Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques最新文献

A simple one-stage sol–gel technique for the synthesis of nanostructured ZnO films modified with Al has been developed. A comparative study of the effect of zinc oxide modification with aluminum, as well as the simultaneous action of methyl orange and ultraviolet radiation on their optical band gap, has been carried out. The contribution of each factor to the transformation of the band structure of the samples has been estimated. It has been shown that for all considered aluminum concentrations, the role of dye adsorption is predominant. A nonmonotonic dependence of the optical band gap of the material on the modifier content has been demonstrated, as well as its significant decrease upon dye adsorption and exposure to ultraviolet radiation. It has been suggested that the growth of the considered value in ZnO with an increase in the Al concentration to 2 at % is associated with the manifestation of the Burstein–Moss effect due to the filling of the lower levels of the conduction band with electrons. The results of the study of the samples by spectroscopy in the visible and ultraviolet wavelength ranges are supplemented by experimental data obtained using scanning electron microscopy. It was found that at all considered aluminum concentrations, the ZnO films are characterized by a nanostructured surface formed by intertwined “branches” of different sizes. A model is proposed that describes the fixation of methyl orange on the surface of the studied samples.

A combination of surface analysis methods and density functional theory calculations showed that the electronic and adsorption properties of nickel nanoclusters on the α-Al₂O₃(0001) film surface toward nitric oxide (NO) molecules strongly depend on the cluster size. The properties of Ni clusters with an effective size not exceeding 2 nm are mainly determined by the formation of a Ni–Al₂O₃ chemisorption bond polarized toward the oxide substrate. As a result, Ni nanoparticles acquire a positive charge, which strengthens the intramolecular bond of NO molecules adsorbed on their surface compared with adsorption on the surface of bulk Ni. With an increase in cluster size, the chemisorption bond is depolarized due to stronger lateral Ni–Ni interactions, and at a coverage thickness exceeding 0.25 equivalent monolayers, the adsorption properties become similar to those of bulk Ni. This size dependence of properties provides a means of controlling the electronic and adsorption characteristics of the metal cluster and the metal–oxide system as a whole.

Experimental data on the yield of nuclear-reaction products from boron-containing crystalline targets irradiated with a deuterium ion beam with an energy of <50 keV at the HELIS ion accelerator (Lebedev Physical Institute) are presented. Natural boron and boron carbide (B₄C) are used as targets. For comparison, experiments on the same setup to measure the yield of nuclear reaction products during the irradiation of boron-containing targets with a neutron flux from a Ti (99.99%) converter target are carried out. Semiconductor detectors, CR-39 track detectors, and neutron scintillation spectrometers are used to record the nuclear-reaction products (charged particles and neutrons). The possibility of initiating nuclear reactions of ¹⁰B + n → ⁷Li + α and p + ¹¹B → 3α with a deuterium ion beam with an energy of <50 keV is demonstrated. However, the high background from the main products of nuclear reactions (D + D) (protons and neutrons) do not allow quantitative estimates of the yield of alpha particles of nuclear-reaction products from proton and neutron capture by boron. The obtained results may be important in the field of radiation medicine for the proton- and neutron-capture therapy of oncological diseases.

Copper-containing zeolites are promising catalysts for the reaction of direct oxidation of methane to methanol. In this work, the structure of copper active centers in mordenite-type zeolites prepared by aqueous ion exchange was investigated using X-ray absorption near edge structure (XANES) spectroscopy and computer modeling. Calculations of theoretical Cu K-edge XANES spectra were performed for a set of models of active copper centers containing one, two, or three copper atoms. The main problem is the difficulty in defining the local atomic structure of copper centers, which are unevenly distributed in the zeolite framework and largely determine the catalytic properties of the material. In order to describe the experimental Cu K-edge XANES spectra corresponding to the oxygen activation stage at a temperature of 200°C, it is necessary to take into account the superposition of models of copper and copper oxide centers. The most probable local atomic environment of copper in the studied material at the considered stage of the catalytic cycle was determined. The results obtained are important for establishing the relationship between the structure and catalytic properties of mordenite-type zeolites, as well as for the development of new efficient catalysts.

The potential of using the method of high-frequency cathode sputtering in an oxygen atmosphere for the synthesis of thin-film lead-containing antiferroelectric materials is investigated. Two films with the chemical composition of the PbHfO₃ target were synthesized on Si(001) and SrRuO₃/SrTiO₃/MgO(001) substrates. The formed films were characterized by single-crystal X-ray diffraction, including reciprocal space mapping, and energy dispersive spectroscopy. It has been demonstrated that this synthesis method makes it possible to grow polycrystalline films based on materials with a perovskite structure. In this case, an epitaxial film with rhombic syngony and a new crystal lattice different from that known for PbHfO₃ was obtained on a heterophase substrate. The revealed ratio of the parameters of the film cells and the intermediate layer is 7 to 6; that is, the coincidence of the nodes of the film and substrate structure occurs when 7 unit cells of the film and 6 unit cells of the SrRuO₃ layer are superimposed. This indicates the complex nature of the orientation. The morphology analysis showed significant differences between the samples in terms of grain size and distribution. The data obtained confirm the high sensitivity of the phase composition to the type of substrate and demonstrate the promise of the high-frequency cathode sputtering method for creating new functional oxide films suitable for use in microelectronics, sensors, and energy-efficient devices.

The results of a study on the quantum yield of various photocathodes designed to detect X-ray radiation with an energy above 40 keV are presented. Experiments have been conducted with photocathode samples made of CsI, LaB₆, CdWO₄, and ZnWO₄ using synchrotron radiation from the wiggler at the VEPP-4M accelerator. These materials have been chosen due to their high atomic numbers Z, which ensures effective interaction with X-rays through the photoelectric effect. The study has been carried out in the energy range 40–100 keV, which corresponds to the conditions of experiments on fast-flowing physical processes requiring high temporal and spatial resolution. The data obtained allow us to determine the most suitable materials for creating effective photocathodes in electron-optical converters for recording fast physical processes.

Detectors based on CMOS (CMOS is a complementary metal–oxide–semiconductor structure) matrices are widely used to solve a wide range of problems that require imaging. In addition to their widespread use in conventional cameras, including mobile phones, today they are increasingly used in various fields of science and technology: dosimetry and imaging neutron and X-ray spectroscopy. On the basis of such devices both X-ray microscopy devices and X-ray telescopes can be built, for example, for studying various astrophysical objects. The possibility of using two CMOS matrices from Sony IMX265LLR-C and IMX226CLJ-C for simultaneous imaging and spectral acquisition in the soft X-ray range is considered. It is shown that in the range from 1 to 22 keV, the detectors have a high energy resolution. A comparison of two matrices is carried out, and their features for use in recording radiation in various energy ranges are considered.

The features of the synergy of high-intensity implantation of chromium ions into Zr1%Nb alloy with simultaneous repetitively-pulsed energy impact of a high-power density beam on the irradiated surface have been studied. The possibility of deep ion alloying (up to 7 µm) with a maximum concentration of implanted atoms at the surface of up to 60 at % has been demonstrated for the first time. It has been revealed that chromium distribution in Zr1%Nb alloy over both the surface and the depth of the target is inhomogeneous. The possibility of providing conditions for deep radiation-enhanced diffusion in the surface layer while preserving the microstructure of the material outside the ion-alloyed region has been experimentally confirmed. The effect of refining the crystal structure in an ion-doped layer under conditions of multiple repetitively-pulsed energy impact of a high-power density ion beam on the alloy surface has been discovered.

It has been experimentally shown that an increase in the water depth from 2 to 4 cm leads to the transition from two-dimensional to three-dimensional turbulence. Waves with a frequency of 6 Hz (wavelength λ = 5.6 cm) propagating on the water surface generate vortex flows penetrating into the water volume. The experiments show that in “shallow” water with a depth of h = 2 cm, the vortex flow is homogeneous and quasi-two-dimensional: the vertical velocity component of tracer particles is zero, and the vorticity vector is oriented vertically. In “deep” water (h = 4 cm), there is a developed three-dimensional chaotic liquid motion: the water layers are mixed due to solenoidal flows with both vertical and horizontal velocity components. Vortices in the liquid interact with surface flows, leading to an increase in their energy. As a result of this interaction, the energy of surface vortices, E(t), after turning off the pumping demonstrates a nonmonotonic dependence on time, which differs from the exponential decay characteristic of shallow water.

In this work, single-phase monocrystalline and thin-film samples of lead selenide have been synthesized. Methods have been developed for the creation of surface oxidized lead selenide with a conductivity different from that of the base PbSe. Using oxidized lead selenide as an interface, Ag/Pb₃OSeO₃/PbSe heterostructures were made, demonstrating stable memristive characteristics. The obtained heterojunctions were investigated for the detection of resistive switching, and the volt -ampere characteristics and the temperature dependence of the resistance of the structures were measured. By changing the external parameters—frequency and magnitude of the electric field voltage applied to the heterocontact—different metastable states were realized. Dynamic effects were studied, and the transition times from one to another metastable state were determined. Single crystal-based memristors were more stable than film structures: reproducible characteristics in single crystal-based memristors were observed for several months.