Solid State Phenomena Vol. 286

Abstract: The objective of this paper is to introduce a patented and eco-friendly method to synthesize aqueous suspension of all types of alkaline-earth metal hydroxides nanoparticles (NPs). This method is based on an ion exchange process; the exchange takes place at ambient temperature/pressure, starts from cheap or renewable reagents and, in one single step, results in the creation of the crystalline desired nanoparticles in only a few minutes. In terms of structural and morphological features, the synthesized nanoparticles are characterized by means of XRD-Rietveld refinement, FTIR, and TEM. In particular, we obtained pure and crystalline magnesium and calcium hydroxide suspensions, showing the typical brucite crystal structure with a hexagonal lamellar morphology and dimensions generally <100 nm. With respect to the strontium and barium hydroxide suspensions, we observed different kinds of hydroxides (either anhydrous and hydrate forms), characterized by orthorhombic or monoclinic crystal lattices with rod-like nanostructured morphologies. Despite the different morphologies, all synthesized nanoparticles appear constituted by a superimposition of primary nanoparticles, of dimensions ranging from a few to 15 nm, correlated to the increase in the atomic number of the alkaline earth metal.

Abstract: In this work, we report on the processing of PVP-capped ZnO nanoparticles employing a simple-polyol method, varying only the molar concentration (0.01 and 0.1 M) of Zn(CH₃COO)₂•2H₂O used as zinc precursor. Synthesis is performed using ethylene glycol (EG) as solvent and polyvinylpyrrolidone (PVP) as capping agent. Physico-chemical characteristics of the as-synthesized particles were studied by X-Ray Diffraction (XRD), Fourier Transform Infrared (FT-IR) spectroscopy, Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). SEM micrographs revealed formation of quasi-spherical secondary particles formed by aggregation of primary nanosized subunits crystallized from 0.01 M precursor. When precursor with a higher concentration is used, no aggregation occurs and only tiny primary particles in the nanosized range are obtained. XRD confirmed that ZnO nanoparticles have the hexagonal wurtzite-type structure. SEM, EDS and FT-IR showed that applied route produced ZnO nanoparticles with functionalized surface. Presented results imply clear dependence of the particles morphology and size from precursor concentration which could be used for rapid, continuous, single-step preparation of PVP-capped ZnO nanoparticles tailored in accordance to application demands.

Abstract: Multi-angular branched ZnO microstructures with rods-shaped tips and nanopushpins with hexagonal cap on top have been synthesized by a simple thermal treatment process of compacted ZnS powder used as starting material and substrate. The structures have been grown at different temperatures (800, 900 and 1000 °C) for 60 min, in a constant nitrogen environment at atmospheric pressure via a catalyst-free process. XRD results of the as-grown products from ZnS powder show a significant reduction in the cubic zincblende phase to the hexagonal wurtzite phase with the increase of treatment temperature, as compared to the bulk value. Post-anneal analyses indicated that the transformation of morphologies of the as-grown structures also depends strongly on the treatment temperature. The proposed method represents an easy and economical way to grow complex structures of ZnO, with a relatively short time, furthermore, without the neediness of use an external substrate to grow. These new and interesting nanostructures have potential in applications such as optoelectronics.

Abstract: ZnO Nano and microstructures were obtained by thermal oxidation using Zn powders as source. To achieve those structures, the Zn powders were annealed at 650°C and 750°C under oxygen environment and atmospheric pressure. SEM results show that these experimental conditions promote the formation of hollow spherical microstructures with nanowires and nano-swords in each sphere. As was observed, the nanostructures start growing from the bottom surface of the spheres unlike those that were reported recently. The EDS results clearly show that those hollow spheres in the deep part make a compound with Zn and the top surface is mainly composed of ZnO. CL emission spectra show a main green emission that belongs to the sphere’s bottom surface; this emission is correlated to the existing defects that are presented. These results could allow the prediction of a possible growth mechanism under specific conditions.

Abstract: In this work, core-shell ZnO@SiO₂ nanoparticles (NPs) were infiltrated into a macro/meso-porous silicon (PS) structure, to study its luminescent properties. The core-shell ZnO@SiO₂ NPs were obtained by colloidal synthesis. The core-shell ZnO@SiO₂ NP was 5 nm in diameter. The macro/meso-PS structure was made in two steps: we obtained the macroporous silicon (macro-PS) layer fist and the mesoporous silicon (meso-PS) layer second. This process was conducted using different electrolyte solutions, and the change of electrolyte led to a decrease in the special charge region over the wall macro-PS layer; this allowed the building of the meso-PS layers on the walls and the bottom of the macro-PS layer. The SEM results show the cross-section of the macro/meso-PS structure with and without core-shell ZnO@SiO₂ NPs. These SEM images show that the core-shell ZnO@SiO₂ NPs that infiltrated into macro/meso-PS structure were more efficiently bonded over all the porous walls. The core-shell ZnO@SiO₂ PL interacted with the macro/meso-PS structure, modifying its PL intensity and controlling a shift toward a lower wavelength.

Abstract: WO₃:Mo and WO₃:Ti thin films have been deposited on FTO/Glass substrates by the pulsed chemical spray technique at a substrate temperature of T_s = 450°C. The influence of Mo and Ti doping on the structural, electrical, and optical behavior of WO₃ thin films, has been studied by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM), Ultra Violet and Visible Spectrometry (UV-VIS), and Surface Conductivity Methods (Four Points). Doped WO₃ films presents similar polycrystalline structures but with noticeable modifications in surface configurations at micrometric and nanometric levels, as the Mo and Ti concentration is systematically increased in the starting sprayed solution. From processed High-Resolution Electron Micrographs (HREM), a low density of structural defects was found on pure and doped WO₃ grains. This lead to conclude that variations in films surface characteristics are mainly related with metallic doping concentrations which in turn, have noticeable influence in electrical and optical behaviors reported in this work.

Abstract: This paper reports a study of Fluorine-doped Tin Oxide (FTO) thin films deposited by the Pneumatic Spray Pyrolysis (PSP) technique. The films were deposited on glass substrates at 450 °C with a ~125 nm thickness, using an F/Sn ratio of 0, 0.2, 0.35, 0.5, 0.65 and 0.85, respectively. The samples were characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), UV-visible Spectroscopy and Hall Effect techniques, respectively. XRD results revealed that the FTO thin films were polycrystalline with a tetragonal rutile-type structure and had preferential orientations along (110) planes. SEM studies showed that FTO thin film morphology was totally affected by an increased F/Sn ratio. The calculated grain mean sizes were 10-35 nm. Optical transmittance spectra of the films showed a high transparency of approximately 80-90 % in the visible region. The optical gap of FTO thin films was in a 3.70-4.07 eV range. Electrical and optical properties of these films were studied as a function of the F/Sn ratio. Therefore, the optimal FTO (F/Sn = 0.5) films revealed a maximum value of the figure of merit approximately 8.05 × 10^-3 (Ω^-1) at λ = 400 nm. The high-conducting and transparent-elaborating FTO thin films may have several promising applications due to its multifunctional properties.

Abstract: In recent years, the development of new procedures and solutions in the field of conservation has been very significant. The purpose of this article is to collect the main contributions of nanotechnology, in its multifunctional solutions applied in heritage, to offer a global vision of the state of the matter for both scientists and restaurateurs.Nanomaterials offer some advantages over traditional products, improved compatibility and efficiency and reducing the use of toxic organic solvents for humans and the environment. Solutions have been developed for both inorganic supports and organic supports for artistic, architectural and archaeological heritage. Especially relevant are the advances in consolidation processes, pH regulation and / or cleaning / elimination of alteration products on murals, frescoes or stone and in materials composed of cellulose and collagen.Also, nanotechnology is still a recent science and has yet to answer certain questions about its use protocols and reduce the possible risks to health.

Abstract: A silica-based nanoproduct - UCAT-10P© - developed and patented by the TEP-243 (Molecular sieves and other nanomaterials) group of the Cadiz University (UCA) is applied on two stone materials – granite and marble – from the stage front of the Roman theater of Merida, World Heritage by UNESCO (1993). Marble shows firstly scaling as the main decay form, and granite, grain-disintegration, which, at the same time, favor an acceleration of their deterioration condition due to physical, mechanical, chemical and biological processes. That is the reason of assessing the efficiency and durability of a multifuncional nanoproduct, with both consolidating and hydrophobing effects. The performance of this product has been evaluated in terms of the appearance of the stone surfaces (color and roughness), the consolidating role (hardness and ultrasound velocity) and the hydrophobing achievements (capillarity and water contact angle). The most distinctive feature of this research is the in situ testing of the stone blocks, the use of mostly non-destructive and portable techniques, and the monitoring of the product performance of the treatment at a short (1 month) and mid-term (12-15 months), proving the efficacy of the product, although its behavior changes with time.