Vol 13, No 5 (2019)

Metal-organic UiO-66, UiO-66-NDC, and MOF-801 frameworks (MOFs) are produced via the solvothermal synthesis technique. The frameworks are composed of Zr₆O₄(OH)₄ clusters that are connected with appropriate linkers, as follows: UiO-66—terephthalic acid; UiO-66-NDC—1,4-naphthalenedicarboxilic acid; and MOF-801—fumaric acid. The single-phase composition of the samples is confirmed by X-ray powder diffraction. The identification of Zr₆O₄(OH)₄ clusters in all the synthesized MOFs is established using X-ray adsorption spectroscopy. The specific surface areas of UiO-66, UiO-66-NDC, and MOF-801 are evaluated, and their hydrogen adsorption–desorption isotherms are measured at 77 K, as well. Comprehensive preliminary characterization of the samples, together with hydrogen-storage-capacity data, allows one to make the following conclusions: (i) at relatively high pressures, the highest hydrogen-storage capacity is found for UiO-66 with the largest specific surface area; (ii) at relatively low pressures, MOF-801 with the smallest pores possesses the optimal structure for hydrogen sorption; (iii) a large π-system of aromatic UiO-66-NDC rings yields effective hydrogen sorption at low pressures, which is retained in pores during desorption.

The results of a comparative experimental study of the structure and morphology of high-temperature glassy carbon of brand SU-2500 after high-fluence (10¹⁸ cm^–2 and higher) irradiation with 30-keV Ar⁺ ions in the temperature range of 60–600°С and glassy carbon samples after treatment at temperatures of 850, 1300, 2000, and 2500°С are reported and discussed. The Raman spectra of irradiated glassy carbon SU-2500 show the amorphous state of the surface layer after irradiation at temperatures below that of dynamic annealing of radiation damage, which is determined from the temperature dependence of the ion-induced electron emission yield, a graphite-like state after irradiation at temperatures of 150–250°С, and a structure typical of glassy carbon samples treated at elevated temperatures after irradiation at temperatures in the range of 250 < T ≤ 600°С. Ion irradiation under conditions of the dynamic annealing of radiation damage leads to a сellular topography, i.e., nanowalls connected by nodes. The sizes of the structure cells are about 150 and 300 nm after irradiation at temperatures of 250 and 600°С, respectively.

The surface of graphene-like structures placed in an electric field with a strength of 1−10 V/μm is found to undergo considerable deformation. This effect is observed in both a direct field (emission current is present) and a reverse field (emission current is absent). The deformation of the surface of cathodes facilitates low-threshold electron emission. The qualitative model proposed here to explain the effect of low-energy electron emission is based on the idea of surface reconstruction and the formation of centers with negative correlation energies (negative-U centers).

The relative concentration of deuterium implanted into a beryllium sample is determined by elastic peak electron spectroscopy (EPES). The method of partial intensities based on solution of the boundary value problem for the transport equation by the invariant embedding method is used for subsequent determination of the energy spectra of reflected electrons. The differential inverse inelastic mean free paths (DIIMFPs) and the differential surface excitation probability (DSEP) are retrieved using a fitting procedure based on numerous solutions of the direct problem with fitting parameters. The high efficiency of the fitting procedure is based on the technique of numerical solution of equations for the partial intensities, which combines precision and a record-high calculation speed. In the work DIIMFP and DSEP are obtained for both the surface region and for a homogeneous array in the bulk. Calculations of DIIMFP and DSEP are carried out for pure beryllium and for beryllium samples implanted with deuterium. The relative concentrations of deuterium into beryllium were determined at a different fluence. The obtained values of the relative deuterium concentrations are n_D/n_Be = 0.12 ± 0.02 and 0.15 ± 0.03 for an irradiation dose of 5.5 × 10²¹ and 20.1 × 10²¹ m^–2, respectively. The results indicate that, in comparison with the methods used earlier, the developed method allows an order of magnitude in of the sensitivity of determining the relative hydrogen-isotope concentration in compounds to be attained.

The review is devoted to modern techniques of the nondestructive determination of the thickness of thin films based on scanning electron microscopy and energy dispersive X-ray analysis. A general approach for determining the thickness of thin films by these methods is described along with detailed specific techniques, their advantages and disadvantages.

The role of porosity and pore size in the morphological changes of nanoporous materials during low-energy ion irradiation is studied in terms of crystalline-silicon models. Molecular dynamics simulations are implemented to study the destruction of porous structures with different values of the porosity and pore size. The obtained dependences of the potential energy and specific surface area on the system temperature are used to determine the material parameters, at which the process of pore compression occurs.

A complex radiation diagnostics facility “DRAGON” has been constructed at the reactor IR-8. The facility includes 3 beams for measurements using neutron and gamma radiation. The parameters of the facility are presented; the main units of the facility are described. The results of radiographic and tomographic experiments on the setup are presented.

An expression for the Helmholtz free energy of a nanocrystal that contains vacancies in lattice and the delocalized (diffusional) atoms is obtained on the basis of the previously proposed three-phase model of a simple matter and the RP(vac)-model of a nanocrystal. A model of the Gibbs surface, on which a portion of cells are vacant and a part of atoms are in the delocalized state, is proposed. The fact that a proportion of delocalized atoms are delocalized in a “bulk” way and a proportion of them are delocalized in a “surface way” is taken into account. The equation of state is calculated for argon, whose atoms interact via the Mie–Lennard-Jones pairwise potential. Calculations for the macrosystem were show that, at average temperatures, the equation of state has two S loops on isotherms corresponding to the crystal—liquid (C—L) and liquid—gas (L—G) phase transitions (PTs). At high temperatures, the S loop of the L—G PT contracts to the critical point. At low temperatures, two S loops of the C—L and L—G PTs merge into one large S loop corresponding to the C—G PT. As the number of atoms (N) in the nanosystem decreases, the S loops of both phase transitions in the isotherm decrease, and the C—L S loop disappears at a certain value of the number of atoms (N₀). It is shown that N₀ increases as the temperature of the isotherm increases and the nanosystem shape deviates from the most energetically optimal one (it is cubic for the RP(vac)-model). The C—L PT disappears in a cluster consisting of N < N₀ atoms. Such a cluster gradually transforms into the liquid phase in the case of an isothermal increase in the specific volume.

The temporal characteristics of a time-of-flight spectrometer installed on the first channel of the IBR-2 reactor are investigated. A change in the flash time of the reactor relative to the start depending on the measurement time from the beginning of the reactor operation cycle is discovered. The neutron deceleration time is measured as a function of the neutron wavelength. A dependence of the half-width of the reflections on the neutron wavelength is established. The measurements are carried out in a wide range of Bragg angles from 0.0567232 to 0.34180977 rad (from ~3° to ~19°). An estimate is made for the mosaic pattern of a single crystal.

The parameters of the mesostructure of amorphous zirconium dioxide and their evolution at different stages of heat treatment are determined by small-angle neutron scattering. Particles of amorphous zirconium dioxide, which form mass fractals with the dimension D_v = 2.21, are rearranged into surface fractals with a surface dimension of D_s = 2.52 upon annealing at a temperature of 400°C or higher. In the resulting system, a shell with a fractal structure is formed over a dense core (a cluster of nanoparticles of zirconium dioxide with a constant density). Transformation of the fractal system from a mass fractal into a surface one is characterized by the appearance of a core, and its growth is due to the crystallization of hydrated zirconia particles at high temperatures. A model for the formation of a fractal particle, implying the existence of a core–shell surface fractal system, is proposed. The characteristic radius of ZrO₂ nanoparticles increases from 14 to 200 Å with an increase in the annealing temperature from 400 to 600°C.

A new IR-spectroscopy (infrared) technique allowing investigation of the transformation of gaseous WF₆ on a W surface heated up to 860 K in a hydrogen and argon atmosphere is proposed. The weak chemical adsorption of WF₆ on W substrates is observed. The intermediate reaction products of WF₆ with solid W above 670 K are penta- and tetra-tungsten fluorides. The presence of other low-valent tungsten fluorides is possible in the form of adsorbed oligomeric molecules (dimers or trimers). It is shown that low-valent tungsten fluorides are strongly adsorbed on the surface of W. The adsorbed layers formed on the W substrate in the WF₆ + H₂ mixture and pure WF₆ str identical in composition.

The paper is devoted to the study of the adsorption of C₆₀F₁₈ fullerene fluoride molecules with high dipole moment on a graphene-like surface in order to investigate the possibility of creating interfaces with given physical and chemical characteristics and controlling their properties. Using atomic force microscopy, X-ray photoelectron spectroscopy, and quantum chemical calculations, the island structure of thin films of C₆₀F₁₈ polar molecules on the surface of highly oriented pyrolytic graphite has been first found. The chemical stability of fluorinated fullerene molecules in the adsorbed film and the island growth of the film according to the Volmer–Weber mechanism up to large degrees of coverage have been established. The nature of the interaction between adsorbate molecules and the substrate has been determined. The influence of collective electrostatic effects on the structure of the monolayer, the total energy of the system, and the shift of the core electronic levels have been concluded.

Single crystals of LaMgAl₁₁O₁₉ with the magnetoplumbite-type structure are grown from the melt. They demonstrate a perfect cleavage in the (0001) plane. According to atomic force microscopy, the surface of the fresh (0001) cleavage of LaMgAl₁₁O₁₉ single crystals is characterized by an extremely low roughness (R_z < 0.05 nm), which is typical for pure atomically smooth crystal faces without steps. The annealing of LaMgAl₁₁O₁₉ single-crystal plates in air at 1200°C results in recrystallization and significant morphological changes in the surface, namely, the formation of flat triangular or hexagonal prisms with strictly parallel sides and dimensions in the plane (0001) up to 0.5 μm and different heights (0.7 and 1.8 nm).

The microstructure and crystallographic orientation of aluminum have a significant effect on the morphology of porous alumina films grown on the surface of Al by anodizing. Most existing works regarding the regularities of aluminum anodizing consider metal foils as isotropic media. The novelty of this study lies in the characterization of porous alumina coatings formed on aluminum single crystals with the same orientation, Al(111). Experiments are carried out in 0.3 M oxalic acid in a wide range of anodizing voltages of 20–140 V. Using scanning electron and atomic force microscopy, the dependence on the anodizing voltage of the degree of porous ordering with the formation of a hexagonal array, as well as height-profile parameters of the metal–oxide interface, are shown. The thickness-to-charge ratio for the used anodizing conditions is determined.

The electron-beam exposure of dielectrics is actively explored in various fields of science. Recently, we have shown the possibility of the selective growth of graphene-like films on oxidized silicon due to an increase in the growth rate of a carbon film on exposed areas. Since the mechanism of the detected phenomenon is unclear, its study is a difficult scientific challenge. In this paper, the potential of atomic-force microscopy as a key instrument for characterization of these films is demonstrated. In particular, the point contact method provides grounds for interpreting processes occurring on the surface in the case of alternating synthesis and exposure to different irradiation doses. This method allows surface topography data and other characteristics (“adhesion” and “gradient” modes) to be obtained in one scan pass. The surface of the graphene-like films is scanned before and after exposure by means of atomic-force microscopy. Analysis of the data obtained shows that the “adhesion” mode enables special features of the samples that are either difficult or impossible to identify in a topographic image to be revealed. The study demonstrates the possibility of obtaining valuable information using cantilever-needle interaction with the surface to measure additional parameters.

A complex of studies of the composition, structure, and properties of nanoscale surface layers of titanium alloy VT6 formed by the ion-beam mixing of a carbon nanofilm is conducted. It is found that ion-beam mixing in the transition layer of a film/substrate system provides conditions for the formation of titanium carbides, the content of which increases to 20 at % with an increase in the irradiation dose. After both the deposition and ion-beam mixing of a carbon film, the hyperfine surface layer of the samples mostly consists of carbon atoms in a disordered state with sp²- and sp³-hybridized C–C bonds. It is revealed that the coherent scattering region of samples decreases after ion-beam mixing; this effect can be attributed to an increase in the dislocation density and the formation of dislocation substructures. The formation of titanium carbides, a disordered carbon structure, and dislocation substructures under ion-beam mixing conditions leads to a more than twofold increase in the microhardness of the samples.

The polarization characteristics of diffraction radiation appearing during the uniform motion of a nonrelativistic charged particle near an ideally conducting sphere and also a hemispherical bulge in a conducting plane are calculated. Our previously developed approach based on the method of images, which is known in electrostatics, is used. It is shown that, in the low-frequency range, radiation at a hemisphere is always linearly polarized, while radiation at a sphere is generally characterized by elliptical polarization.