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The monograph highlights the results of the scientific topic "Theoretical and practical aspects of the use of mathematical methods and information technology in education and science" (registration number 0116U004625) by the Department of Computer Science and Mathematics, Faculty of Information Technology and Management, Borys Hrinchenko University of Kyiv (deadline: March 2016 - March 2021). The main scientific and practical results in the following areas are presented: mathematical and computer modeling, hardware and software of automated control systems, application of digital technologies in the educational process. For scientific and pedagogical, scientific and pedagogical workers who are interested in modern problems of application of mathematical methods and digital technologies in education and science.

The effects of growth rate on the structural, morphological, and electrical properties of InN nanostructures grown on [0001]-oriented GaN substrates by plasma-assisted molecular beam epitaxy is reported. Slowing the growth rate of the nanostructures resulted in extended time for reaching thermodynamically favored crystal facet structures, while at the same time extended the time during which the rf growth plasma can foster damage to the growth. Nanoscale mapping of surface potential and current transport were performed by Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (C-AFM). The results show that increasing the growth rate by ~2.5 times results in more pronounced {10–15} facets of InN nanostructures and decreasing of the residual electron concentration from ~5.8 · 1017 cm−3 to ~2.5 · 1017 cm−3. This is explained by the direct bombardment of indium nitride with plasma species and enhanced decomposition, desorption of adatoms, and an increase in surface dangling bonds that creates surface states traps for electrons. The phenomena of electron accumulation in the near-surface region, as well as the current-voltage hysteresis curves under forward biases for InN nanostructures on GaN(0 0 0 1) substrate are disused.

This work provides a review of commonly used approaches for fine manipulations with nanoobjects by means of scanning probe microscopes and describes an original alternative cost-effective nanomanipulation method. High precision manipulations are important for up-to-date technologies of nanoelectronic, molecular, hybrid and nanomechanical devices and sensor systems especially for the state of the art fundamental and applied researches. A new method to form nanoassemblies by using asymmetric nanoparticles fixed on the surface with the viscoelastic linker has been proposed, theoretically substantiated and experimentally realized. An original theoretical model has been proposed to describe the ordering process of the linked nanorods by means of the multipass interaction with an atomic force microscope (AFM) tip.In addition, an adjustment of the tip-surface interaction has been proposed and implemented which is independent of the AFM. This original approach is based on additional ultrasonic excitation of the surface. This also enabled us to control the degree binding of the nanoparticles with the substrate.With these techniques we were able to form sets of chains (more than 5-μm length) consisting of nanometer-sized (10x50 nm) gold nanorods (NRs) linked to the surface of gallium arsenide by an organic linker. It has been shown that the viscoelastic binding of asymmetric nanoparticles to the surface allows us to create linear assemblies of nanoobjects in just a few passes of the AFM probe.The proposed technique significantly increases manufacturability of nanomanipulations. Direct formation of nanostructures can significantly reduce the cost of their formation in comparison with modern conventional technological approaches, which in many cases may even have some fundamental limitations (in resolution, in materials used, etc.).

Interaction of AsxSe100-x glass thin films with electron beam was investigated by Atomic force microscopy (AFM), Kelvin force microscopy (KFM), X-ray absorption fine-structure (EXAFS) and X-ray-absorption near-edge (XANES). Electron beam induces different surface reliefs depending on the irradiation dose. At doses equal to 7.4*102 μC/cm2 Gausian-like cones are observed. At doses equal to 9.3*107 μC/cm2 craters are formed. We find that film sensitivity to electron beam irradiation correlates with its electrical conductivity. EXAFS measurements indicate that in arsenic rich glasses arsenic coordination number is doubled after e-beam irradiation. XANES data for electron irradiated films show red shifts of absorption edges for three selected glass compositions, which indicate that there is persistent charge accumulated in the glass after e-beam exposure. Red shifts of As-K absorption edges are: 0.7 eV, 1.2 eV and 1.7 eV for As4Se96, As9Se91 and As40Se60 systems respectively. Red shifts of Se-K absorption edges are: 0 eV, 0.6 eV and 1.3 eV for As4Se96, As9Se91 and As40Se60 systems respectively. Observed results indicate that after electron irradiation negative charge is located on arsenic atoms. In arsenic rich glasses, negative charge is also spilled to Se atoms. Charge persistence in electron beam irradiated films is also confirmed by KFM.

Because tungsten (W) is used in present fusion devices and it is a reference material for ITER divertor and possible plasma-facing material for DEMO, we strive to understand the response of different W grades to ion bombardment. In this study, we investigated the behavior of mirrors made of four polycrystalline W grades under long-term ion sputtering. Argon (Ar) and deuterium (D) ions extracted from a plasma were used to investigate the effect of projectile mass on surface modification. Depending on the ion fluence, the reflectance measured at normal incidence was very different for different W grades. The lowest degradation rate of the reflectance was measured for the mirror made of recrystallized W. The highest degradation rate was found for one of the ITER-grade W samples. Pre-irradiation of a mirror with 20-MeV W 6+ ions, as simulation of neutron irradiation in ITER, had no noticeable influence on reflectance degradation under sputtering with either Ar or D ions.

Under irradiation of amorphous $As_{x}Se_{100-x}$ films by band-gap light, it was observed that lateral mass transport of the film material changed the direction of movement in the region (4 < x < 5 at%.) of topological structural transition (crossover "from light to dark" to "from dark to light"). We propose a model that qualitatively describes the observed phenomenon. In experimental testing of the model by Kelvin probe force microscopy, for the first time to our knowledge, it was detected that with the increase of temperature (from ambient to glass-transition temperature, Tg) photo-induced mass transport in glassy semiconductors occurs with the rates, which significantly exceed those at room temperature., 11 pages, 6 figures

Two types of conjugated thiocarbonyl-terminated compounds have been synthesized and their ability to be adsorbed on surfaces of the different nature, namely, glass, polytetrafluoroethylene (PTFE), and gold has been studied. Different morphology of the films prepared by thermal vacuum evaporation and drop-casting from solutions has been observed depending on the surface used. It has been found that gold surface has a unique property to influence self-assembly of both monolayer and larger aggregates or crystals of the compounds, in contrast to glass and PTFE substrates. It was found that thiocarbonyl group is able to be chemisorbed to the gold surface. However, it was concluded that in spite of the fact that the thiocarbonyl groups are important for the chemical interaction with the gold surface, physical adsorption on the substrate surface, compound–compound and compound–solvent (when using solution) interactions are of great significance to drive self-assembly of the final film.

Near-infrared photoresponse is observed in the temperature range of 77-300 K for a photodetector fabricated from undoped In0.35Ga0.65As/GaAs multiple quantum dots grown in a molecular beam epitaxy system. The detectivity is estimated to be on the order of 3.70 times 109 and 2.70 X 107 cm .radicHz/W at 77 and 300 K, respectively. The reduction of the detectivity is attributed to the increase of the dark current as the temperature is increased. The photoresponse is explained in terms of several interband transitions. These transitions are found to be in good agreement with the self-consistent theoretical calculations.

Polytetrafluoroethylene (PTFE) films have been deposited onto polycarbonate (PC) substrates from the products of PTFE evaporation, activated by a cloud of accelerated electrons. A 40.68 MHz glow discharge was used during the deposition process. The polymer films have been characterised by XPS, FTIR and AFM. The use of the low power plasma during film growth led to the formation of PTFE films with modified structure. Films are amorphous and contain more cross-links, but in general, the structure of their macromolecules is still linear. An increase of RF-power leads to the formation of films with large amount of double bonds and enhanced internal stresses. Deposition of PTFE on PC without plasma treatment led to the formation of PTFE clusters up to 50 nm in diameter. The RMS roughness of the films, deposited without plasma, was about 4 nm, while the films deposited with plasma treatment had a roughness of 1.5 nm. The use of plasma has an additional effect if a PTFE coating is deposited on the PC substrate with submicrometer-sized steps. Without plasma the steps retain a rectangular shape. Deposited with the RF-discharge the PTFE layers resemble plasma-polymerised films. Under certain conditions the deposited films can fill trenches in the substrate like a wetting liquid, while under other conditions they avoid trenches and grow in between them.

Films of nanosized composites of poly(N-epoxypropylcarbazole) (pEPC) and poly(3,6-di-Br-N-epoxypropylcarbazole) (pdBEPC) with vanadium pentoxide (V2O5) are produced for the first time ever. The electroconduction in dark and when illuminated, absorption spectra, steady-state photoluminescence spectra, and time-resolved photoluminescence spectra for the composite films are studied. The results are compared with relevant data for the pEPC, pdBEPC, and V2O5films. A conclusion about the formation of donor–acceptor complexes with incomplete charge transfer [pEPC+σ···V2O5-σ] and [pdBEPC+σ···V2O5-σ] is made. The surface morphology of the composites differs in the size of V2O5 fibers and polymer grains; the polymer inclusions in the composites are of different character. A surface morphology study reveals that the composite constituents—polymer base and V2O5 fibers—are nanosized.

A comprehensive microscopy analysis has been undertaken to study three-dimensional quantum dot (QD) ordering in multilayered In 0.4 Ga 0.6 As/GaAs structures grown with an As 2 flux at different substrate temperatures. Atomic force microscopy, transmission electron microscopy, and photoluminescence measurements were employed to fully understand the formation of these extended dot structures. Changes in the lateral pattern of QD ordering are correlated with their vertical alignment. These correlations are analyzed in light of the inherent transformation of the wetting and spacer layers, as well as changes in the shape, strain, and composition of individual QDs. The experimental results are attributed to the anisotropy in the thermally activated surface mass transport and the relaxation of elastic stresses.

Amorphous silicon carbon nitride (SiCN) films were deposited by a plasma enhanced chemical vapor deposition (PECVD) technique using hexamethyl-disilazane as a main precursor by varying discharge power. The films were characterized with X-ray diffraction (XRD), Auger spectroscopy, Atomic force microscope (AFM), Fourier transform infrared spectroscopy (FTIR). The atomic and electronic structures of the amorphous Si 0.5 N 0.5 and Si 0.375 C 0.375 N 0.25 alloys were studied within a first-principles molecular dynamics (MD) simulation. Both experimental and theoretical results show that, in amorphous SiCN films, the main bonds such as Si-C, Si-N, Si-O, C-C, C-H, N-H and C-N are formed. For all the films, the bright emission that has a three-peak structure at 530, 600 and 720 nm was detected at room temperature. Infrared spectra and the results of first-principles MD simulations point to that the 530 nm emission band can be due to tail-to-tail recombination inside the amorphous Si-C-based matrix, whereas the broad signal in the spectral range 600-750 nm can be assigned to the SiC clusters with Si-O bonds. An increase in discharge power promotes an improvement of the amorphous Si-C network and enhances the surface roughness, which leads to the enhancement of PL intensity. It is suggested that hydrogenated SiCN films will be promising for optoelectronic applications.

Lateral ordering of InGaAs quantum dots on the GaAs (001) surface has been achieved in earlier reports, resembling an anisotropic pattern. In this work, we present a method of breaking the anisotropy of ordered quantum dots (QDs) by changing the growth environment. We show experimentally that using As(2) molecules instead of As(4) as a background flux is efficient in controlling the diffusion of distant Ga adatoms to make it possible to produce isotropic ordering of InGaAs QDs over GaAs (001). The control of the lateral ordering of QDs under As(2) flux has enabled us to improve their optical properties. Our results are consistent with reported experimental and theoretical data for structure and diffusion on the GaAs surface.

The interband and intersubband transitions in self-assembled InAs and In0.3Ga0.7As quantum dots grown by molecular beam epitaxy have been investigated for their use in visible, near-, and mid-infrared detection applications. Devices based on InAs quantum dots embedded in an InxGa1−xAs (0 to 0.3) graded well and In0.3Ga0.7As quantum dots were fabricated in order to measure the temperature dependent (77 – 300 K) photoresponse. The dark current was measured in the temperature range of 77 to 300 K for the devices. Room temperature photoresponse ranging between 0.6 to 1.3 μm was observed for the InAs and In0.3Ga0.7As quantum dot photodetectors. Furthermore, a dual band photoresponse in the visible, near-, and mid-infrared spectral regions for both devices was observed at 77 K. Using a self-consistent solution of Schrödinger-Poisson equations, the peak position energies of the interband and intersubband transitions in the two multi-color quantum dot infrared photodetector structures was calculated.

Studied the effect of rapid thermal annealing (RTA) on the parameters of diode structures with Ni-n-SiC-21R(0001) and Ni-n-SiC-21R(0001~) Schottky barriers. Ohmic contacts to these structures were formed by nickel resistive sputtering onto the substrate (heated up to 300/spl deg/C) followed with fusion at T = 450/spl deg/C for 10 min. It was shown that one can, in principle, obtain Ni-n-SiC diode structures (formed at Si- and C-faces of SiC-21R polytype) that are heat-tolerant up to 450/spl deg/C.

Arrays of ZnO nanowires are grown by the vapor-liquid-solid method on a silicon substrate. The results of XRD, SEM, and AFM studies show that the diameters of nanowires vary in the range (50–300) nm, and their length is up to 40 μm. The wires exhibit bright photoluminescence: the band corresponding to the near band edge region and one or two (depending on the growth conditions) defect-related bands. The intensity ratio of the bands reflects the non-stoichiometry of the material and can be controlled by the zinc evaporation temperature and the temperature in the growing zone., Масиви нанодротів ZnO було вирощено за механізмом пара–рідина–кристал на кремнієвих підкладках та було досліджено методами рентгенівської дифрактометрії, скануючої електронної мікроскопії та атомно-силової мікроскопії. результати цих досліджень свідчать про те, що діаметри нанодротів варіюються в межах 50–300 нм, а їх довжина сягає 40 мкм. Для вирощених нанодротів характерна інтенсивна фотолюмінесценція, в спектрі якої домінують близько-крайова смуга та одна чи дві (залежно від умов вирощування) дефектні смуги. Співвідношення інтенсивностей цих смугвідображає нестехіометричність матеріалу і залежить від температури випаровування цинку та температури в зоні росту нанодротів.

The main targets for UV irradiation in biological cells are DNA molecules [1]. Photochemical reactions in DNA caused by UV irradiation are the general processes that we use, in cell biology, to study the DNA damaged area. We analyzed: • known mechanisms of UV induced DNA damage in cells: excited by UV light, nucleotide bases begin to take part in photochemical reactions of cyclobutane-pyrimidine dimmer and (4–6) adducts formation. • absorption DNA spectrum behaviour in the range 200 – 300 nm changes of absorption by bases under UV irradiation. • photoluminescence charge transport behaviour of ds-DNA molecules in wet, dry adsorbed layers with bases changes under UV irradiation. Then the experimental investigations were carried out on 2 mM plant ds-DNA polymerized molecules (Eris, France [11]) that were dissolved in 3 mM NaOH buffer and 2 mM ss-DNA with 15 oligonucleotides bases: 3'-CCA CCG CTG CTG AGG-5', length 5,4 nm, wide 1 nm (Jena BioScience, Germany) were dissolved in 100 mM carbonate/bicarbonate buffer [2]. We prepared ds-DNA polymerized molecules water solutions dissolving 0,1 ml of DNA in buffer solution in 1, 40, 50 ml of water showed a pH of 7,4 (the volume ratios are 1:1, 1:40, 1:50, correspondingly) and ss-DNA water solution dissolving 1 ml of DNA in buffer solution in 5 ml of water showed pH of 7,4. The solutions in quartz cuvettes were irradiated by UV (Л = 200–400 nm) during 5–90 min with the light power 1020 photon/(cm2 s). From absorption spectra of different concentration of ds(ss)-DNA molecules in water solution the influence of UV irradiation on ds(ss)-DNA molecule absorption were revealed. Photochemical reactions in the nucleotide base pairs with formation of dimmers and/or (4–6) adducts, that lead to the change of electronic levels structure of ds-DNA molecule and were revealed in absorption spectra (this spectrum is similar to presented in Figure ​Figure1):1): absorption maximum at 265 nm (4.7 eV) shifts to 269 nm (4.6 eV) – this caused by additional absorption on formed dimmers; maximum at 285 nm (4.3 eV) is absent – absorption on cytosine base becomes minimal: we assume that cytosine was used in dimmer formation. Figure 1 Absorption spectra of ss-DNA molecules in water solution in the range 220 – 300 nm before (a) and after UV irradiation: b, c,..m during 5, 10.... 180 min correspondingly. The dependence of ds-DNA absorption intensity (for wavelengths 252 nm) on UV radiation time is represented in Figure ​Figure2b.2b. Almost all changes in absorption take place during first 30 min of UV radiation, in the comparison with ds-DNA it could be caused by smaller number of adjacent T and C in ss-DNA bases sequence. The band in short wavelengths (λ < 235 nm) with maximum at 220 nm is not sensitive to UV irradiation as and for ds-DNA. These results prove that the UV effect in DNA becomes apparent in the excitation of nucleoside bases (absorption maxima is 235–280 nm) and photochemical reactions in DNA chains. Figure 2 Absorption intensity of: a – ds-DNA molecules at 252 nm; b – ss-DNA molecules at 256 nm versus UV irradiation time. Photoluminescence spectra of wet dsDNA layer with networks have maxima at 432, 440 and 454, 463 nm before and after UV irradiation with 337 nm and 365 nm during one hour, respectively. The presence of photochemical reactions appear in the decreasing of photoluminescence intensity in this layer. Then it is possible intensive emission with participation of electronic states corresponds to molecular orbital systems in the nucleotide base pairs and sides of the ladder having a periodic structure with alternating sugar and phosphate groups. A part of the electron levels that determine photoluminescence spectrum can correspond the formation of dsDNA molecular networks. The presence of the photochemical reactions appear in the decreasing of dry absorbed ds-DNA molecular layer with networks conductivity under periodical switched UV irradiation: as a result the conductivity decreases after first radiation reflecting the reducing of pyrimidine bases (that formed dimmers) contributing to ds-DNA conductivity. The increase of the conductivity value after UV irradiation could be caused by the particular reparation of ds-DNA under applied voltage of 1 V.