Alessandro Patelli

Properties of sputter-deposited MoS2/metal composite coatings deposited by closed field unbalanced magnetron sputter ion plating

It has been proved that the co-deposition of a proper amount of titanium can significantly improve the properties of sputter-deposited MoS2 coatings, leading to the deposition of coatings, which are harder, much more wear resistant and also less sensitive to atmospheric water vapour during tribological testing. The MoS2/Ti coatings, studied here by the authors, also give excellent industrial results in a wide range of applications. In this paper the mechanical and micro-structural properties of MoS2 coatings containing titanium with molar fractions up to 0.44 are studied. The mechanical properties are tested with pin-on-disk and reciprocating wear tests (multipass) in different experimental conditions. Frictional force and friction coefficient against a number of cycles are recorded. Coatings composition is determined by Rutherford and non-Rutherford backscattering (RBS) and coating thickness is measured by cross-section scanning electron microscopy (SEM). Structural analysis is carried out using X-ray diffraction (XRD). The mechanical properties are presented as a function of the Ti content and the optimal titanium concentration is determined. Other metals like Cr, W, Zr and Mo are also investigated. The composition of MoS2/metal composite coatings of the same quality of the MoS2/Ti films (‘optimized’ coatings) is studied by RBS.

Chemical tailoring of hybrid sol-gel thick coatings as hosting matrix for functional patterned microstructures.

A phenyl-based hybrid organic - inorganic coating has been synthesized and processed by hard X-ray lithography. The overall lithography process is performed in a two-step process only (X-rays exposure and chemical etching). The patterns present high aspect ratio, sharp edges, and high homogeneity. The coating has been doped with a variety of polycyclic aromatic hydrocarbon functional molecules, such as anthracene, pentacene, and fullerene. For the first time, hard X-rays have been combined with thick hybrid functional coatings, using the sol-gel thick film directly as resist. A new technique based on a new material combined with hard X-rays is now available to fabricate optical devices. The effect due to the high-energy photon exposure has been investigated using FT-IR and Raman spectroscopy, laser scanner, optical profilometer, and confocal and electron microscope. High-quality thick hybrid fullerene-doped microstructures have been fabricated.

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.

RBS and μPIXE analysis of uranium diffusion from bentonite to the rock matrix in a deep geological waste repository

Abstract The possible diffusion mechanisms of uranium from bentonite to the rock matrix at the granite/bentonite interface of a deep geological radioactive waste repository were studied by means of Rutherford backscattering spectrometry and proton induced X-ray emission. The effects of the presence of clay on uranium diffusion into the granite were analysed. It has been shown that uranium diffuses into the granite either in the presence or in the absence of bentonite, but in presence of the clay, the diffusion coefficient is two orders of magnitude lower. Different diffusion paths were clearly observed in both cases: the uranium in solution penetrates in the rock specifically through certain minerals (Fe–Ti bearing ones), whereas in presence of the clay, the main uranium diffusion paths are defects of the rock (grain boundaries, micro-fractures).

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.

Simultaneous microfabrication and tuning of the permselective properties in microporous polymers using X-ray lithography.

Microchannels are fabricated using a photosensitive polymer to which microporosity is tuned with different X-ray doses. Using hard X-ray irradiation, the micropattern is positioned with various geometries in a multi-level, three-dimensional structure, while controlling the pore size and transport properties of small molecules. This highly reliable fabrication process has potential for use in microfluidic devices with enhanced transport properties through microchannels.

Physical properties and microstructure of sputter deposited aluminum and zirconium oxynitride multilayers

Abstract A study of ZrON/AlON multilayers produced by reactive closed field unbalanced DC magnetron sputtering is presented. These multilayers, studied principally for their thermal and mechanical properties, are formed by depositing alternating aluminum and zirconium oxynitride layers over a Mo/MoN/MoZrAlN/oxynitride interface. The multilayer period (Λ) ranges from approximately 2 to 50 nm. After the deposition the coatings were thermally treated in air at 700 °C for 2 h to test their oxidation behaviour. X-Ray reflectivity (XRR) and TEM measurement has been used to determine the multilayer period. The composition of the layers and of the interfaces before and after the thermal treatments were investigated by ion beam analysis (RBS and n-RBS and nuclear reaction analysis). X-Ray diffraction (XRD) and bi-dimensional XRD (XRD 2 ) analyses have been performed to investigate the multilayer micro-structure before and after the thermal treatments. The hardness of the layers has been measured by means of nano-indentation and correlated to the period of the multilayer and to the composition and microstructure. The oxidation of the films is found to depend on the multilayer period. The layers showed good toughness and adhesion before and after the thermal treatments.

Method for Optimizing Coating Properties Based on an Evolutionary Algorithm Approach

In industry as well as many areas of scientific research, data collected often contain a number of responses of interest for a chosen set of exploratory variables. Optimization of such multivariable multiresponse systems is a challenge well suited to genetic algorithms as global optimization tools. One such example is the optimization of coating surfaces with the required absolute and relative sensitivity for detecting analytes using devices such as sensor arrays. High-throughput synthesis and screening methods can be used to accelerate materials discovery and optimization; however, an important practical consideration for successful optimization of materials for arrays and other applications is the ability to generate adequate information from a minimum number of experiments. Here we present a case study to evaluate the efficiency of a novel evolutionary model-based multiresponse approach (EMMA) that enables the optimization of a coating while minimizing the number of experiments. EMMA plans the experiments and simultaneously models the material properties. We illustrate this novel procedure for materials optimization by testing the algorithm on a sol-gel synthetic route for production and optimization of a well studied amino-methyl-silane coating. The response variables of the coating have been optimized based on application criteria for micro- and macro-array surfaces. Spotting performance has been monitored using a fluorescent dye molecule for demonstration purposes and measured using a laser scanner. Optimization is achieved by exploring less than 2% of the possible experiments, resulting in identification of the most influential compositional variables. Use of EMMA to optimize control factors of a product or process is illustrated, and the proposed approach is shown to be a promising tool for simultaneously optimizing and modeling multivariable multiresponse systems.

Ion beam analysis of low-temperature MO-PACVD coatings

Plasma-assisted CVD using metal organic precursor was studied at process temperatures of 100 and 160 °C in a capacitive coupled plasma reactor. Ion beam analyses were performed to assess the stoichiometry of TiCN, ZrCN and BCN films on AlMgSi and Si substrates. Hydrogen content and desorption correction factors are discussed as a function of the deposition parameters. The plasma does assist the CVD process, even at these low temperatures, in the form of ion beam bombardment during deposition.

Development of multilayer coatings for solar space experiments

Deposition and characterization results of multilayer coatings optimized for HeII 30.4 nm high reflectivity will be presented. Additional characterization of reflectivity at HI Ly-α and in the visible spectral range has been also accomplished in order to investigate the performances of such coatings in view of their application to the UVCI instrument on board of ESA payload SOLO and to HERSCHEL, a sounding rocket experiment.