Defect-induced effects in nanomaterials

Resume : We have investigated optical properties of heavily Ga-doped ZnO (GZO) polycrystalline films, which can be promising low-loss alternatives to metals at the telecommunication wavelength bands around 1300 nm and 1550 nm for plasmonics. Current plasmonic devices based on metals or metal alloys at the optical frequencies face significant challenges due to losses encountered in the materials. We deposited GZO films on glass substrates (200ºC) with various thicknesses ranging from 100 to 350 nm by ion-plating with dc arc discharge. Hall effect measurement results showed that 105- and 344-nm-thick GZO films have electrical resistivity of 2.5×10-4 Ωcm, carrier concentration of 1.08×1021 cm-3 and Hall mobility of 23 cm2/Vs and electrical resistivity of 1.8×10-4 Ωcm, carrier concentration of 1.23×1021 cm-3 and Hall mobility of 29 cm2/Vs, respectivley. Hall mobility increased with thicknesses up to 344 nm, whereas carrier concentration changed a little. Analysis based on Drude model shows that 105- and 344-nm-thick GZO films exhibited negative real permittivity at wavelenghth of more than 1256 nm and 1198 nm, respectively, which shows that the samples had a plasma frequency higher than the desired frequency of the application. Note that all the GZO films exhibited values of the imaginary part of the dielectric function of less than 0.6 in the range of wavelength smaller than 1500 nm. Those findings prove that the GZO films can be a promising material for the plasmonics.

Resume : We discuss, how the one-dimensional confinement affects the electronic and energetic properties of point defects (color centers) in perovskite ultrathin films with respect to the bulk phase. Barium zirconate, BaZrO3, has a perovskite structure and serves as one of the constituent materials in electroceramic capacitors used in wireless communications, high temperature proton conductor and substrate for thin film growth. We have considered BaZrO3 as a model for a wide class of ABO3 perovskite-structured materials with partly covalent chemical bonding. Oxygen vacancies are common defects in perovskites responsible for transport properties. In ultrathin films, confinement effects arise due to the spatial restrictions of ionic relaxation around the defect sites, change of phonon spectra and expansion of the electronic wave function beyond the film boundaries. The study has been carried out performing ab initio simulations within the hybrid HF-DFT LCAO theory. Neutral and charged oxygen vacancies were considered in the bulk phase and in ultrathin films, where the defect was placed in the central layer of slabs with a thickness ranging from 3 to 13 crystalline planes along the [001] direction. As terminating layers of the films, both BaO and ZrO2 crystalline planes have been considered. We analyze the confinement effects through changes in the band structure, phonon spectra, electronic density distribution and the formation energies of defects in ultrathin films.

Resume : The mechanisms of electron and hole trapping in SiO2 and the nature of trapping sites are important for our understanding of a wide range of physical phenomena, such as radiation-induced damage and electrical breakdown, and for applications in fiber optics and micro-electronics. Hole trapping in silica has been relatively well understood with models of trapped holes and several hole trapping defects well established. Using classical and ab initio calculations we demonstrate that extra electrons can be also trapped in pure crystalline and amorphous SiO2 (a-SiO2) in deep band gap states. The structure of trapped electron sites in pure a-SiO2 is similar to that of Ge electron centers and so-called [SiO4/Li]0 centers in quartz. Classical potentials were used to generate amorphous silica models and density functional theory to characterize the geometrical and electronic structures of trapped electrons in crystalline and amorphous silica. The calculations demonstrate that an extra electron can be trapped at a Ge impurity in alpha-quartz in six different configurations. An electron in the [SiO4/Li]0 center is trapped on a regular Si ion with the Li ion residing nearby. Extra electrons can trap spontaneously on pre-existing structural precursors in amorphous SiO2. However, the electron self-trapping in quartz requires overcoming a barrier of about 0.57 eV and self-trapped polarons are unstable with respect to the delocalized state. The precursors for electron trapping in amorphous SiO2 comprise wide (>1320) {O--Si--O} angles and elongated Si--O bonds at the tails of corresponding distributions. Using this criterion we estimate the concentration of these electron trapping sites at ~ 4x1019 cm-3.

Resume : Epitaxial Pb nanoparticles (NPs) were synthesized by high-fluence ion implantation in single crystalline Si, Al and Cu, i.e. three matrices in which Pb has a limited solubility. By varying the fluence, implantation temperature or annealing conditions, the NP size (5-20 nm) and size distribution can be tuned. In combination with the selection of the matrix, the NP lattice parameters can be tuned. The melting/solidification of these Pb NPs reveals large superheating and supercooling effects. These thermal hysteresis effects, which drastically depend on the size of the NPs, are due to the (i) epitaxial alignment and (ii) different lattice mismatch between the Pb particles and the matrices, leading to a different pressure on the Pb NPs. Hence, this effect can be used to modify the melting behavior of the embedded Pb NPs. Pb NPs in Al (two superconductors with different critical parameters) exhibit a single superconducting transition with a critical temperature Tc, which increases linearly with the Pb/Al volume ratio. The good agreement with theoretical predictions of the proximity effect in the Cooper limit for strongly coupled superconductors, illustrates that the quality of the Pb/Al interface is excellent, which we attribute to the ion beam synthesis process. In this presentation, we will discuss the intimate interplay between the structural properties of the Pb NPs, e.g. the particle size, the matrix and the interface quality, and their thermal and superconducting response.

Resume : In the course of the past decade substantial progress has been made in understanding stress generation during thin film growth thanks to real-time and in situ diagnostics based on the measurement of the substrate curvature. Different archetypal stress behaviors have been reported based on the adatom mobility of the deposited material [1]. For deposition conditions that entail the use of hyperthermal species, e.g., magnetron sputtering, cathodic arc and ion beam assisted processes, the development of large compressive stresses is generally reported. For refractory metals, the stress level can reach up to several GPa, which can lead to premature failure by buckling at the film/substrate interface. It is well admitted that defect creation during film growth, as a consequence of the ‘atomic peening’ process, contributes to this compressive stress build-up. However, the intrinsic mechanisms of defect incorporation are not yet fully understood, especially for nanoscale thin films, where grain boundaries may play a significant role. The aim of the present work is to provide a comprehensive picture on the origin of defect-induced compressive stress development during sputter-deposition of low-mobility metals by combining situ wafer curvature (MOSS) and ex situ structural characterization (XRD, XRR, AFM, HRTEM). Examples will be given for Mo and Ta films, deposited in a large range of energetic bombardment conditions, by varying the working pressure, bias voltage and ionization degree of sputtered and buffer gas species (using the sputtering-based technique HIPIMS). The role of grain boundaries will be highlighted by growing films on template layers with controlled grain size. A linear dependence of the compressive stress magnitude with the grain boundary density is revealed from MOSS, suggesting preferential insertion of excess atoms at the grain boundary. This grain boundary densification [2] corresponds to a stress state which is predominantly of biaxial type, as confirmed by ex situ XRD. Above a certain energy threshold, which is material-dependent, incorporation of excess atoms in the grain bulk occurs (mostly as self-interstitials), leading to a hydrostatic stress component at the origin of a lattice expansion. The stability of the growth-induced defects is discussed based on the cohesion energy of the material (stable vs. metastable phases) and stress evolution after ion irradiation (up to 1 dpa). [1] G. Abadias, J.J. Colin, A Michel, C. Jaouen, Vacuum 100 (2014) 36 [2] D. Magnfält, G. Abadias, K. Sarakinos, Appl. Phys. Lett. 103 (2013) 051910

Resume : One of the main limits of doping of pure silicon and pure germanium nanowires (Si and Ge NWs) is its inefficiency when the diameter is reduced, as a consequence of surface segregation of impurities, strong quantum confinement and dielectric mismatch [1]. In the case of doping with boron or phosphorus impurities of Si and Ge NWs the impurity state is deep into the band gap and cannot be electrically activated at typical device temperatures. This phenomenon is responsible of several problems about the real applications of these types of materials for electronic devices. Results of our ab-initio DFT calculations on core-shell silicon-germanium NWs [2] (with diameter of 2.4 nm) show how this limit can be easily overcome by opportune doping with boron and phosphorus impurities. In these nanostructures, in fact, the band offset between the two materials causes localization of the valence states on germanium and of conduction states on silicon. As a consequence of this property, with particular doping conditions, a one-dimensional electron (hole) gas at the band edge is created and the carrier density is uniquely controlled by the impurity concentration without no need of thermal activation. Additionally, SiGe core-shell nanowires, providing naturally the separation between the different types of carriers, electron and holes, are ideally suited for photovoltaic applications. [1] M. T. Bjork, et al. Nat. Nanotech. 4, 103 (2008). [2] M. Amato, et al. Nano Letters, 11, 594, (2011).

Resume : Titania and strontium titanate are well-known semiconductors comprehensively studied in materials science, thanks to their widespread technological applications. Doped TiO2 and SrTiO3 nanotubes (NTs) are known to be potentially promising electrodes for visible-light-driven photocatalytic applications. In this study, ab initio calculations have been performed to study the ground state properties of monoperiodic TiO2 and SrTiO3 nanotubes containing extrinsic point defects. The hybrid exchange-correlation functionals B3LYP and B3PW within the framework of density functional theory have been applied for calculations on NTs with the following substitute impurities: C(O), N(O), S(O), and Fe(Ti). The variations in formation energies obtained for these doped nanotubes have allowed us to predict the most stable compositions, irrespective of the changes in growth conditions. The changes in the electronic structure have been analyzed to show the extent of localization of the in-gap states induced by defect. The mid-gap levels positioned inside the band gaps of defective nanotubes make them attractive for numerous applications. Moreover, inspecting the electronic charge isodensity plots, we have concluded that increased covalency in impurity-host interatomic bonds may enhance adsorption properties of defective NTs. According to obtained results, S-doped TiO2 NT and N-doped SrTiO3 NT make these nanotubes to be good candidates for efficient photocatalyst working under daylight irradiation.

Resume : Titanium dioxide (TiO2) is a strategic material for a very wide range of applications encompassing pigments, nonlinear optics devices, gas sensor and Dye-Sensitized solar cells. Some mixed-phase TiO2 nanoparticles with coexisting polymorph (anatase + rutile, anatase+brookite) exhibit enhanced photoactivity, possibly due to the separation of charge carriers in different phases that suppresses electron−hole recombination. Hence, much research has been performed to elucidate and control the phase transformation between these two phases. Within this framework, achieving a suitable control of the phase transition behavior of nanometer-sized TiO2 materials would represent a significant progress on the way of their full exploitation in different areas of science and engineering. In this work we report visible light induced anatase to rutile structural phase transformation mechanism depending on the surrounding environment and power laser density on the samples. Thermal origin of the process was excluded by in situ Raman measurements that permit the estimation of the local temperature. The mechanism was attributed to surface defects induced by oxygen desorption involving F color centers. The kinetic of desorption process were also studied through intragap excited photoluminescence measurements. Transmission Electron Microscopy images revealed the presence of small polycrystalline aggregates suggesting the coalescence among neighbouring nanoparticles. Finally, a mechanism to promote or inhibit the transformation acting on the concentration and depth of color centers is presented.

Resume : Nano-engineered silicon carbide (NE-SiC) thin films have been grown on Si (100) wafers by low-pressure chemical vapor deposition. These NE-SiC films predominantly exhibit the 3C cubic structure with nanosized columnar grains grown along the [111] direction. A unique feature of these NE-SiC films is the high density of (111) of stacking faults and twins (planar defects) perpendicular to the growth direction that create a nanolayered structure within each grain. The response of the NE-SiC to electron and ion irradiation, as well as helium implantation and subsequent ion irradiation, has been investigated. The results from electron and ion irradiation studies suggest that defect migration is primarily two-dimensional and limited between the planar defects, which increases the resistance of the NE-SiC to irradiation-induced amorphization. Such two dimensional diffusion is supported by density functional theory calculations. The NE-SiC films have also been implanted with helium ions (up to 8000 appm) at 275°C to avoid irradiation-induced amorphization, and no bubble formation is observed. Subsequent irradiation of the helium implanted samples with 9 MeV Au ions at 700°C to 10 dpa revealed preferential bubble growth at grain boundaries, suggesting that helium migration may also be limited by two-dimensional diffusion. The nanolayered structure exhibits surprising stability under irradiation to 10 dpa at 700°C.

Resume : In-situ transmission electron microscopy (TEM) investigations were performed in order to follow the evolution of helium bubbles under heavy ion irradiation (Au, 1.5MeV) in 4H-SiC as a function of fluence. 4H-SiC thin foils containing well-characterized bubble populations consisting of a layer of bubbles with a mean radius of 3nm were used. The SiC / He bubble specimens were then observed and irradiated in-situ in a transmission electron microscope at the JANNuS-Orsay facility*. Results indicated that the effects of displacing irradiation (1.5MeV Au ions) resulted in the gradually decrease of the bubble diameter with dose. A 1-D model showed that half of the ejected–He is re-trapped during the displacing irradiation. At high dose, the excess of vacancies due the combined effects of bubble shrinkage and displacing irradiation concomitant with a large concentration of free-He-atoms leads to the formation of satellite tiny-bubbles. The system evolves toward a steady state of bubble size keeping all the helium atoms in the matrix

Resume : Silicon carbide (SiC) has been attracting an increasing interest for many applications in extreme environments such as structural components in fission and fusion reactors or for microelectronics devices. For all these applications, a comprehensive understanding of its behaviour under ion irradiation appears as a major fundamental issue. In this work, we present a combined experimental and computational study of both the amorphization and recrystallization processes that can take place in SiC under ion irradiation. For the amorphization process, 3C-SiC single crystals have been irradiated with 100 keV Fe ions at different fluences and characterized using RBS/C and XRD. Strain and damage levels have been monitored and compared to values obtained from molecular dynamics simulations that simulated controlled, defective SiC cells and a good agreement has been obtained. Furthermore, the well-known stimulation of the amorphization process has been confirmed and was attributed to the elastic energy stored in the defective layer that contains irradiation defects. Regarding the recrystallization phenomenon, damaged 3C-SiC single crystals have been submitted to swift heavy ion irradiation (870 MeV Pb ions) and a healing effect has been evidenced. The recovery has been observed experimentally using RBS/C and TEM and confirmed by MD calculations combined with thermal spike modelling.

Resume : The effect of a uniform electric field across multibarrier systems (GaAs/AlxGa1-xAs) is exhaustively explored by a computational model using exact Airy function formalism and the transfer-matrix technique. In the case of biased DFHBSL structure a strong reduction in transmission properties was observed and the width of the miniband structure linearly decreases with the increase of the applied bias. This is due to the confinement of the states in the miniband structure, which becomes increasingly important (Wannier-Stark effect).

Resume : One of the main limitations in application of Cyanoacrylate (CA) groups is their mechanical properties such as scratch resistance that is not clearly defined. Based on literature survey done by the authors, there are not any papers concentrated on role of nano-size particles on scratch behavior of Cyanoacrylate glue. Thus the main goal of the current research is focused on the role of nano-size SiO2 on scratch behavior of Cyanoacrylate. For this purpose Alkoxyethyl Cyanoacrylate and silicon dioxide nano powders were used as matrix and reinforcement respectively. Para-toluene solfunic acid and caffeine were added to the glue. All samples were scratched under different loads and the scratch velocity was kept constant. The scratch behaviors of Cyanoacrylate nanocomposites were evaluated using scanning electron microscopy. The results indicated that Cyanoacrylate nanocomposites exhibit a more brittle damage mode, which is evidenced by the regular plastic drawing and crack lines. Various scratch induced damage features, such as mar, pseudo fish-scale, parabolic crack, and material removal, observed in the studied nanocomposites. Microscopic evaluation showed that with addition of nano size SiO2, the Cyanoacrylate scratch mechanism changed.

Resume : The SiGe-based alloy is considered as one of the most promising materials for reliable and high performance microelectronic devices. The use of a lower band-gap material in the channel region of the MOSFET, such as SiGe, is a potential candidate given their compatibility with the process developed for pure Si-based devices. Moreover, the important increasing in the drain current due to the increased electrons mobility in SiGe material is expected. However, the growth of this material is not totally controlled, and the presence of defects is more than expected after a growth run of this material. Therefore, in order to obtain a global view of SiGe-based nanoscale Double Gate (DG) MOSFET performance under critical conditions, numerical modeling of nanoscale SiGe DG MOSFET including Interfacial defect effects (SiGe/Si) is indispensable for the comprehension of the fundamentals of such device characteristics. Based on numerical investigation of a nanoscale SiGe DG MOSFET including the defects in the interface region, in the present paper a numerical model for I-V and small signal characteristics by including the interfacial defects, after considering the uniform function approximation for the interface defects distribution at the drain said, is developed to explain the immunity behavior of the nanoscale SiGe-based transistor against the defect densities. In this context, DC and RF characteristics of the proposed design are analyzed by 2-D numerical simulation and compared with conventional Si DG MOSFET characteristics.

Resume : Study the penetration depth of niobium atoms in Mo (110) and (100), the construction of high-quality model of the niobium atoms near the surface of alloy. Using the low-energy ion implantation method of niobium atoms, monocrystalline samples were obtained from the niobium-molybdenum alloys . Concentration distribution of niobium atoms in a depth monocrystalline molybdenum were determined. Change of the atomic concentration on the subsurface of the alloy has been experimentally shown based on the heat treatment and prolonged heating of the crystal. A maximum concentration of niobium atoms is observed at approx. 4 atomic layer depth of the diluted alloy at a temperature close to 1400 K. A maximum atomic concentration of the niobium atoms on the subsurface of the alloy reaches to approx. 3%. Auger - spectra, spectral dependent quantum yield, and energy dependent photoelectron distribution [1] indicate that the obtained alloys are clean. Analyzing the results obtained are the following experimental facts. When a crystal surface is bombarded by ions of the alloying element, occurs a spraying of surface layer atoms of the crystal, atoms of the impurity element and the atoms of the doping component. The last one give a limit on the number of elements implemented into the surface layer of the target. On the other hand, in the process play role the atomic structure of the crystallographic orientation, the atomic ratio of the sizes niobium and molybdenum, and surface coupling ma

Resume : The results of research of resistance AlGaInP heterostructures with multiple quantum wells to irradiation of 60Co gamma rays are presented. Investigations were performed on the LEDs (λ = 630 nm). Irradiation was performed in the passive mode, i.e. without the application of an electric field, and the level of exposure was characterized by the absorbed dose. It is established that the reduction of the light output power during irradiation by gamma rays occurs in the three stages. At the first stage light output power reduction is a consequence of radiation-induced restructuring initial defects, and the second stage - due to the introduction of radiation defects. In the extreme case, the second stage proceeds to the third stage (the mode of low electron injection). On the boundary between the first and second stages relaxation processes - a partial recovery of the light output power on its overall decline are observed. Heterostructures with a pronounced effect of small doses - restoring light output power due to radiation-induced strain relaxation without the formation of additional structural defects are identified. These process precedes the first stage of light output reduction under irradiation by gamma rays.

Resume : Works carried out showed in recent years that in case of semiconductor and dielectric films in the course of ionic implantation and the subsequent annealing in blankets is formed two - and three- component nanocrystals and nanofilms. Similar researches for metals and metalfloatables weren't carried out so far. This work is devoted to research of change of topography, structure and properties of a surface of Pd and PdBa (Вa-1,5 of %) at ionic bombing and the subsequent annealing. Technological processing (ionic implantation, a thermal activation) and researches of structure, electronic structure, issue properties, degree of a covering of a surface decided by Ba atoms on use by the AES, EELS and UES methods in the conditions of ultrahigh vacuum (Р ≤ 10-6 Pa). The technique of experiment is described in [1]. The topography of a surface was studied by the SEM method in standard Camabax installation. Bombing carried out Ba+ ions with energy of E0 = 0,5-5 keV and a dose of radiation of D = 1014-1017 cm-2. Since a dose of D = 1015 cm-2 on a surface of Pd were formed separate cluster phases enriched with atoms of barium with superficial diameters to 50-60 nanometers. With increase in a dose to D ≈ 5÷6•1015 cm-2 the sizes of these phases increased and formed islands, and at a dose of D ≥ 1016 cm-2 are formed the continuous uniform alloyed layer. After warming up at T=100-1100 K in all above specified cases connections like Pd-Ba, with thickness from 3-4 nanometers (were formed at E0=0,5 keV) to 10-12 nanometers (E0=5 keV). In work the analysis of the received results is given.

Resume : Proton irradiation H (2.5 MeV) have been conducted of the 2-G composite HTS (high temperature superconducting) tapes YBCO(123) to increase the current-carrying capacity and determine the radiation resistance. The HTS tapes have complex multilayer architecture, wherein the superconducting layer takes only 1% in the thickness. TRIM Model calculations have shown that the energy of protons should be about 2.5 MeV so that the path length within the tape was more than 20 microns, and protons could achieve the superconductor layer. Irradiation was carried out on the Dubna accelerator (AG-5) and in MSU. The sample temperature did not exceed 100C during the irradiation. Measurements of Tc and Ic were carried out by the resistive method. The dependence of the critical current on the magnetic field studied in fields up to 8T at 77 K. Critical current increasing was observed at the fluence range 2x10^15 - 6x10^15 ions/cm^2. This fact arises from generation of radiation defects in the superconductor during H irradiation. A threshold was defined: 6x10^16 ion/cm^2 for radiation damage of the 2-G YBCO tape. Since protons do not cause tracks in the material, as in the case of heavy-ion irradiation, therefore the generation of pinning centers have to go through the other mechanism.

Resume : Iron oxides are characterized by a wide variety of compounds, which differ by structural and magnetic properties. The continuing interest for this kind of materials is mainly due to the ability to take advantage of their diversity to find new important applications in several research field. Among iron oxides, γ-Fe2O3 has attracted a growing attention because its use as catalyst, pigment, gas sensitive material. Its potential applications also concern the realization of high density magnetic storage device and in vivo biological studies. In this work we report the structural evolution of -Fe2O3 (maghemite) in bare nanoparticles and in core/shell -Fe2O3/SiO2 systems as a function of laser irradiation and heat treatment by the combined use of Raman spectroscopy, Transmission Electron Microscopy, X-ray Diffraction. In the bare system,-toα- Fe2O3(hematite) phase transformation was obtained with very low beam density powers (less than 2 mW at 632.8 nm focalised with a conventional 10X microscope objective). Phase transformation cannot be obtained by light irradiation in a -Fe2O3/SiO2 core/shell system, but it can be induced by heat treatment at very high temperature (1100°C). Fe2O3 nanoparticles at high temperature can diffuse inside the silica matrix forming aggregates with the  phase and increased size. The key role of the particle surface is discussed and a physical mechanism for the nucleation of hematite crystallites from the bonding of neighbouring maghemite nanoparticles through hydrate defect states is proposed.

Resume : In this work we studied the effect of ion implantation on the surface topography of single-crystal film GaAs. Were obtained electron microscopic image of a GaAs surface after various stages of ion bombardment of Ba+ with energy E0 = 0,5 keV. The surface of the " pure " GaAs has a relatively smooth microtopography. Implantation of barium ions from the dose D=4·1014 cm-2, leads to a change of surface microrelief. At a dose of D=8·1014 cm-2 in the surface region of GaAs appear separate molecular complexes - clusters with modified structure and composition. They arise due to sharp thermal heterogeneity and in some cases reach a diameter of 10-15 nm. Since the dose D=6·1015 cm-2, there is a union of separate sections (clusters) with each other. Increasing the dose of Ba+ ions to 6·1016 cm-2 leads to the complete unification of clusters and surface layers of GaAs completely amorphized. Postimplantation annealing at T=900 K for 30 min causes recrystallization of the surface layer and the formation of ternary compounds such as Ba+Ga+As. In this annealing sample implanted dose D=8·1014 cm-2, results in the formation island film, and annealing the sample implanted with D=6•1016 cm-2, - a continuous film. In both cases, the formed compound with an exemplary ternary composition Ga0.4Ba0.6As.

Resume : TlInSe2 single crystals are typical representatives of chain-layered semiconductors and attract a lot of attention due to their interesting physical properties. These properties include strong anisotropy of the electric parameters related to special features in the crystalline structure. Chain and layered crystals usually contain structural defects, such as vacancies and dislocations. The presence of these defects results in a high density of localized states near the Fermi level. The states localized in the band gap are responsible for most electronic processes occurring in semiconductors. The large anisotropy in chemical bonding (strong, ionic-covalent bonds within the chains and weak, van der Waals forces between the chains) enables effective doping of TlInSe2 single crystals. The concentration and nature of dopants have a significant effect on the electrical properties of TlInSe2 single crystals. The electrical properties (loss tangent, real and imaginary parts of complex dielectric permittivity, and ac conductivity of Er-doped (1 mol % Er) p-type TlInSe2 single crystals have been studied in the frequency range from 50 kHz to 35 MHz. The results demonstrate that the dielectric dispersion in the studied crystals has a relaxation nature. The experimental frequency dependence of the dissipation factor for TlInSe2:Er single crystals is characterized with a monotonic descending with frequency, which is evidence of the fact, that conductivity loss becomes the main dielectric loss mechanism at studied frequency range. At all studied frequencies the ac conductivity of the crystals varies according the law, characteristic of hopping conduction through localized states near the Fermi level. The Fermi-level density of states, the spread of their energies, and the mean hop distance and time have been estimated.

Resume : The effect of high-field injection–thermal and irradiation treatments on MIS structure reliability and decrease defects of the nanothin gate dielectric have been investigated. Injection-thermal treatment (ITT) of MIS structures was the high-field electron injection given the charge in gate dielectric and then the restoration of parameters of MIS structures by means of thermal annealing. MIS structures have been studied using the new techniques of control current stress. The study showed that the ITT can improve the MIS structures reliability, leading to an increase in the charge injected to breakdown and identify structures with defects. This result was attributed to a structural modification of SiO2 and its interfaces as a result of ITT. It is shown that the ITT at elevated temperatures can lead to poor reliability characteristics of MIS devices. This phenomenon seems to be associated with obstruction of the activation of electron and hole traps at elevated temperatures. It has been shown that the irradiation treatment allows to reduce the density of defects in thermal SiO2 films, SiO2 films doped phosphorus and oxynitride films and as a result is increased the reliability of MIS devices.

Resume : The investigation of the initial stage of the epitaxial growth of nanocrustals is needed to get the information on the layer structure and to identify the mechanism of the growth. With the development of the surface sensitive method of low and mean energy electron diffraction and technology tendency to nanofilm systems, the estimations of the degree of the surface perfection at the qualitatively new quasi-two-dimensional level, obtained during the epitaxial growth of real surface are needed. While investigating the ultrafine layers the sensitivity of the diffraction methods to the characteristic manifestations of growth initial stages rises, connected with the growth velocity change. Both the selective deposition with the following island coalescecence and defect annealing on substrate surface and also the development of proper nanofilm defects define the contrast of the structural and hence the electrophysical properties of the transition layers and phase boundaries. An apparatus has been made which allowed to measure the contrast of the diffraction and background intensities of low energy electron diffraction (LEED) patterns and to estimate the structural surface perfection. The initial stage of Bi layer growth on Si(111) and solid-phase epitaxy for Ge on Si(111) have been investigated. The conditions which allow to choose the production processing for atomically smooth Bi surfaces on Si(111) have been determined. The influence of heat treatment conditions for Si(111) sample on the preepitaxial preparation and structure of Ge film during annealing and evaporation stages have been studied.

Resume : Ion-electron technology coupled with atomic-sensitive diagnostic methods is widely used in modern thin film nanoelectronics. In recent years there is an increasing interest in the study of thin films of metal silicides and epitaxial films like CoSi2, CaF2 due primarily uniqueness of their physical properties. On the basis of such silicide films the new of multi-layer systems like silicide -insulator-semiconductor can be created, which are the basic elements of highly complex devices of solid state electronics (LSI, ULSI, radiation detectors, solar elements, electronic storage devices etc.). Although these films have the same crystal structure, they must be in agreement with certain requirements: the presence of strong chemical bonds and low diffuse of atoms of contacting surfaces, the proximity of the lattice constants and of the thermal expansion coefficients. The main optical parameters are the refractive index n, the reflection coefficient r, and the dielectric permittivity. All of these parameters are directly connected with the microscopic parameters of the crystal and depend on the temperature and in some cases on the thickness of the dielectric film. In this paper, the chemical composition and the distribution profile of the impurity atoms in depth of nanofilm CoSi2/SaF2 system grown on the Si (111) by molecular beam epitaxy (MBE) method under ultrahigh vacuum conditions have been studied by use of the Auger Electron Spectroscopy (AES) and by Secondary Ion Mass Spectr

Resume : High dose Fe+ ion implantation into Si assisted by an external magnetic field results in the formation of granular magnetic film with pronounced uniaxial magnetic anisotropy in the film plane[1]. In [2] it was supposed that the anisotropy is caused by the growth of elongated clusters of magnetic silicide Fe3Si and computer simulation of this process was made. Magnetic (ferromagnetic) resonance is one of the methods sensitive both to the shape of ferromagnetic particles and to their spatial arrangement. In the present work, the features of magnetic resonance signals for synthesized Fe3Si films are numerically studied. Shape anisotropy of the clusters leads to large shift of resonance signal depending on the magnetic field orientation. Dipole-dipole interaction between clusters also results in the signal shift, but, more important, strongly influences the absorption line shape (for example, at 10% concentration of clusters in the film the absorption line is bimodal). The results are due to the peculiarities of dipole field distribution over the granular film which are discussed. [1] G.G.Gumarov,V.Yu.Petukhov,V.A.Zhikharev et al. Nucl.Instr.Meth.Phys.Res.B, 267 (2009) 1600 [2] N.A.Balakirev,G.G.Gumarov,V.A.Zhikharev et al. Comp.Material Science, 50 (2011) 2925

Resume : Structure and phase composition of the coatings based on transition metal nitrides can be signifi-cantly improved by addition of silicon. Such thin films are potential candidates for radiation-tolerant materials due to high density of interfaces which act as efficient sinks and recombination sites for radiation-induced point defects. The effects of the irradiation (180 keV Xe2+, doses 1•10^16 сm-2 and 5•10^16 сm-2) on the structure, phase composition and hardness of nanocomposite (TiZr)1-xSixN thin (300 nm) films deposited by magnetron sputtering (silicon concentration x≤0.22) were studied. It was found that the increase in Si content results in the transformation of structure from nanocrystalline (x ≤ 0.06, grain size of 10-18 nm) to nanocomposite (0.09 ≤ x ≤ 0.13, grain size of 4-8 nm) and then to amorphous (x ≤ 0.22) state. The phase composition of the films changes from two-phase (crystalline c-TiZr(Si)N + amorphous a-SiNy) to the amorphous system: a-TiZrSiN. Nanocomposite TiZrSN film is a composite based on c-TiZr(Si)N grains with the size of 4-8 nm surrounded by an amorphous a-SiNy phase. Ion irradiation with Xe ions triggers the crystallization of TiZrN-rich grains for nanocomposite (0.09 ≤ x ≤ 0.13) and amorphous films (x≤0.22). It was found that irradiation leads to a decrease in nanoindentation hardness, due to the accumulation of Xe ion in the coating, as well as the elemental redistribution of solid solution constituents in the area of collisions cascades.

Resume : Epitaxial layers of GaN under investigation were MOCVD-grown on Al2O3 substrate and doped with Si up to 1.6·1019 сm-3 carriers concentration. The width of films was 2.0-2.5 μm varied. Photoluminescence measurements were carried out at room temperature in the 350–650 nm wavelength range using a Perkin-Elmer LS55 PL spectrometer. The spectral dependencies of the optical density of epitaxial structures were measured at 300 K with a spectrophotometer Specord 210 in the 350–1100 nm wavelength range. The treatment in pulse weak magnetic field was at regime with B = 60 mT, f = 10 Hz, τ = 1.2 ms, t=1, 3, 5 and 8 min. All measurements were repeated during the time that was needed to reaching some equilibrium state with non-changed OD and PL spectra. Usually, it was near the month. WMF treatment with different duration leads to different features in OD spectra. The influence of WMF on GaN/Al2O3 device structures leads to the reduction of defects, which exist at the interface film-substrate due to destruction of the metastable complexes. The study of the evolutionary features of GaN/Al2O3 structures OD spectra have shown an exponential dependence of the maximum of WMF-induced effect on the duration of magnetic-field treatment. Such WMF action can be used as a cost-effective method for modification of the structural parameters and decrease of non-equilibrium centres in semiconductor materials and devices

Resume : Light emission from rare earth (RE) doped III-N semiconductors presents great promise for applications in electroluminescence devices. RE exhibit sharp optical emission lines due to the intra-4fn shell transitions making the tuning of light emission from the ultraviolet to the infrared in the AlGaN host realized by an appropriated choice of the dopant ion. This work study AlxGa1-xN samples grown by halide vapour phase epitaxy on (0001) sapphire substrate. Ion implantation was performed with RE ions emitting in the red (Pr3+), blue (Tm3+) and green (Tb3+) region of the wavelength spectrum. The fluences range between 1x1014 at/cm2 and 1x1015 ion/cm2 and the implantations were performed with the beam tilted (10º) or aligned with the c-axis. Two energies, 150 and 300 keV, were selected to investigate the surface effects. The damage accumulation and the RE lattice site location was investigated by Rutherford Backscattering/Channeling Spectrometry (RBS/C) and High Resolution X-ray Diffraction. Rapid Thermal Annealing treatments at 1200 ºC were performed to remove damage and promote optical activation of the rare earth ions. Results show that RE ions occupy two preferential sites, the high symmetry substitutional Ga/Al site and a site displaced along the c-axis from this regular site. In order to establish models for the observed recombination centres, temperature and excitation intensity dependent Photoluminescence measurements were performed for selected samples.

Resume : Radiation influence leads to the degradation of the parameters of semiconductor structures and various manufactured on their basis semiconductor devices. Purpose is researching of "memory effect" under irradiation by fast neutrons in AlGaAs heterostructures. Objects of study - LEDs infrared range based on double heterostructures AlGaAs. Previously we irradiated the LEDs by fast neutrons and performed annealing of radiation defects in the current mode workout. Then radiation power reduction was studied under irradiation by fast neutrons. A result of researches the existence of "memory effect" established. The appearance of "memory effect" leads to an increase in radiation resistance under subsequent irradiation. The possible mechanisms of "memory effect"are considered.

Resume : Radiation effects in solid N2 attract much attention in diverse fields such as material and surface sciences, physics and chemistry of interstellar and solar systems, particle physics. Radiation-induced phenomena were discussed principally in terms of neutral species reactions. The experiments [1] revealed thermally stimulated exoelectron emission (TSEE) from pre-irradiated N2 films. Creation of ionic species N3+ in electron-bombarded solid N2 was reported recently [2]. Charged defect creation and defect-induced effects in electron-bombarded films of solid N2 were studied employing cathodoluminescence (CL), nonstationary luminescence NsL and activation spectroscopy. Recording the CL spectra sequences on exposure time enabled us to monitor defect production, excited particle ejection and fragmentation of molecules. Surface- and bulk-related species were discriminated by varying electron energy, i.e. the penetration depth. Creation and accumulation of N3+, N4+ and trapped electrons (up to 10^15 cm-3) as well as N radicals was detected especially in the nanostructured films. Spectroscopic evidence of excited N2* (C3Πu) molecule desorption was obtained for the first time. Charge recombination reaction N4+ + e → N2 + N2* → N2 + N2 + hν) is supposed to be the stimulating factor for desorption observed. Dynamics of post-irradiation processes was probed with TSL and TSEE. Comparative study of the NsL with dynamics of the TSL spectra and the TSEE yield elucidated the contribution of neutralization and recombination reactions. [1] I. Khyzhniy, E. Savchenko, S. Uyutnov, G. Gumenchuk, A. Ponomaryov, V. Bondybey, Radiation Measurements, 45 (2010) 353. [2] Y-J. Wu, H-F. Chen, S-J. Chuang, T-P. Huang, Astrophys. J. 768: 83 (2013).

Resume : We will report on carbon segregation and precipitation, and on structural transformations in strained layered Si/SiGe/Si and Si/SiSn/Si structures after molecular-beam epitaxial (MBE) growth, carbon ion implantation, and thermal treatment. The idea behind this study is that due to their specific strain distribution, pseudomorphic layers of Si/SiGe and Si/SiSn promote spatial separation of vacancies and interstitials followed by segregation of foreign dopant atoms. Both radiation damage and strain are supposed to have impact on the precipitation of poorly soluble dopants. Based on SIMS data we will demonstrate that the redistribution of the implanted carbon atoms around the strained Si/SiGe layers results in their accumulation on the Si side and depletion on the SiGe side. On the contrary, uphill (ascending) diffusion of carbon into the SiSn layer takes place in the case of the Si/SiSn structure. The TEM study demonstrates formation of plate-like defects, stacking faults and thin carbon-precipitated flakes in the Si/SiGe layers. Raman spectra reveal peaks at 1600 and 2700 cm-1 which might be associated with carbon-related phases, and graphene-like nanoflakes. No such defects are found in the Si/SiSn layers; instead, a very strong effect of retardation of tin precipitation is seen. The concepts of strain-enhanced separation of point defects and dopant precipitation will be discussed.

Resume : 18O/16O exchange annealing and subsequent Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) analysis is used to investigate oxygen transport in dense, nanocrystalline (average grain size d ≈ 300 nm) ceramics of nominally un-doped BaTiO3. All isotope profiles show the same unusual shape: a flattened profile over the first ~100 nm, followed by a short, conventional diffusion profile. We demonstrate that the entire isotope profile can be described quantitatively by a numerical solution to the diffusion equation based on an increase in the local oxygen diffusion coefficient close to the surface. This position-dependent increase is attributed to additional oxygen vacancies that are generated by diffusion of chlorine impurities out of the ceramics. The presence of chlorine derives from the chemical route necessary to produce nanometric powders: it thus indicates a new manner in which nanocrystalline ceramics may differ from their microcrystalline counterparts.

Resume : We studied the influence of 3–4 MeV electron irradiation on the electrical properties of p-n junctions formed inside Si_6/Ge_4 superlattices (SL; The lower indices are the numbers of the Si and Ge monolayers in a SL period). I-V characteristics, C-V profiles and admittance were measured at T = 4.2–300 K. At 300 K, the forward branch of the I-V characteristics (IVC) monotonously shifts with increasing electron fluence, Φ, to lower voltages. On the contrary, at 77 K it shifts to higher voltages. At Ф ≥ 1.5*10^17 cm 2, negative differential conductivity (S-type IVC) is observed. Charge carrier and compensating impurity concentration profiles were calculated from the C-V measurements. The charge carrier concentration monotonously decreases with increasing electron fluence in all sample layers. Its relative change is equal in the SL and buffer. The barrier capacitance and conductance of the structures monotonously decrease with increasing fluence at 4.2–300 K as a consequence of the charge carrier removal in both SL and buffer. Admittance measurements at f = 1 MHz show a steep decrease of the capacitance C in the as-grown sample below 30 K, accompanied by a peak in the G(T) dependence. Upon irradiation, the peak shifts to higher temperatures. From these measurements we obtained the activation energy of the level, whose recharging produces the observed behaviour, to be equal to 44 meV. Most probably it belongs to Sb that was used as a surfactant during the sample growth.

Resume : AlAs/GaAs symmetric superlattices (SLs) with periods of 2.8, 20 and 150 nm grown on SI-GaAs(001) substrates were implanted with 200 keV Ar ions at 20 K with fluences in the range from 1*10^12 to 5*10^15 cm?2. The whole damage profile was placed inside the SL. Defect production was studied in situ by means of Rutherford backscattering/channeling (RBS/C) spectrometry and after warm-up to 300 K by RBS/C and cross-sectional transmission electron microscopy (XTEM). The results were compared to those obtained on a series of Al(x)Ga(1-x)As alloy samples with x ranging from 0 to 1. With respect to the amount of damage, the thinnest-period SL behaved like an alloy of the corresponding composition, whereas the behavior of that with a period of 20 nm was already quite peculiar with no coherent amorphization of the different layers. Finally, for the AlAs/GaAs SL with a period of 150 nm, a selective damage and amorphization behaviour was clearly visible in the RBS spectra. A strong defect annealing occurred following a warm-up to 300 K, whereupon the damage profile became narrower. We found a strong dependence of the recovery on the damage level produced during the low-temperature irradiation. The amorphization mechanism of the SLs and its relation to the compositional intermixing, defect diffusion etc. are discussed from the viewpoint of the current models for amorphization in the (Al,Ga)As system.

Resume : The photoluminescence (PL) of InAs/InP quantum wires (QWRs) is observed between 1300–1550 nm, an important region for the optoelectronic industry. The resistance of optoelectronic devices to particle irradiation is crucial in space-based telecommunication applications. In this work, we report on the influence of 2.4 MeV proton irradiation on the PL of self-assembled InAs/InP QWRs and InAs/InP quantum wells (QWs) that show PL emission at similar wavelengths. The PL spectra of the QWRs consist of three main bands corresponding to families of QWRs of different height. The study of the temperature dependence of the PL reveals several excitation and transport processes of charge carriers between the wires of different heights. The proton irradiation leads to a quenching of the PL intensity both in QWR and QW samples. At the highest proton fluence used (1*10^15 cm–2) the intensity is reduced by somewhat more than an order of magnitude. This fact proves an extremely high radiation hardness of the InAs/InP QWRs because the PL in quantum size structures of other materials systems is completely quenched at such a high dose. The thermal stability of the PL is deteriorated upon irradiation, obviously due to the competition for the capture of photoexcited carriers between the QWRs and irradiation-induced defects. Another possible mechanism is tunnel escape of the captured carriers from the QWRs to neighboring defects.

Resume : ZrO2 offers diverse applications such as catalysts, high temperature and corrosion resistant coatings, sensors, radiation detectors, etc. Present work deals with the study of luminescence and structural properties of Y2O3-ZrO2 nanopowders with different Y2O3 content. The powders were sintered by co-precipitation of Zr and Y nitrates at different calcination temperatures. The structural and light emitting properties were controlled by XRD, TEM and Raman scattering, photo- (PL) and cathodoluminescence (CL) methods. At the same calcinations temperature, the increase of Y2O3 content stimulates the decrease of the sizes of ZrO2 nanograins and the transformation of crystalline phase from monoclinic through the tetragonal to cubic. Generally, room temperature PL spectra showed several bands in UV-orange range, whose shape depends on the excitation light wavelength. Along with this, CL spectra demonstrate additional “red” emission, which intensity exceeds that of other CL bands. At lower temperatures, preferable enhancement of “red” CL band, its narrowing and peak position shift to the longer wavelengths were found. This behaviour testifies to the non-elementary nature of “red” CL band. Its nature and mechanism of its excitation are discussed. It is supposed that complex defects, containing oxygen vacancies and impurities, are responsible for this emission appeared under high-energy excitation only. The dominant contribution of red emission into CL spectra opens some perspectives for its application as a marker for high-energy radiation.

Resume : Layered A3B6 crystals, in particular InSe and GaSe, have unique physical properties. So, their cleaved surface (0001) is atomically perfect and also inert in environment. Therefore, InSe and GaSe can be used for creation and investigation of nanosized objects, including high-energy irradiations. In this work, the effect of bremsstrahlung neutron irradiation (Eeff=8 MeV) on surface changes in A3B6 crystals is investigated by AFM method. The used fluences are: F1=10^13, F2=10^14 and F3=10^15 n/cm^2. For initial InSe and GaSe surfaces the roughness average (Ra) was about of 0.053 and 0.059 nm, respectively, and the maximum height difference of the relief did not exceed 0.36 and 0.56 nm, respectively. The formations on the surface of irradiated crystals are, in fact, vacancies which have a form of wells or pits. Their planar distribution is comparatively homogeneous. For GaSe the Ra value increased to 0.83 and 1.29 nm at fluences F1 and F3, respectively, the density of nanoformations (NF) decreased from ~6x10^9 cm^-2 to 2x10^9 cm^-2. Their vertical dimensions did not exceed 1 nm for the fluence F1, but increased by 2–3 times for F3. In the case of InSe, at fluence F1 density of NF was ~2x10^8 cm^-2 and their vertical dimensions did not exceed 2 nm but at fluence F3 these values became ~4x10^7 cm^-2 and ~10 nm, respectively. Note that for the sample subjected to the maximum irradiation the broadening of separate pits and their coalescence into clusters of a bigger size take place.

Resume : Owing to its properties: high melting point, low vapor pressure, low physical and chemical sputtering yields, low thermal expansion, electrical conductive properties and relative chemical inertness, tungsten seems to be one of the best candidates to be used as shielding material in plasma facing materials (PFM) for future nuclear fusion reactors. Nowadays, the capabilities of nanostructured materials for such applications are being attracted much attention due to their radiation-resistant and self-healing behavior. In this work, the capacity of the nanostructured W (nW) as protective role in PFM is studied and the radiation-induced changes in the structure and mechanical properties have been investigated. For this purpose, high density coatings made of nanometric tungsten columns (nW) were prepared by direct current (DC) magnetron sputtering and later were implanted under different conditions: (i) single implanted with H, (ii) sequentially with C and H, and (iii) simultaneously (co-implanted) with C and H at room temperature. The stress state was analyzed by X-ray diffraction, while the mechanical properties and adhesion to the substrate have been characterized using the nanoindentation and the nanoscratch techniques respectively.

Resume : In many modern applications which employ electric fields of significant strength, such as the Atom Probe Tomography (APT) technique, a successor of field ion microscopy (FIM), or more technological applications such as particle accelerators and vacuum interrupters, it is of great importance to understand the response of surface defects on the field. How strongly atoms on a metal surface or on a semiconductor surface are charged in response to strong electric fields and what is the difference in the mechanisms of surface charge formation can help to understand the atomic behavior in the presence of strong electric fields. We perform electronic structure calculations to study rough features on the Si (100) surface under the influence of external electric field. Charge-transfer dynamics is followed by applying the SIESTA code. Further we use Mulliken and Bader charge analysis tools to estimate the charge excess and depletion on the defects and in their close vicinity. Furthermore, we compare the data obtained for Si surface structural defects with the same defect obtained for metallic electronic structures in the rough Cu surface simulations.

Resume : The cadmium molybdate CdMoO4 are well-known scintillation and phosphor materials currently used in various technological applications. Doping of CdMoO4 with F impurities can be done in wide range of dopant concentrations, from several thousands of ppm to synthesis of anion-substituted material CdMoO3F2. Such doping leads to definite changes in optical, in particular, luminescence properties of cadmium molybdate hosts. In this work, the sequence of cadmium molybdate compounds with various F content is considered in theoretical calculations of the electronic structure. The electronic structures are calculated by the Full-potential Linear Augmented Plane Wave (FLAPW) method realized in Wien2k program package [1]. Perfect CdMoO4, fluorine-doped CdMoO4:F in which the oxygen-to-fluorine ratio ranges from 16:1 to 4:1 as well as perfect CdMoO3F2 crystals are treated in geometry-optimized calculations. Structures of the one-electron bands, spatial distributions of the electron densities, optical absorption and reflection spectra are calculated and analyzed. Obtained results are compared with available experimental data of luminescence and optical spectroscopy of pure and fluorine-doped cadmium molybdate crystals. [1] P. Blaha, et. al., 2001, ISBN 3-9501031-1-2.

Resume : Many important properties of polycrystalline materials are strongly influenced by grain boundaries. High purity metals are polycrystalline materials and they are usually used for fundamental research and for commercially pure materials in modern applications. It is widely known that the structure of grain boundary in these materials influence their mechanical and physical properties. Therefore, the knowledge about the grain boundary effect is very important to understand properties of this systems. To investigate the grain boundary size effect on thin film mechanical properties, we modeled a system with grain boundaries. For simplified polycrystalline geometries, we propose model mimics films intersected by the grain boundaries. To simplify calculation, in our model, we use the grain of rectangular shape. The interactions between metal atoms are described by embedded atom method. The simulation was performed for three-dimensional systems with x-y periodic boundary conditions at a several size of grain boundaries. The grain boundary size was also changed. Simulations show that depending on the size of grain boundaries and a mismatch of the lattice constant in grain and in boundaries leads to various evolution of stress. We applied the kinematical scattering theory for the structural characterization of crystal structures and atomic stress method to analyze simulation data. Relation between stress and diffusion for different size of grain boundaries will be discussed in detail.

Resume : a-Si:H/c-Si heterojunction solar cells have reached record efficiencies of 24.7%. They consist of a n-type crystalline silicon wafer on which a thin (~10 nm) p-type hydrogenated amorphous silicon (a-Si:H) layer is deposited by plasma enhanced CVD at low temperature (~200 °C). The electrical contact is usually achieved by sputtering a thin transparent conducting oxide (80 nm thick) on the cell. Both sputtering and plasma deposition processes may introduce defects at the c-Si/a-Si:H interface which in turn will determine the conversion efficiency of the cell. The goal of this study is to understand the fundamental aspects of this interface via defect formation using a controlled introduction of point defects. Ion implantation of Argon at low energy (1 to 20 KeV) allows the modification of the a-Si:H thin layer. We can control the depth and concentration of irradiation defects by varying the ion energy and fluence. The defect concentration maximum is adjusted at a depth between 4 nm and 20 nm, while defect concentration is changed over 4 orders of magnitude between 1010 cm-2 and 1013 cm-2. The changes in the effective lifetime of minority carriers upon defect creation or annealing are characterized via photoconductance and photoluminescence measurements. The role of hydrogen diffusion within the amorphous silicon layer under low energy ion irradiation and thermal annealing is tentatively proposed as the origin of the heterojunction interface modification and correlated to the solar cell characteristics.

Resume : Mechanical and physical properties of materials in nanoscale are frequently dependent on grain boundaries. Grain boundaries play also an important role in stress generation during growth. In many proposed growth models sources of stress in late stages are connected with mass transport along the boundaries. Therefore, a detailed knowledge about mechanism of diffusion through the grain boundaries is very important to understand properties of this systems. Numerical simulations method are commonly used to study the diffusion length, grain boundary thickness, and the average grain size. In this work we focused on stress changes of deposited films onto the surface consisting of several strips and rows. We consider a surface intersected by the grain boundaries to study influence of the grain boundary size and lattice mismatch on stress in film. We used a three-dimensional molecular dynamics simulations. To simplify calculation, in our model, we use the grain of rectangular shape and the Lennard-Jones (LJ) potential. The LJ potential is not adequate for specific materials. We have chosen this potential to capture the generic feature of such systems. Additionally, the application of simple LJ potential is also motivated by simplification of numerical calculations. Influence of lattice mismatch and grain boundary size on stress will be discussed in detail.

Resume : Reduced activation ferritic-martensitic steels (RAFM) strengthened by yttria precipitates are promising structure materials for future fusion and advanced fission reactors. Oxide dispersion strengthened (ODS) particles hinder dislocation motion effectively resulting in higher strength and better high-temperature creep resistance of ODS steels in comparison to basic materials. Implementation of ODS materials widen the operating temperature, as compared to conventional RAFM steels, as well as they are more radiation resistant. The size, shape and spatial distribution of ODS nanoparticles significantly affect both mechanical properties and radiation resistance. A deep understanding of the mechanism of the ODS particle formation at the atomistic level is essential for ODS steels production [1]. The very initial steps of the ODS particle formation process were modelled by first principles DFT/plane-wave method, as implemented in the computer code VASP 5.3. Stabilization of Y solute atoms in the alpha-Fe lattice was analysed in details. Interaction energies for various combinations of Y solute atoms and vacancies were obtained for use in the future kinetic Monte Carlo calculations. The most probable Y stabilization and precipitation reaction mechanisms were suggested. Y solute atoms create stable complexes with multiple vacancies. Stabilized by vacancies, Y solute atoms exhibit stronger attraction. [1] A. Gopejenko et.al. J. Nucl. Mater., 416, p. 40-44, 2011

Resume : Amorphous iron-zirconium (a-FeZr) films have been studied extensively, much due to their interesting magnetic properties. They show soft magnetic features with low coercive field and large magnetic saturation, but typical Curie temperatures for as-prepared samples are around 250 K. However, by for instance, introducing hydrogen, or employing different preparation schemes for the films, it is possible to increase the Curie temperature to above room temperature. The reason for the changes in the magnetic properties is still under discussion, but the direct exchange interaction is very sensitive to the Fe-Fe distance, and the introduction of extra atoms in the structure is believed to increase the Fe-Fe distance thereby enhancing the ferromagnetic properties. In this contribution we will show that the magnetic properties can also be changed by implantation of keV low mass ions at high fluence. In fact, the implantation technique allows a controlled tuning of magnetic properties of the a-FeZr films, for instance, the Curie temperature within a range of 230 to above 400 K using proper choice of ion, energy and fluence [1,2]. In this study a-Fe0.93Zr0.07 thin films of a thickness of about 40 nm are prepared by magnetron sputtering on Si substrates, where the films are sandwiched between two 5 nm thick layers of Al0.7Zr0.3. Ion implantation is then performed at room temperature using a Danfysik implanter and beam currents low enough to prevent any significant sample heating during the implantation. The implantation technique also makes lateral patterning of the surface, using lithographic techniques, possible. In this way one- and two-dimensional structures of various sizes can be prepared which will help to better understand the magnetic behaviour of these films. The role of volume expansion due to the implanted ions and possible swelling effects due to displacement damage for increasing the Fe-Fe distance will be addressed. [1] A. Zamani et al., J. Magnetism and Magnetic Materials 346, 138 (2013) [2] R. Moubah et al., Appl. Phys. Express 6, 053001 (2013)

Resume : Au-based nanostructures have been the object of strong interest from the scientific community in these years for their linear and nonlinear optical properties. Recently our group demonstrated that enhanced optical functionalities in nanophotonics can be obtained when sub-nanometric Au nanoclusters (made by less than 20 atoms) are formed by ion implantation in silica. Due to quantum confinement effects such molecule-like Au aggregates are characterized by discrete energy levels allowing for efficient radiative relaxation at room temperature. Moreover, the formation of a near-infrared luminescence band correlated to electronic surface states at the Au nanostructures was revealed to be the mechanism that triggers the energy-transfer to photoemitting systems as Er ions and makes sub-nanometric Au nanoclusters very efficient nanoantennas for the Er emission. This has important technological entailments in optoelectronics where many research efforts are being done in these years to increase the small cross-section for Er excitation. In this work we will present the results of some very recent experiments aimed at elucidating the photophysical nature of the interaction between molecule-like Au-based nanoaggregates and Er ions. The results demonstrate that the energy-transfer process is indeed a non-radiative coupling mechanism occurring at very-short range with characteristic length comparable to interatomic distances.

Resume : Co-implantation, with overlapping implantation projected ranges, of Si and doping species (P, As, B) followed by a thermal annealing step is a viable route to form doped Si nanocrystals (NC) embedded in SiO2. This presentation deals with optical characterizations of both doped and undoped Si NC prepared by this method. The NC effective presence in the oxide layer and their crystallinity is verified by Raman spectrometry. Photoluminescence (PL) and PL excitation measurements reveal quantum confinement effects and a gradual PL quenching with increasing dopant concentrations. In undoped NC, the measured Stokes shift remains constant and its value ~0.2 eV is almost twice the Si–O vibration energy. This suggests that a possible radiative recombination path is a fundamental transition assisted by a local phonon. PL lifetime investigations show that PL time-decays follow a stretched exponential. Using a statistical model for luminescence quenching, a typical radius of ~1.1 nm is obtained for As- and P-doped NC, consistent with our previous atomic probe tomography (APT) analyses. APT also demonstrated that n-type dopant (P, As) are efficiently introduced in the NC core, whereas p-type dopant (B) are located at the NC/SiO2 interface. This observation could explain the failure of the luminescence quenching model to determine B-doped NC size. All together these experimental observations question on possible different carrier recombination paths in P or As doped NC compared to B one's.

Resume : Silicon Nanocrystals (NCs) have been widely studied because of their interesting properties and enormous potential for applications in, e.g., photovoltaic industry. The biggest problem is the low emission (photoluminescence, PL) efficiency of Si NCs, which typically does not exceed 15%. This needs to be understood and then improved. In our recent study we have shown that a combination of the presence of a significant amount of defected NCs (termed as "dark" NCs due to the non-emitting character) and energy transfer towards these centers play the dominant role in the efficiency quenching. In the present study, we investigate this energy migration in specially prepared 2- and 3-dimensional (2D, 3D) ensembles of Si NCs where the energy transfer rate is expected to be different. By measuring effective lifetimes and calculating internal quantum efficiencies we are able to visualize and quantize the difference in magnitude of the energy transfer process in the two geometries. We conclude that energy migration is indeed quenched in the 2D system. Combining high-resolution microscopy with PL and spectrally resolved measurements of PL quantum yield, we demonstrate that also the percentage of dark NCs depends on the system's geometry and is smaller for the 2D packing. These findings vouch for a 2D packing of Si NCs in order to increase ensemble emission efficiencies, as in this way energy transfer to defected NCs is mitigated. R.Limpens and T. Gregorkiewicz, J.Appl.Phys, 114 (2013)

Resume : β-Ga2O3 is well known for its properties as a transparent conductive oxide for the visible and UV range. The recent success in the production of high quality, single crystalline wafers is now opening the way to develop β-Ga2O3 based electronic and optoelectronic devices. Furthermore, the synthesis of nano- and microstructures as well the optical functionalization with rare earth ions promise new applications in nanotechnology, photonics and sensing. β-Ga2O3 bulk single crystals as well as β-Ga2O3 nanowires (NWs) were implanted with Eu ions with different fluences and at different temperatures. The structural properties were investigated by Rutherford Backscattering Spectrometry/ channeling and X-ray diffraction and the typical 5D0→7Fj intraionic transitions of Eu3+ have been studied by cathodoluminescence, photoluminescence and ionoluminescence. Implantation at room temperature leads to amorphisation for fluences above ~1E15 at/cm2. This lattice damage can be efficiently removed by rapid thermal annealing at ~1100 °C. However, in the case of bulk crystals, Eu could not be incorporated on substitutional sites and a decreased Eu3+ emission is observed by photoluminescence when compared to NWs. Implantation at elevated temperature (~600 ºC) yields a significant reduction of implantation damage, incorporation of Eu on substitutional Ga-sites and an improved optical activation. This result suggests that ion implantation at elevated temperature could be a better process than post-implant thermal treatment.

Resume : The ion-track technology based on MeV-GeV ion beams greatly benefits from the fact that each ion projectile creates a cylindrical track with a few nanometers in diameter. The small track size in combination with the large ion range (several tens of ?m) allows the fabrication of high-aspect ratio nanostructures. The track etching process provides great flexibility in adjusting their size and geometry under well controllable conditions [1,2]. Ion-track nanostructures are thus considered as excellent model systems to investigate the influence of size-effects on optical, electrical, magnetic, or thermal properties. The development of suitable techniques to precisely tailor the dimensions, orientation, and surface properties of nanowires is illustrated by several novel examples including: ? Metallic and semiconducting self-supporting 3D nanowire networks of adjustable interconnectivity and high mechanical stability [3]. ? Nanowires synthesized by means of pulsed electrodeposition of Au-Ag-Au segments. Dissolving one of the component creates capacitively and conductively coupled dimers of adaptable gap size and with interesting surface plasmon properties [4]. ? Nanotubes (Al2O3, TiO2, SiO2) of adjustable wall thickness produced by atomic layer deposition in ion track membranes. [1] C. Trautmann, Micro- and Nanoengineering with Ion Tracks, in: Ion beams in Nanoscience and Technology R. Hellborg, H. Whitlow, Y. Zhang (Eds.), Topics Appl. Physics 110, 215?264 (2009) Springer-Verlag. [2] M. E. Toimil-Molares, Beilstein J. Nanotechnol. 3 (2012) 860 ? 883. [3] M. Rauber, I. Alber, S. M?ller, R. Neumann, O. Picht, C. Roth, A. Sch?kel, M. E. Toimil-Molares, W. Ensinger, Nano Lett. 11 (2011) 2304-2310. [4] I. Alber, W. Sigle, F. Demming-Janssen, R. Neumann, C. Trautmann, P.A. van Aken, M.E. Toimil-Molares, ACS Nano 6 (2012) 9711-9717.

Resume : Mechanical stresses in swift heavy ion irradiated radiation-resistant insulators are a subject of considerable practical interest in view of the simulation of fission product impact. To date, the build-up and accumulation of stress with swift heavy ion fluence and energy has been studied for a very limited number of ceramics and oxides using mainly X-ray diffraction techniques. Since the radiation damage and correlated stresses induced by swift heavy ions are concentrated within a small volume, surrounding the ion trajectory, it is also interesting to evaluate the stress state of irradiated crystals before and after overlapping of isolated ion track regions. The aim of this study is to collect data of lattice strain as a function of radial distance from the ion track centre using computational methods on TEM micrographs of the ion tracks. This data is of high importance to verify current computational models of track formation based on the temperature spike model. Single crystal Al2O3 crystals were irradiated with 710 MeV Bi and 167 MeV Xe ions and analysed using a JEOL ARM200F TEM

Resume : The performance of organic electronic devices is steadily improving thanks to the advancement in understanding and controlling the organic material molecular structure and electron transport properties. Yet, a few major issues still need to be addressed, such as the achievement of an efficient charge carrier injection. The implementation of low contact resistance devices usually relies on interface physics (matching the metal electrode work function to the molecular energy levels of the semiconductors), or on dedicated device architectures. The electrical doping of organic films can be a very attractive way to further improve the efficiency of organic devices and ion implantation, the process often used to this aim in the fabrication of inorganic semiconductor devices, has not been yet applied to small molecule organic semiconductors on to organic materials. We report on the effects of low energy (30keV) ion implantation on thin films of Pentacene, carried out to investigate the efficacy of this process in the fabrication of organic electronic devices. Two different ions, Ne and N, have been implanted and compared, to assess the effects of a different reactivity within the hydrocarbon matrix. A strong modification of the electrical conductivity, stable in time, is observed following ion implantation. This effects is significantly larger for N implants (up to 8 orders of magnitude), that are here shown to introduce stable charged species within the hydrocarbon matrix, not only damage as is the case for Ne implants. Fully operational Pentacene thin film transistors have also been implanted and we show how a controlled N ion implantation process can induce stable modifications in the threshold voltage, without affecting the device performance. We have monitored the effectiveness of low-energy ion implantation in controlling and stabilizing the organic thin film resistivity over a long time (over 2000 hours), proving how ion implantation can be safely carried out on fully operational OTFTs. The electrical properties of the Pentacene layer and of the OTFT have been investigated by means of current-voltage and photocurrent spectroscopy analyses, while the structural modification induced by ion implantation have been characterized by depth resolved X-ray Photoemission Spectroscopy analyses.

Resume : Ion beams are increasingly being used as a tool for synthesis and modification of nanostructures. It is demonstrated that ion beams can be used for synthesis of graphitic clusters to engineer the sp3/sp2 –bonding ratio and stress in insulating carbon thin films. Such transformation of insulating, diamond-like (sp3-bonded) carbon into conducting, graphite-like (sp2-bonded) carbon within the ion tracks has been demonstrated. Recently, it has been shown that swift heavy ion irradiation of carbon films results in the formation of conducting graphitic nanowires of about 8 nm in diameter embedded within the insulating carbon matrix. Use of swift heavy ion irradiation as a tool to synthesize conducting nanowires has been explored by a few groups. The field emission properties of carbon films are mainly dependent on the chemical bonding structure and the doping with metals (Au, Ag, Ni) into the carbon matrix. Modification of such doped material along ion track by swift heavy ion irradiation is of great interest since it gives not only the way to engineer the sp3/sp2 –bonding ratio and stress in the film, but can give nanowires with significantly increased conductivity. In this contribution the route of swift heavy ion irradiation of carbon films combined with its doping for achieving highly conducting ion tracks in insulating carbon films will be presented. This work is supported by Russian RFBR (grants № 12-08-01197 and 13-02-92709) and DST of India.

Resume : Recent studies have shown that swift heavy ion irradiation may significantly modulate hydrogen and helium behavior in certain materials. This phenomenon is of considerable practical interest for various ceramics and semiconductors, specifically for candidate materials for use as inert matrix fuel hosts (IMs). IMs accumulate He via (n,) reactions and will also be subjected to high energy fission fragments (FFs) in the nuclear reactor environment. The inherent properties of ZrN has led to its identification as a candidate IM. Certain studies have indicated that nanocrystalline (nc) materials have improved radiation tolerance compared to their micro- and single-crystalline counterparts. This suggests that nc-ZrN may have a superior radiation tolerance. In this study low energy He ions were used to simulate -particles and high energy Xe and Bi ions were used to simulate FFs. The combined effects of low and high energy radiation were also studied. TEM and SEM were used to study nc-ZrN irradiated with 30-40 keV He, 167 MeV Xe and 695 MeV Bi ions to fluences of 5×1016 cm-2, 2.65×1014 cm-2 and 1.5×1013 cm-2 respectively. The irradiated samples were annealed at temperatures between 600 and 1000 °C. He irradiation did not lead to amorphization of unannealed nc-ZrN. Post irradiation heat treatment resulted in blistering at depths corresponds to the end-of-range of the He ions. He/Xe irradiated samples revealed that the electronic excitation effects (EEEs) resulting from high energy Xe ions suppress He blister formation. nc-ZrN is prone to the formation of He blisters, which may lead to material failure and is therefore of concern for materials with nuclear applications. These effects may however be suppressed by the EEEs from high energy heavy ions.

Resume : One promising way to produce energy from nuclear fusion reaction is to magnetically confine a hot (D, T) plasma in thermonuclear fusion devices (called tokamaks) and to heat it to ignition. One of the inner walls? role is to transfer the heat loads produced by the fusion reaction to a cooling loop and then to a turbine for producing electricity. In the tokamaks, interactions between plasma and walls lead to impurity transport in the edge machine together with material migration/mixing. Depending on the location in the machine, the impinging particle flux and energy, the initial structure of the material? wall?s temperature is changed, affecting the efficiency of the fundamental mechanisms occurring. Then, it is a challenging question to predict what will be the walls? hydrogen content. This point has been achieved for carbon walls as many studies have yet been done. Especially, a campaign involving the Tore Supra tokamak has been dedicated to measure both the H and C behavior at the scale of the machine and on many years. However, due to the good affinity existing between C and H isotopes leading to a severe safety issue (namely, tritium retention), carbon is not envisaged for the next step machine: the ITER project. Be and W, in which H isotopes can also be retained, have been chosen as the wall materials. For these elements, many studies have to be done before we can be predictive. In this study, we will present the advantage of using Raman spectroscopy at the micron scale (H bonding, structure/defect sensitive, non destructive,?) for fusion applications. As examples, we will use Tore Supra carbon tiles, beryllium implanted with deuterium ions resulting in the creation of D containing nanometric height domes, and tungsten oxides implanted with hydrogen ions.