Vol 10, No 1 (2016)

Spectroscopic characterization of lanthanum beryllate La₂Be₂O₅ (BLO) single crystals doped with trivalent ions of Eu, Nd or Pr, was carried out in the ultraviolet-visible spectral range using synchrotron radiation spectroscopy in combination with conventional optical absorption and luminescence spectroscopy techniques. On the basis of the obtained data, the energy level diagram for these trivalent impurity ions in BLO host lattice was developed; the optical and electronic properties of the crystals were determined; the possibility of the 4f-4f, 4f-5d and charge transfer transitions was analyzed; spectroscopic properties of the lattice defects formed during the introduction of trivalent impurity ions in the BLO host lattice, were investigated. We found that the lattice defects are responsible for a wide-band photoluminescence (PL) in the energy region of 400–600 nm. The most efficient excitation of the defect photoluminescence in the energy gap of BLO occurs in broad PL excitation-bands at 270 and 240 nm. The PL intensity of defects depends on the type of impurity ion and increases in the sequence: Pr-Nd-Er.

By methods of optical, scanning and transmission electron microscopy and microhardness measurement the transformation regularities of structure-phase states, defect substructure, fracture surface and mechanical properties of rail surface layer up to 10 mm deep in process of long-term operation (passed tonnage of gross weight 1000 mln. tons) were revealed. According to the character of fracture and level of structure imperfection the three layers were detected: surface, transition and boundary ones. It has been shown that the surface layer ~20 μm in thickness has a multiphase, submicro- and nanocrystalline structure and it contains micropores and microcracks. The increased density of bend extinction contours at 2 mm depth from the tread contact surface was noted, and it was shown that the maximum amplitude of stress fields was formed on the interphase boundary the globular cementite particle–matrix. The evaluation of stress fields was done.

A technique for recovering the differential inverse inelastic mean free paths (DIIMFP) of electrons in Nb from the reflected electron energy loss spectra (REELS) at initial energies of 5 to 40 keV using a threelayer model of the sample surface is presented. The recovered DIIMFP are used for analyzing X-ray photoelectron spectra measured at different viewing angles. Comparison with experimental data is carried out.

We investigate the structure formation of sol–gel synthesized epoxy–siloxane compositions with a ratio of the main precursors of R_{TEOS/EPONEX 1510} = 27/27 wt %, modified with biocidal additives of detonation nanodiamonds (c_DND = 0.13, 0.27, and 0.58 wt %), titanium dioxide (\(^cTi{O_2}\) = 0.1, 0.3, and 0.5 wt %), and Photosens (c_Ph = 0.04, 0.1, and 0.27 wt %), by small-angle X-ray scattering. Based on small-angle X-ray scattering (SAXS) data, it is revealed that the synthesized epoxy–siloxane xerogels are systems with a twolevel fractal structure, in the formation of which the siloxane component plays the dominant role. It is found that the introduction of small additions of detonation synthesis, titanium dioxide, or Photosens (less than 1 wt %) into the epoxy–siloxane compositions affects both the fractal dimension D_S of the surface and the size d_c1 of primary particles, and the fractal dimension D_M and sizes d_c2 of mass fractal clusters formed from them.

The results of microstructure and texture studies into Sn–Bi and Sn–Pb eutectic alloys produced at melt cooling rates of 2 and 5 × 10⁵ K/s are presented. Ultrafast quenching from the melt is found to initiate the formation of microcrystalline structure. The causes of the transition from the lamellar to the microcrystalline structural phase and the generation of nucleation texture are discussed.

Examples of the application of a cryogenic moderator in the REMUR time-of-flight neutron reflectometer of the IBR-2 pulsed reactor (Dubna) are given. The results of two experiments are presented: spatial beam splitting upon reflection from a magnetically noncollinear film and the recording of a microbeam formed by a layered waveguide. A conclusion concerning the efficiency of the cryogenic moderator for experiments of this type is made.

The electron and spin structure of thick smooth hydrocarbon CD_x films (“flakes”) with a high relative deuterium concentration of x ~ 0.5, redeposited from deuterium plasma discharge onto the walls of the vacuum chamber of the T-10 tokamak and containing ~1 at % of 3d-metal impurities due to erosion of the chamber walls, are studied using electron paramagnetic resonance (EPR) and photoluminescence (PL). The resulting spectra are compared for the first time to the EPR and photoluminescence spectra of polymer (soft) a-C:H(D) films (H(D)/C ~ 0.5), which are considered model analogues of smooth CD_x films. A certain similarity of the CD_x films with a-C:H films was found in the electronic structure of the valence band. At the same time, the differences in the EPR and photoluminescence spectra were observed due to the presence of 3d-metal impurities in the CD_x samples, contributing to the conversion of sp³ → sp² in the formation of films in the tokamak and upon heating and thermal desorption. An impurity of, presumably, 3d metals was detected for the first time by EPR in the a-C:H films in an amount of approximately 0.2 ppm, related to the evaporation of graphite.

The results of studying regions of inhomogeneous magnetization on the surface of permalloy thin films with the use of fabricated highly sensitive probes of magnetic force microscopy (MFM) are presented. The technological features of manufacturing MFM probes with a high sensitivity to magnetic-field gradient are analyzed. Regions of ordering of the vertical component of the magnetic field are revealed, and domain walls are visualized in the thin films under study. Nanoscale measurements of the domain-wall thicknesses are performed.

Using the diagram technique for Hubbard operators, the effect of quasi-two-dimensionality and hybridization of the 4f electrons of cerium ions and p electrons of indium ions on the properties of the antiferromagnetic, superconducting, and mixed phases in heavy-fermion intermetallic compounds of cerium is studied. It is shown that taking into account quasi-two-dimensionality, low-energy hybridization processes renormalize the antiferromagnetic and superconducting order parameters in the broken time-reversal symmetry phase. Estimates of the critical temperatures of antiferromagnetic ordering and Cooper instability, obtained by the developed approach, are in good agreement with experimental data for cerium-based intermetallic compounds.

A method for the fabrication of regular microstructures with a high aspect ratio (for example, X-ray gratings) by direct multibeam vector recording in layers of an SU-8 resist is presented. An X-ray beam with a wavelength from 0.4 to 1.7 Å is used for recording. The features of the method are described. The fabricated samples of regular microstructures of the SU-8 resist and gold-plated X-ray masks are presented as finished products.

The features of the angular distributions of accelerated neutral atoms at grazing angles of incidence on the Al(001) surface are studied using the mathematical modeling method. The interaction of accelerated atoms with crystal-lattice atoms and the electronic properties and atomic structure of the Al(001) surface are calculated using the electron-density-functional method. The angular distributions of scattered atoms are modeled by taking into account their interaction with several atomic layers in the crystal lattice and atomic displacements during thermal oscillations. The influence of crystal surface-layer relaxation on rainbow scattering, i.e., the difference between the distances of planes on the surface and in the volume, is established. The possibilities of using the effect of rainbow scattering to study the structural features of a crystal surface are discussed.

The stability of the physicochemical properties of the (0001) plane of sapphire is largely determined by the accuracy of its orientation. It is shown that at a deviation of the surface from the (0001) plane by 4°, the wear rate increases by 13–22%, the corrosion resistance decreases by a factor of 1.4, thus enabling the rate of chemical mechanical polishing to grow up to 2.3 times.

A device for the excitation and detection of neutron magnetic-moment precession, consisting of a pair of magnetic mirrors placed in a magnetic field, is discussed. The device may be used as the phase-shifting element in a spin-echo neutron spectrometer, which measures the correlation time of the oscillations of a medium or the correlation length of its density. It is shown that in a magnetic field with an intensity of up to 1 kOe, the probability of neutron scattering can be measured from the minimum values of the wave vector of 10^–7 Å^–1 and the transmitted energy of 1 peV.

The structural aspects of PbS-nanoparticle formation in silicate glasses under different conditions of heat treatment are studied using small-angle neutron scattering. It is established that spherical nanoparticles with radii of 3.0 to 3.9 nm form in such glasses. As the duration of sample annealing increases, growth of the mean nanoparticle size is observed and their fractal dimensions change. The structural mechanisms for PbS-nanoparticle formation in a glass matrix are discussed in the case of two-stage temperature treatment.

The structure of a mollusk shell is studied by synchrotron X-ray diffraction and small-angle X-ray scattering methods using a two-dimensional detector. Scattering is measured in the momentum transfer range of q = 0.03–60 nm^–1, which makes it possible to reveal structural features in the size range of 0.1–200 nm. At large q values Bragg scattering is observed whose character shows that aragonite plates are good single crystals without internal inclusions. At small angles scattering mainly occurs at the biopolymer film. This scattering, which has not previously been observed, is strongly anisotropic. The anisotropy type corresponds to the one-dimensional mesostructure of the polymer, which is formed by a system of parallel fibers packed with a step of ~100 nm and has no longitudinal structuring. Information on the biopolymer is obtained in situ without destruction of the nacre.

The effect of the substrate type, ambient relative humidity, water vapor and vapors of organic compounds on the surface morphology of films based on dipeptide L-valyl-L-valine are studied using atomicforce microscopy. It is found that at a low relative humidity the dipeptide is crystallized on a hydrophobic substrate with the formation of pyramidal structures, while at a high relative humidity hollow truncated cones are observed. A dipeptide film coated with irregularly shaped objects is observed on hydrophilic substrates. After saturation of the L-valyl-L-valine film with the vapors of proton-donor solvents the formation of new objects on its surface or the destruction of initial objects can occur, while water vapor does not affect the surface morphology. For proton acceptors the major factor affecting the surface morphology of dipeptide film is their energy of the hydrogen bond with proton donors. It is shown that the effect of organic vapors on the film morphology depends on the substrate type.

The results of investigating the imaging of grooves in silicon with a trapezoidal profile and large side-wall inclination angles, which are obtained using a scanning electron microscope operating in the back-scattered-electron collection mode, are presented. Only two among the four known imaging mechanisms is demonstrated to provide contributions to the image-formation process. The lack of contributions from two other mechanisms is explained.

The results obtained using methods of total current spectroscopy (TCS) and secondary-ion mass spectroscopy (SIMS) under ion bombardment of LiF crystals are analyzed. It is shown that the majority of the products of crystal sputtering contain point defects. A procedure for determining defects in sputtered clusters of ionic crystals is developed.

A hybrid positron-source scheme based on an electron beam of the Sorgente Pulsata e Amplificata di Radiazione Coerente test facility installed at the Laboratori Nazionali di Frascati (Frascati, Italy) is proposed. In the case of a thin (0.1-mm-thick) amorphous converter, the positron yields per primary electron are compared at positron energies of 1–3 MeV under bremsstrahlung generation and (110)-plane channeling conditions. The radiation of 200-MeV electrons (200 MeV is the parameter of the SPARC accelerator at the LNF) channeled in a 10-µm-thick tungsten radiator is demonstrated to create positron yields of 10⁴–10⁵ s^–1 in a 0.1-mm-thick W converter.