Journal of Surface Investigation. X-Ray, Synchrotron and Neutron Techniques

In this work, the concentration and angular dependencies of the ferromagnetic resonance (FMR) linewidth ΔB and the resonance field B of composite films (CoFeZr + Zr₂O₃) with granular and granular-percolation structures are obtained in the range of total concentration of Co, Fe metals x = 22 - 54 at. % and in the range of angles between the film plane and a constant magnetic field φ = 0° - 90°. It is shown that the surface relief and the magnetic structure of the composite films have a significant effect on the resonance field and the resonance linewidth, especially at large angles φ. It is shown that the resonance line width ΔB and the resonance field B weakly depend on the metal concentration x and the angle φ for films with a granular structure at x = 22 - 40 at. % and strongly depend on x and the angle φ for films with a granular-percolation structure at 49 - 54 at. %. It was found that the line width ΔB and the resonance field B increase with increasing angle φ for all films. The presence of two growth regions on the angular dependences of the resonance line width ΔB and the resonance field B is associated with the presence of granular and percolation regions in the composite films. The results of the analysis of the behavior of the concentration and angular dependences of the FMR parameters, relief and magnetic structure of the films indicate a high structural sensitivity of the FMR method in studying the electromagnetic properties of magnetic composite films. Therefore, the FMR phenomenon after improving the technique for measuring the FMR parameters can be used for the structural analysis of composite films.

Memristive states in low-dimensional structures based on graphene and transition metal chalcogenides controlled by structural phase transitions are considered. Graphene/graphene oxide and bigraphenediamane heterostructures obtained by focused electron beam irradiation demonstrate nonlinear behavior and non-volatile memristive states controlled by changing the sp³–sp²-hybridization of carbon atoms. Modeling of the modified bigraphene structure and experimental assessment of the proportion of sp³-hybridized carbon indicate the formation of diamane nanoclusters in bigraphene, the density of which depends on the conditions of electron irradiation. Phase transitions in transition metal chalcogenides with a change in their dimensionality and the possibility of forming non-volatile memristive states for detection and energy-efficient processing of electrical and optical signals are also considered.

The development of hydrogen energy requires the creation of efficient materials for storing hydrogen that can withstand high pressures and temperatures. Carbon nanotubes (CNTs) have great potential for this purpose due to their large surface area and chemical stability. They can be modified structurally and chemically to improve their properties. In this study, we used density functional theory simulations in the SIESTA software to investigate the adsorption of hydrogen molecules on CNTs decorated with titanium and platinum. We considered different types of structural defects in the CNTs, such as single and double vacancies and isomerization defects. We studied the impact of these defects on the binding of metals and hydrogen adsorption properties, as well as the charge density distribution. It has been demonstrated that the presence of defects significantly improves the binding of titanium and platinum to the carbon surface, with titanium showing higher activity. The energy of hydrogen adsorption on CNTs decorated with titanium falls within the desired range of 0.2–0.6 eV, which corresponds to the criteria for reversible hydrogen storage. These results emphasize the significance of considering structural defects when designing nanostructured hydrogen storage systems.

In the present study, we investigated the electrical conductivity and magnetic properties of polymer composites based on thermoplastic polyurethane (TPU) and single-walled carbon nanotubes (SWCNTs). Resistance measurements were carried out using the four-point probe method over a temperature range from 77 to 300K under direct current. Magnetization measurements were performed using a "Faraday Balance" setup, built on the basis of the MGD 3 12 FG spectrometer, at room temperature in a magnetic field range from –5 to 5kOe with a constant magnetic field step varying from 5 to 200Oe using the Faraday method. Analysis of the temperature dependence of the reduced activation energy revealed that the main charge transport mechanism in the studied composites is hopping conductivity, following the 1/4 law (Mott's variable-range hopping mechanism). The observed percolation threshold in the studied composites is exceptionally low 0.04 wt. %, which is an order of magnitude lower than that reported for similar composites in the literature. Magnetization measurements carried out in this work showed that the thermoplastic polyurethane matrix exhibits diamagnetic behavior, while the composite samples demonstrate weak ferromagnetism. This ferromagnetism is attributed to the presence of α-Fe₂O₃ impurities in the carbon nanotubes, distinguishing these composites significantly from previously known TPU/SWCNT-based polymer composites. It is likely that the abnormally low percolation threshold observed in our study may be due to strong internal magnetic fields within the investigated composites.

The absorption spectra recorded in vacuum before and after irradiation with accelerated electrons (in situ) were studied for the original polymethylphenylsiloxane varnish and the varnish modified with SiO₂ nanoparticles with a concentration of 0.1 to 10 wt.%. It was found that irradiation of the varnish resulted in the formation of 6 types of radicals due to the rupture of the main chain of methyl and phenyl groups. An explanation was proposed for the processes of radical formation and accumulation in the original varnish and the varnish modified with nanoparticles. The nature of the radicals was determined from the energy position of the elementary absorption bands: C₃H₃, Si–C, Si–CH, Si–CH₃, Si–O, H–Si–O. The dependences of the areas of the radical absorption bands on the concentration of nanoparticles in the modified varnish were investigated. It was found that with an increase in the concentration of nanoparticles, the number of radicals of all types formed during electron irradiation decreases compared to the unmodified varnish. The decrease in the concentration of radicals during irradiation of the modified varnish may be due to three processes: relaxation of radiation defects on nanoparticles, as on small-sized structural defects; creation of radiation-resistant protective layers from nanoparticles on the surface of the varnish; formation of organoceramic complexes.

Using scanning Kelvin probe microscopy under ambient conditions, flickering of the electric potential of Au-nanoparticles isolated on the SiO₂-surface is detected. It is shown that the flickering reflects thermal fluctuations of the nanoparticle potential associated with single-electron charge jumps on them. A method for verifying the charge quantization law at room temperature is proposed. The possibility of creating a calibrated nanometer-scale potential source for testing scanning Kelvin probe microscopy is considered.