Методом электронной литографии к чешуйкам Bi2Se3, перенесенным скотчем на подложку SiO2, созданы образцы, в которых исследованы процессы резистивных переключений и возможность управления многоуровневыми мемристивными состояниями.

We report the study of YBa2Cu3O7‒delta films, synthesized on SrTiO3(100) substrates by pulsed laser deposition with velocity filtration, using X-ray diffractometry, transport measurements, and scanning electron microscopy. We have revealed the dependence of the structure of 100-200 nm thick YBa2Cu3O7‒delta films on deposition time and velocity of particles in erosion plume, set by velocity filter. After deposition, the films, or their part, close to the substrate, consisted of 3‒10-nm crystals with oxygen index delta = 0.08, the same as in the target. For deposition time from 10 to 60 min, we observed the growth of regular pyramids with triangular and quadrangular bases from 20 to 500 nm in size at the base and spiral pyramids with polygonal bases on the film surface. The maximum oxygen loss up to delta = 0.35 and T (R = 0) up to 77.4 K coincided with the appearance of spiral pyramids up to 100 nm-high. These findings evidence in favor of oxygen depletion of the top layers of YBa2Cu3O7‒delta thin films through the formation and growth of oxygen-deficient pyramids on their surface. The oxygen index in the range of delta = 0.08‒0.15 in both nanocrystals and regular pyramids of 20‒300 nm in size provided T(R = 0) =84‒87 K and the width of superconducting transition DeltaT = 2.5‒3.5 K.

We report the study of YBa2Cu3O7-delta films, synthesized on SrTiO3(100) substrates by pulsed laser deposition with velocity filtration, using X-ray diffractometry, transport measurements, and scanning electron microscopy. We have revealed the dependence of the structure of 100-200 nm thick YBa2Cu3O7-delta films on deposition time and velocity of particles in erosion plume, set by velocity filter. After deposition, the films, or their part, close to the substrate, consisted of 3-10-nm crystals with oxygen index delta=0.08, the same as in the target. For deposition time from 10 to 60 min, we observed the growth of regular pyramids with triangular and quadrangular bases from 20 to 500 nm in size at the base and spiral pyramids with polygonal bases on the film surface. The maximum oxygen loss up to delta=0.35 and T(R=0) up to 77.4 K coincided with the appearance of spiral pyramids up to 100 nm-high. These findings evidence in favor of oxygen depletion of the top layers of YBa2Cu3O7-delta thin films through the formation and growth of oxygen-deficient pyramids on their surface. The oxygen index in the range of delta=0.08-0.15 in both nanocrystals and regular pyramids of 20-300 nm in size provided T(R=0)=84-87 K and the width of superconducting transition Delta T=2.5-3.5 K. Keywords: pulsed laser deposition, surface morphology, film transport properties, film evolution, SrTiO3.

The multilevel nature and plasticity of memristor structures based on bismuth selenide microcrystals (of the "flake" type), which are controlled by the rewriting voltages Vset/Vreset are investigated. It was shown by numerical simulation that the switching is caused by the barrier properties of the defective layer, consisting of two sublayers having different thicknesses, as well as different electrical and thermal conductivities, overheating phenomena have been also taken into account. The change in the device resistance both at ON-OFF and at OFF-ON transitions begins at approximately the same absolute value of the threshold electric field of the order of 10(5) V/cm. Modulation of the barrier formed at the interface between a metal and a strongly doped semiconductor is the most likely model for resistive switching in bismuth selenide-based structures. (C) 2020 Elsevier Ltd. All rights reserved.

Методом электронной литографии созданы мемристивные структуры на основе флейков селенида висмута. Исследованы мемристивные переключения и возможность управления многоуровневыми мемристивными состояниями в полученных микроструктурах.

A correlation was found between the endset temperature of the superconducting transition T(R = 0) of YBa2Cu3O7 – x films 100–200 nm thick, obtained by pulsed laser deposition on SrTiO3(100) substrates with a temperature of ~740°C, and the regimes of high-speed filtering of the erosion plume formed upon ablation of the material the target. Under deposition conditions, we changed the width of the filtering window, the repetition rate of the atomized material passing through the filter onto the substrate, and the radiation energy density of the KrF excimer laser on the target surface. At deposition rates of less than 0.1 nm s–1, the values of T(R = 0) did not exceed 77 K, and pyramids were formed on the surface of the films up to 80 nm in height along the c axis in the form of spirals with rectangular bases and steps of 1–2 nm along the lateral faces. With an increase in the deposition rate from 0.1 to 0.6 nm s–1, T(R = 0) increased to 86 K. These regimes corresponded to a wavy pyramid surface up to 40 nm in height with rounded bases up to 1500 nm in diameter and irregular steps 1–4 nm on the side slopes. Faceted crystals with a width from 20–30 to 500 nm in the base grew along the boundaries between the pyramids during the deposition. This morphology of the growth surface was explained by the high flow rate of the sputtered material, which is determined by the frequency filtering of the erosion plume and the energy density in the pulse upon predominantly surface diffusion.

Abstract A correlation was found between the endset temperature of the superconducting transition T ( R = 0) of YBa_2Cu_3O_7 – _ x films 100–200 nm thick, obtained by pulsed laser deposition on SrTiO_3(100) substrates with a temperature of ~740°C, and the regimes of high-speed filtering of the erosion plume formed upon ablation of the material the target. Under deposition conditions, we changed the width of the filtering window, the repetition rate of the atomized material passing through the filter onto the substrate, and the radiation energy density of the KrF excimer laser on the target surface. At deposition rates of less than 0.1 nm s^–1, the values of T ( R = 0) did not exceed 77 K, and pyramids were formed on the surface of the films up to 80 nm in height along the c axis in the form of spirals with rectangular bases and steps of 1–2 nm along the lateral faces. With an increase in the deposition rate from 0.1 to 0.6 nm s^–1, T ( R = 0) increased to 86 K. These regimes corresponded to a wavy pyramid surface up to 40 nm in height with rounded bases up to 1500 nm in diameter and irregular steps 1–4 nm on the side slopes. Faceted crystals with a width from 20–30 to 500 nm in the base grew along the boundaries between the pyramids during the deposition. This morphology of the growth surface was explained by the high flow rate of the sputtered material, which is determined by the frequency filtering of the erosion plume and the energy density in the pulse upon predominantly surface diffusion.

HTS YBCO films 200–400 nm thick are fabricated by pulsed laser deposition, both without filtration and in the regimes of velocity filtration of particles of an ablation plume. Using AFM and SEM, it is established that the size of large particles in the plane of films during deposition without filtration ranges from 60 to 1000 nm. After filtration, the maximum particle size in the film plane is less than 500 nm. Two types of irregularities are found on the surface after deposition: irregularities obtained from rounded particles and irregularities from faceted crystals. Using the methods of electron lithography and etching with argon ions through a mask, micro- and nanostructures are fabricated from HTS films. A correlation has been found between the characteristic dimensions of the irregularities on the surface of the films and the available lateral resolution of the microstructures obtained. For structures from HTS films that are asymmetric rings with a characteristic line width of 800 nm, the temperature dependences of the superconducting transition are determined and their asymmetric I–V characteristics are observed.

The observations the dc voltage on asymmetric superconducting ring testify that one of the ring segments is a dc power source. The persistent current flows against the total electric field in this segment. This paradoxical phenomenon is observed when the ring or its segments are switched between superconducting and normal state by non-equilibrium noises. We demonstrate that the dc voltage and the power increase with the number of the identical rings connected in series. Large voltage and power sufficient for practical application can be obtained in a system with a sufficiently large number of the rings. We point to the possibility of using such a system for the observation of the dc voltage above superconducting transition and in the asymmetric rings made of normal metal.

The observations the dc voltage on asymmetric superconducting ring testify that one of the ring segments is a dc power source. The persistent current flows against the total electric field in this segment. This paradoxical phenomenon is observed when the ring or its segments are switched between superconducting and normal state by non-equilibrium noises. We demonstrate that the dc voltage and the power increase with the number of the identical rings connected in series. Large voltage and power sufficient for practical application can be obtained in a system with a sufficiently large number of the rings. We point to the possibility of using such a system for the observation of the dc voltage in the normal state of superconducting rings and in the asymmetric rings made of normal metal.

A mobile measuring cell was proposed and created using a focused ion beam as a nanoknife for measuring the electrical characteristics of individual nanowires and nanotubes by the four-wire method. The cell consists of two elements: the basic one, on whose surface a nanoconductor is deposited, and the auxiliary element that provides the electrical connection of the primary element to the wires of the external measuring circuit. Micro- and nanoscale wires in both elements of the cell were formed from gold films deposited on a silicon oxide surface. This provides reliable contacts between a nanoobject and the wires. In this paper, the application of the proposed method was demonstrated using examples of a multiwalled carbon nanotube and a thin platinum nanowire. The electrical resistance of the nanotube was measured using the two-wire method, whereas the current–voltage characteristic for the platinum nanowire was measured via the fourwire method.

Deformations of particular setae of adhesive toe pad of the tokay gecko were investigated by atomic-force microscopy. The effective elastic modulus of the investigated setae varying within 0.34–19 GPa, a pronounced hysteresis was observed during reversible bending of setae. The hysteresis-related energy losses may be as high as 98% of the total bending work. The pronounced viscous features of the setae contradict the hypothesis of dynamic self-cleaning of the gecko adhesive cover, according to which the setae are considered as absolutely elastic cantilever beams.

Single-mode submicrometer-thick strip waveguides on silicon-on-insulator substrates, fabricated by silicon-planar-technology methods are considered. To solve the problem of 1.5-µm wavelength radiation input-output and its frequency filtering, strip diffraction gratings and two-dimensional photonic crystals are integrated into waveguides. The reflection and transmission spectra of gratings and photonic crystals are calculated. The waveguide-mode-attenuation coefficient for a polycrystalline silicon waveguide is experimentally estimated.

Experimental research has been made into coherent spin dynamics of electrons localized in GaAs quantum well planes using an electrically controlled potential. A localizing potential was created by means of a metal gate with submicron windows deposited on the sample surface. The photo-induced magneto-optical Kerr effect was used to study the dependence of electron spin lifetime as a function of temperature, applied bias and magnetic field for gates with various sets of windows. It has been shown that the electrically controlled laterally localizing potential can be used to smoothly vary electron spin lifetime from several hundreds of picoseconds to several tens of nanoseconds. The obtained dependence of spin electron relaxation time on the size of the lateral localization region is in good qualitative agreement with the theoretical prediction.

A new type of a superconducting quantum interference device (SQUID) based on a single superconducting loop without Josephson junctions and with asymmetric contacts has been proposed. This SQUID offers advantages in simplicity of fabrication and a steeper dependence of measured quantities on the magnetic flux. To confirm the possibility of making this type of SQUID, the magnetic field dependence of the critical current in an aluminum ring with asymmetric contacts has been experimentally investigated.

The coherent spin dynamics of electrons localized in a plane of GaAs quantum wells is studied experimentally by the application of an electrically controlled potential. The localizing potential is produced with the use of a metal gate with submicrometer windows deposited onto the sample surface. The photoinduced spin Kerr effect is used to study the electron spin lifetime as a function of the temperature, applied bias, and magnetic field for gates with different sets of windows. It is shown that, with an electrically controlled laterally localizing potential, it is possible to gradually change the electron spin lifetime from several hundreds of picoseconds to several tens of nanoseconds. The dependence of the electron spin relaxation time on the sizes of the lateral localization region is in good qualitative agreement with theoretical prediction.

Using an electron beam, spontaneous polarization on the surface of +Z cuts of lithium niobate crystals of various compositions is switched. Domains 100–200 nm in size are formed in a thin surface layer, with the thickness dependent on the primary-electron energy. The sizes of segments, on which submicron domains are formed, exceed the sizes of the irradiation region. The distributions of domains on the surface in crystals of various compositions are different and depend on the method of moving the electron beam and irradiation conditions. The results are discussed in the context of notions on the charging of dielectric materials by the electron beam. It is assumed that the spontaneous polarization in the surface layer of +Z cuts of lithium niobates is switched by the field of a double layer of charges formed as a result of the charging process near the surface.

Coherent spin dynamics of electrons laterally confined in a wide GaAs quantum well using a special mosaic electrode deposited onto the sample plane has been investigated. Electron spin lifetime measurements have been carried out in structures with different sizes of orifices in the mosaic electrode using the time-resolved Kerr rotation technique. It has been found that the electron spin lifetime in the lateral traps increases significantly with decreasing orifice size in the mosaic electrode. The observed electron spin lifetime dependence can be interpreted in terms of D'yakonov–Perel' spin relaxation mechanism suppression.