S. Carturan

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.

Novel polysiloxane and polycarbosilane aerogels via hydrosilylation of preceramic polymers

We report new polysiloxane and polycarbosilane aerogels, which have been obtained by crosslinking Si–H-containing polymers with a CC-containing crosslinker via hydrosilylation reactions. The crosslinking reaction has been carried out in a highly diluted solution using up to 97 vol% of solvent. The obtained aerogels have a colloidal structure with meso- and macropores. Density as low as 0.17 g cm−3 has been reached, which implies a porosity of ca. 84 vol%.

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.

Glow discharge vapour deposition polymerisation of polyimide thin coatings

Abstract The glow discharge vapour deposition polymerisation method for the preparation of polyimide coatings is presented. This method involves the deposition of the monomer vapours onto a solid substrate in a vacuum chamber. The evaporation of the monomers is obtained by using standard radio frequency magnetron sputtering equipment: the monomer powders are placed on a sputtering source and bombarded by low energy He ions at pressures in the range of 10–20 Pa. By a momentum-transfer mechanism, the ions dissipate their energy causing target heating and sublimation of the monomer molecules. The emission of volatile species from the monomers target surface and their interactions with the plasma components are studied by mass spectrometry and optical emission spectroscopy. Polyimide coatings with thickness ranging from 200 nm to 3 μm have been deposited onto silicon single crystals, sapphire and polyimide substrates. SEM micrographs of these coatings show a homogeneous and crack-free surface. The as-deposited films are mainly made of a mixture of polyamic acid and non-reacted monomers, as revealed by Fourier transform infrared spectroscopy. The imide peaks clearly appear only after thermal treatment (typically 250°C, 1 h, in air or argon). The electrical properties of the polyimide coatings (i.e. bulk and sheet resistivity and dielectric breakdown voltage) are those typical of an insulating material and comparable with the commercial polyimide. These films are characterised by good adhesion to the silicon, sapphire and other polyimide substrates. Chemical resistance to some reagents (acetone, hydrogen peroxide, nitric and hydrofluoric acid) has also been tested.

Optical Study of The Matrix Effect on the ESIPT Mechanism of 3-HF Doped Sol-Gel Glass

In this work we report our preliminary results on the synthesis and characterization of the optical properties of 3-hydroxyflavone (3-HF) doped sol-gel derived glass, to be applied as a wavelength shifting medium in GaAs based near UV-VIS detectors in order to extend the device response down to 350 nm. As already reported by several authors, the intramolecular excited-state proton transfer process (ESIPT) in the 3-HF molecule is strongly affected by the chemical environment. For this reason the evolution of the emission features of the synthesized glasses was investigated by changing the chemical nature of precursor alkoxides used in the sol-gel process. The influence of chemical surroundings on the ESIPT process was studied by analysing the samples with fluorescence spectroscopy. FT-IR spectroscopy was performed in order to study the chemical interactions between the host matrix and the encapsulated dye molecule. The main result of this work is that the Stokes-shifted emission from the 3-HF tautomeric form is enhanced at increasing trifunctional alkoxide amount and at decreasing polarity of the non-hydrolizable groups.

Steering of an ultrarelativistic proton beam by a bent germanium crystal

Curved crystals, thanks to the electrostatic potential generated by the coherent atomic structure, may deflect ultrarelativistic charged particles by means of channeling and volume reflection effects. Most of the experimental knowledge about these phenomena was gathered with Si crystals, though the performance could be improved by using materials with a larger atomic number. In this letter, we investigate planar and axial channeling and volume reflection in a high quality Ge short strip crystal. All the effects are demonstrated to occur in agreement with theoretical expectations, which take into account the stronger confinement potential for an ideal Ge crystal.

Novel 3D silicon sensors for neutron detection

In this paper we report a novel 3D sensor structure to be used as a neutron detector in combination with an organic converter material based on polysiloxane. The first prototypes of the proposed device are presented, with emphasis on the experimental characterization. Selected results from the functional tests (with alpha particle source and pulsed laser scans) are discussed with the aid of TCAD simulations.

Hybrid detectors of neutrons based on 3D silicon sensors with PolySiloxane converter

We report on the first prototypes of hybrid detectors for neutrons from the INFN HYDE project. Devices consist of 3D silicon sensors coupled to PolySiloxane-based converters. The sensor design and fabrication technology are presented, along with initial results from the functional characterization of the devices in response to radioactive sources and neutron beams of different energies.

Hybrid detectors for neutrons combining phenyl-polysiloxanes with 3D silicon detectors

We report on the initial results of a research project aimed at the development hybrid detectors for fast neutrons by combining a phenyl-polysiloxane-based converter with a 3D silicon detector. To this purpose, new 3D sensor structures have been designed, fabricated and electrically tested, showing low depletion voltage and good leakage current. Moreover, the radiation detection capability of 3D sensors was tested by measuring the signals recorded from alpha particles, gamma rays, and pulsed lasers. The converter has been poured into the 3D cavities with excellent coupling, as confirmed by cross-section SEM analyses. Preliminary tests with neutrons have been carried out on the first hybrid detector prototypes at the CN accelerator of INFN LNL. The device design and technology are discussed, along with the first results from the electrical and functional characterization.

Red emitting phenyl-polysiloxane based scintillators for neutron detection

In this work, the performances of new red emitting phenyl- substituted polysiloxane based scintillators are described. Three dyes were dispersed in a phenyl-polysiloxane matrix in order to shift the scintillation wavelength towards the red part of the visible spectrum. PPO, Lumogen Violet (BASF) and Lumogen Red (BASF) were mixed to the starting resins with different wt. % and the analysis of the different samples was performed by means of fluorescence measurements. The scintillation yield to alpha particles at the different dye ratios was monitored by detecting either the full spectrum or the red part of the emitted light. Finally, thin red scintillators with selected compositions were coupled to Avalanche Photodiode sensors, which are usually characterized by higher efficiency in the red part of the spectrum. An increased light output of about 17% has been obtained comparing the red scintillators to standard blue emitting systems. Preliminary results on the detection of fast neutrons with the APD-red scintillator system are also presented.