G. Maggioni

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.

Development of micro-strip gas chambers for high rate operation

Abstract We describe the developments of micro-strip gas chambers able to withstand the very high rates foreseen for operation as vertex detector in high luminosity experiments, and for applications in medical diagnostics. To avoid surface charging-up processes, we have used as supports electron-conducting glass with resistivity in the range 109 to 1012 Ω cm, and boro-silicate glass with thin coatings of lead silicate with surface resistivity between 1014 and 1016 Ω/□. A systematic research has been undertaken to find the purity levels of the gas filling and of the manufacturing materials necessary for long-term stability of operation, the goal being 10 years of operation at LHC (or about 140 mC cm−1 of collected charge). In particular, we have tested high-grade polymers that can be injection-moulded into the shape required to make MSGC frames, and epoxies that satisfy the stringent outgassing requirements. A strong dependence of ageing from the charge rate used in the irradiation has been found, indicating that measurements realized at high current densities may be too optimistic in terms of expected lifetime of the detectors; this seems to be particularly true for MSGCs manufactured on high resistivity boro-silicate glass.

Effects of ion bombardment and gas incorporation on the properties of Mo/a-Si:H multilayers for EUV applications

Abstract A study of Mo/a-Si:H multilayer for EUV mirrors produced by rf-magnetron sputtering in pure Ar, Xe and Ar/H 2 gas mixtures is presented. The high reflectance mirrors are designed for solar space experiments at 17, 19 and 30.4 nm and for the lithography applications at 13 nm. The multilayers are grown in different ion bombardment conditions determined by different bias levels of the substrate. Plasma diagnostics are performed to correctly evaluate flux and energy of plasma ions bombardment. The a-Si:H layers have been obtained by introducing H 2 gas in the sputtering chamber at different partial pressures during silicon deposition. The deposition rates as well as the composition of Mo and Si layers have been investigated by Ion Beam Analysis (RBS and ERDA). The coating microstructure has been characterised primarily by X-ray micro-diffraction (micro-XRD). X-Ray Reflection analysis (XRR) has been carried out to investigate the layer density and the multilayer structure. RBS analyses show that noble gas (Ar, Xe) incorporation is limited to the Si layers and depends on the sample bias. Noble gas concentration is correlated to the different ion bombardment growth conditions that influence also the (110) orientation of Mo nano-crystals. ERD analyses of Si layers show hydrogen incorporation up to 30 at.% as a function of the H 2 partial pressure. Hydrogen incorporation leads to a decrease of the a-Si layer density. Hydrogen content in Mo layers is less than 0.5 at.% even at the highest H 2 partial pressure. The optical properties of these mirrors have been characterised by EUV reflection measurements.

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.

Production of novel microporous porphyrin materials with superior sensing capabilities

New robust microporous cobalt 5,10,15,20-meso-tetraphenyl porphyrin (CoTPP) thin films for sensing applications have been produced by a novel plasma-based deposition technique named Glow Discharge Induced Sublimation (GDS). CoTPP films have been also produced by conventional vacuum evaporation (VE) and spin coating (SPIN) methods for comparison. The chemical properties of the films were assessed by FT-IR and ESI-MS analyses demonstrating the integrity and the purity of the GDS films. The physical properties of the samples were thoroughly analysed: thickness measurements coupled with surface density analyses showed the impressive free volume of the GDS samples (30 times higher than that of VE ones), SEM images show the extremely rough morphology of GDS samples, and physisorption measurements indicate both the extremely high specific surface area (184 m2 g−1) and the microporosity of the GDS porphyrin films. The sensing capabilities of the samples were investigated by exposing them to low concentrations of NO2 and by monitoring their optical absorption changes. These measurements clearly demonstrate that the GDS process leads to superior sensing materials as a result of the distinctive attainable molecular architectures. GDS-grown CoTPP sensors exhibit very high intense and sensitive responses as well as faster responses and much lower detection limits (<1 ppm) than conventionally deposited ones. Finally, the repeatability and reproducibility of sorption–desorption processes demonstrate the robustness of these assemblies. The GDS method can be extended to several other organic receptors, opening the way for the production of new improved sensing materials.

Probing the chemical environment of 3-hydroxyflavone doped ormosils by a spectroscopic study of excited state intramolecular proton transfer

Abstract The spectroscopic properties of 3-hydroxyflavone (3-HF) molecules entrapped in films and in monoliths of sol–gel derived organically modified silicates (Ormosils) xerogels are studied by excitation and fluorescence spectroscopy as a function of the sol–gel precursors used for the synthesis. Different molar ratios of tetraethoxysilane (TEOS), methyltriethoxysilane (MTES) and phenyltriethoxysilane (PTES) as precursors are used for the sol preparation. Emission and excitation spectra in the ultraviolet–visible range and photo-degradation curves as a function of time are collected with a spectrofluorimeter. The 3-hydroxyflavone optical properties change in the different networks, owing to the effects of the chemical environment on the excited state intramolecular proton transfer and to the solubility of the dye molecules in the different sol–gel systems. It turns out that the spectroscopic features can be used to probe the chemical state of the dye molecules microenvironment.

Development of microstrip gas chambers on substrates with electronic conductivity

This paper describes several recent developments on microstrip gas chambers (MSGCs). We have studied the operating behaviour of the detectors in different gas mixtures; maximum stable gains have been achieved in mixtures of argon and dimethyl-ether (DME) in almost equal proportions. Using detectors manufactured on semiconducting glass substrates, capable of withstanding very high rates (above 10/sup 6/ mm/sup -2/ s/sup -1/), we have demonstrated extended lifetime without gain modifications up to a collected charge of 130 mC cm/sup -1/ in clean laboratory operating conditions. We have also verified that relaxing the requirements on cleanness conditions, either in the gas mixing system or in the detector construction, may result in fast ageing of the devices under irradiation. As an alternative to semiconducting glass, we have developed a novel technique to coat regular glass with a thin lead silicate layer having an electron conductivity; a new development consisting in coating already manufactured MSGCs with the thin semiconducting layer is also described. The preliminary results show an excellent rate capability for this kind of device, intrinsically simpler to manufacture. >

Effects of plasma non-homogeneity on the physical properties of sputtered thin films

Abstract The plasma generated in a two-target closed field unbalanced magnetron sputtering system for thin film deposition is characterized by means of Hall probes and cylindrical Langmuir probes as a function of the position inside the vacuum system. The plasma potential, electron density and temperature profiles in different locations are measured by two diagnostic systems equipped with cylindrical Langmuir probes. The plasma non-homogeneity due to the presence of magnetic field gradients is evaluated. In order to test the effects of measured plasma non-homogeneity on the physical properties of sputter-deposited coatings, several substrates are put inside the chamber in regions characterized by different plasma density and plasma potential. The composition, microstructure and morphology of TiN x films grown onto these substrates are then studied by means of nuclear techniques (RBS, n-RBS, NRA, ERDA), X-ray diffraction (XRD) and secondary electron microscopy (SEM). The mechanical properties are determined by micro-scratch test and nanoindentation and correlated to the local plasma parameters.

Deposition and Characterization of Luminescent Eu(tta)3phen‐Doped Parylene‐Based Thin‐Film Materials

Herein, novel host-guest films produced by coarse vacuum cosublimation of the parylene C dimer and Eu(tta)3phen are prepared and studied. Eu(tta)3phen sublimation at different temperatures allows films with different concentrations of the Eu complex to be obtained. The films are characterized by Rutherford backscattering spectrometry (RBS), FTIR spectroscopy, X-ray diffraction (XRD), atomic force microscopy (AFM), and UV/Vis absorption and emission spectroscopy. RBS, FTIR, and XRD reveal the incorporation of Eu(tta)3phen into the parylene matrix. AFM evidences the very flat film surface, which is particularly advantageous for optical applications. UV/Vis absorption and emission analyses confirm that the optical properties of Eu(tta)3phen are preserved in the deposited films. Fluorescence measurements evidence the occurrence of an energy-transfer process between parylene and Eu(tta)3phen, and this results in an increase in the light emitted by the Eu complex that is as much as five times higher than that emitted by Eu(tta)3phen alone.

Deposition of fluorescent organic coatings by glow discharge induced sublimation

Abstract The glow discharge induced sublimation (GDS) is a solvent-free coating deposition method used for the growth of organic thin films on solid substrates. This method involves the sublimation of organic molecules in a vacuum chamber and their condensation onto the substrate. The sublimation is obtained by using a radio frequency magnetron sputtering equipment: the organic compound is placed on the sputtering source and bombarded by low energy noble gas ions, which transfer their energy to the organic molecules. The synthesis of pyromellitic dianhydride-4,4′-oxydianiline polyimide thin coatings by this technique has been previously detailed [1]. This work investigated the deposition of thin coatings consisting of the 3-hydroxyflavone (3-HF) fluorescent organic molecule. 3-HF is widely used in organic scintillators owing to the large Stokes shift due to the intramolecular excited-state proton transfer (ESIPT) process. Plasma sampling mass spectrometry is used to study the sublimation of the 3-HF molecules and their gas–phase interactions with plasma ions and electrons. FT-IR spectroscopy and Ion Beam Analysis (RBS and ERDA) have been performed in order to determine the chemical structure and the composition of the deposited coatings. The spectroscopic properties of the deposited coatings, as related to the ESIPT mechanism, have been analysed by UV–Visible spectrofluorimetry, in order to study the chemical surroundings of the 3-HF molecules in the deposited films. Preliminary results on the synthesis and characterisation of SiO2/3-HF bilayer structures deposited by GDS and sputtering are also reported.