) and E{sup '} centers by electron paramagnetic resonance. The annealing processes of the ODC(II) and H(I) center are shown to be independent of each other, and no conversion mechanisms are evidenced. In contrast, a strong similarity is observed between the annealing curves of the ODC(II) and E{sup '} centers. We tentatively ascribe the annealing processes to reactions of the defects with radiolyticall…

Photoluminescence time decay of surface oxygen deficient centers in un‐doped and Ge‐doped silica

We report a study of the emission decay from the singlet excited state of two fold coordinated Si and Ge centers stabilized on the surface of silica and Ge-doped silica. The PL lifetimes are of the order of nanoseconds and increase on decreasing the temperature. The results suggest that, for the surface centers, the phonon assisted intersystem-crossing process linking the excited states affects the decay rates, is effective down to low temperatures and is distributed because of the inhomogeneity of the defects. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Multitechnique Analysis of the Hydration in Three Different Copper Paddle-Wheel Metal-Organic Frameworks

The structural instability in a humid environment of the majority of metal-organic frameworks (MOFs) is a challenging obstacle for their industrial-scale development. Recently, two water-resistant MOFs have been synthetized, STAM-1 and STAM-17-OEt. They both contain copper paddle wheels, like the well-known water-sensitive HKUST-1, but different organic linkers. The crystal lattice of both the MOFs undergoes a phase transition upon interaction with water molecules. Their unusual flexibility allows the controlled breaking of some interpaddle wheel Cu-O interactions in the so-called crumple zones, with a mechanism called hemilability, which is considered to have a crucial role for the stabili…

Isolation of the CH3˙ rotor in a thermally stable inert matrix: first characterization of the gradual transition from classical to quantum behaviour at low temperatures

International audience; Matrix isolation is a method which plays a key role in isolating and characterizing highly reactive molecularradicals. However, the isolation matrices, usually composed of noble gases or small diamagnetic molecules,are stable only at very low temperatures, as they begin to desegregate even above a few tens of Kelvin.Here we report on the successful isolation of CH3 radicals in the cages of a nearly inert clathrate–SiO2matrix. This host is found to exhibit a comparable inertness with respect to that of most conventionalnoble gas matrices but it is characterized by a peculiar thermal stability. The latter property is related to thecovalent nature of the host material a…

Hydrogen-Related Paramagnetic Centers in Ge-Doped Sol-Gel Silica Induced by γ-Ray Irradiation

We have studied the generation mechanisms of H(II) paramagnetic centers in Ge-doped silica by investigating up to 104 mol ppm sol-gel Ge-doped silica materials. We have considered materials with the same concentrations of Ge but that are produced by two different densification routes that give rise to different concentrations of Ge-related oxygen deficient centers (GeODC(II)). These centers are characterized by an optical absorption band at ∼5.2 eV (B2 β band) and two related emissions at ∼3.2 eV and ∼4.3 eV. The GeODC(II) content was estimated by absorption and emission measurements. The H(II) centers were induced by room temperature γ-ray irradiation and their concentration was determined…

Properties and generation by irradiation of germanium point defects in Ge-doped silica

Ge doped amorphous silicon dioxide (Ge doped silica) has attracted the attention of researchers for more than 50 years. This material is used in many different technological fields from electronics, to telecommunication, to optics. In particular, it is widely used for the production of optical fibers and linear and nonlinear optical devices. The optical fibers, which allow to transmit optical signals with high speed avoiding interferences, are constituted by two regions with different refractive index values: core (inner part) and cladding (external part). To increase the refractive index of the core with respect to that of cladding, Ge doping of silica is commonly used. Moreover, in the Ge…

Excitation processes of the blue luminescence in crystalline SiO 2 probed by synchrotron radiation measurements

Luminescence properties of crystalline α-quartz were investigated by time-resolved spectroscopy under pulsed synchrotron radiation excitation in the vacuum ultraviolet range. Our results evidence that two emission bands overlap at 2.7 eV, both being observed only at low temperature. The first contribution is excited by band-to-band transition and is related to the radiative recombination of a self trapped exciton occurring in a time scale of a few ms, the second is associated with defects induced in quartz by γ- and β-radiation, is excited at 7.6 eV and its lifetime is 3.6 ns at T = 10 K. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Evaluation of the UV Optical Transmission Degradation of Gamma-ray Irradiated Optical Fibers

This paper highlights our recent results on the investigation of the transmission attenuation in the UV spectral range induced by gamma-ray irradiation of optical fibers, and the comparison with results obtained by electron paramagnetic resonance (EPR) and photoluminescence measurements.

Intrinsic generation of OH groups in dry silicon dioxide upon thermal treatments

We show the existence of an intrinsic generation mechanism of OH groups in synthetic dry silica upon thermal treatments. Samples are treated for ~160 h at 390 °C in He at 2.7 or 180 bar, and the growth of the OH IR absorption band at 3670 cm−1 is observed. An OH concentration of ~10^18 cm^−3 is estimated. Possible contributions of reactions with molecules absorbed from the atmosphere are excluded. Reactions with H2O already contained in the samples are rejected by IR measurements. The observed OH generation is attributed to the reaction of network sites with H2 already present in the material. Possible reaction paths are examined

Rapid and eco-friendly synthesis of graphene oxide-silica nanohybrids

EPR investigation on the polyamorphic transformation induced by electron irradiation in SiO2 glass

Performance Analysis of a Prototype High‐Concentration Photovoltaic System Coupled to Silica Optical Fibers

High-concentration photovoltaic (HCPV) systems are one of the most promising technologies for the generation of renewable energy with high-conversion efficiency. Their development is still at an early stage, but the possibility of integrating high-concentration systems into buildings offers new opportunities to achieve the net-zero-energy building goal. Herein, the optical and energetic performance of a hybrid daylighting−HCPV prototype based on pure- or doped-silica optical fibers (OFs) to guide 2000× concentrated sunlight inside the buildings is evaluated. There, the light can either be used to illuminate interior spaces or projected on solar cells to generate electricity. The system equi…

Luminescence Efficiency of Si/SiO 2 Nanoparticles Produced by Laser Ablation

Photoluminescence properties of Si(core)/SiO 2 (shell) nanoparticles produced by pulsed laser ablation in aqueous solution are investigated with the purpose to highlight the microscopic processes that govern the emission brightness and stability. Time resolved spectra evidence that these systems emit a µs decaying band centered around 1.95 eV, that is associated with the radiative recombination of quantum-confined excitons generated in the Si nanocrystalline core. Both the quantum efficiency and the stability of this emission are strongly dependent on the pH level of the solution, that is changed after the laser ablation is performed. They enhance in acid environment because of the H + pass…

Substrate impact on the thickness dependence of vibrational and optical properties of large area $MoS_2$ produced by gold-assisted exfoliation

The gold-assisted exfoliation is a very effective method to produce large-area ($cm^2$-scale) membranes of molybdenum disulfide ($MoS_2$) for electronics. However, the strong $MoS_2/Au$ interaction, beneficial for the exfoliation process, has a strong impact on the vibrational and light emission properties of $MoS_2$. Here, we report an atomic force microscopy (AFM), micro-Raman ($\mu-R$) and micro-Photoluminescence ($\mu-PL$) investigation of $MoS_2$ with variable thickness exfoliated on Au and subsequently transferred on an $Al_2O_3/Si$ substrate. The $E_{2g}$ - $A_{1g}$ vibrational modes separation $\Delta\mu$ (typically used to estimate $MoS_2$ thickness) exhibits an anomalous large val…

Near-Infrared Emission of O2 Embedded in Amorphous SiO2 Nanoparticles

We report an experimental study on the emission properties of O2 molecules loaded by a thermal diffusion process at 200 °C into high-purity silica nanoparticles with mean diameters of 7 and 40 nm. The embedded O 2 features a singlet to triplet emission band peaked at 1272 nm in agreement with the band observed for bulk silica materials. The photoluminescence excitation spectra have been determined in the visible and in the infrared range and are characterized by narrow bands peaked at 691, 764, and 1069 nm, respectively. By comparison of the transition energies, the vibrational quanta have been determined for the ground and for both the excited states; the values found are lower than the co…

Morphological and Chemical Evolution of Gradually Deposited Diamond-Like Carbon Films on Polyethylene Terephthalate: From Subplantation Processes to Structural Reorganization by Intrinsic Stress Release Phenomena.

Diamond-like carbon (DLC) films on polyethylene terephthalate (PET) are nowadays intensively studied composites due to their excellent gas barrier properties and biocompatibility. Despite their applicative features being highly explored, the interface properties and structural film evolution of DLC coatings on PET during deposition processes are still sparsely investigated. In this study two different types of DLC films were gradually deposited on PET by radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) using acetylene plasma. The surface morphology of the deposited samples has been analyzed by atomic force microscopy (AFM). Their chemical composition was investigated by …

High-Efficiency Multi-Junction Photovoltaic Cells in School Physics Laboratory

Energy consumption in the world is increasing more and more due to the huge energy request coming from emerging countries such as China, India, etc. To face the challenge of sustainability, a solution may be the use of solar energy, since it is the most abundant renewable energy source on Earth. The electromagnetic energy coming from the Sun can be converted into usable energy (electricity) by solar cells, whose conversion efficiency is continuously increasing due to scientific and technological progress. The proposed activity is thought to be carried out with secondary as well as high school students to allow teachers to discuss sustainability issues, and to provide students with an introd…

Seed‐Layer‐Free Atomic Layer Deposition of Highly Uniform Al 2 O 3 Thin Films onto Monolayer Epitaxial Graphene on Silicon Carbide

Atomic layer deposition (ALD) is the method of choice to obtain uniform insulating films on graphene for device applications. Owing to the lack of out-of-plane bonds in the sp(2) lattice of graphene, nucleation of ALD layers is typically promoted by functionalization treatments or predeposition of a seed layer, which, in turn, can adversely affect graphene electrical properties. Hence, ALD of dielectrics on graphene without prefunctionalization and seed layers would be highly desirable. In this work, uniform Al2O3 films are obtained by seed-layer-free thermal ALD at 250 degrees C on highly homogeneous monolayer (1L) epitaxial graphene (EG) (amp;gt;98% 1L coverage) grown on on-axis 4H-SiC(00…

Diffusion and outgassing of O<inf>2</inf> in amorphous SiO<inf>2</inf> silica nanoparticles with specific surface properties

Structural and luminescence properties of amorphous SiO2 nanoparticles

We report an experimental study on the photoluminescence band peaked at 2.7 eV (blue band) induced by thermal treatments in nanometric amorphous SiO 2. In particular the emission dependence on the nanometric particles size as a function of their mean diameter from 7 nm up to 40 nm is investigated. We found that the emission amplitude increases on decreasing the particle diameter, showing a strong correlation between the blue band and the nanometric nature of the particles. By Raman spectroscopy measurements it is evidenced that the SiO2 nanoparticles matrix is significantly affected by the reduction of size. Basing on the shell-like model, these findings are interpreted assuming that the de…

Evolution of the sp2 content and revealed multilayer growth of amorphous hydrogenated carbon (a-C:H) films on selected thermoplastic materials

Amorphous hydrogenated carbon (a-C:H) films were gradually deposited on high-density polyethylene (HDPE), polyethylene terephthalate (PET) and polyoxymethylene (POM) via an indirect (f-type) and a direct (r-type) plasma-enhanced chemical vapor deposition (PECVD) process with acetylene plasma. The surface morphologies of the thicker r-depositions on the three different thermoplastics have been analyzed by atomic force microscopy (AFM) at varying micrometer scales. Absorbance spectroscopy has been used to characterize the optical properties of all coatings. Intrinsic stress release phenomena are revealed on thicker layers through the detection of characteristic surface corrugations. Based on …

Coupled irradiation-temperature effects on induced point defects in germanosilicate optical fibers

International audience; We investigated the combined effects of temperature and X-rays exposures on the nature of point defects generated in Ge-doped multimode optical fibers. Electron paramagnetic resonance (EPR) results on samples X-ray irradiated at 5 kGy(SiO2), employing different temperatures and dose rates, are reported and discussed. The data highlight the generation of the Ge(1), Ge(2), E0 Ge and E0 Si defects. For the Ge(1) and Ge(2), we observed a decrease in the induced defect concentrations for irradiation temperatures higher than *450 K, whereas the E0 defects feature an opposite tendency. The comparison with previous post-irradiation thermal treatments reveals peculiar effects…

Optimization of the Optical Components in a Reflective High CPV Module

Characteristics of industrially manufactured amorphous hydrogenated carbon (a-C:H) depositions on high-density polyethylene

Industrially high-density polyethylene (HDPE) was successively covered by two types of amorphous hydrogenated carbon (a-C:H) films, one more flexible (f-type) and the other more robust (r-type). The films have been grown by radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) technique with acetylene plasma. The surface morphology of both types has been studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Contact angle measurements and Raman spectroscopy analysis were done to investigate the surface wettability and carbon chemical composition. Both types display similar morphology and grain growth pattern. Contact angle measurements revealed surfa…

Spectral properties and lifetime of green emission in γ-ray irradiated bismuth-doped silica photonic crystal fibers

Abstract We report an experimental investigation focused on the green emission detected in γ-ray irradiated Bismuth-doped photonic crystal fibers. Our photoluminescence spectra, recorded at room temperature, provide evidence for the presence of two emission bands both located at ~ 530 nm (2.34 eV). One emission is detected only in the Bi-doped core while the other, is detected in the cladding. These two emissions feature different excitation spectra and a fast and a slow decay lifetime. The origin of the fast emission decay, about ten nanoseconds, is tentatively attributed to a silica intrinsic defect, whereas the slow component, having lifetime of about 2 μs and featuring anti-stokes emiss…

Sensing of Transition Metals by Top-Down Carbon Dots

Carbon quantum dots (CQDs) are a new class of carbon-rich materials with a range of unique optical and structural properties. They can be defined as carbon nanoparticles, with sizes in the range of 1–10 nm, displaying absorption and emission activities in the UV-VIS range. Depending on the structure, CQDs display a wide variability of properties, which provides the possibility of finely tuning them for several applications. The great advantages of CQDs are certainly the ease of synthesis, non-toxicity, and the strong interactions with the surrounding environment. Based on this, CQDs are especially promising as selective chemosensors. The present study reports on carbon quantum dots synthesi…

Structural properties of the range-II- and range-III order in amorphous-SiO2 probed by electron paramagnetic resonance and Raman spectroscopy

In the present work we report an experimental investigation by electron paramagnetic resonance spectroscopy on the hyperfine structure of the E. point defect, probing the local arrangement of the network (range-II order), and by Raman spectroscopy on the D 1 and D 2 lines, probing mean features of the network (range-III order). Our studies, performed on a-SiO 2 samples thermally treated at 1000 °C in air for different time durations, show that changes of the hyperfine structure and of the D 1 and D 2 lines occur in a correlated way. These results give strong evidence that the range-II and range-III order properties are intimately related to each other and that these properties are determine…

Temperature dependence of O2 singlet photoluminescence in silica nanoparticles

Defect-related visible luminescence of silica nanoparticles

The high photon emissivity in the visible spectral range is one of the most relevant phenomena emerging from the reduction of silica down to nanoscale; hence it is promising for the development of optical nanotechnologies (down converter, probes, display). It is well accepted that the origin of this luminescence is related to the high specific surface (~100 m2/g) that favors the formation of optically active defects at the nanosilica surface. With the aim to clarify the role of specific luminescent defects, here we report a detailed study of spectral and decay features by time-resolved photoluminescence spectra under a visible-UV tunable laser excitation. Our study is carried out on differe…

The role of impurities in the irradiation induced densification of amorphous SiO(2).

In a recent work (Buscarino et al 2009 Phys. Rev. B 80 094202), by studying the properties of the (29)Si hyperfine structure of the E'(γ) point defect, we have proposed a model able to describe quantitatively the densification process taking place upon electron irradiation in amorphous SiO(2) (a-SiO(2)). In particular, we have shown that it proceeds heterogeneously, through the nucleation of confined densified regions statistically dispersed into the whole volume of the material. In the present experimental investigation, by using a similar approach on a wider set of materials, we explore how this process is influenced by impurities, such as OH and Cl, typically involved in relevant concent…

Aging of MCM41, MSU-H and MSU-F mesoporous systems investigated through the Raman spectroscopy

Here we report an experimental investigation, based on the Raman spectroscopy, on the aging of some mesoporous silica based systems. In details, we studied the aging in air of the MCM41, the MSU-H and the MSU-F materials by acquiring the Raman spectra of as received and of mechanically pressed, at 0.2 and 0.45 GPa, powders. Our data evidenced that the starting powders of the MCM41 and of the MSU-H undergo structural modification when they are exposed to the ambient atmosphere, such modification consisting in the decrease of the D2 Raman band (originated by the three member rings). At variance the powders of the MSU-F appear to be stable. Furthermore, by pressing the starting powders to prod…

Near-Infrared-Responsive Choline-Calix[4]arene-Gold Nanostructures for Potential Photothermal Cancer Treatment

The development of novel chemical approaches for the fabrication of gold nanostructures with localized surface plasmon resonance (LSPR) falling in the near-infrared (NIR) region is one challenging topic in nanomaterials science. Due to their optical and photothermal properties triggered by light excitation in the therapeutic window (λmax = 650-1300 nm), gold-based nanostructures are appealing candidates in anticancer nanomedicine. Here, we report a novel method to prepare water-dispersible gold nanostructures with NIR-LSPR (λmax = 600-1000 nm) properties. The gold nanostructures were achieved in a single step by an unconventional method using NADH as a reducing agent and an amphiphilic chol…

In-situ observation of β-ray induced optical absorption in a-SiO2: radiation darkening and room temperature recovery

Nano-Oxides produced by ns laser ablation in liquids

Laser ablation in liquids was successfully applied to produce nanosized oxides from Si, Ti and Zn targets. The obtained colloidal solutions of nanoparticles were investigated by complementary techniques: AFM, IR and Raman spectroscopies; optical absorption and time resolved photoluminescence. The results demonstrate the production of SiO2, TiO2 and ZnO. The absorption and emission properties of these material have been also investigated and appear to be promising for optical applications.

Interfacial disorder of graphene grown at high temperatures on 4H-SiC(000-1)

This paper presents an investigation of the morphological and structural properties of graphene (Gr) grown on SiC(000-1) by thermal treatments at high temperatures (from 1850 to 1950 ºC) in Ar at atmospheric pressure. Atomic force microscopy and micro-Raman spectroscopy showed that the grown Gr films are laterally inhomogeneous in the number of layers, and that regions with different stacking-type (coupled or decoupled Gr films) can coexist in the same sample. Scanning transmission electron microscopy and electron energy loss spectroscopy showed that a nm-thick C-Si-O amorphous layer is present at the interface between Gr and SiC. Basing on these structural results, the mechanisms of Gr gro…

X-ray irradiation effects on a multistep Ge-doped silica fiber produced using different drawing conditions

International audience; We report an experimental study based on confocal microscopy luminescence (CML) and electron paramagnetic resonance (EPR) measurements to investigate the effects of the X-ray (from 50 krad to 200 Mrad) on three specific multistep Ge doped fibers obtained from the same preform by changing some of the drawing conditions (tension and speed). CML data show that, both before and after the irradiation, Germanium Lone Pair Center (GLPC) concentrations are similarly distributed along the diameters of the three fibers and they are partially reduced by irradiation. The irradiation induces also the Non Bridging Oxygen Hole Center (NBOHC) investigated by CML and other paramagnet…

Concentration growth and thermal stability of gamma-ray induced germanium lone pair center in Ge-doped sol–gel a-SiO2

Abstract We report an experimental study of the concentration growth by γ-ray irradiation of germanium lone pair center (GLPC) in 10 4 part per million molar Ge-doped sol–gel silica. The data show that γ-ray induced GLPC concentration increases linearly up to ∼5 MGy and then it seems to reach a limit value. In addition to the dose dependence, we have studied the thermal stability of the radiation induced GLPC in ambient atmosphere up to 415 °C. We found that the concentration of this latter GLPC starts to decrease at ∼300 °C, at variance to native GLPC, suggesting that the annealing is related to irradiation products. After the thermal treatments the photoluminescence (PL) activity of the γ…

Luminescence mechanisms of defective ZnO nanoparticles.

ZnO nanoparticles (NPs) synthesized by pulsed laser ablation (PLAL) of a zinc plate in deionized water were investigated by time-resolved photoluminescence (PL) and complementary techniques (TEM, AFM, μRaman). HRTEM images show that PLAL produces crystalline ZnO NPs in wurtzite structure with a slightly distorted lattice parameter a. Consistently, optical spectra show the typical absorption edge of wurtzite ZnO (Eg = 3.38 eV) and the related excitonic PL peaked at 3.32 eV with a subnanosecond lifetime. ZnO NPs display a further PL peaking at 2.2 eV related to defects, which shows a power law decay kinetics. Thermal annealing in O2 and in a He atmosphere produces a reduction of the A1(LO) Ra…

Irradiation temperature effects on the induced point defects in Ge-doped optical fibers

We present an experimental investigation on the combined effects of temperature and irradiation on Ge-doped optical fibers. Our samples were X-ray (10 keV) irradiated up to 5 kGy with a dose rate of 50 Gy(SiO2)/s changing the irradiation temperature in the range 233-573 K. After irradiation we performed electron paramagnetic resonance (EPR) and confocal microscopy luminescence (CML) measurements. The recorded data prove the generation of different Ge related paramagnetic point defects and of a red emission, different from that of the Ge/Si Non-Bridging Oxygen Hole center. Furthermore, by comparing the behaviour of the EPR signal of the Ge(1) as a function of the irradiation temperature with…

Photoluminescence and diffusion properties of O2 molecules in amorphous SiO2 nanoparticles

An experimental study by Raman and Photoluminescence (PL) spectroscopies on the emission and diffusion properties of O2 molecules in amorphous SiO2 nanoparticles of commercial origin with diameters from 14 to 40 nm is reported. Stationary and time resolved PL measurements have been carried out to characterize the Near Infrared (NIR) emission at 1272 nm of O2. Emission features similar to those of bulk silica systems with a sharp PL band and excitation channels in the NIR, at 1070 nm, and in the visible, at 765 and 690 nm are found, with peculiarities arising from embedding O2 in nanostructures. The study of the NIR PL lifetime as a function of temperature down to 10 K enabled to reveal the …

Comparison of gamma and beta-ray irradiation effects in sol-gel Ge-doped SiO2

Le indagini scientifiche per lo studio e la conservazione dei beni culturali : un approccio analitico integrato, la conoscenza dei materiali costitutivi e della tecnica esecutiva della Madonna Odigitria di Monreale

The icon Virgin Hodegetria, now in Santa Maria Nuova Cathedral in Monreale near Palermo (Italy), probably dates from the beginning of thirteen century could be considered one of the earliest examples of medieval icon in Sicily. The icon is distinguished from other southern icons by the strong Byzantine matrix and by its size (169x131x3 cm). Since 2015, the icon is part of the Arab-Norman Palermo UNESCO Heritage. This paper will deal with historical and scientific investigations on the icon to better understand the painting materials, the executive technique and to resolve question about on-going restoration in planning a complex conservation project. Examination of the icon was both non-inv…

Temperature and excitation energy dependence of decay processes of luminescence in Ge-doped silica

We report experimental results on the time decay of photoluminescence at 4.2 eV in Ge-doped silica. This optical emission is assigned to a singlet-singlet transition between electronic states localized on an oxygen deficiency nearby a Ge atom and its radiative decay rate is in competition with an intersystem crossing mechanism that populates an excited triplet state. We investigate the dependence of the lifetime of this photoluminescence on the temperature, in the 6--295 K range, and on the excitation energy, in the ultraviolet and vacuum ultraviolet region. The mean value of the decay time decreases on increasing the temperature, in agreement with the phonon-assisted nature of the intersys…

O2 Loaded Germanosilicate Optical Fibers: Experimental In Situ Investigation and Ab Initio Simulation Study of GLPC Evolution under Irradiation

International audience; In this work we present a combined experimental and ab initio simulation investigation concerning the Germanium Lone Pair Center (GLPC), its interaction with molecular oxygen (O2), and evolution under irradiation. First, O2 loading has been applied here to Ge-doped optical fibers to reduce the concentration of GLPC point defects. Next, by means of cathodoluminescence in situ experiments, we found evidence that the 10 keV electron irradiation of the treated optical fibers induces the generation of GLPC centers, while in nonloaded optical fibers, the irradiation causes the bleaching of the pre-existing GLPC. Ab initio calculations were performed to investigate the reac…

Concentration growth and thermal stability of gamma-ray induced Germanium lone pair center in Ge-doped sol-gel SiO2

Luminescence activity of surface and bulk Ge-oxygen deficient centers in silica

Effect of air on oxygen p-doped graphene on SiO2

Stability in ambient air or in vacuum-controlled atmosphere of molecular oxygen-induced p-type doping of graphene monolayer on SiO2 substrate on Si is investigated by micro-Raman spectroscopy and atomic force microscopy (AFM). The Raman 2D and G bands spectral positions and amplitude ratio are affected by the permanence in air atmosphere in a time scale of months whereas the vacuum safely maintains the doping effects determined through Raman bands. No morphological effects are induced by the doping and post-doping treatments. A reactivity of ambient molecular gas with stably trapped oxygen is suggested to induce the doping modification. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Role of vitreous matrix on the optical activity of Ge-doped silica

Abstract We report an experimental study on the relationship between the optical activity of Ge-oxygen deficient centers and dynamic properties and conformational heterogeneity of vitreous matrix in silica. We focus our attention on the absorption band at ∼5.2 eV (B 2β ) and on the two related emissions at ∼4.2 eV (α E ) and at ∼3.1 eV (β). From the temperature dependence of B 2β band we estimate a mean energy value of 26 meV for local vibrational modes coupled to the electronic transition, suggesting that the chromophore and its surrounding have access to low frequency dynamics. From the thermal behavior of the two emissions we distinguish the two competitive relaxation processes from the …

Gamma and x-ray irradiation effects on different Ge and Ge/F doped optical fibers

International audience; We performed electron paramagnetic resonance (EPR) measurements on γ and X ray irradiated Ge doped and Ge/F co-doped optical fibers. We considered three different drawing conditions (speed and tension), and for each type of drawing, we studied Ge and Ge/F doped samples having Ge doping level above 4% by weight. The EPR data recorded for the γ ray irradiated fibers confirm that all the samples exhibit a very close radiation response regardless of the drawing conditions corresponding to values used for the production of specialty fibers. Furthermore, as for the X irradiated materials, in the γ ray irradiated F co-doped fibers, we observed that the Ge(1) and the Ge(2) d…

Luminescence of γ-radiation-induced defects in α-quartz

Optical transitions associated with γ-radiation-induced defects in crystalline α-quartz were investigated by photoluminescence excited by both pulsed synchrotron radiation and steady-state light. After a 10 MGy γ-dose we observed two emissions at 4.9 eV (ultraviolet band) and 2.7 eV (blue band) excitable in the range of the induced absorption band at 7.6 eV. These two luminescence bands show a different temperature dependence: the ultraviolet band becomes bright below 80 K; the blue band increases below 180 K, but drops down below 80 K. Both emissions decay in a timescale of a few ns under pulsed excitation, however the blue band could also be observed in slow recombination processes and it…

Photoluminescence of Carbon Dots Embedded in a SiO2 Matrix

Abstract We synthetized carbon dots by a pyrolitic method, and studied their photoluminescence in aqueous environment and upon trapping in a solid matrix. To this aim, we devised a facile procedure allowing to embed the dots in amorphous SiO2, without the need of any pre-functionalization of the nanoparticles, and capable of yielding a brightly photoluminescent monolith. Experimental data reveal a remarkable similarity between the emission properties of carbon dots in water and in SiO2, suggesting that the chromophores responsible of the photoluminescence undergo only weak interactions with the environment. Time-resolved photoluminescence data reveal that the typical photoluminescence tunab…

Role ofH2Oin the thermal annealing of theEγ′center in amorphous silicon dioxide

The model for the annealing of a radiation-induced point defect in silica, the ${\text{E}}_{\ensuremath{\gamma}}^{\ensuremath{'}}$ center, is identified in the temperature range $(150--550)\ifmmode^\circ\else\textdegree\fi{}\text{C}$. Thermal treatments in controlled atmospheres of water vapor, oxygen, or helium of irradiated amorphous silicon dioxide are carried out. Direct experimental evidences that the annealing of the ${\text{E}}_{\ensuremath{\gamma}}^{\ensuremath{'}}$ center is caused by a reaction with diffusing water molecules are found. A rate equation system describing this annealing process is inferred, and its solutions are compared with experimental data to obtain quantitative …

Combined Temperature Radiation Effects and Influence of Drawing Conditions on Phosphorous‐Doped Optical Fibers

International audience; This work focuses on the effects of high dose ionizing radiation, up to 10 MGy(SiO2), on P‐doped multimode optical fibers (OF) at different irradiation temperatures. The investigation is based on two complementary experimental techniques: radiation‐induced attenuation (RIA) measurements and electron paramagnetic resonance (EPR). The latter technique allows measuring the P1, P2, metastable‐POHC and stable‐POHC defects. Three OF samples are drawn from the same preform to evaluate the influence of changing their drawing conditions of the OFs on the radiation responses. This first study is performed under X‐rays at room temperature. The results are compared with the ones…

Combined High Dose and Temperature Radiation Effects on Multimode Silica-Based Optical Fibers

International audience; We investigate the response of Ge-doped, P-doped, pure-silica, or Fluorine-doped fibers to extreme environments combining doses up to MGy(SiO $_{{{2}}}$) level of 10 keV X-rays and temperatures between 25 C and 300 C . First, we evaluate their potential to serve either as parts of radiation tolerant optical or optoelectronic systems or at the opposite, for the most sensitive ones, as punctual or distributed dosimeters. Second, we improve our knowledge on combined ionizing radiations and temperature (R&T) effects on radiation-induced attenuation (RIA) by measuring the RIA spectra in the ultraviolet and visible domains varying the R&T conditions. Our results reveal the…

Investigation on the microscopic structure of E' center in amorphous silicon dioxide by electron paramagnetic resonance spectroscopy

The E′δ center is one of the most important paramagnetic point defects in amorphous silicon dioxide ( a-SiO 2) primarily for applications in the field of electronics. In fact, its appearance in the gate oxide of metal-oxide-semiconductor (MOS) structures seriously affects the proper work of many devices and, often, causes their definitive failure. In spite of its relevance, until now a definitive microscopic model of this point defect has not been established. In the present work we review our experimental investigation by electron paramagnetic resonance (EPR) on the E′δ center induced in γ-ray irradiated a-SiO 2. This study has driven us to the determination of the intensity ratio between…

Erratum to ‘Raman spectroscopy of β-irradiated silica glass’ by B. Boizot, S. Agnello, B. Reynard, R. Boscaino and G. Petite [J. Non-Cryst. Solids 325 (2003) 22–28]

Study of silica-based intrinsically emitting nanoparticles produced by an excimer laser

International audience; We report an experimental study demonstrating the feasibility to produce both pure and Ge-doped silica nanoparticles (size ranging from tens up to hundreds of nanometers) using nanosecond pulsed KrF laser ablation of bulk glass. In particular, pure silica nanoparticles were produced using a laser pulse energy of 400 mJ on pure silica, whereas Ge-doped nanoparticles were obtained using 33 and 165 mJ per pulse on germanosilicate glass. The difference in the required energy is attributed to the Ge doping, which modifies the optical properties of the silica by facilitating energy absorption processes such as multiphoton absorption or by introducing absorbing point defect…

Spectral heterogeneity of oxygen-deficient centers in Ge-doped silica

Abstract We report an experimental investigation of the emission spectra of a 1000 mol ppm sol–gel Ge-doped silica by fine tuning the excitation energy in the ultraviolet (UV) range, around 5 eV , and in the vacuum-UV range, around 7.3 eV , at room temperature and at 10 K . The sample is characterized by a blue (centered at ∼3.2 eV ) and an UV (centered at ∼4.3 eV ) bands. We have found that the ratio between the area of the blue and the UV bands depends on the temperature and on the excitation energy in both the vacuum-UV and the UV range. At both temperatures the spectral features of the blue and the UV bands are weakly affected when the excitation is varied in the vacuum-UV. At variance,…

Luminescence of gamma-radiation-induced defects in alpha-quartz

Optical transitions associated with gamma-radiation-induced defects in crystalline a-quartz were investigated by photoluminescence excited by both pulsed synchrotron radiation and steady-state light. After a 10 MGy gamma-dose we observed two emissions at 4.9 eV (ultraviolet band) and 2.7 eV (blue band) excitable in the range of the induced absorption band at 7.6 eV. These two luminescence bands show a different temperature dependence: the ultraviolet band becomes bright below 80 K; the blue band increases below 180 K, but drops down below 80 K. Both emissions decay in a timescale of a few ns under pulsed excitation, however the blue band could also be observed in slow recombination processe…

Study of the color centers in optical fibers to be used for ITER plasma diagnostics.

Comparison of γ and β-ray irradiation effects in sol-gel Ge-doped SiO<inf>2</inf>

We report an experimental study on the comparison between the γ or β ray induced Ge related point defects in Ge doped silica. Silica samples doped with ∼2.2 1017 Ge atoms/cm3 produced with the sol-gel technique have been irradiated. The effects of the irradiation have been investigated by optical absorption, photoluminescence and electron paramagnetic resonance spectroscopy in order to evaluate the generation and the dependence on dose of the Ge(1), E'Ge, Germanium Lone Pair Center (GLPC) and H(II) point defects. No relevant differences between the concentrations of γ or β ray induced Ge(1) and E'Ge point defects have been observed. In addition, it is found that both irradiations are able t…

Influence of oxide substrates on monolayer graphene doping process by thermal treatments in oxygen

Abstract The structural and the electronic properties of monolayer graphene made by chemical vapor deposition and transferred on various oxide substrates ( SiO 2 , Al 2 O 3 , and HfO 2 ) are investigated by Raman Spectroscopy and Atomic Force Microscopy in order to highlight the influence of the substrate on the features of p-doping obtained by O 2 thermal treatments. By varing the treatment temperature up to 400 °C, the distribution of the reaction sites of the substrates is evaluated. Their total concentration and the consequent highest doping available is determined and it is shown that this latter is linked to the water affinity of the substrate. Finally, by varing the exposure time to …

Ambipolar MoS2 Transistors by Nanoscale Tailoring of Schottky Barrier Using Oxygen Plasma Functionalization

One of the main challenges to exploit molybdenum disulfide (MoS2) potentialities for the next-generation complementary metal oxide semiconductor (CMOS) technology is the realization of p-type or ambipolar field-effect transistors (FETs). Hole transport in MoS2 FETs is typically hampered by the high Schottky barrier height (SBH) for holes at source/drain contacts, due to the Fermi level pinning close to the conduction band. In this work, we show that the SBH of multilayer MoS2 surface can be tailored at nanoscale using soft O-2 plasma treatments. The morphological, chemical, and electrical modifications of MoS2 surface under different plasma conditions were investigated by several microscopi…

Si-rich sites embedded in a-SiO2 probed by electron paramagnetic resonance spectroscopy

Ultrafast Interface Charge Separation in Carbon Nanodot-Nanotube Hybrids

Carbon dots are an emerging family of zero-dimensional nanocarbons behaving as tunable light harvesters and photoactivated charge donors. Coupling them to carbon nanotubes, which are well-known electron acceptors with excellent charge transport capabilities, is very promising for several applications. Here, we first devised a route to achieve the stable electrostatic binding of carbon dots to multi- or single-walled carbon nanotubes, as confirmed by several experimental observations. The photoluminescence of carbon dots is strongly quenched when they contact either semiconductive or conductive nanotubes, indicating a strong electronic coupling to both. Theoretical simulations predict a favo…

Controlling the oxidation processes of Zn nanoparticles produced by pulsed laser ablation in aqueous solution

We used online UV-VIS optical absorption and photoluminescence spectra, acquired during and after pulsed laser ablation of a Zinc plate in aqueous solution, to investigate the effect of the laser repetition rate and liquid environment on the oxidation processes of the produced nanoparticles. A transient Zn/ZnO core-shell structure was revealed by the coexistence of an absorption peak around 5.0 eV due to Zn surface plasmon resonance and of an edge at 3.4 eV coming from wurtzite ZnO. The growth kinetics of ZnO at the various repetition rates, selectively probed by the excitonic emission at 3.3 eV, began immediately at the onset of laser ablation and was largely independent of the repetition …

Thioflavin-T doped silica nanoparticles by basic-catalyzed sol-gel synthesis

We developed a basic-catalyzed sol-gel procedure that allows to synthesize silica nanoparticles functionalized with Thioflavin-T (ThT). During the synthesis, the formation of the doped silica nanoparticles was monitored by absorbance spectra indicating that the catalyst does not cause the total hydroxylation of the dye. Fluorescence measurements carried out on the ThT doped silica nanoparticles proved the attachment of ThT on silica and Raman spectroscopy provided information about the dye structure.

Micro-photoluminescence of Carbon Dots Deposited on Twisted Double-Layer Graphene Grown by Chemical Vapor Deposition

Carbon-based nanomaterials, such as carbon dots (CDs) and graphene (Gr), feature outstanding optical and electronic properties. Hence, their integration in optoelectronic and photonic devices is easier thanks to their low dimensionality and offers the possibility to reach high-quality performances. In this context, the combination of CDs and Gr into new nanocomposite materials CDs/Gr can further improve their optoelectronic properties and eventually create new ones, paving the way for the development of advanced carbon nanotechnology. In this work, we have thoroughly investigated the structural and emission properties of CDs deposited on single-layer and bilayer graphene lying on a SiO2/Si …

Polyamorphic transformation induced by electron irradiation ina-SiO2glass

We report a study by electron paramagnetic resonance of amorphous silicon dioxide $(a{\text{-SiO}}_{2})$ irradiated by 2.5 MeV electrons in the dose range from $1.2\ifmmode\times\else\texttimes\fi{}{10}^{3}$ to $5\ifmmode\times\else\texttimes\fi{}{10}^{6}\text{ }\text{kGy}$. By measuring the change in the splitting of the primary $^{29}\text{S}\text{i}$ hyperfine doublet of the ${E}_{\ensuremath{\gamma}}^{\ensuremath{'}}$ centers we evidenced an irradiation induced local (around the defects) densification of $a{\text{-SiO}}_{2}$. Our data show that the local degree of densification of the materials is significantly higher than that obtained by mean density measurements, suggesting that the …

Bleaching and thermal recovery of PL emissions in natural silica

Abstract We have investigated the bleaching of two photoluminescence (PL) emissions at 3.1 and 4.2 eV and the related growth of an electron spin resonance (ESR) signal, consisting in a hyperfine doublet split by 11.8 mT, in natural silica γ-irradiated by low doses, up to 1 Mrad. These observations definitely support the existence of a conversion mechanism, from optically active defects to paramagnetic ones. To further investigate this conversion process and the stability of the γ-induced paramagnetic centers, we performed PL and ESR measurements in samples that, after a γ exposure at 1 Mrad dose, were thermally treated at various temperatures ranging from 330 to 430 K. We found that the int…

Photoinduced charge transfer from Carbon Dots to Graphene in solid composite

Abstract The emission in solid phase of Carbon Dots (CDs) deposited by drop-casting technique is investigated by means of micro-photoluminescence. Graphene and SiO2 are used as substrates, and the influence of their different nature – conductive or insulating – on the emission of CDs is highlighed. In particular, a systematic loss of efficiency in the emission of CDs on graphene is found, suggesting a CD-graphene interaction possibly due to a photoinduced electron transfer between the surface states of CDs and the conduction band of graphene. Finally, thanks to the negligible influence on CDs emission, SiO2 substrate is used as support to perform thermal processing of CDs in solid phase, sh…

Intrinsic Point Defects in Silica for Fiber Optics Applications

Due to its unique properties, amorphous silicon dioxide (a-SiO2) or silica is a key material in many technological fields, such as high-power laser systems, telecommunications, and fiber optics. In recent years, major efforts have been made in the development of highly transparent glasses, able to resist ionizing and non-ionizing radiation. However the widespread application of many silica-based technologies, particularly silica optical fibers, is still limited by the radiation-induced formation of point defects, which decrease their durability and transmission efficiency. Although this aspect has been widely investigated, the optical properties of certain defects and the correlation betwee…

Inhomogeneity Effects On Point Defects Studied By Photoluminescence Time Decay In SiO2.

Highly Homogeneous 2D/3D Heterojunction Diodes by Pulsed Laser Deposition of MoS2 on Ion Implantation Doped 4H-SiC

In this paper, 2D/3D heterojunction diodes have been fabricated by pulsed laser deposition (PLD) of MoS2 on 4H-SiC(0001) surfaces with different doping levels, i.e., n− epitaxial doping (≈1016 cm−3) and n+ ion implantation doping (>1019 cm−3). After assessing the excellent thickness uniformity (≈3L-MoS2) and conformal coverage of the PLD-grown films by Raman mapping and transmission electron microscopy, the current injection across the heterojunctions is investigated by temperature-dependent current–voltage characterization of the diodes and by nanoscale current mapping with conductive atomic force microscopy. A wide tunability of the transport properties is shown by the SiC surface dopi…

Luminescence activity of surface and interior Ge-oxygen deficient centers in silica

We report a comparative study on the optical activity of surface and interior Ge–oxygen deficient centers in pressed porous and sol–gel Ge-doped silica, respectively. The experimental approach is based on the temperature dependence of the two photoluminescence bands at 4.2 (singlet–singlet emission, S1! S0) and 3.1 eV (triplet–singlet emission, T1! S0), excited within the absorption band at about 5 eV. Our data show that the phonon assisted intersystem crossing process, linking the two excited electronic states, more effective for surface than for interior centers in the temperature range 5–300 K. For both centers, a distribution of the activation energies of the process is found. Based on th…

UV and vacuum-UV properties of ge related centers in gamma irradiated silica

Photochemical inhomogeneity in the reduction process of the optical activity related to Ge oxygen deficient point defects in silica, characterized by an absorption band centered at 5.15 v eV and two emission bands centered at 3.2 v eV and 4.3 v eV, have been investigated. We have made a comparative study of the stationary and time dependent photoluminescence under excitation in the UV (5 v eV) and in the vacuum-UV (7.4 v eV) ranges in natural silica samples with native and with n -irradiation bleached optical activity. Our measurements evidence that the same spectral features are observed in the native and in the irradiated samples, but for an intensity reduction in the irradiated ones. Mor…

Carbon Dots Dispersed on Graphene/SiO2/Si: A Morphological Study

Low-dimensional carbon materials occupy a relevant role in the field of nanotechnology. Herein, the authors report a study conducted by atomic force microscopy and Raman spectroscopy on the deposition of carbon dots onto graphene surfaces. The study aims at understanding if and how the morphology and the microstructure of chemical vapor deposited graphene on Si/SiO2 may change due to the interaction with the carbon dots. Potential alteration in the graphene's electrical properties might be detrimental for optoelectronic applications. The deposition of carbon dots dispersed in water and ethanol solvents are explored to investigate the effect of solvents with different fluidic properties. The…

IBRIDI FORMATI DA NANOTUBI DI CARBONIO A PARETE MULTIPLA E ESTERI FOSFORICI: PROPRIETA’ E STUDI STRUTTURALI

Nel corso degli ultimi anni i nanotubi di carbonio in virtù delle loro proprietà fisiche, chimiche e meccaniche sono diventati tra i più promettenti materiali per la realizzazione di congegni a livello nanometrico. I CNT trovano numerose applicazioni nel campo, della nanoelettronica, nella costruzione di materiali ad elevata conducibilità elettrica ed elevata resistenza meccanica,2 e vengono, anche, impiegati come agenti di rinforzo dispersi in una matrice polimerica.3 Problema principale di questi materiali è che essi risultano scarsamente solubili in ambiente acquoso e in solventi organici, a causa delle forti forze attrattive di van der Waals che esistono tra le superfici dei CNT, che li…

Optical properties of oxygen-deficiency related centers in amorphous SiO 2 investigated by synchrotron radiation

We report an investigation of the photoluminescence activity at 4.4 v eV in g -irradiated silica under UV and vacuum-UV excitation by synchrotron radiation. Our results evidence two iso-energetic contributions which can be related to two oxygen-deficient centers variants: ODC(I) and ODC(II). The first, excited within the 7.6 v eV absorption, is detected only at low temperature and has a lifetime of about 2 v ns. The second exhibits two excitation maxima peaked at 5.0 and 6.8 v eV, its amplitude decreases by a factor 2 on increasing the temperature whereas its lifetime has a value of about 4 v ns. These features give new insights on the excitation pathway of the 4.4 v eV emission involving t…

Multiscale Investigation of the Structural, Electrical and Photoluminescence Properties of MoS2 Obtained by MoO3 Sulfurization

In this paper, we report a multiscale investigation of the compositional, morphological, structural, electrical, and optical emission properties of 2H-MoS2 obtained by sulfurization at 800 °C of very thin MoO3 films (with thickness ranging from ~2.8 nm to ~4.2 nm) on a SiO2/Si substrate. XPS analyses confirmed that the sulfurization was very effective in the reduction of the oxide to MoS2, with only a small percentage of residual MoO3 present in the final film. High-resolution TEM/STEM analyses revealed the formation of few (i.e., 2–3 layers) of MoS2 nearly aligned with the SiO2 surface in the case of the thinnest (~2.8 nm) MoO3 film, whereas multilayers of MoS2 partially standing up with r…

Role of H2O in the thermal annealing of the E’_gamma center in amorphous silicon dioxide

Dependence of O2 diffusion dynamics on pressure and temperature in silica nanoparticles

An experimental study of the molecular O2 diffusion process in high purity non-porous silica nanoparticles having 50 m2/g BET specific surface and 20 nm average radius was carried out in the temperature range from 127 to 177 °C at O2 pressure in the range from 0.2 to 66 bar. The study was performed by measuring the volume average interstitial O2 concentration by a Raman and photoluminescence technique using a 1,064 nm excitation laser to detect the singlet to triplet emission at 1,272 nm of the molecular oxygen in silica. A dependence of the diffusion kinetics on the O2 absolute pressure, in addition to temperature dependence, was found. The kinetics can be fit by the solution of Fick’s dif…

Graphene p-Type Doping and Stability by Thermal Treatments in Molecular Oxygen Controlled Atmosphere

Doping and stability of monolayer low defect content graphene transferred on a silicon dioxide substrate on silicon are investigated by micro-Raman spectroscopy and atomic force microscopy (AFM) during thermal treatments in oxygen and vacuum controlled atmosphere. The exposure to molecular oxygen induces graphene changes as evidenced by a blue-shift of the G and 2D Raman bands, together with the decrease of I2D/IG intensity ratio, which are consistent with a high p-type doping (∼1013 cm-2) of graphene. The successive thermal treatment in vacuum does not affect the induced doping showing this latter stability. By investigating the temperature range 140-350 °C and the process time evolution, …

Optical absorption and electron paramagnetic resonance of theEα′center in amorphous silicon dioxide

We report a combined study by optical absorption (OA) and electron paramagnetic resonance (EPR) spectroscopy on the E{sub {alpha}}{sup '} point defect in amorphous silicon dioxide (a-SiO{sub 2}). This defect has been studied in {beta}-ray irradiated and thermally treated oxygen-deficient a-SiO{sub 2} materials. Our results have pointed out that the E{sub {alpha}}{sup '} center is responsible for an OA Gaussian band peaked at {approx}5.8 eV and having a full width at half maximum of {approx}0.6 eV. The estimated oscillator strength of the related electronic transition is {approx}0.14. Furthermore, we have found that this OA band is quite similar to that of the E{sub {gamma}}{sup '} center in…

Surface morphology and grain analysis of successively industrially grown amorphous hydrogenated carbon films (a-C:H) on silicon

Abstract Silicon (1 0 0) has been gradually covered by amorphous hydrogenated carbon (a-C:H) films via an industrial process. Two types of these diamond-like carbon (DLC) coatings, one more flexible (f-DLC) and one more robust (r-DLC), have been investigated. Both types have been grown by a radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) technique with acetylene plasma. Surface morphologies have been studied in detail by atomic force microscopy (AFM) and Raman spectroscopy has been used to investigate the DLC structure. Both types appeared to have very similar morphology and sp 2 carbon arrangement. The average height and area for single grains have been analyzed for al…

Formation of optically active oxygen deficient centers in Ge-doped SiO2 by γ- and β-ray irradiation

Abstract We report an experimental study on the comparison between the γ- or β-ray induced Ge related point defects in Ge-doped silica. Silica samples doped with ∼2.2 1017 Ge atoms/cm3 produced with the sol–gel technique have been irradiated with γ-ray or with β-ray. The effects of the irradiation have been investigated by optical absorption, photoluminescence and electron paramagnetic resonance spectroscopy in order to evaluate the generation and the dependence on dose of the Ge(1), E’Ge, GLPC (Germanium lone pair center) and H(II) point defects. No relevant differences between the concentrations of γ- or β-ray induced Ge(1) and E’Ge point defects have been observed and, in addition, it ha…

Competitive relaxation processes of oxygen deficient centers in silica

Physical review / B 67, 033202 (2003). doi:10.1103/PhysRevB.67.033202

Impact of contact resistance on the electrical properties of MoS2 transistors at practical operating temperatures

Molybdenum disulphide (MoS2) is currently regarded as a promising material for the next generation of electronic and optoelectronic devices. However, several issues need to be addressed to fully exploit its potential for field effect transistor (FET) applications. In this context, the contact resistance, RC, associated with the Schottky barrier between source/drain metals and MoS2 currently represents one of the main limiting factors for suitable device performance. Furthermore, to gain a deeper understanding of MoS2 FETs under practical operating conditions, it is necessary to investigate the temperature dependence of the main electrical parameters, such as the field effect mobility (μ) an…

Insight into the defect-molecule interaction through the molecular-like photoluminescence of SiO2 nanoparticles

Luminescence properties due to surface defects in SiO2 are the main keystone with particles that have nanoscale dimensions, thus motivating their investigation for many emission related applications in the last few decades. A critical issue is the role played by the atmosphere that, by quenching mechanisms, weakens both the efficiency and stability of the defects. A deep knowledge of these factors is mandatory in order to properly limit any detrimental effects and, ultimately, to offer new advantageous possibilities for their exploitation. Up to now, quenching effects have been interpreted as general defect conversion processes due to the difficulty in disentangling the emission kinetics by…

Dynamic modification of Fermi energy in single-layer graphene by photoinduced electron transfer from carbon dots

Graphene (Gr)&mdash

Emissive titanium dioxide nanoparticles synthesized py pulsed laser ablation in liquid phase

The remarkable applications of TiO2 nanomaterials, including, e.g. photocatalysis and dye-sensitized solar cells, have inspired in the last two decades an extensive amount of research aimed at understanding the properties of these materials. Photoluminescence is scarcely used to probe the electronic properties of TiO2, because neither bulk or nanosized TiO2 commonly display room-temperature emission. In particular, the fundamental luminescence due to the recombination of the self-trapped exciton in anatase TiO2 is typically observed only at low temperatures. We report the synthesis of luminescent titanium dioxide nanoparticles (NPs) by pulsed laser ablation of titanium in aqueous solution. …

A Comparative Study of Top-Down and Bottom-Up Carbon Nanodots and Their Interaction with Mercury Ions

We report a study of carbon dots produced via bottom-up and top-down routes, carried out through a multi-technique approach based on steady-state fluorescence and absorption, time-resolved fluorescence spectroscopy, Raman spectroscopy, infrared spectroscopy, and atomic force microscopy. Our study focuses on a side-to-side comparison of the fundamental structural and optical properties of the two families of fluorescent nanoparticles, and on their interaction pathways with mercury ions, which we use as a probe of surface emissive chromophores. Comparison between the two families of carbon dots, and between carbon dots subjected to different functionalization procedures, readily identifies a …

UV-Visible down conversion based on nanosized silica promising for CPV applications

Dependence of the emission properties of the germanium lone pair center on Ge doping of silica

We present an experimental investigation regarding the changes induced by the Ge doping level on the emission profile of the germanium lone pair center (GLPC) in Ge doped silica. The investigated samples have been produced by the sol-gel method and by plasma-activated chemical vapor deposition and have doping levels up to 20% by weight. The recorded photoluminescence spectra show that the GLPC emission profile is the same when the Ge content is lower than ∼ 1% by weight, whereas it changes for higher doping levels. We have also performed Raman scattering measurements that show the decrease of the D1 Raman band at 490 cm( - 1) when the Ge content is higher than 1% by weight. The data suggest…

Inkjet printing Ag nanoparticles for SERS hot spots

A novel inkjet printing based approach is developed for the fabrication of a customizable platform on glass substrates allowing for surface enhanced Raman spectroscopy (SERS) detection of analytes up to single hot spots generated by the spontaneous aggregation of Ag nanoparticles (Ag NPs) in pL scale droplets. After drying the printed droplets under ambient conditions, trace amounts of the analyte can be detected by SERS given the proximity to NP hot spots. By employing alizarin (10-5M) as a model system and scaling the ink droplet volume from 1 nL to 10 pL, the absolute quantity of hot spots has been derived in the printed droplets allowing detecting up to a few molecules in proximity to i…

Room Temperature Instability of E′γ Centers Induced by γ Irradiation in Amorphous SiO2

We study by optical absorption measurements the stability of E'(gamma) centers induced in amorphous silica at room temperature by gamma irradiation up to 79 kGy. A significant portion of the defects spontaneously decay after the end of irradiation, thus allowing the partial recovery of the transparency loss initially induced by irradiation. The decay kinetics observed after gamma irradiation with a 0.6 kGy dose closely resembles that measured after exposure to 2000 pulses of pulsed ultraviolet (4.7 eV) laser light of 40 mJ/cm(2) energy density per pulse. In this regime, annealing is ascribed to the reaction of the induced E'(gamma) centers with diffusing H(2) of radiolytic origin. At higher…

Synthesis and self-assembly of a PEGylated-graphene aerogel

Abstract In the frame of this work, we present, for the first time, the synthesis and self-assembly of an aerogel built by graphene oxide-polyethylene glycol. The synthetic route involves at first the coupling of GO with an amino-terminated polyethylene glycol sample by carbodiimide in aqueous environment, and the subsequent conversion of the hydrogel achieved into an aerogel via freeze-drying. The 3D PEGylated graphene-based aerogel, characterized by spectroscopic, morphological, structural and mechanical analyses, displays an ultralight and highly porous (99.7%) network and possesses high mechanical properties together with a good biocompatibility.

Effects of Pressure, Temperature, and Particles Size on O2 Diffusion Dynamics in Silica Nanoparticles

The O2 diffusion process in silica nanoparticles is experimentally studied in samples of average radius of primary particles ranging from 3.5 to 20 nm and specific surface ranging from 50 to 380 (m2/g). The investigation is done in the temperature range from 98 to 177 °C at O2 pressure ranging from 0.2 to 66 bar by measuring the interstitial O2 concentration by Raman and photoluminescence techniques. The kinetics of diffusion can be described by the Fick’s equation with an effective diffusion coefficient depending on the temperature, O2 pressure, and particles size. In particular, the dependence of the diffusion coefficient on the pressure and nanoparticles size is more pronounced at lower …

Entrapping of O2 Molecules in Nanostructured Silica Probed by Photoluminescence

We studied the emission of the O2 molecules embedded in fumed silica (amorphous silicon dioxide) nanoparticles differing for diameters and specific surface. By using a 1064 nm laser as a source we recorded both the O2 emission and the Raman signal of silica. Our experimental data show that the O2 emission/Raman signal (at 800cm-1) ratio decreases with increasing the specific surface both for the as received and the loaded samples. By performing a thermal treatment (600 °C for 2h) we modified the structure and the water content of the smallest nanoparticles without observing any significant change in the O2 emission/Raman signal ratio. Our data are explained by a shell model showing that the…

Phase change and O2 loading in mesoporous silica MCM41, MSU-H and MSU-F

Refractive index change dependence on Ge(1) defects inγ-irradiated Ge-doped silica

We present an experimental study regarding the effects of the $\ensuremath{\gamma}$ radiation on silica glass doped with Ge up to $10\text{ }000$ ppm molar produced by the sol-gel technique. We have determined the irradiation-induced changes in the refractive index $(\ensuremath{\Delta}n)$ as a function of the oxygen deficiency of the samples, evaluated from the ratio between the germanium lone pair centers (GLPC) and the Ge content. $\ensuremath{\Delta}n$ at 1500 nm have been estimated using optical-absorption spectra in the range 1.5--6 eV. We have found that $\ensuremath{\Delta}n$ is independent of Ge differences for GLPC/Ge values $l{10}^{\ensuremath{-}4}$, while it depends on Ge for la…

Near‐IR Radiation‐Induced Attenuation of Aluminosilicate Optical Fibers

The X-ray radiation-induced attenuation (RIA) growth kinetics are studied online in different single-mode aluminosilicate optical fibers in the near-IR (NIR) domain to evaluate their potential in terms of dosimetry. The optical fibers differ by Al contents, core sizes, drawing parameters, and also by a preform deposition process. The data show no dependence of the RIA on all these parameters, a positive result for the design of point or distributed radiation detectors exploiting RIA to monitor the dose. The RIA growth rate is unchanged for dose rates changing from 0.073 to 6.25 Gy(SiO2) s−1, and the RIA linearly increases with the dose up to 2 kGy(SiO2). Small but noticeable RIA changes are…

V Symposium SiO2 and Advanced Dielectrics

Modifications of optical absorption band of center in silica

Abstract We report an experimental study of the modifications induced by gamma ray irradiation and by thermal treatment of both the electron paramagnetic resonance (EPR) and the optical absorption spectra of the E γ ′ center in silica. Our data show that the main g-values of E γ ′ EPR signal change as a function of the irradiation dose together with a red shift of the peak position of the absorption band around 5.8 eV attributed to the same center. Changes in the opposite direction are observed in both signals after thermal treatments. The peak position change of the optical absorption band is in quantitative agreement with the g-values shift. This strict correlation is evidence for the exi…

Overview of radiation induced point defects in silica-based optical fibers

International audience; Silica-based optical fibers, fiber-based devices and optical fiber sensors are today integrated in a variety of harsh environments associated with radiation constraints. Under irradiation, the macroscopic properties of the optical fibers are modified through three main basic mechanisms: the radiation induced attenuation, the radiation induced emission and the radiation induced refractive index change. Depending on the fiber profile of use, these phenomena differently contribute to the degradation of the fiber performances and then have to be either mitigated for radiation tolerant systems or exploited to design radiation detectors and dosimeters. Considering the stro…

Thermally induced structural modifications and O2 trapping in highly porous silica nanoparticles

Abstract In this work we investigate by Raman spectroscopy the effect of isochronal (2 h) thermal treatments in air in the temperature range 200–1000 °C of amorphous silicon dioxide porous nanoparticles with diameters ranging from 5 up to 15 nm and specific surface 590–690 m2/g. Our results indicate that the amorphous structure changes similarly to other porous systems previously investigated, in fact superficial SiOH groups are removed, Si–O–Si linkages are created and the ring statistic is modified, furthermore these data evidence that the three membered rings do not contribute significantly to the Raman signal detected at about 495 cm−1. In addition, after annealing at 900 and 1000 °C we…

Environment assisted photoconversion of luminescent surface defects in SiO 2 nanoparticles

Abstract Time-resolved photoluminescence investigation on SiO 2 nanoparticles was carried out in controlled atmosphere, with the aim to discern the effects induced on the typical blue luminescence band by high power UV Nd:YAG laser photons (4.66 eV) and by some selected molecular species of the air (O 2 , N 2 , CO 2 , H 2 O). These factors ultimately determine both the brightness and photostability of the emitting defect, so as to limit the unique and attracting potentialities offered by this system in many applicative fields. Here it is highlighted that the effects due to photons and molecules, singularly considered, are not additive, the radiation being more dramatic in reducing the emiss…

Instantaneous diffusion effect on spin-echo decay: Experimental investigation by spectral selective excitation

The influence of the instantaneous diffusion process on spin-echo decay of ${E}_{\ensuremath{\gamma}}^{\ensuremath{'}}$ centers in gamma irradiated silica is experimentally probed by spectral selective excitation within their inhomogeneous resonance line. Our results evidence the different effectiveness of this dephasing mechanism on varying the resonance field, manifesting itself by a faster decay of the echo signal when generated by spin packets located in the central part of the spectrum. It is shown that the dependence of the instantaneous diffusion rate on the spectral position of echo-active spins reproduces the shape of the ${E}_{\ensuremath{\gamma}}^{\ensuremath{'}}$ centers resonan…

On-Line Characterization of Gamma Radiation Effects on Single-Ended Raman Based Distributed Fiber Optic Sensor

We report distributed temperature measurements based on Raman scattering performed during steady state $\gamma $ -ray irradiation at a dose rate of 1 kGy( ${\rm SiO}_{2}$ )/h and up to a total ionizing dose (TID) of $\sim 0.1\ \hbox{MGy}$ . We characterize on-line the evolution of the performances of a single-ended Raman distributed temperature sensor (RDTS) during the $\gamma $ -ray exposure of different classes of commercial multimode fibers (MMFs) acting as the sensing element. RDTS is influenced by the radiation-induced attenuation (RIA) phenomena leading to both large errors in the temperature measurements and a diminution of the useful sensing length. The amplitude of the radiation-in…

centers induced by γ irradiation in sol–gel synthesized oxygen deficient amorphous silicon dioxide

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 …

Ultraviolet-visible light-induced solarisation in silica-based optical fibres for indoor solar applications

Abstract The transmission performances of pure- and doped-silica (a-SiO2) optical fibres are compared during the exposure to a high-power broadband light source approximating the solar spectrum. From the Gaussian decomposition of the attenuation spectra, we found that Al- and P-doped fibres show a fast solarisation effect which leads to transmission degradation in the ultraviolet-visible range. Similarly, Ge-doped fibres undergo photoinduced colour-centre formation which, however, does not prevent visible-light propagation. One of the two tested pure-silica fibres results completely unaffected by light exposure whereas the other shows an absorption band probably due to the presence of chlor…

Optical absorption, luminescence, and ESR spectral properties of point defects in silica

Publisher Summary This chapter is divided into two parts: (1) In the introductory part, it describes the problems of point defects in a-SiO2, and (2) in the second part it discusses the experimental results. This chapter focuses on the Oxygen-Deficient Centers (ODCs) species in silica. This chapter investigates the ODC defects in a-SiO2 through their optical absorption, photoluminescence, and electron spin resonance activities. The effects of γ-ray irradiation are also investigated to evidence their ability to generate or transform structural defects. The aim of this chapter is to understand the optical activity of such defects to help in the characterization of their structure. The propert…

Structural inhomogeneity of Ge-doped amorphous SiO2 probed by photoluminescence lifetime measurements under synchrotron radiation.

We report a study of the photoluminescence (PL) time decay of the B-type center, characterized by an optical absorption band peaked at similar to 5.2 eV and two related PL bands peaked at similar to 3.2 eV and similar to 4.3 eV, in sol-gel Ge-doped a- SiO2 under excitation by synchrotron radiation. Measurements were carried out by excitation in UV and in vacuum-UV (VUV), and were performed in the temperature range from 8 K up to 300 K in order to isolate the effects of the intersystem-crossing process, proposed to link the two emission bands of the center. Repeating the time decay measurement at several emission energies falling inside the 4.3 eV band, we have observed a variation of the PL…

Aluminum oxide nucleation in the early stages of atomic layer deposition on epitaxial graphene

In this work, the nucleation and growth mechanism of aluminum oxide (Al2O3) in the early stages of the direct atomic layer deposition (ALD) on monolayer epitaxial graphene (EG) on silicon carbide (4H-SiC) has been investigated by atomic force microscopy (AFM) and Raman spectroscopy. Contrary to what is typically observed for other types of graphene, a large and uniform density of nucleation sites was observed in the case of EG and ascribed to the presence of the buffer layer at EG/SiC interface. The deposition process was characterized by Al2O3 island growth in the very early stages, followed by the formation of a continuous Al2O3 film (2.4 nm thick) after only 40 ALD cycles due to the isla…

'School adopts an experiment': the photoluminescence in extra-virgin olive oil and in tonic water

We report a laboratory activity, carried out along with high- and secondary-school students, that can be done to increase the interest of the young in scientific studies. Groups of selected students ‘adopted’ experiments at physics research laboratories, under the guidance of university researchers. Subsequently, the students demonstrated the experiments to the public at large during the annual science festival organized in Palermo by the association PalermoScienza, in collaboration with the University of Palermo. Experiments on the magnetic levitation of superconductors and on the photoluminescence of several substances were proposed. We discuss the experiment on photoluminescence as a cas…

Electron paramagnetic resonance investigation on the hyperfine structure of the center in amorphous silicon dioxide

Abstract We report an experimental investigation by electron paramagnetic resonance (EPR) spectroscopy on the hyperfine structure of the E δ ′ center in γ-ray irradiated amorphous silicon dioxide materials. This study has driven us to the determination of the intensity ratio between the hyperfine doublet and the main resonance line of this point defect. This ratio was obtained for a variety of silica samples and compared with the analogous ratio obtained for the E γ ′ defect. The comparison definitively confirms that the electronic wave function involved in the E δ ′ center is actually delocalized over four nearly equivalent Si atoms.

Twofold coordinated Ge defects induced by gamma-ray irradiation in Ge-doped SiO2

We report an experimental study by photoluminescence, optical absorption and Electron Paramagnetic Resonance measurements on the effects of exposure of Ge-doped amorphous SiO2 to gamma ray radiation at room temperature. We have evidenced that irradiation at doses of the order of 1 MGy is able to generate Ge-related defects, recognizable from their optical properties as twofold coordinated Ge centers. Until now, such centers, responsible for photosensitivity of Ge-doped SiO2, have been induced only in synthesis procedures of materials. The found result evidences a role played by gamma radiation in generating photosensitive defects and could furnish a novel basis for photosensitive pattern wr…

Effect of irradiation temperature on the radiation induced attenuation of Ge-doped fibers

International audience; The UV-visible radiation induced attenuation (RIA) was studied in Ge-doped optical fibers, during X-ray (10 keV) irradiations at different temperatures. By comparing the spectra recorded in dissimilarly irradiated samples we evidenced the impact of the irradiation temperature. In details, we highlighted that, from a certain dose, increasing the temperature the RIA decreases for wavelengths lower than 470 nm, whereas at higher wavelengths the RIA depends only on the dose. Such findings suggest that it is possible to distinguish the irradiation temperature by comparing the signal at two different wavelengths. From the microscopic point of view, it appears that the RIA …

Wide range excitation of visible luminescence in nanosilica

The visible luminescence of nanometer-sized silica particles (7 nm mean diameter) was investigated using time resolved spectroscopy. This luminescence is characterized by a wide excitation in the visible and ultraviolet range. The emission spectrum is centred at 2.72 eV with a full width at half maximum of 0.70 eV when excited above 3.5 eV, whereas it progressively empties on the high energy side when excited below 3.5 eV. Moreover, the lifetime falls in the ns timescale and decreases on increasing the emission energy. These features are due to the exceptionally broad inhomogeneous distribution of the emitting centres peculiar to the silica nanoparticles. © 2010 Elsevier B.V. All rights res…

Optical absorption band at5.8eVassociated with theEγ′centers in amorphous silicon dioxide: Optical absorption and EPR measurements

Line shape modifications induced by thermal treatment in the optical absorption and electron paramagnetic resonance (EPR) signals associated with the ${E}_{\ensuremath{\gamma}}^{\ensuremath{'}}$ center are experimentally investigated in various types of $\ensuremath{\gamma}$-irradiated amorphous silicon dioxide $(a\text{\ensuremath{-}}\mathrm{Si}{\mathrm{O}}_{2})$. The $g$ values of the EPR main resonance line of the ${E}_{\ensuremath{\gamma}}^{\ensuremath{'}}$ center show a shift correlated with the peak energy variation of the absorption band at about $5.8\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ associated with this defect. These spectroscopic changes are proposed to originate from structu…

S29i attribution of the 1.3 mT hyperfine structure of the E′γ centers in amorphous SiO2

We report an experimental investigation by electron paramagnetic resonance of the doublet of lines split by ∼1.3 mT and centered on the E′γ; center resonance line in the spectrum of irradiated amorphous SiO2 . Commercial and sol-gel materials, some of which subjected to hydrogen-deuterium exchange, were investigated. Exposure to γ or Β rays at room temperature of the samples and subsequent thermal treatments were carried out to induce the defects and to study their thermal stability. In all the materials used the ratio between the signal of the E′γ centers and that of the 1.3 mT doublet is constant and independent of the OH and OD contents. Furthermore, the 1.3 mT doublet and the E′γ center…

Study of color centers in optical fibers to be used for ITER plasma diagnostics

Thermally induced doping in controlled atmosphere on Graphene

Since its experimental breakthrough discovery in 2004, Graphene (Gr) paved the way for the study of the "flatland" of two dimensional (2D) materials. These systems are an emerging topic of interest in solid state physics and amterial sciences, but nont only, and today count a family of monoatomic layer of C atoms in hexgonal honey comb crystalline structure.

Raman spectroscopy study of β-irradiated silica glass

International audience; Natural and synthetic silica glass samples with different OH content have been submitted to β-irradiation at different doses from 106 to 5 × 109 Gy in a Van de Graaff accelerator. Structural changes under irradiation have been analyzed by Raman spectroscopy. The main findings are: (i) a decrease of the Si–O–Si angular dispersion and the average Si–O–Si angle as a function of dose and (ii) an increase of number of three-membered SiO4 ring concentration during irradiation. These results show therefore that purely electronic excitation from β-irradiation induces in a-SiO2 small but significant structural changes of the SiO4 membered ring statistics (size and dispersion)…

Comparison Between Point Defect Generation by $\gamma$-rays in Bulk and Fibre Samples of High Purity Amorphous ${\hbox {SiO}}_{2}$

We compare the E', H(I) and Si-ODC(II) contents in a low-OH high-purity a-SiO2 either in bulk or fibre forms. We found that the H(I) centre appears during irradiation and tend to increase with the dose if the fibre contains hydrogen excess. This behaviour is believed to be one the possible reason to explain the apparent radiation-sensitivity enhancement in the blue-UV spectrum when the fibre is hydrogenated and irradiated at high dose. However for the hydrogen-treated fibres, no experimental repeatability could be evidenced in the measurements of E' and Si-ODC(II) although an acceptable agreement was still found in normal samples. This suggests a possible complex reactional mechanisms in pr…

Fluorescent nitrogen-rich carbon nanodots with an unexpected β-C3N4nanocrystalline structure

Carbon nanodots are a class of nanoparticles with variable structures and compositions which exhibit a range of useful optical and photochemical properties. Since nitrogen doping is commonly used to enhance the fluorescence properties of carbon nanodots, understanding how nitrogen affects their structure, electronic properties and fluorescence mechanism is important to fully unravel their potential. Here we use a multi-technique approach to study heavily nitrogen-doped carbon dots synthesized by a simple bottom-up approach and capable of bright and color-tunable fluorescence in the visible region. These experiments reveal a new variant of optically active carbonaceous dots, that is a nanocr…

Alpha and deuteron irradiation effects on silica nanoparticles

We present an experimental investigation focused on the effects of alpha and deuteron irradiation on different silica nanoparticles. The study has been devoted also to characterize the induced point defects and the eventual structural modifications to evaluate the effects of the different irradiation source in comparison with the bulk materials. After irradiation up to about 10^16 ions cm^-2, we performed electron paramagnetic resonance (EPR), photoluminescence (PL), infrared (IR) absorption, Raman, and atomic force microscopy (AFM) measurements. We found that the two types of irradiation qualitatively induce comparable effects. Furthermore, irradiation generates the socalled twofold coordi…

Electron paramagnetic resonance line shape investigation of the Si-29 hyperfine doublet of the E'γ center in a-SiO2

We report an experimental study by electron paramagnetic resonance (EPR) spectroscopy of the E′γ center and of its hyperfine structure, consisting in a pair of lines split by 42 mT. Our results show that two types of E′γ centers can be distinguished on the basis of the EPR line shapes of their main resonance line and hyperfine structure. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Fluorescence of carbon dots embedded in a SiO2 host matrix

Carbon dots (CD) are an emerging class of recently discovered carbonaceous nanomaterials, which have attracted a large interest because of their bright and characteristically “tunable” fluorescence, and their potential for suggestive applications. Despite quite an intense research, the fundamental properties of these systems are poorly understood and still lively debated. Here we report on a series of experiments on N-doped CDs prepared by thermal decomposition of citric acid and urea. We studied these CDs by steady-state and nanosecond time-resolved photoluminescence, optical absorption, infrared absorption and atomic force microscopy. CDs (3 nanometers-sized) are found to emit two co-exis…

Growth of paramagnetic defects by gamma rays irradiation in oxygen-deficient silica

Abstract We report an electron paramagnetic resonance (EPR) study of gamma rays irradiation effects on an oxygen-deficient silica obtained from fused quartz. We have found that three types of E′ centers, E α ′ , E γ ′ and E δ ′ , and a paramagnetic defect in a spin triplet state (S = 1) are induced. The EPR signals dependence on the microwave power have been investigated. The concentrations of these centers as a function of gamma ray irradiation show that for high dose a limit value is reached suggesting a generation process from precursors.

Monolayer graphene doping and strain dynamics induced by thermal treatments in controlled atmosphere

Time dynamics of doping and strain induced in single layer graphene by thermal treatments up to 300 degrees C in vacuum, nitrogen, carbon dioxide and oxygen controlled atmosphere are deeply studied by Raman spectroscopy and they are compared with its morphological evolution investigated by Atomic Force Microscopy. The reaction dynamics in oxygen treatments is determined down to a time scale of few minutes as well as that of dedoping process made by water vapor treatment. The interplay of strain modification and doping effects is separated. The strain is clarified to be strongly influenced by the cooling time. The doping removal is dominated by the water vapor, showing that the concentration…

Experimental evidence for two different precursors of E’γ centers in silica

Electron paramagnetic resonance measurements of concentration and line shape of centers induced by γ ray irradiation are presented for natural and synthetic commercial silica with different OH contents. Synthetic materials with OH content >200 ppm by weight show one line shape for all investigated doses. In contrast, the other materials show a different line shape at low irradiation doses. Differences are also observed in the concentration growth of the centers in synthetic wet materials and in the other materials. The results are interpreted as evidence of two centers distinguishable by their line shape and having different precursors.

Status of the EPIC thin and medium filters on-board XMM-Newton after more than 10 years of operation I: laboratory measurements on back-up filters

After more than ten years of operation of the EPIC camera on board the X-ray observatory XMM-Newton, we have reviewed the status of its Thin and Medium filters by performing both laboratory measurements on back-up filters, and analysis of data collected in-flight. We have selected a set of Thin and Medium back-up filters among those still available in the EPIC consortium, and have started a program to investigate their status by different laboratory measurements including: UV/VIS transmission, X-ray transmission, RAMAN IR spectroscopy, X-Ray Photoelectron Spectroscopy, and Atomic Force Microscopy. We report the results of the measurements conducted up to now, and point out some lessons lear…

Combined heat and power generation with a HCPV system at 2000 suns

In the framework of the FAE “Fotovoltaico ad Alta Efficienza” (“High Efficiency Photovoltaic”) Research Project funded by the Sicilian Region under the program PO FESR Sicilia 2007/2013 4.1.1.1, we have developed an innovative solar CHP system for the combined production of heat and power at the high concentration level of 2000 suns [1]. This work shows the experimental results obtained on FAE-HCPV modules and analyses the behaviour of the system. The solar radiation is concentrated on commercial InGaP/InGaAs/Ge triple-junction solar cells designed for intensive work. The primary optics is a rectangular off-axis parabolic mirror (with a size of 46x46 = 2116 cm2 in a projection normal to the…

Effects induced by UV laser radiation on the blue luminescence of silica nanoparticles

The effects induced on the blue luminescence centered around 2.8 eV, characteristic of silica nanoparticles, were investigated by monitoring its intensity during and after exposure to the third and the fourth harmonic of a Nd:YAG pulsed laser. The luminescence trend is found to be dependent on the UV photon energy: 3.50 eV photons induce a partial bleaching followed by a recovery in the post-irradiation stage; 4.66 eV photons cause a total bleaching permanent after the irradiation. These results are interpreted as the conversion of luminescent defects towards stable and metastable configurations.

Metal thin-film temperature sensor embedded in heat-sink for CPV cells characterization

The efficiency of a photovoltaic cell is dependent on its temperature, for this reason an accurate measurement of this parameter is important to fully characterize the device and to optimize its performance. For CPV applications a significant heat flux is needed to remove excess heat from the cell towards a heat sink, making it difficult to derive the cell temperature. In fact, measurements performed directly between the cell and the heat-sink, by use of commercial bulk sensors, would produce a significant disturbance in the heat flow; on the other hand, a measurement performed out of the cell / heat sink axis would be subject to large uncertainties, due to the high radial temperature gradi…

Streptomyces coelicolor extracellular vesicles

This study may reveal the importance of extracellular vesicles in the physiology of S. coelicolor and may also have important biotechnological implications.

Coupled theoretical and experimental studies for the radiation hardening of silica-based optical fibers

International audience; We applied theoretical and experimental spectroscopy tools to ad hoc silica-based "canonical" samples to characterize the influence of several dopants and of some drawing process parameters on their radiation sensitivities. We present in this paper, the recent advances and results occurring from our coupled approach. On the experimental side, we studied the doping influence on the response of optical fibers and showed that changing the drawing parameters has a negligible influence on the fiber response in the case of specialty fibers. We focus mainly on the ${rm SiE}^prime$ defect that is observed through Electron Paramagnetic Resonance (EPR) measurements in all cano…

Irradiation temperature influence on the in-situ measured radiation induced attenuation of Ge-doped fibers

International audience; We report an experimental investigation on the radiation induced attenuation (RIA) in the ultraviolet-visible domain for Ge-doped optical fibers, during X-rays (10 keV) exposure at different temperatures. The objective is to characterize the impact of the irradiation temperature on the RIA levels and kinetics. Our data highlight that for dose exceeding 1 kGy(SiO2) the RIA spectrum changes with the irradiation temperature. In particular, for wavelengths below 470 nm the RIA depends both on the dose and on the irradiation temperature, whereas at higher wavelengths the RIA depends only on the dose. From the microscopic point of view the origin of this behavior is explai…

Synthesis of luminescent glass monoliths embedding water-soluble Carbon dots

Carbon dots (CD) are an emerging class of nanomaterials, currently motivating an intense scientific interest because of their bright and characteristically tunable fluorescence, and their possible applications such as sensors, lasers, imaging agents, white light emitting devices [1]. While most studies focused on CDs in liquid phase, a strong effort is being recently devoted to produce fluorescent solids embedding highly dispersed CDs. Many of these procedures are elaborate and require pre-functionalization of the dots [2]. Here we report a novel and very facile route to prepare glass monoliths containing CDs with no need of pre-functionalization of the dots. Our low-cost synthesis method p…

Properties of methyl radical trapped in amorphous SiO2 and in natural SiO2-clathrate Melanophlogite

Abstract We report an experimental investigation by electron paramagnetic resonance (EPR) on methyl radical (CH3 ) observed in γ-ray irradiated high-purity amorphous silicon dioxide (a-SiO2) and in a polycrystalline sample of Melanophlogite, a rare natural form of SiO2-clathrate. From the analysis of the EPR spectra we estimate the correlation time of the hindered rotational motion of CH3 molecules at T = 77 K in the two different materials. This physical quantity gives a quantitative measure of the freedom of motion of CH3 molecules trapped in the two solid systems, putting forward relevant information on the properties of the cavities/interstices in which the radicals are confined. In par…

Generation of a 7.4 mT ESR doublet induced by γ rays in amorphous-SiO2

Abstract Paramagnetic defects induced by γ rays, in a dose range from 1 to 1000 Mrad, have been investigated by electron spin resonance (ESR) spectroscopy in various types of natural and synthetic silica, having different OH content. A doublet with a field splitting of 7.4 mT, arising from the hyperfine interaction of an unpaired electron with a H nucleus associated with the H(I) center, was detected in all the investigated samples. This ESR structure exhibits a sublinear growth with the γ dose linearly correlated with the γ-induced photoluminescence band at 4.4 eV. The intensity ratio of these two signals depends on the OH content of the sample. Our results agree with a model in which the …

Resonance Raman of oxygen dangling bonds in amorphous silicon dioxide

We investigate the origin of a resonance Raman band induced by ionizing radiation in amorphous silicon dioxide (silica glass), which can be detected under ultraviolet laser excitation. A silica sample, rich of oxygen-excess related defects, was prepared by treating some length of a pure-silica-core multimode fiber in an O2 atmosphere (at high temperature and pressure) and by irradiating it with X-rays at 10 MGy(SiO2) dose. A micro-Raman study revealed a gaussian band peaking at 896 cm−1 with a full width at half maximum of 32 cm−1, which could be detected by exciting the sample with the 325-nm line of a HeCd laser. This spectral feature is absent in the Raman spectra performed with the 442-…

Variability of the Si-O-Si angle in amorphous-SiO2 probed by electron paramagnetic resonance and Raman spectroscopy

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.

Silica-Based NIR Nano-Emitters for Applications in Vivo and Process for Production Thereof

Production of paramagnetic and phosphorescent nanoprobes, obtainable starting from nanometric silica particles by methods of synthesis and enrichment with O2 following suitable thermal treatments in a controlled environment. The nanoprobes thus obtained display emission in the near infrared (NIR), are excitable in the visible and in the NIR, and are characterized by a lifetime of the order of one second. These nanoprobes have considerable scientific and commercial potential in the market of the confocal spectroscopy for bio-imaging and in the market of the medical pharmaceutical applications of drug labelling and drug delivery.

Influence of Drawing Conditions on the Properties and Radiation Sensitivities of Pure-Silica-Core Optical Fibers

International audience; The structure and radiation sensitivities of three different pure-silica-core fluorine-doped-cladding optical fibers, made from the same original preform, were investigated by several experimental techniques. The fibers were obtained by changing the drawing speed and tension in the typical ranges of values used for the radiation-tolerant waveguides. The Raman spectroscopy revealed no significant difference among the fibers before irradiation. At variance, the comparison between the fibers and their associated preform highlighted an increase in the amplitude of the D2 band that is related to the concentration of 3 member rings. Moreover, in the zones where the D2 incr…

Silica nanoparticle core structure examined by the E?Si? center 29Si strong hyperfine interaction

Abstract β-Ray irradiation up to 1.2 GGy was employed to induce E′Si γ defects and to study the structure of silica nanoparticles with diameters from 7 up to 20 nm. Defect concentration and their 29 Si strong hyperfine doublet were investigated through electron paramagnetic resonance measurements. Our data indicate that stable defects are located in the nanoparticle core. Furthermore, the E′Si γ hyperfine interaction evidences that the core structure is denser than bulk silica and independent from the particle size. Finally, we put in evidence that the core structure is stable and unaffected by the irradiation in the investigated dose range maintaining the specific features of nanoparticles.

Ag nanoparticles agargel nanocomposites for SERS detection of cultural heritage interest pigments

Agarose gel (agargel) composites with commercial and laboratory made silver nanoparticles were prepared by a wet solution method at room temperature. The gel composites were used for pigment extraction and detection by Raman spectroscopy. Red (alizarin) and violet (crystal violet) pigments deposited on paper were extracted by the composites and were investigated by micro-Raman spectroscopy. Evaluation was carried out of the surface-enhanced Raman spectroscopy (SERS) effect induced by the silver nanoparticles embedded in the gel. A kinetic approach as a function of time was used to determine the efficiency of pigments extraction by composites deposition. A non-invasive extraction process of …

Influence of Ge doping level on the EPR signal of Ge(1), Ge(2) and E'Ge defects in Ge-doped silica

Abstract We present an experimental investigation on the Ge doping level dependence of the Electron Paramagnetic Resonance (EPR) signal spectral features of the Ge(1), Ge(2) and E'Ge defects induced in Ge doped silica. We have studied samples produced by sol–gel or PCVD techniques and doped with different amounts of Ge up to 20% by weight. The samples were gamma or beta ray irradiated and successively they were thermally treated to isolate the EPR signals of the different point defects. The data show that the EPR line shapes of the Ge(1) and the Ge(2) centers are progressively modified for doping level higher than 1%, whereas the line shape of the E'Ge defect appears independent from the do…

Radiation Response of Ce-Codoped Germanosilicate and Phosphosilicate Optical Fibers

We report an experimental investigation on the effects of Ce-codoping in determining the radiation response of germanosilicate and phosphosilicate Optical Fibers (OFs) in the UV-Visible domain and up to doses of $1~\hbox{MGy}({\rm SiO}_{2})$ . We show that the addition of Ce strongly impacts the Radiation Induced Attenuation (RIA) of both types of fibers. In the first case the radiation induced losses increase, whereas in the second one decrease. By combining the online RIA measurements with the Electron Paramagnetic Resonance (EPR) ones, we are able to infer the basic microscopic mechanisms taking place under irradiation, which involve the cerium codopant and some of the known Ge-related o…

Diffusion process of molecular oxygen in silica nanoparticles

Ge-doping dependence of gamma-ray induced germanium lone pair centers in Ge-doped silica

We report an experimental study on the y irradiation effects in Ge-doped sol-gel silica samples doped with Ge from 10 2 up to 10 4 part per million molar. The samples were exposed to the radiation generated by a 60 Co source up to an accumulated dose value of 10 MGy. Our data evidence that the γ irradiation significantly increases the number of Germanium Lone Pair Centers (GLPC). Such defects are induced with a concentration that depends on the Ge content of the employed material in those samples where no optical activity related to -s GLPC was detected before irradiation. Furthermore an increase of the GLPC concentration was detected also in a sample that already contains this defect after…

Transient and Steady-State Radiation Response of Phosphosilicate Optical Fibers: Influence of H2 Loading

The radiation response of a phosphorus-doped multimode optical fiber is investigated under both transient (pulsed X-rays) and steady-state ( $\gamma $ - and X-rays) irradiations. The influence of a H2 preloading on the fiber radiation-induced attenuation (RIA) in the 300–2000-nm wavelength range has been characterized. To better understand the impact of this treatment, online behaviors of fiber samples containing different amounts of gas are compared from glass saturation (100%) to less than 1%. In addition to these in situ experiments, additional postirradiation spectroscopic techniques have been performed such as electron paramagnetic resonance or luminescence measurements to identify the…

The relevance of point defects in studying silica-based materials from bulk to nanosystems

The macroscopic properties of silica can be modified by the presence of local microscopic modifications at the scale of the basic molecular units (point defects). Such defects can be generated during the production of glass, devices, or by the environments where the latter have to operate, impacting on the devices’ performance. For these reasons, the identification of defects, their generation processes, and the knowledge of their electrical and optical features are relevant for microelectronics and optoelectronics. The aim of this manuscript is to report some examples of how defects can be generated, how they can impact device performance, and how a defect species or a physical phenomenon …

E’_gamma centers induced by gamma irradiation in sol-gel synthesized oxygen deficient amorphous silicon dioxide.

Hyperfine structure of the E'delta centre in amorphous silicon dioxide

Photoluminescence time decay of surface oxygen-deficient centers in pure and Ge-doped silica

Interfacial disorder of graphene grown at high temperatures on 4H-SiC(000-1)

This paper presents an investigation of the morphological and structural properties of graphene (Gr) grown on SiC(000-1) by thermal treatments at high temperatures (from 1850 to 1950 °C) in Ar at atmospheric pressure. Atomic force microscopy and micro-Raman spectroscopy showed that the grown Gr films are laterally inhomogeneous in the number of layers, and that regions with different stacking-type (coupled or decoupled Gr films) can coexist in the same sample. Scanning transmission electron microscopy and electron energy loss spectroscopy shoed that a nm-thick C-Si-O amorphous layer is present at the interface between Gr and SiC. Basing on these structural results, the mechanisms of Gr grow…

Structure effects induced by high mechanical compaction of STAM-17-OEt MOF powders

Financial support by PJ-RIC-FFABR_2017 and the EPSRC grant EPSRC industrial CASE award (grant EP/N50936X/1) are acknowledged. The research programme Nanoporous materials (P1-0021) financially supported by Slovenian Research Agency (ARRS) is acknowledged as well. Metal-organic frameworks (MOFs) are promising materials for many potential applications, spacing from gas storage to catalysis. However, the powder form of which they are generally made is not suitable, mainly because of the low packing density. Powder compaction is therefore necessary, but also challenging because of their typical mechanical fragility. Indeed, generally, they undergo irreversibly damages upon densification processe…

Luminescence decay excited by synchrotron radiation in gamma-irradiated alpha-quartz