Issue 1, 2025

Crystallization of thin films GST alloy under the action of ultrashort pulse laser radiation

A. A. Burtsev$^1$, A. V. Kiselev$^1$, A. A. Nevzorov$^1$, V. A. Mikhalevsky$^1$, V. V. Ionin$^1$, N. N. Eliseev$^1$, A. A. Lotin$^1$

The paper presents electrical resistivity and optical transmission and reflection coefficients of thin films of Ge2Sb2Te5 (GST) alloy thin films changing dynamics during the femtosecond laser radiation induced crystallization studying results. It is shown that the most effective of ultrashort laser pulses on the phase state of the film is a multi-pulse mode, which is associated with a high stochasticity of GST crystallization. It is experimentally demonstrated that for films thicker than 100 nm, the most accurate control of the crystalline phase fraction is obtained at energy densities from 10 to 20 mJ/cm2. The switching time of the electrical properties does not exceed 100 ns, which is due to the formation of conducting crystalline paths in the film material. The dynamics of the optical properties allows to distinguish two time sections. The sharp jump can be explained by both the increase in carrier concentration and the process of recalescence and reamorphization. The slow relaxation is explained by the formation of the crystalline phase (nucleation and crystallite growth). An important result is the experimental detection of X-ray diffraction peaks of a new crystalline phase (simple cubic phase). The formation of this phase is related both to the rearrangement of the atomic structure and to the depletion of the formation of chemical bonds due to the interaction of electrons with ultrashort duration radiation.

D. V. Vasilyev, V. V. Amelichev, D. V. Kostyuk

Spin tunnel magnetoresistive nanostructures containing a synthetic antiferromagnet significantly improve the signal-to-noise ratio and power consumption of magnetoelectronic products. Magnetic annealing of spin-tunnel magnetoresistive nanostructures promotes crystallization of the amorphous CoFeB film at the boundaries with the MgO barrier layer, providing coherent tunneling of electrons and a significant increase in the magnetoresistive effect. In particular, during thermomagnetic treatment it is possible to form the required direction of the unidirectional anisotropy axis to create a crossed magnetic configuration of free and fixed layers, which makes it possible to obtain linearization of the magnetoresistive curve in the region of weak magnetic fields. It has been found out that thermomagnetic treatment can be effectively used to control the static and dynamic magnetic properties of spin-tunnel magnetoresistive nanostructures with a synthetic antiferromagnet; therefore, an urgent task is to study their magnetic properties after magnetic annealing. The nanostructures Ta / Co95Fe5 / Ru / Co95Fe5 / Ta and Ta / Co40Fe40B20 / Ru / Co95Fe5 / Ta were measured on a specialized equipment, and their magnetization reversal loops after thermomagnetic treatment were determined. As a result of magnetic annealing of spin-tunnel magnetoresistive structures with a thickness of the non-magnetic layer of a synthetic antiferromagnet corresponding to the first antiferromagnetic maximum, the destruction of the antiferromagnetic coupling of the layers occurs at temperatures below 300 °C.

D. M. Rusakov$^1$, D. V. Gusev$^1$, K. A. Gonchar$^{1,2}$, A. S. Vorontsov$^1$, A. S. Ilin$^1$

In recent years, silicon nanowires (SiNWs) have gained significant attention due to their unique electrical and optical properties, making them promising for applications in various fields, including nanoelectronics and sensors. This study presents a comprehensive analysis of SiNWs synthesized from crystalline wafers with resistances of 10–20 Ω·cm and 1–5 mΩ·cm, focusing on their electrical properties. Special attention is given to current-voltage characteristics (I-V curves), frequency-dependent conductivity, and impedance spectroscopy. These methods enable the iden-tification of key factors influencing the behavior of nanostructures and reveal correlations be-tween the properties of crystalline wafers and the electrical characteristics of the material. The results show significant changes in conductivity as the wafer resistance decreases, indicating im-proved electrical performance of the SiNWs. The I-V characteristics of samples with 1–5 mΩ·cm resistance in both planar and sandwich configurations, as well as the sandwich configuration of the 10–20 Ω·cm sample, exhibit distinct diode-like behavior, which can be attributed to potential barrier formation at the layer interfaces. Hopping conduction is found to be the dominant mecha-nism across all samples.

Sliding with Friction and The Brachistochrone Problem

A. V. Kurilin

New formulas for a family of extreme curves are obtained that provide a minimum descent time between given points in a gravity field taking into account the force of dry sliding friction. Parametric equations for these curves depend on the friction coefficient and generalize the equation of the cycloid (brachistochrone for a smooth surface) to the case of sliding with friction. The results of numerical calculations in the program "Mathcad" prove that the found curves really provide a minimum descent time for the given parameters of the problem and can claim to be brachistochrone with friction.

P. K. Silaev, A. V. Tolokonnikov

The behavior of the lowest electron level of a hydrogen atom in a space bounded by a plane surface, on which the Robin boundary condition is imposed for the electron wave functions, is considered. We assume that the Robin condition parameter is a double periodic function, which seems to be reasonably in the case of adsorbents with periodic structure. It is shown that depending on the condition characteristics, two modes of adsorption of an atom on the sample surface are possible. In the first case, the effective atomic potential as a function of the distance between the nucleus and the boundary has a clearly expressed minimum at finite distances, which corresponds to the effect of the atom ``soaring'' above the plane. The second case occurs under the condition of a low initial concentration of hydrogen inside the sample and a large positive electron affinity of the sample surface. In such a situation, the minimum of the effective potential is located near the sample surface, and a significant amount of energy can be released during the adsorption process. The results were obtained using direct numerical calculations via the finite element method.

C. G. Azra$^1$, E. A. Bonvech$^2$

The reconstruction of the arrival direction of extensive air showers (EAS) is an important part of the data analysis methodology in the SPHERE experiment. Knowledge is necessary to construct an optimal criterion for nuclei separation, used to determine the mass composition of primary cosmic rays (PCR). This work presents a step-by-step development of the algorithm to determine the arrival direction of air showers for the SPHERE-2 and SPHERE-3 telescopes, based on parabolic approximation of the front. It is being developed and tested on the basis of artificial EAS events. The algorithm was applied to experimental events registered in 2012 and 2013 by the SPHERE-2 telescope.

P. N. Nikolaev

In the paper it is investigated the history of the introduction of entropy into thermodynamics and statistical mechanics. The role of entropy in the construction of a closed thermodynamic apparatus, the creation of a method of thermodynamic potentials, and the formation of the theory of thermodynamic equilibrium is considered. The role of statistical mechanics in explaining the laws of thermodynamics based on classical mechanics is investigated. Boltzmann's solution to this problem is presented. The connection between the introduction of probability into physics and the introduction of entropy is shown.