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

Existence of Reaction-Diffusion Waves with Nonlinear Boundary Conditions

The paper is devoted to a reaction-diffusion equation in an infinite two-dimensional strip with nonlinear boundary conditions. The existence of travelling waves is proved in the bistable case by the Leray-Schauder method. It is based on a topological degree for elliptic problems in unbounded domains and on a priori estimates of solutions

Binary Zr-Ni/Co metallic glass films: Role of the structural state on their durability

cited By 5International audienceThin film metallic glasses are a new class of promising materials for advanced structural applications. In this work, binary Zr-based thin film metallic glasses (TFMGs) were deposited by the magnetron co-sputtering process from pure metal targets. Two similar enrichments were investigated (44 at.% for the nickel, 43 at.% for the cobalt), in order to determine the effect of the alloying element's nature on the structural, mechanical and electrochemical behaviors. Structure of films was determined by in situ XRD measurements carried out during heating up to 600 °C, while their morphology was characterized by SEM observations. Mechanical properties of amorphous and crystallized films (hardness and Young's modulus) were measured by nanoindentation. Intrinsic electrochemical properties are deduced from polarization curves and electrochemical impedance spectroscopy measurements carried out in Na2SO4 aqueous solution. It is found that the surface morphology of TFMGs was very smooth with a compact and dense microstructure. When heated, glassy films exhibit a high structural stability (up to 440 °C) with crystallization occurring through a multistage process for the Co-containing film. Whatever the coating, Zr affords its beneficial passive-ability, while crystallization process accelerates the global corrosion kinetics. Corrosion mechanisms of the Zr-based TFMGs were discussed in the light of the alloying element (Ni or Co) and the structure of films (amorphous or crystallized). © 2015 Acta Materialia Inc

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

Thin films of Ag–Au nanoparticles dispersed in TiO2: influence of composition and microstructure on the LSPR and SERS responses

Thin films containing monometallic (Ag,Au) and bimetallic (Ag-Au) noble nanoparticles were dispersed in TiO2, using reactive magnetron sputtering and post-deposition thermal annealing. The influence of metal concentration and thermal annealing in the (micro)structural evolution of the films was studied, and its correlation with the localized surface plasmon resonance (LSPR) and surface enhanced Raman spectroscopy (SERS) behaviours was evaluated. The Ag/TiO2films presented columnar to granular microstructures, developing Ag clusters at the surface for higher annealing temperatures. In some cases, the films presented dendrite-type fractal geometry, which led to an almost flat broadband optical response. The Au/TiO2system revealed denser microstructures, with Au nanoparticles dispersed in the matrix, whose size increased with annealing temperature. This microstructure led to the appearance of LSPR bands, although some Au segregation to the surface hindered this effect for higher concentrations. The structural results of the Ag-Au/TiO2system suggested the formation of bimetallic Ag-Au nanoparticles, which presence was supported by the appearance of a single narrow LSPR band. In addition, the Raman spectra of Rhodamine-6G demonstrated the viability of these systems for SERS applications, with some indication that the Ag/TiO2system might be preferential, contrasting to the notorious behaviour of the bimetallic system in terms of LSPR response.CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico(CFUM-BI-23/2016-UID/ FIS/04650/2013)info:eu-repo/semantics/publishedVersio