ISSN (print): 1063-7834, ISSN (online): 1090-6460 Editor-in-Chief: Publisher: Ioffe Institute Indexed in: RUS White List (level 2), Scopus, Web of Science (SCIE)
Физико-технический институт им. А.Ф.Иоффе РАН
International Conference “Mechanisms and Nonlinear Problems of Nucleation and Growth of Crystals and Thin Films” Dedicated to the Memory of Professor V.V. Slezov, an Outstanding Theoretical Physicist
This issue of Physics of the Solid State publishes the proceedings of the International Conference “Mechanisms and Nonlinear Problems of Nucleation and Growth of Crystals and Thin Films” (MGCTF-2019) dedicated to the memory of Vitalii Valentinovich Slezov, an outstanding theoretical ph-ysicist.
Degenerate Structure of Transformation Twins and Estimation of Dislocation Density in Martensite Crystals
In the dynamic theory of martensitic transformations, the wave mechanism of controlling martensite crystal growth is determined by the superposition of wave beams of quasi-longitudinal (or longitudinal) waves carrying the “tensile–compression” deformation in the orthogonal directions. The wave beam formation is considered to be a result of the formation of excited (vibrational) states. The existence of transformation twins is interpreted as a result of a matched propagation with respect to long-wave (l waves) and short-wave (s waves) shifts. The matching condition is analyzed for the γ–α martensitic transformation in iron-base alloys. It is shown for the first time that the transition to a degenerate twin structure with the allowance for the medium discreteness enables one to estimate the dislocation density in crystals with habit {557}, which agrees with that observed experimentally.
Preparation and Formation Mechanism of Nano-Mg Materials Prepared by Physical Vapor Deposition
The magnesium nanoparticles, magnesium nanowires, as well as magnesium nanoporous materials have been successfully prepared by a physical vapor deposition method. The results show that by using inert gas condensation device the magnesium nanoparticles are prepared at the evaporation temperature of 773 K. The nanoparticle size is about 10–50 nm in diameter with the morphology of chain structure. By using vapor deposition device, the magnesium nanowires and magnesium nanoporous materials are prepared. [11‒20]-oriented magnesium nanowires are obtained at 703 K, with the length of about 1.6 μm and diameter of about 75 nm. The magnesium nanoporous materials are obtained at 723 K, with the substrate perpendicular to vapor direction. The diameter of nanopore is about 280 nm and the porosity is about 10.5%. The formation mechanisms of these nano magnesium are explained based on the classical crystal growth theory.
Modeling of Radiation-Induced Segregation in Fe–Cr–Ni Alloys
In the model of radiation-induced segregation based on the first and second Fick laws and taking into account the inverse Kirkendall effect, concentration profiles of the components of the concentrated Fe‒Cr–Ni alloy and radiation point defects at various temperatures, dislocation densities, and dose gain rates were obtained. Calculation of concentration profiles was carried out from the moment of the beginning of irradiation to reaching the stationary mode. The sensitivity of the concentrations of the components of the alloy near the surface from the input parameters (migration energies of vacancies Cr, Ni, Fe, migration energy of interstitial atoms, etc.) is analyzed.
Metastable Dispersed States Arising upon Three-Component Alloy Decomposition
In this paper, we consider the conditions for inhibiting the growth of precipitates from a metastable supersaturated solid solution and at the evaporation-condensation stage during spinodal decomposition of a three-component alloy. The formation of a “locking” shell around precipitates was shown to be an effective mechanism for inhibiting decomposition, provided that the solubility or diffusion coefficients of the alloy components are reduced in the shell. The thermodynamic and kinetic conditions for the appearance of such shells are formulated. The features of decomposition inhibition mechanisms in specific alloys are discussed.
Structural, Magnetic, and Thermal Properties of the Compound Tb0.8Sm0.2Fe2 with a Laves Phase Structure
A complex study of the structure, phase composition, features of the surface topology, magnetostriction and thermal properties of the compound Tb0.8Sm0.2Fe2 was carried out. Peculiarities of the structure at the micro- and nanolevel were found; information on the magnetic domain structure at room temperature was obtained. X-ray structural studies in a wide temperature range from 90 to 760 K, including the Curie point, are presented. Experimental data on the thermal expansion and magnetostriction in magnetic fields up to 12 kOe were obtained and analyzed. Anomalies on the thermal expansion curve Δl/l(T) and on the magnetostriction dependence λ(T) in the low-temperature region were revealed. The magnetostriction effect in the studied compound was found to be almost constant in a wide temperature range of 100–300 K and in fields up to 3.5 kOe.
The Effect of Additional Severe Plastic Deformation at Elevated Temperatures on the Microstructure and Functional Properties of the Ultrafine-Grained Al–0.4Zr Alloy
The effect of severe plastic torsion deformation (SPTD) at elevated temperatures of 230 and 280°C on the microstructure, mechanical properties, and electrical conductivity of ultrafine-grained (UFG) Al–0.4Zr alloy samples is studied. The initial UFG structure in the material under study is preliminarily appeared in the SPTD process at ambient temperatures. It is shown that simultaneous significant increases in the strength from 140 to 230–280 MPa and in the electrical conductivity from about 47.5% to 52–54% IACS take place as a result of additional deformation of the UFG Al–0.4Zr alloy at elevated temperatures. The results are compared with the effect that annealing at the same temperatures exerts on the microstructure and properties of the UFG Al–0.4Zr alloy. It is established that severe plastic deformation at comparable temperatures leads to a more efficient, compared to annealing, formation of nanoscale precipitates of the Al3Zr secondary phase and, consequently, to a larger decrease in the concentration of Zr in the solid solution, which ensures a significant increase in the electrical conductivity. Based on the obtained parameters of the microstructure, the contributions of various strengthening mechanisms to the general strengthening and electron scattering mechanisms to the electrical resistance are estimated. An comparative analysis of theoretical estimates with experimental results indicates that the strengthening in the UFG structure of the Al–0.4Zr alloy that is caused by additional SPD at elevated temperatures cannot be described by the action of only strengthening mechanisms traditional for UFG materials. Possible reasons for the obtained colossal strengthening are discussed.
Method for Controlling the Polarity of Gallium Nitride Layers in Epitaxial Synthesis of GaN/AlN Heterostructures on Hybrid SiC/Si Substrates
The effect of the inversion of polarity in gallium nitride layers from the N-polar GaN layer to the Ga-polar GaN layer was discovered during the sequential growth of GaN films on hybrid SiC/Si(111) substrates by nitrogen plasma-assisted molecular beam epitaxy and chloride–hydride vapor phase epitaxy. A new method has been developed for the formation of crack-free Ga-polar GaN/AlN heterostructures on hybrid SiC/Si(111) substrates. The method includes two stages of growing gallium nitride layers. At the first stage, the transient N-polar GaN layer is grown on the SiC/Si(111) surface by nitrogen plasma-assisted molecular beam epitaxy. At the second stage, two layers are grown on the obtained N-polar GaN layer by chloride–hydride vapor phase epitaxy, namely, the AlN layer and then the GaN layer, which at this stage grows in the Ga-polar orientation. Etching in a KOH solution affects only the N-polar GaN transition layer and leads to its complete removal. This procedure separates the main Ga-polar GaN layer from the SiC/Si(111) substrate completely. The method enables one to grow crack-free and elastically unstressed thick GaN layers and transfer them to substrates of other materials.
Photoemission Studies of the Electronic Structure of GaN Grown by Plasma Assisted Molecular Beam Epitaxy
The results of experimental studies of the electronic and photoemission properties of the GaN epitaxial layer grown by molecular beam epitaxy with plasma activation of nitrogen on a SiC/Si (111) substrate are presented. The electronic structure of the GaN surface and the ultrathin Li/GaN interface was first studied in situ under ultrahigh vacuum with various Li coatings. The experiments were carried out using photoelectron spectroscopy with synchrotron radiation in the photon energy range of 75–850 eV. Photoemission spectra in the region of the valence band and surface states and photoemission spectra from N 1s, Ga 3d, and Li 2s core levels are studied with various submonolayer Li coatings. It is found that Li adsorption causes significant changes in the general form of the spectra caused by charge transfer between the Li layer and the lower N and Ga layers. It is established that the GaN surface has predominantly the N polarity. The semiconductor nature of the Li/GaN interface is shown.
Growing Bulk Aluminum Nitride and Gallium Nitride Crystals by the Sublimation Sandwich Method
The results of the growth of bulk crystals of aluminum and gallium nitrides on foreign seeds by the sublimation sandwich method are reviewed. The kinetics and mechanism of sublimation and condensation are analyzed depending on the growth conditions, vapor phase composition, crystal orientation, and the distance between the source and the seed. It is experimentally found that during joint annealing of aluminum nitride and silicon carbide, the sublimation rate of aluminum nitride substantially increases due to the formation of a liquid phase on the crystal surface. The inhomogeneous distribution of the liquid phase, localized mainly near structural and morphological defects, leads to the selective nature of surface etching and causes a deterioration in the quality of the growing crystal. A process of growth of bulk AlN crystals with simultaneous seed evaporation was implemented, which yields crystals without cracks and with improved parameters. Bulk crystals of aluminum nitride and gallium nitride up to 2 inches in diameter were grown on SiC seeds.
On Thermomigration Velocity of Liquid Cylindrical Inclusions in a Crystal under Stationary Thermal Conditions
The dependences of the velocity and the cross section shape of the inclusion on the cross sectional area at the various interfacial energy density, degree of its anisotropy, and degree of difficulty of the interfacial processes have been calculated and analyzed on the basis of model ideas on the cross section shape of the liquid cylindrical inclusion migrating in a crystal under the action of a temperature gradient in stationary thermal conditions. The possibility of the nonmonotonic dependence of the velocity of the cylindrical inclusion on the area and thickness of its cross section is shown.
High Resolution Investigation on the NiAu Ohmic Contact to p-AlGaN|GaN Heterostructure
The low-resistance ohmic contact NiAu|p-type AlGaN|GaN was carefully investigated by high resolution electron microscope (HRTEM) and X-ray photoelectron spectroscopy (XPS) after two-step annealing at 550 and 750°C. It is shown that complicate double-direction diffusion and reaction occur in the metal layer and underlying GaN layer. The stacks of Ni|Au|Ni|Au turn into one alloyed layer and an intimate relationship establishes at the NiAu|GaN boundary which should play a primary role in ohmic contact to lower the contact barrier. A great part of Ni is oxidized as dispersive NiO nanoclusters in the metal layer, which might have an effect to hinder Ga atoms migrating upward. So at the intimate interface, the metal layer close to the contact enriched with Ga and Au, and the GaN upper layer metallized by Au and Ni should reduce the lattice mismatch and the contact barrier. Dense vacancies in the upper GaN layer and dislocations connected with the contact boundary also have the effects to improve the current carrier transportation. So the low ohmic contact to p-GaN should be obtained by the combination of these microstructural characteristics.
Dependence of Properties of Variable Gradient Porous Structures of Silicon on the Method of Formation
A series of samples of gradient-porous silicon structures with crystallographic orientations (100) and (111) by deep anode etching was obtained. Dependences of the rate of deep anodic etching and the depth of the porous layer of the samples on the anode current density are shown. The absorption and reflection coefficients of the samples were investigated by optical spectrometry, depending on their crystallographic orientation and the depth of the porous layer. The influence of water solutions on the optical properties of the samples was determined.
Effect of Gamma Irradiation on Conductivity of Cd1 – xFexTe
The effect of γ-irradiation at the dose Dγ = 605.6 kGy on the temperature dependences of conductivity and dielectric permittivity of Cd1 – xFexTe semimagnetic semiconductors were investigated. The character of the ε(T) dependences of the irradiated Cd1 – xFexTe changes: there is a drop in the curves in the temperature range of 300–400 K at measurement frequencies 10 kHz–1 MHz, and ε increases by 20 times. In the σ(T) dependence, at all measurement frequencies a maximum appears at a temperature of 400 K and conductivity increases by 40 times. We assume that the character of the temperature dependences of dielectric permittivity and conductivity corresponds to the ionic conductivity.
Study of Elastic Properties of SiC Films Synthesized on Si Substrates by the Method of Atomic Substitution
The elastic properties of nanoscale silicon carbide film grown on a silicon substrate by the method of atomic substitution were studied. The Young modulus of nanoscale silicon carbide was for the first time measured by nanoindentation method. The structural characteristics of silicon carbide film on silicon were studied by the optical profilometry and spectral ellipsometry; the roughness and thickness of film were m-easured.
Impact of Elastic Stress on Crystal Phase of GaP Nanowires
In most cases, III–V compounds form a crystal structure, which is stable under certain experimental conditions. Meantime crystal phase of III–V nanowires may differ from the stable phase of bulk structures. In this work, we show that the elastic stress could be the sole factor responsible for nanowire growth in the metastable phase. Depending on the experimental conditions of GaP nanowire growth, the elastic stress contribution to nucleation barrier can be greater than the difference in the energy of the formation of the cubic and hexagonal phase, and thus, it causes the growth in metastable wurtzite crystal phase.
Dislocation Reactions in a Semipolar Gallium Nitride Layer Grown on a Vicinal Si(001) Substrate Using Aluminum Nitride and 3C–SiC Buffer Layers
Transmission electron microscopy was used to study the interaction of a + c and a dislocations in a thick (14 μm) semipolar GaN layer grown by hydride vapor phase epitaxy on a 3C-SiC/Si(001) template. It is shown that the propagation of a dislocation half-loop with a Burgers vector b = \(\frac{1}{3}\left\langle {1\bar {2}10} \right\rangle \) during cooling can be blocked due to its reaction with a threading dislocation with a Burgers vector b = \(\frac{1}{3}\left\langle {\bar {1}2\bar {1}3} \right\rangle \) with the formation of a dislocation segment with a Burgers vector b = 〈0001〉. The gain in energy of the system as a result of such reaction is theoretically estimated. Within the approximation of dislocation linear tension, this gain is ~7.6 eV/Å, which gives ~45.6 keV for new dislocation segment with a length of ~600 nm. The contribution of the energy of the dislocation core is estimated as ~19.1 keV.
Growth Anisotropy and Crystal Structure of Linear Conjugated Oligomers
The results of a study of the influence of the crystal structure features of organic linear conjugated oligomers on the trends of their crystallization from solutions are given.
Formation of AgInS2/ZnS Colloidal Nanocrystals and Their Photoluminescence Properties
Colloidal nanocrystals of AgInS2 were synthesized in aqueous solution using L-glutathione as a ligand. Wider bandgap semiconductor ZnS shell was deposited on the nanocrystal cores in order to enhance luminescence properties and stability. Thus prepared nanocrystals generally had an asymmetric multiple band emission spectrum. Variation of cation ratio [Ag+] to [In3+] led to a variation in the spectrum so that raising indium content caused an intensity increase of longer wavelength emission band. Photoluminescence and absorption spectroscopies, transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy were used for the sample characterization.
Forming the GaN Nanocrystals on the Graphene-Like g-AlN and g-Si3N3 Surface
The formation of GaN nanocrystals on the graphene-like AlN (g-AlN) modification and graphene-like (g-Si3N3) silicon nitride by ammonia molecular beam epitaxy has been investigated. It has been found that the GaN growth on the g-Si3N3 surface leads to the formation of misoriented nanocrystals. During the GaN growth on the g-AlN surface, the epitaxial growth of similarly oriented GaN quantum dots of the graphite-like modification has been observed. The lattice parameters and energy structure of two graphite-like GaN modifications with the alternating AB (graphite structure) and AA+ (hexagonal boron nitride structure) layers have been calculated.
GaN Selective Epitaxy in Sub-Micron Windows with Different Depths Formed by Ion Beam Nanolithography
A significant difference in the growth mechanism of spatially closed structures of gallium nitride during selective growth in submicron windows with and without penetration into the GaN sublayer was demonstrated. The mechanisms of generation and development of dislocations, their role in the formation of self-organizing coaxial structures were modeled.
Mechanism of Diffusion of Carbon and Silicon Monooxides in a Cubic Silicon Carbide Crystal
The main processes that occur during diffusion of gaseous carbon CO and silicon SiO monoxides through a layer of a single-crystal silicon carbide SiC of the cubic polytype are described. This problem arises as a single-crystal SiC layer is grown by the method of matched atomic substitution due to the chemical reaction of a crystalline silicon substrate with CO gas. The reaction products are an epitaxial SiC layer and SiO gas. CO and SiO molecules are shown to decompose in the SiC crystal into individual atoms. The oxygen atoms diffuse over interstitial sites only in the [110] direction with the activation energy 2.6 eV. The Si and C atoms displace by the vacancy mechanism in the corresponding SiC sublattices with activation energies 3.6 and 3.9 eV, respectively, and only in the [110] direction.
A New Method of Growing AlN, GaN, and AlGaN Bulk Crystals Using Hybrid SiC/Si Substrates
The main principles of a new method of growing bulk single-crystal AlN, AlGaN, and GaN films with thickness from 100 μm and more on silicon substrates with a buffer silicon carbide layer with its subsequent detachment from Si substrates are presented. The main substance of this method is a combination of the method of chloride-hydride epitaxy that determines high growth rates of III nitride layers and the use a Si substrate with a buffer layer of nanoscale SiC film grown by the atomic substitution method as the growth substrate. The Si substrate with a SiC layer grown by the atomic substitution method has a number of structural, physical, and chemical features as compared to SiC layers grown on Si by the standard methods. It is shown that it is precisely this feature that enables the growth on their surfaces of thick crack-free AlN, AlGaN, and GaN layers with subsequent and quite simple their detachment from the substrate. The single-crystal crack-free AlN layers with thickness to 300 μm, AlGaN layers with thickness to 400 μm, GaN layers with thickness to 200 μm, and GaN films of the semipolar (\(11\bar {2}4\)) orientations with thickness to 30 μm have been grown.
Studies of Thermoelectric Properties of Superlattices Based on Manganese Silicide and Germanium
In this paper, we present the results of the study of thermoelectric materials formed by pulsed laser deposition on sapphire substrates and representing thin MnSi1.74 films with intermediate germanium layers. A sharp decrease in the thermal conductivity coefficient of superlattices based on manganese silicides and germanium in comparison with single layers of manganese silicide with an equivalent thickness is shown. This allows significantly increasing the thermoelectric figure of merit. The obtained values of the coefficient of thermoelectric figure of merit are comparable with the known literature values that are typical for similar structures.
Effect of Solid-State Epitaxial Recrystallization on Defect Density in Ultrathin Silicon-on-Sapphire Layers
The main technological problem in the manufacture of electronics on silicon-on-sapphire (SOS) structures is the high density of defects in silicon-on-sapphire layers. The modern method of obtaining ultrathin SOS structures using solid-phase epitaxial recrystallization and pyrogenic thinning can significantly reduce the defectiveness in these layers. Nevertheless, the effect of the defectiveness of submicron SOS layers on the structural perfection of ultrathin layers remains unclear. In this work, ultrathin (100 nm) SOS structures have been obtained on submicron (300 nm) SOS structures with different structural quality. The crystallinity of 300 nm layers before the recrystallization process and ultrathin layers has been determined using X-ray diffraction and transmission electron microscopy. It has been found that the lowest values of the full width at half maximum (FWHM) of 0.19°–0.20° have been observed for an ultrathin SOS structure obtained based on the most structurally perfect SOS layers of 300 nm. It has been shown that a more perfect near-surface layer of the basic SOS structure of 300 nm and a double implantation regime make it possible to reduce the density of structural defects in the ultrathin Si layer by an order of magnitude to achieve ~1 × 104 cm–1.
Features of Forming the Electronic Structure at Synthesis of Ti2AlC, Ti2AlN, Ti2SiC, and Ti2SiN Compounds
The electronic structure and the total energy of Ti2AlC, Ti2AlN, Ti2SiC, and Ti2SiN compounds have been explored by the methods of the density functional theory and pseudopotentials. Density curves of electronic states for the crystal systems and for the systems differing in the degree of order have been plotted. It is shown that the qualitative similarity of electronic structure with the electronic structure of corresponding crystalline compounds is observed even in completely disordered systems. This similarity increases with the ordering. The total energy of the studied systems grows with the increase in disorder in approximately the same way for all the systems investigated, except Ti2SiC. In the latter case, the system is much more sensitive to the degree of disorder, most likely due to the greater role of the covalent component of the interatomic bonds.
Quartz Glass Obtained from Ramenskii Sand on Dinur Plasma Torches: Features of Crystallization on Polished Surface
Quartz sand produced by the Ramenskii mining and processing plant has been used as a raw material for the melting of quartz glass at OJSC DINUR. The performance of reactors (plasma torches) and the quality of the ingots obtained depends significantly on the quality of sand (content of impurity components, such as aluminum and iron oxides). It is established that the product of melting quartz sand from feedstock with a high content of impurities is characterized by reduced resistance to crystallization.
Formation of Thin Films and Fine Single Crystals from Gas Phase on Ionic Crystal Surfaces under Heating and an Electric Field
The behavior of surfaces of ionic crystals of various crystallographic orientations and surfaces of cleavage under heating in an electric field was studied. On the surfaces, viscous liquid drops or fine single crystals were observed. The charge appearing on crystal surfaces resulted from depletion or saturation of the near-surface layers with positive ions that led to a stoichiometric change in the crystal substance. Single crystals were formed from ionic gas, which appeared due to the sublimation of matrix ions from cleaved surface.
Effective Charge in LiNbO3 Films Fabricated by Radio-Frequency Magnetron Sputtering Method
Amorphous Li–Nb–O films were deposited onto Si substrates by radio-frequency magnetron sputtering method. The fabricated heterostructures demonstrated the presence of effective oxide charge Qeff having both negative and positive components. Thermal annealing (TA) of as-grown heterostructures leads to the crystallization of a Li–Nb–O system with the formation of LiNbO3 films. The Qeff changes with TA, reaching a minimum at the annealing temperature of about 470°C, corresponding to the entire film’s crystallization.
Glycine–Nitrate Synthesis of Solid Solutions of Barium–Strontium Metatitanate
The influence of composition of glycine–nitrate systems on the completeness of the formation of solid solutions of barium–strontium metatitanate was studied. It was shown that the decomposition of all studied glycine–nitrate compositions starts at 180°C; however, its character depends on the glycine content and composition’s pH value. The volume combustion mode obtained by exceeding the content of the reducing agent over the oxidant in composition provides the optimum conditions for the formation of single-phase products. Such compositions allow obtaining nanoscale powders of Ba1 – xSrxTiO3 solid solutions (0 ≤ x ≤ 0.4) by calcination at 550°C and introducing them into the composites based on porous magnetic glass, avoiding the interaction between the forming ferroelectric phase and glass matrix.
Effect of External Factors on Magnetism of Fluctuating Low-Dimensional Electron and Spin Correlations in Frustrated Manganites La1 – ySmyMnO3 + δ (y = 0.85, 1.0)
The effect of external factors on the temperature dependences of the magnetization of frustrated manganites La1 – ySmyMnO3 + δ (δ ~ 0.1, y = 0.85, 1.0) is studied. Two sharp peaks M(T) of different intensities detected in both samples at close temperatures Т1 and Т2 slightly higher than the critical temperature Tc of the coherent superconducting transition corresponds to the Lindhard divergence χL(qnest) of the temperature dependence of the paramagnetic susceptibility of stripelike 1D electron/spin correlations modulated with wave vectors qnest1 = 2kF1 and qnest2 = 2kF2. The formation and evolution of magnetization features with increasing field are explained by the appearance of spatial modulation of electrical and magnetic properties in ab planes in the case of total nesting of electron–hole areas of the Fermi surface. This appears as two fragments of two fluctuating quasi-one-dimensional charge/spin density waves with wave vector q1 || a and q2 || b directions incommensurate with the lattice. It is assumed that the strong dependence of the magnetization of fluctuating 1D charge/spin density wave correlations on external influences is caused by the immediate vicinity of sample properties to the quantum critical point.
Magnetic Properties of Bi1 – xCaxFeO3 – δ Nanocrystals
The nanocrystalline magnetically ordered materials based on bismuth orthoferrite doped with calcium are synthesized via glycine-nitrate combustion. X-ray diffractometry, helium pycnometry, BET, scanning electron microscopy, and elemental energy dispersive microanalysis data showed that they are isostructural to bismuth orthoferrite and have an average crystallite size of about 40 nm to form particles with an average size of 0.3 μm. Mössbauer spectroscopy and magnetometry data showed that their magnetic properties and those of pure bismuth orthoferrite are significantly differed. We found that the samples contain nanocrystals with other magnetic parameters and a low-dispersed phase fractions with a magnetic order.
Surface Morphology, Microstructure, and Piezoelectric Response of Perovskite Islands in Lead Zirconate Titanate Thin Films
Features of the microstructure and piezoelectric response of perovskite islands in a pyrochlore phase matrix in lead zirconate titanate thin films prepeared by the radio-frequency magnetron sputtering method are investigated. The radial inhomogeneity of the surface morphology and piezoresponse of the islands are revealed. The role of two-dimensional mechanical stresses acting on the thin film from the silicon substrate side is discussed.
Proton-Conducting Composite Materials Based on the Cs6H(HSO4)3(H2PO4)4 Compound
xCs6H(HSO4)3(H2PO4)4 + (1 – x)AlPO4 — composition proton conducting materials were obtained in the mass range (x = 0.9–0.7). Their physicochemical and transport properties have been studied by X-ray phase analysis, impedance spectroscopy, and electron scanning microscopy.
Influence of Orientation of a Silicon Substrate with a Buffer Silicon Carbide Layer on Dielectric and Polar Properties of Aluminum Nitride Films
Dielectric and polar properties of aluminum nitride (AlN) thin films epitaxially grown on differently oriented silicon substrates with the p-type conduction and a buffer silicon carbide (SiC) layer and on vicinal planes are investigated. The results of studies of the polar properties by two independent methods—the dynamic pyroelectric effect and the piezoresponse force microscopy—show that the SiC buffer layer application considerably improves polar properties of the aluminum nitride thin layer.
Flexocaloric Effect in Thin Plates of Barium Titanate and Strontium Titanate
Based on the Love–Kirchhoff approach, the flexoelectric effect in a thin plate of a ferroelectric with cubic symmetry is studied. The electric and elastic fields in the ferroelectric are described within the framework of the Landau–Ginzburg thermodynamic potential. The influence of inhomogeneity of the polarization distribution in the plate is taken into account. The obtained values for the plate bending caused by applying the electric field make it possible to calculate the dependence of changes in entropy on temperature in plates of barium titanate and strontium titanate (the flexocaloric effect).
Growth of Faceted Pores in a Crystal by the Burton–Cabrera–Frank Mechanism
The growth of a faceted pore in a crystal by the Burton–Cabrera–Frank mechanism under action of a mechanical tensile load is considered. The growth is determined by the diffusion of vacancies existing in a crystal to the terraces and steps on the pore surface. The expressions for the speed of movement of a single step and a group of parallel steps, and also for the dependence of the normal growth rate of a pore by the spiral mechanism under action of applied load have been found. It is shown that, in a certain range of low tensile loads, the rate has a quadratic dependence on the load, while the dependence is linear at high loads. The influence of impurities on the crystal fracture by the pore growth mechanism under consideration is discussed.
Thermal Conductivity of Single-Crystal ZrO2-Based Solid Solutions Co-Alloyed with Scandium, Cerium, and Yttrium Oxides
The thermal conductivity of single-crystal solid solutions (ZrO2)1 – x – y – z(Sc2O3)x(CeO2)y(Y2O3)z (x = 0.08–0.10; y = 0.005–0.01; z = 0–0.005) was measured in the temperature range 50–300 K. Phase composition and defective structure of crystals were studied.
Growth and Study of Scintillation Properties of BaBrI Crystals Activated by Samarium Ions
BaBrI crystals activated by Sm2+ ions were synthesized by the Bridgman method. The Sm content in the samples was analyzed by the method of mass spectrometry with inductively coupled plasma. The results of the study of the optical and scintillation characteristics of the synthetic crystals, such as photoluminescence, X-ray luminescence, and absorption spectra, are reported. The light yield of the luminescence of the studied samples was estimated.
Effect of Uncontrollable Impurities on the Absorption Spectrum of a NaGd(WO4)2 Laser Crystal
Three NaGd(WO4)2 single crystals were grown by the Czochralski method using charges of different chemical purity. The impurity compositions of the grown crystals were analyzed by inductively coupled plasma mass spectrometry. The optical absorption spectra of the crystals were measured, and the effect of uncontrollable impurities on their optical properties and color was analyzed. The green color encountered in NaGd(WO4)2 crystals in some cases was shown to be due to the uncontrollable impurities of d elements, among which the chromium impurity had the most significant effect.
Study of Phase Transformations in (Cs,NH4)4(HSO4)3(H2PO4) Crystals
Phase transitions in crystals of (Cs,NH4)4(HSO4)3(H2PO4) solid solutions have been investigated by synchronous thermal analysis and polarization microscopy at different temperatures. The temperatures of structural modifications are established; it is shown that the replacement of Cs cations with NH4 in Cs4(HSO4)3(H2PO4) crystals reduces the temperatures of phase transformations.
Some Properties of NiCl2 · 6H2O Single Crystals
A single crystal of nickel chloride hexahydrate has been grown by isothermal evaporation of a saturated aqueous solution. The transmission-spectrum parameters and thermal stability of the sample are investigated.
Molecular Dynamics Simulations of Ti Crystallization with Solid–Liquid Configuration Method
The computation models were created with the solid-liquid configuration method. The molecular dynamics simulations were performed to exhibit the crystallization process of liquid pure Ti to hexagonal close packed (HCP) and face-centered cubic (FCC) structure crystals. The results showed that both HCP and FCC crystallizations start from the solid–liquid interfaces and develop toward the middle. The system energy sharply falls at the beginning of crystallization, then is reduced slowly, and finally has a sudden down jump at the end of crystallization. The first peak of RDF is increased significantly with time and some new secondary peaks occur, which is consistent with configuration evolution. The HCP crystal has a longer crystallization process but lower stable energy than the FCC crystal.
Nucleation and Growth of New-Phase Nuclei in Heterogeneous Reactions
Expressions for the nucleation and growth rates for condensed particles in a heterogeneous reaction of a definite kind have been derived, which allows the kinetics of the formation of the condensed phase in some complex systems to be described. Methods of the classical nucleation theory and an assumption about the reaction development mechanism were used.
Modeling of Nucleation in Binary Alloys on the Basis of the Free-Energy Density Functional
An approach based on the method of the free-energy density functional for calculating the nucleation rate of the second-phase precipitates has been developed. The nucleation rate, as well as the characteristics of the critical nucleate, are calculated directly from the modeling results of evolution of the concentration field obtained by solving the deterministic or stochastic Kahn–Hilliard equation.
Phenomenological Models of Nucleation and Growth of Metal on a Semiconductor
Four modes of metal growth on a semiconductor substrate have been detected and distinguished on the basis of experimental data obtained under similar conditions using hot wall epitaxy. These modes are achieved at certain ratios between translational kinetic energy of vapor deposited onto substrate and its temperature. The mechanism of adaptation to the substrate of nanophase wetting coating of metal is proposed when the mode of pure metal growth is implemented, as is the structural model of this coating.
Determination of the Crystallization Temperature of Mullite by Luminescence Spectra of Europium and Chromium Ions
The luminescence spectra of Cr3+ and Eu3+ ions embedded in mullite ceramic samples are studied. The samples were annealed at temperatures from 600 to 1200°C. From the temperature of 800°C, the spectra demonstrated the presence of a newly-formed crystal phase. The appearing of the crystalline phase is revealed by significant changes in some parameters of the luminescence spectrum. At temperatures from 920 to 1200°C, the crystalline form manifested itself as a stable mullite phase.
Growth of New Linear Phenylene-Oxazole Oligomers with a Central Benzothiadiazole Fragment from Solutions of Crystals
For the first time, the results on the solubility and growth of new oligomers with a single conjugated core from solutions of organic crystals are reported. The new oligomers consist of benzothiadiazole, phenylene, and oxazole units and have various terminal substituents. Using DSC and TGA methods, melting parameters are found and thermal stability upon heating is studied.
On the Probability-Free Mechanism of Macroscopic Irreversibility and Microscopic Foundation of Thermodynamics
It is shown that retardation of the interactions between particles leads to the nonexistence of potential energy and the Hamiltonian of the particle system. This leads to the impossibility of calculating the thermodynamic functions of the system by the methods of statistical mechanics. The dynamics of a system of particles with delayed interactions is described by a system of functional differential equations. The qualitative properties of the solutions of this system of equations are investigated. The solutions are irreversible with respect to time reversal. The number of degrees of freedom of even a finite system with retarded interactions is infinite.
The Origin of Phase Transition and the Usual Evolutions of the Unit-Cell Constants of the NASICON Structures of the Solid Solution LiTi2 – xGex(PO4)3
Ge-doped LiTi2(PO4)3 has been synthesized by a conventional solid-state reaction. Compounds LiM\(_{2}^{{{\text{IV}}}}\)(PO4)3 with LTP-type structure present a different behaviour depending on nature of M(IV). For M(IV) = Ti and Ge, the structure shows the space group R3c, whereas for M(IV) = Ge the space group is R3. Differences in behaviour of LiTi2(PO4)3–LiGe2(PO4)3 solid solutions are discussed in relation to the composition. Their structures LiTi2 – xGex(PO4)3 (0 ≤ x < 2) were determined from X-ray powder diffraction method (XRD) using Rietveld analysis. A sharp change in the lattice parameter a is observed between the compositions with x = 1. The lattice parameter c increases as the Ge content increases in the whole range of composition. The space group R3c becomes R3 for the composition with x > 1. The SEM micrographs of the samples show relative porous microstructures due to the effect of the substitution.
A Thermodynamic Model of Nucleation of p-Terphenyl Crystals with Surface Energy Anisotropy at the Liquid–Air Interface
An analysis of the variation of Gibbs free energy ΔG upon the formation of a plane nucleus of the p-terphenyl crystal at the liquid–air interface is presented, in which the anisotropy of the surface energy of faces are considered. The values of the surface energy of faces of the p-terphenyl crystal are calculated using the OPLS atomic force field method based on structural data. Experimental data on the growth of crystals from solutions and their surface properties are used in the analysis of the model.
Synthesis of Quasicrysalline Powders and Coatings by Vacuum Arc Plasma Evaporation
Quasicrystalline coatings of the Al–Cu–Fe system were obtained by sputtering the cathode using a pulsed high-current low-pressure arc discharge followed by deposition on a hot (600°C) and cooled substrate (25°C). The surface morphology, chemical and phase composition of evaporation products in the powder form and the resulting coatings were studied. Powders and coatings were also annealed and the phase composition change was studied. It was found that during the evaporation process a significant change in chemical composition occurs in the form of loss of Al from the surface of particles and coating, that leads to a decrease in the content of the ψ-phase. However, subsequent annealing and spraying onto a hot substrate leads to an increase in the ψ-phase, as well as the density and hardness of the coatings.
Aromatic-Like Carbon Nanostructures Created on the Vicinal SiC Surfaces
Electronic structure of the ultrathin Cs, Ba/SiC(111)-4°, 8° interfaces have been studied in situ in an ultrahigh vacuum using synchrotron-based photoelectron spectroscopy. Change in the C 1s and Si 2p core level spectra was studied upon the adsorption of Cs or Ba within the submonolayer coverage range. The formation of a new, previously unknown carbon nanostructure was revealed under adsorption of Cs or Ba atoms. Data show that the nanostructure is formed exclusively on SiC vicinal surfaces in the presence of stabilizing adsorbed metal atoms, such as Cs or Ba atoms. It is established that the carbon nanostructure consists of carbon rings, in which chemical bonds are similar in nature to the bonds inherent in aromatic compounds.
Effect of Elastic Stresses on the Formation of Axial Heterojunctions in Ternary AIIIBV Nanowires
The effect of elastic stresses on the formation of axial heterojunctions in ternary AIIIBV nanowires has been studied theoretically. The composition profile of the axial InAs/GaAs heterojunction in self-catalytic GaxIn1-xAs nanowires have been obtained. The InAs/GaAs heterojunction width is shown to be several dozen of monolayers and it increases with an increase in the nanowire radius due to elastic stresses. The el-astic stress relaxation on the lateral surfaces of the nanowires at typical growth temperature (about 450°C) and a nanowire radius higher than 5 nm does not lead to the formation of an miscibility gap in the GaxIn1 ‒ xAs system.
C–C20 Carbyne–Carbinofullerene Chains
The results of computer simulation of a new one-dimensional carbon structure representing chains composed of C20 carbinofullerene fragments linked with carbon atoms are given. The bond energy values are determined. Their thermal stability is studied by the method of molecular dynamics. The tensile strength of these chains is also studied and compared to the tensile strength of C20 carbinofullerene chains without intermediate carbon atoms. It is shown that the fusion of neighboring carbinofullerene moieties is a preferred channel for thermal decomposition and the separation of terminal carbinofullerene moieties from the chain is a preferable channel for deformational decay. The ultimate strains of the chains and the temperature dependences of their lifetime until the time of decay are determined. The values of activation energies and frequency factors of the Arrhenius law are determined for the decay process.
Layer Crystallization in PZT/LNO/Si Heterostructures
A Pb(Zr0.52Ti0.48)O3–LaNiO3–Si composition and LaNiO3 thin films are synthesized using chemical solution deposition and studied by transmission electron microscopy. The polycrystalline, porous structure of LaNiO3 is found to misalign the columnar structure of lead zirconate titanate. The effect that thermal treatment has on the structure and phase composition of lanthanum nickelate is addressed. The morphological features of LaNiO3 film structure such as its layered character, porosity, and misalignment are observed in samples subjected to annealing at a temperature of 550°C and are more pronounced upon raising the temperature to 800°C.
Impurity Effects on Nucleation and Growth of SiC Clusters and Layers on Si(100) and Si(111)
A kinetic Monte Carlo model of silicon carbide growth on silicon surface is proposed. Based on this model, the growth of silicon carbide clusters on silicon in the presence of a pre-deposited impurity of various types: attractive and repulsive, is studied. The density of silicon carbide clusters on silicon is calculated. Calculations of the dependencies of the silicon carbide clusters density on the impurity mobility are carried out. The process of redistribution of the species in the multi-component C|Ge|Si structure during annealing is studied in the framework of the kinetic approach. Concentration profiles of the structure components are determined.
Low-Temperature Synthesis of α-SiC Nanocrystals
Thick SiCx films have been deposited on a c-Si surface by radiofrequency (rf) magnetron sputtering (150 W, 13.56 MHz, Ar flow 2.4 L/h, 0.4 Pa) of graphite and silicon targets. The X-ray diffraction study shows that fast annealing of the SiCx film deposited on the c-Si surface for 3 h leads to the low-temperature (970°C) formation of hexagonal structural phases α-SiC (6H-SiC and other) along with the cubic modification of silicon carbide β-SiC. The IR spectroscopy has shown the formation of SiC nanocrystal nuclei due to the energy action of the rf plasma ions on the upper layer of the SiC film during its growth. The data of X-ray reflectometry demonstrate a high density of the films up to 3.59 g/cm2 as a result of formation of dense C and SiC clusters in the layers under action of the rf plasma.
Ion-Beam and X-Ray Methods of Elemental Diagnostics of Thin Film Coatings
We show how the combined use of the methods of Rutherford backscattering of ions and X-ray fluorescence analysis under conditions of total external reflection of the flow of exciting hard X-ray radiation and registration of the X-ray radiation output during ion excitation allows to effectively diagnose the elemental composition of thin-film coatings and films of dry residues of liquids. These methods and the features of their experimental application are briefly described. Examples of the complex methodological analysis of real objects are given. The possibility of increasing the efficiency of the methods of X-ray fluorescence analysis of materials due to the inclusion in the X-ray optical schemes of experimental measurements of flat X-ray waveguide resonators is indicated.
Nanosized Potential Fluctuations in SiOx Synthesized by Plasma-Enhanced Chemical Vapor Deposition
This work was devoted to studying the atomic structure and electron spectrum of a-SiOx : H films created on silicon and glass substrates by means of plasma-enhanced chemical vapor deposition (PECVD). Depending on the conditions of oxygen supply into the reactor, the stoichiometric parameter x of the films was varied from 0.57 to 2. The structure of the films and the specific features of their electron structure were characterized depending on the parameter x with a complex of structural and optical methods and ab initio quantum-chemical simulation for the model SiOx structure. The studied SiOx : H films were established to consist predominantly of silicon suboxides SiOy, SiO2 clusters, and amorphous silicon. Based on the spatial fluctuations of their chemical composition, the model of bandgap width and potential fluctuations was proposed for SiOx electrons and holes. The obtained data would provide the charge transport in a-SiOx : H films with more precise modeling important for the creation of nonvolatile random-access memory (RAM) elements and memristors on their basis.
Relationship of Mg2Si Phase-Content and Thermal Expansion Properties of Mg–Si and Mg–Si–Ca Alloys
The thermal expansion properties of Mg–xSi (x = 1, 1.38, 2, 3, and 4 wt %) binary alloys and Mg–4Si–yCa (y = 0.2, 0.4, 0.6, 0.8, and 1.0 wt %) alloys over a temperature range of 25–300°C were systematically studied. The results show that the Mg–Si binary alloys consist of α-Mg and Mg2Si phases. The volume fraction of Mg2Si phase increases with the increase of Si content in Mg–Si alloys, from 30.72 to 46.50% when Si content increases from 1 to 4 wt % Si. The coefficient of thermal expansion (CTE) of Mg–xSi binary alloys decreases with the increase of Mg2Si volume fraction. The addition of Ca element to Mg–4Si alloys has an obvious modification effect on the Mg2Si phase. When the Ca content increases constantly, the CTE of the Mg–4Si–Ca alloys increases at first, then it continues to decline. The mechanism is mainly related to the formation of the CaMgSi phase.