Bulletin of the Russian Academy of Sciences: Physics最新文献

Ferroelectric domain inversion by nano-scale tips of atomic-force microscopes shows a strong (mu )m-sized lateral domain expansion upon application of voltage pulses. We propose a simple self-consistent physical model of this phenomenon based on the concept of domain-wall conduction. The model is capable of a quantitative explanation of a large body of experimental data relevant to lithium niobate crystals. It provides not only the necessary charge compensation far from the tip, but also the absence of the known electrostatic field singularities at the domain edges.

The vibrational properties and crystal structures of rare-earth oxides, specifically yttrium (Y₂O₃) and lanthanum (La₂O₃) ones, were investigated using a combination of density functional theory (DFT) calculations and experimental Raman spectroscopy. Simulated Raman scattering spectra for the reference oxides enabled the identification of vibrational mode symmetries for each phase. By correlating the measured spectra of high-entropy (Y_0.2Eu_0.2Gd_0.2La_0.2Er_0.2)₂O₃ ceramics with DFT results, the crystal structure of the material was determined, and the symmetries of its vibrational modes were assigned. Comparative analysis revealed the presence of the principal La₂O₃ vibrational mode of E_g symmetry at 365 cm^–1 in the high-entropy ceramics. DFT-based modeling provides a useful tool for probing the optical characteristics of rare-earth oxides and can support structural and vibrational characterization. The calculated Raman spectra showed good agreement with both existing theoretical data and experimental results within the acceptable calculation error. This result confirms the applicability of DFT-based modeling for probing the optical characteristics of high-entropy materials, and rare-earth oxide ceramics.

Nanosecond laser structuring of aluminum alloy was investigated to optimize microchannel geometry for enhanced capillary rise. Microchannels with varying density of scan lines were fabricated and characterized. Medium densities yielded the highest deionized water rise velocity and stable transport, following the Lucas–Washburn law. The efficiency was attributed to hierarchical micro/nanostructures and the aluminum oxide layer formed during processing, enhancing hydrophilicity. High densities caused channel merging, reducing flow directionality. Results demonstrate the potential of nanosecond lasers for producing cost-effective, high-performance supercapillary surfaces.

The impact of magnetic nanoparticles (MNPs) on the differentiation of human blood monocytes into dendritic cells (DCs) was studied with focus on potential enhancement of immunotherapy efficacy by targeted delivery of MNPs-loaded DCs to lymph nodes using an external magnetic field. Spherical γ-Fe₂O₃ MNPs sized ~14 nm were obtained by laser target evaporation technique followed by synthesis of stabilized water-based suspension. Their physicochemical properties were characterized in detail. Monocytes were differentiating to DCs at two experimental conditions to define the effect of “extracellular” nanoparticles and MNPs uptaken by cells. The immunophenotype of DCs was analyzed by flow cytometry. Secretory activity of cells was measured by enzyme-linked immunosorbent assay (ELISA). Monocytes actively acquired MNPs and retained them during differentiation into DCs. The differentiation process was not interrupted by MNPs, but the phenotype of DCs was modified compared to native DCs: MNPs enhanced the expression of receptors functionally important for interaction with T-lymphocytes and increased secretion of pro-inflammatory cytokines. At the same time, they inhibited the expression of CD86 costimulatory receptor and stimulated the production of tolerogenic cytokine IL-10. The impact of MNPs on monocytes-DCs differentiation is most likely due to engulfed nanoparticles. However, the contribution of MNPs adhered to cells’ surface cannot be excluded.

Extremely complex transfer processes characterize the technology of waveguides production by proton exchange method in the lithium niobate single crystal. The melt of benzoic acid C₆H₅COOH, which acts as a source of protons, is used most often as a working fluid. Proton exchange occurs because of dissociative absorption of protons into the crystal, accompanied by the extrusion of lithium ions back into the working fluid. Electrokinetic transport phenomena in the melt of benzoic acid are fundamentally different from diffusion processes in the crystal, however, these processes are interrelated. However, the dynamics of crystal protonation is of greatest interest to technologists, which is why, historically, the first calculations were made for proton exchange process, as a result of which optical waveguides are formed in it. Experimental data reliably show that the concentration front of protons in the volume of the crystal moves in dependence on time according to the approximately square root law and has a sharp, practically stepped profile. It is even more surprising that the so-called nonlinear diffusion equation is the most efficient for describing the penetration of protons deep into the crystal. It is obtained from a more general quasi-linear second order diffusion equation in the consequence of assumption about a power dependence of the diffusion coefficient on the concentration. The difference from classical diffusion is expressed by the stepped nature of the profile and means the finite speed of disturbance propagation in the system.

Detection of minimally ionizing particles in rare processes requires the creation of fast detectors with high efficiency and low noise levels. For a device consisting of two MCP assemblies, the possibility of increasing the detection efficiency of minimally ionizing particles (~95%) with a simultaneous increase in the signal-to-background ratio and with high resistance to electromagnetic interference is shown. These results indicate that dual-MCP architecture offers a promising approach for high-precision, low-noise particle detection in challenging experimental environments.

We have studied the evolution of the isolated domains created in the bulk by tightly focused femtosecond near infrared laser irradiation under the action of uniform electric field in strontium barium niobate Sr_0.61Ba_0.39Nb₂O₆ single crystals. The samples were cut with a deviation from the polar axis of about 3°. The initial domain structure representing the matrix of domains in the bulk of the single domain sample was created in three steps: (1) thermal depolarization, (2) laser irradiation, (3) removing of the nanodomain structure. Laser irradiation leads to formation the matrix of the spindle-shaped domains surrounded by nanodomains. All created domains were strictly oriented along the direction of the laser beam. It was shown that the application of positive field pulse led to growth in the polar direction of new domains from the deepest ends of the created domains. The average threshold field of new domains appearance and mobility of their growth were extracted. We have created the unique domain shape, which represents two united cylindrical parts in the crystal bulk formed as a result of laser irradiation of the sample with nanodomain structure in the direction deviated from the polar direction and application of the uniform external electric field after removing of nanodomains. The growth direction of the first domain part is governed by orientation of the laser beam, and the second domain part—by orientation of the polar axis. Obtained results are important for developing domain engineering methods in ferroelectrics based on domains nucleation by the focused femtosecond laser irradiation and their growth in homogeneous electric field.

We fabricated polyvinylidene fluoride (PVDF) based composites comprised polar inclusions of deuterated triglycine sulfate (DTGS) oriented during the crystallization to enhance pyroelectric activity, as well as study their pyroelectric and dielectric properties. The calculated pyroelectric coefficient yields values ranging from 0.01 × 10^–4 to 0.2 × 10^–4 C/(m² K), depending on the filler concentration. This value coincides with the pyroelectric coefficient for PVDF films manufactured by the standard method. The dispersion of dielectric properties of PVDF-based composite samples does not depend on the film manufacturing method noticeably. However, the dielectric permittivity of films obtained by the standard method is approximately 10–15% lower.

The dielectric response dispersion in the solid solution 0.9Pb_0.95Sr_0.05(Zr_0.52Ti_0.48)O₃–0.05Pb(Zn_1/3Nb_2/3)O₃–0.05Pb(Mn_1/3Sb_2/3)O₃ + 0.1 mol % CeO in the vicinity of a diffuse ferroelectric phase transition was studied within the temperature range of 20–500°C at frequencies of 25 Hz–100 kHz. Observed dielectric relaxation process is characterized by features inherent in both conventional and relaxor ferroelectrics. It was shown that the temperature dependence of the relaxation time can be satisfactorily described by the Arrhenius law with a temperature-dependent activation energy.

Thin ferroelectric films of Ba_0.5Sr_0.5TiO_3, grown on various substrates (Sp, LaAlO₃ polycor) using Rf spattering technology, were studied using spectroscopic methods (IR absorption, Raman scattering, second harmonic generation). The actual properties of these films (thickness, rate of grows temperature dependence of order parameter e.a.) were obtained.