Magnetic and resistive properties of a SrMnO 3 /La 0.7 Sr 0.3 MnO 3 antiferromagnetic/ferromagnetic heterostructure are studied in a temperature range of 50–300 K using magnetotransport measurements. It is established that, in the heterostructure, the SrMnO 3 layer is in an antiferromagnetic state at room temperature, which is above its Néel point for a single layer, and the magnetization of the heterostructure exhibits the properties of unidirectional anisotropy. This conclusion is also confirmed by the ferromagnetic resonance spectra.

Magnetic and resistive properties of the antiferromagnet–ferromagnet SrMnO3 La0.7Sr0.3MnO3 heterostructure were studied in the temperature range of 50–300 K using magnetotransport measurements. It is established that in the heterostructure, the SrMnO3 layer is in an antiferromagnetic state at room temperature, which is higher than its temperature for a single layer, and the magnetization of the heterostructure exhibits the properties of unidirectional anisotropy. This conclusion is also confirmed by the ferromagnetic resonance spectra

Magnetic and resistive properties of the antiferromagnet–ferromagnet SrMnO3 La0.7Sr0.3MnO3 heterostructure were studied in the temperature range of 50–300 K using magnetotransport measurements. It is established that in the heterostructure, the SrMnO3 layer is in an antiferromagnetic state at room temperature, which is higher than its temperature for a single layer, and the magnetization of the heterostructure exhibits the properties of unidirectional anisotropy. This conclusion is also confirmed by the ferromagnetic resonance spectra

Abstract—CoPt films obtained by electron beam evaporation with deposition of ten Co and Pt bilayers with a total thickness of 8 nm are experimentally investigated. The Hall effect and longitudinal magnetoresistance measurements were carried out with a temperature change from 8 to 300 K. At room temperature, using magnetic force microscopy, images of domain structures corresponding to different points of the magnetization reversal curve were obtained. The possibility of studying the Hall effect on artificially created domain structures formed by the local magnetic field of the probe of an atomic force microscope is demonstrated.

The results of experimental studies of the conductivity of AlGaAs/GaAs heterostructure with two-dimensional electron gas at temperatures of 10-300 K are presented. At low temperatures, with a decrease in the distance between the contacts to the structure from 100 to 20 µm, a resistance increase was observed. To explain this anomalous dependence, a numerical simulation of the piezoelectric effect in a semiconductor on the channel conductivity is carried out. It is shown that it is necessary to take into account the crystallographic orientation of the channel and the effect on its potential of remote piezo-charges.

The electric conductivity of the AlGaAs/GaAs heterostructure with two-dimensional electron gas has been experimentally studied in a temperature range of 10–300 K. At low temperatures, electric resistance of the structure exhibited growth when the distance between contacts decreased from 100 to 20 μm. For explaining this anomalous behavior, numerical simulation of the influence of piezoeffect in the semiconductor on the channel conductivity was carried out, which showed that it is necessary to take into account the crystallographic orientation of the channel and the influence of remote piezoelectric charges on its potential.

AbstractIn this paper, we studied the effect of the magnetic field and temperature on conductivity of Bi_2 ‒ _ x Sb_ x Te_3 – _ y Se_ y topological insulators of different composition to identify electronic surface states in these films. The experimental data can be explained based on the model with two types of charge carriers. Thermoactivation conductivity, electron or hole, is observed in the film bulk depending on the sample composition while metal-like electronic states are found on the surface. The noticeable contribution of surface topological states to the total conductivity opens up the possibility of studying them.

In this paper, we studied the effect of the magnetic field and temperature on conductivity of Bi 2 ‒ x Sb x Te 3 – y Se y topological insulators of different composition to identify electronic surface states in these films. The experimental data can be explained based on the model with two types of charge carriers. Thermoactivation conductivity, electron or hole, is observed in the film bulk depending on the sample composition while metal-like electronic states are found on the surface. The noticeable contribution of surface topological states to the total conductivity opens up the possibility of studying them.

In the study of electron transport in low-dimensional structures, semiconductor heterostructures with a two-dimensional electron gas are often used. The conductive channel of these structures is separated from the gates by insulating regions, which can be formed in a varitey of ways. The peculiarities of such structures are the high quality of the initial plates and the need to change the topology in the research process. This makes the use of photolithography ineffective.This paper discusses the technology of forming insulating grooves using an atomic force microscope — a method of pulsed force nanolithography, which allows both working with individual samples and forming narrow and deep grooves on the semiconductor that provide good insulating characteristics. The measured transport characteristics of the nanostructures created by this method confirm the presence of quantization of the channel conductivity and the absence of a noticeable number of introduced defects.

In this paper, we studied the effect of the magnetic field and temperature on conductivity of Bi2 ‒ xSbxTe3 – ySey topological insulators of different composition to identify electronic surface states in these films. The experimental data can be explained based on the model with two types of charge carriers. Thermoactivation conductivity, electron or hole, is observed in the film bulk depending on the sample composition while metal-like electronic states are found on the surface. The noticeable contribution of surface topological states to the total conductivity opens up the possibility of studying them.

We present a first study of films of the quaternary Bi2-xSbxTe3-ySey solid solutions on (0001) sapphire substrates grown by atmospheric pressure MOVPE. Trimethylbismuth, trimethylantimony, diisopropy-lselenide and diethyltelluride were used as precursors. To passivate the free bonds of the substrate and to improve the epitaxy, a thin (15 nm) ZnTe buffer layer was first grown. EDX analysis of the films grown at a temperature of 445 degrees C and about 10-fold excess of chalcogen in the vapor phase indicates on their compliance with V2VI3 stoichiometry. AFM and SEM investigations showed that at the initial stage of deposition the Stranski-Krastanov growth mode is dominant. Complete coalescence of nanoislands occurs at a thickness about 60 nm and further film formation is in the 2D layer-by-layer growth mode. A high mole fraction of antimony in the vapor phase leads to bad crystalline quality of the films and even to their discontinuity. Transport properties of the Bi2-xSbxTe3-ySey films were evaluated using Van der Pauw Hall effect measurements in the range of temperatures of 10-300 K. Some films are always n- or p-type; in other samples the change of conductivity from p-to n-type was observed when the temperature decreases. (C) 2017 Elsevier B.V. All rights reserved.

Квазиодномерные полупроводниковые структуры с изменяемым продольным потенциальным рельефом созданы методом импульсной силовой нанолитографии, выполняемой с использованием атомно-силового микроскопа. Структуры изготавливались на основе гетероструктур AlGaAs/GaAs с глубоким (130 нм от поверхности) залеганием двумерного электронного газа. Потенциальный профиль канала формировался с помощью секционированных планарных затворов, созданных по обеим сторонам канала. Электрические параметры полученных структур, измеренные при температурах до 1.5 K, подтвердили эффективность примененного метода для создания изолирующих областей с латеральными размерами ~ 10 нм. DOI: 10.21883/FTP.2017.11.45106.20

The films of Sb-Te system have been deposited by MOVPE on (0001) Al2O3 substrates with thin ZnTe buffer layers at different temperatures and Te/Sb ratios in the vapor phase. X-ray diffractometry, SEM microscopy, Raman and EDX spectroscopy were used to study as-grown films. The surface morphology and stoichiometry of Sb-Te films strongly depend on Te/Sb ratio in vapor phase. We have deposited the phases of homologous series nSb2·mSb2Te3 with following stoichiometries: Sb2Te3, Sb4Te5, Sb8Te9, Sb10Te9, Sb4Te3, Sb2Te, Sb8Te3, Sb10Te3, Sb16Te3, Sb18Te3 and Sb. Transport properties of Sb2Te3, Sb4Te5, Sb8Te9, Sb4Te3, Sb2Te were evaluated using Van der Pauw technique at 300K.

Quasi-one-dimensional semiconductor structures with a variable longitudinal potential profile are fabricated by pulse power nanolithography, which is carried out using an atomic force microscope. Structures are fabricated on the basis of AlGaAs/GaAs heterostructures with a deep (130 nm from the surface) twodimensional electron gas. The channel potential profile is formed with the help of sectioned in-plane gates formed on both channel sides. The electrical parameters of the structures measured at temperatures down to 1.5 K confirmed the efficiency of the applied method to fabricate insulating regions with lateral sizes of ~10 nm.

We report on a metal organic vapor epitaxy (MOVPE) of Bi2Te3−xSex films over the entire range of compositions (0≤x≤3) for the first time. The films were grown on Al2O3(0001) substrates at 465°C using trimethylbismuth (Bi2Me3), diethyltellurium (Et2Te) and diisopropylselenium (iPro2Se) as metalorganic sources. To realize the 2D growth mode and to grow films with flat surfaces and high crystalline quality, a thin ZnTe buffer layer was used. As-grown films were studied using optical and AFM microscopy techniques and X-ray diffraction. It was found that under steady growth conditions the composition of Bi2Te3−xSex films strongly depends on the film thickness. But a high rate of interdiffusion of chalcogens at the growth temperature rapidly leads to a homogeneous composition of the film in the growth direction. Dependence of the intensity of X-ray reflection (0012) on the composition of Bi2Te3−xSex films x has extremes near x=1 (Bi2Te2Se) and x=2 (Bi2Se2Te). The AFM micrographs and profiles show large (above 2μm) triangle-shaped atomically flat terraces with step height of a quintuple layer (0.90nm) of the tetradymite-type compounds. The electronic properties of the grown films have been characterized via four probe magnetotransport measurements.

Magnetic force microscopy is used to investigate two different types of samples: thin metal films and ferrite garnet films. It is pointed out for garnet films that magnetic force microscopy allows us only to judge the domain structure of surface layers. Problems associated with conducting measurements in external magnetic fields, the effect of the magnetic field of the probe on the investigated domain structure, and using magneto-polarized optics in combination with magnetic force microscopy are considered.

Методами магнитно-силовой микроскопии исследованы два различных типа образцов: тонкие пленки металлов и пленки ферритов-гранатов. Отмечено, что в гранатовых пленках магнитно-силовая микроскопия позволяет судить лишь о доменной структуре приповерхностного слоя. Рассмотрены вопросы, связанные с проведением измерений во внешних магнитных полях, влиянием магнитного поля зонда на исследуемую доменною структуру, а также с использованием поляризационной магнитооптики в комбинации с магнитно-силовой микроскопией.

Transistor structures with one-dimensional conducting channel and three-sectioned side control gates have been created based on GaAs/AlGaAs heterostructures with two-dimensional electron gas by means of local anode oxidation with the aid of a scanning probe microscope. It is demonstrated that gates in this structure allow the potential profile in the channel to be controlled. The measured dependences of the channel conductance on the gate voltage exhibit plateaus (including those not multiple of 2e (2)/h) and maxima, the positions of which are determined by the ratio of potentials applied to the gates.

Factors that affect the accuracy and sensitivity of the method of dynamic I-V characteristics for ion currents of metal/oxide/semiconductor structures with a low (N S ∼ 109–1010 cm−2) concentration of mobile ions in the oxide are analyzed comprehensively. Simultaneous measurements of the dynamic I-V and low-frequency C-V characteristics show that the measurement error is about 10% for concentrations of no less than 109 cm−2.