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

The formation of amorphous thin surface layers of nanoporous Ge with various morphologies during the low-energy high-dose implantation by metal ions of different masses, namely ⁶³Cu⁺, ¹⁰⁸Ag⁺, and ²⁰⁹Bi⁺, on single-crystal c-Ge substrates was experimentally demonstrated using high-resolution scanning electron microscopy. The structure of the obtained nanoporous Ge layers was studied using backscattered electron diffraction. Under irradiation with low-energy ions, such as ⁶³Cu⁺ and ¹⁰⁸Ag⁺, needle-like nanostructures constituting a nanoporous thin Ge layer form on the surface of c-Ge. However when employing havier ²⁰⁹Bi⁺, the implanted layer consists of densely packed nanowires. At high ion-irradiation energies, the morphology of the thin surface layers of nanoporous Ge undergoes a sequential transformation in shape from three-dimensional reticulated to spongy as the mass of the implanted ions increased. Such a spongy structure was formed by sparse individual intertwining nanowires. The general potential mechanisms for pore formation in Ge during low-energy high-dose ion implantation are discussed, including the cluster–vacancy mechanism, local thermal microexplosion, and localized heating accompanied by surface melting with effective sputtering.

The temperature dependences of the sputtering of negative ions of silicon–oxygen clusters are studied for the first time by the method of ultrahigh-vacuum secondary ion mass spectrometry. In the temperature range of 100–200°C, an increase in the yield of negative ion clusters of silicon suboxide and dioxide is observed, while after a maximum at 200°C and up to 800°C the yield decreases exponentially. At 800°C, the yield of silicon oxide clusters stops while the desorption of suboxide is still observed. The yields of negative oxygen ions correlate with the temperature dependences of the yield of silicon–oxygen clusters and indicate the presence of oxygen adsorbed on the surface and dissolved in the bulk of the silicon crystal. In this work, for the first time, to assess the contribution of these processes a signal from negatively charged silicon dimers, which are an adsorbed silicon atom on a silicon atom located at a substrate lattice site, is used. The temperature dependence of the thermal desorption of negatively charged silicon trimers is measured. In our opinion, this signal is due to a decay negative cluster ion of a surface defect center, the so-called P_b-center, of an adsorbed silicon tetramer—three silicon atoms on the surface closed at the top by an additional silicon atom.

Diffraction radiation is widely used for the nondestructive diagnostics of charged particle beams. In the series of previous works, a method was developed for describing the diffraction radiation of a nonrelativistic particle on a perfectly conducting sphere, based on the method of images well-known from electrostatics. This method allows one to derive the analytic formulas for two main radiation characteristics, i.e., spectral angular density and polarization. The characteristic features of these values allow the possibility of developing, on their basis, new methods for monitoring the parameters of the trajectory of a moving particle in relation to the sphere center. In this work, formulas are obtained that describe the polarization of the coherent diffraction radiation on a metal sphere from a pancake-bunch of charged particles. It is shown that the polarization of the radiation in this case makes it possible to estimate the positions of bunch edges relative to the center of the sphere. This can be used for the nondestructive measurement of characteristic bunch dimensions.

The structure of aqueous dispersions of phospholipid transport nanosystem (PhTNS) based on soybean phospholipids developed at the Institute of Biomedical Chemistry (Moscow, Russia) was studied by the method of small-angle X-ray scattering. The PhTNS concentrations in water were 20, 25, 31.25, and 37.5%. The structural parameters of vesicles (inner radius, thicknesses of the regions of hydrophobic tails and polar heads) were determined in the “core/multi-shell model” approximation with variations in the scattering length densities of vesicle different parts, as well as the solution that was inside and outside the vesicle. A difference in the photon scattering length densities was detected between the solution volume and the inner region of the vesicle due to the uneven maltose dissolution, which was part of PhTNS. With an almost constant thickness of the lipid bilayer, a decrease in the vesicle radius from ~150 to ~130 Å was observed with increasing concentration of the system which was due to increasing osmotic pressure. The hydrophobic volume of vesicles was determined to be 7.45 × 10⁶ ų at the lowest concentrations of 20% and 5.85 × 10⁶ ų at the highest concentration of 37.5%.

We investigate the structure and properties of magnesium-aluminate spinel films synthesized by the reactive anodic evaporation of Al and Mg from separate crucibles in a low-pressure arc (Ar–O₂ mixture at 0.7–1.2 Pa) and vapor deposition onto a substrate at 400–600°C. A discharge current with a self-heating hollow cathode is distributed between the anode (10–30 A) and the crucibles containing Mg (0.8–1.6 A) and Al (4–16 A), which allows for independent adjustment of the deposition rate of the films, plasma density, partial pressures of metal vapors, and elemental concentrations in the films. A decrease in the oxidation rate of Mg and stabilization of the evaporation process are achieved by increasing the power density of the electron beam on the Mg surface inside the crucible and transitioning from the sublimation mode to the evaporation mode from the liquid state by narrowing the aperture of the Mg crucible. The high vapor-flux density of Mg in the small aperture prevents oxygen from entering the crucible. The crystallization temperature of the spinel under ion bombardment of the growing film, with ions having an energy of 25–100 eV at a current density of 2 mA/cm², is approximately 400°C. The films are characterized using scanning electron microscopy, X-ray phase analysis, and microhardness testing. The cubic spinel films exhibit a strong (100) texture and a crystal-lattice distortion level of ~1%. The deposition rate of nonstoichiometric spinel films, with a relative Al-to-Mg atomic content adjustable within the range of 1.2–2.4, is 1–3 μm/h.

The study investigates high-voltage gradual p⁰–i–n⁰ junctions in solid solutions of Al_xGa_1 – xAs_1 – ySb_y with y up to 15%, which are capable of absorbing radiation with a wavelength of 1064 nm, grown on GaAs substrates by liquid-phase epitaxy through self-doping with background impurities. The composition of the liquid phase and the temperature range of growth are selected so that the aluminum-compound content x decreased steadily from the specified values of about 34% to a few percent at the surface of the epitaxial layer, while the antimony-compound content y increased. In this case, the band-gap width gradually decreased from the substrate to the surface of the lightly doped layer, reaching the desired value of ~1.16 eV. By measuring the capacity–voltage characteristics and deep level transient spectroscopy in them, configurationally bistable DX centers associated with donor impurities Si and Se/Te are identified. The investigated heterophase epitaxial layers reveal the absence of deep energy levels associated with dislocations. The effective lifetime of minority charge carriers in the base layers of the Al_xGa_1 – xAs_1 – ySb_y/GaAs diode is determined using reverse recovery of the diode. Assuming that the minority-carrier lifetime is mainly determined by the capture of holes by the acceptor-like deep level DX ^– of Si in the n⁰ layer of the material, the hole capture cross section on the DX ^– level is estimated. The capture cross section is found to be 6 × 10^–15 cm².

The paper proposes an experiment to measure the neutron lifetime by storing ultracold neutrons in a rotating magnetic trap. The magnetic trap is a set of NdFeB permanent magnets. By rotating the trap around a horizontal axis, it is possible to carry out the gravitational capture of ultracold neutrons and their holding. A design option is presented when two traps are located in one installation on the same axis: material and magnetic. The sensitivity of the magnetic trap is assessed in comparison with the material one under equal measurement conditions. One of the factors influencing the systematic error of the experiment will be the process of neutron depolarization in a magnetic field. Therefore, the paper considers the issue of developing a magnetic system that minimizes the probability of neutron depolarization. The so-called turbine effect is also considered, which can manifest itself in a change in the energy of ultracold neutrons during rotation due to interaction with the flat faces of the trap. The proposed gravitational capture of ultracold neutrons in a magnetic trap is a fundamentally new approach that has never been implemented before. The experiment can be carried out on the ultracold neutron source under construction at the PIK reactor.

The atomic and electronic structures of two organosilicon polymers [–Ph₂Si–(C≡C)₂–]_n (P1) and [–Ph₂Si–(C≡C–C≡C)₂–]_m (P2) (where Ph is a phenyl group) of acetylene and diacetylene types are studied using the methods of density functional theory and X-ray emission spectroscopy. The SiK_β1 X-ray emission spectra of these polymers are interpreted on the basis of analysis of the distribution of partial electronic states obtained from quantum chemical calculations. The quantitative characteristics of the parameters of the chemical interaction of atoms, such as population, natural charges, and electronic configurations in the studied polymers, are obtained on the basis of analysis of hybrid natural bond orbitals. The values of the polarization coefficients of natural bond orbitals indicate the localization of electron density predominantly on carbon atoms. The electronic configurations for carbon atoms in different fragments differ significantly. For the C atoms of ethynyl (diethynyl) fragments, they are close to the linear σ bond of the sp^1.03 (P1) and sp^0.95 (P2) type, while for the C atoms of phenyl fragments, they are sp^2.42, which are intermediate between sp² and sp³, in accordance with molecular geometry. The natural charges on Si in both polymers are almost the same: +1.58e, +1.59e (e is the elementary charge), while the natural charges for carbon atoms of the diethynyl group decrease in comparison with the charge for the carbon atom of the ethynyl group from –0.42e to –0.36e.

Burnishing is a well-known, low-cost yet effective super finishing method that involves the plastic deformation of the surface layer, resulting in cold working, which improves mechanical characteristics and increases component operating life. Surface quality is primarily related to component service qualities such as wear resistance, corrosion resistance, and fatigue life. This leads to the investigation of ball burnishing as a supportive technique to improve component durability. The purpose of this study is to explore and optimize the ball burnishing process using the Taguchi approach in order to determine the most suitable combination of process parameters to reduce the specific wear rate and coefficient of friction of AISI 1040 steel components. Post-burnishing, hardness improved from 195 to 287 Hv and roughness of surface reduced from 0.447 to 0.101 μm. The optimization findings revealed that 52.35% improvement in wear resistance, whereas coefficient of friction was reduced by 61.53% as compared to the turned surface. The results confirm that ball-burnishing technique enhanced the functional properties of AISI 1040 steel.

Based on small angle neutron-scattering data from a nanocomposite composed of fullerene C₆₀ (16.5 wt %) in an isotactic polypropylene matrix, we receive information on the clusterization of nanoparticles and define their geometric parameters and dimensionality. This study proposes an interpretation of the aggregation of particles with surface fractal properties in the size range up to 80 nm, as observed in a small-angle-neutron-scattering experiment. Based on well-known theories about the defect structure of the fullerene C₆₀ molecule in non-Euclidean metrics, specifically disclinations and monopoles in the two-dimensional spherical space of Gödel type, we formulate a lattice version of the monopole gas model. Within this framework, we use the Monte Carlo method on a lattice with the Abelian projection to estimate the energies of monopole currents at various monopole concentrations. The proposed model enables the calculation of the fractal properties of C₆₀ nanoparticles in a polymer composite, as well as the interpretation of the evolution of disclinations.