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When the coatings are in nano-scale, the mechanical properties cannot be easily estimated by means of the conventional methods due to: tip shape, instrument resolution, roughness, and substrate effect. In this paper, we proposed a semi-empirical method to evaluate the mechanical properties of thin films based on the sputtering rate induced by bombardment of Ar + ion. The Ar + ion bombardment was induced by ion gun implemented in Auger electron spectroscopy (AES). This procedure has been applied on a series of coatings with different structure (carbon films) and a series of coating with a different density (ZnO thin films). The coatings were deposited on Silicon substrates by RF sputtering plasma. The results show that, as predicted by Insepov et al., there is a correlation between hardness and sputtering rate. Using reference materials and a simple power law equation the estimation of the nano-hardness using an Ar + beam is possible. [ABSTRACT FROM AUTHOR]

Abstract: In many applications and in particular those requiring protective coatings, material characterization in terms of mechanical properties is of importance. The most appropriate technique to obtain these properties is nanoindentation. As coating and substrate form a composite system, it is crucial to know the energy repartition during the indentation process, in order to find the intrinsic properties of the film or the composite properties of the whole system. In this work, the elastic and dissipated works of indentation, estimated from the load displacement curves in nanoindentation measurements and described by the unload-to-load indentation work ratio, were followed in function of indentation depth. This parameter was used to examine the behaviour of four carbon film/substrate systems: hard C film on silicon, hard C film on polyethylene terephthalate (PET) substrate, soft C film on silicon and soft C film on PET. The harder carbon films were sputter-deposited in a RF plasma in Ar–H2 from a graphite target, while the so-called soft films consisted of polymer-like carbon growth by PECVD in CH4–N2–H2 plasma. Different behaviours were observed for the four systems. The results allow to distinguish between cases of elasto-plastic behaviour of the materials and those where a fully plastic deformation of the film or of the substrate affect the determined hardness values. In the case of an elasto-plastic behaviour, a curve fit of the depth profile of unload-to-load indentation work ratio to a Hill function allowed to define a critical depth which limits the depth zone of a film only property. [Copyright &y& Elsevier]

Abstract: Fundamental and applied investigation of ZnO has been recently experiencing a renaissance due to its prospective use in various technological domains and, in particular, as transparent conductive oxide (TCO). In this respect, the present work aims to study the structural and physical properties of ZnO thin films deposited by RF sputtering in pure Ar and Ar–H2 plasmas, at various concentrations (0–50%). The plasma chemical species were followed in function of the different gas mixture settings by optical emission spectroscopy (OES). X-ray photoelectron spectroscopy (XPS) and ATR-FTIR (Attenuated Total Reflection Fourier-Transformed Infrared) spectroscopy were used to study the bulk and surface chemical composition of the films, X-ray Diffraction (XRD) analysis allowed lattice structure and grain size determination while samples morphology was checked with a scanning electron microscope (SEM). The films were also characterized for their electrical and optical properties. The introduction of hydrogen in the plasma phase strongly affected the structural, chemical and physical properties of the films. In particular a pronounced change in the film electrical behavior was observed which become conductive when H is added in the gas mixture ([H2]>6%). The film transparency was on the other hand maintained. By combining XPS, ATR-FTIR and OES data we could correlate the established conductivity and its variations with intentional hydrogen incorporation in the crystal structure in the form of hydroxide species. [Copyright &y& Elsevier]

The interest towards aptamer-based surfaces in the field of bioaffinity assays is constantly growing. A crucial aspect is related to the ability of maintaining the high specificity of these molecules once immobilized on the surface. In this article we compare the immobilization of aptamers on a silanized silicon nitride surface as well as on a soft polymeric layer. An innovative immobilization approach, based on a copolymer, N-dimethylacrylamide-N-acryloyloxysuccinimide-3-(trimethoxysilyl)propylmethacrylate (DMA-NAS-MAPS) coating, able to crosslink itself to the substrate and to bind amino-modified biomolecules is proposed. Comparing this coating with a more classical functionalization process based on silane chemistry, we propose that the better results obtained on the polymeric layer are due to an increased binding efficiency of the aptamers bound to a soft material. The high specificity of immobilized DNA-aptamers is demonstrated using two sequences specific for thrombin detection and a non-sense sequence as negative control. The coating provides higher sensitivity compared to classical self-assembled silane coatings, probably due to a better mobility of bound aptamers. The aptamer immobilization on both surfaces was characterized and optimized using atomic force microscopy, X-ray photoelectron spectroscopy, contact angle and fluorescence microscopy. The comparison between the two different functionalizations highlights the better performances of the copolymer coating in terms of protein recognition, demonstrating thrombin detection down to 0.011 nM in buffer solution and 4.9 nM in complete human serum. Moreover, the localized immobilization of the aptameric sequences, utilized in this work, suggests the possibility of employing this platform also for multianalyte detection. [ABSTRACT FROM AUTHOR]

Nanocrystalline diamond (NCD) coatings with thickness of about 3 μm were grown on silicon substrates at four deposition temperatures ranging from 653 to 884 °C in CH4/H2/Ar microwave plasmas. The morphology, structure, chemical composition and mechanical and surface properties were studied by means of Atomic Force Microscopy (AFM), X-Ray Diffraction (XRD), Raman spectroscopy, nanoindentation and Water Contact Angle (WCA) techniques. The different deposition temperatures used enabled to modulate the chemical, structural and mechanical NCD properties, in particular the grain size and the shape. The characterization measurements revealed a relatively smooth surface morphology with a variable grain size, which affected the incorporated hydrogen amount and the sp2 carbon content, and, as a consequence, the mechanical properties. Specifically, the hydrogen content decreased by increasing the grain size, whereas the sp2 carbon content increased. The highest values of hardness (121 ± 25 GPa) and elastic modulus (1036 ± 163 GPa) were achieved in NCD film grown at the lowest value of deposition temperature, which favored the formation of elongated nanocrystallites characterized by improved hydrophobic surface properties. [ABSTRACT FROM AUTHOR]