A. Quaranta

Experimental study of copper-alkali ion-exchange in glass

Copper–alkali ion exchange was performed by immersing different silicate glasses (soda-lime and BK7) in different molten eutectic salt baths (CuSO4:Na2SO4 and CuSO4:K2SO4). The obtained optical waveguides were characterized by m-lines spectroscopy for the determination of refractive index profiles, and by secondary ion mass spectrometry for the concentration profiles of the ion species involved in the exchange process. The different oxidation states of copper inside the glass structure were studied by electron paramagnetic resonance and x-ray absorption techniques. Interdiffusion copper coefficients were also determined. The Cu–alkali exchange was observed to give rise to local structural rearrangement of the atoms in the glass matrix. The Cu+ ion was found to mainly govern the exchange process, while competition between Cu–Na and K–Na exchanges occurred when a potassium sulfate bath was used. In this case, significant waveguide modal birefringence was observed.

Use of silica microspheres having refractive index similar to bacteria for conversion of flow cytometric forward light scatter into biovolume

This research describes an alternative approach for the rapid conversion of flow cytometric Forward Angle Light Scattering (FALS) into bacterial biovolume. The Rayleigh-Gans theory was considered for explaining the main parameters affecting FALS intensity: sensitivity analysis of the model was carried out, taking into account the parameters characteristic of bacterial cells and characteristics of the flow cytometer. For particles with size in the typical range of bacteria, the FALS intensity is affected mainly by volume and refractive index of bacterial cells and is approximately independent of the shape of the cells. The proposed conversion from FALS intensity into bacterial biovolume is based on a calibration curve determined by using silica microspheres having relative refractive index as far as possible similar to that of bacteria. The approach was validated for two different flow cytometers (the first equipped with an arc lamp and the second with a laser) by comparing the biovolume distribution obtained from FALS conversion with the biovolume measured conventionally under epifluorescence microscopy. The specific case of bacteria taken from a WWTP was addressed. Compared to the time-consuming conventional microscopic approach, the application of FALS for sizing bacterial biovolume could be a very promising tool being completed in few minutes, simultaneously to the enumeration of bacteria during the flow cytometric analysis.

Structure and optical properties of Au-polyimide nanocomposite films prepared by ion implantation

Au-polyimide nanocomposites have been synthesized by implanting different doses of Au+ ions in 100nm thick films of pyromellitic dianhydride-4,4′ oxydianiline polyimide, prepared by glow discharge vapor deposition polymerization. Unambiguous evidence of Au nanoclusters growth is found only at the highest implantation doses (5×1016Au+∕cm2). Structural, compositional, and optical characterizations show that the implantation induces the compactation of the initial film due to H and C loss. The resulting structure is a composite containing 2–3nm gold nanoparticles arranged in a layer of about 40nm and, just beneath the sample surface, a 15nm thick carbon-rich layer. Optical simulations suggest the presence of a gold-carbon core-shell structure in the nanoparticles.

Silver nanocluster formation in ion-exchanged glasses by annealing, ion beam and laser beam irradiation: An EXAFS study

Extended X-ray absorption fine structure analysis is used to determine the silver local environment in silicate glasses doped by the Ag-alkali ion-exchange process, followed by different treatments, namely, ion irradiation, thermal annealing in reducing atmosphere, laser irradiation. The obtained results indicate that metal nanocluster composites with different cluster structures may be formed with these multistep methodologies, pointing out the role of the preparation parameters in giving rise to different features. Lattice parameters and cluster diameter were determined by grazing incidence X-ray diffraction.

SYNTHESIS OF GaN QUANTUM DOTS BY ION IMPLANTATION IN DIELECTRICS

GaN nanocrystals (in the wurtzite phase) were synthesized by sequential implantation of Ga and N ions into either crystalline (quartz, sapphire) or amorphous (silica) dielectrics, followed by annealing of the samples in flowing NH3 gas at 900 °C. GaN was formed by reaction of implanted Ga with NH3 combustion products and/or via conversion of Ga oxide/oxynitrides. A blueshift of the near-band-edge photoluminescence (quantum-confinement effect) was observed for GaN nanocrystals with size ⩽2–3 nm, present in all the substrates.

Optical and Scintillation Properties of Polydimethyl-Diphenylsiloxane Based Organic Scintillators

Polysiloxane based scintillators with high light yield have been synthesized. The polymer consists in cross-linked polydimethyl-co-diphenylsiloxane with different molar percentages of phenyl units. 2,5-diphenyl oxazole (PPO) and 2,5-bis(5-ter-butyl-2-benzoxazolyl)thiophene (BBOT) have been dispersed in the polymer as dopants. The energy transfer and scintillation capabilities have been investigated, for two different amounts of phenyl groups in the polymer network and for different concentrations of dye molecules, by means of fluorescence spectroscopy, ion beam induced luminescence (IBIL) and scintillation yield measurements with ¿ particles from an 241Am source. The luminescence features and the scintillation yields have been correlated to the composition of the scintillators.

Organic Semiconducting Single Crystals as Next Generation of Low-Cost, Room-Temperature Electrical X-ray Detectors

Direct, solid-state X-ray detectors based on organic single crystals are shown to operate at room temperature, in air, and at voltages as low as a few volts, delivering a stable and reproducible linear response to increasing X-ray dose rates, with notable radiation hardness and resistance to aging. All-organic and optically transparent devices are reported.

Microstructural evolution of thermally treated low-dielectric constant SiOC:H films prepared by PECVD

Low-dielectric constant amorphous-SiOC:H films were prepared by using plasma-enhanced chemical vapor deposition technique and then treated in vacuum at temperatures ranging between 400 and 900°C for 30 min. The evolution of the film microstructure was investigated by means of vibrational spectroscopy, i.e., by Raman scattering and Fourier transform infrared (FTIR) absorption. FTIR absorption spectra consist of several vibrational bands: namely, Si-O-Si rocking at 450 cm -1 , Si-O-Si asymmetric stretching at 1034 cm -1 , symmetric deformation of -CH 3 group in Si-CH 3 configuration at 1270 cm -1 , C-H stretching of -CH x groups in the region between 2750 and 3050 cm -1 , and -OH related vibrational bands in the range between 3150 and 3700 cm -1 . On annealing the samples up to 500°C, it is observed that both spectral shape and intensity exhibit minor changes with increasing temperature, indicating that this material exhibits a good thermal stability. In samples undergoing thermal treatments at temperatures higher than 500°C a progressive hydrogen release occurs which is evidenced by the intensity decrease of the C-H x related bands. A deeper inspection of the evolution of these spectral features evidenced that thermal treatment of samples induces a preferential release of hydrogen than of -CH x groups, which results in the transformation of -CH 3 groups into -CH 2 groups. Raman spectroscopy carried out on the same samples evidences the presence of carbon nanoclusters. In fact, in the films treated at temperatures higher than 500°C both D and G bands, typical of sp 2 -hybridized carbon, are observed, due to the formation of C-C bonds within the film following the hydrogen release. The intensity of these D and G bands becomes more pronounced in samples annealed at higher temperatures, thus indicating a progressive precipitation of carbon within the amorphous matrix of films. In conclusion, the H-release process is accompanied by a structural rearrangement with the formation of an amorphous silicon oxide matrix, and free-carbon inclusions embedded in it.

Polymer film degradation under ion irradiation studied by ion beam induced luminescence (IBIL) and optical analyses

In this work the real time evolution of luminescence properties of ion-irradiated polymer thin films was studied by means of ion beam induced luminescence (IBIL) measurements. The plastic scintillator NE102, a fluorinated polyimide and PMMA were irradiated by H+ (1.85 MeV), He+ (2.2 MeV) and N+ (1.2 MeV). The optical properties after irradiation were analysed with UV–Visible absorption, fluorescence spectroscopy and Fourier transform infrared spectroscopy (FT-IR), in order to correlate the IBIL measurements to the evolution of the optical and chemical properties of the matrix.

Novel polysiloxane-based scintillators for neutron detection

Polysiloxane-based scintillators are promising for employment in harsh environments, owing to their outstanding radiation resistance and thermal properties over the traditional plastics (polyvinyltoluene and polystyrene). In this work, cross-linked polydimethyl-co-diphenylsiloxane (PMPS) scintillators with 22% molar percentage of diphenylsiloxane units have been synthesised. 2,5-Diphenyloxazole and Lumogen Violet (BASF) were employed as primary and secondary fluor, respectively. Thermal neutrons sensitivity was achieved through the addition of 3% wt of ortho-carborane. Scintillation yield measurements were made by exciting with (241)Am alpha source samples with different concentrations of dye molecules. PMPS-based scintillators with ∼50% light yield as compared with the commercial plastic scintillator EJ212 were produced. The scintillation yield of the B-loaded samples under thermal neutrons was tested with a moderated Am-Be source and compared with the commercially available EJ254 (5% wt B). 2.2 MeV neutrons were produced by irradiating with a 4.0 MeV proton beam an LiF target, thus exploiting the reaction (7)Li(p,n)(7)Be. Time-of-flight measurements were performed to distinguish pulses due to neutrons or gamma. A similar test was performed with an EJ254 commercial scintillator for comparison. Using the same set-up, polyethylene bricks were used as a moderator to produce low-energy neutrons for testing B-loaded samples.