Strontium barium niobate SrxBa1 – xNb2O6 films, grown by plasma sputtering on layers of indium tin oxide and platinum on silicon and sapphire substrates, are investigated. Such materials are used in pyroelectric electro-optical converters of a new generation. A two orders of magnitude higher sensitivity to temperature change is detected in some of the investigated films compared to crystalline SrxBa1 – xNb2O6, the pyroelectric coefficient of which is γ 6 × 10−4 C/m2 K. The observed phenomenon is explained by the emergence of mobile elements in the “substrate–bottom electrode–ferroelectric–top electrode” system when the top electrode is detached from the ferroelectric. Leakage currents are unevenly distributed across the surface, often concentrated at local points or areas that can be considered one dimensional. It is known that the boundaries of ferroelectric domain walls exhibit abnormally high conductivity. In contrast to a tightly pressed electrode, where charge leakage may occur through it, in this structure, all the charge resulting from the change in spontaneous polarization during heating is transferred to the external circuit. This process occurs because the leakage-current points are local, and in the absence of a pressed electrode, the current flows along the surface.

The surface preparation of topological insulators (TIs) is a critical task in order to realize their efficient applications. A chemical treatment in an anhydrous solution of hydrogen chloride in isopropanol (HCl-iPA) and a subsequent annealing at relatively low temperature in ultrahigh vacuum (UHV) was successfully used for the surface preparation of bulk 3D (0 0 0 1) TIs Bi2Te3, Sb2Te3, Bi2Se3 and an MBE - grown Bi2-xSbxTe3-ySey (BSTS) thin films. The surface treatment showed a significant modification of the initial TI surfaces, which was free from the structural disorder, oxidation and chemical impurities determined by X-ray photoelectron spectroscopy and low-energy electron diffraction. The insulating nontrivial bulk gap and well resolved gapless surface states with a linear dispersion of a massless Dirac cone were observed by angle-resolved photoelectron spectroscopy (ARPES). In the BSTS film, the Fermi level is located within the bulk band gap. The negative magnetoconductance corresponding to weak antilocalization demonstrated the contribution of the surface states of BSTS, that promise to be protected from backscattering. The surface treatment method proposed in this work is highly efficient for both bulk and thin TI films that can be useful for the deposition of an insulators/metals to fabricate transistor and spin valve systems.

Уважаемые коллеги!Благодарим Вас за проявленный интерес к Четвертой российской конференции «Графен: молекула и 2D кристалл» и желание принять участие в её работе.Конференция проходит в научно-образовательном центре города Новосибирска -Академгородке.Мероприятие посвящено актуальным направлениям исследований и разработок в области углеродных и низкоразмерных материалов.Проведение конференции поможет координации усилий ученых в решении современных проблем материаловедения и привлечению молодых исследователей для решения актуальных научных задач.Оргкомитет выражает особую благодарность НГУ, Центру компетенций НТИ «Моделирование и разработка новых функциональных материалов с заданными свойствами», компаниям «Диаэм», «НТ-МДТ Спектрум Инструментс» и корпорации "Графеновая Долина" за финансовую поддержку и журналам Аналитика, Наноиндустрия и РЭНСИТ за информационную поддержку.Искренне надеемся, что пребывание в Новосибирском Академгородке и в стенах Новосибирского государственного университета оставит множество положительных эмоций и

We present the results of GaAs annealing experiments in the conditions near equilibrium, which clarify the reasons of the transition from surface smoothing to roughening at temperatures above 650 °C. The roughening is due to kinetic instabilities arising under deviation of annealing conditions towards growth or sublimation. These instabilities reveal themselves in appearing islands (for sublimation) and pits (for growth) of multilayer heights and depths, respectively. The islands and pits appear due to the motion of atomic steps through surface spots, at which sublimation and growth are suppressed. Pinning of the steps at these spots also lead to step bunching at surfaces with sufficiently small terrace widths. This explanation is consistent with Monte Carlo simulations of atomic processes on the GaAs surface. The similarity and distinctions in surface roughening under sublimation and growth, along with the role of Schwöbel barrier, are discussed. Annealing experiments in the cavities, which are formed by GaAs substrates with well-controlled atomic step densities enabled us to clarify the roughening mechanisms and to improve the efficiency of GaAs thermal smoothing technique by increasing smoothing temperature up to 775 °C.

A prototype of a metal–insulator–semiconductor field-effect transistor based on PbSnTe:In/(111)BaF2 film with an Al2O3 gate dielectric was designed for the first time. With the gate voltage applied in the range – 7.7 V < Ugate < +7.7 V the relative modulation in the drain-source current Ids/Ids attained near five-fold change at T = 4.2 K. When illuminated with rela-tively low (~100 photon/s) fluxes, negative photoconductivity was detected accompanied with a decrease in Ids by ~104 times and a simultaneous decrease in Ids by ~103 times or even more. The estimated detectivity was about 71016 cmHz0.5W-1 at a wavelength  about 25 micron with the accumulation time about 0.5 s. A qualitative model is discussed which assumes the ex-istence of deep traps and a photo-capacitance effect.

In this study, an atomically clean and structurally ordered Bi2Se3 (0001) surface is obtained without molecular beams and vacuum cleaving. It is shown that the chemical treatment of Bi2Se3 (0001) in an anhydrous solution of hydrogen chloride in isopropyl alcohol leads to the removal of native oxides and enrichment of the surface with an elemental selenium layer. Heating in an ultrahigh vacuum at a temperature of 170°C leads to the desorption of the elemental selenium layer from the surface and the formation of a structurally ordered unreconstructed Bi2Se3 (0001) surface with the linear dispersion law.

The surface topology of epitaxial films of lead tin telluride solid solution (including with In additive, Pb1 – xSnxTe:In) has been examined using atomic force microscopy. The films have been grown on BaF2(111) single-crystal substrates and on a CaF2/BaF2 buffer layer covering a Si(111) wafer. It has been shown that the relief statistical parameters depend on film growth conditions and the incorporation mechanism of indium, an excess amount of which has been detected on the surface by ex situ XPS.

BiySb2-yTe3-xSex (BSTS) topological insulator (TI) thin films were grown by physical vapor deposition (PVD) and molecular-beam epitaxy (MBE) and compared by growth parameters, substrate selection, preparation, and resulting film properties. For the MBE-grown BSTS on Si(111)-(7 x 7), preliminary deposition of the Bi2Te3 buffer layer at the Te-rich growth condition was found to improve the film structural properties. Using a BSTS crystal as the main source for deposition allows us to significantly decrease the molecular Te flux. For the PVD growth, optimal conditions (gas flux, source, and substrate temperatures) were found for a morphologically smooth BSTS film on mica. In order to grow the epitaxial BSTS film on a Si/SiO2 substrate, graphene was successfully used as the pre-epitaxial layer. A newly developed chemical preparation method of atomically clean and structurally ordered epi-layer surfaces allowed us to study the electronic structure of the grown TI films without using capping layers. The surface states with Dirac-like dispersion at the Gamma-point in the surface Brillouin zone were detected by angle-resolved photoelectron spectroscopy. Photoemission measurements showed a change in the surface Fermi level position depending on the composition of BSTS films. The magnetoconductivity data demonstrated a strong dependence of the parameters describing a weak antilocalization on the substrate used.

In present work, the effect of Pb1-xSnxTe In In (1 1 1) surface in HCl-isopropanol (HCliPA) solution led to removal of native oxides and surface enrichment by elemental tellurium of several nm thickness. Subsequent anneals in vacuum led to desorption of elemental tellurium and revealing (1x1) surface structure. We present angle resolved photoemission spectroscopy (ARPES) measurements of the surface states on chemically prepared (1 1 1) oriented MBE-grown films of Pb1-xSnxTe, a three-dimensional topological crystalline insulator (TCI). The surface states with Dirac-like dispersion at Gamma in the surface Brillouin zone were detected. The dark current and photocurrent were found in strong dependence on the surface chemical procedure and composition. The relative simplicity of the preparation technique is encouraging, and suggests a clear path for future investigations of TCI states on alternative surface orientations in (Pb,Sn)Te solid solutions and applied aspects of TCI research.

•The chemical treatment of Pb1-xSn xTe (111) films with HCl-iPA solution removed native oxides.•Further annealing in vacuum led to the formation of structurally ordered Pb1-xSn xTe (111)-(1x1) surface.•ARPES demonstrated the surface topological states of a crystalline insulator with Dirac dispersion.•A significant effect of the HCl-iPA treatment on electrophysical properties was demonstrated.

The characteristics of MIS structures based on insulating PbSnTe:In films grown by molecular beam epitaxy (MBE) with compositions near the band inversion are studied. It is shown that a number of their features can be induced by a ferroelectric phase transition with the Curie temperature in the range of 15-20 K. The injection and detection of spin-polarized electrons in PbSnTe:In are studied by using ferromagnetic contacts Co and Co40Fe40B20. A spin-valve effect is discovered by measuring the magnetoresistance in local geometry at a distance of more than 30 mum from ferromagnetic contacts. The presence of a surface spin-polarized state with a linear dispersion law is demonstrated by means of the photoemission with angular and spin resolution.

Бинарные соединения Bi2Te3, Bi2Se3 и Sb2Te3 являются классическими примерами трехмерных (3D) топологических изоляторов (ТИ). Одной из возможных областей практического применения этих материалов является детектирование терагерцового излучения [1]. Однако, халькогениды висмута и сурьмы – это материалы с высокой проводимостью, обусловленной легированием собственными дефектами, что затрудняет исследования поверхностных топологических состояний. Так, в Bi2Te3 и Sb2Te3 избыток металла занимает узлы решетки Te и действует как легирующая примесь p-типа. Поэтому, чтобы осуществить исследования транспортных свойств ТИ, связанные с их топологическими поверхностными состояниями, необходимо уменьшить вклад объемных состояний в проводимость. Одним из вариантов решения данной проблемы является рост твёрдых растворов тройных и четверных соединений. Так в работе [2] было показано, что электрофизические свойства соединения (BixSb1-х)2(SeyTe1-y)3 (BSTS) зависят от содержания компонент.

The characteristics of MIS structures based on insulating PbSnTe:In films with compositions in the vicinity of a band inversion grown by molecular beam epitaxy (MBE) were studied. It has been shown that a number of their features can be caused by a ferroelectric phase transition with a Curie temperature in the range T ≈ 15–20 K.

The characteristics of metal-insulator-semiconductor (MIS) structures based on insulating PbSnTe:In films with compositions in the vicinity of band inversion grown by molecular-beam epitaxy (MBE) are studied. It is shown that a number of features of the films can be due to a ferroelectric phase transition with a Curie temperature in the range of about T ≈ 15–20 K.

The dependence of the photoconductivity sign on the bias voltage, intensity and duration of illumination was studied in PbSnTe:In films in the space charge limited current regime. The role of traps with a complex energy spectrum, including the surface traps, in the observed effects is discussed

The dependence of the photoconductivity sign on the bias voltage, intensity, and duration of illumination is studied for PbSnTe:In films in the space-charge-limited current regime. The role of traps (including surface ones) with a complex energy spectrum in the effects under observation is discussed.

Surface morphology evolution of flat GaAs epitaxial layers grown on mesa structured substrates is studied under annealing in the presence of a saturated Ga-As melt. At high temperatures T 700 degrees C, when the annealing conditions are shifted from the equilibrium towards sublimation, the initially flat surface roughens by unwinding spiral monatomic steps, which are induced by screw dislocations. This process leads to the formation of "inverted pyramid" spiral pits. Along with the spiral pits, the roughening consists in multilayer island formation on terraces, at the surface spots where the sublimation is inhibited. The mechanism of island formation is reproduced in the Monte Carlo simulation. The obtained data allowed us to estimate the relative undersaturation of -0.015 and Ga adatom diffusion length of 15 nm at T = 750 degrees C. Annealing at higher temperature T = 775 degrees C resulted in a peculiar "vortex"-like surface morphology, which consists in deep spiral pits covering the major part of the surface area.

The growth temperature dependences of the capacitance–voltage characteristics and chemical stability of the CaF2/BaF2 buffer layers formed on Si by molecular beam epitaxy have been investigated. Secondary ion mass spectrometry and X-ray photoelectron spectroscopy studies of the CaF2/Si interface suggest that the observed variations can be caused by the enrichment of the Si surface layer with calcium.

The paper shows the results of XPS and RHEED investigation of chemically treated Pb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Te/BaF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (111) films surfaces grown with MBE method. The elemental tellurium enrichment is observed after chemical treatment in HCl-iPA solution on the Pb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Te surface. The thickness of the oxide layer of the initial surface and the thickness of the elemental tellurium layer after treatment in HCl-IPa solution were estimated. Subsequent heating led to native oxides removal and to clean and structurally ordered surface.