Production of high-quality manganite-based films on an improved VUP-5M magnetron device

The design of an additional thermal and electric shield intended to improve the quality (crystal lattice, thickness uniformity) of deposited films is described. This shield makes it possible to use a more powerful heat source to heat a substrate and to optimize epitaxial film growth. Simultaneously, the shield plays the role of an additional anode, which changes the plasma dynamics in the working space and homogenizes the radial distribution of the neutral particle flux density from a target to a substrate.     

Role of the electronic subsystem in formation of the composition of binary compounds

We consider theoretically the composition of A₂B₆ compounds in the case of evaporation into a vacuum with the participation of the free electrons taken into account. A system of kinetic equations is derived for defect atoms and vacancies on the surface of the crystal and inside the volume. It is shown that the steady-state values of these components are controlled by the electronic subsystem and by the rate of evaporation (sublimation) of the crystal.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 1, pp. 78–81, January–February, 1990.     

Diophantine properties of IETs and general systems: quantitative proximality and connectivity

Three properties of dynamical systems (recurrence, connectivity and proximality) are quantified by introducing and studying the gauges (measurable functions) corresponding to each of these properties. The properties of the proximality gauge are related to the results in the active field of shrinking targets. The emphasis in the present paper is on the IETs (interval exchange transformations) $( \mathcal {I},T)$ , $\mathcal {I}=[0,1)$ . In particular, we prove that if an IET T is ergodic (relative to the Lebesgue measure λ), then the equality A1 $$ \liminf_{n\to\infty} \, n\, \bigl|T^n(x)-y \bigr|=0 $$ holds for λ×λ-a.a. $(x,y)\in \mathcal {I}^{2}$ . The ergodicity assumption is essential: the result does not extend to all minimal IETs. Also, the factor? n? in (A1) is optimal (e.g., it cannot be replaced by n?ln(ln(lnn))). On the other hand, for Lebesgue almost all 3-IETs $( \mathcal {I},T)$ we prove that for all ?>0 A2 $$ \liminf_{n\to\infty} \, n^ \epsilon \bigl |T^n(x)-T^n(y)\bigr| = \infty,\quad\text{for Lebesgue a.a.} \ (x,y)\in \mathcal {I}^2. $$ This should be contrasted with the equality lim?inf _n→∞?|T ⁿ (x)?T ⁿ (y)|=0, for a.a. $(x,y)\in \mathcal {I}^{2}$ , which holds since $( \mathcal {I}^{2}, T\times T)$ is ergodic (because generic 3-IETs $( \mathcal {I},T)$ are weakly mixing). We introduce the notion of τ-entropy of an IET which is related to obtaining estimates of type (A2). We also prove that no 3-IET is strongly topologically mixing.     

Regular step systems on clean Si(<Emphasis Type="Italic">hhm</Emphasis>)7 × 7 surfaces

The preparation conditions and atomic structure of regular step systems on clean Si(hhm) surfaces are studied. Regular single- and triple-step structures with different periodicities have been fabricated in ultrahigh vacuum using various heat treatment procedures. The atomically resolved scanning tunneling microscopy data demonstrate several stable triple-step configurations on vicinal Si(hhm) surfaces.     

Visualization of electron orbitals in scanning tunneling microscopy

Scanning tunneling microscopy (STM) is one of the main techniques for direct visualization of the surface electronic structure and chemical analysis of multi-component surfaces at the atomic scale. This review is focused on the role of the tip orbital structure and tip-surface interaction in STM imaging with picometer spatial resolution. Fabrication of STM probes with well-defined structure and selective visualization of individual electron orbitals in the STM experiments with controlled tunneling gap and probe structure are demonstrated.     

The Distribution of Gaps for Saddle Connection Directions

Motivated by the study of billiards in polygons, we prove fine results for the distribution of gaps of directions of saddle connections on translation surfaces. As an application we prove that for almost every holomorphic differential ?? on a Riemann surface of genus g ?? 2 the smallest gap between saddle connection directions of length at most a fixed length decays faster than quadratically in the length. We also characterize the exceptional set: the decay rate is not faster than quadratic if and only if ?? is a lattice surface.     

Copper electrodeposition into ion-exchange materials

Electrodeposition of copper into spherical granules of ion-exchange materials KU-23 and KU-2 out of acid sulfate solutions is studied by a method of cyclic voltammetry. It is discovered that the discharge of copper ions in an ion-exchange matrix is characterized by a cathodic overvoltage that is higher than the overvoltage of the same process on a graphite substrate by 0.08 V, which is most probably connected with a limited mobility of ions localized at fixed groups [RSO ₃ ^? ]. The cyclic voltammogram exhibits an additional cathodic peak in the potential region corresponding to the reduction of single-charged copper ions that form as a result of their accumulation inside pores of the ion-exchange matrix during anodic dissolution of metal deposited previously. It is fixed microscopically that the process of deposition begins at the graphite substrate/ion-exchanger interface and passes into bulk upon the formation of an electron-conducting layer saturated with copper. Preliminary saturation of the ion-exchanger by copper deposited chemically facilitates uniform electrodeposition of copper over the entire volume of pores of the ion-exchange matrix.     

Phase state diagrams of the poly(dimethylsiloxane)—poly(diethylsiloxane) system

Phase equilibria in the poly(dimethylsiloxane)(PDMS)—polydiethylsiloxane (PDES) system in the amorphous and liquid-crystal states were studied by optical interferometry. The findings obtained were compared with the data of calorimetric measurements. The experiments were carried out in a wide range of molecular weights and temperatures, and the phase diagrams were constructed. Thermodynamic analysis of the experimental data was performed in the framework of the Flory—Haggins theory for polymeric solutions. The analytical expressions for calculation of the pair interaction parameter using the binodal and liquidus curves were obtained. The pair interaction parameters of polymers and their dependences on the temperature and molecular weight were determined. The pair interaction parameter was shown to decrease with increasing the molecular weight of the oligomer component, approaching asymptotically a limiting value, which characterizes the interaction of the high molecular-weight PDMS and PDES. It was shown that the phase equilibria in the PDMS—PDES systems can be predicted quantitatively and qualitatively.     

Rheological properties of poly(dimethylsiloxane)-poly(diethylsiloxane) blends

The rheological behavior of poly(dimethylsiloxane)-poly(diethylsiloxane) blends in the range 20 to 100°C, including the region of existence of poly(diethylsiloxane) in mesomorphic and amorphous states has been studied by capillary viscometry. The flow of these blends within the studied shear stress interval between 10³ and 10⁵ Pa obeys a power law. If poly(diethylsiloxane) is introduced in the mesomorphic state and serves as a matrix, the blends behave as viscoplastic bodies and feature the yield stress. The flow of these blends is accompanied by an appreciable orientation of the poly(diethylsiloxane) phase. Blends in which the mesomorphic poly(diethylsiloxane) is a disperse phase flow as abnormally viscous fluids in which poly(diethylsiloxane) plays the role of a structuring filler. The isotropization of poly(diethylsiloxane) leads to a reduction in its viscosity and, accordingly, in the viscosity of the blend. The logarithm of the effective viscosity of such blends both at the constant shear rate and constant shear stress is the linear function of their composition. The addition of poly(diethylsiloxane) to poly(dimethylsiloxane) strongly affects the degree of swelling of an extrudate at the exit of a capillary, and this parameter depends on the phase state of poly(diethylsiloxane) and its content in the blend. Upon incorporation of a small amount of a poly(dimethysiloxanel)-poly(diethylsiloxane) block copolymer (compatibilizer) into the blend, the viscosity of the blend approaches that of the predominant component. This phenomenon is apparently related to the fact that the block copolymer facilitates development of a more uniform morphology of the blend, in particular, the continuous dispersion phase. This factor, along with the specifics of the deformational behavior of poly(diethylsiloxane), also manifests itself during drawing and subsequent shrinkage of crosslinked resins prepared from the blends under study.