focused ion beam and nanomechanical tests for high resolution surface characterisation new resources for platinum group metals testing

*Email: [email protected] Recently, the increasing importance and scope of nanotechnology has extended the need for high resolution characterisation tools beyond their traditional domains. As a consequence, advanced high-resolution tools at the nanoscale are now increasingly used in research and development (RD and nanoindentation testing. After a brief description of both techniques (architecture, probe-sample interaction basics and operation modes), the effectiveness of this combined approach is demonstrated for microstructural and nanomechanical investigations on very small samples. The advantages are low cost, fast and site-specific sample preparation for transition electron microscopy (TEM) analysis; study of the mechanical hardening effect on microstructure and hardness profile at the micron scale; failure analysis; and understanding of plasticity and elasticity behaviour. Two specific case studies related to a platinum-copper alloy for jewellery use and a platinum-rhodium alloy for sensor manufacturing are presented and discussed

Niobium–niobium oxide multilayered coatings for corrosion protection of proton-irradiated liquid water targets for [18F] production

Abstract Chemically inert coatings on Havar ® entrance foils of the targets for [ 18 F] production via proton irradiation of enriched water at pressurized conditions are needed to decrease the amount of ionic contaminants released from Havar ® . During current investigation, magnetron sputtered niobium and niobium oxide were chosen as the candidates for protective coatings because of their superior chemical resistance. Aluminated quartz substrates allowed us to verify the protection efficiency of the desirable coatings as diffusion barriers. Two modeling corrosion tests based on the extreme susceptibility of aluminum to liquid gallium and acid corrosion were applied. As far as niobium coatings obtained by magnetron sputtering are columnar, the grain boundaries provide a fast diffusion path for active species of corrosive media to penetrate and to corrode the substrate. Amorphous niobium oxide films obtained by reactive magnetron sputtering showed superior barrier properties according to the corrosion tests performed. In order to prevent degrading of brittle niobium oxide at high pressures, multilayers combining high ductility of niobium with superior diffusion barrier efficiency of niobium oxide were proposed. The intercalation of niobium oxide interlayers was proved to interrupt the columnar grain growth of niobium during sputtering, resulting in improved diffusion barrier efficiency of obtained multilayers. The thin layer multilayer coating architecture with 70 nm bi-layer thickness was found preferential because of higher thermal stability

Mechanical exfoliation and layer number identification of single crystal monoclinic CrCl3

After the recent finding that CrI3, displays ferromagnetic order down to its monolayer, extensive studies have followed to pursue new two-dimensional (2D) magnetic materials. In this article, we report on the growth of single crystal CrCl3 in the layered monoclinic phase. The system after mechanical exfoliation exhibits stability in ambient air (the degradation occurs on a time scale at least four orders of magnitude longer than is observed for CrI3). By means of mechanical cleavage and atomic force microscopy (AFM) combined with optical identification, we demonstrate the systematic isolation of single and few layer flakes onto 270 nm and 285 nm SiO2/Si~(100) substrates with lateral size larger than graphene flakes isolated with the same method. The layer number identification has been carried with statistically significant data, quantifying the optical contrast as a function of the number of layers for up to six layers. Layer dependent optical contrast data have been fitted within the Fresnel equation formalism determining the real and imaginary part of the wavelength dependent refractive index of the material. A layer dependent (532 nm) micro-Raman study has been carried out down to two layers with no detectable spectral shifts as a function of the layer number and with respect to the bulk

Tecnologie PVD per l'integrazione di proprietà strutturali e funzionali di materiali

I film sottili sono rivestimenti metallici o ceramici spessi dalle decine di nanometri ad alcuni micron; introdotti industrialmente negli anni ’60 hanno avuto un’enorme diffusione e oggi hanno raggiunto un elevato grado di sviluppo tecnologico. Il lavoro della mia tesi ha avuto quindi come focus la tenacità a frattura dei rivestimenti sottili come key technology enabler per una nuova generazione di rivestimenti PVD anticorrosione, capaci di unire proprietà funzionali (protezione dalla corrosione) e strutturali (resistenza al graffio, durezza, resistenza a usura) ; lo sviluppo dell’argomento è stato duplice, con una prima parte del dottorato dedicata allo sviluppo di metodi affidabili per la misura di questa quantità nei rivestimenti sottili e una seconda parte dedicata allo sviluppo di rivestimenti sottili ad elevata tenacità a frattura, utilizzando la tecnica di misura precedentemente sviluppata. Questa attività di tesi è il coronamento di una successione di progetti di ricerca incentrati sui film sottili, dove sono state studiate separatamente molte delle tematiche affrontate poi nel progetto finale. Gli articoli pubblicati nell’ambito dei progetti summenzionati sono: · Produzione e caratterizzazione di rivestimenti in nitruro di alluminio su leghe di alluminio, Proceedings AIMAT 2012,2012,Mattia Piccoli, Marco Sebastiani,Marco Renzelli e Edoardo Bemporad · Rivestimenti PVD di nitruro di alluminio su alluminio, Galvanotecnica e Nuove Finiture, 2013, 64 149-156,2013 Mattia Piccoli, Marco Renzelli, Marco Sebastiani, Rashid Ali · Focused Ion Beam and nano-mechanical testing for high resolution surface characterization: new resources for Platinum group metals testing” Platinum Metals Review 58 (1) 3-19 2014, Marco Sebastiani, Marco Renzelli ,P.Battaini, Edoardo Bemporad · Characterization of Thin Films Using High Definition Confocal Microscopy, Leica Science Lab 2014, Marco Renzelli, Edoardo Bemporad · Multi scale assessment of the toughness of a PVD coating, Proceedings of the 28th SMT Conference, Tampere, Finland,2014, Marco Renzelli, Edoardo Bemporad · Design of Stress-optimized Ti/TiN Multilayer PVD coatings for mechanical application, Proceedings of the 28th SMT Conference, Tampere, Finland,2014, Rashid Ali, Marco Sebastiani, Marco Renzelli, Edoardo Bemporad · 10B enriched film deposited by e-beam technique on Al2O3 substrates for high efficiency thermal neutron detector, Surface and Coatings Technology,2014, G. Celentano, A. Vannozzi,A. Mancini, A. Santoni et al · Niobium-Niobium oxide multilayered coatings for corrosion protection of proton-irradiated liquid water targets for [18F] production, Thin Solid Films, 2014, Hanna Skliarova, Marco Renzelli, Oscar Azzolini et al · Corrosion resistance of decorative thin films: fulfill the expectations, Marco Renzelli, Edoardo · Determination of the Wear Coefficient of Coated Samples Using a Novel Methodology, Giuditta Montesanti, Cesare Di Cesare, Marco Renzelli, Edoardo Bemporad, Proceedings of the 11th European Vacuum Coaters Symposium, Anzio 2014. · Thin film deposition and characterization for neutron detection applications, C. Misiano, D.M. Trucchi, Marco Renzelli, Edoardo Bemporad, A.Santoni, A.Vannozzi, G.Celentano, European Physical Journal. Ai congressi internazionali ICMCTF-2013 e ICMCTF-2014 sono stati presentati i risultati ottenuti nell’ambito dei progetti sul Nitruro di Alluminio e Ossinitruro di Cromo, e due manoscritti sono in corso di pubblicazione. Un secondo articolo sul progetto dei rivestimenti in Niobio è in scrittura, mentre è prevista la pubblicazione futura in una rivista peer-reviewed dei risultati del lavoro oggetto della tesi. La mia attività si è intesa fin da subito come un proof of concept dell’idea stessa di una ottimizzazione di questo tipo, quindi è stato scelto una tipologia di rivestimento di composizione tradizionale, ben conosciuto in letteratura, in modo da poter esplorare questa nuova variabile nello spazio dei parametri senza avere l’handicap di ulteriori incognite. E’ stato eseguito uno studio approfondito della fisica di processo ed è stata studiato il comportamento dell’impianto di deposizione (curve di avvelenamento) con le stesse tecniche impiegate dai maggiori esperti in sputtering reattivo in DC. Il risultato di questi sforzi è stato lo scoprire come piccoli cambiamenti della composizione del gas di processo hanno enormi influenze nella tenacità a frattura dei rivestimenti PVD, con differenti campioni che sottoposti alla stessa prova di indentazione sferica si cominciano a fratturare a carichi molto diversi, 1500 N vs 3500 N. Questi risultati mostrano come anche per un materiale conosciuto come il CrN ci sia ancora spazio di ottimizzazione della tenacità a frattura in complementarietà con gli studi sulla creazione di multilayer ottimizzati per l’applicazione

Focused ion beam and nanomechanical tests for high resolution surface characterisation: New resources for platinum group metals testing

Recently, the increasing importance and scope of nanotechnology has extended the need for high resolution characterisation tools beyond their traditional domains. As a consequence, advanced high-resolution tools at the nanoscale are now increasingly used in research and development (R&D) activities, offering the chance for a better understanding of submicron feature size dependence. This paper gives an overview of the synergic application of two high resolution techniques on the platinum group metals (pgms): focused ion beam (FIB) coupled with electron beam imaging, milling and deposition techniques; and nanoindentation testing. After a brief description of both techniques (architecture, probe-sample interaction basics and operation modes), the effectiveness of this combined approach is demonstrated for microstructural and nanomechanical investigations on very small samples. The advantages are low cost, fast and site-specific sample preparation for transition electron microscopy (TEM) analysis; study of the mechanical hardening effect on microstructure and hardness profile at the micron scale; failure analysis; and understanding of plasticity and elasticity behaviour. Two specific case studies related to a platinum-copper alloy for jewellery use and a platinum-rhodium alloy for sensor manufacturing are presented and discussed

Design, fabrication and characterisation of multilayer Cr-CrN thin coatings with tailored residual stress profiles

Compressive residual stress in hard coatings can improve adhesion and in-service toughness, since they can inhibit crack nucleation and propagation. However, the role of through thickness residual stress profile is not fully understood. This is because of (a) lack of knowledge of stress evolution mechanisms and (b) limitations of experimental techniques used for stress profiling. The present work deals with design, deposition and characterization of Cr-CrN multilayer coatings, produced by Magnetron Sputtering Physical Vapour Deposition (MS-PVD). Analytical modelling was used to determine the optimal residual stress distribution for a range of contact loading situations. On the basis of modelling activities, three different Cr-CrN multilayers were produced, with the aim of obtaining different stress gradients, as measured by incremental micro-scale focused ion beam (FIB) ring-core method, while keeping the same average stress value and same average hardness in the film. Results show a significant correlation between the observed residual stress profiles and scratch adhesion, where different optimal stress profiles are identified for different loading conditions. In particular, we show that a lower interfacial compressive stress and a reduced through thickness stress gradient gives improved scratch adhesion, when using 10 μm and 200 μm sphero-conical indenters

Effects of Residual Stress Distribution on Interfacial Adhesion of Magnetron Sputtered AlN and AlN/Al Nanostructured Coatings on a (100) Silicon Substrate

The present study investigated the influence of nanoscale residual stress depth gradients on the nano-mechanical behavior and adhesion energy of aluminium nitride (AlN) and Al/AlN sputtered thin films on a (100) silicon substrate. By using a focused ion beam (FIB) incremental ring-core method, the residual stress depth gradient was assessed in the films in comparison with standard curvature residual stress measurements. The adhesion energy was then quantified by using a nanoindentation-based model. Results showed that the addition of an aluminum layer gave rise to additional tensile stress at the coating/substrate interface, which can be explained in terms of the differences of thermal expansion coefficients with the silicon substrate. Therefore, the coatings without the Al layer showed better adhesion because of a more homogeneous compressive residual stress in comparison with the coating having the Al layer, even though both groups of coatings were produced under the same bias voltage. Results are discussed, and some general suggestions are made on the correlation between coating/substrate property combinations and the adhesion energy of multilayer stacks. The results suggested that the Al bond layer and inhomogeneous residual stresses negatively affected the adhesion of AlN to a substrate such as silico

Thin-film deposition and characterization for neutron detection applications

Solid state physics experimental techniques and characterization tools can provide a valuable contribution to the research and development activity on He-free neutron detection systems, for both detector assessment and performance improvement. Presently, a He replacement strategy relies on the use of6Li - and/or10B -based neutron-to-charged particle converters coupled to radiation detectors (solid state, gaseous and scintillators). These topics have been discussed during a devoted session within the HeRe (He- Replacement) in Italy Workshop held in Frascati at the ENEA Research Centre, and this paper aims at presenting a brief overview on possible deposition and characterization techniques of thin films that have been subject of discussion. © 2015, Società Italiana di Fisica and Springer-Verlag Berlin Heidelberg

10B enriched film deposited by e-beam technique on Al2O3 substrates for high efficiency thermal neutron detector

In the framework of the research and development activity on He-free neutron detection systems, the solid state physics experimental techniques and characterization tools can provide a valuable contribution for detector assessment and performance improvement. Presently, a He-replacement strategy relies on the use of Li-and/or B-based neutron to charge particle converters coupled to particle detectors (solid state, gaseous, scintillators). In particular, in this paper the detailed structural and chemical-physical characterization of B-10-enriched films deposited by e-beam evaporation onto alumina substrates is reported. X-ray diffraction and photoelectron spectroscopy investigations have revealed that high B content (about 78%) can be achieved on these films, contaminants being mainly C and O most likely coming from the B targets. Microstructural investigation carried out by AFM, SEM and nanoindentation techniques have mainly revealed that B films replicated the alumina substrate microstructural features. The described B-10/Al2O3 samples were successfully tested in a Gas Electron Multiplier based neutron detector with measured detection efficiency in full agreement with the expectations. (C) 2015 Elsevier B.V. All rights reserved