arXiv subjects

Mykola Yelisieiev

Publications and source records attributed to Mykola Yelisieiev.

9 recordsLinked to original sources

arXiv2026

Pyroelectric thermo-wave probing of BaZr0.2Ti0.8O3 ceramics

BaxZr1-xTiO3 ceramics with 0.15 < x < 0.25, which have high dielectric permittivity, small leakage currents and low dissipation factor, are promising materials for tunable capacitor devices, multilayered ceramic capacitors and piezoelectric actuators. These materials reveal relaxor properties due to the local chemical strains caused by the isovalent substitution of Ti4+ ions by Zr4+ ions with a larger ionic size. However, to the best of our knowledge, the pyroelectric properties of BaxZr1-xTiO3 ceramics with x~0.2 have not been studied. To fill the gap in knowledge, we perform the pyroelectric thermo-wave probing of BaZr0.2Ti0.8O3 ceramics prepared by the solid-state synthesis. Results of the thermo-wave probing of the most interesting polar states, namely polarized, depolarized, relaxed and restored polarized states, reveal the pronounced pyroelectric response that can be strongly asymmetric with respect to the opposite surfaces of the ceramics. The asymmetry and profiles of pyroelectric response depend significantly on the pre-history of the electric field cycling indicating possible non-ergodic relaxor-type polar states in the ceramic sample. X-ray diffraction spectrum, recorded at room temperature, reveals the virtual absence of the macroscopic tetragonality and the weak asymmetry of the (200) peak, which indicate the small tetragonality inside the Ti-enriched polar nanoregions. Decrease of the relative intensity of the Raman band at 714 cm-1 occurring upon heating evidences the diffuse ferroelectric-paraelectric phase transition between 30 C and 40 C. The temperature dependence of the dielectric permittivity obeys modified Curie-Weiss law with power 1.4, indicating that both ordered ferroelectric and relaxor states coexist in the BaTi0.8Zr0.2O3 ceramics.Results can be useful for elaboration of lead-free relaxor ferroelectric ceramics for advanced pyroelectric applications.

cond-mat.mtrl-sci↗

arXiv2026

Flexo-Strain Engineering of Phonons and Ferrons in Thin Films of Van der Waals Ferrielectrics

The influence of the flexoelectric coupling on the fluctuations of electric polarization and elastic strains can lead to the principal changes of the dispersion law of soft optical and acoustic phonons and ferrons in a bulk van der Waals ferrielectric. Since the size, gradient and strain effects determine phase diagrams and polarization behavior in thin films, it is reasonable to assume that the flexocoupling and mismatch strains should have a strong influence on the dispersion of phonons and ferrons in thin ferroelectric films. Using the Landau-Ginzburg-Devonshire approach, in this work we reveal that the dispersion of soft optical and acoustic phonons and ferrons is strongly dependent on the sign and magnitude of elastic strains, which originate from the lattice constants mismatch in thin strained films of van der Waals ferrielectric CuInP2S6. In particular, the frequency of acoustic phonons and ferrons approaches zero at nonzero wavevectors k>k_cr, where the critical value of the wavevector k_cr is determined by the mismatch strain, flexoelectric coupling strength and temperature. Zeroing of the acoustic phonon frequency, that appears with increase of tensile strains, indicates a possible emergence of a spatially modulated incommensurate polar phase induced by the flexo-strain effects. Analytical results, derived in this work, open the way for flexo-strain engineering of soft phonon and ferron dispersion in thin films of van der Waals ferrielectrics.

cond-mat.mtrl-sci↗

arXiv2024

Electron transport in quasi-ballistic FETs subjected to a magnetic field

We report the study of quasi-ballistic electron transport in short FETs subjected to magnetic field. Spatial distributions of electron concentrations, velocities, Hall currents and voltages in the short FET channels are determined. The basic properties of current-voltage characteristics of quasi-ballistic FETs in magnetic field are analyzed, among these the kink-like characteristics of the near-ballistic device. Peculiarities of magnetoresistance of such FETs are studied for low and high magnetic fields, and different current regimes. For nonlinear current regimes we revealed significantly larger magnetoresistance for the devices with higher ballisticity. Numerical estimates of studied effects are presented. We suggest, that the found results contribute to the physics of short FETs and can be used for developing nanoscale devices for particular applications.

cond-mat.mtrl-sci↗

arXiv2024

Effective Dielectric Response of Dense Ferroelectric Nanocomposites

We measured the temperature dependences of the capacity and dielectric losses of the tape-casted dense ferroelectric composites consisting of 28 vol.% BaTiO3 nanoparticles (average size 24 nm) in the polyvinyl butyral polymer and 35 vol.% BaTiO3 microparticles (0.5-0.7 μm) dispersed in the ethyl-cellulose, as well as the ceramics made from the nanoparticles using the annealing at 1250oC. The composite films were covered with Ag electrodes and the measurements were performed in a wide frequency range. Using the Lichtenecker effective media approximation, we analysed the effective dielectric response of the dense ferroelectric composites. To establish the phase state of the nanoparticles, we analysed the static 137Ba NMR spectra of BaTiO3 nanoparticles in a wide temperature range from 200 to 400 K. Obtained results revealed that the ferroelectric properties of the nanoparticles contribute to the effective dielectric response of the composites in a significantly different way than predicted by the effective media model. This counterintuitive conclusion indicates on the strong crosstalk effects in the dense ferroelectric nanocomposites, which can be very promising for their applications in nanoelectronics and energy storage.

cond-mat.mtrl-sci↗

arXiv2022

Theory of quasi-ballistic FET: steady-state regime and low-frequency noise

We present the theoretical analysis of steady state regimes and low-frequency noises in quasi-ballistic FETs. The noise analysis is based on the Langevin approach, which accounts for the microscopic sources of fluctuations originated from intrachannel electron scattering. The general formulas for local fluctuations of the carrier concentration, velocity and electrostatic potential as well, as their distributions along the channel are found as functions of applied voltage/current. Two circuit regimes with stabilized current and stabilized voltage are considered. The noise intensities for the devices with different ballisticity are compared. We suggest that the presented analysis makes better comprehension of physics of electron transport and fluctuations in quasi-ballistic FETs, improves their theoretical description and can be useful for device simulation and design.

cond-mat.mes-hall↗

arXiv2022

Size Effect of Local Current-Voltage Characteristics of MX$_2$ Nanoflakes: Local Density of States Reconstruction from Scanning Tunneling Microscopy Experiments

Local current-voltage characteristics for low-dimensional transition metal dichalcogenides (LD-TMD), as well as the reconstruction of their local density of states (LDOS) from scanning tunneling microscopy (STM) experiments is of fundamental interest and can be useful for advanced applications. Most of existing models are either hardly applicable for the LD-TMD of complex shape (e.g., those based on Simmons approach), or necessary for solving an ill-defined integral equation to deconvolute the unknown LDOS (e.g., those based on Tersoff approach). Using a serial expansion of Tersoff formulae, we propose a flexible method how to reconstruct the LDOS from local current-voltage characteristics measured in STM experiments. We established a set of key physical parameters, which characterize the tunneling current of a STM probe - sample contact and the sample LDOS expanded in Gaussian functions. Using a direct variational method coupled with a probabilistic analysis, we determine these parameters from the STM experiments for MoS2 nanoflakes with different number of layers. The main result is the reconstruction of the LDOS in a relatively wide energy range around a Fermi level, which allows insight in the local band structure of LD-TMDs. The reconstructed LDOS reveals pronounced size effects for the single-layer, bi-layer and three-layer MoS$_2$ nanoflakes, which we relate with low dimensionality and strong bending/corrugation of the nanoflakes. We hope that the proposed elaboration of the Tersoff approach allowing LDOS reconstruction will be of urgent interest for quantitative description of STM experiments, as well as useful for the microscopic physical understanding of the surface, strain and bending contribution to LD-TMDs electronic properties.

cond-mat.mtrl-sci↗

arXiv2021

Probing phonon softening in ferroelectrics by the scanning probe microwave spectroscopy

Microwave measurements have recently been successfully applied to measure ferroelectric materials on the nanoscale, including detection of polarization switching and ferroelectric domain walls. Here we discuss the question whether scanning probe microscopy (SPM) operating at microwave frequency can identify the changes associated with the soft phonon dynamics in a ferroic. The analytical expressions for the electric potential, complex impedance and dielectric losses are derived and analyzed, since these physical quantities are linked to experimentally-measurable properties of the ferroic. As a ferroic we consider virtual or proper ferroelectric with an optic phonon mode that softens at a Curie point. We also consider a decay mechanism linked to the conductance of the ferroic, and thus manifesting itself as the dielectric loss in the material. Our key finding is that the influence of the soft phonon dispersion on the surface potential distribution, complex impedance and dielectric losses are evidently strong in the vicinity (10-30 K) of the Curie temperature. Furthermore, we quantified how the spatial distribution and frequency spectra of the complex impedance and the dielectric losses react on the dynamics of the soft phonons near the Curie point. These results set the stage for characterization of polar phase transitions with nanoscale microwave measurements, providing a complementary approach to well established electromechanical measurements for fundamental understanding of ferroelectric properties as well as their applications in telecommunication and computing.

cond-mat.mtrl-sci↗

arXiv2021

The free path and the generation rate of a fast-moving electron interacting with a dielectric media

In the framework of macroscopic continuous medium approach, we studied the interaction between a fast-moving charged particle and dielectric or semiconducting media with low energy electrically active excitations. The excitations contribute to frequency dispersion of the media dielectric permittivity. Two types of processes induced by a moving charged particle are considered: electron-hole generation under interband transitions and excitation of polar optical phonons. For both processes we calculated and analyzed the time- and space-dependent electric potential generated by the charged particle, polarization of the media, energy losses of the particle and other important constituents of the interaction patterns. Obtained results can contribute to deeper understanding of the charged particle beams interaction with a semiconducting medium, as well as may be useful for versatile applications of charged beams.

cond-mat.mtrl-sci↗

arXiv2021

Fundamental miniaturization limits for MOSFETs with a monolayer MoS$_2$ channel

We propose a theoretical model for describing the operation of a transistor with a MoS2 monolayer channel, which allows to obtain an analytical approximation of the potential in the channel. This potential depends on the drain and gate voltages. On this basis we make estimates for the minimum channel lengths due to the fundamental restriction of quantum tunneling through the barrier. It is shown that the relatively large effective mass of electrons in the MoS2 monolayer allows to predict the creation of devices with channels of a significantly shorter (2.5 - 3 nm) length than in traditional silicon MOSFETs. These devices can be promising for the ultra-fast electronics of new generation.

cond-mat.mes-hall↗