The process of acoustic wave propagation in piezoelectric crystals has been investigated. The scanning electron microscopy, X-ray diffraction, and X-ray topography methods at synchrotron radiation source were used as the main investigation methods. Scanning electron microscopy allows to visualize the propagation of different types of acoustic waves (surface acoustic wave (SAW), pseudo-surface acoustic wave (PSAW), Lamb wave) on the surface of piezoelectric crystals in the real-time mode. This method made it possible to visualize the diffraction phenomena in acoustic beams. Rayleigh surface acoustic waves and Lamb waves excited in a thin LiNbO3 crystal by the same interdigital transducer (IDT) but at different frequencies are visualized. The process of X-ray diffraction on the crystal surface modulated by surface acoustic waves was studied using high-resolution X-ray diffraction. SAW amplitudes and power flow angles were determined based on the analysis of X-ray diffraction spectra. Acoustic wave fields on the crystal surface were visualized at a synchrotron radiation source BESSY II using the Talbot effect.

The process of X-ray diffraction on the X-112° Y-cut of a LiTaO3 crystal excited by surface acoustic waves (SAW) with a wavelength of Ʌ=4 μm was studied at a synchrotron radiation source in a scheme of a double-crystal X-ray diffractometer. The sinusoidal acoustic modulation of the crystal lattice leads to the appearance of diffraction satellites on the rocking curve; the number and intensity of satellites depend on the amplitude of the SAW. Analysis of X-ray diffraction spectra allowed us to determine the velocity (VSAW=3300 m/s) and amplitudes of the SAW. For the first time experimental investigations have demonstrated the presence of the power flow angle in the X-112° Y-cut of a LiTaO3 crystal, i.e., a situation where the direction of acoustic energy propagation (PFV) does not coincide with the direction of the SAW wave vector KSAW. The measured power flow angle was PFA=0.41°. This PFA value is important for designing acoustoelectronic devices in order to reduce acoustic signal losses.

An interdigital transducer structure was fabricated from multilayer graphene on the surface of the YZ-cut of a LiNbO3 ferroelectric crystal. The multilayer graphene was prepared by CVD method and transferred onto the surface of the LiNbO3 substrate. The properties of the multilayer graphene film were studied by Raman spectroscopy. A multilayer graphene (MLG) interdigital transducer (IDT) structure for surface acoustic wave (SAW) excitation with a wavelength of Λ=60 μm was fabricated on the surface of the LiNbO3 crystal using electron beam lithography (EBL) and plasma chemical etching. The amplitude–frequency response of the SAW delay time line was measured. The process of SAW excitation by graphene IDT was visualized by scanning electron microscopy. It was demonstrated that the increase in the SAW velocity using graphene was related to the minimization of the IDT mass.

Zinc oxide is a promising material for the creation of various types of sensors, in particular UV detectors. In this work, arrays of ordered nanorods were grown by chemical vapor deposition. The effect of environmental humidity on the sensing properties of zinc oxide nanorod arrays was investigated, and a prototype UV sensor using indium as an ohmic contact was developed. UV photoresponses were measured for the samples stored in dry and wet atmospheres. The increase in sensitivity and response of the ZnO nanorod arrays was observed after prolonged exposure to a wet atmosphere. A model was proposed to explain this effect. This is due to the formation of hydroxyl groups on the surface of zinc oxide nanorods, which is confirmed by FTIR spectroscopy data. For the first time, it has been shown that after storage in a wet atmosphere, the sensory properties of the structure remain stable regardless of the ambient humidity.

The SAW excitation and propagation on the X-112 degrees degrees Y-cut of a LiTaO3 crystal were studied using a triple-axis Xray diffractometer with a laboratory X-ray source. Simulation of X-ray rocking curves with the Takagi equation system enabled the determination of surface acoustic wave amplitudes on the crystal surface. The SAW excitation process in the frequency range of an acoustoelectronic device, determined by the excitation band or interdigital transducer structure, was studied.

Abstract X-ray diffraction by surface acoustic waves is investigated by the method of triple-crystal X-ray diffractometer on the laboratory source of X-ray radiation. This approach allows to determine the amplitudes of the surface acoustic waves (SAW) and to study the features of the diffraction process for different materials, to study the characteristics of fabrication of the structures of the interdigital transducers (IDT) for SAW excitation. The influence of the metallization coefficient of the IDT on the SAW excitation process is considered.

The ordered Ca3TaGa3Si2O14 and disordered La3Ga5SiO14 crystals of the lantangallium silicate family were grown via the Czochralski method. The independent coefficients of thermal expansion of crystals αc and αa were determined using X-ray powder diffraction based on the analysis of X-ray diffraction spectra measured in the temperature range of 25~1000 °C. It is shown that, in the temperature range of 25~800 °C, the thermal expansion coefficients are linear. At temperatures above 800 °C, there is a nonlinear character of the thermal expansion coefficients, associated with a decrease in the Ga content in the crystal lattice.

Congruent and stoichiometric ferroelectric lithium niobate-tantalate crystals LiNb(1-x)TaxO3 of different compositions were grown by the Czochralski method. The stoichiometric crystals were grown using the top seeded solution growth method using LiWO4, which increases the Li content in the melt and in the grown crystal. Also, the use of a solvent can significantly reduce the temperature of the melt. The composition of the crystals was studied by inductively coupled plasma mass spectrometry using laser ablation, which allow studying the change in the composition of the grown crystals along the length and diameter. It is demonstrated that the content of Ta in the crystals exceeds the content of Ta in the initial charge, i.e., in the process of crystal growth, the melt becomes depleted in Ta. It is shown that the Ta content decreases along the crystal length due to the decrease in the Ta content in the melt. In the LiNb0.88Ta0.12O3 crystals, the piezoelectric moduli d22 and d33, and the velocities of bulk and surface acoustic waves were measured. The values of piezoelectric moduli and acoustic wave velocities are shown to occupy an intermediate position between LiNbO3 and LiTaO3 crystals.

Results from studying the effect of an applied electric voltage on the Raman spectrum of graphene deposited on a lithium niobate crystal substrate with a ferroelectric domain structure are presented. The use of the principal component method for data processing in combination with correlation analysis made it possible to reveal the contribution to the change in the spectra associated with the linear deformation of the substrate due to the inverse piezoelectric effect. An effect of the graphene coating peeling was found. Furthermore, bending deformations of the graphene coating associated with the presence of a relief on the substrate were found. An analysis of the change in the spectra of graphene under the application of an electric voltage made it possible to determine the height of this relief.

The process of acoustically stimulated charge transport in the graphene film on the surface of the YZ−cut of a LiNbO3 crystal was investigated. It was found that the dependence of the current in the graphene film on the frequency of the surface acoustic wave (SAW) excitation repeats the amplitude-frequency response of the SAW delay time line. It is shown that increasing the SAW amplitude leads to an increase in the current in the graphene film, and the current in the graphene film depends linearly on the amplitude of the high-frequency input signal supplied to the interdigital transducer (IDT, in dB). It is demonstrated that at a positive bias potential on the graphene film, the SAW propagation allows to change the direction of the current in the graphene film by changing the amplitude of the SAW. It is also shown that in the frequency range of the amplitude-frequency response of the SAW delay time line, the current in the graphene film can vary from positive to negative values depending on the frequency. The capability to control the SAW excitation frequency or the SAW amplitude makes it possible to control the value and direction of the current in the graphene film. The SAW propagation lets to collect and transport the photo-stimulated charges in the graphene film on the crystal surface.

X-ray diffuse scattering from the Ca3NbGa3Si2O14 (CNGS) crystal was measured with a triple axis X-ray diffractometer under the conditions of an external electric field. It is found that the nature of the intensity distribution of the asymmetrical part of diffuse scattering depends on the value of the applied electric field. This phenomenon is apparently associated with different piezoelectric characteristics of defect regions and the rest of the single crystal.

Band structure engineering by changing the parameters of Moire = superlattices enables creation of materials with outstanding properties for twistronics, straintronics and quantum nanoelectronics applications. Herein, twisted multilayer graphene (tMLG) with various combinations of twist angles (0) and numerous Moire = superlattices was synthesized. The strong dependence of the transport properties of tMLG on the structural characteristics was demonstrated using synchrotron-based core-level spectroscopy methods combined with micro-Raman spectroscopy. It has been shown that tMLG with a large content of the twisted phase with the twist angles between the adjacent graphene layers of 0 = 26-30 degrees over the entire tMLG thickness is characterized by a perfect structure of the single layer graphene (SLG) and extraordinary transport characteristics. At low temperatures, the asymmetry of charge carriers and atypical temperature dependence of average carrier mobility m were observed. In such tMLG, m was higher than 105 cm2V-1s-1. Decrease in the content of the twisted phase with 0 = 26-30 degrees, as well as increase in the contents of other twist angles and AB-stacked phase (0 = 0 degrees), leads to a significant decrease in m. Hence, tMLGs are a better choice for the nanoelectronics industry because, having outstanding transport properties, they are, contrary to SLG, insensitive to the specific features of process procedures.

The propagation process of the surface acoustic waves (SAW) and the pseudo-surface acoustic waves (PSAW) in a bonded layered structure of a 41° YX-cut of a LiNbO3 crystal/Si(100) crystal was investigated. The scanning electron microscopy (SEM) method,in the low-energy secondary electrons registration mode, made it possible to visualize the SAW and PSAW in the LiNbO3/Si layered structure. The process of the SAW and PSAW propagation in a LiNbO3/Si layered structure and in a bulk 41° YX-cut of a LiNbO3 crystal were compared. It was demonstrated that the SAW velocities in the layered LiNbO3/Si structure exceed the typical SAW velocities for LiNbO3 and Si single crystals. In the layered structure, the SAW and PSAW velocities were 4062 m/s, 4731 m/s, and 5871 m/s. It was also demonstrated that the PSAW velocities are the same in the LiNbO3/Si layered structure and in the bulk 41° YX-cut of a LiNbO3 crystal.

In this research, beam focusing in lithium niobate plate was studied for fundamental anti-symmetric (A0) and symmetric (S0) Lamb waves, and the shear-horizontal (SH0) wave of zero-order. Using the finite element method, appropriate configuration of the interdigital transducer with arc-like electrodes was modeled accounting for the anisotropy of the slowness curves and dispersion of the modes in the plate. Profiles of the focalized acoustic beams generated by the proposed transducer were theoretically analyzed. Based on the result of the analysis, relevant delay lines were fabricated and transfer functions (insertion loss) of the line were measured for SH0 wave in YX-lithium niobate plate. Using an electron scanning microscope, distribution of the electric fields of the same wave were visualized. The results of this study may be useful for hybrid devices and sensors combining nano and acoustoelectronic principles.

Because of their unique atomic structure, 2D materials are able to create an up-to-date paradigm in fundamental science and technology on the way to engineering the band structure and electronic properties of materials on the nanoscale. One of the simplest methods along this path is the superposition of several 2D nanomaterials while simultaneously specifying the twist angle between adjacent layers (θ), which leads to the emergence of Moiré superlattices. The key challenge in 2D nanoelectronics is to obtain a nanomaterial with numerous Moiré superlattices in addition to a high carrier mobility in a stable and easy-to-fabricate material. Here, we demonstrate the possibility of synthesizing twisted multilayer graphene (tMLG) with a number of monolayers NL = 40-250 and predefined narrow ranges of θ = 3-8°, θ = 11-15°, and θ = 26-30°. A 2D nature of the electron transport is observed in the tMLG, and its carrier mobilities are close to those of twisted bilayer graphene (tBLG) (with θ = 30°) between h-BN layers. We demonstrate an undoubtful presence of numerous Moiré superlattices simultaneously throughout the entire tMLG thickness, while the periods of these superlattices are rather close to each other. This offers a challenge of producing a next generation of devices for nanoelectronics, twistronics, and neuromorphic computing for large data applications.

We present a novel method of temporal modulation of X-ray radiation for time resolved experiments. To control the intensity of the X-ray beam, the Bragg reflection of a piezoelectric crystal is modified using comb-shaped electrodes deposited on the crystal surface. Voltage applied to the electrodes induces a periodic deformation of the crystal that acts as a diffraction grating, splitting the original Bragg reflection into several satellites. A pulse of X-rays can be created by rapidly switching the voltage on and off. In our prototype device the duty cycle was limited to ∼1 ns by the driving electronics. The prototype can be used to generate X-ray pulses from a continuous source. It can also be electrically correlated to a synchrotron light source and be activated to transmit only selected synchrotron pulses. Since the device operates in a non-resonant mode, different activation patterns and pulse durations can be achieved.

Electrical conductivity and acoustic loss Q−1 of single crystalline Li(Nb,Ta)O3 solid solutions (LNT) are studied as a function of temperature by means of impedance spectroscopy and resonant piezoelectric spectroscopy, respectively. For this purpose, bulk acoustic wave resonators with two different Nb/Ta ratios are investigated. The obtained results are compared to those previously reported for congruent LiNbO3. The temperature dependent electrical conductivity of LNT and LiNbO3 show similar behavior in air at high temperatures from 400 to 700 °C. Therefore, it is concluded that the dominant transport mechanism in LNT is the same as in LN, which is the Li transport via Li vacancies. Further, it is shown that losses in LNT strongly increase above about 500 °C, which is interpreted to originate from conductivity-related relaxation mechanism. Finally, it is shown that LNT bulk acoustic resonators exhibit significantly lower loss, comparing to that of LiNbO3.

Lithium niobate and tantalate are among the most important and widely used materials of acoustooptics and acoustoelectronics. They have high piezoelectric constants enabling their use as actuators. Their use is however restricted by the thermal instability of lithium niobate crystals and the low Curie temperature TC of lithium tantalate crystals. Overcoming these drawbacks typical of some compounds is possible by growing LiNb1-xTaxO3 single crystals. Good quality LiNb1-xTaxO3 single crystals have been grown using the Czochralsky technique. High-temperature poling process of LiNb1-xTaxO3 single crystals has been studied. The main differences between the process modes required for poling of congruent LiNb1-xTaxO3 single crystals and congruent LiNbO3 single crystals have been demonstrated. Parameters of high-temperature electric diffusion processing of LiNb1-xTaxO3 single crystals that provide for singledomain crystals for further study of physical properties have been reported.

The possibility of creating resonant ultraviolet (UV) sensors based on the structure of ZnO nanorods/La3Ga5SiO14 microbalance (LCM) has been investigated. The principle of sensor operation is based on the desorption of oxygen from the surface of ZnO nanorods upon irradiation with UV light and an increase in the concentration of charge carriers that leads to an increase in the capacitance of the structure of ZnO nanorods/LCM. It has been shown that UV radiation intensity affects the resonance oscillation frequency of the LCM sensor. After the end of irradiation, the reverse process of oxygen adsorption on the surface of ZnO nanorods occurs, and the resonance frequency of the sensor oscillations returns to the initial value.