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

In this work, computer molecular dynamics and experimental studies of the enzyme alcohol dehydrogenase (ADH) and its cofactor nicotinamide adenine dinucleotide (NAD) solvated with water on a graphite carbon surface were carried out. Computational molecular dynamics (MD) simulations of the (ADH + NAD + water) system were performed to track the adsorption process on the surface of graphitic carbon during long-term 100 ns dynamic conformational and rotational changes. MD analysis provides mapping of the adsorption orientation of the ADH+NAD enzyme, which allows detailed observation of changes in protein conformation in the region of titratable amino acid residues of ADH. Identification of the characteristic conformation of key titratable amino acids may become a necessary stage in further ¹research and implementation of a numerical experiment, which will be carried out by varying the pH and charge values. MD simulation data are compared with experimental observations, which indicate the atomic-molecular mechanism of the influence of solution pH on the conformation and orientation of protein adsorption.

The effect of heat treatment in air at 200–250°C on the magnetic properties and their uniformity in ribbon samples of the cobalt-based amorphous soft magnetic alloy AMAG-172 (Co–Ni–Fe–Cr–Mn–Si–B) was studied. In the quenched state, the nonuniformity of the magnetic properties of the ribbons is related to the manufacturing process, namely, the presence of cooling rate gradients. Heat treatment in air within the studied temperature range, with various durations of isothermal holding, was found not to improve the magnetic properties of the ribbon or enhance their uniformity. The formation of bimodal and trimodal field dependences of magnetic permeability indicates that the ribbon becomes stratified across its thickness during annealing. The decrease in maximum magnetic permeability is attributed to the reorientation of magnetization perpendicular to both the ribbon plane and the ribbon axis within its plane. The results are explained by the influence of anisotropic stresses induced by oxidation, hydrogenation of the ribbon surface, and its surface crystallization.

Thin NiO films with thickness from 40 to 170 nm were obtained by pulsed laser deposition on c‑Al₂O₃ substrates using the second harmonic of YAG:Nd³⁺ laser for ablation of a metal Ni target in a vacuum chamber at an oxygen pressure of 7.5 mTorr and a substrate temperature of 370°C. Using X-ray diffraction, all NiO films were shown to have high crystalline perfection and the [111] orientation. The surface roughness of the obtained films was in the range from 1.6 to 2.3 nm. It was found that with increase in NiO film thickness the charge carrier concentration decreases and the specific resistance increases. According to measurements of the optical properties of the films, the band gap increases from 3.43 to 3.63 eV with decreasing thickness.

Returning spacecraft, when passing through Earth’s atmosphere, are characterized by intense destruction of the frontal heat shield caused by the impact of a high-speed oncoming gas flow. As a result of ablation, which occurs over several minutes, the products of destruction enter the surrounding plasma layer and partially settle on the surface of the spacecraft. The design features of the Soyuz descent vehicle made it possible to study the results of the interaction between the plasma flow and the surface of the porthole located in the leeward zone. To examine the characteristics of individual particles and their aggregates, both direct imaging of surface relief fragments and various methods of sample preparation were used. The results of experimental studies of the plaque on the porthole were obtained by various methods: optical microscopy, laser scanning confocal microscopy, X-ray diffraction, and electron microscopy. The physicochemical conditions of plasma component deposition on the glass surface are discussed. The obtained data on the phase composition, morphology, and elemental composition of the microparticles are analyzed. A classification of particles formed on the surface of the spacecraft during interaction with the plasma flow while passing through the atmosphere is proposed.

Thin MoS₂ films with a thickness of three to 30 monolayers of a large area on c-Al₂O₃ substrates were obtained by pulsed laser deposition. The MoS₂ films were synthesized using MoS₂ targets manufactured according to the developed technique at a substrate temperature of 700 and 770°C. The influence of laser synthesis conditions and substrate temperature on the deposition rate and optical and electrical characteristics of the MoS₂ films was studied. The film thickness was controlled by the number of laser pulses, which was confirmed by atomic force microscopy and Raman spectroscopy. A clear dependence of the characteristic phonon modes of Raman scattering on the number of monolayers was observed in the spectra of the MoS₂ films. With an increase in the number of monolayers in the film, the position of the photonic modes (E_{{2g}}^{1}) and A_1g were found to shift to the red and blue regions of spectrum, respectively, and the distance between them changed from 25 to 26.9 cm^–1 for the number of pulses increasing from 24 to 720, respectively, at a growth temperature of 770°C.

The paper presents the results of a study of high-temperature oxidation in air of the metal-ceramic layered Ti₃Al(Si)C₂/Ta composites. The composites were made of preceramic papers filled with Ti₃Al(Si)C₂ and metal foils (Ta) by spark plasma sintering. The sintering temperature was 1250°C, the holding time was 5 min, and the pressure was 50 MPa. The corrosion resistance of the laminated Ti₃Al(Si)C₂/Ta composites was estimated based on the results of high-temperature oxidation in air. The phase composition and microstructure of the oxide layers were analyzed by X-ray diffraction and scanning electron microscopy, respectively. It has been found that the Ti₃Al(Si)C₂/Ta composites demonstrate high oxidation resistance in the temperature range 800–1200°C due to the formation of a dense Al₂O₃ layer on the outer surface of Ti₃Al(Si)C₂. With an increase in the oxidation temperature to 1300°C, a complex oxide layer is formed, consisting of an outer TiO₂/SiO₂/Al₂TiO₅ layer and an inner TiO₂/Al₂O₃ oxide layer. The thickness of the TiO₂/Al₂O₃ oxide layers formed on the surface of the Ti₃Al(Si)C₂/Ta composite at oxidation temperatures up to 900°C is less than 1 μm, at a temperature of 1200°C the thickness of the oxide layers is 3.5 μm, and at 1300°C it is 56 μm.

The phase composition and microstructure of samples obtained by hot pressing of β-FeSi₂ and Co powders have been studied using scanning electron microscopy. It is experimentally shown that during the thermal diffusion of Co into the volume of thermoelectric β-FeSi₂, zones are formed within which the concentrations of all elements (Si, Co, Fe) change. The CoSi phase is also formed. The β-FeSi₂ phase retains mechanical strength.

The influence of the laser radiation power density during laser shock peening (LSP) of the titanium alloy Ti–6Al–4V (VT6) on the properties of the surface layer—geometry, microhardness, degree of riveting, residual stress level, and microstructure—is studied. Comparative fatigue characteristics of samples strengthened under different laser shock peening modes are presented. A fractographic analysis is carried out, and the relationship between the laser shock peening modes and the depth of fatigue crack initiation is established.

The method of high-intensity implantation of high-power ion beams with submillisecond duration predetermines significant pulsed heating of the irradiated target’s surface layer with subsequent ultra-fast cooling. The numerical modeling was used to study dynamic variations in temperature fields in titanium (Grade 2), aluminum alloy (1013), Zr–1Nb alloy (E110), stainless steels (321 and 5140) differing significantly in physical and mechanical properties. The article has considered the temperature gradient dynamics in the near-surface layer and at great depths of matrix materials under the influence of submillisecond ion beams with a pulsed power density of up to 1 × 10⁹ W/m². The parameters of ion beams providing pulsed heating of the surface layer of various materials to the melting temperature have been determined. Both single-pulse and repetitively-pulsed irradiation were studied, including taking into account the heating of the material’s entire volume. It has been shown that after the end of the ion beam pulse, the high-speed heating of the surface layers of metals and alloys turns into ultra-fast cooling due to heat transfer into the main volume of the matrix material due to thermal conductivity.

Thin films of tin(II) phthalocyanine (SnPc) were thermally evaporated in vacuum onto substrates at different temperatures (T_g). Their transmission spectra in the UV, visible, and near-IR ranges were measured. A 100 nm thick SnPc film was found to become an almost panchromatic photoabsorber: the “green gap” characteristic of porphyrinoids narrowed to the range 410–490 nm, and the long-wavelength edge of the Q band extended to 1100–1200 nm, depending on the growth conditions. At T_g below room temperature, the films were X-ray amorphous, and at T_g > 25°C, the triclinic polymorph accumulated. The structure of the films was always granular, but the size, shape, and packing of grains strongly depended on T_g. The specific conductivity of SnPc thin films was measured in the dark and under continuous white light (solar simulator) or filtered near-infrared light. For SnPc films grown at elevated T_g, the photo-to-dark current ratio exceeded an order of magnitude under residual illumination at wavelengths longer than 1 µm.