Results 1 - 10 of 18673
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[en] Stainless steel and copper technical substrates have been coated by free standing graphene using electrophoretic deposition technique, with the final goal to obtain chemically inert low secondary electron emission surfaces. This class of materials is of utmost interest in future accelerators in order to increase further the flux of accelerated charged particles in the beam. The measured maximum total electron yield of pristine graphene, which has been previously characterized by electron microscopies and X-ray photoelectron spectroscopy, appears to be about 1.0. The deposition parameters have been optimized in order to obtain surfaces with lowest total electron yield, but also composition and morphology close to that of pristine graphene. When applying these optimized deposition parameters graphene coatings on two substrates, i.e. stainless steel and copper, the maximum total electron yield of about 1.04 was obtained. The composition of coatings and the relative amounts of sp2 bonds are slightly worse than those of the pristine graphene, while the surface morphology appears to be the same. Annealing at 150 °C for 64 h in high vacuum, showed that vacuum baking did not affect considerably the electron emission properties of the coatings. © 2019 Elsevier B.V.
[en] The present study deals with modification of tungsten surface with high-intensity (∼1015 W/cm2) femtosecond laser in air and vacuum surrounding. Specific findings include: (a) the applied intensities produce crater-like damages with depth ∼31.0 μm in vacuum and ∼7.2 μm in air; (b) peripheral region of the damages is diffuse in air atmosphere unlike vacuum where it is more sharply defined; (c) hydrodynamic features, while present in vacuum, are dramatically reduced in air; (d) characteristic chemical surface changes occur at the surface, and (e) plasma forms in front of the target in both surroundings. The obtained results imply that the employed intensities, in a certain sense, can be used for simulation of some processes in the fusion reactor and for highly precise material removal and tungsten surface processing (by fine tuning of given fs laser parameters). © 2018 Elsevier B.V.
[en] Investigation and synthesis of anisotropic magnetic nanostructures, such as wires, rods, fibers, tubes and chains, is an important field of research due to the beneficial properties and great potential for practical applications ranging from magnetic data storage to biomedicine. Silica coated iron oxide nanochains of length up to 1 μm and diameter ∼80–100 nm have been synthesized by the simultaneous magnetic assembly of superparamagnetic iron oxide nanoparticle clusters (SNCs) as links (viz. maghemite, γ-Fe2O3) and the fixation of the assembled SNCs with an additional layer of deposited silica. We reveal that is possible to achieve either superparamagnetic or ferromagnetic behavior with the nanochains depending only on their physical orientation. The superparamagnetic behavior is observed for random orientation of nanochains whereas ferromagnetic properties (HC ≈ 100 Oe) come to the fore when the orientation is mainly parallel. These peculiar magnetic properties can be related to: (1) the specific size, which is ∼9 nm, of primary building blocks of the nanochains, i.e. of maghemite nanoparticles; (2) to the anisotropic chain-like shape of the particles; and (3) to inter-particle interactions. Large pore volume and pore size of silica shell as well as good colloidal stability and magnetic responsiveness of such nanochains enable applications in biomedicine. © 2019 Elsevier B.V.
[en] Organic contamination may decrease the targeted performances of coated surfaces. To study the contamination induced by surrounding materials, a method using a thermal extractor is presented in the first part of this work. Besides its normal operation (analyses of outgassing compounds from a material), this device is used in an original way to contaminate and decontaminate samples. Efficiency of contamination and decontamination protocols are assessed by automated thermal desorption and gas chromatography coupled with mass spectrometry and by secondary ion mass spectrometry coupled with a time of flight mass analyzer. This enables to study the contamination induced by a bulk material outgassing and to take in consideration the possible competition between out-gassed species. This method is then applied to investigate contamination of Laser MegaJoule sol-gel coated optics by a retractable sheath. The impact of the temperature on the outgassing of the sheath has been highlighted. Increasing temperature from 30 to 50 C enables the outgassing of organophosphorous compounds and increases the outgassing of oxygenated compounds and phthalates. Chemical analyses of contaminated optics have highlighted affinities between the sol-gel coating and phthalates and organophosphorous, and low affinities with aromatics and terpenes. Finally, samples with increasing levels of contamination have been realized. However a saturation phenomenon is observed at 90 ng cm"2. (authors)
[en] We report on glycine-free and glycine-assisted hydrothermal synthesis of microsized superstructures composed of self-assembled hematite nanoparticles. An X-ray powder diffraction measurements of the samples confirm good crystallization of the hematite nanoparticles with hydrothermal reaction time-dependent crystallite sizes in a range from ∼15 nm (45 h) to ∼26 nm (90 h). The FTIR and Raman spectroscopy confirm hematite structure, whereas TEM measurements reveal nanoparticle sub-units (subparticles). The computational analyses of particle shape show that the addition of glycine surfactant in hydrothermal reaction leads to more spherical shape of hematite hierarchical structures and smaller sizes. We found strong coercivity increases (up to ∼3 times) in the samples synthesized in the presence of glycine. The coercivity values from HC = 1305 Oe (mushroom-like shape synthesized by glycine-free hydrothermal reaction) to HC = 3725 Oe (sphere-like shape synthesized by glycine-assisted hydrothermal reaction) were obtained at 300 K. These results and their comparison with other described in the literature (e.g. bulk, wires, urchin-like, rods, tubes, plates, star-like, dendrites, platelets, irregular, nanocolumns, spindles, disks hematites, etc.) reveal that the hematite superstructures possess good magnetic properties. We propose that the glycine, oriented subparticles, exchange and dipole-dipole interactions may play an important role in the development of magnetic properties.
[en] Highlights: ► Plasma-sprayed YSZ coatings were modified by a novel chemical densification process. ► A lower porosity and a higher microhardness were achieved by the post treatment. ► The enhanced adhesive strength of the ceramic top coat was evaluated by shear tests. ► Mechanisms of this processing were proposed. - Abstract: Plasma-sprayed yttria stabilized zirconia (YSZ) ceramic coatings have been widely used as wear- and corrosion-resistant coatings in high temperature applications and an aggressive environment due to their high hardness, wear resistance, heat and chemical resistance, and low thermal conductivity. The highly porous structure of plasma-sprayed ceramic coatings and their poor adhesion to the substrate usually lead to the coating degradation and failure. In this study, a two-layer system consisting of atmospheric plasma-sprayed 8 wt.% yttria-stabilized zirconia (8YSZ) and Ni-based alloy coatings was post-treated by means of a novel chemical sealing process at moderate temperatures of 600–800 °C. Microstructure characteristics of the YSZ coatings were studied using an electron probe micro-analyzer (EPMA). Results revealed that the ceramic top coat was densified by the precipitated zirconia in the open pores. Therefore, the sealed YSZ coatings exhibit reduced porosity, higher hardness and a better adhesion onto the bond coat. The mechanisms for the sealing process were also proposed.
[en] Evolution of the structure of cobalt-silicon films during Xe ions irradiation has been studied and the same is correlated with magnetic properties. The polycrystalline cobalt films were deposited by electron beam evaporation method to a thickness of 50 nm on crystalline silicon (c-Si) and silicon with pre-amorphized surface (a-Si). After deposition the layers were irradiated with 400 keV Xe ions to the fluences in the range of 2-30 x 10(15) ions/cm(2). Structural analysis was done by means of transmission electron microscopy, atomic force microscopy (AFM) and X-ray diffraction (XRD), while the magnetic properties were analyzed by using magneto-optical Kerr effect (MOKE) technique. For the both types of substrate the AFM and XRD results show that after Xe ions irradiation the layers become more rough and the grain size of the crystallites increases; the effects being more evidenced for all fluences for the layers deposited on pre-amorphized Si. The MOKE measurements provided the in-plane azimuthal angular dependence of the hysteresis loops and the change of magnetization with the structural parameters. Although the coercive field is influenced by the surface roughness, in the case of c-Si substrate we found it is much more determined by the size of the crystallites. Additionally, independently on the substrate used the magnetic anisotropy in the Co films disappeared as the Xe ion fluence increased, indicating that the changes of magnetization in both systems occur for similar reasons. (C) 2018 Elsevier B.V. All rights reserved.
[en] In this study, we demonstrated the formation of a new type of AuAg@Ag nanostructure in titanium nitride (TiN) thin films using sequential implantation of Au and Ag ions. The TiN films deposited by DC reactive sputtering were sequentially implanted with 200 keV gold ions at fluences of 0.5 × 10 16 and 1 × 10 16 ions/cm 2 and 150 keV silver ions at fluences of 1 × 10 16 , 2 × 10 16 , 3 × 10 16 , and 4 × 10 16 ions/cm 2 . Formation of spherical-like particles with dimensions below 10 nm, homogeneously distributed along the ion track of implanted ions is verified by high resolution transmission electron microscopy. Specific nanostructure containing Au–Ag alloy in the center of the particle and only silver on the periphery was found in the TiN sample sequentially implanted with 1.0 × 10 16 ions/cm 2 of Au and 4 × 10 16 ions/cm 2 of Ag using high angle annular dark field scanning electron microscopy together with elemental mapping analysis. On the other hand, for the sample implanted with 0.5 × 10 16 ions/cm 2 of Au and 4 × 10 16 ions/cm 2 of Ag only formation of Au–Ag alloy was observed. A mechanism for the formation of a new type core/shell nanostructure in ion implanted TiN thin films is proposed. By varying the implantation fluence of the gold and silver ions properly, the optimized experimental parameters for creation of a specific AuAg@Ag core/shell nanoparticles were achieved. © 2019 Elsevier B.V.
[en] Highlights: • Metal Ir coatings were deposited onto the endocardial electrode tips by MOCVD. • The formation of coatings with fractal-like morphology was achieved. • The metal coatings were electrochemically activated in acid media to form AIROFs. • The AIROF samples obtained are characterized by high capacitance. • MOCVD is the alternative method for deposition of Ir coatings for medical equipment. - Abstract: The present work demonstrates the application of the Metal-Organic Chemical Vapor Deposition technique to fabricate metal iridium coatings onto the pole tips of endocardial electrodes. Using iridium (III) acetylacetonate as a volatile precursor, the target coatings were successfully applied to the working surface of cathodes and anodes of pacemaker electrodes in the flow type reactor in hydrogen atmosphere at deposition temperature of 550 °C. The coating samples were characterized by means of XRD, SEM, Raman- and XPS-spectroscopies. The formation of non-textured coatings with fractal-like morphology and 7–24 nm crystallite size has been realized. The electrochemical properties of the coatings were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The charge storage capacity values of the electrochemically activated samples were 17.0–115 mC cm−2 and 14.4–76.5 mC cm−2 for measurements carried out in 0.1 M sulfuric acid and in phosphate buffer saline solutions, respectively. A comparison of some characteristics of the samples obtained with commercially available cathode of pacemaker electrodes is also presented.