Vol 23, No 3 (2023)

Background and Objectives: Membranes in the form of highly ordered nanostructures of porous anodic aluminum oxide (PAAO) with adjustable pore properties were obtained by electrochemical anodizing. PAAO nanostructures were prepared in an oxalic acid electrolyte at a direct current electrochemical potential of 30–60 V. The ready-made nanoporous membranes were modified with thin silver films 1.8, 3.6 and 5.4 nm thick. The study of the membrane surface by scanning electron microscopy has shown that nanoporous membranes have hexagonally arranged and highly ordered arrays of pores with a diameter of (30±4) nm and a packing density of about 1.8 · 10¹⁰ cm–2. Optical interference spectra of PAAO were recorded in the wavelength range of 300–900 nm. The optical properties of nanoporous membranes with a free and silver-modified surface changed depending on the time of interaction of the membrane surface with the ammonia gas flow, which led to changes in the interference pattern and, in turn, to changes in the effective optical thickness (EOT) of the membranes. Features of the influence of the membrane surfacemodified with silver onthe shape and sensitivity ofthe optical signal ofthe sensor have been revealed. The aim ofthis work was to experimentally study the temporal characteristics of the optical spectral response of nanoporous anodic alumina membranes with a free pore surface and modified with thin silver films in an ammonia gas flow. Materials and Methods: The thickness of the PAAO membrane, determined profilometrically, did not exceed 1.0 µm. The average inner diameter of Al2O3 nanopores is (30±4) nm. The silver films were deposited by magnetron sputtering at direct current. Changes in the effective optical thickness are used to quantify changes in the optical properties of the membrane. Changes in the effective optical thickness will be mainly determined by the effective refractive index of the PAAO-Ag molecular film of the adsorbed gas structure. The effective refractive index of the membrane was determined from the measured position of the interference maxima and the given membrane thickness. Results: Association processes have been considered, i.e. binding of analyte molecules to the surface of the PAAO nanoporous membrane. A stream of gaseous ammonia was chosen as the analyte. According to the Langmuir isotherm model, the sensor response during real-time measurements should follow a negative exponential trend. It has been shown that the shape of the sensor’s optical signal qualitatively repeats the shape of the theoretical curve of real-time optical probing in the regions of molecular binding and equilibrium. The molecular association time of the free surface of the PAAO nanoporous membrane was 7 ± 1 minutes. The deposition of thin silver films on the surface of a nanoporous PAAO membrane leads to a change in the shape of the optical signal and a decrease in its magnitude. Conclusion: On the basis of the synthesized nanoporous PAAO membranes with a free surface and modified with ultrathin silver films, experimental studies of the effect of ammonia flow on multibeam light interference in such membranes have been carried out. It has been found that the surface roughness and size effect of the silver film thickness have a significant effect on the transmission spectra and sensory sensitivity of the membranes. It has been shown that the largest relative change in the refractive index of the membrane in an ammonia flow is observed for the thinnest silver film 1.8 nm thick. It has been noted that there is a threshold value of the thickness of a silver film deposited on the surface of a nanoporous PAAО membrane, above which the use of such films in optical sensors with the mechanism of multipath light interference is not advisable, and the use of a different mechanism is required, for example, the mechanism of localized surface plasmon resonance.

Background and Objectives: Cellular labeling with fluorescent molecules appears to be one of the key methods of cell biology that continues to evolve with the advent of new fluorescent probes possessing unique properties. Ternary AgInS2/ZnS quantum dots occupy a special position comparedto other fluorescentmolecules duetotheir size-adjustable photoluminescence combined with broadband excitation and long emission lifetime. For the use of quantum dots of AgInS2/ZnS composition as a fluorescent probe in in vitro applications, they should have low physiological toxicity and good stability in physiological pH range. The objective of this work is therefore to evaluate the change of photoluminescent properties of AgInS2/ZnS quantum dots with changing pH of the medium and ionic strength. Materials and Methods: To evaluate the effect of pH and ionic strength on the photoluminescence properties of AgInS2/ZnS quantum dots, a size-selective precipitation procedure was carried out and the photoluminescence and absorption spectra of the quantum dot fractions were analyzed. Results: Ternary photoluminescent AgInS2/ZnS quantum dots stabilized in water by thioglycolic acid have been obtained by direct synthesis. Size-selective precipitation allowed to discriminate of 11 AgInS2/ZnS quantum dots fractions from the initial ensemble, revealing distinctly various optical properties. The effect of different pH and ionic strengths on the photoluminescent properties of AgInS2/ZnS quantum dots fractions has been studied. While in strong acidic and basic media the dramatic changes have been observed, the pH and ionic strength range corresponding to the biological fluids has shown no significant influence on the photoluminescent properties of all quantum dots fractions. Conclusion: This indicates the potential application of these nanoobjects as photoluminescent probes in various bioapplications.

Background and Objectives: The nonlinear effects of high-harmonic generation in various materials provide new tools for studying ultrafast electron dynamics and open up a possible way to create coherent light sources in currently inaccessible frequency ranges. Graphene is regarded as one of the most promising materials for these purposes. To describe nonlinear processes in it, it is necessary to be able to reproduce the change in the population of electronic states in the conduction band under the action of an intense external electric field and the effects observed in this case. Materials and Methods: The work is devoted to demonstrating the applicability of the quantum kinetic equation method and the software solution developed on its basis for these purposes. The implemented approach provides an accurate reproduction of the response of the electronic subsystem of the material to an external pulse action in a wide range of frequencies, durations and strength of the field. The characteristics of the plasma field accessible to an external observer are reproduced and analyzed. The method allows considering various initial states of the model. This can be a vacuum state with a complete absence of electrons in the conduction band or an equilibrium distribution of carriers at a given temperature. The use of the relaxation time approximation in the kinetic equation makes it possible to estimate the influence of dissipative processes on the behavior of the model. Results: The demonstration was carried out on the example of modeling the observed effects of a short infrared pulse on a graphene monolayer and comparing the results with experimental data. The presented results have been obtained for a version of the kinetic equation defined in the massless fermion approximation. The reproduction of the high-harmonic generation effect has been confirmed. The effect of the electron-hole plasma relaxation on the simulated results has been demonstrated. The processes of intraband carrier dynamics and interband transitions under the influence of an external electric field have been singled out and available for separate analysis. The dependence of the high-harmonic generation effect on the type of polarization of the external pulse field has been demonstrated. Conclusion: The presented results have been the applicability of the developed method and its software implementation for modeling the generation of higher harmonics under the conditions of nonlinear interaction of graphene with external high-frequency fields. The method works in a wide range of sample and external field parameters. 

Background and Objectives: The activities of Professor Dmitriy Alexandrovich Usanov, Honored Scientist of the Russian Federation, Honored Inventor of the Russian Federation, at Saratov State University (SSU) were multifaceted, distinguished by high professionalism, a rare harmonious combination of scientific achievements and relevant applied solutions built on this basis. His achievements include organizational activities aimed at the development and support of research work at SSU at the world level, which was the most important trump card when Saratov University won the status of a National Research University, the development of the Department of Solid State Physics, which provides training of specialists in the direction of bachelor’s and master’s degree “Electronics and Nanoelectronics”, highly qualified personnel in the specialty “Miro electronic component base- and nanoelectronics, quantum devices”, support for the functioning of the network of dissertation councils at SSU and the publication of several series of journal “Izvestiya of Saratov University”, determining the policy and quality of publications in the journal “Izvestiya of Saratov University. Physics”, 30-year leadership of the dissertation council in several physical and mathematical scientific areas, organization of deep educational work in the field of preserving historical memory and patriotism, methodological activities aimed at improving the quality of education and research. Materials and Methods: Milestones of Dmitriy A. Usanov’s life path are comprehensively reflected in the article based on the analysis of his diverse and large-scale activities, compiling a bibliography of his main scientific, methodological and educational works. Conclusion: An integral idea of the activities of an outstanding scientist, inventor, teacher, educator of youth is being formed.