38 research outputs found
Functional behaviour of TiO2films doped with noble metals
To evaluate the effects of different concentrations of noble metal in a TiO2 matrix, different films
of both Ag:TiO2 and Au:TiO2 systems were prepared. Mechanical and tribological
characterization was carried out to evaluate the coatings response as a function of the noble metals
composition and (micro)structure of the films. The overall set of results indicates that the
amorphous films reveal better results than the crystalline ones. For the amorphous samples, the reduced Young’s modulus and the adhesion critical loads followed similar tendencies in both sets
of films. Wear rates were similar for all samples except for the one with the highest silver content.
To improve brittleness of TiO2 films, the results seem to indicate that a slight metal doping is
preferred, and Au showed to be a better choice than Ag. In fact, the sample with the lowest Au
content revealed a better mechanical behaviour than the pure TiO2 film.This research was sponsored by FEDER funds through the COMPETE program (Programa
Operacional Factores de Competitividade) and by FCT (Fundação para a Ciência e a Tecnologia),
under the projects PEST-C/FIS/UI607/2013 and PEst-C/EME/UI0285/2013. The authors also
acknowledge the financial support by the project Nano4color – Design and develop a new
generation of color PVD coatings for decorative applications (FP7 EC R4SME Project No.
315286)
Thin films composed of Ag nanoclusters dispersed in TiO2: Influence of composition and thermal annealing on the microstructure and physical responses
Noble metal powders containing gold and silver have been used for many centuries, providing different colours in the windows of the medieval cathedrals and in ancient Roman glasses. Nowadays, the interest in nanocomposite materials containing noble nanoparticles embedded in dielectric matrices is related with their potential use for a wide range of advanced technological applications. They have been proposed for environmental and biological sensing, tailoring colour of functional coatings, or for surface enhanced Raman spectroscopy. Most of these applications rely on the so-called localised surface plasmon resonance absorption, which is governed by the type of the noble metal nanoparticles, their distribution, size and shape and as well as of the dielectric characteristics of the host matrix. The aim of this work is to study the influence of the composition and thermal annealing on the morphological and structural changes of thin films composed of Ag metal clusters embedded in a dielectric TiO2 matrix. Since changes in size, shape and distribution of the clusters are fundamental parameters for tailoring the properties of plasmonic materials, a set of films with different Ag concentrations was prepared. The optical properties and the thermal behaviour of the films were correlated with the structural and morphological changes promoted by annealing. The films were deposited by DC magnetron sputtering and in order to promote the clustering of the Ag nanoparticles the as-deposited samples were subjected to an in-air annealing protocol. It was demonstrated that the clustering of metallic Ag affects the optical response spectrum and the thermal behaviour of the films.This research was sponsored by FEDER funds through the COMPETE program (Programa Operacional Factores de Competitividade) and by FCT (Fundação para a Ciência e a Tecnologia), under the projects PEST-C/FIS/UI607/2013 and PEst-C/EME/UI0285/2013. The authors also acknowledge the financial support by the project Nano4color – Design and develop a new generation of color PVD coatings for decorative applications (FP7 EC R4SME Project No. 315286). J. Borges also acknowledges the support by the European social fund within the framework of realising the project “Support of inter-sectoral mobility and quality enhancement of research teams at Czech Technical University in Prague”, CZ.1.07/2.3.00/30.0034. C. Lopes acknowledges FCT for the PhD grant SFRH/BD/103373/2014. F.M. Couto acknowledges CAPES – Foundation, Ministry of Education of Brazil, Brasília – DF 70040-20, Brazil, funding by stage sandwich doctorate, through PDSE – Doctoral Program Sandwich
Tantalum oxynitride thin films: mechanical properties and wear behavior dependence on growth conditions
Tantalum oxynitride (TaNxOy) thin films were produced by magnetron sputtering. This work analyzes and
compares the mechanical properties and the wear behavior of the films, taking into account the differences
promoted by changes in composition and structure, caused by the variation of the partial pressure of the reactive
gases (P(N2+O2)) and by the polarization of the substrate holder.
Besides the change in composition, the variation of P(N2+O2) causes significant changes in the morphology and
structure of the films. Those produced with low P(N2+O2) evidence a higher crystallinity and, in these conditions,
the films exhibit hardness around 20 GPa. Films producedwith higher P(N2+O2) exhibit higherO content,
are amorphous and the hardness is significantly lower.
The substrate bias does not influence the adhesion of the films to the high speed steel substrate, but influences
the mechanical properties, particularly the hardness, at low P(N2+O2) regime. Films with higher crystallinity
exhibit higher hardness, but in the low P(N2 + O2) regime, those who were produced with polarization are
harder. Although some dependence may be established for set B films, the hardness is not as influent on the
wear resistance of the TaNxOy films as the friction coefficient.This work was supported by FEDER through the COMPETE Program
and by the Portuguese Foundation for Science and Technology (FCT) in
the framework of the Strategic Project PEST-C/FIS/UI607/2013 and by
the Sectoral Operational Programme Human Resources Development
(SOP HRD), financed by the European Social Fund and by the
Romanian Government under the project number POSDRU/159/1.5/S/
134378
In-situ XRD vs ex-situ vacuum annealing of tantalum oxynitride thin films: Assessments on the structural evolution
The purpose of this work is to discuss the main structural characteristics of a group of tantalum oxynitride (TaNxOy) thin films, with different compositions, prepared by magnetron sputtering, and to interpret and compare the structural changes, by X-ray diffraction (XRD), when the samples are vacuum annealed under two different conditions: i) annealing, followed by ex-situ XRD: one sample of each deposition run was annealed at a different temperature, until a maximum of 800 ◦C, and the XRD patterns were obtained, at room temperature, after each annealing process; ii) annealing with in-situ XRD: the diffraction patterns are obtained, at certain temperatures, during the annealing process, using always the same sample. Insitu XRD annealing could be an interesting process to perform annealing, and analysing the evolution of the structure with the temperature, when compared to the classical process.
A higher structural stability was observed in some of the samples, particularly on those with highest oxygen content, but also on the sample with non-metal (O + N) to metal (Ta) ratio around 0.5.Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UID/FIS/04650/2013.info:eu-repo/semantics/acceptedVersio
Anion-dependent micelle formation using electro-generated ferrocene surfactants
The syntheses and characterization of two ferrocene oils, 4-octyloxy-2-{5-[1,1,3,3-tetramethyl-3-(11-oxo-11-ferrocenyl-undecyl)-disiloxanyl]-pentyloxy}-benzoic acid 4'-undecyloxy-biphenyl-4-yl ester, Fc1SiM and an octakis(ferrocene) species, Fc8Si8M' are reported, and their biphasic aqueous voltammetry contrasted. Surprisingly, both hydrophobic species undergo single-wave electrochemical dissolution. This can be advantageous to electroanalytical applications. (C) 2008 Elsevier B.V. All rights reserved
Composition and structure variation for magnetron sputtered tantalum oxynitride thin films, as function of deposition parameters
Tantalum oxynitride thin films were produced by magnetron sputtering. The films were deposited usinga pure Ta target and a working atmosphere with a constant N2/O2ratio. The choice of this constant ratiolimits the study concerning the influence of each reactive gas, but allows a deeper understanding of theaspects related to the affinity of Ta to the non-metallic elements and it is economically advantageous.This work begins by analysing the data obtained directly from the film deposition stage, followed bythe analysis of the morphology, composition and structure. For a better understanding regarding theinfluence of the deposition parameters, the analyses are presented by using the following criterion: thefilms were divided into two sets, one of them produced with grounded substrate holder and the otherwith a polarization of −50 V. Each one of these sets was produced with different partial pressure of thereactive gases P(N2+ O2). All the films exhibited a O/N ratio higher than the N/O ratio in the depositionchamber atmosphere. In the case of the films produced with grounded substrate holder, a strong increaseof the O content is observed, associated to the strong decrease of the N content, when P(N2+ O2) is higherthan 0.13 Pa. The higher Ta affinity for O strongly influences the structural evolution of the films. Grazingincidence X-ray diffraction showed that the lower partial pressure films were crystalline, while X-rayreflectivity studies found out that the density of the films depended on the deposition conditions: thehigher the gas pressure, the lower the density. Firstly, a dominant -Ta structure is observed, for lowP(N2+ O2); secondly a fcc-Ta(N,O) structure, for intermediate P(N2+ O2); thirdly, the films are amorphousfor the highest partial pressures. The comparison of the characteristics of both sets of produced TaNxOyfilms are explained, with detail, in the text.This work was supported by FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Project PEST-C/FIS/UI607/2013. This paper was also supported by the Sectoral Operational Programme Human Resources Development (SOPHRD), ID134378 financed from the European Social Fund and by the Romanian Government
Evolutionary Study of the Retinal Nerve Fiber Layer for the Patients with Glaucoma and Diabetes Mellitus
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