Technical Physics

The morphology, structure, and optical properties of composites with biodegradable polymeric particles, which are based on poly-ε-caprolactone–polyvinyl alcohol (stabilizer) mixtures and contain 5-Fluorouracil (an antitumor preparation), have been studied by atomic-force and optical microscopy, X-ray diffraction, and dynamic and static light scattering. Studies have shown that the morphology of synthesized composites sustains appreciable transformations depending on their stabilizer content. No crystalline reflections corresponding to 5-Fluorouracil have been revealed, thus arguing for a high dispersity of this preparation in the polymeric matrix of caprolactone. The correlations between the structural and morphological parameters, composition, stabilizer concentration and the efficiency of the encapsulation of 5-Fluorouracil by the composites have been established.

The technological prospects for the creation of a system of microfocus X-ray tubes with the use of silicon field emission of nanocathodes have been discussed. A numerical analysis of the field-emission current from a nanoscale semiconductor cathode regulated by voltage on a grid electrode has been carried out on the basis of which a scheme for controlling the elements of the matrix of field-emission cathode assemblies has been proposed. The current–voltage characteristics of silicon field emission nanocathodes have been measured. They are in good agreement with the theoretical estimates of the field-emission current. A full technological cycle of the development of elements of microfocus X-ray tubes (a set of field-emission cathode assemblies and a set of anode assemblies) has been performed. The results can be used to create systems of microfocus X-ray tubes for nanolithographic equipment of a new generation.

A model is proposed to describe reflection and refraction of a moving charge that crosses a tilted interface of a scattering medium and vacuum. A distribution function of a charged particle that is involved in multiple Coulomb scattering in an infinite medium is used to construct the mathematical model. A refraction angle and reflection coefficient are numerically calculated.

We analyze the effect of heat transfer in metals on parameters of the thermoelastic and thermoelectric responses of metals to a pulsed laser action. It is shown that two-stage analysis of the dynamic problem of thermoelasticity and the thermoelectric effect makes it possible to obtain an adequate description of experimental results. The results described here demonstrate a considerable dependence of the response parameters on the microstructure, which indicates the possibility of development of a high-efficiency method of nondestructive control of metal quality.

X-ray diffraction is used to study changes of fine structure of carbon fibers caused by an increase in the heat-treatment temperature. It is shown that the fiber material is heterogeneous and its composition is determined by heat-treatment regimes and depends on orientation angle φ of coherent domain relative to the fiber axis.

We report on the results of experimental investigation and mathematical simulation of penetration of rod strikers made of porous materials into metallic obstacles for an axisymmetric high-speed impact. The results of investigation indicate a considerable influence of striker material porosity on the penetration process, which leads to an increase in the penetration depth as compared to monolithic strikers of the same mass and diameter at ultrahigh impact velocities. This effect is associated with accelerated formation of localized shear zones followed by fragmentation of the material. One possible approach to estimating the penetration depth is the proposed approximate (engineering) technique in which the dynamic strength characteristics of materials of interacting bodies is considered. The results of calculations based on the proposed technique are compared with experimental data and show good qualitative and quantitative agreement.

We have analyzed the dielectric spectra of thin (1200 Å) films of vanadium dioxide, a material with strong electron–electron correlations. We have tested both undoped and germanium-doped VO₂ : Ge films. The latter exhibits an additional peak in the frequency spectrum of the tangent of the dielectric loss angle. We have analyzed the fine structure of the spectra and provided physical interpretation of two peaks on the frequency dependence of the tangent of dielectric loss angle and two semi-circles on the Cole–Cole diagram. Analysis of results has been performed based on equivalent electric circuit diagrams of samples, viz., one-loop RC circuit for the undoped VO₂ film and two-loop circuit for VO₂ : Ge film. The numerical values of parameters of model systems have been determined.

With the aim of developing a gas-jet technique for depositing diamond structures, the flow of a hydrogen–methane mixture through hot coaxial tungsten cylindrical channels with a tungsten coil inside has been investigated. Emphasis has been placed on tungsten surface carbidization during gas-jet deposition and the influence of carbidization on the deposition rate and morphology of applied coatings. Several experiments on tungsten surface carbidization under different conditions for hydrogen–methane mixture supply have been conducted. Simulation of the mixture flow by direct simulation Monte Carlo method has been performed. Possible ways of how methane and its fragments fall on the surface of the coil has been discussed.

The amorphous-crystalline transition in Fe₈₄B₁₆ alloys prepared by melt spinning and high-energy ball milling was studied. Time-resolved X-ray diffraction showed that the kinetics of transition into a crystalline state depends on the method of preparing a metastable alloy. In amorphous Fe₈₄B₁₆ alloy prepared by melt spinning, crystallization proceeded within a time period of below 1 s and was accompanied by the formation of eutectic α-Fe–Fe₃B. At temperatures above 600°C, metastable phase Fe₃B was found to transform into Fe₂B and α-Fe. In the high-energy ball milling produced alloy, structural changes were accomplished in 4–8 s and the transition into a state with a perfect crystalline structure was caused by the growth of nanocrystallites formed during processing.

The possibility of replacing classical sol-gel operation methods of high-temperature annealing by photo-annealing using ultraviolet-range radiation has been analyzed. A technique for synthesizing hierarchically organized zinc oxide films using sol-gel technology based on the parallel combination of low-temperature treatment and UV photo-annealing is proposed. Spectroscopic studies of the qualitative composition of the film-forming sol and nanomaterials based on it, obtained on various types of substrates, have been carried out before and after initiation of photochemical reactions.

The formation of Au/Mo/Ti ohmic contacts to p-diamond epitaxial films has been studied. Specifically, the influence of annealing on the electrical properties and structure of contacts has been investigated. It has been shown that the upper gold layer protects the contact system against oxidation up to 850°C during RTA unlike the case of a “simplified” Au-free Mo/Ti system frequently used in today’s solutions. In Mo-free Au/Ti systems, high-temperature annealing causes effective diffusion of titanium into the gold layer, which deteriorates the protective properties of the latter and enhances oxygen diffusion toward the interface with diamond. Oxidation of the Ti/C contact area prevents the formation of a titanium carbide conducting layer, which has high adhesion to diamond. The role of various factors, namely, annealing to form titanium carbide, heavy doping of diamond with boron, and crystal perfection of diamond films, in lowering the contact resistance, has been estimated. For doped epitaxial films grown on single-sector substrates, unalloyed ohmic contacts with a record low contact resistance of 4 × 10^–7 Ω/cm² have been obtained.

Experimental results on anomalous conductivity in specifically synthesized copolymer films are analyzed. Polyacetylene molecular fragments with variable concentration are introduced into polyvinylchloride macromolecules. It is shown that such samples exhibit spontaneous and stimulated conductivity jumps by 13 orders of magnitude and the lifetime of such states may range from several minutes to a day. A qualitative model is proposed to describe the anomalous behavior of the polyvinylchloride composite including effects that provide stabilization of the high-conductivity states, conditions for development of instability in the transitions between the states, and the reasons for long-lived high-conductivity state even in the absence of external voltage. Simple numerical estimations that prove the proposed effects are considered.

Electrostatic turning devices are electron- and ion-optical elements changing the direction of movement of a parallel monochromatic beam of charged particles by a given angle without affecting a beam’s parallelism. The trajectory similarity principle for electric fields homogeneous in Euler terms ensures the fulfillment of this property for the fields with a homogeneity of a zero power. The Donkin formula for 3D homogeneous harmonic functions produces extremely wide class of analytic expressions describing homogeneous electric potentials of a zero power. This paper considers the algorithm of synthesis of electrostatic turning devices that transform input parallel monochromatic beams into output parallel monochromatic beams. The algorithm is based on the Donkin formula and ensures beam stability for small deviations from the electric field’s symmetry plane.

The macro- and microstructure of doped LiNbO₃ crystals is studied, their transmission spectra are investigated, and the effective coefficients characterizing the dopant impurity distribution are determined. We analyze the literature data on phase diagrams of the ternary system Li₂O–Nb₂O₅–dopant oxide and the electron configurations of dopant elements, and the results suggest that this can be used as a basis for designing technological conditions for growing doped lithium niobate crystals and predicting their quality. With p‑elements (boron), structurally and compositionally uniform LiNbO₃ crystals can be grown, with the doping impurity not being incorporated in the crystal. s- and d-metals (magnesium and zinc) have a similar effect on the melt and properties of resulting LiNbO₃ crystals, which have periodic domain structures and similar types of point defects. Due to their electronic structure, f-metals (cerium) bring the melt to such a structure that this enables the formation of a periodic domain structure in LiNbO₃ crystals during their growth.

Field-induced extraction of ions from a polar solution is implemented with the aid of an interface that represents a polymer track membrane with a conducting coating. A time-of-flight spectrum of ions extracted from a KI solution in a water–glycerol mixture is obtained using nanosecond electric-field pulses. Application of the conducting coating allows a significant decrease in the voltage of the extracting pulse and suppression of the effect of secondary processes on the composition of ions generated in a pulsed membrane ion source.

The structural and physicochemical mechanisms of interaction of bone tissue with titanium implants under conditions of tuberculous osteitis are studied using scanning electron microscopy, X-ray diffraction analysis, IR spectroscopy, and thermal analysis. Physiological regeneration of bone tissue during treatment of tuberculous osteitis is accompanied by an increase in the organic component, embrittlement of the mineral phase of the bone matrix, and its decomposition to fine particles. The presence of titanium implants under physiological conditions contributes to the activation of the synthesis of the apatite phase in the regenerating bone. The primary mechanism of implantation osteogenesis in tuberculous osteitis is the formation of an inorganic phase of hydroxyapatite mainly in the regions of destruction of the titanium alloy.