Defect-induced effects in nanomaterials

Resume : Defects are usually seen as imperfections in materials that could significantly degrade their performance. However, at the nanoscale, defects could be extremely useful since they could be exploited to generate innovative and useful materials and devices. Defect engineering is applied here to hybrid organic-inorganic perovskites (HOP) with 3D structures. HOP materials have become one of the most promising low-cost alternatives to traditional semiconductors in the field of photovoltaics and light emitting devices. A better knowledge of the electronic properties of such materials is obviously a prerequisite for their use and optimization in opto-electronic devices. We use here Helium ion irradiation in the range 10-30 keV as a tool for the introduction of point defects in a controlled way. At low fluences, mainly point defects are created that introduce defects energy levels and modify the electronic and light emitting properties of the materials. Contrary to usual semiconductors, like crystalline silicon for instance, where irradiation defects act as recombination centers for the electron-hole pairs and quench very efficiently the luminescence, we observe here an enhancement of the optical emission at low temperature. We can deduce from this observation that irradiation defects act here as active optical centers, essentially in the low-temperature orthorhombic phase as seen in the dependence of the total photoluminescence integrated intensity. Another effect of the ion irradiation directly observable is the emission through new exciton processes after Helium ion irradiation of (CH3NH3)PbBr3 polycrystalline thin films. The temperature dependence of the spectra evidences light amplification after ion irradiation at low temperature both with (CH3NH3)PbI3 and (CH3NH3)PbBr3. These behaviours are very intriguing and need further studies for a better understanding of the specificity of defects and their impact over opto-electronic properties in HOP materials.

Resume : Diffusion of point defects determines microscopic processes in nuclear materials. The promising way for controlling radiation damage of these materials could be achieved by switching from conventional materials to nanomaterials [1]. Сomputer modeling and simulation plays the crucial role in achieving this ambitious goal. This work was motivated by the study of point defects in U-Mo metallic fuel. The EAM model for U has been proposed based on DFT calculations [2]. Recently, we have carefully analysed the phDOS for U at different T for this model [2] and for 4 newer classical models. Since gamma-U is unstable at T=0, we have used several finite-T techniques. The results have been compared with experiments available and illustrate the current level of accuracy of the classical models for uranium. We have developed the GTH pseudopotential for U [3] and report its accuracy as well. We have used the metadynamics-based approach for calculation of the temperature dependence of migration energies of defects that captures the anharmonic effects important for gamma-U. We have calculated the formation energies of defects and revealed the peculiarities of their dependence on temperature. Finally, we discuss the temperature effects in the context of kinetic Monte-Carlo simulations. [1] Ackland G., Science 327, 1587 (2010) [2] Smirnova, D.E., Starikov, S.V., Stegailov, V.V. J. Phys.: Cond. Mat. 24, 015702 (2012) [3] Smirnov, G., Stegailov, V. Lobachevskii J. Math. 38, 974 (2012)

Resume : The radiation-resistant oxides (MgO, Al2O3, MgAl2O4, BeO etc) are important materials for applications in fusion reactors. It is very important to predict/simulate not only the kinetics of diffusion-controlled defect accumulation under neutron irradiation, but also a long-time defect structure evolution including thermal defect annealing after irradiation. In thus work, the kinetics of the F-type center annealing after electron, heavy ions or neutron irradiation was treated as the bimolecular process with equal concentrations of the complementary F and Oi defects. The appropriate migration energies were obtained from available from literature annealing kinetics for electron, neutron and ion irradiated MgO, Al2O3, MgAl2O4, BeO, ZnO, PLZT etc. The results obtained are compared with recent ab initio calculations of interstitial oxygen migration. Special attention is paid to: (1) dose effects on F center annealing in neutron and fast electron irradiated MgO and MgF2; (2) a detailed comparison of diffusion-controlled F center thermal annealing in neutron, electron and heavy-ion irradiated MgO, MgF2, Al2O3, ZnO and MgAl2O4; (3) the F center annealing and metal colloid formation in thermochemically reduced MgO, Al2O3 and BeO.

Resume : Boron carbide is a material with a peculiar structure, consisting in icosahedra (mainly made of boron atoms) and triatomic chains connecting them. The commonly accepted structure for the B4C stoichiometry is the B11C-CBC structure, however vacancies and substitutions both on the icosahedra are suspected to be present. Boron carbide has various technological applications, including the role of neutron absorber in nuclear reactors. In this case nuclear reactions produce helium, for which concentrations on the order of a few atomic percent can be attained. It is thus of primary importance to know the distribution and kinetics of helium atoms in boron carbide. In spite of a variety is of experimental works devoted to the characterization of the microstructure and He bubbles in boron carbide irradiated in reactor, there is a serious lack of knowledge concerning the basic mechanisms governing helium kinetics. This study is devoted to the stability and mobility of helium atoms in carbon rich boron carbide. The lowest energy He insertion sites were screened through density functional theory and the most probable migration paths and energy barriers were investigated using the nudged elastic bands (NEB) approach. The results suggest that in a wide range of temperatures He interstitials undergo 2D diffusion confined between two 〈111〉 planes. The onset of 3D diffusion is expected, according to our calculations, with an activation energy close to 2 eV [1]. Our result is in qualitative agreement with the observation of flat bubbles with 〈111〉 orientation. Under irradiation, however, the role of vacancies cannot be neglected. On the basis of further NEB calculations for a variety of configurations including vacancies and He atoms we discuss the possible vacancy assisted diffusion of He in boron carbide, also in relation to recent experimental results.

Resume : Nanopillar III-N LEDs (NP-LEDs) emitting in UV, blue, and green spectral ranges have certain inherent advantages over their planar counterparts. In this talk we'll concentrate on the top-down fabrication of such NP-LEDs by reactive ion etching (RIE) of planar MQW LED structures via nanomasks. We'll demonstrate that effects of nonradiative recombination due to dislocations can be effectively suppressed in these RIE-produced NP-LEDs, the detrimental consequences of RIE-induced defects can be mitigated by proper choice of annealing and surface passivation routines, that the overgrowth of the nanopillar structures can seriously improve the crystalline quality and enhance the performance of blue and green LEDs, that nanoparticles producing surface plasmons, when placed between the nanopillars or in nanoholes of blue and NUVLEDs, substantially improve the efficiency of NP-LEDs. Robust ohmic contacts to NP-LEDs can be made by deposition of graphene or of Ag nanowires. Color conversion techniques involving interaction with quantum dots can be effectively used to generate white color LEDs. When compared to bottom-up NP-LEDs produced by selective growth the top-down NP-LEDs have the advantages of relative ease in achieving the necessary high density and uniform height and diameter of nanopillars, and the use of well established technology in fabrication of high-quality planar MQW LED structures.

Resume : Cu(In,Ga)Se2 (CIGS) based thin film solar cells, in spite of their already superb electrical performance, need to start incorporating different solar cell architectures in order to improve from its current performance. We propose strategies that allow for very low interface recombination based on a nanometric point contact structure through a dielectric layer. We study ultrathin solar cells with ~ 350 nm thick CIGS layers with a nanopatterned Al2O3 layer on top of the Mo back contact. This 25 nm layer is etched with openings of 200-400 nm separated by 2000 nm and it is effectively capable of passivating the CIGS rear interface as demonstrated by the superior electrical performance of these layers compared with reference devices, most notably an increase of Voc of ~90 mV and Jsc of 2.3 mA/cm2. Furthermore, photoluminescence measurements and detailed optical simulations based on the experimental results, show that by including the nanopatterned point contact structure, the interface defect concentration is reduced. Both, an enlarged rear optical reflection and electrical effects contribute to the improvements of the short circuit current as shown by the external quantum efficiency results, photoluminescence. However, from the difference of 2.3 mA/cm2, only 0.9 mA/cm2 can be attributed to the increased rear reflection, as shown by the optical simulations. A detailed discussion about the concrete effects of chemical passivation and of field effect passivation is performed.

Resume : Metallic nanowires are known to break up into a string of nanoclusters due to diffusion of the surface atoms in a process called Rayleigh instability. In this work we show, using experiments and computer modelling, that crossing two nanowires will nucleate the fragmentation of the wires around the junction, where a central cluster will form. We have performed a series of experiments on gold and silver nanowires and nanowire junctions at fixed temperatures 473, 673, 873 and 973 K during a time period of 10 min. We show that nanowires are especially prone to fragmentation around junctions and crossing points even at comparatively low temperatures. The speed of the fragmentation process is highly dependant on the temperature. We have also developed a Kinetic Monte Carlo model for gold atomic surfaces and we can demonstrate that the nanowire junction fragmentation can be fully explained by surface atom diffusion. These findings could be used as a technique where nanowires aligned in regular grids results in arrays of nanodots, which have important applications in e.g. electrochemical sensors.

Resume : As a broad-bandgap semiconductor, Zinc oxide (ZnO) has a large bandgap (~ 3.44 eV) and an exciton binding energy of 60 meV at room temperature (RT), which is larger than GaN (26 meV) or ZnSe (25 meV). Also, ZnO has several favorable properties, such as high electron mobility, good transparency, and strong room-temperature (RT) luminescence. So, many researchers have studied about ZnO for long times. In the photolumines-cence (PL) spectra, ZnO has emission bandgaps in the ultraviolet (UV) and visible (red, yellow, green, blue and violet) regions. The UV emission regions usually have rele-vance to direct bandgap of ZnO. But, the vis-ible emission regions are usually linked closely to defects located within bandgap of ZnO ; Zni, VO, VZn and so on.[1] It has been revealed that ZnO-nanocarbon hybrid nano-particles could effectively improve the opti-cal[2] and electrochemical properties of ZnO.[3] Herein, we report on the synthesis of ultra-small size quasi consolidated ZnO-graphene nanoparticles. This nanoparticle has dominantly defect states at 3.02, 2.58, 2.67 and 2.51 eV. By conjugating the graphene, we could perfectly convert the green (2.2 eV) and red emission (1.83 eV) path related to the defects of oxygen vacancy (VO) of ZnO into violet-purple-blue emission. Also, we per-fectrly explain the mechanism about the elec-tronic transition in both ZnO and ZnO-graphene nanoparticles by measuring the time- resolved photoluminescence (TR-PL). Based on this ZnO-graphene QDs, we suc-cessfully fabricate the white phosphor UV-LED.

Resume : In recent years, 2D transition metal dichalcogenides (TMDs) have been the focus of intense investigation as a potential replacement for Si in logic devices and numerous other novel applications. However, growth of large area 2D TMDs invariably leads to the formation of grain boundaries (GBs) that can significantly degrade electrical transport by forming large electrostatic barriers. While there have been recent studies of the electrical transport across GBs in single layer TMDs [1], there is still a lack of understanding of the impact of GBs in multilayer systems. Here, we investigate the effects of GBs on the electronic properties of CVD grown MoS2 with thicknesses varying from one to four layers by Conductive Atomic Force Microscopy (C-AFM). We show that the electrostatic barrier from the GB extends vertically into the top layer. Thus, the presence of GBs effects electrical transport not just within its own layer, but also in the surrounding layers. Furthermore, under reverse bias we observe that exposed GBs become more conducting, while embedded GBs are always less conducting. We attribute this behavior to oxidation of the exposed GBs. The results signify the importance of the quality of each layer on the electrical transport in multilayer devices. [1] Ma, R. et al. Nano Lett. 17, 5291 (2017); T. H.Ly, et al. Nat. Commun. 7, 10426 (2016); Ly, T. H. et al. Nat. Commun. 7, 10426 (2016); Shehzad, M. A. et al. Nano Res. 9, 380 (2016).

Resume : 2-dimensional layered materials have opened a new era in the field of nanotechnology owing to their tremendous physical properties which are attributed to charge confinement in 2-dimensional plane [1]. These properties have been extensively exploited in the field of electronics, energy storage and catalysis for more than a decade. Physical and chemical vapor depositions (PVD, CVD) techniques have been used in order to synthesize these 2d materials, such as Graphene, MoS2 and HfSe2 etc., on large continuous area. Thin film synthesized from these two techniques has number of defects such as pin holes, strained lattice and grain boundaries. Out of these defects grain boundaries are inevitable to avoid and significantly effects electronic and mechanical properties of 2-dimensional materials [2,3.] However the presence of these defects doesn’t confine to synthesize thin films but the oxidation also induces irreparable damage. One example of this is Black Phosphorus which is an excellent semiconductor but it’s highly reactive nature poses a great challenge in its use. Liquid Crystal have been using in order to visualize gain boundaries and other defects in the past [4]. Here in this work we have used to study the grain boundaries of HfSe2 which was grown by RF sputtering followed by annealing in Selenium environment. Also we have successfully visualized oxidation on single crystal BP with the aid of Liquid crystal. We believe this work will prove fore-bearer in order to gain insight of these defects and to get defect free 2-dimensional materials. References : [1] Butler, S. Z.; Hollen, S. M.; Cao, L.; Cui, Y.; Gupta, J. A.; Gutiérrez, H. R.; Heinz, T. F.; Hong, S. S.; Huang, J.; Ismach, A. F.; et al. Progress, Challenges, and Opportunities in Two-Dimensional Materials beyond Graphene. ACS Nano 2013, 7, 2898–2926. [2] Huang, P. Y.; Ruiz-Vargas, C. S.; Van Der Zande, A. M.; Whitney, W. S.; Levendorf, M. P.; Kevek, J. W.; Garg, S.; Alden, J. S.; Hustedt, C. J.; Zhu, Y.; et al. Grains and Grain Boundaries in Single-Layer Graphene Atomic Patchwork Quilts. Nature 2011, 469, 389–392. [3] Shehzad, M. A.; Hussain, S.; Khan, M. F.; Eom, J.; Jung, J.; Seo, Y. A Progressive Route for Tailoring Electrical Transport in MoS2. Nano Res. 2016, 9, 380–391. [4] Shehzad, M. A.; Hussain, S.; Lee, J.; Jung, J.; Lee, N.; Kim, G.; Seo, Y. Study of Grains and Boundaries of Molybdenum Diselenide and Tungsten Diselenide Using Liquid Crystal. Nano Lett. 2017, 17, 1474–1481

Resume : The kinetics of defect formation and reduction dynamics of micron-sized defects created on chemical vapor deposition (CVD) grown graphene through scanning probe lithography (SPL) and pulsed laser two-photon oxidation (2-PO) are reported. CVD grown graphene was locally oxidized using either SPL or 2-PO and subsequently reduced making use of a focused beam of soft x-rays. During this whole process, the reduction dynamics was monitored using a combination of micro-Raman spectroscopy (micro-RS) and micro-x-ray photoelectron spectroscopy (micro-XPS). After x-ray reduction, the chemical and structural composition of the graphene can be identical to or different from the original graphene, depending on the supporting substrates used. By modelling the dynamics of conversion from C-O to C-C related bonds reduction process with coupled rate equations, the conversion from C-C to C=C bonds was found to be the limiting rate, and phenomena of redox similar to graphene oxide can be observed over a certain threshold of functional group concentration. More interestingly, under inert gas environment, the two photon process can lead to defect generation that results in ?forging? of two dimensional graphene into three dimensional shapes. The optical forging process is controllable and complex patterns can be fabricated through this techniques.

Resume : Revealing the properties of novel solid-state quantum emitters is crucial for a number of applications, ranging from quantum optics to biology. Quantum emitters (QEs) in 2D-materials have recently been discovered and defects in hexagonal boron nitride (hBN) has proven to efficiently supply single photons at room temperature with narrow emission lines and great photostability[1]. These QEs have been studied at different emission wavelengths and operating temperatures. Various mechanisms to create defects or modify the emission wavelength have been investigated. Nevertheless, up to date, details of the emitters? level structure remain elusive. Here,[2] we present a study of the energy level structure using photoluminescence excitation spectroscopy on single QEs. We varied the excitation wavelength, and monitored the emission spectrum and intensity through a fiber-coupled spectrometer and APDs in a HBT-configuration. The saturation curves for the emission lines indicate that the saturation intensity and the saturation count rate vary with excitation wavelength. Furthermore, our results show that bright single photon emission with high quantum efficiency is highly dependent on matching the excitation wavelength to the individual emitter. This is a strong indication that the level scheme is complex and cannot be described by simple two level systems. The excitation dependence of the emission thus allows us to gain further insight to the internal level scheme and demonstrate how to distinguish different emitters both spatially as well as in terms of their photon correlations. [1] Tran et al. Nature Nanotech. 2015, 11, 37-41 [2] Schell, et al Adv Materials 2018 (Accepted)

Resume : By contrast to the atomically thin graphene, the puckered structure of layered transition metal dichalcogenides (TMDs) enables the possibility of impurity interstitial. We recently demonstrated from density functional theory calculations that various elements are energetically favourable at interstitial sites inside single-layer TMDs. Interstitial doping has the potential to overcome experimental challenges related to chemical (i.e. adsorbed elements) and substitutional doping and present good chemical stability. Furthermore, the change in the physical and chemical properties of interstitial doped TMDs provides novel routes to tune carrier concentrations, improve its catalytic activity, lower contact resistance with metals, and increase its magnetic moment. We asses the possibility of interstitial doping in molybdenum and tungsten dichalcogenides with a large portion of the periodic table. The high-throughput simulations consist in the evaluation of the energetics of atoms adsorbed at various sites on the surface of TMDs compared to substitution and interstitial sites. We developed an automated analysis of the electronic structure based on the density of state capable of detecting band edges and defects in the band gap that allows us to showcase trends of doping across the entire periodic table. Both n-type and p-type semiconductors are predicted; n-type conduction can be achieved via interstitial doping with early transition metals or group V and VI elements while p-type conduction is predicted for interstitial doping with Mg, Sc, Al and In. Finally, we will discuss the extension of interstitial doping to other emerging puckered two-dimensional materials.

Resume : Two-dimensional (2D) semiconductor transition-metal-dichalcogenides (TMDCs) show appealing and unique electrical and optical properties including indirect to direct band-gap transition in monolayer crystals with strong optical emission at room temperature, which makes them ideal candidates for optoelectronic and photonic applications (1). The recent discovery of single photon emission in 2D materials at low and room temperature has triggered an intensive research of new procedures for the deterministic fabrication of such emitters (2). In a previous work we showed that WSe2 monolayers can be encapsulated with a dielectric film by pulsed laser deposition (PLD) without inducing modification of their photoluminescence (PL) emission (3). Here we report on the generation of defects in WSe2 monolayer flakes in order to modify their PL. The defects are induced upon deposition of ultra-thin Al2O3 layers by PLD (≤ 10 nm). The PL of the encapsulated WSe2 monolayers has been assessed by micro-PL studies at RT and 10 K. Our findings show that as a result of the PLD deposition the characteristic PL emission of the WSe2 monolayers can be tuned by varying the deposition conditions. We discuss the influence of the nature and concentration of the induced defects on the PL, and how these defects can be modified by varying the kinetic energy of the ions during deposition. (1) Bhimanapati, G. R. et al. Recent Advances in Two-Dimensional Materials beyond Graphene. ACS Nano 9, 11509–11539 (2015); (2) Grosso, G. et al. Tunable and high-purity room temperature single-photon emission from atomic defects in hexagonal boron nitride. Nat. Commun. 8, 705 (2017); (3) Martín-Sánchez, J. et al. Effects of dielectric stoichiometry on the photoluminescence properties of encapsulated WSe2 monolayers. Nano Res. 1, 1–16 (2017).

Resume : Liquid-flow-induced generation of electricity using graphene, particularly graphene-water interface, has received attention for energy harvesting. We have investigated the effect of graphene surface condition on flow-induced voltage generation, which is controlled by heteroatom doping. Here, we have obtained voltage generation from a single water droplet motion on graphene. Nitrogen?doped graphene shows three times higher voltage (220 mV) generation compared to pristine graphene (80 mV). In this case, surface is negatively charged by the unshared electron pair of nitrogen. A negative local charge at the graphene surface affects the inside of a water located on the top of graphene. Thus a local charge reduces the thickness of the electric double layer in water, resulting in the formation of a steep electric potential. The enhanced electric field is dragged by a moving droplet and results in a higher voltage being generated. Therefore, doped nitrogen contributes to enhance voltage generation from graphene-water interface. In addition, enhancing voltage generation by doping is advantageous in system and product design for water-flow-induced power generation.

Resume : Graphene, a single sheet of carbon atoms forming a honeycomb lattice (HCL). The T3 or dice lattice presents the same structure as HCL with an additional site at the center of each hexagon. The corresponding band structure presents the same one as HCL with an additional flat band at the Dirac point. An uniaxial strain on the T3 lattice induces a moving and a deformation of Dirac cones. At moderate deformation, the dispersion relation remain linear in all direction but for a suitable strong strain, the two Dirac points merge into a single one and the dispersion relation becomes quadratic in one direction and linear in the other direction, which is known as the T3 semi-Dirac model. We study theoretically the quantum transport in the T3 semi-Dirac model. We focus on the effect of the direction of the strain axis on the transmission across a potential barrier, on the conductivity as well as on the shot noise. Particularly, for an energy equal half the barrier hight, the barrier becomes nearly opaque when it is perpendicular to the strain axis and totally transparent in the other direction, i.e. the super Klein tunneling [1]. [1] D.F. Urban, D. Bercioux, M. Wimmer and W. Häusler, Phys. Rev. B 84, 115136 (2011).

Resume : Studying Hydrogen Evolution Reaction Activity on Nanocarbon Electrodes and Effect of Defects Yang Cao1, Milo Shaffer1 and Klaus Hellgardt1 1Department of Chemistry, Imperial College London In recent years, hydrogen has drawn increasing attention as a new energy vector, particularly in combination with fuel cells[1-2]. In order to obtain green hydrogen efficiently, via electrolysis using renewable electricity, high quality and inexpensive catalysts are required to promote the hydrogen evolution reaction(HER). Typically, precious metals(Pt, Pd) have been adopted as the main HER catalysts,due to their high cost and limited availability is a significant obstacle. Therefore, many types of catalysts based on non precious metal(Fe, Ni) has been developed to overcome this problem. Electrocatalysts must be supported on a conductive, porous frame work designed to optimize the flux of the various species involved. Increasingly, nanocarbons such as carbon nanotube(CNTs), graphene and carbon spheres are being deployed to build electrode support, exploiting their high electrical conductivity, unique porous network structure and the high accessible surface area. Doped heteroatoms introduced in the nanocarbon can improve the properties of the catalysts, either by direct catalysis or by synergistic interactions with the metal nanoparticle catalysts to expose more active sites, as well as increasing the electron density to promote HER. In this work, we focus on the origin of the HER activity on nanocarbons, exploting the effects of defects and crystalline perfection on electrochemical performance. We examine the electrode properties of a series of nanocarbon networks by CVs and LSV, and correlated the results to the electrodes’ microstructure collected by SEM, TEM, XPS, Raman and TGA. Keywords: hydrogen; nanocarbon; defects References [1] Turner, J. A. Science 1999, 285, 687. [2] Dresselhaus, M. S.; Thomas, I. L. Nature 2001, 414, 332. [3] Deng, J.; Ren, P.; Deng, D.; Bao, X. Angew. Chem., Int. Ed. 2015,54, 2100. [4]Zou, X. X.; Huang, X. X.; Goswami, A.; Silva, R.; Sathe, B. R.Mikmekova, E.; Asefa, T.Angew. Chem., Int. Ed. 2014, 53, 4372.

Resume : The radiation resistance of the perovskite-based solar cells (SC) based on semiconductors depends strongly on the structure of the cell interfaces. The presence of nanofractal interface leads not only to its excessive area, but also to the change of their electronic properties and, hence, radiation stability [1], associated with the decrease of the smoothing by radiation-stimulated diffusion of generated defects. The most important mechanism of the radiation defect formation is the Dexter-Varley mechanism (see [2]). Since this process is probabilistic, it is governed by the Debye frequency ωD and by the width of the zone of Tamm states ΔΕT, so that the destruction cross section is proportional to η~exp[-ΔΕT/(ωDh)] [2]. ΔΕT value is varied on the nanofractal surface: the Tamm zone width is larger on convexes and smaller on the cavities. This, in turn, leads to the conclusion that the probability of destruction of convex domains of nanofractal surface is greater Hence, the radiation-stimulated diffusion gives the smoothing of nanofractal structure of interfaces and degradation of perovskite-based solar cells, in particular, reducing their photocurrent. [1] B.L.Oksengendler, N.R.Ashurov, S.E.Maksimov et al .Appl. Solar Energy. 2017. 53(4). 326. [2] B.L.Oksengendler, S.E.Maksimov, M.B.Marasulov. Nanosystems 2015. 6(6). 825. [3] B.L.Oksengendler, V.N.Nikiforov, S.E.Maksimov. Doklady Physics. 2017. 62(6). 281.

Resume : Oxide Dispersed Strengthened (ODS) steels are considered to be a promising material for advanced fission and future fusion reactors due to their high radiation resistivity. The most common oxide for ODS steels is Y2O3, known for its high mechanical strength, temperature stability, chemical and erosion resistance. Introduced into the steel by mechanical alloying, followed by powder consolidation, yttria particles vary in size and shape. Atomic Tomography experiments confirmed the presence of yttrium and oxygen within the host iron matrix also in a form of solute atoms. Interacting with each other, Y and O solutes give rise to various nanoclusters. Along with relatively large ODS particles, these small nanoclusters determine stability of ODS steel. By means of the DFT method, as implemented in the computer code VASP 5.3, the most energetically stable configurations of small (1,2)Y/(1,2)O clusters have been found. For all calculated configurations full atomic optimization has been performed with the parameters of the 4×4×4 supercell kept fixed. Each configuration is uniquely described by the mutual distances between all the comprising impurities in terms of the nearest neighbors of the corresponding sublattice. Chemical bonding between V_Fe-stabilized Y and O solutes within the host Fe matrix has been analyzed by the Bader charge transfer calculation. The electron density redistribution has been visualized, with respect to neutral isolated Y and O atoms, and the host matrix.

Resume : The radiation-resistant oxide Al2O3, is one of the very important materials for applications in fusion reactors. In this work, we analysed the kinetics of the F-type center annealing after electron, heavy ions or neutron irradiation. All kimetics were treated as the bimolecular process with equal concentrations of the complementary F and Oi defects. Such process is controlled by the interstitial oxygen ion mobility, which is much higher than that of the F centers. The F center annealing begins at temperatures 500-700 K, when both F and F+ centers are practically immobile, due to the recombination with mobile Oi defects. It is demonstrated how the shape of the F-annealing curves is determined by two control parameters: Ea and effective pre-exponential factor and strongly depends on irradiation conditions. The appropriate migration energies were obtained from original and also available from literature annealing kinetics for electron, neutron and ion irradiated Al2O3 .The results obtained are compared with recent ab initio calculations of interstitial oxygen migration. Special attention is paid to a detailed comparison of diffusion-controlled F center thermal annealing in neutron, electron and heavy-ion irradiated Al2O3.

Resume : Cathodoluminescence (CL) spectra of the aluminum nitride nanotubes and nanoparticles, synthesized by using a highly nonequilibrium dc-arc plasma method have been measured at 80 K and room temperature (RT) under electron irradition with 10 keV energy. Low-temperature CL spectra of nanostructured AlN have been compared with those of the commercially available AlN powder. The significant difference between emission spectra of the three investigated samples has been established. Commercial AlN has been found to emit a band peaked at 3.47 eV which is commonly ascribed to oxygen impurities. Emission of the AlN nanoparticles is centered around 3.66 eV while CL spectrum of AlN nanotubes show complex character with at least three peaks at 2.2, 3.0 and 3.5 eV in the photon energy range of 1.8 – 3.8 eV. CL intensity of the nanostructured samples has been found to decrease significantly at RT, most probably due to a combination of non-irradiative relaxations at the surface, electron-phonon interactions and the reabsorption of the emitted light. CL of AlN-nanotube/CsI-scintillator composites has been also studied. Energy transfer via luminescence emission from CsI scintillator to AlN nanotube is demonstrated. Luminescence properties AlN nanotube/polymer composites were also studied and compared with those obtained for AlN nanotubes and nanoparticles.

Resume : A nanocrystalline copper thin film was irradiated with 1 MeV Kr ions in-situ in a TEM at ambient temperature. Grain boundary migration under the impact of ion bombardment was observed for grain boundaries of higher curvature while others seemed to remain stable. In one instance, contiguous grains of limited relative mis-orientation seemed to coalesce under irradiation, a process not often observed under irradiation. The impact of the initial grain size distribution on the occurence of such processes in this copper film is discussed in light of similar ion experiments done previously on nanocrystalline copper with different initial size distribution.

Resume : In order to design perovskite solar cells (PSCs) which are viable outside the lab environment, a detailed understanding of the various degradation agents affecting their performance must be established. Degradation of PCSs is known to be related to water vapour[1], as well as light in the presence of oxygen, where degradation is thought to be facilitated by ionic defects[2]. Potential relationships between these processes are not well understood. We describe our experiments to assess how the activation energies for ion migration are affected by introducing various partial pressures of vapour water content in the perovskite lattice under various temperatures, in order to verify theoretical assumptions that exist in the literature[3]. Subsequently, our experiments concerning the effect of ion migration and their accumulation near the electrode interfaces of PSCs under applied bias, will elucidate whether they foster the generation of O2- ions in the presence of oxygen, which are known to be a major deterioration parameter for the light and oxygen induced degradation of perovskite-based structures[4]. 1. M. L. Petrus, Y. Hu, D. Moia, P. Calado, A. Leguy, P. R. Barnes and P. Docampo, ChemSusChem, 2016, 9, 2699-2707. 2. N. Aristidou, C. Eames, I. Sanchez-Molina, X. Bu, J. Kosco, M. S. Islam and S. A. Haque, Nature Communications, 2017, 8, 15218. 3. U. Jong, C. Yu, G. Ri, A. P. McMahon, N. M. Harrison, P. R. F. Barnes and A. Walsh, J. Mater. Chem. A., 2018, 6, 1067-1074. 4. N. Aristidou, I. Sanchez‐Molina, T. Chotchuangchutchaval, M. Brown, L. Martinez, T. Rath and S. A. Haque, Angewandte Chemie International Edition, 2015, 54, 8208-8212.

Resume : Periodic metallic nanoparticles (PMN) allow a precise control of the interaction between emitters and the plasmonic effect. They can be produced by electron-beam lithography, which offers better resolution and precision in comparison to other techniques. PMN exhibit, at short period (less than the resonance wavelength) only localized surface plasmon resonance (LSPR), and they give rise to the so-called Plasmon Lattice Resonance (PLR) at long period (comparable to the resonance wavelength). These PLR appear, in addition to LSPR, near a Rayleigh anomaly of the array. This type of PMN structures are of a great interest for enhancing the emitter spontaneous emission and its directivity and coherence. In this work, we focus on the engineering of the plasmonic resonance peak of square PMN gratings of long period to obtain narrow linewidth plasmonic resonances at wavelengths around 550-650nm, the emission wavelengths of the most efficient organic emitter. For that, we fabricate and investigate a series of Ag-PMN structures with periods ranging from 150nm to 500nm. Experimental results indicate that PMN of periods 150nm to 200nm present a broad single LSPR peak for which only a near-field coupling is possible. For long grating periods (> 200nm), in addition to the LSPR peak, narrow peaks appear in the extinction spectrum and the grating mode exhibits a delocalized photonic feature. Thus, these PMN structures allow a strong far-field coupling with a narrow spectral width.

Resume : The doping of ceria with trivalent dopants is known to enhance its oxide ion conductivity, which is important for a number of applications such as solid oxide fuel cells, oxygen sensors and catalysis. Samarium (SDC) and gadolinium (GDC) doped ceria are known to display high oxide ion conductivity in the range of 600-800°C which is desirable for such applications. As nanostructuring of these materials becomes more prominent the behaviour of extended defects such as surfaces and grain boundaries is becoming more important. It has been suggested that the interfaces in these materials can result in reduced oxide ion conductivity; however, the majority of studies consider only the average effect of the interface and not the possible effects of different specifically defined interfaces. Despite their importance, there is little information about the effects of specific interfaces which is amenable to molecular dynamics simulations. Here, we employ a force field derived for a range of trivalent dopants in ceria from ab initio data, a dipole polarizable ionic model (DIPPIM). We have simulated and will discuss the effect of the specific tilt grain boundaries Σ3(111), Σ9(221) and Σ5(210) on the performance of SDC and GDC as oxide ion conductors. Interestingly, different behaviour is observed depending on which interface is considered. Oxygen vacancy segregation, and ionic diffusion parallel and perpendicular to the boundary are studied.

Resume : The addition of boron during growth of GaAs nanowires leads to consumption of the catalyst droplet, termination of vapor-liquid-solid (VLS) growth and subsequent sidewall growth. Boron-rich phases on the GaAs nanowire (NW) sidewalls, confirmed via Energy-dispersive X-ray Spectroscopy (EDS) measurements, indicate that this is due to a surfactant effect, which leads to a change in the adatom diffusion length on the NW sidewalls, and thus changes the growth dynamics. Electrical measurements indicate that the NWs show p-type conductivity, which can be attributed to boron antisite defects. The conductivity is high, with Ohmic contacts easily formed to NWs of 60nm diameter at a nominal B content of 0.22%, reaching a maximum at a nominal B content of 0.26%, before falling again while retaining Ohmic characteristics. These results are significant for the growth of B-containing III-V alloys, which are interesting for strain engineering in epitaxial heterostructures. In addition, they indicate a route to obtaining high p-type doping in GaAs nanowires, and further work should help elucidate the properties of the nanowires? modified surface chemistry.

Resume : The aim of the study is the investigation of the electronic structure of O vacancy (VO), O polyvacancy, interstitial O and Ta atoms, O-to-Ta substitution in Ta2O5 to clarify the trap nature responsible for the charge localization and transport. The simulations carried out for the ?-Ta2O5 168-atom supercell in terms of the DFT in Quantum-ESPRESSO code. The calculated bandgap of ?-Ta2O5 is 4.2 eV. All types of native defects, except for the O interstitial, form defect states into the ?-Ta2O5 bandgap. The value of trap thermal ionization energy 0.5 eV are comparable to the experimental ones 0.7-0.8 eV, and optical trap energy 0.9 eV for the VO indicate that the VO in Ta2O5 can act as the charge trap, and participate in charge transport. The width of density of states defect peaks indicate the charge localization in space. The electron localization on the VO in Ta2O5 is due to the polaronic effect. The negative charge distributed between the nearest Ta atoms and it reflects the bonding character of the Ta orbitals charge density. Its allows us to conclude that the chains of closely located oxygen vacancies in TaOx can act as a conductive shunt and participate in the resistive switching. Each subsequent O vacancy forms near the already existing one, and no more than 2 removed O atoms, related to Ta atom. The O polyvacancy forms a filled defective band in Ta2O5 bandgap. The work is supported by the Russian Science Foundation grant #17-72-10103.

Resume : The aim of the study is the investigation of the oxygen vacancy (VO) role for the stabilization of orthorhombic noncentrosymmetric (Pbc21) phase in Hf0.5Zr0.5O2 films. The simulations carried out in terms of the hybrid DFT using Quantum-ESPRESSO code for the four low temperatures Hf0.5Zr0.5O2 crystalline phases: orthorhombic ferroelectric (of-), monoclinic (P21c), orthorhombic oI (Pbca) and orthorhombic oII (Pnma). It is shown that the VO concentration increasing leads to the fact that the pressure range under which the of-Hf0.5Zr0.5O2 structure can exist is narrowed. It is concluded that high VO concentration has a negative impact on the ferroelectric phase stabilization even for thin Hf0.5Zr0.5O2 films. It is established that of-Hf0.5Zr0.5O2 with O vacancies in any concentration is not stable for bulk crystal at any value of external pressure in which the structure is able to exist. However, it is shown that VO have a positive impact on the stabilization of the centrosymmetric oII phase of Hf0.5Zr0.5O2. Thus, the presence of oxygen vacancies and polyvacancies not only does not contribute to the Hf0.5Zr0.5O2 ferroelectric phase stabilization, but also leads to the destruction of the ferroelectric structure. This is consistent with the hypothesis that the degradation ferroelectric response of FeRAM elements during repeated reprogramming, is caused by the oxygen vacancies generation. The work is supported by the Russian Science Foundation grant #14-19-00192.

Resume : The aim of the study is the ab initio simulation of the electronic structure of O-polyvacancies in different charged states for bulk monoclinic ZrO2. The simulations carried out in terms of the spin-polarized hybrid DFT in Quantum-ESPRESSO code using 96-atom ZrO2 supercell. It is energetically favorable to form the next oxygen vacancy (VO) close to existing one, and no more than 2 removed O atoms, related to Zr atom. The distances between neighboring VOs are in range of (4.06-4.26) Å. Electronic structures of charged oxygen polyvacancies are qualitatively similar to the known electronic structures of isolated VO. VO complexes form the electron-filled states in the band gap. The O polyvacancies in ZrO2 is the amphoteric defects and it can act as an electron and hole trap. The values of electron (hole) thermal and optical ionization energies of OV in different charged states are slightly (about 0.1 eV) increased (decreased) with the polyvacancy size growth. Consequently, the charge transport in nonstoichiometric ZrO(x<2), should be described by the same models with similar value of parameters as the transport ZrO2 with a low VO concentration. Spatial distributions of localized single electron in O polyvacancies are almost uniform. Thus, one can conclude that the VO chain in m-ZrO2 is able to form a chain of potential wells for electrons and act as a conductive filament in zirconia based ReRAM cells. The work is supported by the Russian Science Foundation grant #16-19-00002.

Resume : The allotropic transformations of carbon provide an immense technological interest for tailoring the desired molecular structures in the scalable nanoelectronic devices. Herein, we explore the effects of morphology and geometric alignment of the nanotubes for the re-engineering of carbon bonds in the heterogeneous carbon nanotube (CNT) networks. By applying alternating voltage pulses and electrical forces, the single-walled CNTs in networks were predominantly transformed into other predetermined sp2 carbon structures (multi-walled CNTs and multi-layered graphitic nanoribbons), showing a larger intensity in a coalescence-induced mode of Raman spectra with the increasing channel width. Moreover, the transformed networks have a newly discovered sp2–sp3 hybrid nanostructures in accordance with the alignment. The sp3 carbon structures at the small channel are controlled, such that they contain up to about 29.4% networks. This study provides a controllable method for specific types of inter-allotropic transformations/hybridizations, which opens up the further possibility for the engineering of nanocarbon allotropes in the robust large-scale network-based devices.

Resume : Structural and electronic modulation of titanium oxide nanomaterials induced by the co-introduction of fully disordered glass phase and oxygen vacancies can lead to remarkable advances in the electrode performance in emerging energy storage systems. We present the effective co-creation of fully amorphous nanofibers (NFs) composed of black TiO2-x and conductive carbons throughout the NF structure, and assess the materials as potential anodes in sodium-ion batteries. The black TiO2-x nanofiber is successfully prepared by electrospinning followed by a two-step sequential thermal treatment in different atmosphere. The NF electrode could deliver higher 2nd discharge capacity and an excellent kinetic performance even under high rates compared to that delivered by anatase (white) TiO2 NFs used as reference, because of (i) an inherent free volume in the glass phase corresponding to the enlarged Na+ sites, (ii) increased electrical conductivity (low bandgap) resulting from the presence of Ti3+, (iii) introduction of conductive carbon agents around the TiO2-x domain, and (iv) one-dimensional NF feature allowing numerous Na+ reaction sites at the electrochemical interface. We also elucidate the morphological and structural changes in the nanofibers after discharge and charge by ex-situ characterizations.

Resume : The development of nanotechnology and the urge of scale reduction of semiconductor materials have been creating new perspectives on the development of optoelectronic devices in which a nanostructure plays a fundamental role. Since carbon nanotubes were discovered by Iijima in 1991 great importance is given to de growth of nanostructures (nanowires, nanobelts, nanoparticles, quantum dots) and different approaches are commonly used to this purpose such as vapor-solid-liquid process (VLS), vapor-solid process (VS), Vapor-Solid-Solid process (VSS) and so forth. Within the nanostructured materials group we can quote Transparent Conductive Oxides (TCO) as an important class materials which can be synthesized in nanostructured form and have interesting electronic and optical properties which makes them interesting for applications in gas sensors, chemical sensors and field effect transistors. Antimony trioxide is a transparent conductive oxide that is commonly used as flame retardant but was recently synthesized in nanostructured form and presents important properties such as wide band gap (3.3 eV), great optical transparency and chemical activity as catalytic agent. Aiming to add data on electrical and optical properties of nanostructured Sb2O3, in this work, it was synthesized branched microbelts and nanobelts of antimony oxide through vapor-solid (VS) growth method associated with a carbothermical reduction process. The synthesized samples were characterized by using x-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman Spectroscopy and new data on the growth method, crystalline structure and quality, morphology and possible preferential growth regions on the synthetized samples were found. Samples were found to be orthorrombic with a possible preferential growth direction in [222] (Punctual group Fd-3m, PDF 01-072-1334). The examination of Raman selection rules in both orthorhombic and cubic samples revealed solid evidence on the presence of native defects, which we believe to be oxygen vacancies. Symmetric Schottky barriers were constructed to orthorhombic Sb2O3 samples and the main features of the devices such as barriers height ΦB = 0.44 eV and ideality factor n = 1.03 for Au/Ti contacts were found. The temperature-dependent resistance measurements show the expected behavior for semiconductor materials. Moreover, the electronic transport was found to be governed by the variable range hopping (VRH) in a wide range of temperatures (from 118 K to 418 K).

Resume : [FePt(15 nm)/Au(7,5 nm)/FePt(15 nm)]2x thin films were deposited by dc magnetron sputtering onto thermally oxidized Si(100) substrates at room temperature, using FePt alloy (99,95 %) and Au (99,9 %) targets. Post-annealing of the film samples in temperature range of 500°C – 800°C was carried out in flowing Ar and Ar + H2 (3 vol.%) atmospheres for 30 s, using a fixed heating rate of 10°C/s. Structural properties of the as deposited and post-annealed films were investigated by the grazing-incidence wide-angle X-ray scattering (GIWAXS) method. Magnetic properties were measured by superconductive quantum interference device-vibrating sample magnetometry (SQUID-VSM). It was founded, that H2 introduction into annealing atmosphere allows to reach high coercivity (21 kOe) after annealing at 600oC. Hydrogen presence leads to residual oxygen reduction from the heat treatment atmosphere and as a result to ordering process suppression. It was concluded that chemical ordering, texture formation of ferromagnetic grains and its size in our case are not determining factors for provision of coercivity high values because these properties were almost equal after annealing in both investigated atmospheres. Hydrogen incorporation into Au crystal lattice can lead to breaking of interatomic bounds and point defects formation. This effect could be related to acceleration of Au grain boundary diffusion into L10-FePt phase under mechanical stresses influence.

Resume : Nd:YAG laser operating at 1064 nm was used to irradiate, at different intensities, graphene oxide foils placed in vacuum and in air. The laser irradiated GO foils were analysed successively by using different techniques such as 2.0 MeV alpha particle Rutherford backscattering spectrometry, X-ray photoemission spectroscopy, optical absorption and SEM- EDX. In particular, in vacuum irradiated graphene oxide samples oxygen reduction has been observed with increment of the carbon composition. In air irradiated GO samples an increase in oxygen has instead been highlighted. Furthermore thermal and chemical effects are induced by the photon irradiation. Results will be presented and discussed. Acknowledgements The research has been realised at the CANAM (Center of Accelerators and Nuclear Analytical Methods) infrastructure LM 2015056 and has been supported by GACR project No. P108/12/G108. Z.S. was supported by Czech Science Foundation (GACR No. 16-05167S) and by specific university research (MSMT No 20-SVV/2017).

Resume : Graphene and its derivates, have attracted scientific interest in recent years due to their unique properties. This study is to explore the quality of synthesized graphene oxide and reduced graphene oxide foils under the irradiation of protons and helium ions of the same energy. The effects of parameters such as type of ions, their current and irradiation time is studied. The quality of large-scale fabrication of graphene oxide and reduced graphene oxide (rGO) is important for industrial and research applications of this materials. Characterization by UV-VIS and Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy are presented. Acknowledgements The research has been realised at the CANAM (Center of Accelerators and Nuclear Analytical Methods) infrastructure LM 2015056 and has been supported by GACR project No. P108/12/G108. Z.S. was supported by Czech Science Foundation (GACR No. 16-05167S) and by specific university research (MSMT No 20-SVV/2017).

Resume : Structural and compositional modification of 2D materials as graphene oxide (GO) are topical objects of nowadays study due to the many technological applications. Ion irradiation of graphene based materials started recently, as the method for surface properties improvement. Ion mass, energy and implantation fluence are crucial for GO electrical, optical and mechanical properties engineering. In this work, we focus on He and Ga ions varying in their mass, leading to the different electronic/nuclear stopping power ratio and thus differing in ion beam induced defects. GO was irradiated using 500 keV He+ and Ga+ ions with fluencies in range from 1014 to 1016 cm-2. The elemental composition of the GO irradiated surface layer was investigated using RBS and ERDA. The chemical composition, structural changes and optical properties of the GO foils were characterized by spectroscopy techniques including XPS, ATR-FTIR and Raman spectroscopy and the electrical properties were studied by using standard two point method. The ion beam analyses indicate deoxygenation and dehydrogenation of irradiated GO foils which depth and degree differs with mass of used ions as well as Ga depth profiles were followed and compared to SRIM prediction. XPS, ATR-FTIR and Raman spectroscopy revealed about the removing of oxygen functionalities and structural modification as a function of ion fluence and ion mass that lead to the surface resistivity decrease after ion irradiation in dependence on the ion fluence.

Resume : SYNTHESIS IN THE RADIATION FIELD AND LUMINESCENCE OF CERAMICS BASED ON MgF2 V. Lisitsyn1, A. Dauletbekova2, L. Lisitsyna3, M. Golkovskyi4, D. Musakhanov1, Zh. Karipbayev2, A. Akilbekov2 1National Research Tomsk polytechnic University Tomsk, Russia 2L.N. Gumilyov Eurasian National University, Astana, Kazakhstan 3Tomsk State University of Architecture and Civil Engineering, Tomsk, Russia 4Budker Institute of Nuclear Physics, Siberian Branch of RAS, Novosibirsk, Russia Samples of ceramics based on MgF2 with an activator introduced as tungsten oxide (WO3) and a co-activator in the form of lithium hydroxide (LiOH) were synthesized. After synthesis, the samples were annealed at 1000 °C for 7 hours. Excitation of the resulting ceramics by UV radiation and high-energy electrons leads to luminescence. in the 480 nm region. Photoluminescence and cathodoluminescence characteristics of the samples obtained before and after annealing were studied. Luminescence is excited by light in the 200-300 nm range. The luminescence spectra for photo- and electrons excitation are similar in the 480 nm region. Electron beams and optical radiation at 200 nm excite an additional luminescence at 715 nm. The possible nature of luminescence is discussed.

Resume : Iono- and photoluminescence characterization of radiation damage in oxide crystals induced by swift heavy ion irradiation A.Dauletbekova1, N.Kirilkin2, A.Akylbekov1, A.Seitbayev1, V.A. Skuratov2,3,4, Yu.G.Teterev1, M.Koloberdin5, M.Zdorovets5,6 1) L.N. Gumilyov Eurasian National University, Astana, Kazakhstan 2) Flerov Laboratory of Nuclear Research, Joint Institute for Nuclear Research, Dubna, Russia 3) National Research Nuclear University MEPhI, Moscow, Russia; 4) Dubna State University, Dubna, Russia 5) Astana Branch of Institute of Nuclear Physics, Astana, Kazakhstan 6) Ural Federal University, Yekaterinburg, Russia In this report we summarize results of high energy ionoluminescence (IL) experiments aimed at comparative studies of radiation defects and associated stresses in MgO and Al2O3 single crystals. These materials demonstrate different sensitivity to dense ionization effects. As known, swift heavy ions induce formation of latent tracks in alumina [1], while no tracks as well as no amorphization have been observed in magnesium oxide even at very high ion fluences [2]. Dose dependence of the IL spectra measured from Al2O3 during 1.2- 1.6 MeV Kr and Xe ion irradiation clear evidences different stages in damage and stress accumulation at fluences before and after ion track overlapping. Contrary, real-time examination of MgO at the same experimental conditions did not reveal the changes in the IL spectra which could be ascribed to mechanical stresses in the irradiating crystals. 1.V.A. Skuratov, J. O’Connell, N.S. Kirilkin, J. Neethling. Nucl. Instr. Meth. B326 (2014) 223. 2. T. Aruga et al. Nucl. Instr. Meth. B197 (2002) 94.

Resume : We herein systematically investigated the self-doping of titanium nanotube array (TNA) with respect to the physico-chemical properties and activities under photochemical (PC, UV or visible light), electrochemical (EC, potential bias of 1 V NHE), and photo-electrochemical (PEC) conditions. The self-doping of crystalline (anatase) TNA reduced the band gap to 2.4 eV (blue TNA), while the same sequence for amorphous TNA even further narrowed the gap to 1.4 eV (black TNA). Depth profiles of X-ray photoelectron spectroscopy indicated that the dopants (Ti3+) were exclusively located on surface for the blue TNA, whereas they penetrated into the bulk tube structure for the black TNA which was accompanied with quasi-permanent lattice distortion as confirmed by X-ray diffraction patterns. Therefore, the electrical conductivity in terms of donor density was found to be greater for the black TNA. The buffering intensity of the doping electrolyte switch the relative level of proton intercalation in comparison with oxygen vacancy formation, demonstrated by time-of-flight and dynamic secondary ion mass spectrometry analysis. Consequently, methylene blue degradation was mostly fastest on the black TNA (doped in buffer), particularly in PC (UV) and PEC (UV/visible light) conditions. In contrast, the black TNA doped in non-buffer solution showed the best activity in PC (visible light) owing to the oxygen vacancy propagation through amorphous structure. The blue TNA allowed greater photocurrents in PEC (UV) condition, which were in proportions to the molecular hydrogen generation. The results of this study would broaden the usage of TiO2 nanomaterials by tuning the physico-chemical characteristics depending on variable energy input scenarios.

Resume : As crystalline nanoporous materials, metal-organic frameworks (MOFs) are also known to contain several different types of defects throughout their structures. These defects inevitably affect the resulting performance of the material, and successful engineering of defects can lead to desirable modifications in MOF properties. In this study, we combine the concepts of linker vacancy and inaccessibility to propose a defect engineering scheme that can induce a significant gas uptake enhancement in MOFs. Inaccessible pores in MOFs can be interpreted as hidden adsorption sites yet to be exploited. Then, introduction of linker vacancy defects can create new diffusion pathways into these previously inaccessible regions, expanding the total volume available for adsorption. To test this defect engineering scheme, high-throughput computational screening of a large MOF database was first performed to identify MOFs containing inaccessible pores, with methane as the adsorbate of interest. Then, linker vacancy defects were modeled into the MOFs with methane inaccessible pores to study the resulting changes in their methane adsorption capacities. As a result, we successfully identified 13 MOFs that show significant improvements in their methane storage capacities with the introduction of linker vacancies, with the top candidate MOF showing a 55.6% enhancement in methane adsorption with just a small proportion of vacancy defects. This highlights rational defect engineering as a novel method to further control the pore geometry and topology of MOFs, which can be used to greatly enhance the performance of thousands of existing MOFs in the areas of gas capture, separation, and storage.

Resume : Nanomaterials of different types are of great interest now. Among them are layered nanowires, consisted of alternating layers of magnetic and nonmagnetic metals. Such wires demonstrated effect of “giant magnetoresistance” and could be used as a sensors. In this work arrays (ensembles) of nanowires, consisting of alternating layers of nickel and copper were obtained using method of template (matrix) synthesis. The method used in this work is based on the difference of the equilibrium potentials of metal deposition. Based on article, the optimal potentials for deposition of the Cu layer were chosen to be 0.8 V, and for deposition of the NiCu layer - 1.8 V. After electrodeposition, the matrix was removed, and we obtained an array of nanowires. After “freeing” from the host polymer matrix the obtained ensembles of nanowires were investigated using a scanning electron microscope (Fig.1). To confirm the presence of layers with different compositions, an elemental analysis was necessary. For this purpose, a separate NW was examined using a TEM (fig.2). As can be seen from fig. 2, the layers are clearly separated. Thereby confirming the possibility of obtaining heterostructural nanowires by this method, which was the main goal of the study. This work was supported by RFBR grant No. 15-08-04949.

Resume : We have calculated doping formation energy, the lattice distortion angle, and vacancy concentration after doping Y atoms in In3SbTe2 (IST) phase change material and predicted that the Y atom is an ideal dopant since the thermodynamic stability is improved due to negative formation energy. Though the ab initio molecular dynamics simulation of the Y doped IST (Y-IST) at high temperature (1200K), the energy difference between the amorphous and the crystalline IST is 0.26 eV/atom and that of the Y-IST is 0.18 eV/atom, which means that the phase transition of Y-IST from crystalline to amorphous is as fast as 2.83 times of that of the IST. Lattice images of the Y-IST also indicate that the maximum angular difference between the inter-planar angles of the IST and the distorted Y-IST is 1.98°, which is fairly well matched with 2.00° calculated by the density functional theory and vacancy concentration is also increased with the lattice distortion. Experimentally, it is confirmed that the lattice distortion causes fast set/reset operations of phase change memory and synaptic operations.

Resume : An important problem of optoelectonics is the creation of efficient CMOS-compatible light emitters for the wavelength range around 1.5 um. A possible solution of the problem is the formation of silicon dislocation structures with a D1 luminescence line using ion-beam technology. Unfortunately, the intensity of luminescence is insufficient for the practical application. One of the promising approaches to improve light-emitting properties is the application of ion doping, which leads to the change in defect-impurity atmospheres of dislocations. Another approach relies on using external gettering to exclude the impact of accidental impurities as centers of nonradiative recombination. In this report, the significant increase in intensity of dislocation-related photoluminescence and the upward shift of intensity maximum on the temperature scale (to 110 K) are achieved by a joint application of B implantation and external Al gettering for dislocation structures, synthesized by the implantation of silicon ions in n-type silicon with subsequent oxidizing annealing at 1100 C. The results can be implemented in the technology of silicon photonics as well as they are useful for understanding the origin of D1emission line. The research is supported by the Ministry of Education and Science of the Russian Federation (State Assignment No. 16.2737.2017/4.6), RFBR (17-02-01070) and the fellowship of the President of the Russian Federation (SP-1147.2018.3).

Resume : ZrO2(Y) is a promising switching material for memristors due to the presence of intrinsic oxygen vacancies forming conductive filaments. The self-consisted kinetic Monte-Carlo (kMC) simulation of electroforming in ZrO2(Y) film taking into account ion and electron motion and Joule heating has been for the first time realized. The conventional approach based on solving the heat equation is not applicable since the mean free path of phonons is larger than the characteristic dimensions of the modeled filament. Therefore, the kMC simulation of heating and its effect on the ion migration, as well as the calculation of electron current are carried out by solving the kinetic Boltzmann equation for phonons. The heating is provided by phonon generation under the electron transitions from higher to lower vacancy energy levels in the local electric field. It is found that a significant amount of energy is released, and the temperature can reach 800 K in the region of growing filament. This is equivalent to a decrease in potential barrier and increase in hopping frequency by six orders of magnitude compared to room temperature and permits to realize the filament growth at rather high value of energy barrier (~ 1 eV) for vacancy migration. At the same time, the greatest amount of thermal energy is released in the region of maximal field concentration located around the tip of the growing filament. The study is supported by the Russian Ministry of Education and Science (RFMEFI58717X0042).

Resume : The BAC model coupled to k.p theory and Pikus-Bir theory was used to determine the electronic properties of GaNxAs1-x-yBiy strained highly electronegativity alloys. This investigation was performed at room temperature in terms of electronic band structure, energy levels and spin-orbit splitting energies and with a bismuth and nitrogen concentrations range varying from 0 to 12%. The incorporation of a small N or Bi content affects the strain types and induces a large variation in the properties of these semiconductors. As results, we note essentially that, for strained GaAsBi and GaAsN ternaries, a significant reduction of the bandgap energy E_g^c of about 54 meV/%Bi and 99 meV/%N were found, respectively. In addition, the spin-orbit splitting ∆_(0 )^cwas increased by 39meV/%Bi for GaAsBi and decreased by 5meV/%N for GaAsN. On the other hand, for typical concentrations (x = 4% ; y = 5%) of strained GaNxAs1-x-yBiy, the energies E_g^c, ∆_(so ) and the valence band splitting VBS are equal to 0.66 eV, 0.54 eV and 17 meV respectively. Finally, we applied these results in the investigation of GaAs/GaN.03As.90Bi.07/GaAs and GaAs/GaN.02As.93Bi.05/GaAs single quantum well structures under compressive stress emitting at 1.3 and 1.55 μm./ Keywords: GaNAsBi/GaAs ; k.p theory ; BAC model; Strain structures ; 1.3 and 1.55 μm emissions

Resume : Dilute bismide-nitride compound GaNAsBi is a promising candidate for use in GaAs-based optoelectronics devices in the near-infrared region. In this work, we report results of the electronic band structure of GaNAsBi/GaAs strained multiple quantum wells (MQWs). The band structure was modeled within the 16-band anti-crossing model, envelop function formalism and Bir-Pikus theory in conjugation with k·p Hamiltonian method. This investigation was used to describe the optoelectronics properties behavior of these structures such as band offsets, subband energies, strength of inter-band transitions and absorption coefficient spectra. We show that absorption coefficient spectra of GaN.04As.91Bi.05/GaAs strained single QWs has two maxima respectively located at 5,24 104 cm-1 for Τ_(e1-hh1) and 6, 37 104 cm-1 for〖 Τ〗_(e1-lh1). In addition, we have presented the results of the GaNAsBi-based strained double QWs (DQWs). We have deduced that the combined effects of strained and coupling between two wells enhance considerably the absorption coefficient compared to uncoupled DQWs. Keywords GaNAsBi-based strained QWs, Double QWs and coupling, Bir-Pikus theory, Absorption coefficient Optoelectronics properties

Resume : Thin metal films can disintegrate into particles upon annealing at temperatures below the melting point. Similar effect was observed under ion irradiation. This process is referred to as solid-state dewetting and limits the service conditions of fuel cells, optical and microelectronic devices. Dewetting occurred under various conditions can also be used for film nanostructuring. These films in turn can be used as a template for the fabrication of nanowires and other structures through metal-assisted chemical etching of underlying substrate. Nano- and microstructured silicon, in particular silicon nanowires (Si NWs), attract attention due to their special electrooptical properties. Depending on the morphology, Si NWs are considered as promising materials for sensing, optoelectronics, photonics, photovoltaic, energy storage and biosecurity. In this contribution we describe modification of Au thin film deposited on Si substrate by monatomic Ta and molecular BF2 and PF4 ions at RT. Ion-irradiation-induced change in morphology of thin Au film on Si substrate will be discussed and effect of ion mass and nuclear energy deposited in the film and underlying layer will be revealed. Results of chemical etching of Si covered by various ion-beam-formed Au nanostructures by the metal-enhanced catalytic etching of silicon (MACE) will be shown. The effect of ion irradiation on morphology and photoluminescent properties of the obtained structures will be demonstrated.

Resume : Oyster shell wastage has created serious problem in disposal of the food processing industry and aquaculture. Researchers have been finding better management and application of oyster shells in nearly years. In the present work, oyster shells have been annealed to 1000℃ for in nitrogen/Air atmosphere for 1 hour and then ground into powder(OSP1000N/OSP1000Air). After annealing process, Calcium Oxide has been synthesized by the thermal decomposition of Calcium Carbonate contained in oyster shells. The main composition and impurities of obtained samples were characterized by XRD, SEM with EDX, XPS and ICP. Cathodoluminescence spectra of OSP1000N and OSP1000Air both showed a strong peak at 600nm (orange light). The luminescence mechanism due to point defects and structure defects in was discussed in this work.

Resume : Two-dimensional (2D) transition metal dichalcogenides (TMDs) have shown diverse electrical and mechanical properties. Especially, TMDs such as MoS₂ and WS₂ with S as chalcogens have been actively studied. In this study, we investigated the doping effects of Cl on electrical and optical properties of MoS₂ or WS₂ nanosheets via the vacancy sites of chalcogens. The device was doped using dichloroethane (DCE) as a dopant by dipping the devices into DCE. As the Cl ions fill the S vacancy of WS₂ and MoS₂, the device properties of the nanosheet channel are significantly changed, indicating the doping effects on the TMD layers. With the help of chlorine ions as dopants of WS₂ and MoS₂, various heterojunction devices could be obtained with different effects of stacking or doping processes.

Resume : GaN/AlN quantum dots (QDs) are promising for ultraviolet and visible light-emitting devices, infrared photodetectors and switches, and room-temperature single photon sources. Tunneling interaction between QDs and defects can influence on the carrier recombination dynamics, can lead to such effects as QD «blinking», and can create one of the nonradiative recombination channels. In this work we propose a model of carrier tunneling between GaN/AlN QDs and defects. Defects located in the AlN matrix, GaN QD material and at the GaN/AlN interface have been considered. The defect potential has been approximated by the zero-radius model for the tunneling probability calculations. Full integration over vibrational wave functions was conducted in the proposed model. The ionization energies of the defects and parameters of the configuration diagrams have been calculated by density-functional theory. The tunneling probability has a maximum when the difference between electron energy level in the QD and at the relaxed defect is equal to the defect vibrational relaxation energy in the corresponding charge state transition. At the electronic energies of the defect sufficiently far from this maximum the tunneling probability shows thermally activated growth with increase of the temperature, while near the maximum the tunneling probability shows a weak dependence on the temperature and slightly decreases with the temperature increase. This work was supported by RFBR (grant 17-52-04023).

Resume : Establishing the correlation between the structural defects and ZnO nanoparticles (NPs) properties is important with the view of the development of p-doped ZnO nanostructures controlled synthesis. In the present work N–doped and N, Ag–co-doped ZnO nanoparticles (NPs) were synthesized by laser ablation and post-irradiation processes in liquid. Several schemes were applied: sequential laser ablation of Zn and Ag in NH4NO3 solution as well as laser irradiation of the mixture of Ag and ZnO colloids. The crystal structure, phase composition of the NPs formed were examined by TEM, SAED, Raman, FTIR and XPS techniques. Laser ablation of Zn in NH4NO3 solution was shown to be suitable for ZnO N-doping while Zn-Ag-sequential laser ablation in NH4NO3 solution can be used for dual acceptor doping of ZnO with N and Ag. The introduced structural defects modify the photoluminescence (PL) properties manifested in the red shift and a suppression of band edge UV emission along with the intensification of the visible emission. It was revealed that laser treatment of the ZnO nanostructures by the second harmonic of the Nd:YAG laser improves the conditions of the introduction of N acceptors into the ZnO lattice with no observable change in the morphology of particles. This can be explained on the basis of incorporation of impurity levels by the dopant along with intrinsic defect such as oxygen vacancies in the band gap of ZnO.

Resume : The use of FePt films needs the decrease of the L10 phase formation temperature and control of easy c-axis magnetization orientation during heat treatment. Rapid thermal annealing (RTA) is a promising approach to form ordered L10 FePt films with pronounced (001) texture. The purpose was to investigate the effect of substrates (SiO2/Si(001), Al2O3 (10-10) ) on L10 phase formation and magnetic properties in [Pt(4.2 nm)/Fe(3.2 nm)]4 films. Multilayer films were deposited by magnetron sputtering on SiO2(100 nm)/Si(001) and Al2O3 substrates at RT. Heat treatment of the samples was carried out in N2(RTA) in the range of 500 - 800ºC for 30 s. The phase composition and crystal structure of the films were characterized by XRD, SQUID and AFM. On XRD of as-deposited [Pt/Fe]4 samples on Al2O3 substrate the (111) Pt peak appears while on SiO2(100 nm)/Si(001) substrate Pt-Fe solid-solution peak and satellites are exhibited due to different coefficient of thermal expansion and level of thermal stresses. It is established that the stress state affect on structure, L10 phase formation temperature and magnetic properties. The ordered L10 phase forms in [Pt/Fe]4 during RTA annealing at 600°C on Al2O3 substrate. Higher level of compressive thermal stresses in as-deposited films on SiO2/Si(001) substrate promotes decreasing of ordering temperature on 100°C as well as (001) texture formation. This is also reflected in greater values of coercivity in temperature range of 500-700°C.

Resume : Gallium-doped Tin Sulphide (SnS:Ga) has been grown by Chemical Bath Deposition (CBD) at different doping concentrations (0, 4, 6, 8, and 10 %). In this work we studied the intrinsic defect density and doping-induced defects by optical and electrical characterization of these films. The optical properties (absorption coefficient, refractive index, bandgap energy) were determined using Optical Transmission and Spectral Ellipsometry. The electrical properties (electrical conductivity, mobility, trap charge density) were studied by Microwave Transient Reflection (MWTC) and Transient Photoconductivity (TPC). We observe various growth-dependent parameters linked to modest Ga doping in the widening of the Urbach tail, the increase in microcrystallinity, and in the appearance of slow tails in the microwave transient data beyond the initial characteristic decay time of a few microseconds. Inverse Laplace transform of TPC data leads to a peak at 0.45 eV in the associated density-of-states distribution. Keywords: Microwave Transient Reflection, Electrical Conductivity, SnS:Ga Thin Films, Bandgap Energy

Resume : Molecular systems based on carbon nanostructures and polymethine dyes are widely used in different areas - nanoelectronics, solar energetics, photodynamic therapy ets. Irradiation can be effective tool for the controlled modification of electron, vibration, mechanical properties of nanocomposites. We have applied electron bombardment E=1,8 eV (absorption doses were 50, 150 MGy) in order to study behavior of photoluminescence properties of films based on fullerenes and base dyes. The steady-state photoluminescence spectra of nanocomposite has maxima at 520 nm (maximum in the pure dye film is at 480 nm, in fullerene film 720 nm). Two components short- and long living (150 and 2300 ps) for the luminescence decay of nanocomposite were detected. It was established that times of both components in the film C60-dye increase, especially long living component up to 2700 ps at absorption dose of 150 MGy. The behavior can be explained by creation of defects that leads to breaking of pi-conjugation in C60 molecular cage, change of intermolecular interaction and increase of electron-hole recombination time.

Resume : The development of present day nanotechnologies has significantly stimulated interest in efficient methods for obtaining cluster particles with different stoichiometry and in studying their fundamental properties [1]. Ion sputtering has a series of advantages over other ways of cluster generation because it allows one, by celecting the sputtered material and kind of bombarding ions, to obtain clusters that are hard to synthesize by other methods [2]. In this work we have made some approcsimation for developing method – defect mediated colloid (cluster ) formation in thin films of alkali halogens [3]. Processes of the defect formation in thin LiF films on Si(111) under the bombardement by electrons with the energy within the range of 12-32 eV have been investigated by the method of total current spectroscopy. It has been shown that with increasing of the energy and dose of the electron irradiation the concentration of colloid (cluster) centers in 1.6±0.2 eV increases. It has been studied influence of the irradiation temperature and annealing temperature on size and number of colloid centers. The colloid concentration decreases with raising the irradiation temperature from 20 to 3000 C. Sizes of colloidal centers have maximal value at annealing temperature in range of 350-4500 C. Negative charge accumulation on LiF surface has been revealed after the electron irradiation of the film. Also the influence of the target temperature in the range of 25-4000 C on formation of point defects in thin LiF/Si(111) films under bombardement by low energy electrons (Ep=20 eV) have been investigated . It was shown that with increasing target temperature the concentration of the X- and colloidal centers increase. The mass- spectrometric analysis of cluster sputtering the LiF surface by Cs with energy 0.1-3 keV have been shown that positive charged cluster ions of Lin (n=1-3) and negative ion clusters Fm- (m=1-4) were observed. With increasing temperature the formation of the large clusters have been found.

Resume : In this paper, for the first time we present an experimental results on the composition and the electron density of valence electrons of a free Cu (100) film with a surface nanofilm Si of various thicknesses (dSi ≈ 50-500Å). In all cases, the film thickness of Cu(100) was ~ 450Å. The investigation was carried out using the methods of CEELS, AES and the spectroscopy of ions passed through the films. Before measurement, each sample was degassed for 2-3 hours. The results of experiments obtained by the CEELS method have shown that at a thickness dSi≈50Å, the height of the peak of the bulk plasmon of copper decreases sharply and a new peak of the bulk plasmon characteristic for the metal silicide appears. At the same time, there are practically no Si peaks on the spectrum. At a thickness of the silicon film of 100Å, the peaks of the surface and bulk (ħωs and ħωv) plasmons, characteristic of pure silicon, appear on the spectrum. With increasing, a film thickness from 100 to 200Å, the intensity of the surface silicon plasmon peak does not change appreciably, and the volume plasmon increases to 1.5 times. At dSi≈50Å, all Si atoms mixing with copper atoms form a compound of the CuxSiy type. At dSi >50Å with increasing thickness, a silicon film is formed on the surface of this silicide. The profiles of the silicon distribution in depth for the Si-Cu system (dSi≈400Å) were obtained by the AES method in combination with ionic etching. It is shown that due to the interdiffusion of Si and Cu atoms at the Si-Cu interface, a transition layer of silicide CuxSiy with d≈100-150Å . The spectra of past Na+ ions (E0 = 18 keV) for a copper film with d≈450Å and for copper with a silicon film dSi ≈ 50Å and dSi ≈200Å were obtained. In the case of ultrathin films, epitaxial growth of silicon does not occur on the Cu (100) surface.

Resume : In this work are researched the processes of Si/SiO2/Si system formation on the bombardment of Ar ions. SiO2 film, obtained Si (111) by thermal oxidation in the atmosphere of dry oxygen at a temperature of about 1250 K. SiO2 film thickness was about 60 nanometers. Before the bombardment, SiO2/Si (111) films were degenerated in a high vacuum (10-6 Pa) at Т = 1200 K for 4-5 hours. The SEM results showed that the surface of the film structures is characteristic for polycrystalline samples. The width of the band gap was about 8 eV. The study of the dynamics of changes L23VV Auger-peak oxide silicon with E=76 eV at bombardment SiO2 with different doses of Ar ions at E=1 keV showed that for ion bombardment occur decomposition SiO2 on the components and partial evaporation of oxygen from the surface. At low doses ions (D = 5•1014 см-2) get on the individual film sections. After the heating in T = 1000 K for 30 min. fully sets the L23VV Auger-peak of the clear Silicon. The thickness of pure Si silicon films is 15 – 20 Å, the thickness of the SiOx transition layer is 30 – 40 Å. In this case, the spectrum contains very weak peaks of SiO2 and SiOx, which may be due to the release of Auger-electrons from the surface layers of the Si/SiO2 system. Further increase in the energy of Ar ions to 2 keV led to a practical smoothing of these peaks.

Resume : ON/OFF operations of flash memory with floating gate are driven by tunnel injections of electrons and holes via thin 1.8-8.0 nm (tunnel) SiO2 layer. The current via the tunnel oxide during ON/OFF operations by applying strong (≈10 MV/cm) electric field in the oxide increases the conductivity of the layer at low fields (≈1 MV/cm). This is caused by the additional current components via the tunnel oxide. This phenomenon is called Stress Induced Leakage Current, SILC. The SILC limits reprogramming cycles number of the flash memory cells, leads to accelerate the charge draining the flash during data storing. Despite the fact that the SILC study is a subject of numerous articles, the nature of the phenomenon is still a debatable issue. This study describes evolution of the transport in SILC with a decrease in SiO2 thickness. The SILC and transport measurements @25-70°C were performed on FET transistors with the floating gate, manufactured using the 180 nm design rule technology. The p-Si substrate and the n+-type poly-Si floating gate were used as the contacts. The tunnel SiO2 layer thickness was 2-8 nm. The charge trap parameters were estimated using ab initio simulation within the scope of DFT+B3LYP hybrid functional. It was found that in (3-8)-nm-thick SiO2 the transport in SILC mode is limited by phonon-assisted tunnelling between traps, wherein the charge flow via SiO2 generates oxygen vacancies, increasing the leakage currents. In 2-nm SiO2 trap-assisted tunneling works.

Resume : Recently, ferroelectric properties were discovered in based on hafnia thin films. Of particular interest is the fact that ferroelectricity was also demonstrated in thin solid solutions HfZrO which synthesis conditions are compatible with the CMOS technology. Ferroelectricity in HfZrO is associated with the ability to stabilize Pbc21 phase. Considering the advantages of FRAM, the discovery of ferroelectric effect in HfZrO gave an impetus for the development of the universal memory concept which may lead to a significant breakthrough in the development of memory devices. Unsolved problems in the way of FRAM development are the reason of memory window (MW) reducing, e.i. fatigue. One of the possible reasons for these effects is the presence of defects in HfZrO films. The aim of this work is studying the charge trap density evolution in ferroelectric HfZrO after on/off cycling. Using experiments on transport TiN/HfZrO/TiN structures, P-V plates and leakage currents were extracted and analyzed in terms of defect presence after 1-10^8 on/off cycles. Is was found that as soon as the MW began to decrease, the distance between traps (oxygen vacancies in this case) also began to fall decrease. Two possible models were suggested to explain our results: a model of O-vacancy killer and depol pinning on trapped charges. Both models were supported by ab initio simulations of defects in Pbc21 phase of HfZrO. The work was supported by the Russian Science Foundation, grant #14-19-00192.

Resume : Hafnia-based high-? dielectrics are used in MOS devices, perspective RRAM and FRAM cells, dopand of ceramics in teeth prosthetics. The electronic properties of HfO2, such as leakage currents and luminescence, are defined by traps and defects. The trap presence increases the conductance of dielectric, electron or hole localization on traps shifts the threshold voltage and leads to the MOSFET degradation. In active layers of RRAM, traps act as precursors of a filament during the HRS/LRS switch. The trap density ?10^22 cm^-3 is a huge for degeneration of devices, but is very low for analytical methods. Recently, it was reported that comparison measured J-V dependences with multiphonon transport models allows extracting the trap (oxygen vacancy, VO) density in the HfO2. In the study, we try to get correlations between the trap density and optical properties of hafnia films. Variation of the trap density in HfO2 was supported by different conditions of film synthesis using ALD technique and different precursors: TEMAH H2O and Hf(thd)4 O2. Dispersion dependencies of refractive index were measured by spectral and laser ellipsometry. Also, cathodoluminescence spectra were measured. It was found that the refractive index grows as films are depleted of oxygen. The intensity of the blue CL band (2.6-2.7 eV) depends on the VO density non-monotonically, exhibiting a pronounced maximum at ~10^21 cm^-3. The work was supported by the Russian Science Foundation, grant #16-19-00002.

Resume : Two-dimensional (2D) molybdenum sulfide (MoS2) is one of the most widely studied transition metal dichalcogenides for the various potential low-dimensional device applications such as, logic devices, optoelectronic. However, the intrinsic physical and chemical properties of the 2D-MoS2 are very subjective to adsorbents and surface oxidation. Therefore, it is important to understand the correlation between surface chemical state and physical properties of the 2D-MoS2 for better usages in near future. In this presentation, we showed the experimental results of the correlation between the surface chemical state and work function of MoS2 under various annealing environments. Specifically, MoS2 was annealed under various temperatures (RT ~ 350 oC) in O2 (1 mbar) + Ar (1 mbar) environment and in-situ monitored using the ambient pressure X-ray photoelectron spectrometer. As a result, we found that surface oxidation of MoS2 was unchanged. On the other hand, the work function increased owing to the decrease in carbon/H2O contamination from RT to 200 oC. Further increased temperature, the MoS2 transformed into MoO3, resulting in the increased work function. At 350 oC, MoS2 completely disappeared and MoO3 was formed. Therefore, the variation of work function was associated with degree of surface oxidation of MoS2. This work is supported by NRF-Korea (NRF-2015R1D1A1A01058672 and NRF-2017K1A3A7A09016305) and Korea Basic Science Institute Research Grant (C38116). *E-mail: psk@pusan.ac.kr

Resume : In this presentation, we show the correlation between the interfacial strain and the insulator-metal-transition (IMT) of VO2 films. The (020) oriented epitaxial VO2 films were grown on Al2O3(0001) using RF-magnetron sputtering at various deposition time to obtain different interfacial strain state. As deposition time increased, the in-plane (out-of-plane) compressive (tensile) strain decreased from -1.64 % (0.23 %) to -0.21 % (-0.04 %). Furthermore, IMT temperature shifted to higher temperature with decreasing the interfacial strain. From the local structure analysis, we found that a V-V chain length was more sensitive to the interfacial strain than an apical and equatorial V-O bond length. According to the DFT calculations, the d*// orbital occupancy was shifted to the Fermi level with increasing the V-V chain length suggesting, the shift of transition temperature. In addition, the variation of d*// orbital occupancy was also experimentally confirmed by polarization-dependent X-ray absorption spectroscopy. These results provide a better understanding of the interfacial strain induced IMT mechanism. This work is supported by NRF-Korea (NRF-2015R1D1A1A01058672 and NRF-2017K1A3A7A09016305) and Korea Basic Science Institute Research Grant (C38116). *E-mail: psk@pusan.ac.kr

Resume : In present work we consider features of direct and indirect excitation of erbium ions and their spectral-luminescence properties in Gd2O3 nanoparticles – material that is promising for developing of new generation of UV radiation convertors. One of the main advantages of Gd2O3:Er system is that there is no need to introduce into the matrix the ions acting as donors of excitation because this role is played by intrinsic defects of host lattice – irregular Gd3+ ions which provide a new channel for radiation conversion via Gd3+→Er3+ energy transfer. We reveal two types of non-equivalent Gd3+ donor centers with non-discrete optical parameters by analysis of temperature behavior of Er3+ acceptor’s luminescence. The energy transfer efficiency as well as the quantum yield of emission under UV-visible conversion are estimated. The thermal activation barrier for realization of non-radiative transitions takes a larger value for nanoparticles with a lower concentration of Er3+ ions (1%). It indicates that the conversion of UV radiation in such nanoparticles occurs with improved efficiency due to the small thermal losses.

Resume : Defects like vacancy could affect many kinds of physical properties of material. It could tailor the band structure, which could enhance the conductivity and broaden the range of absorption for better photocatalytic performance. On the other hand, the presence of oxygen vacancies could increase or worsen the recombination rate of electron-hole pairs, which also affects the efficiency of some photocatalytic reactions. The challenge for the inefficiency in water splitting caused by photoresponse range and recombination rate of electron-hole pairs could be significantly improved by controlling the oxygen vacancy. In this work, we control the concentration of oxygen vacancy by varying vacuum level in the synthesis system. The type II heterostructure of SnO2/In2O3 was synthesized in low vacuum furnace and ultrahigh vacuum (UHV) system, respectively. X-ray photoelectron spectroscopy, photoluminescence measurement and absorption spectrum were used to investigate the effect of amount of oxygen vacancy with different vacuum level treatment. The fundamental nanostructures of these heterostructures were also well analyzed by TEM. Moreover, the appropriate condition of the structure formed in UHV environment could be chosen with in siu TEM observation. The amount of oxygen vacancy is correlated to the efficiency improvement in hydrogen production measured by gas chromatography.

Resume : In the present study the formation, structure and electronic properties of MoS2(1-x)Se2x monolayer alloy are investigated within DFT framework. For MoS2(1-x)Se2x monolayer alloy substitution rates (x) from 0 to 1 are considered. Different distributions of the substitution atoms (Se in MoS2 matrix) in the supercell of MoS2(1-x)Se2x alloy have been studied. The analysis revealed that the most likely structural arrangement of atoms (Se, S) in alloy during the synthesis is a structure with a symmetric filling of the top and bottom chalcogen planes. A detailed analysis of the formation energy of the alloy demonstrated that the range of substitution rate x splits on the region with a negative (x <0.65) and positive (x> 0.65) formation energy of the alloy. The fundamental and optical band gap of MoS2(1-x)Se2x monolayer alloy were calculated using recently proposed GVJ-2e method. The GVJ-2e fundamental band gaps of the alloy are in the range of 2.39 eV – 2.12 eV (GVJ-2e fundamental band gaps of MoS2 and MoSe2 monolayers). The electron states were analysed and effective masses of the electrons and holes of the MoS2(1-x)Se2x alloy have been calculated from Kohn-Sham band structures. It is shown that the physics of the formation of MoS2(1-x)Se2x alloy is well described within the framework of the percolation theory.

Resume : We study electronic and transport properties of (un)strained graphene with struc-tural imperfections: point and extended (line) defects. Point defects are modelled as resonant (neutral) adsorbed atoms or molecules, vacancies, charged impurities, and local distortions. Line defects are attributed to atomic steps and terraces in epitaxial graphene, and grain boundaries, nanoripples or wrinkles in polycrystalline gra-phene. Results are obtained numerically using the quantum-mechanical Kubo?Greenwood formalism and tight-binding approach. Calculated behaviours of elec-tronic density of states and conductivity indicate that deviations from perfection can be useful: they make possible tailoring graphene electrotransport properties for achievement of new functionalities. Particularly, the ordering of point defects can open a band gap in the energy spectrum of graphene, enhance its conductivity up to dozens (10?30) of times; and orientation correlation of linear defects can increase the conductivity up to 4?5 times. If there are both types defects, their ordering and correlation may improve the conductivity up to hundreds of times as compared with their random distribution. Effective manipulating the band gap in the uniaxially strained graphene requires balanced content of ordered dopants: their concentration should be sufficient for a significant sublattice asymmetry effect, but not so much that they may suppress the band gap or transform it into the ?quasi- (or pseudo-) gap?.

Resume : Dr. Neretina?s laboratory has developed a new synthetic procedure for generating periodic arrays of metallic nanostructures shaped as hexagonal or triangular nanoplates using a room temperature light-activated growth mode. Such structures have the potential to act as the active components for the detection of biological and chemical analytes using various sensing modalities (e.g., Surface Enhanced Raman Scattering (SERS)). The synthesis is reliant on the formation of Au seeds exhibiting planar defects ? without such defects the growth mode is deactivated. Through the engineering of defects, which have been extensively studied using Titan TEM imaging and electron diffraction, such structures have now been produced in high yield.

Resume : In recent years, research in two-dimensional (2D) transition metal dichalcogenides (TMDs), has flourished for their potential in replacing traditional semiconductors in novel nano-and optoelectronic devices. In particular, MoS2 has received much interest because of superb properties. Obviously, technological application will require synthesis of large-area high quality 2D layers. Not different from other semiconductors, the performance of such layers in devices crucially depends on controlling structural defects in the crystal lattice, making defect characterization indispensable to enable progress. Here, electron spin resonance (ESR) arises as an exclusive tool for selective atomic identification and quantification of defects. This is shown here by successfully applying, for the first time, ESR on few-layer (3 - 6) MoS2 grown by large-scale chemical vapor deposition (CVD), and subsequently transferred onto SiO2, revealing a pristine nearly isotropic signal of g ≈ 1.9996. Based on a comprehensive comparison of the signal properties with first principles simulations and previous ESR results on geological and synthetic MoS2 grown by sulfurization, the newly observed signal can be tentatively assigned to an intrinsic defect, likely a Mo or MoS3 vacancy at grain boundaries. The defect is present with a relatively high density of ~ 2.7 x 1011 cm-2, raising the importance of its characterization as it will pose an intolerable threat to the carrier mobility of the 2D material.

Resume : Photocatalytic solar fuels production represents one of the most potential strategy for replacing the dying-up fossil feedstocks and dealing with the environmental problems caused by the combustion of fossil fuels. However, this technology has not been widely applied because of its low solar energy conversion efficiency which is usually limited by the microstructure and the electronic structure of the semiconductor photocatalysts. After more than 10 years studies on this area, we found well designed defect-rich atomic scale materials have peculiar advantageous as high performance photocatalysts for N2 or CO2 reduction under ambient conditions. Here we systematically present a discussion in detail on the relationship between the crystal microstructure, the electronic structure and the photocatalytic performance which is apparently affected by the light response, charge carrier separation/migration, and reactants activation etc. The material is focused on atomic scale bismuth, tungsten, and molybdenum based semiconductor material. Their facile synthesis process will also be introduced.

Resume : The unique properties of semiconductor nanowires (NWs) give these nano-building blocks an outstanding potential for electronic, photonic, mechanical, biological, and energy-conversion applications. In the case of GaAs NWs, it is well-known that their optical and electrical properties are strongly influenced by the simultaneous occurrence of zinc-blende (ZB) and wurtzite (WZ) crystalline structures along the NW’s axis. Doping is another crucial issue for NWs applications. In this work, we study the effect of Si doping on the electronic structure of GaAs NWs grown on GaAs (111)B substrates by molecular beam epitaxy, with four nominal Si doping levels (nominal free carrier concentrations of 1x1016, 8x1016, 1x1018 and 5x1018 cm-3. Using a vast collection of techniques, X-ray diffraction, cathodoluminescence, transmission electron microscopy and photoluminescence, we demonstrate that the presence of fluctuating potentials, mainly along the NW’s axis for the samples with higher doping levels, drastically decreases the influence of polytypism on the electronic structure. Such decrease prevents the localization of charge carriers at the WZ/ZB interface. Furthermore, these modifications induced by the increase of the doping level are deeply discussed in the scope of the fluctuating potentials model. The electronic structure of highly Si-doped GaAs NWs as well as the observed increase of the luminescence intensity open up new optoelectronic applications based on III-V NWs.

Resume : Fine-grained materials, such as thin ZrO2 films, differ from bulk materials of the same elemental composition because of the large contribution from the structurally defective surface of nanocrystals in relation to their inner regions. ZrO2 in nanocrystalline form and in stabilized cubic phase can exhibit enhanced ionic conduction, high dielectric permittivity and be magnetized nonlinearly in external fields. In connection with the demand for materials, which could be applied in the novel memories because of their advanced magnetic and electric properties, five-layer structures consisting of alternately deposited ZrO2 and Co3O4 films were constructed in this study. The films were grown by ALD at 300oC from ZrCl4, Co(acac)3 and O3. All the films were crystallized in the as-deposited state. The multilayered structure was well-defined with interfaces between constituent, chemically and structurally distinct, layers. The dominant phase observed was the cubic ZrO2 polymorph. The performance of the laminate films was dependent on the relative content of constituent oxide layers. The magnetization in these films was nonlinear, saturative, and with very weak coercive fields. Electrical measurements revealed the formation of significant polarization vs. external field loops, probably markedly influenced by interfacial polarization. Current-voltage measurements implied some tendency towards memristive behaviour with characteristic switching between lower and higher resistance states.

Resume : The perpendicular magnetic anisotropy (PMA) at the FeCo/MgO interface is the basis of the perpendicular magnetic tunnel junction (pMTJ) used in spin-transfer-torque magnetic random-access memories (STT-MRAM) [1]. Improved STT-MRAM switching efficiency is expected by setting an easy-cone anisotropy in the pMTJ free-layer [2]. Such an easy cone requires a second-order PMA term, K2<0, alongside a first-order K1>0, and has been observed in MgO/FeCoB/Ta stacks within a narrow range of FeCoB thicknesses [3]. While K1 stems from Fe-O orbital hybridization [1], K2 likely emerges from structural and magnetic inhomogeneities such as fluctuations of K1 [3]. All those structural properties, and thus the PMA, may be modified by ion irradiation [4]. Here, we demonstrate the control of the anisotropy direction in MgO/FeCoB/X/FeCoB/MgO (X = W or Ta) free-layers by 400 keV Ar+ irradiation. Ferromagnetic resonance revealed a linear decrease of K1 with increasing Ar+ fluence up to 10^15 cm-2, caused by elemental mixing at the FeCoB/MgO interfaces, which allowed us to induce easy-cone states in free-layers initially with an out-of-plane anisotropy, without increasing the damping. Underlying irradiation-induced structural effects before and after post-irradiation annealing will also be discussed. [1] Rev. Mod. Phys. 89, 025008 (2017) [2] Phys. Rev. B 95, 184409 (2017) [3] Phys. Rev. B. 96, 014412 (2017) [4] J. Phys. D: Appl. Phys. 37, R179 (2004)

Resume : Effects of strain on the Raman scattering and X-ray diffraction in Ge-Sn epilayers F. Oliveira1, A. S. Vasin2, M.F. Cerqueira1,3, E. Alves4, S. Magalhães4, J. Schulze5, M. I. Vasilevskiy1,* 1Departamento de Fisica, Universidade do Minho, 4800-058 Guimarães, Portugal 2Department of Physics, N. I. Lobachevsky University of Nizhny Novgorod, Nizhny Novgorod 603600, Russia International Iberian Nanotechnology Laboratory, 4715-330 Braga, Portugal 3International Iberian Nanotechnology Laboratory, 4715-330 Braga, Portugal 4ITN, Lisboa, Portugal 5Institut für Halbleitertechnik, Universität Stuttgart, Pfaffenwaldring 47, D-70569 Stuttgart, Germany *Corresponding author: fcerqueira@fisica.uminho.pt Group IV based crystalline semiconductor alloys GeSn and GeSnSi have been the object of intense research in the 21-st century. The interest is related to the possibility of making a silicon-compatible direct band gap material with controlled lattice constant and band gap energy. These achievements would allow for the development of new optoelectronic devices, such as infra-red photodetectors, quantum emitters and modulators, which are the necessary ingredients for integrated photonics. In this work, the structural properties and strain states of SnxGe1-x alloy layers grown by molecular beam epitaxy are studied both experimentally and theoretically. X-ray diffraction (XRD), Raman spectroscopy and Rutherford backscattering spectrometry will be used for this study. In particular, XRD data were used to evaluate the strain components. Raman spectroscopy yielded the positions of characteristic phonon modes, which are influenced by two effects: (i) local atomic environment of the vibrating atoms, and (ii) strain. Their relative importance has been analysed and will be discussed in the framework of an appropriate theoretical consideration based on the Tersoff empirical potential model. The calculations provide vibrational Raman spectra of SnxGe1-x crystalline alloys as well as statistical distributions of bond lengths and angles between adjacent bonds. Using this approach we have able to evaluate the tin-content-dependent shifts due to the local environment and strain effects observed in the Raman spectra and compare them with our experimental results.

Resume : Defect states in semiconductors have a range of possible uses arising from their light emission properties. For example, the well-known NV- defect in bulk and nano-diamond [1] provides a source of quantum emission that is becoming a key component in many quantum technologies. Understanding the atomic origin of this emission has required advances in both the experimental and theoretical domains. The recent discovery of single-photon emission from hBN [2] has generated considerable interest and efforts are underway by a number of groups to characterise the spectroscopy of this emission [3]. The most widely used approach to this problem computationally is to use Density Functional Theory based methods offering a good balance between computational expediency and reliability. The HSE06 functional reproduces bandgaps in semiconductors well and, combined with methods to constrain orbital occupation, is perhaps the most favoured approach for calculating defect excited states. In this paper we evaluate the performance of DFT methods by benchmarking against high level coupled-cluster and multi-reference methods. Many of the electronic states for these defects are inherently multi-reference open-shell and closed-shell states and involve broken chemical bonds and charge-transfer states. We find that some DFT methods can perform very poorly, for example PBE. HSE06 works well for excitations among the triplet states but underestimates triplets relative to closed-shell singlets, and fails with regard to open-shell singlet states. Long-range corrected functionals such as CAM-B3LYP perform much better, but their implementations so far have been restricted to non-periodic codes. We also show that there can be significant differences between cluster and periodic-slab models of these defects implying that implementation of such functionals in periodic codes is needed. This work was supported by resources provided by the National Computational Infrastructure (NCI), and Pawsey Supercomputing Centre with funding from the Australian Government and the Government of Western Australia, as well as Chinese NSF Grant #1167040630. SA acknowledges receipt of an Australian Postgraduate Award funded by ARC DP 150103317. Funded is also acknowledged from ARC DP 160101301 [1] For example, M W Doherty, N B Manson, P Delaney, F Jelezko, J Wrachtrup, L C L Hollenberg, Phys Rep 528(1) 1 (2013) [2] T T Tran, K Bray, M J Ford, M Toth, I Aharonovich, Nature Nanotech, 11 37-41(2016) [3] M Abdi, J-P Chou, A Gali, M B Plenio, arxiv:1709.05414v1 (2017); M Abdi, M-J Hwang, M Aghtar, M B Plenio, Phys Rev Letts 119 233602 (2017); F Wu, A Galatas, R Sundararaman, D Rocca, Y Ping, Phys Rev Materials, 1 071001(R) (2017); S A Tawfik, S Ali, M Fronzi, M Kiannia, T T Tran, C Stampfl, I Aharonovich, M Toth, M J Ford, Nanoscale 9(36) 13575 (2017); A Sajid, Jeffrey R Reimers, Michael J Ford, Phys Rev B (2018) DOI: 10.1103/PhysRevB.97.064101; J Reimers, S Ali, M Ford, J Chem Theory and Comp (2018) Accepted

Resume : In recent years, hybrid halide perovskites attracted great attention for their potential use as light-harvesters in solar cells, due to their exceptional photo-electrochemical properties[1-2] yielding device efficiencies exceeding 22%. However, to account for the relevant features underlying such performances, one must consider not only the electronic transport, but also the significant ion conduction present in these materials.[3-4] In this contribution, we study the nature of this ionic conductivity by investigating methylammonium lead iodide (MAPbI3), the archetypal halide perovskite, by means of many electrochemical and nuclear magnetic techniques.[5] We observe a significant ionic conductivity under equilibrium conditions, and we identify the dominant electronic and ionic charge carriers as electron holes and iodine vacancies.[6] Interestingly, by applying similar characterisations to the situation under illumination we observe, for the first time, a striking enhancement of ionic conductivity by more than 2 orders of magnitude in MAPbI3, alongside the expected increase in electronic conductivity.[7] These surprising findings are discussed with respect to the equilibrium conditions and in the context of simple defect chemical models. This leads us to the proposal of a mechanism for the photo-enhanced ion conduction that relies on electron-ion interactions. [7] References [1] C. Stoumpos, C. Malliakas and M. Kanatzidis, Inorg. Chem. 2013, 52, 9019. [2] D. Shi, V. Adinolfi, R. Comin et al., Science 2015, 347, 519. [3] Z. Xiao, Y. Yuan, Y. Shao et al., Nat. Mater. 2015, 14, 193. [4] T.-Y. Yang, G. Gregori, N. Pellet et al., Angew. Chemie 2015, 54, 7905. [5] A. Senocrate, I. Moudrakovski, G. Y. Kim et al., Angew. Chemie 2017, 56, 7755. [6] A. Senocrate, T.-Y. Yang, G. Y. Kim et al., Solid State Ion. 2018, 321, 69. [7] G. Y. Kim, A. Senocrate, T. –Y. Yang et al., Nature Mater. 2018, 17, 445.

Resume : The influences of hydrostatic pressure combined to the size effect on the behavior of the exciton in 2D GaN/AlN quantum ultra thin disk on binding energy and optical absorption coefficient are investigated. Our approach is performed in the framework of effective mass theory and by using a variational method with a robust trial wave function and taking into account the dependence of the size, the dielectric constant and the effective masses on the pressure. Variations of the excitonic binding energy, optical transition energy are determined according to hydrostatic pressure. The results of our numerical calculations show that the applied pressure favors the electron-hole attraction leading to an increase of the ground state exciton binding energy, and caused a shift of the absorption coefficient toward the high energy (blue shift).

Resume : The possibility of creating nano-sized clusters in crystals is shown in this work. It was shown that formation of intrinsic point defects in the near-cluster area leads to appearance of color centers with new optical properties not known before. Near-cluster color centers in lithium, sodium and magnesium fluorides nanocrystals have been found. It was established that in these crystals several different types of near-cluster color centers are formed as a result of γ-rays and electron beams exposure. The optical characteristics of these defects were studied. The fundamental differences in their characteristics from similar characteristics of color centers of the same composition in the bulk crystal were established. The effect of pre-radiation annealing on the efficiency of formation of these defects was determined.

Resume : It is well known that the presence of grain boundaries in nanocrystalline materials governs plastic deformation. Experimental and simulation studies exist that illustrate the nucleation and evolution of dislocations, particularly during tensile and compression tests. A notable phenomenon observed is the inverse Hall-Petch behavior below critical grain sizes. The present talk takes these studies a step further by examining how grain boundary chemistry (through segregation of impurities) affects the behavior of nanocrystalline Fe. The experimental setup simulated is that of nanoindentation, since limited information is available regarding the deformation mechanisms that arise upon indenting in the proximity of grain boundaries. In the case of pure nanocrystalline Fe, grain boundary migration occurs when a 4nm radius tip is within 5 nm from the boundary, and it is revealed that deformation is governed by a competition between twin formation and dislocation nucleation. Introducing 0.008wt% C impurities on the grain boundaries of the same nanocrystal inhibits grain boundary migration and deformation is governed by the interaction between dislocation and grain boundaries. The simulations are performed for different grain sizes in order to capture how segregation affects the inverse Hall-Petch dependence. In addition to C impurities, the same Fe nanocrystal is simulated but with Si impurities segregation at the grain boundaries. The simulation results are modeled using a gradient plasticity framework that introduces a mechanically induced interface energy term that can explicitly account for the present of grain boundaries.

Resume : Nano-laminated architectures, such as thin films and nanomultilayers (NMLs), present an important class of nanomaterials, which find numerous application in the areas related to plasmonic deviced, nano-joining technologies and optical coatings. NML configurations, in which alternating nanolayers of a metal or alloy (e.g. Al, Al-Si, Ag-Cu) and a chemically-inert barrier material (e.g. carbon, nitride, oxide, refractory metal) are stacked, have been proposed as novel type of nanostructured brazing filler for joining miniaturized devices and heat-sensitive (nano)materials at ever-reduced temperature. In such systems, by controlling the phase composition and microstructural characteristics (e.g. grain size, coherency of the interfaces), an extensive mass transport by solid-state diffusion and size-dependent melting point depression (MPD) can be achieved. The study presents a comprehensive experimental investigation of the driving forces and underlying mechanisms which govern the phase stability and atomic mobility of Al-Si/AlN coatings (with a 3 nm thick AlN barrier layers and 5 nm thick Al-Si layers) upon heating. For this purpose, a combinatorial analytical approach using Scanning Electron Microscopy (SEM), High Resolution Scanning Transmission Electron Microscopy (HR-STEM) and Auger Electron Spectroscopy (AES) is employed. For the better insight, the thus obtained results are compared with Al/AlN nanomultilayer system that exhibits the superheating effect.

Resume : Broad Si+ ion-beam irradiation on Si-SiO2 structures can be used to induce atomic mixing over the Si and SiO2 interface boundaries. Kinetic Si ions in the beam modify the SiO2 matrix on nanoscale level, by introducing an abundance of Si atoms from the surrouding Si layers. The excess Si can be used to construct nanostructures inside the SiO2 layer. The ion-beam process was simulated with molecular dynamics (MD), using a speed-up scheme, significantly reducing computation time. To assess the qualitative reliance of the method, two Si–O potential models were used, the Stillinger-Weber-like Watanabe potential and the Tersoff-like Munetoh potential. The MD simulations, up to a total fluence of 1×10^15 cm^−2, were assessed with binary collision approximation (BCA). The BCA simulations showed similar atomic-density distributions as MD, however, with slightly less Si mixing into the buried SiO2 layer. The speed-up scheme used here, may cause stress build-up in the structure. Further, we noticed an abnormal densification of the SiO2 layer, especially with the Munetoh potential, which seemed to cause significantly more over-coordination than the Watanabe one. The Watanabe potential is more suitable for simulating prolonged irradiation, as it resulted in fewer coordination defects and more reasonable densification of SiO2, compared to the Munetoh potential. This work has been funded by the European Union's Horizon 2020 research and innovation program under grant agreement No 688072.

Resume : Topological defects (TD) play crucial role in reform of fundamental electronic properties of the graphene, and consequently its performance in various applications. For example, a negative curvature of the graphene significantly enhances the capacity of graphene-based electrodes [1]. The TDs also alter equilibrium topographic states of the graphene [2]. By introducing the topographic corrugations in a controlled manner, manifold modifications can be achieved. The strategies include transfer of the graphene on substrates decorated with nanoparticles [3], fullerenes [4] and nanopillars [5], or count on different thermal expansion of the graphene and the supporting substrate [6]. Consequently, spatial modulation of the strain and doping is achieved. Both the curvature of the graphene and the position of the Fermi level are the key factors influencing its local reactivity. Their impact will be demonstated on hydrogenation applied to a single-layer graphene with carefully controlled topography. [1] Odkhuu D. et al, Carbon (2014), 66, 39. [2] Yazyev O.V. et al, Phys. Rev. B (2010), 81, 195420; [3] Vejpravova J. et al, Sci. Rep. (2015) 15061; Pacakova B. et al, Carbon (2015),95, 573 [4] Vales V. et al, Nanoscale (2016), 8, 735; Verhagen T. et al, Diamond. Relat. Mater. 75 (2017) 140. [5] Pacakova B. et al, Sci. Rep. (2017), 10003. [6] Verhagen T. et al, Phys. Rev.B (2015), 92, 125437; Verhagen T. et al, phys. status solidi b 253 (2016) 2342; Verhagen T., et al, Carbon 119 (2017) 483.

Resume : Defect chemistry has given the possibility to control and tune properties to obtain better functional bulk materials. In comparison, and despite the recent interest and prospects of two-dimensional materials, their defect chemistry remains mainly unexplored. We believe that an understanding of the influence of the dielectric environment on the defect chemistry and properties is crucial for further developing new and superior 2D materials. Here, we present results for molybdenum disulphide (MoS2) films on Si/SiO2 substrates. Methods comprise magnetron sputtering of Mo with subsequent annealing in H2S atmosphere (resulting in a mix of the 1T- and 2H-phase) and the chemical vapour transport method. The films and defects are characterised by AFM, XPS, photoluminescence, optical microscopy and Raman spectroscopy in addition to electrical measurements in controlled atmospheres. Ab initio computations on a variety of point defects and defect clusters further elucidate the defect chemistry.

Resume : Developing advanced catalysts for active hydrogen evolution reaction (HER) plays a pivotal role in reducing the overpotential and consequently increasing the efficiency for electricity-to-hydrogen conversion. Transition-metal dichalcogenides (TMDs), have been regarded as a promising electrocatalyst to replace noble Pt electrode for efficient HER with the advantages of low cost and good electrochemical stability in acid. Given that the stable structure and the high conductivity favoring fast electron transport, the metallic VS2 delicate nanostructures which has a similar layered structure to MoS2 would be a potentially superior HER electrocatalyst. In this presentation, VS2 nanosheets featuring rich defects and an expanded (001) interlayer spacing as large as 1.00 nm, which is ~74% expansion as relative to that (0.575 nm) of the pristine counterpart, are synthesized by a simple one-pot solvothermal method. The interlayer-expanded VS2 nanosheets show extraordinary kinetic metrics for electrocatalytic hydrogen evolution reaction (HER), exhibiting a low overpotential of 43 mV at a geometric current density of 10 mA cm−2, a small Tafel slope of 36 mV per decade and long-term stability of 60 h without any current fading. The performance is much better than that of the pristine VS2 with a normal interlayer spacing, and even comparable to that of the commercial Pt/C electrocatalyst. The outstanding electrocatalytic activity is attributed to the expanded interlayer distance and the generated rich defects. Increased numbers of exposed active sites and modified electronic structures are achieved, resulting in an optimal free energy of hydrogen adsorption (∆GH) from density functional theory (DFT) calculations. The present work opens up a new door for developing TMDs nanosheets as high active HER electrocatalysts by interlayer and defect engineering. Acknowledgements This work was financially supported by the National Natural Science Foundation of China (No. 21671096), the Shenzhen Key Laboratory Project (No. ZDSYS201603311013489), the Natural Science Foundation of Shenzhen (No. JCYJ20170412153139454, JCYJ20150630145302231, JCYJ20150331101823677), and the Fundamental Research Funds for the Central Universities (No. JZ2016HGTB0725). References [1] J. J. Zhang, C. H. Zhang, Z. Y. Wang, J. Zhu, Z. W. Wen, X. Z. Zhao, X. X. Zhang, J. Xu, Z. G. Lu, Small 2017, DOI: 10.1002/smll.201703098. [2] X. Zou, Y. Zhang, Chem. Soc. Rev. 2015, 44, 5148. [3] X. Chia, A. Y. Eng, A. Ambrosi, S. M. Tan, M. Pumera, Chem. Rev. 2015, 115, 11941. [4] H. Wang, H. Yuan, S. Sae Hong, Y. Li, Y. Cui, Chem. Soc. Rev. 2015, 44, 2664. J. Feng, X. Sun, C. Wu, L. Peng, C. Lin, S. Hu, J. Yang, Y. Xie, J. Am. Chem. Soc. 2011, 133, 17832. [5] J. Feng, L. Peng, C. Wu, X. Sun, S. Hu, C. Lin, J. Dai, J. Yang, Y. Xie, Adv. Mater. 2012, 24, 1969. [6] H. Liang, H. Shi, D. Zhang, F. Ming, R. Wang, J. Zhuo, Z. Wang, Chem. Mater. 2016, 28, 5587.

Resume : Molybdenum disulfide (MoS2), as a representative material of transition metal dichalcogenides (TMDs) with two-dimensional structure, has attracted great attentions due to its promising applications in electronics, photonics, energy and electrochemistry. Defects in MoS2 play an essential role in altering the electronic, magnetic, optical and catalytic properties of MoS2, presenting a new useful way to engineer the functionality of MoS2. The mechanisms by which lattice defects affect the MoS2 properties are still unsettled. In this work, we reveal systematically how the lattice defects affect the electronic structure and electro-catalytic activity of MoS2. We fabricated single layer MoS2 model system with well-defined structure and chemistry by chemical vapor deposition (CVD), and created defects in MoS2 by ion irradiation with different ion species (Au, Ar, N), ion fluence (ranges from 5×1011 to 5×1013 ions/cm2) and energy (ranges from 500eV to 6MeV). We assessed how irradiation condition impacted the defect states such as the defect type and density in MoS2 by performing Raman and photoluminescence spectroscopies, X-ray photoelectron spectroscopy, and scanning tunneling microscopy/spectroscopy measurements. Our results showed that ion irradiation is an effect tool to engineer the defects state of MoS2 and can be used to tune the properties of MoS2 and other TMDs for applications such as electronics, optoelectronics and electrochemistry.

Resume : Perovskites from the series (La,Sr)(Co,Fe)O3-δ show fast oxygen exchange kinetics, as well as high electronic and significant ionic conductivities. These materials are frequently applied as cathodes in intermediate temperature solid oxide fuel cells (IT-SOFCs) which are operated at 600-800°C. However, long-term degradation phenomena which affect the first few to first few hundred nanometres of the cathode surface lead to a significant decrease in the oxygen exchange activity. In-situ dc-conductivity relaxation studies and post-test analyses by complementary methods such as scanning (transmission) electron microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy, show that the cathode deactivation is caused by surface poisoning reactions. In the early stage of degradation segregation of strontium takes place via grain boundary paths from the bulk towards the surface. The Sr-rich surface and near-surface regions react with impurities from ambient air (SO2) or from the SOFC system (Cr, Si) forming secondary phases, which are thermodynamically more stable than the original bulk phase, but electrically insulating and chemically inactive in the oxygen exchange reaction. The deeper insight into the critical factors and mechanisms limiting the stability of complex perovskite oxides thus obtained is the basis for developing IT-SOFC cathode materials with improved long-term stability and fast oxygen exchange kinetics.

Resume : It is well known Wigner crystallization of two-dimensional free electron gas on the liquid helium surface. Electrons create two-dimensional periodic structure with triangle lattice. In the present report, we for the fist time observed three-dimensional gas of electrons localized on deep traps in dielectric. The concentration of non-filled neutral traps in HfO2 we determined from charge transport experiments. It was established that charge transport in HfO2 is governed by phonon assisted trap ionization. The trap concentration and thermal energy determined from experiment are equal to Nt=7*10^(19) cm^(-3), Wt=1.25 eV. The filled traps concentration was experimentally determined with capacitance-voltage characteristics hysteresis in Si-HfO2-Al structures. It was obtained that the concentration of filled negatively charged traps is equal to nt=1*10^(18) cm^(-3). Hence, the concentration of negatively charged filled traps in HfO2 is by 70 times less than the concentration of nonfilled neutral traps. The small concentration of filled traps in HfO2 is related with coulomb repulsing of localized by traps electrons. Hence, we observed the Wigner crystallization of localized by deep traps electrons in dielectric.

Resume : Our reports (2012-2015) of non-classical (non-Newnham) electrostriction in Gd-doped ceria thin films pose a question whether such electromechanical activity is limited to thin films and Gd-dopant. Here we report on the longitudinal electrostriction strain coefficient (M33) of Gd- and Sm-doped ceria ceramics, measured with a proximity sensor. Elastic moduli were determined by pulse echo sound velocity (SV) and nanoindentation (NI) techniques. SV data for fluorite-phase Gd- and Sm-doped ceria ceramics reveal that all moduli decrease linearly by 0.5% per mol% dopant. For double-fluorite-phase ceramics (i.e. high dopant concentration), the Young’s and shear moduli are larger than expected from this linear decay, while the bulk modulus is not. At 150 mN (NI) loading, Gd- and Sm-doped ceramics exhibit primary, room temperature creep with anelasticity (relaxation time  2 s). In quasi-static electric fields (~1 Hz), M33 remains constant up to 15 mol% doping (-7±210-17 m2/V2), decreasing ~100 fold up to 35 mol% doping. M33 also displays marked relaxation as the field frequency increases: above 50 Hz, M33-2±110-18 m2/V2 for both dopants, independent of concentration. We present strong evidence that the anelastic and electromechanical behavior derive from point defects on the anion sub-lattice. Ceria-based devices, essential in modern technology, must be designed with these unanticipated properties in mind. Funding by the Israeli MoS&T 3-12944 is acknowledged.

Resume : Amorphous and nanocrystalline indium zinc oxide (IZO) films have excellent opto-electronic properties, which are exploited in transparent thin film transistors and display devices. We used the pulsed laser deposition technique to grow thin films of IZO with In/(In+Zn) values from 0.1 to 0.9 on Si and glass substrates at room temperature. The films were irradiated by gamma radiation to investigate the effects of radiation on their structure and properties. The films surface morphology, investigated by atomic force microscopy, was smooth, with rms values below 1 nm. X-ray reflectivity (XRR) and X-ray diffuse scattering techniques were used to investigate the films density and surface and interface morphology. In addition, we also used optical reflectometry and photoluminescence (PL) to characterize the changes of the optical properties caused by irradiation. The results showed that after gamma irradiation, the surface roughness slightly changed, the rms values increasing from 1 nm to 2-3 nm. Also, the films density, extracted from simulations of the acquired XRR curves, decreased by a few percent, which resulted in a small thickness increase. Spectroscopic ellipsometry measurements indicated that the refractive index values also decreased by 1-2 percent, consistent with the observed changes in density. The optical band gap values, extracted from Tauc plots, slightly decreased by few tenths of eV, while the resistivity was almost unchanged. PL measurements for different ratios of In/(In+Zn) showed that the light emission increased after irradiation due to defects formation. The results showed that these amorphous transparent oxide films could withstand a high level of gamma radiation without adverse effects upon their structure, stoichiometry or optical and electrical properties.

Resume : For achieving high quality InGaN/GaM heterostructure with minimum defect concentration it is need to optimize growth conditions. The process of InGaN/GaN heteroepitaxial growth of sapphire-SiC substrates usage requires to reduce mismatching the parameters layers and substrates by buffers. For this purpose, the low-temperature amorphous buffer (nucleus) GaN layer and special additional doping profile - such investigation was carried out by simulation and lately heterostructures were grown based on such recommendations. Such approach usage makes it possible to reduce the density of penetrating, structural dislocations upto 108 cm-2, as well as to increase the mobility of charge carriers and improve the uniformity of surface morphology. During growth the main influence of defects occurs from III/V flows ratio and doping barriers by Indium atoms. Different flows ratio and additional barriers doping were investigated and after growth optimal surface was achieved. A decrease in the V/III ratio upto 1320 at the stage of the precipitated growing low-temperature nuclei leads to the formation of a smaller number of growth islands, and also increases the rate of growth in the lateral direction. This leads to a decrease in the density of dislocations, since the probability of their formation decreases when the islands layer is intergrown. At next investigation temperature changes and carrier-gas influence also were investigated and optimum correlations was detected.

Resume : In this work epitaxial 3C-SiC layers were grown by sublimation epitaxy in a vacuum. As substrates served semi-insulating substrates of the 4H polytype. The growth was performed on polar C and Si (0001) faces of the substrate. The growth temperature was 1950-2000ºC; growth duration 10 min; area of a 3C-SiC layer, 1 cm2. The irradiation with 8 MeV protons was performed on a MGTs-20 cyclotron at irradiation doses (D) in the range from 3.0×1014 to 4.0×1015 cm2. Samples have been studied by the Hall effect, C-V method, DLTS and photoluminescence. It was found that the carrier removal rate reached a value of ~110 cm--1. Full compensation of samples with an initial concentration of (1-2) x 1018 cm -3 was estimated at doses of about 6 1015 cm -2. Compared with the 4H and 6H silicon carbide in 3C-SiC was no observed significant increase in the intensity of so-called "defective" photoluminescence. It was found that the 3C-SiC epitaxial layers grown in the study have approximately the same radiation hardness under irradiation with protons as that for 6H-SiC and 4H-SiC. The effect of detected radiation defects on the processes of radiative and nonradiative recombination was analyzed.

Resume : Ferroelectric perovskites are used in many electronic devices, which are the subject of a general trend towards miniaturization. For this reason the interest in the preparation of defined-shape ferroelectric nanoparticles has recently increased significantly. In particular, ferroelectric particles with anisotropic shapes such as needles and plates are attracting increasing attention because of their unique shape- and size-dependent properties at low dimensions. In addition, an ordered arrangement of defined-shape ferroelectric particles based on self-assembly enables the preparation of oriented films that exhibit the potential for several piezoelectric applications, including energy harvesting. In this study the formation of ferroelectric plates (BaTiO3, Ba1-xSrxTiO3 and BaTiO3/SrTiO3) was realized by the in-situ topochemical conversion of a Bi4Ti3O12 template. The size, shape and preferential orientation of the formed ferroelectric plates were controlled by the template size and the conversion conditions. Their piezoelectric characteristics and ferroelectric domain switching and stability were studied by means of piezo-response force microscopy. The ferroelectric plates were self-assembled on the substrate and packed with a polymer or sol-gel solution. The functional properties of these films were determined and discussed in terms of their application to energy harvesting. A literature review and a comparison of similar energy-harvesting systems will be presented.

Resume : The outstanding efficiencies of organic-inorganic perovskite thin film based solar cells led to interest in increasing the range of perovskite materials. One such family of materials is the all inorganic CsPbX3 colloidal nanocrystals (NCs). Despite the recent surge of synthetic protocols producing different shapes and crystal structures, there are still significant gaps in the understanding of their formation mechanism. Here we try to address the growth mechanism and reveal the importance of the ligand shell on determining the size, habit and phase. We have identified that the formation of CsPbX3 NCs follows through two separate stages. First, seed mediated nucleation through the formation of metal Pb NCs. Second, further growth is attained through oriented attachment. We show the impact of delicate changes in the ligand environment on the stoichiometry and crystal structure of cesium lead halide perovskites NCs. We show that small changes in the oleate:ammonium ratio generated by the addition of a Lewis base determines the size, shape and crystallographic structure of CsPbX3 NCs. Using this understanding we could synthesize materials such as CsPbBr3 nanowires, CsPbCl3 bulk-like crystals and CsPbI3 orthorhombic nanowires of length ranging from 200 nm to several microns. Moreover, we show how a robust reversible transformation that involves also a stoichiometric change, from cubic CsPbX3 to rhombohedral Cs4PbX6 which can be achieved via control of the OA to OLAm Brønsted acid−base type equilibrium. We present surface analysis revealing the differences in the ligand shell of cubic CsPbBr3 versus Cs4PbBr6. In addition, we show evidence that the transition mechanism involves an exfoliation and recrystallization processes. This mechanism is supported by crystallographic data showing a Cs4PbBr6, 0D layered rhombohedral phase. The formation of a layered Cs4PbBr6 habit indicates a direct path for transformation that is controlled by thermodynamic surface stabilization provided by the ligand shell. We believe this work will lead to the development of improved strategies for rational design of synthesis and more importantly, the stabilization of perovskite NCs which may offer an advantage for perovskite NCs over thin films for photovoltaics and other potential applications.

Resume : Transition metal dichalcogenides (TMDs), such as MoS2 and WSe2, are the potential candidates for next 2D materials because atomically thin layers of TMDs exhibit unique and versatile electrical and optical properties. Although bulk TMDs materials have an indirect bandgap, an indirect-to-direct bandgap transition is observed in monolayers of TMDs (MoS2, WSe2, and MoSe2). Controlling structural defects are a potential method for improving the optical properties of TMDs films. Large-area spatial tuning of the optical transition of bulk MoS2 films was achieved by applying structural defects such as edge- and terrace-terminated using a nanomesh structure using an anodic aluminum oxide (AAO) template. Strong photoluminescence emission peaks with a band gap of 1.81 eV was observed, which possibly stems from a radiative defect transition at defects sites. This work shows that the AAO template lithography method has potential for the production of homogenous large-scale nanomesh structures for practical semiconductor processing applications in future MoS2-based electronic and optical devices.

Resume : This works deals with a new method to growth sculptured silver oxides (AgxO) thin films based in the Glancing Angle Deposition (GLAD). The procedure involves the oxidation of high purity silver at a range of temperature between 200 and 300°C. Silver can be oxidized thermally in free air or pure oxygen. Oxidizing in air or oxygen produces AgO and Ag2O depending on the thermodynamic stability of the oxides. The Ag films were deposited at different incidence angle to obtain a variable microstructure with different rotational ways of oblique substrate, such as helical and z-shape. After air annealing, the Ag-O films are characterized by X-ray diffraction, scanning electron microscopy and UV-Vis-NIR spectrophotometry. The obtained transmittance spectra in the range 300 – 1800 nm at normal incidence angle are used to investigate the optical properties of the films such as band gap energy, refractive indices, the birefringence, packing density, … XRD Study confirm the conversion from metal to semiconductor, the obtained phase are dramatically different, and the choice of material Ag2O or AgO could be well controlled depending on the choice of the annealing temperature. The morphological properties show that by growing films under alternating the inclination of a substrate to the vapor flux, it is possible to grow columnar zig-zag structures. The pore morphology of zig-zag coatings is found to depend strongly on the angular distribution of the incident flux. For a continuous small speed rotation with inclined substrate, GLAD technique leads to the formation of individual helical columns. It has been also shown that when the incident flow is made oblique, the asymmetry in the vapor distribution produces asymmetric shadowing, leading to creation of anisotropic properties in the grown films.

Resume : Ceramic materials are very studied due their diverses applications. In this context, different structures of the calcium vanadate (Ca10V6O25) family have been studied recently due to their optical applications. Therefore, the aim of our study was evaluate the optical properties of Ca10V6O25 that is little known in the literature. Ca10V6O25 superstructure was obtained by the coprecipitation method at 96 °C. The sample was structurally characterized by XRD, which sample was indexed to PDF 52-649, characteristic of Ca10V6O25 phase with hexagonal structure. FEG-SEM images showed the formation of tube bundle aggregate with a mean diameter ~ 200 nm. The optical measurements of the material were made by by UV-vis diffused reflectance (DRS) and photoluminescence (PL). DRS showed an absorbance near ~300 nm, with Egap around 4.10 eV, ultraviolet region. The PL with temperature variation and excitation at 325 nm, it was observed the presence of different electronic levels inside the band gap of the sample. At temperatures lower than 180 K (<180 K) a greater predominance of deep defects in the sample with emission around 2.0 eV (red region). At temperatures above 180 K (>180 K) were observed deep defects emissions around 2.3 eV (green region). The PL spectrum at room temperature with excitation at 350 nm showed a predominance of emission in the blue region, around 2.75 eV, with higher emission of shallow defects that are located closer to the valence and conduction band.

Resume : The family of TMDCs comprises materials with electronic properties spanning from insulating to semiconducting and metallic. Such a breadth of properties were key towards the development of various technological studies and processes to be exploited in different potential applications such as energy conversion and storage, electronics and sensors. Here, we report on a safe, fast and low cost electrochemical intercalation process of MoS2 crystals via lithium ion intercalation in dimethyl sulfoxide (DMSO). We perform the exfoliation under ambient conditions in short time (< 1 hour) by dissolving the lithium chloride in DMSO, 1 mol/L solution. The exfoliation is performed in ambient air and leads to the formation of mono- and few-layer thick nanosheets with a low fraction of metallic phase (?35%), characterized by morphological and spectroscopic analysis. We have investigated the electronic properties of the nanosheets through the fabrication and characterization of back-gated field-effect transistors (FETs) based on individual MoS2 nanosheets. The latter display a unipolar n-type behavior with ION/IOFF ratios up to ?10^2 and field-effect mobilities ranging between 10-3 and 10-2 cm2V-1s-1, likely limited by structural defects and disorder ? e.g. coexistence of different polytypes ? created during the intercalation/exfoliation process. Upon exposure of the devices to vapors of butanethiols, the field-effect mobility increases by over a factor 3, suggesting that sulfur vacancies are an abundant type of defects generated during the intercalation/exfoliation process.

Resume : Among alkali halides, lithium fluoride (LiF), in pure and doped form, is a well-known dielectric material for photonic applications and dosimetry. The irradiation of LiF crystals and films with ionising radiation induces the stable formation of laser-active defects, known as colour centres (CCs). Among them, F2 and F3+ CCs (two electrons bound to two and three close anion vacancies, respectively) possess almost overlapping absorption bands located at a wavelength of ~450 nm, which together form the so called M band. Under light excitation in this spectral range, they emit broad photoluminescence (PL) bands peaked at 678 nm and 541 nm, respectively. Polycrystalline LiF thin films were grown by thermal evaporation on glass and Si(100) substrates in controlled conditions and were irradiated by 3 MeV proton beams, produced by the TOP-IMPLART linear accelerator for protontheraphy under development at ENEA C.R. Frascati, at doses higher than 105 Gy. Structural and morphological analyses were performed together with PL and photoexcitation (PLE) spectroscopy. F2 and F3+ PL and PLE spectra were carefully analysed. Differences in their spectral and intensity behaviours were observed and are under further investigation

Resume : Zinc oxide (ZnO) is a one of the most extensively studied materials in the last decades and has been employed in a wide variety of applications. Among those, we highlighted its excellent prospects as photocatalytic agent for degradation of organic pollutants. In this work, different morphologies of ZnO crystals (nanotetrapods and microrods) were produced by laser-assisted flow deposition (LAFD), a very high yield method that allows the production of different ZnO morphologies with very high optical and structural quality. By adding silver to the precursor rods it is possible to produce ZnO/Ag composites in a single and short step, resulting in a synergetic combination of the properties of both materials. The structures produced were morphological, structural and optically characterized. Moreover, the photocatalytic activity of the produced crystals is analysed using methylene blue as a model-test contaminant. It was found that the nanostructures exhibit a better performance than the microrods in the degradation of the dye. This effect is further enhanced by the presence of silver at the surface of the ZnO crystals. PL measurements showed different PL features for the two distinct morphologies, as well as additional changes resultant from the introduction of silver during the growth process. The relationship between the optical properties of the different samples, the presence of different defect-related optical centres and/or defect distribution, together with their photocatalytic dye degradation is discussed.

Resume : It is well established that ion implantation is a convenient method to introduce Rare Earth (RE) ions into group III-N host material in a controlled manner with a reproducible profile [1]. Since, energetic heavy ions penetrate a crystalline host, this technique can induce lattice damage, which can be recovered by post-implant thermal annealing at high temperatures. In this work, the implantation of europium (Eu) was performed on AlGaN/GaN heterostructures in order to tailor the original properties towards achieving high efficiency red emitting structures. The Eu ions are introduced in the as-grown heterostructure with two different fluences. The as-implanted samples were further submitted to high temperature and high pressure thermal annealing at 1400 °C in 1 GPa N2 pressure. The optical properties of the modified heterostructures are studied in detail demonstrating that such annealing conditions successfully decreased the implantation damage and optically activated the Eu ions. The Eu3+ luminescence was observed in all samples with the most intense emission assigned to the 5D0-7F2 transition in the red spectral region. A higher thermal stability of the intra-4f6 lines was found for the sample implanted with the higher Eu fluence. In addition to the Eu-related emission, the photoluminescence spectra exhibit a broad yellow-green emission typically involving deep defect levels. [1] Lorenz et al. Chapter 2, ISBN 978-90-481-2876-1, Ed. K. O’Donnell & V. Dierolf (Springer 2010).

Resume : Redox-based resistive random access memories (ReRAM) are one of the key technologies for revolutionizing the memory market. Tantalum oxide (TaO(x))-based ReRAM devices show high endurance and high switching speed. The resistive switching in TaO(x)-based devices is commonly explained by the filamentary valence change mechanism, in which the formation / dissolution of a conductive filament plays a key role. Defects, such as oxygen vacancies, are known to be important for the formation of the filaments. However, the filament structure, its exact composition and its impact on the performance of the devices are still a matter of debate. We targeted these questions by performing a detailed study of the electronic transport through conductive filaments in Ta(2)O(5)-based ReRAM devices in the low-resistance state at temperatures from 300 K down to 2 K. We then performed similar measurements on substoichiometric TaO(x) thin films in the van der Pauw geometry. The TaO(x) films with x ~ 1 exhibit the same transport behavior as the conductive filaments in the devices. Not only the behavior of the conductivity is the same in the measured temperature range, but also a similar positive magnetoresistance is observed below 50 K. This correlation shows that the transport in both cases is determined by the same mechanisms. Therefore, detailed analytical studies on the TaO(x) films will provide a much needed insight in the conductive filaments of Ta(2)O(5)-based ReRAM devices.

Resume : Gallium nitride high electron mobility transistors (GaN HEMTs) are ubiquitous in the field of radio frequency power amplifiers. However, they suffer from long-term memory effects which severely alter their radio-frequency performance [1]. These effects have been linked to deep-level traps in the buffer layer that act as charge traps [2]. Using a Shockley-Read-Hall theory-based model [2] along with I/V curves measured at pulsed conditions and with sinusoidal excitation, we investigate how GaN HEMT channels affected by deep level traps satisfy the two fundamental memristive criteria: (i) a pinched hysteretic trajectory in the ids/vds phase plane when the device is excited by a sinusoidal stimulus, and (ii) a hysteresis area that decreases monotonically and vanishes for increasingly higher frequencies [3,4]. [1] Filipe M. Barradas et al., IEEE Trans. Microwave Theory and Techniques 65, 3379 (2017) [2] James G. Rathmell and and Anthony E. Parker, Proc. SPIE 6798, Microelectronics: Design, Technology, and Packaging III, 67980R (2007) [3] Leon O. Chua and Sung Mo Kang, Proc. IEEE 64, 209 (1976) [4] Shyam P. Adhikari et al., IEEE Trans. Circuits and Systems I: Regular Papers 60, 3008 (2013)

Resume : (In,Fe)Sb layers with a Fe content up to 13 at. % have been grown on (001) GaAs substrates using pulsed laser deposition. Transmission electron microscopy shows that the layers are epitaxial and free of second-phase inclusions. The observation of anomalous Hall effect, hysteretic negative magnetoresistance curves and ferromagnetic resonance at temperatures up to 300 K, as weel as the investigations of magnetic circular dichroism reveal that the Curie point lies above room temperature. The resonant character of magnetic circular dichroism confirms the intrinsic ferromagnetism in the (In,Fe)Sb matrix. We assume that the origin of the ferromagnetic properties of the (In,Fe)Sb matrix is the mechanism of superexchange interaction between Fe atoms. Hence, the obtained (In,Fe)Sb is a single-phase zincblende crystal with room temperature intrinsic ferromagnetic properties which manifest themselves in the carrier transport. [1] J. Appl. Phys. 122, 183901 (2017)

Resume : The double perovskite Sr(2)FeMoO(6-d) (SFMO) has a number of potential applications, such as energy-independent magnetoresistive random-access memories (MRAM), magnetic reading heads for hard-disk drives, ultrasensitive magnetic field sensors, electrodes for solid fuel cells, etc. For the implementation of these devices, structurally perfect SFMO materials with high values of the Curie temperature, spin polarization degree and other parameters are needed. We have synthesized a series of SFMO specimens and studied them using neutron diffraction. We have found out that the O1-Fe/Mo-O1 and O2-Fe/Mo-O2 bond lengths, aligned along the (001) and (110) planes, decrease with increasing d value and degree of the superstructural Fe/Mo cation ordering. This leads to a reduction of the elementary cell volume. As a consequence, the covalence of the bond increases, which stimulates a redistribution of the electron density and a rise in the density of spin-down-polarized charge carriers located in the conduction band on the Mo(t2g)? electron orbitals. It is supposed that the exchange interaction in SFMO is mediated by free spin-polarized electrons according to the Ruderman-Kittel-Kasuya-Yosida (RKKY) mechanism. It has also been found that the oxygen desorption rate is several times higher than the rate of the superstructural ordering of the Fe/Mo cations. This work was supported by the European project H2020-MSCA-RISE-2017-778308 SPINMULTIFILM.

Resume : Ba(2-x)Sr(x)FeMoO(6) double perovskite solid solutions in the composition range x = 0.0-2.0 were investigated. High-resolution neutron diffraction spectra yielded precision information on the variation of the crystal and magnetic structure with increasing Sr content, as well as data on the sample microstructure. The calculation of the crystal structure for two Ba(2-x)Sr(x)FeMoO(6) compositions was carried out for the orthorhombic and tetragonal lattices. In the first case, the rise of the Sr and Fe ion concentrations causes a stronger lattice distortion at low temperatures, which manifests itself in a bigger difference between the a and b unit cell parameters. The diminution of the unit cell volume upon substitution of Sr for Ba is explained by the difference of their ionic radii. This substitution changes the crystal structure from cubic (at x=0) to tetragonal (x=0.4), to tetragonal or orthorhombic (x=1.0), and to tetragonal (x=1.6-2.0). These changes are accompanied by an increase of the Curie temperature and microdeformations. A negative magnetoresistance (MR) was observed in Ba(2-x)Sr(x)FeMoO(6) at x = 0.0-2.0. The MR is caused by the quantum tunneling of electrons between the Ba(2-x)Sr(x)FeMoO(6) grains. The charge transfer becomes spin-dependent, and the maximum MR = -34.8% was observed for x=1.0 in a field of 10 T at 15 K. This work was supported by the European project H2020-MSCA-RISE-2017-778308 SPINMULTIFILM.

Resume : Sr2FeMoO6-d (SFMO) films were obtained from nanopowders synthesized by the sol-gel technique. Initially, a solution has been prepared containing 1.0 g of polyvinylpyrrolidone (PVP) and 15 ml ethanol, after which the 1.5 g of SFMO powder was added. Further, the solution was mixed in a magnetic stirrer, after which its ultrasound treatment has been done during 20 min. The SFMO thin film was obtained on a polycore substrate from the solution, using the spin-coating technique The film was dried during 2 h at 70 °?. Measurements of electrical resistivity were carried out at room temperature in transverse magnetic field (B) of up to 0.15 ?. A following characteristic feature of the MR(B) was revealed: the MR reaches a maximal value + 33% at ? = 0.046 ?, after which it decreases passing to the negative region (-7%) in the field 0.15 ?. A reason for a negative MR is obvious: an appearance of tunneling MR in strong magnetic fields is supposed for the SFMO particles, surrounded by a polymer. Since the electric charge transfer is realized between the SFMO grains with a metallic conductivity, which are separated by dielectric interlayers, the non-linear character and positive MR in the low magnetic fields is caused by a dominating activation character of the charge transfer. The authors are grateful for the support to the DFG (Grant No. MA 2359/30-1) and the European project H2020-MSCA-RISE-2017-778308 SPINMULTIFILM.

Resume : A single layer of black phosphorus, also called phosphorene, displays very unusual behavior under mechanical strain: not only is the layer very flexible, but its mechanical properties are highly anisotropic due to the puckered bonding network. Using ab initio electronic structure calculations, we investigate how these properties can be modified by single-atom vacancies or doping. In particular, we are attempting to exploit the anisotropy for tuning the electronic and magnetic properties of imperfect phosphorene by applying strain. We find that (i) compressive strain can reduce the band gap of pristine phosphorene and induce a semiconductor-to-metal transition; and (ii) compressive strain up to 10%, both biaxial and uniaxial along the zigzag direction, reduces the formation energy of single-atom vacancies with respect to the pristine configuration and can stabilize these defects in phosphorene. Moreover, tensile biaxail or compressive uniaial strain may induce a magnetic moment even at vacancy structures that were non-magnetic in the strain-free material. Our results also show that carbon-doping induces magnetism and a semiconductor-to-metallic transition; compressive biaxial strain has been found to suppress this magnetism whereas tensile strain opens the band gap and leads to an increased magnetic moment. Our findings suggest that doping and applying strain are important methods to tune the electronic and magnetic properties of monolayer phosphorene.

Resume : The MAX phases are a family of nanolaminated materials [1]. They are not only known for their unique combination of ceramic and metallic properties, but they have recently been shown to exhibit magnetic properties as well [2]. Further, they are the precursors for the synthesis of a class of 2D-materials, the MXenes, having potential applications in several domains (energy storage, catalysis) [3]. However, most of the studies on magnetic MAX phases have been focused on chromium-based materials, which reveal unstable for the production of MXenes. In this work, we have studied Mn-doping of Ti2AlC thin films (20 nm) grown on Sapphire by magnetron sputtering. The Mn implantations were carried out at medium energy and the effect of fluence, implantation temperature and of a post-implantation annealing were investigated by XRD and STEM-EELS. For the highest fluences, phase transformation occurs. Nevertheless, the MAX phase structure is recovered after annealing, even for 2.6% Mn introduced in the film. STEM-EELS analysis reveals that part of the implanted Mn is diluted in the thin film and part is segregated at the grain boundaries. The characterization of the magnetic properties of the films is in progress. [1] M. Radovic et al., A. Ceramic Soc. Bulletin 92 (2013) 20 [2] A. S. Ingason et al., J. Phys. Cond. Matter 28 (2016) 433003 [3] N. Naguib et al., Adv. Mater. 26 (2014) 992

Resume : Nickel oxide (NiO) is a p-type semiconducting oxide with potential applicability in gas sensors, electrochromic devices, batteries or smart windows [1]. Different methods have been used to prepare NiO, usually in form of thin films or nanoparticles, however less has been done in the fabrication of elongated micro- and nanostructures, so far. Moreover, doping NiO with Sn can modulate its optical and electrical properties leading to improved applicability. In this work, a catalyst free vapor–solid method has been used to fabricate NiO micro and nanostructures, using metallic Ni as precursor and thermal treatments at temperatures from 800 to 1400oC and durations 5 – 15 h under a controlled Ar flow. Large microcrystals were grown on the surface of the treated pellets at temperatures of 1000-1200 ºC, most of them showing surfaces with a high number of ordered micro-hollow cavities with square sections of hundreds of nm. At 1400 ºC NiO microwires tens of microns length were also grown. By using a controlled mixture of Ni and SnO2 as precursor, the growth of thinner NiO micro- and nanowires is highly enhanced. Variation of the precursors, mixture ratio and parameters of the thermal treatment can lead to the growth of Sn doped NiO and even SnO2/NiO p-n heterostructures. Raman and XRD confirm that the samples consist of NiO with cubic rock-salt structure, and no other Ni oxides or metallic Ni were observed. The cathodoluminescence and photoluminescence study show an emission centered at 1.7 eV and a wide emission between 2.0 and 2.5 eV, which origin is still under discussion, although it could be associated with extended defects formed during the growth. XPS measurements confirm the low presence of Sn in the Sn doped NiO samples. [1] C. Liu, C. Li, K. Ahnemd, Z. Mutlu, C.s. Ozkan and M. Ozkahn. Sci. Reports 6, 29183 (2016)

Resume : We investigated the effects of the post-annealing treatment on crystallinity, strain, and gas sensing performance of MoS2 sheets. The MoS2 sheets were synthesized using a hydrothermal process in HCl solutions, and annealed from RT up to 400oC in 5% H2/Ar atmosphere. The sheets were mechanically strained and had morphology of thin and curled shape with high density of defects. With increasing the annealing temperature, the MoS2 sheets became flatter and their crystallinity was increased. In addition, the annealing process significantly reduced the organic residues and other second phase resulting from undissolved S solutes. To evaluate gas sensing performance, we fabricated a resistance type sensor. Au/Ti electrode were deposited using e-beam evaporation on a SiO2/Si substrate, and MoS2 suspended in ethanol was coated on the electrode and dried. In contrast to the non-annealed MoS2 sensor which did not respond to changing gas concentration, the annealed sensors were highly reactive to exposed NO2 gas, resulting from the elimination of absorbed impurities. As the annealing temperature increased, gas performances of sensitivity, response, and recovery were considerably varies, and the relation between the performance and microstructure of the MoS2 will be presented.

Resume : Light-emitting diodes (LEDs) operate under the conditions of ionizing irradiation. The purpose of this work is to research the influence of preliminary irradiation by fast neutrons on changing watt-ampere characteristic of the LEDs during operation. The objects of the research were LEDs based upon double AlGaAs heterostructures. Long-term operation conditions were simulated by accelerated step-by-step tests. Analysis of the watt-ampere characteristic shape provides an opportunity to mark several distinctive areas that are defined by electron injection level in active region of the LED. The marked areas can be characterized by corresponded threshold currents. The threshold currents go up when step number rise accompanied with increase of ohmic contact resistance during step-by-step tests and under irradiation by fast neutrons. Preliminary irradiation by fast neutrons leads to a shift in the threshold currents depending on fluence of fast neutrons. Preliminary irradiation by fast neutrons with fluence in the field of radiation-stimulated reconstruction of the initial defect structure makes it possible to increase the resistance of ohmic contacts during operation and, therefore, to increase their reliability. Preliminary irradiation by fast neutrons in the field of impact of only radiation defects leads to the accelerated increase of resistance of ohmic contacts during operation, which decreases their reliability. Preliminary irradiation by fast neutrons can be used in the manufacturing technology of the LEDs with the purpose of the reliability increase.

Resume : Nowadays infrared wavelength range light-emitting diodes (IR-LEDs) are broadly used in various microelectronic devices that operate in space conditions, in the upper regions and at nuclear power plants. Severe operation conditions of LEDs require knowledges of their radiation resistance and reliability taking into account combined influence of these damaging factors. In this case, the combined influence is the impact of two or more factors spread out over a period of time. Analysis of the available data showed that such information is practically absent in the literature. Therefore, the purpose of this work is to research the combined influence of long-term operation and radiation factors on the change of emissive power of the IR-LEDs. The objects of the research were industrial IR-LEDs based upon double AlGaAs heretostructures. Long-term operation conditions were simulated by step-by-step tests when operation current increased gradually from step to step with constant chamber temperature (+65 0C). Duration of each step was 24 hours. The IR-LEDs were irradiated by stationary gamma-equipment based on Cobalt-60. We have been established that the long-term operation factors decreased the resistance of IR-LEDs to subsequent gamma-irradiation. The partial recovery of emissive power of IR-LEDs is observed under irradiation by gamma-quanta with doses in the range of 4.7*10^5..9.9*10^5 Gy. It can be attributed to the radiation-stimulated annealing of ?initial defect + radiation-induced defect? complexes. Probable causes of observable results are discussed.

Resume : Infrared wavelength range light-emitting diodes (IR-LEDs) are broadly used as a basis for microelectronic devices that operate in space conditions, in the upper regions and at nuclear power plants. Therefore, the strict requirements of reliability and radiation resistance are applied to these LEDs. Presence of dislocations in the initials devices, their effects on characteristics of the LEDs and precipitation under the influence of external factors are the factors that have influence with characteristics of the LEDs. Analysis of literature date is shown that the dislocation can be presented as parallel p-n junction with a series ohmic resistance connected to the p-n junction of the LED. Therefore, the purpose of this work is to research the influence of dislocations on electrophysical characteristics of the LEDs. The objects of the research were industrial IR-LEDs based upon double AlGaAs heretostructures before and after operation and ionizing irradiation. We have been analyzed that the forward-bias region of a volt-ampere characteristic of the LED and its change under influence of external factors allow detecting the presence of dislocations in the initial LEDs. Furthermore, the analysis makes possible to reveal effects of the dislocations in the LEDs under the influence of external factors. The problems of prediction of catastrophic failures probability of the LEDs through the control of forward-bias region of a volt-ampere characteristic are discussed.

Resume : Sodium-ion batteries (SIBs) have attracted extensive attention as a potential alternative to lithium-ion batteries (LIBs), due to low cost, the abundance of sodium resources, and the similar chemistry to that of LIBs. However, there are challenges to overcome such as a suitable host material for Na+ insertion due to the relative larger radius of Na+ compared with that of Li+. As for anode materials, graphite, the commercial anode for LIBs, does not function in SIBs due to its extremely low capacity. This can be alleviated with solvent co-intercalation, but such a method brings about its own set of challenges. Moreover, comparing the ionic radii, the Na+ ion (1.02 nm) is larger than the Li+ ion (0.59 nm), so Na+ has much more difficulty in intercalating into graphite than Li+, which is also conducive to the reduced rate performance of graphite electrode in SIBs. As a result, exploring suitable anode materials to accommodate reversible Na+ insertion/extraction is crucial for the development of SIBs. Among the various carbon-based anode materials, graphene with similar composition as graphite has been significantly explored as an electrode material for SIBs, owing to its high surface area (2630 m2g-1), sufficient porosity, superior conductivity (104 Scm-1), and excellent mechanical stability. Moreover, few studies have demonstrated that the electrochemical performances of graphene could be further improved by chemical activation. This activated graphene has a large fraction of meso- and micropores that provide the pathways for easy accessibility of electrolytes and fast transportation of Na+ ions and therefore improve high reversible capacity, good cycling stability and high rate capability. In this study, we report an activated graphene with high Na+ storage capacity and good rate capabilities by high-temperature annealing with ZnCl2 as the etching agent. The superior electrochemical performance of ZnCl2-assisted activated graphene is due to the meso- and micropore structure, which makes the activated graphene for the fast diffusion of the relatively large-sized Na+ with low ion-transport resistance and effective storage of Na+ during charge-discharge processes. More details about the electrochemical properties of ZnCl2-assisted activated graphene will be discussed in the meeting.

Resume : Sodium-ion batteries (SIBs) are gaining more attention as alternatives to lithium-ion batteries (LIBs), due to the abundance of sodium salts, as well as the similar chemistry to LIBs. The performances of SIBs are generally governed by the properties of the electrode materials. As for anode materials, graphite, the commercial anode for LIBs, does not function in SIBs due to its extremely low capacity. This can be alleviated with solvent co-intercalation, but such a method brings about its own set of challenges. Moreover, comparing the ionic radii, the Na+ ion (1.02 nm) is larger than the Li+ ion (0.59 nm), so Na+ has much more difficulty in intercalating into graphite than Li+, which is also conducive to the reduced rate performance of graphite electrode in SIBs. Therefore, numerous attempts have been made to find suitable anodes for SIBs. Among the various carbon-based anode materials, graphene with similar composition as graphite has been significantly explored as an electrode material for SIBs, owing to its high surface area (2630 m2g-1), sufficient porosity, superior conductivity (104 Scm-1), and excellent mechanical stability. Moreover, few studies have demonstrated that the electrochemical performances of graphene could be further improved by chemical activation. This activated graphene has a large fraction of meso- and micropores that provide the pathways for easy accessibility of electrolytes and fast transportation of Na+ ions and therefore improve high reversible capacity, good cycling stability and high rate capability. In this study, we report an activated graphene with high Na+ storage capacity and good rate capabilities by high-temperature annealing with ZnCl2 as the etching agent. The superior electrochemical performance of ZnCl2-assisted activated graphene is due to the meso- and micropore structure, which makes the activated graphene for the fast diffusion of the relatively large-sized Na+ with low ion-transport resistance and effective storage of Na+ during charge-discharge processes. More details about the electrochemical properties of ZnCl2-assisted activated graphene will be discussed in the meeting.

Resume : SrTiO3 is an important model oxide but also a promising candidate for different applications based on thin films. Unfortunately, the deep knowledge on the bulk defect chemistry cannot be straight forwardly applied to thin films and nanosized particles. The origin of these differences is not yet completely understood, but it is often assumed that the modified microstructure can play a significant role. Also effects of nonstoichiometric composition, strain as well as higher dimensional defects are possible. Further systematic investigations of the thin films is required to gain a deeper understanding of the structure-property relation. In this contribution, slightly Fe-doped SrTiO3 (Fe:STO) thin films were deposited on Nb-doped SrTiO3 substrates by pulsed laser deposition. Different deposition parameters like laser frequency, laser energy as well as oxygen partial pressure were systematically varied. In addition to a standard polycrystalline target, single crystalline Fe:STO and off-stoichiometric compositions (Sr excess or depletion) were used as target materials. The obtained thin films were investigated by means of inductively coupled plasma optical emission spectroscopy (ICP-OES) and high resolution X-ray diffraction measurements (HRXRD). A combination of these methods gives insights into the thin film composition, particularly into the presence of A/B site off-stoichiometry and the (micro-)structure. This allows identification of crucial preparation parameters and the possibility of defect engineering of metal oxide thin films. The gained knowledge on structure-property relations can not only be valuable for SrTiO3 thin films but can be applied to a broad range of functional oxides.

Resume : In 2011, it was found that doping HfO2 leads to the appearance of a ferroelectric effect. Currently, the research and development of high-speed memory devices which retain information when their power is off, are conducted on a large scale using a ferroelectric effect in doped HfO2. The aim of this work is an experimental and theoretical study of the charge transport mechanism in hafnium oxide doped with lanthanum La:HfO2. We used four theoretical models for charge transport experiments simulation: the Frenkel model of isolated coulombic trap ionization, the Hill model of overlapping coulombic traps, the multiphonon Makram-Ebeid and Lannoo model of isolated neutral trap ionization and the Nasyrov-Gritsenko model of a phonon-assisted tunneling via traps. It is shown that the widely excepted Frenkel model of isolated coulombic trap ionization does not quantitatively describe the charge transport in La:HfO2. The charge transport in La:HfO2 is quantitatively described by the recently proposed Nasyrov-Gritsenko model. The trap parameters in La:HfO2 are quantitatively determined. It is established that in La:HfO2, oxygen vacancies act as traps, i.e. oxygen vacancies are responsible for leakage currents in La:HfO2. Based on this conclusion, a recommendation for reducing leakage currents in La:HfO2 is proposed. This work is supported by the Russian Science Foundation under grant 14-19-00192

Resume : It is known that the shape of metallic nanostructures determines their plasmonic properties. One of the simplest approaches for controlling the shape is using templates. In this work SiO2/p-Si template was used for formation silver nanostructures. Porous SiO2/p-Si template was obtained using swift heavy ion-track technology including irradiation and chemical etching. The formation of silver nanostructures in the porous SiO2/p-Si templates by electroless wet-chemical method was investigated. The morphology of the nanostructures depending on the process kinetics’ like solution temperature (20-50°C) was studied and the different crystals morphology were determined. It was found dendritic silver architectures are formed at 35°C. Possible localization of "hot spots" on the dendrites surface was proposed. Such nanostructures can amplify the Raman signal from Nile blue up to 10-6 M by using the different excitation wavelengths of 473, 532, and 633 nm. This opens up the possibility of using Ag nanostructures as SERS-active surfaces for different branches of (bio)sensorics. The authors acknowledge the support of the work in frames of H2020 - MSCA - RISE2017 - 778308 - SPINMULTIFILM Project, the Scientific-technical ‘program Technology-SG’ [project number 3.1.5.1], and Belarusian Foundation for Basic Research [project number Ф17М-005].

Resume : This work is dedicated to the study of possibility of using of SiO2/n-Si porous template to formation of copper nanostructures (CuNS) with different morphology for the surface enhanced Raman spectroscopy (SERS) applications. CuNS in the pores of SiO2/Si are formed by the electrochemical deposition technique. The studies of potentiodynamic current-voltage curves has made it possible to determine the characteristic features of copper deposition on n-Si substrate from an electrolyte, containing 0.5 M boric acid and 0.01 M copper sulfate, as well as to select the Cu deposition modes in the porous SiO2 template, which has made it possible to form a compact copper deposit (with the potential of minus 0.5 V) or dendritic one (with potential of minus 1.0 V). An analysis of the efficiency of CuNS for SERS using the water solution of the Rhodamine 6G dye has made it possible to determine that for the entire studied frequency range, the amplification coefficient of the corresponding signal is in the area 103, with a maximum (3.4•103) for the line 1650 cm-1. The authors acknowledge the support of the work in frames of H2020 - MSCA - RISE2017 - 778308 - SPINMULTIFILM Project, the Scientific-technical ‘program Technology-SG’ [project number 3.1.5.1], and Belarusian Foundation for Basic Research [project number Ф17М-005].

Resume : The study of ionizing radiation effect on materials, including nanostructures, is one of the tasks of modern materials science, because it has both fundamental aspect of irradiation effect on structure and physical properties of materials and an applied aspect - development of sensible or resistant to ionizing radiation materials and devices. The paper presents results of synthesis of Zn nanotubes obtained by electrochemical deposition in pores of polymer matrices and study of their structural and electrophysical properties after forward modification by ionizing radiation with different doses. Structural features of polycrystalline Zn nanotubes are studied by scanning electron microscopy, X-ray diffraction and energy dispersive analysis methods. The influence on crystal nanotubes structure of irradiation with Ar8+ ions with energy of 1.75 MeV/nucleon and dose in the range from 1 × 109 to 5 × 1011 ion/cm2 is demonstrated. As a result of irradiation, there are insignificant changes in lattice parameter of Zn nanotubes. At high doses, localized highly defect zones are detected. Such zones lead to critical change in the structure and physical properties of nanotubes. It is shown that modification of crystal structure leads to change in electrical conductivity of nanotubes: at low doses the electrical conductivity increases, but after overcoming threshold value (1011 ion / cm2) - sharply decreases. The changes in crystal structure and corresponding changes in conductive properties of nanotubes due to irradiation confirm possibility of using Zn nanotubes arrays as a base material for creating compact and lightweight elements of flexible electronics, including those intended for operation under extreme conditions.

Resume : Ion irradiation is not only an attractive method, which enables to determine applicability limits of nanostructures in extreme conditions, but also a technological process, which allows to obtain nanomaterials with novel properties in the long term. In this paperwork, effect of C3+ions irradiation with energy of 28- MeV C3+ and fluences up to 5*1011 cm-2 on the structure and properties of template-synthesized nickel nanotubes with length of 12 ?m, diameters of 400 nm and wall thickness of 100 nm is studied. It is demonstrated that the main factor influencing the degradation of nanostructures, which are under irradiation in PET template, are processes of nanostructures material mixing with polymer, which surrounds them. The influence of irradiation with various fluences on crystal structure, electrical and magnetic properties of nickel nanotubes is studied.

Resume : Even though defects are always present in solids, they are not easy to be theoretical and rigorously addressed, since their presence breaks down the Bloch theorem and the reciprocal space. In the past, perturbative methods were frequently used for their analysis. In this work, we present a renormalization plus convolution method developed for the Kubo-Greenwood formula to investigate the effects of local and correlated defects on the electronic transport in nanomaterials. This method combines the convolution theorem with the real-space renormalization technique, being able to address in an exact way the macroscopic multidimensional systems without translational symmetry [1]. We have analytically proved the existence of null and ballistic conduction states in periodic chains with Fano defects [2], as well as a novel ballistic conduction state in nanobelts with a non-periodic arrangement of atoms [3]. Moreover, improvements to the ballistic alternating current (AC) conductivity are observed in non-periodically segmented nanowires [4]. This work has been supported by CONACyT-252943 and UNAM-DGAPA-IN114916. Computations were performed at Miztli of DGTIC-UNAM. [1] V. Sanchez, C. Wang, Phys. Rev. B 70, 144207 (2004). [2] C. Ramirez, V. Sanchez, Phys. Status Solidi A 210, 2431 (2013). [3] C. Wang, C. Ramirez, F. Sanchez, V. Sanchez, Phys. Status Solidi B 252, 1370 (2015). [4] F. Sanchez, V. Sanchez, C. Wang, J. Non-Cryst. Solids 450, 194 (2016).

Resume : As a powerful method, ion implantation has been widely used to synthesize various nanostructures embedded in dielectrics. In this work, ion implantation together with post annealing has been carried out to realize both synthesis and modification of the TiO2 nanostructures embedded in SiO2. Optical-grade silica samples were implanted with 105 keV Ti ions to the fluence of 1×1017/cm2, and were then subjected to furnace annealing in oxygen ambient at high temperature to form TiO2 nanofilms. The obtained TiO2 nanofilms was irradiated by 100 keV Cu or 120 keV Ag ions to the influences of 3.0×1016/cm2 or 5.0×1016/cm2, respectively. Structure, spatial distribution, optical absorption properties of the synthesized nanostructures and their thermal evolution have been investigated in detail by using various techniques. Our results clearly show that high fluence Ti ion implantation could lead to formation of TiO2 nanofilms with rutile phase after high temperature annealing, which gives an absorption band edge at about 365 nm. The post-irradiation of Cu or Ag ions could not only largely enhance thermal growth of TiO2 nanoparticles, but also significantly narrow their band gap energy. Moreover, XTEM and AFM measurements demonstrate that the post-irradiation of Cu ions could cause the formation of the TiO2 nanorods, which may be responsible for the large redshift of the absorption behavior obtained in the Cu irradiated TiO2. However, there is nearly no change for Ag ions irradiated TiO2 samples, which is consistent of the negligible redshift in optical absorption spectrum. We suggest that thermal evolution of the TiO2 nanoparticles may be closely related to the stable oxidization of Cu in the substrate.

Resume : The initial coarse-grained one-phase powders of nonstoichiometric cubic (space group Fm-3m) vanadium carbide VCy with different composition within its homogeneity interval from VC0.65 to VC0.88 have been synthesized by high-temperature solid-state vacuum sintering of vanadium powder and carbon black. Nanocrystalline VCy powders have been produced by high-energy ball milling with different milling duration of the initial coarse-grained VCy powders. The crystal structure, chemical and phase composition, microstructure, morphology and particle size distribution of the coarse-grained and produced nanocrystalline VCy powders have been studied by the X-ray and laser diffraction, scanning and transmission electron microscopy, helium pycnometry and BET method. A functional dependence of an average nanoparticle size (more exactly, coherent scattering region) on the VCy composition, energy and duration of milling is established. The effect of milling energy and nonstoichiometry of cubic vanadium carbide VCy on deformation anisotropy, value of microstrains in crystallites, and the particle size of nanopowders has been studied experimentally. Experimental dependences of pycnometric density of coarse-grained and nanocrystalline VCy powders on the vanadium carbides composition and average particle size are determined. This research work is financially supported by the Russian Science Foundation (Grant 14-23-00025-P) through the Institute of Solid State Chemistry of the Ural Branch of the RAS.

Resume : It is well known that positive oxide charge formation occurs in Si-SiO2 system during Si thermal oxidation depending on the oxidation condition (temperature, time, cooling rate, ambient). It is due by oxygen vacancies in SiO2 film and unsaturated Si3.bonds at the interface. Until now these process is not completely studied. The purpose of present work is investigation of charge formation in the Si-SiO2 system and its diminishing by choose of appropriate oxidation condition by means of EPR and NMR spectroscopy, IR spectroscopy, CV curves, TEM and deflection measurements. Laser irradiation and ultrasonic treatment was use for interface properties modification. It has been established that at oxidation temperature 11250C at the interface formed low positive or negative oxide charge connected with Si vacancies at the interface. The obtained results coincide with point defects generation kinetic model in Si-SiO2 proposed in [1] and confirmed in[2]. References. 1.T.Y.Tan,U.Gösele,Appl.Phys.,A37,1(1985). 2. D.Kropman,S.Dolgov,T.Kärner,Appl.Phys.A62.469(1996).

Resume : Weak magnetic fields (WMF) induce modification (μB<

Resume : Single crystals of the AgGaS2 compound belong to the class of wide-band-gap semiconductors with a high specific resistance. AgGaS2 thiospinel is a multifunctional high-photosensitive semiconductor in the visible range of spectrum and may be used as active material for creation of solar cells and various optoelectronic devices. The rather large values of the effective atomic number and the energy gap make AgGaS2 a suitable material for the fabrication of X-ray detectors. The aim of this work was to study the X-ray dosimetric characteristics of AgGaS2 thiospinel. Therefore, the fabrication of AgGaS2 crystals and the experimental studies of their X-ray conductivity at room temperature became our priority direction. The X-ray intensity was controlled by varying the current in the tube at each value of the applied accelerating voltage (Va). During the measurements the effective radiation hardness was Va = 25-50 keV and interval of dose rate E = 0.75-78.05 R/min. All measurements were taken at T = 300 K. It is found that the X-ray sensitivity coefficients of AgGaS2 crystals are 1.310-11–1.410-10 (Аmin)/(VR) at effective radiation hardness Va = 25-50 keV and dose rate E = 0.75-78.05 R/min. The dependence of the steady X-ray-induced current in AgGaS2 on the X-ray dose is described by linear law. It was shown that the roentgen current in AgGaS2 crystals does not relax with time. Thus, it can be concluded that studied AgGaS2 single crystals are highly sensitive to X-rays and can be used for fabrication of fast-response X-ray detectors, which do not require cooling.

Resume : The n-type and p-type a-GaN films were successfully grown on the r-sapphire substrate with smooth mirror surface morphology. A horizontal MOCVD reactor was used at low pressure. The growth rate versus the growth temperature dependence was investigated. The holes concentration (8x1017 cm-3) was achieved by the Cp2Mg flow optimization and the parameters of thermal annealing in nitrogen. The GaN film growth rate dependence versus temperature at a constant hydrogen flow through a TEG source was studied. It was detected that the best quality of GaN films, from the point of view of crystallographic perfection and surface morphology, was observed at a growth temperature of 900-925 °C. X-ray analysis and SEM were used for samples investigation. Diffraction reflection curves were obtained and the electron and hole concentration dependences versus annealing time were studied. The measured half-width of the rolling films curve is 1.5-2 times larger than for films with ?polar orientation?. Differences are associated with different density structure defects in GaN layers of different orientations, namely nanopipes, packing defects, screw, edge and mixed dislocations. With film thicknesses rise, the crystal perfection increases, which is due to the decrease in the effect of edge dislocations. Based on the etch pits shape, the dominant type of dislocations is a mixed dislocation. Optimum parameters of doping with acceptor and donor impurities - 8x1017 and 4x1018 cm-3 are determined.

Resume : Perovskite, lead-free materials have become very attractive lately for a broad range of applications such as photovoltaic, photocatalytic, electronics. This is the case of perovskite materials with small band gap values such as bismuth ferrite (BiFeO3- BFO) which have become very attractive for photovoltaic and photocatalytic applications. By high resolution transmission electron microscopy (HR-TEM) we have evidenced nanostripe domains with alternating compressive and tensile strain in the Y-doped BiFeO3 epitaxial thin films. The joined role of doping and epitaxial strain on the dielectric enhancement was corelated with the easy response of nanodomains to electrical stimulus. Another example of how the strain engineering in thin films approach can be applied for growing thin films with enhanced the dielectric and piezoelectric responses, is for the case of (Ba1?xCax)(ZryTi1?y)O3 (BCZT) materials. Epitaxial thin films of BCTZ have been deposited on single-crystalline substrates with different lattice parameters (SrTiO3, LaAlO3, GdScO3) substrates by pulsed laser deposition. The high dielectric permittivity of BCZT thin films was attributed, besides to their high structural quality, to the enhanced susceptibility of the nanoscale domain configuration to a small external perturbation.

Resume : High Resolution Transmission Electron Microscopy (HRTEM) is the premier tool for understanding of the internal microstructure of materials at nanometer level. This method allows to distinguish real-space nano-scale peculiarities in material, and simultaneously from Fast Fourier Transform (FFT) diffraction patterns obtain the information about crystalline lattice of the investigated specific regions in the nanostructures, such us, nanoparticles, quantum dots, and etc. In this work, MBE grown and thermally treated GaAsBi/AlAs quantum wells were studied by structural (High-Resolution X-ray Diffraction, HRTEM) and optical (PL) characterizations. The analysis of profile of GaAsBi/AlAs QWs containing Bi-nanoparticles measured by HRTEM and Scanning Tunnelling Electron Microscopy in High-Angle Annular Dark-Field (STEM HAADF) mode were performed to evaluate the influence of annealing on orientation of nanoparticles and strain distribution in whole quantum structure. Energy Dispersive X-ray Spectroscopy (EDS) mapping and STEM HAADF revealed re-distribution of Bi atoms in GaAsBi quantum wells during high temperature annealing and formation of semiconducting Bi nanoparticles in the wells of GaAsBi with lower Bi content. The significant changes in crystalline lattice of GaAsBi quantum wells were shown by HRXRD ω-2θ scans. Also, the PL measurements demonstrated the additional low-energy peak appeared in the spectra after thermal treating, and attributed to semiconducting Bi-nanoparticles.

Resume : Ab initio computer simulation of electronic properties of heterostructures, composed of single layers of two-dimensional crystals (MoS2, WS2, WSe2 and MoSe2) with or without defects is performed. Different variants of the mutual layers arrangement are analyzed. It is established that all configurations demonstrate semiconductor properties, however, in contrast to individual layers, several heterostructures show an indirect-gap character. The energy gap values of the heterostructures considered are 0.88, 1.25, 1.06 and 1.07 eV for MoS2/MoSe2, MoS2/WS2, WS2/WSe2 and MoSe2/WSe2 structures, respectively. The influence of vacancy defects and substitutional impurities (Te atom on the chalcogen site) on the electronic properties of the considered systems is established. It was found that both defect types lead to the reduction of the band gap. The prospects of the band-gap engineering realized by modifications of atomic structure into fabricated heterostructures are shown.

Resume : The influence of γ-irradiation on the spectral characteristics (intensity, peak position and half-width) of two types of uncapped InxGa1-xAs/GaAs (8 ML, x = 0.4) quantum dots (QD) grown on GaAs (100) substrates is studied. The radiation doses varied from 1×105 to 1×108 rad. The structures of A type are characterized by double-peak distribution of QDs sizes while in B type samples the distribution is rather wide. Irradiation with low doses of γ-quanta (105, 106 rad) improves the luminescence intensity of both types of samples due to passivation of non-radiative recombination centers and annihilation of defects within QDs and at the interface. High doses of γ-quanta ( 107 rad) cause further increase of emission intensity in A sample and decrease in B sample. Spectral positions of luminescence bands in both types of samples shift with the dose increase. However, samples A demonstrate monotonous blue shift while in the spectra of B samples the red shift at low doses is followed by the blue shift at high doses. The behavior observed was interpreted based on the specific configuration of defects and stresses in two types of systems, interdiffusion of components and change of QDs sizes under high irradiation doses. To explain the non-trivial intensity behavior in A-type samples the model of exchange by carriers between QDs and wetting layer is advanced.

Resume : Method of variation of humidity sensing characteristics of thin nonstoichiometric nanocrystalline tin dioxide films was proposed in this work. Nanocrystalline tin dioxide films were fabricated by means of DC magnetron sputtering of tin target with the following two-stage annealing process in air. The 1st stage included heating up to 200 °C and isothermal annealing during 2 hours. In order to obtain tin dioxide films with different concentration of oxygen vacancies responsible for film conductivity the annealing temperature on the 2nd stage was varied in the range 300–450 °C. Characterization of structural properties of nanocrystalline tin dioxide films was made using Raman spectroscopy and X-ray diffraction analysis. Concentration of charge carriers in films prepared at different annealing temperatures was determined by Hall measurements. Correlation between stoichiometric composition (concentration of oxygen vacancies) of tin dioxide films and humidity sensitivity was found. This work was supported by the EU Programme Horizon 2020 (Grant Nos. H2020-MSCA-RISE-2015-691010 HUNTER and H2020-MSCA-RISE-2015-690968 NANOGUARD2AR).

Resume : SnS is a promising earth-abundant, less toxic, low cost, p-type semiconductor material for photovoltaic (PV) applications because of its direct bandgap varying between 1.3 to 1.5 eV and high absorption coefficient. A small variation in the elemental concentration of a chemical compound could lead the formation of additional electronic defect states in the material, thereby altering the overall microstructure and thus induced properties. In this work, we observed chemical constitution-induced modification in the morphology and optoelectronic properties in SnS. To this end, SnS particles were prepared using the solution chemical route and were characterized using a wide range of experimental techniques, such as XRD, FESEM, HR-TEM, EDS, XPS, UV-Vis spectrophotometer and STM/STS. All these SnS particles are found to be Sn-rich and p-type. However, distinctly different morphologies (i.e., flower-like and aggregated ones) are observed, which are then correlated with the electronic defect states, induced because of the presence of Sn vacancies, Sn antisites and/or Sn interstitials. A combination of XRD, EDS, XPS and STM/STS data confirmed the presence of higher concentration of Sn vacancies along with lower quantities of Sn antisites in the SnS particles with flower-like morphologies, hence giving rise to higher hole concentration, which then leads to reduced transport, optical band gaps, and barrier heights.

Resume : An interest in PbS quantum dots (QDs) is caused by the possibility of changing their energy spectrum in a sufficiently wide range from 0.43 eV to several eV, depending on the QD size. However, the origin of the luminescence in the PbS QDs - the dark exciton state [1] or the trap states associated with the surface defects [2] - has not been clear until now. Therefore, in this work we have investigated the optical properties of PbS QDs with different types of surface states, namely, the PbS QDs surrounded by - 1) the organic Langmuir-Blodgett matrix (behenic acid), 2) alkanes - the residues of the LB matrix and 3) PbS surface oxide. Based on the QD size distribution (obtained by the TEM), the calculation of the photoluminescence (PL) spectra of QDs has been made and they have been compared with the experimental ones. It has turned out that in the QDs in the LB matrix, the PL dominates with a maximum near 1.6 eV, while its position coincides with the calculated position of the quantum levels. The annealing of the samples accompanied by the enlargement of the QDs and an increase in the concentration of the surface defects leads to the disappearance of PL. At the same time, the formation of the oxide on the surface of the enlarged PbS QDs passivating the surface defects leads to the appearance of PL with an energy of 0.8 eV which is equal to the calculated one. [1] M.S. Gaponenko et al. Physica E 53, 63–65 (2013) [2] Kim D, Kuwabara T and Nakayama M, J. Lumin. 119/120, 214 (2006).

Resume : Nitride-based thin films are widely used as protective coatings due to their specific combination of properties suitable for numerous applications. One of the significant potential applications of such coatings is the development of radiation tolerant coating materials for nuclear applications. Radiation environment induces different kinds of damages in the materials, which results in their degradation. One of the radiation induced effects is the appearance of point defects. The presence of boundaries proved to be very effective in reducing the number of such defects. Therefore, multilayer systems are considered as coating materials. In the present study, we consider multilayer thin coatings ZrN/Si3N4 with different thicknesses of monolayers: unirradiated and irradiated by He ions. In order to estimate the effect of radiation on these coatings, we investigate the modification of microstructure before and after irradiation. One of the effective methods used for structural characterizations of materials is the X-ray diffractometry. Due to the presence of texture, performing the measurements in coplanar geometry (e.g. conventional θ/2θ scan) turns out to be not effective: it does not enable to obtain a sufficient number of reflections for a reliable analysis (only two or even one reflection). In order to perform more comprehensive analysis of microstructure, it is necessary to use more reflections. Taking into account the presence of texture, one can evaluate the directions in which the best conditions for the observation of different reflections are realized. The use of noncoplanar measurement geometry enables the accessibility to a larger number of measured Bragg reflections comparing to other measurement geometries. Such type of measurement requires a special type of experimental data processing. In this investigation, the diffraction profile broadening is conditioned by a small grain size and instrumental function, the grains being modeled by an ellipsoidal shape with two equal in-plane axes. The measured profiles are connected into a single scan for the simultaneous fitting by the theoretical curve. As a result of the fitting procedure, the microstructural parameters of multilayer coatings were estimated. The results obtained by X-ray diffraction are in a good agreement with those obtained from high-resolution and scanning transmission electron microscopy images.

Resume : Partial replacements of the RE cations with iso- and heterovalent ions in the REVO4 compounds lead to various changes of their physical and chemical characteristics. Doping of the EuVO4 nanoparticles with Ca2+ cations was applied to make compounds with improved luminescent characteristics. The Eu1-xCaxVO4 compounds with x = 0, 0.05, 0.1, 0.15 and 0.20 were prepared by aqueous nitrate–citrate sol–gel synthesis. The obtained samples were characterized by XRD and SEM analysis. The Eu1-xCaxVO4 samples are crystallized in tetragonal structure. Phase composition of the sample depends on the x value. Increasing calcium ions concentrations leads to formation of the EuVO4 and CaV2O6 phases’ mixture. Luminescence spectra of the synthesized Eu1-xCaxVO4 nanoparticles in the 580 – 720 nm spectral range are presented by intensive linear emission typical for f-f transitions in the Eu3+ ions. The Ca-doping leads to formation of two types of emission centers and arising of additional excitation band near 400 nm. The conclusion was made that formation of the second type of emission centers in the Eu1-xCaxVO4 samples is connected with impure CaV2O6 phase. The additional wide excitation band in the 360 - 425 nm spectral range is related with transitions in the VO43- anions distorted by the Ca2+ cation defects.

Resume : For intercalation with Ga, were used GaS single crystalline plates, with thicknesses of 0.1-2 mm, obtained by cleavage of the single crystals, grown by vertical Bridgman method. The intercalation was done by thermal annealing (TA) of GaS lamella in Ga at 1100K, for 24 h. The electrical conductivity in the perpendicular and parallel directions to the lamella surface was ~2•10-8 Ω-1•cm-1 and ~5•10-5 Ω-1•cm-1, respectively. The intercalation process is facilitated by both the layered structure of the GaS compound and the weak, polarization, interlayer forces. Ga island layers, with transmission coefficient of ~0.3 at λ=0.53 μm, were formed in the interlayer space of the GaS plates as a result of the TA. Raman analysis of several surface regions of both plates kept in atmosphere and freshly cleaved plates, showed that the structure of the spectra depends on the Ga islands position. Although the valence bonds at elementary packings (S-Ga-Ga-S) surface are closed, the impurities adsorption occurs in normal atmosphere, and it manifests itself by the presence of the vibration bands associated to the polar molecules (e.g. CO, H2O, N2O). In the case of the freshly cleaved plates these bands are missing. For the intercalated crystals, a shift of the band gap towards low energies with ~25 meV is observed in the absorption spectra. It is related to the crystal lattice deformation as a result of the intercalation. The Ga presence leads to a small widening of the GaS XRD lines.

Resume : The intrinsic nanoscale point defects generating in the crystal lattice of ZnSe during the crystal growth and annealing strongly influence on chemical activity both the surface and the solid. This is also true for the doping process as well as the dopant solubility. ZnSe:Fe laser fabrication deals with the problem of Fe distribution control in ZnSe crystal. To manage Fe concentration we used a chemical coprecipitation of ZnS/ZnSe and FeSe from solution on a polished surface of CVD-grown ZnSe crystals with different nonstoichiometry. The influence of precipitation conditions on the film surface morphology was analyzed by SEM. Subsequent annealing under controlled Se/Zn partial pressure and further high-temperature gas-static pressing (HIP) processing resulted to the controlled profile of Fe concentration up to 1020 cm-3. As a result of the control of the intrinsic point defects, nonstoichiometry, surface morphology, and Fe-dopant profile we achieved the large quantities of differential efficiency of the produced ZnSe:Fe2 laser as ηslope = 50%. The research was financially supported by the Russian Science Foundation grant № 15-13-10028П.

Resume : We show that a stacking defect or a shift has a striking effect on transport properties of bilayer graphene. The tunneling through a ballistic n–neutral–n junction of shifted bilayer graphene may result at normal incidence in a zero-energy cloaking effect. States normally incident on the barrier are confined under it, depending on their pseudospin orientation. These confined states are perfectly decoupled from continuum states having the opposite pseudospin orientation. The barrier at normal incidence acts as a cloak for confined states. We also show a shift-dependent asymmetric zero-energy Fano resonance at near normal incidence arising from the interference between continuum and confined states. These zero-energy cloaking effect and Fano resonance are unique since they are achieved due to the stacking defect. They do not exist in the same setup of perfectly Bernal-stacked bilayer graphene.

Resume : Gallium Nitride (GaN) has been the root of some of the most revolutionary technologies in the past decades. It has set standards in a variety of fields, ranging from Light Emitting Diodes to High Electron Mobility Transistors. More recently, GaN is set to raise the bar once again, this time in the field of radiation hard electronics. Extreme radiation environments, such as space and nuclear reactors, pose significant technological challenges requiring novel semiconductors for more efficient and enduring devices. Although the response of GaN to low energy radiation is fairly well understood, the same cannot be said for high energy radiation. Focusing on this regime, here a study will be presented on the interaction of Swift Heavy Ions (SHI) with GaN. SHI of different energies are used to study the different mechanisms governing the interaction such as track amorphization and recrystallization, overlap effects, defect creation, voids and hole formation near the surface. Experimental results, obtained with different techniques, will be shown and compared with the predictions obtained with a Molecular Dynamics-Two Temperature Model simulation scheme. The good agreement between the experimental and modeled results, in particular the track morphology and the damage concentration, leads to an improved knowledge of the interaction. The resultant model can be applied not only in additional studies but also to engineer future technologies.

Resume : Two-dimensional molybdenum-disulfide (MoS2) layers can achieve a high catalytic activity for hydrogen evolution reaction upon appropriate modification of its surface. In its unmodified form, crystalline MoS2 shows low-performance due to its inert basal planes. In order to overcome this, one can either increase the amount of catalytically active side edges or create sulfur vacancies.1 Swift heavy ion irradiation is a well-known tool for surface modifications on the nanoscale.2 By irradiating single-layer MoS2 sheets we artificially induced catalytically active low-coordinated Mo atoms and sulfur depleted regions. This results in a remarkably low overpotential of just 0.03 V, as well as in a strong enhancement of the electrochemical current density by over 160 % compared to a non-irradiated MoS2 surface. References: 1) Kibsgaard, J. et al.; Nat. Mat. 2012, 11 2) Madauß, L. et al.; 2D Mat. 2017, 4

Resume : The work is devoted to the investigation of the influence of radiation defects induced by Xe ions (167 MeV), Kr (107 MeV) and Ar (48 MeV) ions on the critical properties of superconductor tapes of the 2nd generation based on the GdBCO produced in the company SuperOx. The dependences of the critical current at T = 77 K in the self magnetic field, the critical temperature, and the width of the superconducting transition ΔTc on the ion irradiation in the wide range of the fluences are obtained. It is shown that irradiation can create additional Abrikosov vortex pinning centers. The result obtained enable us to estimate the radiation resistance of this HTSC-2 tape to the used irradiation. As for the critical temperature, its decrease begins at considerably higher fluences than the decrease in the critical current, and ΔTc also changes. At present, the results on cuprate HTSCs are increasingly explained in the framework of the phonon pairing model of Cooper pairs, namely, a decrease in Tc at high fluences can be due to a strong deformation of the Cu-O plane, which leads to a decrease in the density of states due to the smearing of the van Hove singularity on the surface Fermi. The decrease in the critical current can be explained by the partial amorphization of the superconductor as a result of the metal-insulator phase transition.

Resume : Y-substituted BaZrO3 (BZY) exhibits high grain interior proton conductivity [1], but grain boundaries have large resistances attributed to charge carrier depletion in space charge layers next to positively charged grain boundary cores [2,3]. The positively charged grain boundary cores are believed to originate from the segregation of charged defects. In this work, we perform DFT computations to calculate defect segregation energies in several BZY grain boundaries. Due to the large number of possible supercells for each grain boundary, it is not straightforward to select which supercell to perform computations on. The obvious choice of mapping out all possible supercells with DFT calculations is ruled out due to high computational cost. An alternative is to guess supercell structure based on intuition, but then low energy supercell structures may be missed. Instead, we apply a Machine Learning-based selection procedure called the Gaussian Process. In this procedure, we apply a statistical model that effectively maps out the most likely regions for low energy supercells. Hence, we are able to find the low energy grain boundary supercells at a low computational cost. Acknowledgement: This work is part of the nationally coordinated project Functional OXides for Clean Energy Technologies (FOXCET, RCN, 102006684-1), with SINTEF, NTNU and UiO as active partners. [1] E. Fabbri, D. Pergolesi, and E. Traversa, ?Materials challenges toward proton-conducting oxide fuel cells: a critical review,? Chemical Society Reviews, vol. 39, pp. 4355?4369, 2010. [2] X. Guo and R. Wasser, ?Electrical properties of the grain boundaries of oxygen ion conductors: Acceptor-doped zirconia and ceria,? Progress in Materials Science, vol. 51, pp. 151?210, 2006. [3] J. Nowotny, The CRC Handbook of Solid State Electrochemistry, CRC Press, 1997.

Resume : Hafnia is a high-κ dielectric, which is used in different electronic devices. The electronic properties of HfO2 (e.g. leakage currents) are defined by defects and traps, namely by oxygen vacancies (VO). The trap generation leads to dielectric breakdown, increasing the leakage, that leads to the FET and FRAM degradation. Active layers of RRAM utilize traps as precursors for HRS/LRS switch. The aim of the work is predicting the defect formation in dielectrics in strong electric fields using analytical, numerical and ab initio models. Despite the strides in computational performance, the ab initio simulations still require great time and efforts. Thus, analytical and half-analytical solutions of the problem can be helpful in a way of predicting conditions for defect forming. The rate of the new defect generation in the HfO2 with only one VO was calculated using the heat transfer equation with a strong positive loopback. The analytical and half-analytical solutions were found and compared with numerical ones. The most probable new defect positions and required values of the electric field were found. These results were compared with ab initio (DFT) studies of O polyvacancy structure in monoclinic HfO2. It was found that the most favorable spatial configuration of an O polyvacancy is a chain: each subsequent vacancy forms near the already existing one, no more than 2 removed O atoms are related to Hf atom. The distances between neighboring VO are (4.05-4.21) Å.

Resume : Cerium dioxide (CeO2) is industrially important material because it exhibits high ionic conductivity, has high electrostriction coefficient and is able to catalyze select chemical reactions. Experimental data shows that defects, such as oxygen vacancies and doping atoms from the lanthanide series, may affect these and other properties of CeO2. In this work we calculated structural, electronic and energetic properties of oxygen vacancy in Tb-doped CeO2. We combined the spin-polarized DFT U calculations as implemented in VASP code [1,2] with the so-called site-symmetry approach [3]. It allowed us to analyze interactions between the oxygen vacancy and the surrounding cations and the Ce and Tb ions reduction. We, thus, explored all possible Wyckoff positions within the given supercell size for the Ce-site substitution and the oxygen vacancy with an aim to find the most stable configuration. The emphasis was put on the analysis of magnetic configurations and electron localization effects using the density of states and charge density plots.

Resume : Narrow band gap semiconductors such as TiNiSn half-Heusler alloys or PbTe are considered as promising materials for application in thermoelectric devices. The perspective way to improve the desired properties is in using these materials obtained by sintering of nano-powders. This may increase Seebeck coefficient together with significant decrease of thermal conductivity. Much less is known about the role of dopants segregating to grain boundaries (GB) in changing the conduction properties. We report the results of ab initio calculations aimed at determining the role of impurities that may change the type of conductivity in these two classes of materials. It is demonstrated that alloying of PbTe with small amount of Na substituting for Pb leads to p-type conductivity, while Cl substituting for Te makes PbTe an n-type material. Calculations for TiNiSn show that alloying with Cu makes the material of n-type, and alloying with Fe leads to p-type conductivity. For nano-structured materials the situation is different. It is shown that Na or Cl segregated at GB in PbTe the n-type conductivity should be observed. In Cu-doped nano-structured TiNiSn the decrease of n-type charge carriers caused by localization of electrons between Ti and Cu atoms is found. Segregation of Fe at GB leads to vanishing of band gap, and to semi-metal type conductivity of the material. These results are confirmed by the calculations of the maps of the electron density distribution in the vicinity of GB.