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Electrical responses of pre-percolation PEDOT:PSS polymer 30 micron thick films with incorporated single-walled carbon nanotubes were studied by means of impedance spectroscopy technique. The quantitative description of conductivity features is attempted using equivalent circuit modeling. The proposed model is applied to the experimentally investigated nanocomposite systems with different loadings of the nanofiller.

We proposed a highly luminescent and electrically conducting polymer composite material based on polylactide acid (PLA) polymer filled with reduced graphene oxide (RGO) or graphene oxide (GO) nanoplatelets covered by organic Eu(III) complexes tris-dibenzoylmethane mono-1,10-phenanthroline europium(III) [Eu(DBM)3Phen]. No Eu(DBM)3Phen luminescence quenching by RGO and GO nanoplatelets has been observed in emission decay. Partial luminescence intensity decrease is caused by graphene nanoplatelets absorption. Conductivity of the composite film is increased by more than five orders of magnitude as compared to the pure polymer. The proposed material is suitable for 3D printing technology and wide applications in optoelectronics.

Synchrotron radiation is applied to study visible and UV luminescence spectra and their excitation spectra of undoped as well as In and Sb doped cadmium iodide crystals at 10 K. The origin of principal luminescence bands and the role of impurities in the formation of emission centers are discussed. The luminescence properties have been explained based on the electronic structure of CdI2 crystals.

This work was supported by National Research Foundation of Ukraine, project 2020.02/0217. IK would also like to thank VIAA, State Education Development Agency for Latvian state fellowship. HK would like to thank Ministry of Education and Science of Ukraine, project for young researchers No. 0119U100435. In addition, SP and AAP are thankful for financial support from Latvian Council of Science via grant lzp-2018/2-0083. HK and AAP are grateful for the support from the COST Action CA17126., The paper discusses the results of temperature studies of polymer-based nanocomposites obtained by incorporating multi-walled carbon nanotubes in thin layers of poly(3,4-ethylenedioxythophene):poly(4-styrenesulfonate), specifically focusing on interesting features in the dependencies of electrical properties across the wide range of temperatures from ambient one down to 10 K. --//-- This is the preprint version of the following article: I. Karbovnyk, H. Klym, S. Piskunov, A. A. Popov, D. Chalyy, I. Zhydenko and D. Lukashevych,The impact of temperature on electrical properties of polymer-based nanocomposites, Low Temperature Physics, 46, 1231 (2020), DOI https://doi.org/10.1063/10.0002479, which has been published in final form at https://aip.scitation.org/doi/10.1063/10.0002479., National Research Foundation of Ukraine, project 2020.02/0217; VIAA; Ministry of Education and Science of Ukraine, project for young researchers No. 0119U100435; Latvian Council of Science via grant lzp-2018/2-0083; COST Action CA17126; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART².

The electronic structure and Raman scattering from face-centered cubic LiF with three types of vacancies — an F-center, an F ′ -center and a vacancy without electrons ( v F ) — has been calculated by means of hybrid exchange–correlation functional within density functional theory. Our modeling predicts the effective charge of 0.87 e , 1.50 e and 0.10 e on the defect, respectively. The F-center induces two in-gap energy levels for two spin states split by 3.4 eV, while the F ′ -center and the v F induce a single in-gap level 3.8 eV and 2.9 eV below the bottom of conduction band, respectively. The calculated Raman spectra are thoroughly discussed and are found to match well the earlier experimental data. Several peaks are found to shift consistently with the increase of the charge on the vacancy at the rate of about - 35 cm - 1 / e .

In this study, we have manufactured sensory films based on poly(3,4-ethylenedioxythiophene)/carbon nanotubes/reduced graphene oxide nanocomposite. The charge transport in obtained films was analyze...

Aligned organic thin films with polarized luminescence are obtained by means of the slow vapor deposition of fluorescent blue emitting organic liquid crystalline dipolar molecules, 4-(n-penthyl)-3-chloro-4‴-trifluoromethoxy-[1,1ʹ,4ʹ,1ʺ,4ʺ,1‴-quaterphenyl] (M-BLUE), and red emitting molecules, 4-(dicyanomethylene)-2-(4-amylcyclohexyl)-6[4-(dimethylaminostyryl)]-4H-pyran molecule (M-RED), on the surface of the rubbed conducting polymer (PEDOT:PSS). The polarization degree of M-BLUE thin film was found to be 31%, and for M-RED it is 48%. Essential luminescence quenching by PEDOT:PSS was observed. Strong blue shift of M-RED luminescence on PEDOT:PSS substrate is caused probably because of strong interaction between these counterparts.

The composite material based on ZnO microneedles and Alq3 thin film has been obtained. The photoluminescence study shows a tenfold enhancement in the band-edge UV emission (390 nm) of ZnO microneedles and 2 × enhancement in visible emission of the hybrid composite, when excited by 266 nm laser beam. This enhancement can be explained by the interaction between ZnO and Alq3 molecules and the energy transfer from ZnO to Alq3 molecule. Discussed composite structures can find interesting applications as emitting layers in OLED devices.

The influence of adsorbed water on the change of free volume and nanopores in the MgAl 2 O 4 ceramics sintered at 1100 °C for 2 $h$ been studied using positron annihilation lifetime method. It is shown that after immersion of ceramics in water the positron and ortho-positronium trapping occurs more intensely. After drying of ceramic part of the water remains, as evidenced by the parameters of the third component of the annihilation spectrum. It has been established that adsorption processes in MgAl 2 O 4 ceramics lead to the fragmentation of nanopores, while desorption causes their agglomeration

In thе work, changes in the surface electrical resistance of p-Si crystals were investigated under the simultaneous action of the magnetic field and elastic uniaxial deformation. It was established that a sharp decrease (leap) of resistance occurs at the moment of transition from compression to unclamping at a magnitude of a mechanical load exceeding 18 MPa. Such a leap of resistance is not observed under the elastic uniaxial deformations, which do not exceed 14 MPa. This can be explained by the fact that due to the deeper and more prolonged penetration of the dislocation loops, and the corresponding increase in their length, they accumulate a significant number of charged defects that remain unplaced at the beginning of the release (reduction of the field of mechanical stress). A fluctuation of the resistance value in the direction of increase or towards the reduction occurs in the magnetic field. The diffusion of magnetically sensitive defects into the near-surface region can be explained by the repetition of the processes described in time. In a deformed crystalline lattice, diffusion processes occur more rapidly, which increases the frequency of oscillations of the resistance value. By investigating the IR absorption spectra of experimental samples, it was shown that the decay of defects on the surface (111) of p-Si crystals occurs during a long-term action (288 h) of a constant magnetic field (B = 0.354 T). Such defects are hydrogen-containing and oxygen-containing complexes (Si–O–Si, Si–Si, Si–H2, Si–C, O–Si–O, Si–O–C, Si–CH3, H–OH, H2O, Si–OH). This leads to an increase in the surface resistance of the experimental samples of silicon.

In this paper we initiate further discussion on phase diagrams and structural transitions in tetrahedrally bonded semiconductors with particular emphasis on GaN. Comprehensive experimental data and the most important theoretical predictions are comprised in an effort to bring up a generalized universal scheme that explain melting that may or may not be accompanied by the change of the coordination number. The scheme considers the “anomalous” melting temperature dependence on pressure for GaN. Principal possibility of GaN melting into low density semiconducting liquid is demonstrated and challenges on the way to experimental observation of such liquid phase are disputed. Prospects of future experiments that can provide reliable information on the nature of atomic bonding for different GaN phases are laid out.

Peculiarities of crystallization behavior of the 80GeSe2-20Ga2Se3 chalcogenide glasses caused by thermal treatment at 380 °C for 10, 25, 50, 80 and 100 h were studied using X-ray diffraction method. It is shown that crystallization processes indicate on the formation of GeGa4Se8, Ga2Se3 and GeSe2 crystallizes in nanoparticle form in the inner structure of the studied glasses. Crystallites are formed in different modifications: GeGa4Se phase of low-temperature and high-temperature modifications as well as α, γ-modification of Ga2Se3 phases. The most significant changes in the 80GeSe2-20Ga2Se3 glasses occur after thermal treatment for 25 and 50 h. Following crystallization for 80 and 100 h does not reflect the increase in intensity which indicate the further formation of phases in the inner structure of glasses.

Phase compositions, microstructural properties and pore size distribution in the Cu 0.4 Ni 0.4 Co 0.4 Mn 1.8 O 4 ceramics in micro and macro modifications were investigated. It is shown that the micro and macro modified Cu 0.4 Ni 0.4 Co 0.4 Mn 1.8 O 4 ceramics are single-phase (contains only the main cubic spinel phase with cell parameter of 8.36504 (19) Aand 8.36505 (20) A for the micro and macro modified Cu 0.4 Ni 0.4 Co 0.4 Mn 1.8 O 4 , respectively). Different modifications of ceramics are displayed in the size and shape of pores. In micro modified Cu 0.4 Ni 0.4 Co 0.4 Mn 1.8 O 4 ceramics there is a more intensive growth of the contact area between the grains. increases the specific surface area. The grain is combined into agglomerates. One peak with nanopore with radius centered near ~ 2 nm is peculiar to macro modified Cu 0.4 Ni 0.4 Co 0.4 Mn 1.8 O 4 ceramics. Double maximum is characteristic to micro ceramics (~2.3 and 5.5 nm).

Peculiarities of electrical properties of compound materials fabricated by introduction of single- and multiwalled carbon nanotubes with high level of purity into polymer host matrix were studied. Detailed investigation of lateral resistances of the prepared samples in the range of temperatures from 50 to 200 K were performed. Analysis of the conductivity mechanisms in this temperature range was performed by applying Arrhenius equation-based models. Temperature dependencies of lateral resistance were fitted to extract respective activation energies. Distinctions between fabricated specimens reinforced with multi-walled nanotubes and those doped by single-walled carbon nanotubes were demonstrated. It is concluded that composites with multiwalled carbon nanotubes generally exhibit lower resistances as compared to their single-walled counterpart.

In the paper, we explain an automated LabVIEW-controlled setup that enables interferometric measurement of refractive indices in crystalline materials using a laser light source. The setup combines a mechanical system, a microcomputer-controlled gearless drive, a Michelson interferometer, an optical detector, a data acquisition system, and a LabVIEW virtual instrument for an accurate nondestructive determination of the refractive index of given plane-parallel samples. We explain the concept, implementation, and hardware/software peculiarities of the developed system. Test experiments on different crystals yielded results that are in good agreement with available reference data. The range of potential applications of the proposed setup extends from fundamental optical research to biophotonics instrumentation, where efficient delivery of light is of crucial importance and reliable automated probing tools are needed for optical component characterization.

It is shown that at a deformation rate of 0.41 kg/min, the characteristic feature of the dependence of the surface resistance of the p-Si sample on the magnitude of its elastic deformation (R(σ)) is the reduction of the resistance during compression and unclamping. With the increase in the number of “compression-unclamping” cycles, the difference between the positions of the compression and unclamping curves decreases. The transformation of two types of magnetically sensitive defects occurs under the impact of a magnetic field on p-Si crystals. The defects are interrelated with two factors that cause the mutually opposite influence on the conductivity of the crystal. The first factor is that the action of the magnetic field decreases the activation energy of the dislocation holders, which leads to an increase in the electrical conductivity of the sample. The second factor is that due to the decay of molecules of oxygen-containing impurities in the magnetic field, the stable chemisorption bonds appear in the crystal that leads to a decrease in its conductivity. If the sample stays in the magnetic field for a long time, the one or the other mechanism predominates, causing a slow growth or decrease in resistance around a certain (averaged) value. Moreover, the frequency of such changes is greater in the deformed sample. The value of the surface resistance of p-Si samples does not change for a long time without the influence of the magnetic field.

Nanostructured organic thin film with polarized luminescence is obtained by means of the vapor deposition of fluorescent liquid crystalline dipolar molecules in the presence of polarized laser irradiation outside the absorption band. It was shown that irradiation of molecules by non-resonant polarized laser beam during deposition strongly decreases the formation of aggregated molecules that is confirmed by atomic force microscopy, fluorescent microscopy and luminescent spectroscopy.

The work describes the framework that allows performing a computer simulation of complex random networks of conducting nanotubes embedded in the dielectric medium. The representative volume element filled with a large number of interconnected nanotubes is modeled and the tunneling conduction mechanism between adjacent tubes is considered. The principal goal is to develop a computational approach for the three­dimensional multielement structure simulation, which will be relatively simple, yet capable of producing realistic results. The connectivity formation processes among nanotubes in random nanotube networks are studied using the elements of graph theory. All stages of the modeling process are discussed in details. The system conductivity model with taking into account the tunnel effect and intrinsic nanotube conductivities is formulated. The random resistor model is used to calculate the total equivalent conductivity of the network. The results of the computer experiments on electrical conductivity simulations for different systems are presented. The dependencies of the electrical conductivity of nanotube networks in the insulating medium on the concentration of nanotubes, geometric parameters and properties of tunneling conductivity between individual tubes are investigated. It is found that the percolation threshold corresponds to the nanotube loading of 0.5 % when the aspect ratio of nanotubes is 160. Non­linear dependence between the aspect ratio and the percolation threshold was established. The analysis of computational complexity and calculation time is performed for quad­core computing systems. Computer experiments carried out in a systematic fashion within the proposed framework can be useful when designing novel CNT­polymer composites for state of the art electronic applications. By following the predictions of the proposed model, tailoring of electrical properties of such composites can be made easier when adjusting the parameters of nanotubes and their concentration during the fabrication of the nanocomposite samples.

Polycrystalline BaGa 2 O 4 ceramics doped with Eu3+ ions (1,3 and 4 mol%) were obtained using solid state sintering. Structural properties of these ceramics were investigated using scanning electron microscopy and X-ray diffraction methods. It is shown that BaGa 2 O 4 ceramics are characterized by advanced structure of grains, grain boundaries and pores. Base undoped BaGa 2 O 4 ceramics contain three phases, samples with 3 and 4 mol% of Eu2o3 are the mixtures of two phases (BaGa 2 O 4 and EU 3 GaO 6 ), while BaGa 2 O 4 ceramics with 1 mol% of Eu2o3 contain only one (Ba,Eu)Ga 2 O 4 phase of own structural type.

Crystallization ability of the 80GeS 2 -20Ga 2 S 3 , 82GeS 2 -18Ga 2 S 3 and 84GeS 2 -16Ga 2 S 3 chalcogenide glasses were studied using X-ray diffraction and calorimetric methods. It is shown that structure of these glasses is characterized by short range ordering. It is established that Ga 2 S 3 and GeS 2 phases can be crystallized in Ge-Ga-S system.

Multichannel positron and positron- positronium trapping models were developed to study of free volumes in functional nanostructured materials. Proposed model applied to investigation of free volumes and/or nanopores in such nanostructured functional materials as Ga- Ga-Se/s chalcogenide glasses and MgAl 2 O 4 spinel ceramics.

We report on the development and research of a new class of crystalline nanocomposites with tailored anisotropy for micro- and nanoelectronics, targeting applications in telecommunication networks working in optical and subterahertz wave ranges. Different induced optical effects in mentioned materials are analyzed by extreme surfaces method that allows to determine the global maxima of a specific interaction. The results are obtained for the family of novel nanocomposite materials based on the host nanoporous matrices from silica (SiO 2 ) and anodized aluminium oxide (AAO) filled with nanostructured KDP, ADP, TGS, Ba(NO 3 ) 2 and KB-5 crystals. Changes due to various pore diameters, inter-pore spacing and morphology are analyzed.

Degradation kinetics in thick films based on Cu 0.1 Ni 0.1 Co 1.6 Mn 1.2 O 4 ceramics at temperature of 170 oC have been investigated. Analytical description of processes in these materials was performed using relaxation functions. It is shown, that studied degradation kinetics are adequately described by compression-exponential relaxation function.

Mechanism of thermo-induced degradation kinetics in thick films based on Cu 0.1 Ni 0.1 Co 1.6 Mn 1.2 O 4 ceramics at temperature of 170°C have been investigated. Analytical description of processes in these materials was performed using relaxation functions. It is shown, that studied degradation kinetics are adequately described by compression-exponential relaxation function.

The nanostructured humidity-sensitive sensors based on MgAl 2 O 4 ceramics in bulk performance and temperature-sensitive multilayered thick-film sensors of different design based on semiconducting Cu 0.1 Ni 0.1 Co 1.6 Mn 1.2 O 4 and Cu 0.1 Ni 0.8 Co 0.2 Mn 1.9 O 4 ceramics were fabricated and studied. It is shown that temperature-sensitive thick-film sensors possess sensitivity in the region of 298…358 K and humidity-sensitive sensors are sensitive in the region of 30…98 %. Designed sensors were used in the portable system realized on Arduino for monitoring and control of microclimate parameters. Obtained system were tested using Android application.

Surface topology of silver and gold ultrathin films is studied by means of atomic force microscopy. Films under study comprise metallic phase and insulating (voids) phase, therefore can be considered as metal-dielectric composites. Principal parameters of such structures are estimated depending on film thickness and substrate temperatures. Different types of fractal dimension are determined.

Nanocomposite layers of PEDOT:PSS polymer which incorporate randomly dispersed carbon nanotubes were thoroughly examined by means of high-resolution scanning electron microscopy and subjected to electrical studies at different frequencies in a wide range of temperatures. Comparison between the performance of pure PEDOT:PSS layers, layers reinforced with single-walled nanotubes and those reinforced with multi-walled nanotubes is made.

Microstructural peculiarities in comparison with electrical properties in the temperature-sensitive thick films based on Cu0.1Ni0.1Co1.6Mn1.2O4 ceramics before and after annealing (ageing test at 170 oC for 500 h) are investigated. It is shown that annealing of thick films results in diffusion of Ag from contact area in region of grain boundaries. Obtained thick films with stabile electrical properties can be used as temperature-sensitive elements micro- and nanoelectronics.

The work was supported by the Ukrainian Ministry of Education and Science. H. Klym thanks Prof. O. Shpotyuk for the fruitful discussion., Investigation of nanopores in the humidity-sensitive MgO-Al2O3 ceramics modified at 1100°C for 2 hours was performed using positron annihilation lifetime spectroscopy method. Lifetimes of the third and fourth components of positron annihilation lifetime spectra obtained by four-component fitting procedure were used for calculation of nanopores radii. Transformation in free volumes was studied in ceramics after drying and exposure to water vapor. It is established that the lifetime of the third component decreases and the intensity of this component increases in ceramics exposed to water vapor reflecting ortho-positronium decay in nanopores simultaneously with annihilation in water bubbles. The characteristics of the fourth component (lifetime and intensity) decrease in ceramics exposed to water vapor reflecting ortho-positronium trapping in free-water volume of nanopores. Final drying of the MgO-Al2O3 ceramics results in returning of ortho-positronium lifetimes and intensities to the initial values confirming good desorption of water from nanopores of ceramics., Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²

The influence of CsCl content on the void evolution in (80GeS2-20Ga2S3)100-x(CsCl)x, x = 0; 5; 10; 15, chalcogenide glasses and changes of the optical response of these glasses due to CsCl addition are investigated. It is shown that structural agglomeration of voids occurs at addition and increasing of CsCl amount in base glasses. Supersaturation of GeS2-Ga2S3-CsCl glasses by CsCl results in the contraction of void volumes in (80GeS2-20Ga2S3)85(CsCl)15. By applying positron-positronium decomposition algorithm it was established that CsCl not only transforms voids in glass, but also forms new positron-trapping sites in Ge-Ga-S glassy matrix. Therefore, CsCl addition results in the shift of fundamental transmission edge in the visible region. It is shown that doping by larger concentrations of CsCl may lead to “supersaturation” of base glasses and that adding 10 mol% of CsCl is apparently an optimal doping level in view of further modification of glasses with rare-earth ions.

We studied the incorporation of Mg-related impurity centers in GaN crystals depending on the direction of the crystallization front. Two series of GaN crystals – (i) undoped and (ii) Mg-doped – were grown by High Nitrogen Pressure Solution (HNPS) method under otherwise identical conditions. Each series contained four samples with ( 10 1 ¯ 0 ) , ( 11 2 ¯ 0 ) , ( 20 2 ¯ 1 ¯ ) and ( 20 2 ¯ 1 ) orientations. The low-temperature photoluminescence (PL) spectroscopy was used for characterization of the obtained crystals. The observed differences in the PL spectra of GaN:Mg crystals suggested that Mg incorporation in GaN grown by HNPS method depends considerably on the orientation of crystallization front. The concentration of Mg impurity incorporated into the GaN crystals subsequently increases for the following sequence of planes: ( 10 1 ¯ 0 ) , ( 11 2 ¯ 0 ) , ( 20 2 ¯ 1 ¯ ) and ( 20 2 ¯ 1 ) . For ( 10 1 ¯ 0 ) , ( 11 2 ¯ 0 ) and ( 20 2 ¯ 1 ¯ ) planes the blue band is related only to ON – MgGa donor-acceptor pair (DAP) transitions, while for ( 20 2 ¯ 1 ) plane the incorporation of Mg-H complexes occurs additionally to the formation ON – MgGa DAP.

Thin films of 1-pentyl-2 / ,3 / -difluoro-3 /// -methyl-4 //// -octyl- p -quinquephenyl and 9,10-Bis (4-pentylphenylethynyl)antracene organic molecules were grown on optical glass, silicon and porous silicon substrates. First optical and luminescent properties of such hybrid composites are thoroughly studied using spectroscopic techniques. The strong decrease of aggregation in thin films of 1-pentyl-2 / ,3 / -difluoro-3 /// -methyl-4 //// -octyl- p -quinquephenyl on porous silicon was observed. The possibility of simultaneous red, green and blue tunable photon emission from organic film/porous silicon hybrid structure is demonstrated.

The radiation properties and the electronic structure of hybrid composites based on suspension polystyrene (PS) and nanocrystals of BaZrO3 (BZO) (d < 50 nm) have been studied using luminescent spectroscopy and x-ray analysis. A strong cathodoluminescence (CL) in BZO-nanocrystals is observed in temperature range 80–293 K. It is modified in BZO-PS composites: both the low- and a high-energy bands (near 4 eV) appear, together with a significant reduction in the CL intensity. A decrease of the lattice parameter a for BZO phase in the composite and the modification of CL spectra indicate for changes in the nanocrystalline structure induced by the polymer.

The synthesis of forsterite-based ceramic nanopowders using sol–gel method assisted by further thermal treatment has been performed. X-ray diffraction and SEM analysis of the obtained nanopowders are presented. Detailed impedance spectroscopy study of the forsterite nanoceramics doped with Cr3+, Y3+ and Zr4+ ions has been carried out. Impedance spectra are interpreted in terms of equivalent circuits. Peculiarities of the electrical properties for each of the materials under study are discussed.

Atomic force microscopy studies of the dynamics of the nanostructure formation on a van der Waals surface of CdI2 crystals during aging in air environment under near-equilibrium thermodynamic conditions have been carried out. The nanostructure growth process is found to consist of three stages. At the first stage, there appear nano-sized pores due to the lattice dissolution at the outcrops of screw dislocations or other structural defects. At the second stage, the cone-shaped nanoclusters arise and grow in those nano-sized pores. At the third stage, the nanoclusters coagulate. The growth kinetics of cone-shaped nanoclusters is described by a diffusion model based on the interdiffusion approximation for the components. The growth rate of nanoclusters is shown to depend on the time evolution of the concentration gradient of Cd2+ ions in the near-reaction zone., Методами атомно-силової мiкроскопiї дослiджено динамiку формування нанорозмiрних структур на ван-дер-ваальсовiй поверхнi кристалiв СdI2 пiд час їхнього витримування в атмосферi повiтря за термодинамiчних умов, близьких до рiвноважних. У формуваннi поверхневих наноструктур виявлено три стадiї: на першiй утворюються нанопори через розчинення матрицi у мiсцях виходу гвинтових дислокацiй або iнших структурних дефектiв ґратки, на другiй у цих нанопорах зароджуються конусоподiбнi нанокластери, якi з часом збiльшуються у розмiрах, i на останнiй третiй стадiї вони коагулюють. Кiнетика росту поверхневих конусоподiбних нанокластерiв описана дифузiйною моделлю, яка ґрунтується на зустрiчнiй дифузiї компонентiв, що входять до їхнього складу. Показано, що швидкiсть росту цих нанокластерiв залежить вiд часової змiни градiєнта концентрацiї iонiв кадмiю у приреакцiйнiй областi.

In this paper a new interference technique for material permittivity determination in the extremely high frequency range using a vector network analyzer is described. The novelty of this technique is the absence of a reference interference channel and there is no need to rotate the experimental sample that simplifies the measurement process and increases its accuracy. In order to approve this technique, the respective experimental setup was designed. The setup structure and theoretical background of interference fringe minimum formation were described. Based on the quasi-optical principle of the setup operation, the formula for the calculation of the material permittivity was derived. Two different dielectric materials were subjected to test measurements using the created experimental setup. Obtained average values of permittivity in the $50\div 70$ GHz range are $\varepsilon =$ 10.67 ± 0.09 and $\varepsilon =$ 2.35 ± 0.03 for sapphire and optical glass, respectively. For the purposes of result verification, the time-domain processing technique was also applied to calculate the permittivity of these materials. Besides, the obtained data are compared with those reported in the literature.

H. Klym thanks to the Ministry of Education and Science of Ukraine for support and Dr. P. Demchenko for the assistance in XRD experiments., Crystallization transformation in the 80GeSe2-20Ga2Se3 chalcogenide glasses caused by annealing at 380 °C during different duration (25, 50, 80 and 100 hours) are studied using X-ray diffraction and atomic force microscopy methods. It is established that GeGa4Se phase of low- and high-temperature modification, Ga2Se3 phase (α- and γ-modification) and GeSe2 phases are crystallized during this process. It is shown that annealing duration over 50 h does not lead to further internal structural crystallization, while annealing for 80 h result in processes of surface crystallization., Ministry of Education and Science of Ukraine; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²

The morphology of nanostructures formed in non-stoichiometric CdI2 crystals has been studied, by using the atomic force microscopy methods. Morphological changes are observed, when the concentration of cadmium atoms approaches a non-stoichiometric threshold value of 0.1 mol%. The features in the phase composition of nanostructures are analyzed with the help of Raman and infrared absorption spectroscopies. The influence of the researched nanostructures on the optical characteristics of non-stoichiometric CdI2 crystals is analyzed., Методами атомно-силової мiкроскопiї дослiджено морфологiю нанорозмiрних структур, якi формуються у нестехiометричних кристалах СdI2. Встановлено iснування граничної концентрацiї надстехiометричних атомiв кадмiю (0,1 мол.%), при якiй спостерiгається змiна морфологiї. Особливостi фазового складу сформованих наноструктур вивчалися методами комбiнацiйного розсiяння свiтла та iнфрачервоного поглинання. Проаналiзовано вплив цих наноструктур на оптичнi характеристики нестехiометричних кристалiв СdI2.

It is shown that the micro and macro modified $Cu_{0,4}Ni_{0,4}Co_{0,4}Mn_{1,8}O_{4}$ ceramics are single-phase (contains only the main cubic spinel phase). Different modifications of ceramics are displayed in the size and shape of pores. In micro ceramics there is a more intensive growth of the contact area between the grains, increases the specific surface area. The grain is combined into agglomerates. One peak with nanopore with radius centered near ~ 2 nm is peculiar to macro ceramics. Double maximum is characteristic to micro ceramics (~ 2.3 and 5.5 nm).

Electrical properties of single- and multi-walled carbon nanotubes composites were investigated in the range of 50 to 200 K. It is established that composite films with multi-walled nanotubes loading show lower resistances as compared to their single-walled counterpart.

Analysis of percolation phenomenon in the system of straight nanotubes is carried out and an appropriate model of the process is proposed. An algorithm for finding the probability of nanotubes percolation is implemented using three-dimensional graphics visualization tools. The effect of geometric size and concentration of the nanotubes on the percolation probability was investigated. Based on the analysis of the dependence of percolation probability on the values of the dispersion angles determining the nanotubes orientation, the basic regularities of the conductive cluster formation under the influence of an electric field are established. The optimal parameters of the nanotube system with field-controlled percolation were determined.