Results 1 - 10 of 18662
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[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] 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.
[en] Highlights: • Provided direct visualization of SEI layer information of Fe3O4 for the first time. • Lack of stable SEI layer resulted in gas and dendrite formation. • Call for better electrolytes and sophisticated carbon coating techniques. - Abstract: Present study provided visual evidence of solid electrolyte interphase (SEI) layer formation on Fe3O4 anode during charge and discharge using in situ electrochemical atomic force microscopy. AFM images show that SEI layer formed on Fe3O4 electrode from fluoroethylene carbonate (FEC)-based electrolyte was more stable and compact than that formed from ethylene carbonate (EC)-based electrolyte. In addition, presence of surface cracks on the electrodes indicated poor formation of an intact SEI layer. This observation was more apparent in the EC-based electrolyte. Lack of an intact SEI layer resulted in decomposition of electrolytes which were reflected by presence of large air bubbles and dendrites on the electrode during CV. Although FEC-based electrolyte improved the performance of Fe3O4 anodes in lithium ion batteries, its protective effects were far from perfect. To accelerate the application of Fe3O4 or other metal oxide anodes in lithium ion batteries, better electrolytes and sophisticated carbon coating techniques are needed.
[en] Highlights: • Cu2O/ZnO nanowires (NWs) were obtained by combining Atomic layer Deposition (ALD) and Electrochemical Deposition (ECD). • These scalable processes allow applications in photovoltaic field. • The crystallinity, morphology and photoconductivity properties of the Cu2O/ZnO NWs were investigated. • High density of interface states and high resistivity of Cu2O film were the main reason of the low photovoltaic performances. - Abstract: Cu2O/ZnO nanowires (NWs) heterojunctions were successfully prepared by combining Atomic layer Deposition (ALD) and Electrochemical Deposition (ECD) processes. The crystallinity, morphology and photoconductivity properties of the Cu2O/ZnO nanostructures have been investigated. The properties of the Cu2O absorber layer and the nanostructured heterojunction were studied in order to understand the mechanisms lying behind the low photoconductivity measured. It has been found that the interface state defects and the high resistivity of Cu2O film were limiting the photovoltaic properties of the prepared devices. The understanding presented in this work is expected to enable the optimization of solar cell devices based on Cu2O/ZnO nanomaterials and improve their overall performance.
[en] Highlights: • CS or CS-REC was electrosprayed to nanospheres to enlarge their surface area. • CS-REC immobilized on PS mats could improve the hydrophilicity. • The intercalation of CS chains with REC interlayers was helpful for adsorption. • Ca2+-REC with cation exchange could improve the adsorption capacity. • The composite mats kept high adsorption ability after three cycles. - Abstract: Chitosan (CS), as a kind of well characterized biopolymer, has been used for heavy metal adsorption due to its low cost and high efficacy. However, when used directly, chitosan particles had small surface area and weak mechanical strength which is unfavorable to metal adsorption and reused. Besides, it cannot be easily recycled that may cause a secondary pollution. In this paper, CS and layered silicate rectorite (REC) were fully mixed and the mixtures were subsequently electrosprayed nano-sized spheres, which were immobilized on the surface of electrospun polystyrene (PS) mats for metal adsorption. The morphology analysis taken from SEM confirmed that CS-REC nanospheres were loaded on the surface of PS fibrous mats. Small Angle X-ray diffraction patterns showed that the interlayer distance of REC in composite mats was enlarged by the intercalation of CS chains; such structure meant bigger surface area which was helpful for metal adsorption. The data of contact angle implied that PS mats coated with CS-REC nanospheres exhibited better hydrophilicity than PS mats, which was conductive to adsorption rate. Besides, the copper ions adsorption of composite mats was tested at different conditions including the adsorption time, the initial pH and the initial concentration of copper ion. The results demonstrated that PS mats coated with CS-REC nanospheres had the adsorption capacity up to 134 mg/g. In addition, the addition of REC containing Ca2+ could also improve the metal adsorption because of cation exchange. The desorption assay indicated that PS mats immobilized with CS and CS-REC still kept high adsorption ability which retained 74% and 78% after three adsorption-desorption cycles.
[en] Highlights: • Formation and optical properties of Au particles in CrN films were investigated. • CrN layers were implanted with Au+ ions at fluences in the range of 1016 cm−2. • For the fluence of 2 × 1016 cm−2 gold particles of ∼200 nm in diameter were formed. • With increasing Au ion fluence the particles coalesce into clusters. • The shift of a SPR peak indicates a strong interaction between Au particles. - Abstract: We report on the formation of gold particles in 280 nm thin polycrystalline CrN layers caused by Au+ ion implantation. The CrN layers were deposited at 150 °C by d.c. reactive sputtering on Si(100) wafers and then implanted at room temperature with 150 keV Au+ ions to fluences of 2 × 1016 cm−2 to 4.1 × 1016 cm−2. The implanted layers were analysed by the means of Rutherford backscattering spectrometry, X-ray diffraction, atomic force microscopy and spectroscopic ellipsometry measurements. The results revealed that the Au atoms are situated in the near-surface region of the implanted CrN layers. At the fluence of 2 × 1016 cm−2 the formation of Au particles of ∼200 nm in diameter has been observed. With increasing Au ion fluence the particles coalesce into clusters with dimensions of ∼1.7 μm. The synthesized particles show a strong absorption peak associated with the excitation of surface plasmon resonances (SPR). The position of the SPR peak shifted in the range of 426.8–690.5 nm when the Au+ ion fluence was varied from 2 × 1016 cm−2 to 4.1 × 1016 cm−2. A correlation of the shift in the peak wavelength caused by the change in the particles size and clustering has been revealed, suggesting that the interaction between Au particles dominate the surface plasmon resonance effect.
[en] Highlights: • The surface functionalization produces the buckling phenomena. • The molecular orbitals (HOMO/LUMO) energies present an oscillatory behavior with the percentage of functionalization. • The electronic properties (gap, molecular hardness and electrophilicity) present an oscillatory behavior with the percentage of functionalization. • The system present spin polarization for selected percentage of functionalization. - Abstract: Carbon nanotubes (CNTs) have important electronic, mechanical and optical properties. These features may be different when comparing a pristine nanotube with other presenting its surface functionalized. These changes can be explored in areas of research and application, such as construction of nanodevices that act as sensors and filters. Following this idea, in the current work, we present the results from a systematic study of CNT's surface functionalized with hydroxyl and carboxyl groups. Using the entropy as selection criterion, we filtered a library of 10k stochastically generated complexes for each functional concentration (5, 10, 15, 20 and 25%). The structurally related parameters (root-mean-square deviation, entropy, and volume/area) have a monotonic relationship with functionalization concentration. Differently, the electronic parameters (frontier molecular orbital energies, electronic gap, molecular hardness, and electrophilicity index) present and oscillatory behavior. For a set of concentrations, the nanotubes present spin polarized properties that can be used in spintronics.
[en] Highlights: • A novel in-situ XPS study was performed on plasma-deposited Ru-based catalytic films. • The content of various Ru oxidation states can be controlled by the Ox/Red processes. • The key role of temperature in changes between Ru oxidation states is demonstrated. - Abstract: A novel in-situ study of the surface molecular structure of catalytically active ruthenium-based films subjected to the oxidation (in oxygen) and reduction (in hydrogen) was performed in a Cat-Cell reactor combined with a XPS spectrometer. The films were produced by the plasma deposition method (PEMOCVD). It was found that the films contained ruthenium at different oxidation states: metallic (Ru0), RuO2 (Ru+4), and other RuOx (Ru+x), of which content could be changed by the oxidation or reduction, depending on the process temperature. These results allow to predict the behavior of the Ru-based catalysts in different redox environments.