1,721,025 research outputs found
Liquid-Phase Preparation and Characterization of Zinc Oxide Nanoparticles
No full textZinc oxide (ZnO) nanoparticles have been prepared by a wet chemical method,
from zinc acetate and LiOH ethanol-based solutions. The resulted nanoparticles
were dispersed in a solvent. The effect of solvent (ethanol or butanol) and surfactant
(polyethylene glycol-PEG 200) on the average size and size distribution of the nanoparticles
was investigated by light scattering measurements. Smaller size was
observed for ZnO nanoparticles dispersed in butanol and PEG 200. The statistical
parameters of the Gaussian size distribution curves were calculated. ZnO nanoparticles
have been prepared to be used as seeds on a substrate for the growth of ZnO
nanowires. The morphology, surface roughness, crystalline structure, and orientation
of the nanoparticles deposed on silicon substrate were characterized by atomic
force microscopy and x-ray diffraction, respectively
Simultaneous in situ and Time-Resolved Study of Hierarchical Porous Films Templated by Salt Nanocrystals and Self-Assembled Micelles
No full textTime-resolved simultaneous experiments using synchrotron radiation have been realized to study in situ the concurrent formation of different templates in hierarchical porous thin films. Silica hybrid organic-inorganic films have been dip-coated and processed to obtain two porous nanostructures: spherical ordered mesopores templated by surfactant micelle, and cubic pores formed by crystallization of sodium chloride salts. The experimental setup has allowed following in real time the chemical-physical processes behind the formation of the two different templating agents. During deposition, the self-assembly and organization of the micelles have been studied by grazing incidence small-angle X-ray scattering while the crystallization of the salt template has been monitored by wide-angle X-ray scattering. After processing, the films have been further characterized by transmission electron microscopy, two-dimensional grazing incidence small-angle X-ray scattering and X-ray diffraction. The in situ analysis has revealed a short time delay between micelles and salt crystals formation; the micelles self-assemble and organize at the end of the first evaporation stage, when ethanol evaporates, while salt starts nucleating and growth only during the second stage, when water evaporation begins
Sol-Gel Processing of Bi(2)Ti(2)O(7) and Bi(2)Ti(4)O(11) Films with Photocatalytic Activity
No full textA new sol-gel synthesis based on chloride compounds as precursors has been used to prepare bismuth titanate (BT) films. The films have been deposited by dip-coating and fired at different temperatures in air; they remain amorphous up to 500 degrees C, and crystallize into the pyrochloric cubic phase Bi(2)Ti(2)O(7) between 600 degrees and 700 degrees C while at higher temperatures of firing the stable Bi(2)Ti(4)O(11) monoclinic phase is formed. The films have been characterized by X-ray diffraction analysis at gracing incidence, X-ray photoelectron spectroscopy, ellipsometric spectroscopy, UV-visible absorption, and atomic force microscopy. The photocatalytic properties of the films have been evaluated by exposing a methyl orange solution containing the BT films to UV light. The test has shown that the Bi(2)Ti(2)O(7) films have a higher activity in comparison with reference anatase titania films
Recent Advances in Perovskite Single-Crystal Thin Film Optoelectronic Devices
Full text linkAmong novel semiconductors, perovskites have gained significant attention due to their versatility, combining tunable optoelectronic properties with relatively easy fabrication processes. However, certain issues still hinder their widespread use, often related to the presence of defects and traps within the material. Beyond defect passivation in polycrystalline thin films, an alternative approach to enhancing material quality lies in the fabrication of single crystals. This review aims to provide an overview of the promising approaches explored to address specific challenges of perovskites that benefit from the single crystal nature, restricting our analysis to perovskite single crystal thin films (PSC-TF). We will discuss novel fabrication techniques and highlight recent achievements in devices, such as photodetectors, solar cells, and transistors. By examining the fundamental properties already discovered and showcasing the latest advancements, we aim to provide an overview of the perspectives and open challenges for PSC-TF in next-generation optoelectronic devices
Controlling shape and dimensions of pores in organic-inorganic films: nanocubes and nanospheres
No full textPorous organic-inorganic hybrid films with well defined pore shape and dimension have been obtained via a salt-template route. Sodium chloride precipitates during film deposition as templating for cubic shape pores; combining this salt-template route with controlled phase separation, pores of spherical shape in the same film have been also obtained. The dimensions of the nanocubes and nanospheres are in the 20-200 nm range and can be modulated through the film processing conditions. We have systematically investigated the effect of precursor solution aging and surfactant concentration on the porous film structure using infrared spectroscopy, spectroscopic ellipsometry, X-ray diffraction, Raman imaging, atomic force microscopy and transmission electron microscopy. Only a very specific combination of different synthesis parameters, such as surfactant concentration and aging of the precursor solution, allows the formation of the pore templates
An alternative sol-gel route for the preparation of thin films in CeO(2)-TiO(2) binary system
No full textThin films of titania-ceria have been prepared via sol-gel processing by employing titanium and cerium chloride compounds in highly acidic conditions for the precursor sol. This sol-gel route allows obtaining titania-ceria and cerium titanate films, CeTi(2)O(6), after thermal treatment in air. The films exhibit a high optical transparency which is modulated by controlling the composition and the thermal treatment. The materials have been characterized by X-ray diffraction, UV-visible spectroscopy, ellipsometric spectroscopy and atomic force microscopy. The titania-ceria films show, as a function of the composition, the formation of different phases after thermal treatment in air at 800 degrees C. In particular, with the composition Ce25-Ti75 we have obtained a pure cerium titanate phase, CeTi(2)O(6), which can be formed only in a very strict range of compositions. (C) 2009 Elsevier B.V. All rights reserved
Formation of cerium titanate, CeTi(2)O(6), in sol-gel films studied by XRD and FAR infrared spectroscopy RID D-5301-2009
No full textThe process of formation of cerium titanate films as a function of annealing temperature and composition has been studied by combining X-ray diffraction analysis and far infrared spectroscopy. The films have been prepared by a sol-gel synthesis using metal chlorides as precursors; the synthesis allows obtaining cerium titanate films upon annealing in air. A brannerite type, CeTi(2)O(6), phase has been identified by X-ray diffraction and Rietveld analysis on thin films. CeTi(2)O(6) is formed upon annealing at 700 A degrees C and in a limited range of ceria-titania mixed compositions. The far infrared spectra are useful to observe the formation of crystalline phases at the beginning of the crystallization process at lower firing temperatures, when the XRD analysis is not enough sensitive
Pore-confined synthesis of mesoporous nanocrystalline La–Ce phosphate films for sensing applications
No full textA new method for the preparation of fluorescent mesoporous La–Ce phosphate films by spin coating is
reported here. The structure is obtained by a pore-confined synthesis involving an in situ growth of
La0.5Ce0.5PO4 nanoparticles inside the pores of a mesoporous silica thin film and the subsequent partial
sintering. The removal of the sacrificial mesoporous silica matrix is achieved by chemical etching, which
leaves on the substrate a La0.5Ce0.5PO4 mesoporous film exhibiting good adhesion properties and high
fluorescence intensity that can be quenched by a water solution containing organo-phosphate bearing
nitrophenyl groups. The sensing capabilities of these materials have been tested for the detection of
pesticides in water
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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