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Un-doped (uZO) and silver-doped zinc oxide (SZO) films were prepared by oblique incidence sputtering deposition under different process parameters. The crystalline structure, chemical composition, and surface morphology were correlated with the optical properties, as well as with the wettability of the films. In the case of uZO films, the orientation, inclination, and morphology of the columnar structure determined the wettability of the layer, moving from a hydrophilic- to hydrophobic-like character. In the case of SZO films, although almost all of them displayed hydrophobic behavior, the hydrophobic character increased with the Ag content. The most hydrophobic surface was obtained when the Ag content in the layers was greater than 7 at.% and, in these cases, the structural results indicate that the layers were formed by a disordered mixture of Zn and Ag oxides., This research was funded by grant TED2021-129876B-I00 of the Ministerio de Ciencia, Innovación y Universidades (Spain).

A new approach for in-situ specific functionalization of graphene with carboxylic groups through a single-step growth is presented. Depending on the fabrication parameters, it is possible to synthesize functionalized single layer or multilayer graphene. The homogeneity and functionalization degree are evaluated combining micro-Raman and XPS spectroscopies. The obtained COOH content reaches around 5%, similar to the values obtained by the other methods but with significantly lower contents of the other oxygen groups (carbonyl and hydroxyl) and of other sp defects which are detrimental for electronic transport. The obtained COOH- functionalized single-layer graphene presents optimum values of the sheet resistance, around 8 kΩ, and high mobility, around 800 cmVs. Anchoring of antibodies is demonstrated through the immobilization of IgG1–FITC by the carbodiimide method, showing that these COOH- functionalized single-layer graphene can be very promising materials for electronic sensing applications., Funding by the Spanish Ministerio de Economía y Competitividad (MINECO) under Project MAT2015-65356-C3-1-R and Comunidad de Madrid Excellence Network under Project S2013/MIT-2740 is acknowledged. S.C. acknowledges BES-2016-076440 and L.A.-F. BES-2013-062759 FPI grants from MINECO.

Graphene is grown by chemical vapour deposition on ruthenium ultrathin films down to a nominal thickness of 5 nm. While at 910 °C multilayer graphitic films are obtained, single layer defective graphene is formed at 1000 °C. The extremely thin Ru films allow the formation of a novel nano-crystalline ruthenium carbide phase to be discerned by combining synchrotron X-ray diffraction, synchrotron X-ray absorption spectroscopy and electron diffraction. The ruthenium carbide (Ru-C) phase formed at or above 1000 °C presents cubic symmetry (cP) with a lattice parameter of 2.927 Å and a Ru-C distance of around 2.31 Å. The increase of C solubility in ruthenium seems to be sufficient to trigger the stabilization of the Ru-C phase during graphene growth preferentially in grains with orientation different to (0001). The structural transition from hcp Ru to cP Ru-C is not limited to a shell; it occurs for the whole grain. The formation of the carbide seems to favour the synthesis of single layer graphene by hindering the segregation of carbon to the surface during cooling. This simple method allows nano-crystalline ruthenium-carbide films to be obtained as well as graphene covered Ru nanograins, both with size control. These new materials are foreseen to present interesting mechanical, catalytic and sensing properties.http://doi.org/10.1039/C7TC02855E, Funding by the Spanish Ministerio de Economía y Competitividad (MINECO) under Project MAT2015-65356-C3-1-R and Comunidad de Madrid Excellence Network under Project S2013/MIT-2740 is acknowledged. We also acknowledge the MINECO for financial support and provision of synchrotron radiation facilities at the BM25 SpLine of The Spanish CRG Beamline at the ESRF. L. A.-F. acknowledges a FPI grant (BES-2013-062759) from MINECO.

The increase of charge mobility in transparent conductive indium molybdenum oxide (IMO) films is correlated with the presence of hydroxyl groups. The introduction of H in the chamber during sputtering deposition compensates the excess charge introduced by cationic Mo doping of indium oxide either by oxygen or hydroxyl interstitials. Films present a linear increase of carrier mobility correlated with H content only after vacuum annealing. This behavior is explained because vacuum annealing favors the removal of oxygen interstitials over that of hydroxyl groups. Since hydroxyl groups offer lower effective charge and smaller lattice distortions than those associated with interstitial oxygen, this compensation mechanism offers the conditions for the observed increase in mobility. Additionally, the short-range order around molybdenum is evaluated by extended X-ray absorption fine structure (EXAFS) spectroscopy, showing that Mo is placed at the In site of the indium oxide., We acknowledge financial support to Spanish MINECO, Madrid Regional Government and CSIC though contracts MAT2012-37276-C03-01, P2013/MIT-2740 and 201660E016, respectively.

We report on the formation of highly stable and robust hybrid semitransparent electrodes based on a percolated mesoscale copper grid covered with graphene. Copper films sputtered on transparent substrates are used to synthesize graphene by CVD and annealed to form metallic grids covered with graphene. The copper grid density can be controlled by varying annealing temperature and time, obtaining excellent sheet resistance ( < 0.7 Omega/sq). The single layer graphene that covers the whole sample modifies the preferred crystalline orientation favoring (110) copper grains when treated up to 1050 degrees C. However, when annealed few degrees below bulk copper melting temperature, graphene is partially eliminated, probably due to the high pressure of copper vapor generated underneath, and copper forms isolated dots with mainly (111) orientation. During graphene synthesis, similar to 70% of the copper film is evaporated but, once graphene layer is completed the remaining copper fraction is constant up to almost bulk copper melting temperature demonstrating that graphene is an excellent barrier against copper evaporation. Contrary to the enhanced oxidation of copper foils with graphene, these graphene-Cu grids are extremely stable in ambient conditions maintaining an almost unchanged performance for years. The copper based meso-grids are highly stable and robust and present a suitable surface for organic- and biomolecules provided by the continuous graphene layer.

Understanding the interaction between graphene and its supporting substrate is of paramount importance for the development of graphene based applications. In this work the interplay of the technologically relevant graphene-Cu system is investigated in detail as a function of substrate grain orientation in Cu polycrystalline foils. While (100) and (111) Cu grains show the well-known graphene-enhanced oxidation, (110) grains present a superior oxidation resistance compared to uncovered Cu and an anomalous shift of its graphene 2D Raman band which cannot be explained by the known effects of strain and doping. These results are interpreted in terms of a weak graphene-Cu coupling at the (110) grains, and show that graphene can actually be used as anticorrosion coating, contrary to previously reported. The anomalous shift is suggested to be the result of an enhanced outer Raman scattering process which surpasses the usually dominant inner process. Since Raman spectroscopy is widely used as first and main characterization tool of graphene, the existence of an anomalous shift on its 2D band not only challenges the current theory of Raman scattering in graphene, but also has profound implications from an experimental point of view.

Solar selective coating multilayers deposited by magnetron sputtering and containing Mo:Si 3 N 4 cermet as the absorber layer and Ag as infrared reflector (IR-mirror) have shown excellent optical characteristics for concentrated solar power applications at high temperatures. However, mechanical reliability of such optical coatings is a concern due to the large thermal mismatch between the Mo:Si 3 N 4 cermet and the Ag IR-mirror layer. The substitution of the Ag IR-mirror layer by a Ti/Ag bilayer can improve mechanical reliability at the operating conditions, but at the expense of deteriorating the optical properties of the solar selective coating. In this work, we study the evolution of the mechanical and optical properties of Mo:Si 3 N 4 /Ti/Ag solar selective coatings, as a function of the Ti/Ag ratio, with the objective of finding a compromise between the optical and mechanical properties. The substitution of Ag by Ti improves the multilayers scratch resistance without deteriorating the optical properties. As a result, we suggest an optimal composition of the Ti/Ag IR-mirror bilayer.

A novel selective coating material based on Mo-Si3N4 has been investigated for the first time. Accurate combination of the individual component layers based on optical simulations and precise control of layers thickness and composition leads to high solar absorptivity (α Sol=0.926) and low thermal emissivity (ε25 C=0.017) on a silver film, resulting in a high solar thermal energy conversion efficiency. The tandem absorber is stable in moderate vacuum at temperatures above 600 C showing low emissivity (estimated value at 600 C is ε 600 C=0.109) evidencing its relevance for high temperature solar selective applications. A full optical and thermal analysis of a parabolic trough concentrator (PTC) system confirmed the potential of the novel coating material to be used for CSP technology. © 2013 Published by Elsevier B.V. All rights reserved., This work has been supported by European Commission under HITECO Collaborative project contract no. 256830 from the FP7-ENERGY program.

The detection, identification, and quantification of different types of molecules and the optical imaging of, for example, cellular processes are important challenges. Here, we present how interference-enhanced Raman scattering (IERS) in adequately designed heterostructures can provide amplification factors relevant for both detection and imaging. Calculations demonstrate that the key factor is maximizing the absolute value of the refractive indices' difference between dielectric and metal layers. Accordingly, Si/Al/AlO/graphene heterostructures have been fabricated by optimizing the thickness and roughness and reaching enhancement values up to 700 for 488 nm excitation. The deviation from the calculated enhancement, 1200, is mainly due to reflectivity losses and roughness of the Al layer. The IERS platforms are also demonstrated to improve significantly the quality of white light images of graphene and are foreseen to be adequate to reveal the morphology of 2D and biological materials. A graphene top layer is adequate for most organic molecule deposition and often quenches possible fluorescence, permitting Raman signal detection, which, for a rhodamine 6G (R6G) monolayer, presents a gain of 400. Without graphene, the nonquenched R6G fluorescence is similarly amplified. The wavelength dependence of the involved refractive indices predicts much higher amplification (around 10) for NIR excitation. These interference platforms can therefore be used to gain contrast and intensity in white light, Raman, and fluorescence imaging. We also demonstrate that surface-enhanced Raman scattering and IERS amplifications can be efficiently combined, leading to a gain of >10 (at 488 nm) by depositing a Ag nanostructured transparent film on the IERS platform. When the plasmonic structures deposited on the IERS platforms are optimized, singlemolecule detection can be actively envisaged., L.A.-F. acknowledges a FPI grant (BES-2013-062759) from Spanish Ministerio de Economía y Competitividad (MINECO). The research leading to these results has received funding from MINECO (MAT2012-37276-C03-01 and MAT2015-65356-C3-1-R) and Comunidad de Madrid (S2013/MIT-2740, PHAMA2.0-CM).

The oxidation and corrosion of copper are fundamental issues studied for many decades due to their ubiquitous and transversal impact. However, the oxidation of copper used as catalyst for graphene synthesis has opened a singular problem not yet solved. Contradictory results are reported about the protecting or enhancing role of graphene in copper oxidation. We study short- and long-term oxidation of copper with different characteristics, such as oxygen content and morphology, with and without graphene, and in polycrystalline copper foils and almost totally textured (100) and (111) copper films on MgO and sapphire substrates, respectively. We propose a mechanism to explain the enhanced oxidation of polycrystalline copper originated by oxygen encapsulated by the graphene impermeable layer during graphene growth. The initial oxygen content and the existence of grain boundaries are the main factors that determine the relevance of this process. Graphene is shown to prevent oxidation from the atmosphere for any of the copper substrates but also promotes slow oxidation derived by the release of out-of-equilibrium encapsulated oxygen. The formation of bubbles after several months evidence this slow release. The occluded oxygen in graphene covered copper is demonstrated by comparing the oxygen to copper ratio at different depths using hard X-ray photoelectron spectroscopy for samples with and without graphene., Funding by the Spanish Ministerio de Economía y Competitividad (MINECO) under Projects MAT2015-65356-C3-1-R and MAT2012-37276-C03-01 and Comunidad de Madrid Excellence Network under Project S2013/MIT-2740 is acknowledged. We also acknowledge the MINECO for financial support and provision of synchrotron radiation facilities at BM25 SpLine The Spanish CRG Beamline at the ESRF. L.A-F. acknowledges a FPI grant (BES-2013-062759) from MINECO.

Stable Graphene/gas/Cu bubbles are formed by the spontaneous oxidation at room conditions of the Cu substrates used as the catalyst agent in chemical vapor deposition growth of graphene. The non homogeneous copper oxidation produces discontinuous CuO films where atmospheric molecules get trapped by the impermeable graphene layer forming bubbles. Raman Interference effects are calculated both for graphene and CuO phonons in graphene/CuO/Cu system using the transfer matrix method finding that CuO thickness is limited to 20 nm and maximum Raman enhancement of graphene is 10. Nevertheless, enhancement values up to 60 are detected for micrometric graphene bubbles on copper which, according to the simulations, are 70 nm height. AFM measurements confirm the bubble dimensions and show that they are mechanically softer than graphene on copper. Consistently, the Raman characteristics of the graphene bubbles coincide with free standing undoped graphene with small strain, in the range 0-0.3%, while graphene on CuO presents hole doping and larger strain fields. The simulations indicate that interference Raman enhancement can reach values >10 in graphene/dielectric/Aluminum trilayers (dielectric = gas, oxide or polymer). These systems are therefore interesting platforms for optical sensing where graphene is the adequate bio-compatible layer for metallic nanoparticles and molecules deposition., A-F. acknowledges a FPI grant from Spanish Ministerio de Economía y Competitividad (MINECO) (BES-2013-062759) and E.C-P from the European Union Seventh Framework Program under grant agreement n° 604391 “Graphene Flagship”. The research leading to these results has received funding from Spanish MINECO (MAT2012-37276-C03-01 and MAT2015-65356-C3-1-R) and Comunidad Autónoma de Madrid (S2013/MIT-2740, PHAMA2.0-CM).

The optical and electrical properties of indium tin oxide (ITO) films deposited at room temperature on glass and polyethylene terephthalate (PET) substrates were investigated. A clear evolution of optical transparency and sheet resistance with the content of H2 in the gas mixture of H2 and Ar during magnetron sputtering deposition is observed. An optimized performance of the transparent conductive properties ITO films on PET was achieved for samples prepared using H2/(Ar + H2) ratio in the range of 0.3–0.6%. Moreover, flexible ITO-PET samples show a better transparent conductive figure of merit, ΦTC = T10/RS, than their glass counterparts. These results provide valuable insight into the room temperature fabrication and development of transparent conductive ITO-based flexible devices., We acknowledge financial support from Spanish MINECO though contracts MAT2012-37276-C03-01 and from the Madrid Regional Government though contract P2013/MIT-2740.

A complete experimental study of temperature dependence of the total spectral emissivity has been performed, for the first time, for absorber-reflector selective coatings used in concentrated solar power (CSP) systems for energy harvesting. The coating consist of double cermet layers of silicon oxide with different amounts of molybdenum over a silver infrared mirror layer. The experimental measurements were carried out by a high accurate radiometer (HAIRL) with controlled atmosphere in the mid-infrared and for temperatures between 150 and 600 C. The spectral emissivity is nearly constant in this temperature range. Therefore, the temperature dependence of the total emissivity is given by Planck function. These results were compared with those obtained with the usual calculus using room temperature reflectance spectrum. Finally, the performance of the coating was analyzed by comparison of coated respect to non-coated stainless steel., This work was financially supported by the European Commission (project HITECO FP7-ENERGY-2010-1Collaborative N. 256830) the Spanish Ministry of Science and Innovation (projects FUNCOAT CSD2008-00023, RyC2007-0026) and program ETORTEK of the Consejería de Industria of the Gobierno Vasco in collaboration with the CIC-Energigune Research Center. L. González-Fernández acknowledges the Basque Government the support through a Ph.D. fellowship.