The specific features are presented of the two-stage synthesis of structured microsystems based on zinc-oxide nanorods by ultrasonic spray pyrolysis and the low-temperature hydrothermal method, with ...nucleation suppressed in the bulk of the solution. It is shown that the use of two-stage synthesis provides control over the size and aspect ratio of separate nanorods and over the structure of the microsystem of nanorods as a whole. It is proposed to monitor the concentration of intrinsic surface defects by measuring the photocurrent under irradiation through narrow-band interference light filters.
Controlling the hydrophilic properties of the surface of nanomaterials is of interest for various applications including optics, photocatalysis, and spintronics. Methods for designing the defect ...structure of the surface layers of faceted zinc-oxide nanorods with sacrificial doping with iodine in the framework of hydrothermal synthesis are described. The features of the chemical composition of the surface of the obtained layers are studied using X-ray photoelectron spectroscopy. It is found that there are no peaks corresponding to the binding energy of iodine in X-ray photoelectron spectra. The spectrum of the 1
s
level of oxygen O for iodine-doped zinc-oxide nanorods shows an additional peak with a binding energy of 531.8 eV, which corresponds to the oxygen of OH groups. During heat treatment of the synthesized layers, iodine volatilizes, which leads to a change in the surface composition and an increase in the oxygen content of surface hydroxyl groups. A model is proposed for explaining the obtained experimental results. It is established that X-ray-photoelectron-spectroscopy techniques are efficient for analyzing the defect structure of the surface of functional layers based on faceted zinc-oxide nanorods.
Hydrophilic layers of porous silicon are prepared by single- or two-step anodization and characterized by evaluating their surface hydrophilicity and contents of functional groups using IR ...spectroscopy and adsorption of acid-base indicators with different p K a values. The surface functional composition of the synthesized samples is shown to be adjustable depending on the anodization current density. The surface of samples obtained at anodization current density 30 mA/cm2 is predominantly occupied with p K a 2.5 corresponding to ≡Si–OH groups. The increase of current density to 80 mA/cm2 results in the increase of surface functional nonuniformity with the formation of versatile centers, primarily Lewis acidic sites corresponding to Si atoms, as indicated by selective indicator adsorption in agreement with the disappearance of Si–H bonds in IR spectra and overall surface disordering according to SEM and AFM data.
A characteristic feature of I—III–VI ternary chalcogenide compounds, which has a significant effect on the possibility of controlling the functional properties of materials on their base, is a strong ...tendency toward a deviation from stoichiometry. In this paper, we substantiate the existence of ternary semiconductor compounds with ordered vacancies in nanocrystals of the I—III–VI system using the triangulation method (Goryunova method for predicting the composition of diamond-like semiconductors). Vacancies are presented as a pseudoelement of the periodic system of the zero group assuming the formation of electrically neutral defect complexes consisting of a vacancy in the position of the group-I atom and a doubly ionized antistructural defect. In this case, the compound is considered from the standpoint of a concentration tetrahedron, and triangulation operations pass into tetrahedral operations. In the presence of such a “virtual” element, a set of ternary compounds known from publications with an ordered content of vacancies corresponding to semiconductors having four bonds per individual atom is determined instead of a single composition in the I—III–VI
2
system.
Abstract
The paper presents a study of the optical properties of porous alumina membranes obtained by electrochemical anodizing in electrolytes based on sulfuric and orthophosphoric acids. The pore ...size was analyzed by SEM. The degradation of transmittance of membranes after one year and six years storage was studied. The change one year later in optical properties was explained by the adsorption of water molecules. Six years later, an increase in throughput is observed for all membranes. At present, there are no theoretical models that can explain obtained experimental results and additional studies in this area are necessary.
The published works representing the current state of research in the field of the synthesis and application of zinc stannate are reviewed. The data on crystalline modifications of ZnSnO
3
are ...provided and the primary areas of the application of zinc stannate are investigated. Options of various synthesis methods, such as chemical vapor deposition, reactions under high pressure, hydrothermal synthesis, ion-exchange and solid-phase reactions, the coprecipitation method, and the sol-gel method, are demonstrated.
This work is devoted to the analysis of factors responsible for the high-frequency shift of the complex permeability (μ⁎) dispersion region in polymer composites of manganese–zinc (MnZn) ferrite, as ...well as to the increase in their thermomagnetic stability. The magnetic spectra of the ferrite and its composites with polyurethane (MnZn–PU) and polyaniline (MnZn–PANI) are measured in the frequency range from 1MHz to 3GHz in a longitudinal magnetization field of up to 700Ое and in the temperature interval from −20°С to +150°С. The approximation of the magnetic spectra by a model, which takes into account the role of domain wall motion and magnetization rotation, allows one to determine the specific contribution of resonance processes associated with domain wall motion and the natural ferromagnetic resonance to the μ⁎. It is established that, at high frequencies, the μ⁎ of the MnZn ferrite is determined solely by magnetization rotation, which occurs in the region of natural ferromagnetic resonance when the ferrite is in the “single domain” state. In the polymer composites of the MnZn ferrite, the high-frequency permeability is also determined mainly by the magnetization rotation; however, up to high values of magnetizing fields, there is a contribution of domain wall motion, thus the “single domain” state in ferrite is not reached. The frequency and temperature dependence of μ⁎ in polymer composites are governed by demagnetizing field and the induced magnetic anisotropy. The contribution of the induced magnetic anisotropy is crucial for MnZn–PANI. It is attributed to the elastic stresses that arise due to the domain wall pinning by a polyaniline film adsorbed on the surface of the ferrite during in-situ polymerization.
► Polyaniline (PANI) coating significantly changes magnetic properties of MnZn ferrite. ► Coated ferrite exhibits higher coercivity, thermomagnetic stability, and resonance frequency shifts. ► Changes are due to magnetic anisotropy induced through pinning of domain walls by PANI.
Abstract
Ammonia is widespread chemical compound found both in nature and in human body, and its detection is very important in biology and medicine as well as in environmental monitoring systems. ...This work is aimed at fabrication and study of precise, technological and relatively cheap ammonia sensors compatible with a liquid medium. Here we use GaP epitaxial nanowires (NWs) as adsorption elements capable of ammonia detection fabricated via a simple protocol. The device properties are studied in terms of change in sensor impedance spectrum upon presence of ammonia. Physical interpretation of the impedance spectra in the presence of water and ammonia is given. GaP–based device exhibit sufficient response to the ammonia presence with the detection limit lower than 2.5 ppm.
This work is devoted to the study of mesoporous structure parameters of calcium hydroxyapatite powders on the basis of data obtained by nitrogen thermal desorption method. The isotherms of nitrogen ...desorption/adsorption on the samples of hydroxyapatite and the changes in their porous structure parameters depending on the temperature of the heat treatment are discussed.
A comprehensive analysis of the current level of research in the development of intelligent hybrid nanosystems based on porous inorganic materials, in particular porous alumina, is carried out. The ...presented works show interesting opportunities for the development of intelligent, multifunctional optical devices with a microchip design.
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