Vol 11, No 4 (2017)

X-ray studies of dipalmitoylphosphatidylcholine (DPPC) single layers on the surface of a liquid provide detailed information on the interaction of metal particles with a single layer upon an increase in the surface pressure up to the collapse. Two complementary X-ray methods are used: grazing incidence diffraction and the X-ray standing waves method. The experimental results obtained for a single layer formed on a colloidal solution of magnetite nanoparticles reveal that the increase in the surface pressure is accompanied by an increase in the concentration of nanoparticles near the surface. In a series of experiments where metal particles of submicron size are sputtered onto a DPPC single layer, a sharp decrease in the intensity of the fluorescence yield from metal atoms is observed while the single layer is compressed. These data suggest that metal particles deposited onto the surface of a single layer were extruded into the aqueous subphase.

The mode of propagation of relativistic, positively charged particles through a system of mutually oriented and periodically arranged ultrathin crystals whose thicknesses are equal to the half-period of the particle trajectory during planar channeling in a thick crystal is considered. In the case of an incidence angle that is less than the critical channeling angle, a certain fraction of particles is specularly reflected from the atomic planes of the crystal. Therefore, passing through a stack of crystals, a particle moves along quasiundulator trajectories. The characteristics of the radiation of a particle passing through such a “multicrystal microundulator” are found. The radiation spectrum is discrete, and the first-harmonic frequency and the number of harmonics in the spectrum are dependent on the distance between the crystals, the particle energy, and the potential of atomic planes of the crystal. Radiation is concentrated in a narrow cone in the direction of the average velocity of particles and is mainly polarized in a plane that is orthogonal to the atomic planes of the crystal. The microundulator can be composed of separate crystals with micron thicknesses and can be fabricated using modern methods of microlithography and micromechanics with deep, for example, plasmochemical etching of the crystal surface.

A technique for fabricating self-bearing pseudometallic structures, which hold promise for utilization as quasi-optical frequency-selective elements in the terahertz range of the electromagnetic spectrum, is discussed. The technique is based on microstructuring a continuous dielectric layer via stencilled X-ray lithography involving synchrotron radiation with subsequent metallization of the entire structure surface. The main manufacturing schemes are described, including fabrication of the initial substrates and X-ray masks. Examples of samples of the produced selective elements, such as frequency filters and flat lenses, as well as their operating characteristics, are presented.

The photoluminescence of Zn₂SiO₄:Mn²⁺ ceramics with a particle size of 120 ± 10 nm, which is excited in the range of 3.5–5.8 eV and subjected to synchrotron radiation with photon energies of up to 20 eV, is investigated. Nanoscale Zn₂SiO₄:Mn²⁺ ceramics possesses intense luminescence with a maximum of 2.34 eV, the position and half-width of the band are independent of the excitation energy. It is found that the photoluminescence at 2.34 eV decays nonexponentially upon ultraviolet excitation. In the case of nanoscale ceramics is irradiated by vacuum ultraviolet, an additional photoluminescence-excitation channel is likely to occur due to interaction of band states and intrinsic vacancy-like defects of the Zn₂SiO₄ matrix.

Catalytic layers are prepared by the vacuum ion-beam-assisted deposition of tin and platinum onto carbon-based AVCarb® Carbon Fiber Paper P50 and Toray Carbon Fiber Paper TGP-H-060 T supports to produce electrocatalysts for direct methanol and ethanol fuel cells with a polymer-membrane electrolyte. The layers are formed in the mode of ion-assisted deposition, wherein ions of the deposited metal are used as ions assisting deposition. Metal deposition is performed from a neutral vapor fraction, while mixing of the deposited layer with the substrate by accelerated ions of the same metal is carried out from the vacuum arc discharge plasma of a pulsed electric arc ion source. The morphology and composition of the layers is studied using scanning electron microscopy, electron probe microanalysis, X-ray fluorescence analysis, and Rutherford backscattering spectrometry. It is demonstrated by means of voltammetric measurements that the resulting electrocatalysts exhibit activity in the oxidation of methanol and ethanol.

The features of the propagation of undamped thermal (temperature) waves in air are investigated. The presence of these waves is a consequence of solution of the heat equation taking into account the relaxation of local thermal perturbation. It is shown that such waves can exist only in media with a finite (nonzero) time of local thermal relaxation, and their frequencies are determined by this time. The time of relaxation in air depends on the gas composition, its temperature and increases with a decrease in pressure. Under normal conditions, the minimum frequency of undamped waves in air corresponds to 70–80 MHz. One of the methods for exciting these waves is associated with pulsed heating of the surface of a medium bordering air. Pulsed heating on account of the application of shock waves generated during water jet cavitation is used. It is shown for the first time that these waves with frequencies in the range of 70–500 MHz can propagate in air without damping over a distance of up to 2 m.

Hyperdynamics is the method of accelerated molecular dynamics simulation based on lowering energy barriers while performing the dynamic simulation of a nano/atomic system. A system with reduced energy barriers between different states is obtained by changing the potential of interaction, namely, by constructing the so-called bias potential. An approach allowing a bias potential to be obtained is considered. To demonstrate this method, the hyperdynamics simulation of the diffusion of an atom, adsorbed on a 2D crystal surface, and a vacancy, located in its bulk, is carried out. The results are compared with relevant results obtained by molecular dynamics. It is shown that the hyperdynamics approach makes it possible to obtain statistical results, similar to those provided by molecular dynamics. This allows the accelerated simulation of atomic systems to be conducted with minor losses in the accuracy of results.

Articles devoted to methods for improving the structural quality of epitaxial films, which utilize the high-temperature interaction between hydrogen and silicon as well as solid-phase recrystallization process, are reviewed. A correlation between the quality of the epitaxial layer and the radiation resistance of the microcircuits obtained thereon is also considered. A method for creating capture/recombination centers in sapphire during the implantation of helium ions is proposed, yielding high-quality radiation-resistant silicon-on-sapphire films.

Carbon films 110–180 nm thick are fabricated on nickel substrates by the ion sputtering of graphite with simultaneous electron irradiation and subsequent ion irradiation. Irradiation leads to the formation of bonds in the films in various proportions due to the sp and sp³ hybridization of orbitals (sp-and sp³-bonds). Ion irradiation induces, to a greater extent, the formation of sp bonds, while concurrent electron irradiation increases the portion of sp³ bonds. Electron and ion irradiation increases the film microhardness which reaches a value of 12 GPa. A model of the kinetics of creating carbon allotropes in a deposited film is proposed, which is based on the competition between the formation and breakage of carbon bonds during hybridization of different types. Electron and ion irradiation influence the probabilities of the formation and breakage of carbon bonds in the deposited film. The model provides a qualitative interpretation of the observed content ratios of carbon phases in the deposited film.

The chemical structure of Fc and Fab fragments of immunoglobulin G (IgG) is studied by means of X-ray photoelectron spectroscopy. The purpose of studies is to apply the given technique in determining the chemical composition of fragments obtained via papain hydrolysis. Fragments with specified biological properties can be used as an effective agent in a vaccine developed for the treatment of human rheumatoid arthritis, which is prepared from the IgG Fc fragment.

The tribological and mechanical properties of Al–Cu–Si–Sn–Pb alloys are studied. The effect of different alloying elements on the structure of their surface and its tribological properties is estimated. The alloys are studied at different stages of their production, i.e., after casting and homogenizing annealing. The character of surface transformations under friction simulated on fiction machines is investigated. The surface is visualized by means of optical and scanning probe microscopy and scanning electron microscopy combined with elemental analysis. Great amounts of oxygen leading to the formation of oxide particles with abrasive properties are revealed on the contact surfaces. The mass transfer of chemical elements also occurs in the contact area: the material of an insert “spreads” over the shaft to form a film of secondary structures. At small thicknesses, this film serves as a solid lubricant, but might promote the formation of scoring during the development of microrelief. The application of two hardness measurement methods, such as “microindentation” and “nanoindentation”, give mutually complementary results. The highest mechanical properties (hardness, up to 0.5 GPa) are established to be attained in silicon- and copper-containing alloys. Homogenizing annealing at 400°C is also revealed to decrease the hardness, but improve the plasticity, which is important for antifriction materials.

The features of 10-keV electron propagation through a cylindrical channel made of borosilicate glass are experimentally studied. Experimental results indicate that a fast electron beam can be controlled using tapered capillaries fabricated from the given material. The charge distribution formed inside the channel provides conditions under which no less than 20% of beam electrons pass through the channel without considerable energy losses even if the inclination angles exceed the geometric angle of transmission.

Results of modeling by the Monte Carlo method of signals from a scanning electron microscope examining rectangular grooves in silicon are compared with experimental results obtained for a scanning electron microscope operating in the secondary slow electron collection mode. The comparison is performed for the peaks of signals characterizing the primary electron beam near the walls of rectangular grooves: the widths and amplitudes of the peaks, the integral contributions of the peaks, and the positions of the peaks relative to the walls of the grooves. The parameters and their dependences on the primary electron energy are compared. All dependences are very different in terms of the parameters of the peaks and their dependence on the primary electron energy. This proves that the traditional representation of the Monte Carlo method does not work in scanning electron microscopy.

The results of X-ray studies of the structure of components of composite materials based on milled microcrystalline cellulose are presented. The 3D model of the atomic arrangement in the short-range order of amorphous carbon can be described by a mechanical mixture of two types of clusters in the ratio of 1 : 2. One type of clusters is formed by two planar graphene single layers shifted relative to each other and containing vacancies, and the other type is presented by six graphene grids. The cellulose matrix with silicon nanoparticles has a low photoluminescence-signal degradation rate. The introduction of fullerenes into nanomaterial as a third nanofraction, as well as the action of ozone, leads to anomalous luminescence kinetics under UV (ultraviolet) photoexcitation, which can be associated with competing processes of hydrogen and oxygen adsorption on the surface of silicon nanoparticles. A change in the ionic conductivity of the porous cellulose matrix upon exposure to ozone can be used to develop effective ozone detectors. Such a filler as amorphous-crystalline carbon causes not only ionic but also electronic conductivity in the sample; however, the processes of space-charge redistribution remain dependent only on the ion-current component. An increase in the total current passing through the pressed sample eliminates the need for a further increase in the signal in the design of ozone sensors.

An approximate method that is analogous to the eikonal approximation in quantum scattering theory is developed to solve the problem оf the scattering of an electromagnetic wave in the case of its oblique incidence onto an infinite circular cylinder. The limits of applicability of the method include, in particular, the X-ray range. It is shown that inclusion of the finiteness of the cylinder thickness leads to significant asymmetry of the angular distribution of the scattered radiation. The results can be used to improve the kinetic theory of radiation propagation in a system of parallel fibers.