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

Bimetallic Au–Pt nanoparticles with different molar ratios were obtained using laser synthesis (Nd:YAG laser with the parameters: 1064 nm, 180 mJ, 7 ns, and 20 Hz). The bimetallic nature of the particles was confirmed by X-ray diffraction and UV-visible spectroscopy. According to the transmission electron microscopy data, it was found that the bimetallic nanoparticles were represented by the alloy particles of an elongated shape with a diameter of 5–10 nm. Then, the bimetallic particles were decorated with a powder of highly defective dark titania by impregnation.The photocatalytic activity of the TiO₂ with deposited bimetallic particles was estimated in the reactions of Rhodamine B dye decomposition and hydrogen production under LED irradiation with a wavelength of 375 nm. It was found that the highest photocatalytic activity in the series was exhibited by the samples with the deposited bimetallic particles, where the Au : Pt ratios was 50 : 50 and 30 : 70. It was also shown that the TiO₂ nanoparticles decorated with the bimetallic Au : Pt NPs exhibited higher activity compared to the samples successively modified with monometals in the same ratios.

Viscoelastic properties of collagen hydrogels with different protein content (from 0 to 100%) was studied by Brillouin spectroscopy as a model system of biological tissue. From the analysis of the Brillouin spectra, the dependencies of the Brillouin peak width (FWHM) and the value of the gigahertz elastic modulus as a function of the protein concentration in the hydrogel were determined. It is shown that the behavior of the elastic modulus, which changes by almost an order of magnitude, is described with good accuracy in the full range of concentrations considered by the Reuss model. Analysis of the behavior of the Brillouin line width revealed a nontrivial behavior of the FWHM value with increasing protein concentration (FWHM increased almost 8 times), with a maximum at a collagen content of ∼70%. The discovered behavior can be caused by both the heterogeneity of the samples on scales of ∼100 nm during hydrogel dehydration and the influence of the relaxation spectrum on the Brillouin peak.

The study delves into the creation of films formed from aluminum and platinum nanoparticles with varying absorbance from 0.1 to 1.1, fabricated using dry aerosol printing techniques. Metal nanoparticles were synthesized through real time gas discharge process combined with printing nozzle. The influence of printing parameters, including the speed of the substrate and the step for film patterning, has been examined in relation to the absorbance of metal nanostructures. Plasmon enhanced photoluminescence of bovine serum albumin (BSA) in presence of produced polydisperse aluminum and platinum nanoparticles with median sizes 16 and 93 nm, correspondingly, were theoretically demonstrated to prove its potential for sensing applications.

Glasses, which are important materials for photonics, have inherent fluctuations of elastic constants on the nanometer scale. The heterogeneous elasticity theory connects these fluctuations with the boson peak, a characteristic feature of the vibrational spectra of glasses in THz frequency range. We use a version of this theory to find the temperature dependence of shear modulus nanometer-scale fluctuations in glycerol, a paradigmatic glass-former, in the supercooled and liquid state. The main input parameter of the theory is the frequency of the boson peak, determined from light scattering spectra. We measured the Landau–Placzek ratio in glycerol at the same temperatures and found out that its temperature dependence is in a good agreement with that of the normalized mean-square fluctuation of the shear modulus.

A spectroscopic study of the reaction medium consisting of reverse AOT/water micelles in reverse water/AOT/heptane microemulsions, in which ZnS nanoparticles are synthesized in real time, was carried out. The synthesized nanoparticles were characterized using X-ray fluorescence analysis and UV absorption spectroscopy. The sensitivity of the Raman spectral characteristics to changes in the reaction medium parameters was found. Methods for remote express diagnostics of the reaction medium are proposed, allowing real time monitoring of the Na₂S precursor concentration with an accuracy of 2.5% and determining the completeness of the ZnS nanoparticle synthesis stages by the intensity of the H–S stretching vibration band.

Hydrothermal treatment of a mixture of citric acid (CA) and ethylenediamine (EDA) is known for production of carbon dots (CDs) with intense photoluminescence (PL) in the blue region with a quantum yield up to ∼95%. However, the specific result of the synthesis depends significantly on treatment’s parameters. In this manuscript, by studying CDs synthesized from an EDA : CA mixture of 1 : 1 at temperatures of 80, 140, or 200°C for 0.5–6 h, it was found that, in addition to the main PL peak with a maximum in the region of λ_ex/λ_em 350/440 nm/nm, 6 different peaks with lower PL intensity are observed at different stages of the synthesis, corresponding to different luminophores. The parameters and conditions of formation of these luminophores were studied, the quantum yields of their luminescence obtained.

The relative influence of two different crystal structures of the composite compound Bi₂(Sn_0.7Fe_0.3)₂O₇/Bi₂Fe₄O₉ with a ratio of 91/9% studied using Raman scattering method. The Raman spectra were studied in the temperature range 93–520 K and the frequency range 1–2000 cm^–1. The types of lattice vibrations are determined. A decrease of the frequency of Raman spectra modes was found in the regions of phase transitions Bi₂(Sn_0.7Fe_0.3)₂O₇ and Bi₂Fe₄O₉. A new mode 406 cm^–1 has been established, which is a mixed oscillation of SnO₆ in Bi₂(Sn_0.7Fe_0.3)₂O₇ polyhedra (F_2g) at a frequency 400 cm^–1 and stretching vibrations of the FeO₆ octahedral at a frequency 426 cm^–1 Bi₂Fe₄O₉.

Laser nanostructuring is a powerful tool to produce different nanomaterials such as nanoparticles and surface relief structures. It was shown that pulsed laser ablation of thin 250 nm Fe film in acetone allows obtaining core-shell Fe@FeO nanoparticles with a mean size of 90 nm. Fabrication of femtosecond laser-induced periodic surface structures on a Si substrate surface with subsequent deposition of a NiFe/IrMn exchange-biased bilayer causes the appearance of an additional out-of-plane magnetization component with keeping exchange bias. Obtained nanomaterials look promising for designing magnetic biosensors with an improved detection limit.

Integration of quantum key distribution (QKD) into existing optical transport network is one of the important problems that should be solved to expand the applicability of QKD systems and to develop quantum networks. When multiplexing a quantum channel with classical ones, researchers and engineers are faced with a high background count rate caused by spontaneous Raman scattering. This paper presents the results of Raman noise measurement in the O-band at different distances and launched power of the C-Band channels. Based on this data, the 1310 nm QKD system capable to integrate into DWDM optical network was developed. Its performance has been experimentally confirmed in testing on coexistence with intense C-band signals. The experiments were carried out on the propagation of classical and quantum signals in the same fiber as well as in the opposite directions. As a result, the stable QKD over a distance up to 60 km with a total launched power of classical channels up to 20 mW has been demonstrated.

Brillouin spectra of barium strontium niobate thin films SBN-75 on sapphire substrate were measured in different scattering geometries. The spectral shape of the LA mode in the backscattering and 90A geometries were analyzed. The results are compared with the corresponding measurements on a relatively thick barium strontium niobate film and a bulk crystal. It is shown that a broad anomalously large peak in the vicinity of 25 GHz appears in the Brillouin scattering in SBN-75 films on a sapphire substrate after annealing. Spectral and scanning electron microscopy experimental studies were carried out (to identify the nature of this peak).