Volume 64, Nº 11 (2019)

We propose an algorithm and present results of micromagnetic simulation of the resonant response of a probe pickup (cantilever) of a magnetic resonance force microscope. Simulation of induced oscillations of sample magnetization makes it possible to calculate the varying component of the force exerted on the probe by the sample and to construct spectra in the form of dependences of the amplitude of oscillations of the cantilever on the external magnetic field strength. Simulation of time dependences of all magnetization field components makes it possible to analyze the spatial distributions of spin-wave resonances of samples. For test objects in the form of rectangular permalloy microstrips, good agreement between model and experimental spectra is achieved.

We report on the results of investigation of a gas-jet laser-plasma source of extreme ultraviolet radiation based on a conical supersonic nozzle. As a target, we used molecular-cluster CO₂ jets. Different regimes of the gas flow were obtained by varying the gas parameters at the gas inlet and the influence of these regimes on the emission and technical characteristics of the radiation source was analyzed. It has been shown experimentally that radiation emission is intensified upon an increase in the amount of clustered material in the jet.

Local resistive switching by complex nonstationary signals in zirconium-dioxide-stabilized films on conducting substrates has been studied by atomic-force microscopy with a conducting probe. Film resistance was switched by triangular voltage pulses on which a high-frequency sinusoidal signal was superimposed. It is found that the ratio of currents through the junction between the probe and film surface in high-resistance and low-resistance states increases after the superposition of a sinusoidal signal (as compared to switching by simple triangular pulses). An increase in the temporal stability of the current strength in these states was also found when switching with a sinusoidal signal. This effect is associated with resonant activation of oxygen ion migration over vacancies in an external ac electric field.

The optical, mechanical, and thermal properties of free-standing structures based on nitrided molybdenum and zirconium silicides have been studied. It has been shown that silicide nitriding considerably improves the thermal stability of films. While as-prepared amorphous MoSi₂ and ZrSi₂ films crystallize in the interval 330–370°C, nitriding of films has made it possible to increase their working temperatures in vacuum to 600–700°C (at least, for x ≥ 0.25, y ≥ 1.3). Tensile tests have shown that the ultimate strength of MoSi₂N_x films (0 ≤ x ≤ 0.55) depends on nitrogen content only slightly. Comparison between the properties of MoSi₂N_x and ZrSi₂N_y films magnetron-sputtered at the same partial pressure of nitrogen has demonstrated that with transmission coefficients of films at a wavelength of 13.5 nm being close to each other, ZrSi₂ films are more effective as protection coatings (they are less prone to oxidation and more degradation-resistant).

An inhomogeneous ferroelectric (triglycine-sulfate (TGS) single crystal with a TGS–TGS+Cr periodic growth impurity structure) has been investigated by scanning capacitance force microscopy (SCFM). The specific features of mapping capacitance variations when detecting the electrostatic force at double and triple resonance frequencies are considered. The piezoelectric response, surface potential, and surface topography have been measured. It is shown that the capacitance contrast is formed both on domain walls and on TGS and TGS+Cr stripes. It is demonstrated that SCFM at the electrostatic-force double resonance frequency makes it possible to observe the spatial impurity distribution in the ferroelectric structure in the range of Cr concentrations of about 0.02–0.08 wt %.

We have studied the properties of spin-wave excitations in a structure that is a junction of two regular magnon waveguides. The proposed structure enables the transmission of spin-wave signals in an irregular structure in the propagation mode of a surface magnetostatic wave. Using the method of micromagnetic simulation, the characteristics of the wave process have been calculated when changing the structure parameters, magnitude and direction of a magnetization field. It is shown that a system with translational symmetry violation can be used to transmit a signal in three-dimensional configurations of magnon networks.

We have analyzed the self-action effects in the propagation of surface magnetostatic wave (SMSW) pulses in a 1D magnonic crystal–dielectric–metal structure in which the region of anomalous dispersion controlled by the selection of thickness h of the insulator and ensuring the fulfillment of the Lighthill criterion in the generation of SMSW solitons is formed. It is shown that when the metallization-induced region of anomalous dispersion coincides with the Bragg resonance frequency range, no SMSW solitons form.

We have developed technology for manufacturing chains of CoFe/Al₂O₃/NiFe tunnel magnetoresistive (TMR) elements with pinning on the IrMn antiferromagnetic layer. We have studied the dependence of the shape of magnetoresistance curves on the geometric parameters of laterally bounded TMR contacts, as well as on the mutual orientation of the external magnetic field and the axis of unidirectional anisotropy of the pinned CoFe layer. The chain resistance ranges from several tens of kiloohms to hundreds of megaohms depending on the thickness of the tunnel-transparent dielectric layer with a magnetoresistive effect of 10–15%. The developed technology can be used in manufacturing tunneling magnetic field sensors.

The arrays of permalloy particles with shape anisotropy, prepared via microsphere lithography, have been characterized using atomic force microscopy and magnetic force microscopy. The size effect from spherical particles used as the lithographic mask on the magnetization distribution in the produced particles has been investigated. The magnetic force images of particles have been simulated in order to obtain quantitative values. A comparison of shape reproducibility of particles prepared using microsphere lithography and scanning probe lithography is performed as well.

The results of studying the formation of graphene layers during thermal pyrolysis of methane on the surface of polycrystalline nickel are presented. The studies have been carried out using a technique that allows controlling the change in the surface topology with high spatial resolution using a scanning tunneling microscope located directly in the reaction chamber providing no contact between the formed graphene with air. The measurements have revealed the formation of graphene layers in the form of a set of nanobubbles with characteristic sizes of about 100 nm. It has been found that the local topology of the graphene layer can change under the influence of a tunneling microscope probe depending on the applied voltage.

A method for fabrication of a concave spherical mirror made of crystalline quartz is proposed and X-ray optical properties of the mirror are studied. The radius of curvature is 1630 mm. The shape of the mirror surface is studied using an interferometer with a diffraction reference wave. In the entire processing region, the maximum deviation from the nearest sphere is about 0.2 μm and the rms is 34 nm, so that high quality of imaging is provided with an angular error of about 2″ (angular seconds). Reflection coefficient (about 7%) and lower bound limit of spectral selectivity (λ/δλ ≈ 1775) are determined in the vicinity of a wavelength of λ = 0.834 nm, which is close to the working wavelengths of the MgXII doublet (λ = 0.8418 and 0.8423 nm). Position of the Bragg peak and spectral selectivity remain unchanged upon bending of the crystal mirror within measurement accuracy.

The performance of multilayer Mo/Si mirrors with B₄C and Be spacers near a wavelength of 13.5 nm has been studied. It has been shown that four-component Mo/Be/Si/B₄C mirrors outperform Mo/Si and Mo/Si/B₄C mirrors in reflection coefficient by 2.0 and 1.3%, respectively. In addition, Mo/Si mirrors offer the widest transmission band width at half maximum (Δλ_1/2 = 0.535 nm). An explanation for these findings has been given.

An experimental setup and results on aberration of sources of a reference spherical wave (SRSW) based on a single-mode optical fiber with a subwavelength output aperture obtained with the aid of an optical part of recording system (OPRS) are presented. SRSW and OPRS are developed for referenceless interferometer with diffraction reference wave. Methods for minimization of the measurement error are proposed. The SRSW and OPRS provide subnanometer measurement accuracy for optics. An increase in the measurement accuracy of the interferometer to a picometer level is discussed.

We present the results of studies on the optimization of the synthesis of Bi-substituted iron garnet (Bi : IG) films by liquid-phase epitaxy and vacuum deposition followed by crystallization. The effect of the parameter of mismatch between the crystal lattices of the film and the substrate on the functional properties of thin single-crystal high-coercive Bi : IG films is demonstrated. The regime of high-temperature annealing of deposited films was optimized in order to form layers with a high bismuth concentration for magnetophotonic and magnetoplasmonic structures. It was established that annealing of the Bi : IG layer under a SiO₂ layer deposited on top will reduce the roughness of interfaces in multilayer structures.

We propose a method for determining electrophysical characteristics (free charge carrier concentration, mobility, and conductivity) of semiconductors from the results of measurements of the microwave spectrum of the impedance of a coaxial probe as a function of applied constant voltage U. The sought parameters have been determined by solving the corresponding inverse problem using the theory of a near-field antenna that was developed earlier. We have developed a computer program that seeks the solution by minimization of the multiparametric residual function in accordance with the Nelder–Mead algorithm. The precision of the method has been analyzed from the results of simulation in which the impedance was calculated preliminarily considering resultant concentration profile n(x, U) of the depleted layer in the vicinity of the metal–semiconductor contact. The possibility of diagnostics with a micrometer lateral resolution has been demonstrated.