Defect-induced effects in nanomaterials

Resume : Ion tracks are narrow cylindrical defects resulting from the interaction of swift heavy ions with materials. They are generally between 5-10 nm in diameter, tens of micrometers long and have been observed in many materials. An important application of ion tracks is the fabrication of nanopore membranes governed by preferential chemical etching of the damaged material in the tracks. Such membranes have applications in medical and bio-sensing, filtration and separation processes, nano-fluidics, and nano-electronic and nano-optic devices. We are currently developing a technology for controlled fabrication of nano-pore membranes using 0.5-2 μm thin SiO2 and Si3N4 layers. The use of these materials enables integration with routine semiconductor fabrication processes and the membranes exhibit superior thermal stability compared to commonly used polymer membranes. Freestanding SiO2 and Si3N4 membranes were irradiated with swift heavy ions and subsequently chemically etched. Small angle X-ray Scattering (SAXS), in combination with advanced Monte-Carlo (MC) simulation techniques, was used for characterisation of the complex pore structures formed in SiO2. These structures can exhibit conical or double conical shapes, depending on the etching conditions. Compared to cross-sectional transmission and scanning electron microscopy, SAXS in combination with MC simulations allows a more accurate reconstruction of the size and shape of the pores as well as taking advantage of superior statistics, since a large number of pores may be measured simultaneously. SAXS also enables in situ studies of the etching kinetics and the pore evolution in liquid environments.

Resume : Actinide materials, perhaps more than any other material composition class, often find applications in which they are subjected to extreme environments – usually combinations of high temperatures and intense radiation fields. In this presentation, I will summarize recent work done as part of the Center for the Materials Science of Actinides, an Energy Frontier Research Center. The presentation will focus on actinide oxides, related rare-earth oxides and ceramic oxides that may incorporate transuranium elements. We will examine the effects of swift heavy ion irradiations on actinide materials, particularly in combination with high-temperature and high-pressure. Of particular importance is the observation that under these extreme conditions, phase transformation pathways that are otherwise energetically or kinetically precluded can become accessible. As an example, irradiation of bixbyite-structured (C-type) compounds in the lanthanide sesquioxide (Ln2O3) system with swift heavy ions yields transformations to various crystalline and amorphous phases, with the final structure formed showing dependence on material composition and ion velocity. A remaining challenge is the characterization of these nano-scale modifications. The complete characterization requires a unique combination of very different analytical techniques, such as transmission electron microscopy, synchrotron x-ray diffraction, small angle x-ray scattering, and neutron scattering.

Resume : Grazing-incidence irradiation of surfaces with swift heavy ions has allowed probing the crystalline structure of the target as well as the processes of heat-transfer induced by the energy loss of the impinging ion. Strongly depending on the ion/surface combination used, different types of surface structures have been found: lines of hillocks, trenches, double-structures, as well as cutting and folding of thin layers. In order to probe the two-temperature theory used to describe the observed surface modifications, the bulk near the surface was studied. FIB foils of SrTiO3 containing the ion-induced tracks were observed by means of transmission electron microscopy. The results are compared to the surface structures created during these interactions.

Resume : Electronic sputtering effects caused by ~1 MeV u-1 Au ions impinging on (111) CaF2 surfaces are investigated by the catcher technique [1]. Sputtered nanoparticles are collected on different catcher surfaces and analyzed by Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM), and Medium-Energy Ion Scattering (MEIS). While the nanoparticle diameters obtained by analyses of TEM images display a bimodal distribution, AFM images show that the larger nanoparticles are composed of aggregates. These two complementary techniques (TEM reveals the planar projection of an object while AFM records its height) suggest the emission of spherical nanoparticles of about 5 nm in diameter. Depending on the areal density, the sputtered nanoparticles are isolated, overlap or completely coat the catcher. Modelling such deposition with the PowerMEIS code [2] yields good agreement with MEIS spectra. By performing measurements at different collection angles for a fixed incidence angle of the primary ions, the data allow the determination of total yields as well as angular distributions. Independent of beam incidence, electronic sputtering of CaF2 exhibits a jet-like component normal to the sample surface, as previously observed for LiF [3]. [1] Assmann et al., Topics Appl. Phys. 110 (2007) 401. [2] Sortica et al., J. Appl. Phys. 106 (2009) 114320. [3] Toulemonde et al., Phys. Rev. Lett. 88 (2002) 057602.

Resume : Monolayer graphene exfoliated on SiO2/Si substrate and bulk HOPG were irradiated by swift heavy ions (SHIs, 479 MeV 86Kr and 112Sn) and highly charged ions (HCIs, 4 MeV 86Kr19+). The different irradiation effects caused by these two different kinds of ions were investigated by Raman spectrometer. It is found that, both SHIs and HCIs irradiation exposures results in appearance of strong disorder D band and D′ band indicating damage in the graphene and HOPG lattice sites. The intensity ratio of D peak to G peak (ID/IG) in the case of HCI was higher than that of SHI for the same ion fluence in HOPG. The larger ID/IG indicates that synergistic effects of kinetic and potential energies of medium energy HCI has to be considered during the energy deposition process. Moreover, a turning point was detected in the evolution progress of ID/IG with the fluence obtained from SHIs and HCIs impacted graphene, while such point was never found in HOPG in the fluence range of this work. The Lucchese’s phenomenological model was improved to give full line fitting of the ID/IG evolution progress of HOPG and graphene. According to the improved model, energetic ions would induce both structurally disordered and activated regions in graphene. The competing mechanism of these two regions results in three variation regions of the ID/IG of graphene. Moreover, lager activated region was observed in graphene impacted by HCIs than that impacted by SHIs. In HOPG, however, only activated region is induced by energetic ions, then no turning point of ID/IG could be detected.

Resume : Although III-nitride light emitting diodes have revolutionized lighting technology, most of their applications revolve around the highly efficient blue (~450 nm) emitting InGaN/GaN Quantum Wells (QWs). Attempts to shift the emission to longer wavelengths by increasing the InN content in the QW are foiled by polarisation effects and Auger losses, leading to a strong drop in efficiency. Altering the QW shape by introducing a compositional gradient between the barrier and the QW by quantum well intermixing (QWI) was suggested as a solution to mitigate these effects [1]. Although simple in concept, its implementation by conventional post-growth ion implantation along with annealing turned out to be difficult [2]. The approach presented uses Swift Heavy Ion (SHI) irradiation to induce QWI. Green emitting InGaN QWs and GaN reference samples were irradiated with 185 MeV Au ions to 1011, 1012, 1013 cm-2. The damage build-up, studied using Rutherford Backscattering Spectrometry, suggests the onset of strong dynamic annealing when ion tracks start to overlap. The radius of the ion tracks was estimated using a statistical analysis of the damage profiles. Strain induced in the crystal lattice and QWI were assessed by X-Ray Diffraction and Reflectometry revealing efficient intermixing. Luminescence studies further confirm that QWI does indeed occur, resulting in a blue shift of the QW emission. [1] O’Donnell et al. PSS RRL 6 (2012) 49 [2] Sousa et al. Scientific Reports 5 (2015) 09703

Resume : The study of latent track morphology in oxides irradiated with swift heavy ions is an important aspect in the ongoing quest to understand the mechanisms responsible for their creation. Latent tracks are usually assumed to be cylindrical when employing indirect methods such as RBS/c and CEMS to determine damage cross sections and infer equivalent track diameters from this data. Track diameters obtained in this way are then compared with direct TEM observations (usually in plan view) for validation. Since TEM specimens have a maximum thickness of around 100 nm in order to be electron transparent, such specimens can be either thinned prior to irradiation or after irradiation in which case the final specimen may include the original irradiated surface or could be extracted from within the bulk of the irradiated specimen but still within the projected range of the ions from the surface. We will present recent results obtained from TiO2 single crystals irradiated by high energy Xe and Bi ions in both the pre-thinned and post-thinned regimes. As we will show, the resulting track morphology of pre-thinned and near surface specimens are vastly different to the track morphology within bulk specimens. This has tremendous implications for the correct interpretation of indirectly obtained track parameters. This phenomenon is not unique to TiO2 and has also been observed in Al2O3 which suggests that it might be a common phenomenon at least for similar oxide materials.

Resume : Nanostructured materials have attracted worldwide attention in recent years due to their unique properties. In this framework, swift heavy ion irradiation can be used to produce nanotracks in insulator oxides and controlled modification of materials properties at a nanoscale. The main goal of this work is to achieve both structural and microstructural tailoring of oxides for desired properties. Rare-earth oxides (RE2O3) possess remarkable physico-chemical properties that are interesting for technological applications. Actually, these compounds find use as high-κ dielectrics, nanoparticles for biomedical imaging, materials for ultrafast lasers, neutron absorbers in nuclear fuels and scintillators for the detection of ionizing radiation. RE2O3 compounds exist in three main polymorphic forms (cubic, monoclinic, hexagonal) depending on the RE. Some of their properties are linked to the crystalline phase: for instance, the europium photoluminescence in Eu2O3 is different between cubic and monoclinic polytypes. Pellets of cubic-RE2O3 (RE=Gd, Eu, Ho, Dy, Er) were irradiated with swift heavy ions (96 MeV-Xe, 94 MeV-Pb, 1 GeV-Xe) supplied by the GANIL accelerator in Caen in order to investigate the effect of the chemical composition on the structural changes induced by high electronic excitation. X-ray diffraction, with in situ measurements, Raman Spectroscopy and Transmission Electron Microscopy were implemented to determine the modifications induced by irradiation. Results show that the structural changes are strongly dependent on the sample composition and that irradiation induces a cubic-to-monoclinic phase transition. Moreover, the radiation-induced monoclinic phase shows a strong preferential orientation. Tracks in Gd2O3 consist of a new crystalline phase (probably with a monoclinic structure) that is misoriented from the cubic structure of the matrix. The diameter of these tracks is about 6 nm. Further experiments are in progress to investigate the changes in the properties of irradiated materials.

Resume : The ability to modify materials on the nanoscale using swift heavy ions (SHI)s has a broad range of potential applications. The unique one-dimensional geometry of the damage track enables the material properties, such as conductivity, dielectric constant and optical properties, to be modified in a controllable way to produce nanoscale devices. The resistance to amorphisation and the rapid dissipation of the deposited energy due to their high electronic conductivity have meant that metals have received much less attention in this area than band gap materials. Nevertheless, is has been shown by Dunlop and coworkers [1,2,3] that damage can be produced in some metals, and pre-existing damage could be annealed in others, by SHI irradiation. The electronic thermal conductivity and the heat capacity were found to be the dominant parameters that determine whether damage is created or annealed [4]. In this paper we model the response of tungsten to SHI irradiation using a coupled two temperature molecular dynamics (2T-MD) methodology [5]. The high melting temperature and strength of tungsten combine to make it an important material for operation under extreme conditions, such as the divertor of a furure fusion reactor. It is, therefore, important to understand the detailed response of tungsten to high energy radiation events. Here we simulate radiation events with a range of stopping powers and investigate the resulting damage evolution and residual defects. We find that, unlike cascade simulations which generally create isolated vacancies close to the path and interstitial clusters further away, SHIs create interstitial clusters near the ion path and isolated vacancies further from the path. The highly excited electronic state that is created along the track of a SHI redistributes the electron density and, consequently, modifies the interatomic interactions. Such effects can be accounted for in 2T-MD via electronic temperature (Te) dependent interatomic potentials that modify the potentials according to the local electronic temperature. Such potentials have recently been developed for tungsten [6]. We employ these Te dependent potentials in our SHI simulations along with the ground state, unmodified potentials. Comparison of defect evolution for the two types of potential allows us to decouple thermal effects, due to energy deposition to the lattice via electron-phonon coupling, and non-thermal effects induced by modified interatomic interactions. [1] Dunlop A. and Lesueur D. 1993 Radiat. Eff. Defects Solids, 126, 123 [2] Dunlop A, Legrand P, Lesueur D, Lorenselli N, Morillo J, Barbu A and Bouffard S 1991 Europhys. Lett. 15, 765 [3] Dufour C, Audouard A, Beuneu F, Dural J, Girard J P, Hairie A, Levalois M, Paumier E and Tou-lemonde M 1993 J. Phys.: Condens. Matt. C 5 4573 [4] Duffy D.M., Itoh N., RutherfordA.M. and StonehamA.M. 2008 J. Phys.: Condens. Matter 20, 082201 [5] Duffy D M and Rutherford A M 2007 J. Phys.: Condens. Matter 19, 016207 [6] Murphy, S.T. Daraszewicz S.L., Giret, Y., Watkins, M., Shluger,A.L., Tanimura, K. and Duffy D.M. 2015 Phys. Rev. B 92, 134110

Resume : We simulate with a two temperature MD code the damage induced by swift heavy ions in a free-standing graphene layer and compare the results with the data from Raman mapping. The experiment shows that for stopping powers over the defect threshold 1.3 KeV/nm the defects increase with the stopping power. Stopping powers under the threshold give fewer defects and hint a purification of graphene through annealing. We couple the electronic subsystem to the MD lattice through an electron-phonon coupling and solve recursively the heat equations for the coupled system. We reduce the number of free parameters required by the model and obtain the electronic heat capacity and the electron phonon coupling for different doping levels from first principle calculations. We fit only the electronic thermal conductivity of graphene, analyzing its effect on the threshold stopping power which results in structural defect sensed by Raman spectroscopy. We observe in our simulations that the radius of the damaged area grows with the stopping power above the threshold value and that the defect formation shows low dependence on the doping level. We compare the simulation results with the experimental data and report a correlation between the size of the damaged area and the defects observed with Raman mapping.

Resume : We propose a new type of strain-mediated magnetoelectric coupling in artificial multiferroics, in which strain induced by a ferroelectric or piezoelectric drives the magnetic material (with which it is interfaced) between different magnetic states. We outline the principle, identify γ-Fe as a suitable magnetic material, and demonstrate that γ-Fe nanoparticles (2-5 nm) can be epitaxially embedded in SrTiO3 (representative of the class of perovskite-type ferroelectrics) by ion implantation of Fe into SrTiO3, followed by adequate thermal annealing. Showing that ferromagnetic γ-Fe is structurally compatible with SrTiO3 is a crucial step towards the proposed new type of artificial multiferroics in which SrTiO3 is replaced by a related ferroelectric. Since the magnetic ground state of γ-Fe (ferro/antiferro/paramagnetic) is strongly dependent on the atomic volume, we propose that such hybrid systems would exhibit a new type of strain-mediated magnetoelectric coupling in which strain induced by the ferroelectric matrix drives γ-Fe nanoparticles or thin-films between ferromagnetic and paramagnetic states. The proposed new type of artificial multiferroic has the potential to exhibit strong magnetoelectric coupling, since the ferromagnetic state can in theory be switched on and off, reversibly.

Resume : The properties of ferromagnetic nanoparticles (NPs) in a nonmagnetic matrix is very interesting for its wide applications in high-density magnetic storage media. Swift heavy ion (SHI) irradiation induced elongation of NPs can lead to improved perpendicular magnetic shape anisotropy required for such storage devices. Ni-SiO2 nanogranular films were deposited by co-sputtering of Ni foils and SiO2 target. On exposing these films to different fluences of SHI, we found gradual increase in magneto anisotropic energy (MAE) with increasing SHI fluence upto a certain limit (5x1013 ions/cm2). However, on further increase in fluence, the anisotropy gets reduced. We have explained this anomaly from a combined experimental and theoretical state-of-the-art methods consisting of EXAFS measurements and DFT based simulations. While experimentally the structural anisotropy was found first to increase and then to decrease, theoretical calculations explain that these modified atomic structures at intermediate fluences are the manifestations of electronic spin interactions at thermal spike induced high temperatures. This affects the second-shell atomic coordination and results in elongated shape having highest MAE. As one goes to even higher fluence, the structural disorder destroys this spin-spin interaction, elongated shape and thereby reduce the MAE. Hence, magnetic shape anisotropy introduced in Ni NPs strongly depends on local atomic environment and the underneath spin-spin interactions.

Resume : The keen interest to N_2 solids is associated with the prospect of their application as high energy-density materials, their use as moderators and source of photons. These solids attract also much attention as astromaterials. The data on the thermally stimulated exoelectron emission TSEE [1] from pre-irradiated N_2 films and the creation of ionic centers N_3^+ [2] and N_4^+ [3] were published recently. Although much is known about radiation effects in N_2 solids, some fundamental aspects like charging and accumulation of uncompensated charge remain scarcely studied. We studied electrostatic charging of nanostructured N_2 films employing optical and current emission spectroscopy: cathodoluminescence CL, thermally or optically stimulated luminescence TSL, OSL and exoelectron emission TSEE, OSEE. A growth of the CL intensity with an exposure time followed by saturation was found. The dose dependence, fitted by the exponential function: I(t)=Isat[1-exp(-t/τ)], indicates accumulation of radiation-induced defects. The experiments performed with a variable voltage applied to an electrode for current detection demonstrated significant accumulation of negative charge. The TSEE current in low-temperature range was detected at negative voltages up to -30 V. An accumulation of N_3^+, N_3^-, N_4^+ and trapped electrons (up to 10^16 cm-3) as well as N and N_3 radicals was detected. The part played by pre-existing and radiation-induced defects in electrostatic charging is discussed. [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 (2013) 83. [3] E. Savchenko, I. Khyzhniy, S. Uyutnov, A. Barabashov, G. Gumenchuk, A. Ponomaryov, V. Bondybey, Phys. Stat. Sol. C, 12 (2015) 49.

Resume : The multilayer nanofilm systems based on CaF2 have great prospects to create instruments and devices of micro- and optoelectronics. However, due to the strong three-dimensional growth and interdiffusion of atoms at the border of these films is very difficult to obtain a heteroepitaxial film with a thickness of less than 10 - 20 nm. Our research has shown that low-energy ion implantation allows to form on the Si surface of the barrier layer, which leads to a marked decrease in the diffusion of the contacting metal atoms into the target. In this paper influence of bombardment of ions Ar + on diffusion atoms of contacting metals and on density of electronic states of films CaF2/Si (111) for the first time is investigated. To determine the effect of forming a thin layer Ca on the surface of CaF2 on redistribution of atoms at the metal - insulator by us are investigated the interphase border of Al - CaF2, Al - Ca - CaF2. Thin films of Ca with θ = 10 - 15 Å obtained by implantation of Ar+ ions in CaF2 with E0 = 0.5 - 1 keV and a dose of D = 6 • 1016 cm-2. The thickness of the Al films in all cases was 800 Å. It is found that on border of section Al - CaF2 (111) depth of penetration Al in CaF2 makes 350 - 400 Å, depth of penetration of atoms F in film Al - 250-300 Å, and Ca 150 - 200 Å. The depth of interdiffusion of atoms in the case of Al - Ca - CaF2 markedly reduced. For example, depth of penetration Al in Ca - CaF2 makes approximately 200 - 250 Å. Reduction of depth of diffusion Ca and F in Al was observed also. In this paper is given the analysis of the obtained results.

Resume : MgO film characterized by a high binding energy that determines its chemical resistance and wide bandgap. These films are widely used in the creation of unique micro- and optoelectronics, and MgO is a component of the first wall of fusion reactor. This paper presents the results of experimental studies of the electronic and crystal structure of nanofilms and nanocrystals Mg, formed in the bombardment of MgO. The ion energy varied E0 = 0.5-5 keV, and the dose of D = 1014 - 1017 cm-2 ions Ar+. Studies were conducted using the methods of secondary and photoelectron spectroscopy, scanning, electronic and atomic force microscopy. The results showed that during the ion bombardment is decomposed into components MgO, evaporation of O atoms and enrichment of Mg atoms. At low doses (D ≤ 1015 cm-2) form a single cluster phases, and at high doses (D> 1016 cm-2) solid film Mg. After heating at T = 1100 K, these structures fully crystallize into the cubic structure. The thickness of the crystalline silicon films (phase) Mg, which depends on the energy of the ions is 5 - 20 Å. Between Mg and MgO film formed transition layer with a thickness of 10 - 30 Å. At the paper studied the electronic structure of the system magnesium - transition layer - magnesium oxide.

Resume : We discuss and compare several ceramic perovskite materials for cathodes for solid oxide fuel cells (SOFC) and protonic ceramic fuel cells (PCFC), in order to optimize oxygen reduction with oxygen incorporation (SOFC) or water formation (PCFC), respectively. For cathodes on oxide ion conducting electrolytes, it has been shown that the cathode should be conducting for oxygen ions to allow the oxygen reduction reaction to extend beyond the gas/cathode/electrolyte three-phase (and that furthermore a high vacancy concentration and mobility is also beneficial for a fast surface reaction [1]). Analogously, for PCFC the cathode should exhibit a certain proton concentration and corresponding proton conductivity. So far, proton concentrations were reported only for few cathode materials such as Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) and Ba0.5Sr0.5Fe0.8Zn0.2O3-delta (BSFZ [2]). In particular, we performed large scale ab initio calculations (CRYSTAL09 computer code with hybrid PBE0 functional [3]) for nonstoichiometric La1-xSrxFeO3-delta as a potential PCFC cathode material, with and without protons, accompanied with thermogravimetry and impedance spectroscopy [2]. Computer simulations suggest atomistic understanding of the key parameters determining proton uptake in perovskite materials. It is shown that equilibrium proton concentrations lie within several percents, with a mobility comparable to commonly used electrolyte Ba(Zr,Y)O3, which is sufficient for oxygen reduction by so-called “bulk path” to be discussed in detail. [1] M. M. Kuklja, E. A. Kotomin, R. Merkle, Y. A. Mastrikov, J. Maier, Phys. Chem. Chem. Phys. 15 (2013) 5443. [2] D. Poetzsch, R. Merkle, J. Maier, Faraday Discussions 182 (2015) 129. [3] R. Dovesi, B. Civalleri, R. Orlando, et al., Rev. Comput. Chem. 21 (2005) 1.

Resume : Intrinsic electron localization in non-crystalline materials is usually associated with states near the conduction band minimum (CBM). Recent evidences suggest that in some amorphous oxides intrinsic electron localisation is possible also in deep states, where the effect of local disorder is amplified by polaronic relaxation of amorphous network. To investigate whether these states can be caused by intrinsic electron trapping, we modelled the behaviour of extra electrons in stoichiometric a-HfO2 structures. 35 models of a-HfO2 were produced using classical force fields and ab-initio calculations producing densities in the range of 9.2-9.9 g/cm3, averaging at 9.6 g/cm3. The electronic structures of the models with one extra electron were then calculated using DFT with hybrid functional PBE0. In all models, the extra electron is initially partially delocalized at the CBM, but the structure relaxation demonstrates that it can trap spontaneously in a deep state in the band gap. These states are located at ~2.0 eV below the CBM, ranging from 1.0-2.7 eV, in a good agreement with the experimental data. This energy depends on the a-HfO2 density and on the local environment. Extra electrons are localized typically on two or three Hf ions associated with longer Hf-O bonds or under-coordinated Hf atoms in the structures and induce strong polaronic distortion of the surrounding network. Our results broaden the concept of intrinsic polaron trapping to the disordered oxides.

Resume : The radiation-resistant Al2O3 is a promising material for fusion reactors, e.g. for components of the diagnostic systems. 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. Here we developed and applied the advanced theoretical approach based on the formalism of the correlation functions [1-2] describing spatial distribution of both similar (F-F centers) and dissimilar defects (a Frenkel pair of defects: an F center – an interstitial Oi ion) which suits for the study of defect kinetics and aggregation much better than generally accepted rate equations. On the basis of our calculations, we estimated the migration energy of the F centers and interstitial oxygen defects Oi, their interaction energies and metal colloid size upon annealing. Two types of experiments were simulated. The kinetics of the F and F+ center annealing after heavy ions (2.4 GeV 238U) or neutron irradiation was treated as the bimolecular process with equal concentrations of the complementary F and Oi defects. It 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 500-600 K, when both F and F+ centers are practically immobile, due to the recombination with mobile Oi de-fects.It is demonstrated how the shape of the F-annealing curves is determined by two control parameters: Ea and effective pre-exponential factor. The calculated migration energies (0.20-0.22 eV) were compared with those obtained from available in literature annealing curves for neutron and ion irradiated Al2O3. Another simulated experiment is the F center annealing in thermochemically reduced crystals, where the F center annealing is controlled by mutual defect attraction and ag-gregation, resulting in the metal colloid formation. The latter process occurs above 1600 K. The appropriate migration energies for interstitial oxygen ions reported in different experiments vary considerably, ranging from 0.8 eV down to 0.2 eV. This difference can be only partly related to the interstitial trapping effects by pre-existing defects, and is mostly caused by the rarely discussed radiation dose effect. The results obtained are also compared with recent ab initio calculation of interstitial oxygen migration as well as with the appropriate experimental results obtained for other similar type oxides (MgO and MgAl2O4). [1] V.N. Kuzovkov, E.A. Kotomin, and W. von Niessen. Phys. Rev. B 58, 8454 (1998). [2] V.N. Kuzovkov, A.I. Popov, E.A. Kotomin et al. Phys. Rev. B 64, 064102-5 (2001).

Resume : Because of high radiation resistance and wide band gap, Al2O3 (corundum) is widely used as an effective detector of ionizing radiation. Its potential applications include also components of breeder blanket and diagnostic windows. Radiation-induced changes in the structural and optical properties of corundum are mainly associated with primary Frenkel defects: neutral and charged interstitial oxygen atoms Oi, as well as oxygen vacancies VO (F-type color centers). Unlike the latter, the former are not well studied yet. In this study, we present results of periodic ab initio simulations on basic properties and mobility of the charged oxygen interstitials using the CRYSTAL14 computer code. The defect geometries and migration energies, Mulliken atomic charges and the electron density distributions for neutral and charged impurities are compared. It has been shown that the single-charged interstitial ion forms a dumbbell with a regular oxygen ion shifted from one of the nearest lattice sites (which distance is 1.87 Å and bond population 1.73 e) preserving С2 site symmetry. In turn, the double-charged oxygen interstitial ion tends to occupy a regular lattice site, but not preserving site symmetry. In all the cases, oxygen interstitials form the bonds with regular Al ions in corundum lattice rather than occupy centers of octahedron consisting of six nearest Oreg ions as one could intuitively expect. The calculated migration energies are compared with available experimental data.

Resume : Weak Josephson links in high-temperature superconductor materials (HTSC) count for a great deal of research activity. The existence of grain boundaries and a small coherence length (~0.1 mum) in HTSC ceramics, e.g., in YBa(2)Cu(3)O(7-d) (YBCO), leads to a reduction of the maximum width of the potential barrier Cooper pairs can pass without dissipation. However, the temperature (T) range in which a high magnetoresistance (MR) is observed, is relatively narrow. A quite topical task is the search for magnetosensitive YBCO-based materials exhibiting high MR values in moderate magnetic fields and in a broad T-range below Тс, as well as high excess resistivity values. It appears interesting to study composite materials of the type YBCO+М, in which the YBCO grain boundaries are modified through the addition of a non-superconductive magnetic ingredient (M). We have chosen the strontium ferromolybdate Sr(2)FeMoO(6-d) (SFMO) as the magnetic ingredient. Electrical transport in the YBCO+SFMO composite was studied as a function of the temperature and magnetic field. Four different ranges in the T-dependence of the resistivity were found between 300 and 4.2 K. From 300 K down to T_c1 a semiconducting conductivity is observed, whereas below T_c2 the first transition into a superconducting state sets in. Upon further cooling down, the semiconducting behaviour appears again below T_min< T_c1, and then a second superconducting transition starts at T_c2< T_min continuing down to 4.2 K. The MR is negative above T_c1 and positive below it, achieving at 5 K a huge value of ~5700%. We discuss the role of the weak links between the YBCO grains represented by the SFMO interlayers on the magnetotransport in the composite. The study was supported by FCT of Portugal (project UID/CTM/50025/2013) and NUST “MISiS” (grant no. K3-2015-003).

Resume : Ferrimagnetic half-metals Sr(2)FeMoO(6–d) (SFMO) with an ordered double perovskite structure are among the most promising materials for spintronic devices. They have a high magnetoresistance (MR~50% in a magnetic field of 1 T at T = 50 K), high values of Curie temperature (Tc = 400–450 K) and almost 100% degree of spin polarization. We studied the sequence of phase transformations during the SFMO crystallization by citrate-gel method for powders synthesized with initial reagent solutions with different pH values (4, 6 and 9). It was found that the synthesis of SFMO solid solution proceeds through a series of parallel chemical reactions with the formation of intermediate phases SrMoO(4), SrCO(3) and Fe(3)O(4). The relative amount of intermediate phases is reduced with increasing temperature. This leads to an increase of the content of the Sr(2)FeMoO(6–d) phase. Therefore, the lowest amount of SrMoO(4) was observed for T=1220 K, in the case that the initial solution had pH=4. The initial reagents were found to be more reactive at pH=4 and led to the SFMO formation at relatively low temperatures (870 K). The x-ray diffraction peaks are broadened and shifted at the initial stages in all cases studied. This indicates that the initially formed double perovskite is enriched with Fe, and its chemical formula becomes Sr(2)Fe(1+x)Mo(1–x)O(6–d), where 0< х< 1. With increasing annealing temperature the Mo content in SFMO increases. Based on the information obtained through the analysis of pH and temperature effect on the phase composition and morphology, an improved procedure was designed, based on an initial solution with pH=4. Single-phase SFMO with an average grain size of ~68 nm and a superstructural ordering of 88% was obtained. The study was supported by RFBR (project № 16-38-50018 mol_nr), FCT of Portugal (project UID/CTM/50025/2013) and NUST “MISiS” (grant no. K3-2015-003).

Resume : High-dose implantation of ions of transition metals (Fe, Ni, Co) may result in the formation of granular films consist of magnetic metal particles or magnetic compound clusters. Magnetic resonance method (ferromagnetic (FMR) or superparamagnetic (SPR) resonances) is usually used to obtain the information about the shapes of magnetic particles, their size distribution and the inter-particle interactions. The inter-particle interactions are responsible for strong dependence of FMR absorption on the orientation of static magnetic field relatively to the film plane. This “film-like” behavior of resonance absorption can remain even in the case when the particle density in the granular film is so low that inter-particle interactions can be neglected. This occurs, for example, when the particles possess uniaxial magnetic anisotropy and anisotropy axes lie in the film plane. Such a situation is supposed to take place at magnetic field assisted ion-beam synthesis of granular film of magnetic silicide Fe3Si. In this case the synthesized films reveal noticeable in-plane magnetic anisotropy, which can be caused by the ordered arrangement of uniaxial magnetic particles. In the present work the FMR absorption is calculated for granular film consisting of non-interacting elongated ellipsoids, the longest axes of which lie in the film plane. The cases of ordered and disordered arrangements of the axes within the film plane are considered. It is shown that FMR investigation can give an evidence for the suggestion that in-plane magnetic anisotropy of ion-beam synthesized Fe3Si films is originated by Fe3Si particle elongation when growing during magnetic field assisted ion implantation.

Resume : The possibility to induce dehydrogenation of single 5,14-DHTAP molecules embedded in highly organized monolayer (ML) is investigated by the means of scanning tunneling microscopy (STM). The 5,14-DHTAP molecules self-assemble in a highly organized ML, lying flat on the surface in a head to tail configuration allowing the establishment of H-bond between neighboring molecules[1]. The dehydrogenation of single 5,14-DHTAP molecules embedded in the self-assembled ML is achieved by low temperature STM via the dissociation of the N-H bond, which is induced either by I(V) scans or by I(t) measurements at constant voltage. The dehydrogenation leads, in the first ML, to the formation of 5,7,12,14-tetraazapentacene (TAP), a compound with electronic properties similar to pentacene that cannot be synthesized by common chemical methods. In the second ML, the dehydrogenation leads to the formation of TAP and other azapentacene compounds. The very high resolution of STM images allows us to compare images of the molecular orbitals of these compounds to DFT calculations of isolated molecules in order to unequivocally assign the chemical nature of the compound. The successive dehydrogenation of single 5,14-DHTAP molecule turned out to be a reversible process. It is thus possible to use the 5,14-DHTAP molecules as molecular switches. [1] Lelaidier et al. Langmuir, 2014, 30 (20), pp 5700–5704

Resume : We present a scanning transmission electron microscopy study of defects in graphene and nanopores in MoS2, which epitomize the family of two-dimensional materials. To transform a pristine, hexagonal graphene membrane into a disordered 2D carbon structure containing pentagons, hexagons, heptagons and octagons, we used electron beam irradiation. The rate of amorphization due to increasing defect density was monitored via changes in the observed diffraction pattern. To hinder the destructive effects of chemical etching during the process, these experiments were carried out at 150 °C. By contrast, MoS2 monolayers were irradiated with 7000 Xe30 ions/µm² and 500 Xe40 ions/µm². The atomic structure of the created defects was later imaged with a Nion UltraSTEM 100, operated at 60 kV. In addition to static atomic resolution imaging of vacancies and impurity atoms, dynamical behavior, such as their movement through the lattice as well as bond rotations were observed. Detailed analysis of both of the structural defects in graphene and the pore size distribution in MoS2 will be presented.

Resume : We have studied radiation and high-field injection methods of modification of nanothin gate dielectric layers of MIS structures and features of methods usage in order to change characteristics, decrease defectiveness and improve the reliability of the MIS devices. We have shown that injection-thermal and radiation-thermal treatments to find and eliminate MIS structures having rough defects of isolation and charge defects. We have found out that both the injection and radiation treatments could improve characteristics of MIS devices based on SiO2 films, SiO2 films doped with phosphorus, oxynitride and other films. These treatments improve injection and radiation hardness of the gate dielectric because of creation in its volume a required density of electron traps. As a result a mean value of charge injected into the dielectric until breakdown increases and an amount of defective structures having a low value of charge injected into the dielectric until breakdown decreases. This effect can be explained by healing of “weak spots” in the gate dielectric because of accumulation being trapped negative charge (traps were created by the treatment) in it and, in consequence, by rising of potential barrier and reduction of values of local injection currents.

Resume : Highly oriented pyrolytic graphite (HOPG) was irradiated with 40.5 MeV Sn ions at a range of fluence:1×1012-1×1014 ions/cm2. A new Raman band was observed at ~864 cm-1 which grows with increasing the irradiation fluence. This band has been observed in Raman spectra of HOPG and natural graphite crystal edge planes, only when the incident light is polarized perpendicular to the basal planes and it has been assigned to the out-of-plane Raman-inactive B2g mode which becomes Raman active due to a slight rearrangement of lattice structure at the edge. However, we first obtained this band in Raman spectra of basal planes of irradiated HOPG with the polarization of the incident light parallel to the basal planes. Then, a half-wave plate was used to change the polarization direction of the incident light in the HOPG basal planes. The intensity of the band at 864 cm-1 is almost independent of the incident light polarization direction. We suggest that re-crystallized graphite with random lattice orientations are formed during ion irradiation, which gives rise to the B2g band. The conclusion is confirmed by transmission electron microscopy images, showing that there are some randomly orientated nanoscale graphite crystals surrounded by amorphous carbon.

Resume : We will present a comparative atomic force/Raman microscopies study about graphite exposed to H, D and He plasma at fluencies from 1016 to 1018 cm-2, with ion energies ranging from 40 to 800 eV, the ion incidence being either perpendicular (Highly Oriented Pyrolitic Graphite) or parallel (carbon/carbon composite) to the basal plane [1]. When increasing the impinging ion energy, the growth of nanometric domes at the surface has been observed by atomic force microscopy and the incident kinetic energy has been found as the parameter determining their height. Two different Raman signatures related to (i) a graphitic nano-crystalline component similar to that of a 1014 cm-2 bombarded 1-, 2-, 3-layer graphene, and to (ii) an amorphous component, have been evidenced in the 1000-1800 cm-1 spectral range, giving rise to 5 overlapped bands. Polarization studies have revealed that these components are related to regions with either in-plane or out-of-plane disorder, coexisting in the material. These Raman studies have also revealed that both the defect-defect distance in the first case and the aromatic domain size in the second case are typically 1 nm. When the number of vacancies created in the material increases, the number of in-plane defects decreases to the benefit of the out-of-plane defects. In order to extract additional information about the defects in the bombarded graphite, we will also focus on the 300-900 cm-1 and 2D spectral regions investigated using multiwavelength Raman spectroscopy [2]. [1] C. Pardanaud, el al Journal of Raman Spectroscopy 46 (2015), 256 [2] C. Pardanaud et al, in preparation

Resume : Boron nitride (BN) has been known as a thermally good conductor and an electrical insulator with a large bandgap. In theoretical calculations, several researchers predicted that defective hexagonal BN nanosheet (BNNS) and nanotube (BNNT) can behave as an electrical conductor due to a new energy state of a defect between conduction and valence band. In this study, we present a method to create vacancy defects in BN networks consisting of BNNS and BNNT, and a change in the electrical properties of the BN networks. BNNS and BNNT were dispersed in ethanol and the solution was dropped between electrodes on SiO2/Si substrate to form BN networks. Then, the BN networks were impregnated with Co precursor and heated at about 200℃ under air atmosphere to form vacancy defects in the structures of BNNS and BNNT via catalytic oxidation. After the oxidation, transmission electron microscopy analysis revealed the presence of multi-vacancies in both BNNS and BNNT. In electrical measurements, the pristine BN networks did not showed any electrical response, but surprisingly displayed an electrically metallic behavior after catalytic oxidation.

Resume : In this work, the thin-layered highly oriented pyrolytic graphite (HOPG) samples with thickness less than 100 nm were irradiated with heavy ions of kinetic energy 9.5-25.0 MeV/u at the HIRFL accelerator of IMP (Lanzhou) in vacuum. The irradiations were performed at room temperature by applying fluences between 1×1010 and 5×1012 ions/cm2. The topography of irradiated samples was observed by high-resolution transmission electron microscopy (HRTEM). The damage evolution in graphite was investigated as a function of ion fluences and electronic energy losses by confocal Raman spectroscopy. The results were compared with that in bulk graphite. The mechanisms of ion induced track formation are discussed in thin and bulk graphite samples.

Resume : To date, electronic and phonon properties in nanosystems of different dimensions were investigated separately in detail, however, properties determined by interaction between electrons and phonons have not been studied well. In this work, we theoretically studied features of vibron effects in two types of nanosystems: bubblons and clusters. 1. Effects of bubblon deformation. Self-trapping of an electron inside bubbles is possible in liquid helium and leads to the formation of bubblons. Total energy of the system was calculated from the study of electronic structure of such nano-scaled formations taking into account reconstruction of a bubble surface. In some cases, energy of bubblon deformation was compensated by decreased electron energy of bubblon. Such deformed nano-sized bubblon exhibits the Jahn–Teller effect, where increased value of the energy is associated with confinement of electron in bubblon. 2. Effects of distortion of internal cluster structure. Spherically asymmetrical deformation of an atomic structure was observed in quantum-chemical calculations of electronic and atomic structures of some clusters (in particular, silicon) containing impurity atom. It was found that an increase in energy of impurity electron could be compensated by the emergence of asymmetrical potential gaps, arising from the change of the local atomic structure of the cluster. This effect was observed in small silicon clusters, and can be attributed to the stronger confinement of impurity electron.

Resume : Quasi periodic zipper-like dislocation arrays emerging across the grain boundary between two (111) copper grains that are mis-oriented by a few degrees are studied by scanning tunneling microscopy. The shifts of atomic positions associated with these zipper-like dislocation and period of the zipper-like dislocation array are determined. We demonstrate that the zipper-like dislocation consists of one Shockley dislocation from each side of the grain boundary and that zipper-like dislocations are bent across the grain boundary. Moreover the tensile stress at these boundaries result in unexpected build-up of atoms in the boundary region that is responsible for observer corrugation in the zipper-like structure.

Resume : Memristor – is a memory resistor capable of changing resistance in dependence on the voltage applied and of imitating the role of biological synapse. The advantages of memristive devices are simple structure and scalability due to nanometer size of the local switching region of a material placed between two electrodes. The realization of adaptive behavior is based on a gradual switching between the resistive states. Some researchers attribute the gradual RESET phenomenon in a valence-change memristive device to the change in microscopic properties of a single filament and its environment. However, in the devices of relatively large area that can cover a lot of filaments, the inhomogeneities of active volume begins to play the dramatic role. In the present report, the adaptive behaviour is analyzed for the memristive devices on the basis of magnetron-sputtered ZrO2(Y) thin films that reveal polycrystalline columnar structure with oxygen-deficient grain boundaries. The switching kinetics for the filaments composed of oxygen vacancies has been simulated by the kinetic Monte-Carlo approach. The effect of geometric and structure parameters on the current transport in a multi-filament system during the RESET process is established. Our simulation shows that, in a system of 100 more filaments, the statistical distribution of switching voltages leads to the overall gradual RESET process. The study is supported by the grant of Russian Science Foundation (project № 16-19-00144).

Resume : The passive mode-locking with the nonlinear Kerr effect in an optical fiber when the intensity-dependant change of the polarization state combined with the intra-cavity polarizer acts as an artificial saturable absorber usually is used to achieve generation of ultrashort laser pulses. The reliable self-starting mode-locking can be achieved by introducing a Semiconductor Saturable Absorber Mirrors (SESAM). For operational wavelength of the Yb-doped fiber lasers, a SESAM based on the InxGa1-xAs/GaAs super-lattice saturable absorber and AlAs/GaAs Bragg mirror is a common choice, but its long term reliability is still an unsolved problem. It is possible to control operational parameters (recovery time, saturation fluence, modulation depth, absorption wavelength) of a SESAM by controlling the growth parameters of the semiconductor material and properly choosing the cavity design. Typical carrier recombination time for a bulk semiconductor material is usually up to ns, but for a stable modelocking of a fiber laser it should be reduced down to a few ps. It might be done by varying the SESAM's growth temperature or it might be tuned after the growing process using ions implantation into InxGa1-xAs quantum well region. In this work, we discuss the influence of defects introduced during implantation of H, O, As ions with various energy to quantum well region on the operational parameters as well as on the degradation dynamics of SESAM structures after irradiation with ultrashort pulses from a fiber laser.

Resume : Metallic Ni1-xVx alloys have been shown to exhibit a ferromagnetic to paramagnetic quantum phase transition (QPT) at x ~ 11.4 %, the quantum critical concentration (QCC), in bulk. However, the quantum critical non-Fermi liquid behaviour, supposed to arise around the QPT, is masked by the appearance of a quantum Griffiths phase (QGP) in a narrow x and small temperature range on the paramagnetic side. In the Griffiths phase, the physical observables follow power-law temperature dependences with non-universal exponents. In this regard, it is quite intriguing to explore these quantum phenomena in nanostructures of these alloys since materials in nano-dimensions are known to exhibit properties different from their bulk counterpart due to quantum confinement effects and large surface areas. In the present work, occurrence of QPT and QGP are explored in chemically prepared Ni1-xVx nanoalloys of mean diameter 10-20 nm with x in the neighbourhood of the QCC. The size, the phases and the compositions were determined by Field-emission Secondary Electron Microscopy, X-ray Diffraction, X-ray Photoelectron Spectroscopy, Energy Dispersive Analysis of X-ray methods and high-resolution Transmission Electron Microscopy. Further, magnetization measurements reveal a superparamagnetic to blocked ferromagnetic phase transition, akin to magnetic nanoparticles, at blocking temperature which varies with x around 250 K for all compositions. Below 50 K, but at a temperature varying with x, a paramagnetic-like increase of the magnetization is observed with the decrease in temperature. This is found to correspond to a paramagnetic contribution due to randomly oriented surface moments. For V compositions in the nearest vicinity of the QCC, however, the paramagnetic part of the magentization follows a non-universal power law, indicating the presence of QGP’s in the alloys of these compositions. Complimentary low temperature resistivity measurements confirm the occurrence of the additional paramagnetic-cum-QGP phase as peaks in the normal linear behaviour at corresponding temperatures.

Resume : GeTe is not only a prototype material to study technologically important, related Ge- and Te-based alloys for data storage applications, but also itself a archetypical displacive ferroelectric material. Despite such diverse interests, atom-resolved studies of single crystalline GeTe surface have been lacking so far. Here we report on the investigation of as-cleaved and annealed surfaces of GeTe single crystals by using low temperature scanning tunneling microscopy (STM) and spectroscopy (STS). Cleaved at 120 K, GeTe(111) reveals at least two types of terraces at 78 K, with each attributed to Ge- and Te-terminated surfaces of layered binary material, respectively. These terraces exhibit distinctive I-V spectra and scan stability conditions, and stably imageable terraces show subsurface defects consistent with Ge vacancies, and a small number of surface layer vacancies that produce quasiparticle interference patterns of three-fold symmetry. Annealing of GeTe(111) surfaces to moderately elevated temperature gives rise to one-dimensional networks of extended defect structures, indicating strongly anisotropic defect-defect interactions. Our investigation sheds light on intricate roles of the vacancy defects towards the phase transformation in GeTe and related materials.

Resume : The thermodynamic stability of the system demands the formation of structural defects in real crystals. An ‘ideal crystal’ is the one, in which all the basis (atoms or ions) occupies the regular lattice points governed by the symmetry rules, to establish a long range periodic order. However, the real crystals differ from an ideal one, as it contains a number of crystal defects. Here, we have investigated the crucial role of point defects (particularly the oxygen vacancies present in the metal oxide lattice), in the gas sensing mechanism of solid state metal oxide (MO) gas sensors. Often, while evaluating the basic mechanism of MO gas sensors, major attention is paid towards the physical size and dimensionality of the MO material rather than the defects, chemical stoichiometry and related attributes. Hence, it is necessary to consider this crucial aspect in order to develop the complete understanding of the chemoresistive MO gas sensors, which still seems to be far from reality. In this talk, the indirect spectroscopic ways such as Optical, Raman spectroscopy and X-ray photoelectron spectroscopy of characterizing the structural point defects are discussed. The defects which are further tuned and utilized in understanding their effect on the gas sensor mechanism. To summarize, the talk shall present a novel perspective to understand the mechanism of the metal oxides semiconductor gas sensor operation, through probing the defect structure. Albeit, there is a wealth of a literature published in the field of MO gas sensors in last few decades, the approach of the researchers has been empirical, which could be a limiting factor for further advancement in the field. Hence, one needs to be more keen to study the structural aspects to obtain a colossal improvement. The only possible approach could be, to gain more insight into the mechanism and standardizing the criteria for choice of materials thereof. Here, the mechanism involved in the MO chemoresistive gas sensors is discussed in detail and the prime focus on effect of structural defects, which influence this mechanism significantly.

Resume : Their unusual electronic and structural physical properties promote carbon nanotubes as promising candidates for a wide range of nanoscience and nanotechnology applications. However, like in most materials, the presence of defects in carbon nanotubes has been demonstrated experimentally. These defects may take different forms: vacancy, bi-vacancy, Stone-Wales defect, 5/7 pair, atoms in substitution… The introduction of defects in the carbon network is an interesting way to modify its intrinsic properties and to create a new potential nanodevices. On the other hand, it was found also that structural defects make possible the functionalization of carbon nanotubes. In this work, we have investigated the chemical functionalization of (5,0), (8,0) and (13,0) zigzag single wall carbon nanotubes (SWNTs) by carboxyl, amine and hydroxyl groups on Stone-Wales (SW) defect by using spin-density functional calculations. Geometric changes of the regular hexagonal nanotube structures as well as alterations of their energetic, magnetic, and electronic characteristics induced by the presence of the defect and the functional group are recorded and discussed as a function of the tube diameter.

Resume : Grooving of thin film surfaces by combined surface and grain boundary (GB) diffusion is a problem of technological importance hence it provides a mechanism for VLSI interconnect failure. In this study, we examine the effects of mechanical loading conditions on the morphology and kinetics of grooving at a finite grain size by assuming that the GB remains perpendicular to the free surface during the overall process. The displacements due to a constant applied uniaxial tension to free standing and strongly bonded (to its substrate) thin films, as well as that of a strained thin film on a rigid substrate were computed at the interior (GBs) and the boundary (free surface and film/substrate interfaces) points using the indirect boundary element method. The motion of the triple junction and the evolution of stress/strain fields within the film were followed while systematically considering the effect of elastic dipole tensor interaction, between the stress field and the mobile atomic species situated at the surface and GB layers, for each of the loading conditions.

Resume : The N(B)-doped carbon nanotubes (CNSs) are intensively studied at present as components of carbon/oxide composite materials for various practical applications. Such composite materials can reveal additional useful properties not accessible by their components separately. Efficient functionalization of carbon materials is possible only if carbon surface is able to create chemical bonds with functionalizing compounds. Theoretical modeling of molecular adsorption of the surfaces of CNTs and graphene is widely used for prediction of chemical bonding between carbon nano-structured materials and compounds from various chemical classes. In this work we expand these studies to oxide compounds considering adsorption of XO42- (X = Cr, Mo, W) molecular oxyanions on the surfaces of pristine and N(B)-doped SWCNTs and graphene. A DFT-based geometry-optimized calculations of the electronic structures of SWCNTs and graphene molecular clusters with adsorbed oxyanions are carried out by Gaussian 03 program package [1]. Relaxed geometries, binding energies between oxyanions and adsorbents, energy barriers for desorption, electronic wavefunction contours are calculated. Obtained results were analyzed in the context of efficient functionalization of carbon nano-structured materials by compounds containing molecular oxyanions. [1] M.J. Frisch, G.W. Trucks, H.B. Schlegel, et al. // Gaussian 03 (Gaussian, Inc., Wallingford, CT, 2003).

Resume : The LaVO4:Eu compounds are now studied intensively as perspective light emitting material and a more cheaper analog of the YVO4:Eu luminophore. We have investigated the LaVO4:Eu nanoparticles synthesized by various methods (solid state, co-precipitation, sol-gel synthesis). Their emission spectra consist of narrow lines in the 578 – 720 nm range. Spectra of some compositions are formed by transitions in two types of emission centers. Contribution of the second type of centers essentially increases total luminescence intensity of the LaVO4:Eu nanoparticles. Origin and structure of these centers are under discussion. They can be connected with residual inclusions of monoclinic phase in tetragonal crystal lattice or with surface effects. In order to obtain more information about symmetry of surrounding and structure of the Eu emission centers, the crystal field (CF) calculations are applied in this work. Based on the measured splitting of the 5D0 ® 7F1 emission transition for the different types of centers the S2 scalar CF strength, B02 and B22 parameters were calculated for the both types of centers. The calculated values of the S2 scalar CF strengths parameters are closed for the both types of centers, whereas the B02 and B22 parameters are rather different that reveal the same crystal field and different symmetries of surrounding of the Eu3+ ions in the I type and II type centers. Such situation can be caused by two different types of defects involved in the formation of the Eu3+ emission centers. Taking into account obtained results we suppose that mentioned two types of the centers are associated with Eu3+ ions located at the particle surface („at - surface“ centers) and with Eu3+ ions located in volume of the particles („in-volume“ centers).

Resume : Structural and magnetic properties of Fe doped ZnO films deposited by Pulsed Injection Metal-Organic Chemical Vapour Deposition (PI-MOCVD) were analyzed in order to clarify the role of secondary phases in the occurrence of ferromagnetism. The film texture was analyzed by x-ray diffraction (XRD) in the Q-2Q geometry. Energy dispersive x-ray spectroscopy was used to estimate the actual Fe content (x = Fe/(Zn+Fe)) in the films. The obtained value varied between 0.11 and 0.86, always above the solubility limit. Magnetization measurements were carried out in a SQUID magnetometer. Ferromagnetic resonance (FMR) was measured in the temperature range from 4 to 400 K using an EPR spectrometer at a frequency of ~9.4 GHz. For the lower Fe content films (x < 0.25) the XRD shows only peaks associated with the ZnO wurtzite structure, while for x > 0.25 peaks related to the fcc spinel structure appear. The sixfold symmetry of both sapphire and ZnO imposes a [111] texture in these phases. The magnetization vs. temperature and FMR measurements reveal the existence of a ferromagnetic behaviour up to 400 K. The magnetic properties of the films can be understood as due to the presence ZnFe2O4-Fe3O4 solid solutions, with Fe3O4 being the dominant phase in the films with x = 0.86. In conclusion, our results show that spinel structure inclusions are at the origin of the room temperature magnetism detected in Fe doped ZnO films, supporting the indication that secondary phases, barely visible by standard XRD, can be accountable for the magnetic behaviour detected in many transition metal doped ZnO systems, in contrast to the assumption of an intrinsic diluted ferromagnetic semiconductor system.

Resume : Detailed studies investigating the effects of radiation on the structure and properties of various materials have been performed on single crystals or pellets having large grain sizes. However, there are some specific applications that require the use of polycrystalline or even nanocrystalline thin films to protect some areas or encapsulate nuclear fuel. Recent investigations of the effects of radiation on such films found differences with respect to the results obtained for large grains samples. The small grain sizes in such films allow for short diffusion distances of the created defects towards grain boundaries that act as sinks. The role of strain present in thin films should also be taken into account when investigating the lattice parameter changes induced by defects. The Pulsed Laser Deposition (PLD) technique is very suitable to grow nanocrystalline thin films possessing a smooth surface morphology, which allows for the use of characterization techniques such as X-ray reflectivity, grazing incidence X-ray diffraction, X-ray photoelectron spectroscopy, or nanoindentation that all possess depth resolutions of the order of few nm. The effect of Ar ion irradiation on the microstructure, chemical composition, mechanical, optical and electrical properties of ZrC and ZrN thin films grown by PLD on Si substrates were investigated and compared with those obtained on single crystalline materials.

Resume : The results of a theoretical study of 2DEG electron concentration and mobility in AlGaAs / InGaAs / GaAsheterostructures are presented. The heterostructures have been grown at the ISP SB RASwith the use of a new technique of donor-acceptor doping. These AsGa-based structures with optimized quantum well and additional potential barriers are promising in terms of getting high-performance transistors. To carry out the study the three-scale mathematical model developed by our group earlier was modified, allowing calculation of heterostructures with an arbitrary number of delta-layers (delta-doped layers and interfaces with uncompensated charge). As a result of numerical simulation, the factors have been identified which significantly influence the electron concentration in 2DEG. The numerical results are in a good agreement with the experimental data. The use of the modified mathematical model allows us to further optimize the parameters of the AsGa based heterostructures.

Resume : We present a comprehensive study of the effects of the defects produced by electron irradiation on the electrical and crystalline properties of graphene and MoS2 monolayers. We realized electrical devices from monolayer MoS2 or graphene crystals suspended on a 50nm SiNx membrane. The devices are exposed to electron irradiation inside a 200kV transmission electron microscope (TEM) and we perform in situ conductance measurements[1] and subsequently ex-situ raman cartography. We correlate the damage to the crystalline lattice measured by diffraction with the observed decrease in the conductivity of the devices and the variation in the Raman phonon modes. The change in the diffraction pattern is fitted to a kinematic model. The variation of the phonon modes is fitted to DFT simulations. The evolution of the conductivity with the defect concentration is explained in the percolation theory framework, using a resistance network model. [1] Towards sensitive graphene nanoribbon-nanopore devices by preventing electron beam induced damage. M. Puster, J. A. Rodriguez- Manzo, A. Balan, M. Drndic. ACS Nano, 10.1021/ nn405112m

Resume : Since the mid-eighties of the twentieth century, molecular beam epitaxy and metalorganic chemical vapor deposition allow for growth of nanometer-thin layered semiconductor structures such as quantum wells and superlattices with interfaces being flat on the atomic scale. This opened a new area for demonstrating and exploring quantum effects. Since then ion-beam induced effects have been studied in these structures. By now, ion-beam modified multilayered semiconductor structures entered the field of practical applications. In this contribution ion-beam induced effects in multi-layered semiconductor structures will be reviewed. The main emphasis will be placed on group III - arsenide and group III - nitride systems with other multi-layered semiconductor systems being mentioned for comparison. Additionally, results on ion-beam induced effects in buried quantum dots will be presented. Besides doping, important effects occurring during ion irradiation are defect formation and diffusion, amorphisation and intermixing. It will be shown that these processes cannot be treated independent from each other. For example, at a GaAs/AlAs interface amorphisation of GaAs is delayed due to local intermixing with AlAs whereas, once GaAs got amorphous, AlAs at the interface can be amorphised with much lower ion fluences than that required for amorphisation of bulk AlAs due to a process called IBIIA (ion beam induced interfacial amorphisation). Regarding intermixing it was found that arsenide structures can be easier mixed than nitride structures, which may be connected with the high radiation resistance of the group III - nitride compounds. At the end few applications of ion implanted multi-layered semiconductor systems will be addressed.

Resume : SiO2/Si samples were irradiated at DC-60 accelerator (Astana, Kazakhstan) with Xe ions (133 MeV, 1×109 cm-2). The thickness of thermally grown SiO2 layer was 600 nm. Ion tracks in SiO2 were etched in 4% hydrofluoric acid. Afterwards the etched conical nanopores were fulfilled at room temperature with Zn precipitates using both chemical and electrochemical techniques. A part of samples after Zn deposition was annealed at 250 ºC in argon atmosphere or in air. Photoluminescence (CARY ECLIPSE Fluorescence Spectrophotometer) and scanning electron microscopy (JSM-7500F) were used for SiO2/Si structures characterization. The electrochemical technique is more effective for pores filling with Zn precipitates in comparison with the chemical one. In PL spectra of SiO2/Si structures two bands are registered in UV- and visual range: a weak band at 376 nm and an intensive one at 492 nm. We ascribe these bands to ZnO emission. The band at 376 nm can be assigned to ZnO exciton annihilation while the intensive band at 492 nm can be attributed to oxygen vacancies in ZnO. Thus, we can conclude that the oxidation of metal precipitates takes place during the Zn deposition process. Possible mechanisms of SiO2/Si PL spectra transformation after annealing are discussed.

Resume : The role of close Frenkel pairs is commonly considered to be insignificant for different radiation processes in single crystals due to the fact of the short lifetime of close pairs determined by a period of thermal oscillations of a crystal lattice. This approach might not be completely correct for the nano-objects. The binding energy of atoms in a crystal lattice of nano-objects might be significantly less and therefore the quasi-equilibrium concentration of mobile point defects is higher at a given temperature. It is noted that the equilibrium concentration depends on surface conditions connected with the growth of surface oxide layers and others and the formation of stress fields that determine a defects behavior in a volume of nanocrystals. The investigation examines this claim in relation to phenomena such as decreasing the melting temperature, changing the radiation damage threshold and its temperature dependence as well as radiation hardness, phase transitions single crystal – amorphous state, radiation plasticity [1,2]. The results of irradiation of porous silicon and silicon nanopowders with the size of nanocrystals in the range of 10-50 nm are presented. The dimensional threshold of radiation hardness, phase transitions single crystal – amorphous state upon ion bombardment is investigated. A physical model of the radiation hardness of nanocrystals compared with single crystals is considered. The reasons of the existing contradictions in published papers are discussed. [1] Mayr S. G., et al. Phys. Rev. Lett. 90, 5, 055505 (2003). [2] Pecora E. F., et al. Appl Phys. A 102, 13–19 (2011).

Resume : Modern photonic devices such as microresonators, ultraviolet detectors and electrically driven nanolasers require material with high crystalline quality. The presence of defects has great impact on material properties, such as carrier lifetime or mobility. Understanding the incorporation of defects is of no doubt an essential step to optimize device performance. As an example, we will address the electrical properties of ZnO bulk material, epitaxial ZnO thin films grown by pulsed-laser deposition and ZnO microwires grown by carbothermal evaporation. A detailed analysis of temperature-dependent transport properties and results of space-charge spectroscopy will be provided. For the later the realization of Schottky contacts is necessary and room temperature properties of Schottky diodes will be discussed. Further we show for the case of In2O3 that pn-heterodiodes are a viable alternative for space-charge spectroscopic investigations in case high-quality Schottky barrier diodes are not available.

Resume : Using a supercell model, we have performed ab initio B3PW calculations on the atomic and electronic structure of F-center both in SrZrO3 bulk and on the ZrO2-terminated (001) surface. The atomic relaxation and electronic density redistributions around the F-center are discussed. The O vacancy on the ZrO2-terminated (001) surface attracts 1.10e (vs. 1.25e in the SrZrO3 bulk), while the remaining electron density is localized mostly on the atoms nearest to a vacancy. The calculated surface defect formation energy is slightly smaller than in the bulk, which may lead to the vacancy segregation towards the surface. The calculated vacancy induced energy level on the (001) surface lies closer to the bottom of the conduction band than in the bulk. The key effect for BaTiO3/SrTiO3, SrZrO3/PbZrO3 and SrTiO3/PbTiO3 (001) interfaces is the strong dependence of the band gap for all three heterostructures on the external AO or BO2 (001) termination [1,2]. This effect is much stronger, than the dependence of the interface band gap on the number of augmented layers on the substrate. References: 1. S. Piskunov and R. I. Eglitis, Solid State Ionics 274, 29 (2015) 2. S. Piskunov and R. I. Eglitis, Nucl. Instr. & Meth. Phys. Res. B, doi:10.1016/j.nimb.2015.07.003

Resume : The new approaches are presented for elucidating a microscopic mechanism of surface atomic diffusion, nucleation and heteroepitaxial growth of nanostructures on substrates with a patterned surface by using multiscale computer modelling with the molecular dynamics and Monte Carlo methods. In this study we present a atomistic 3D model of heteroepitaxy of Ge on Si(100) which takes into account the diamond-like crystal lattice and contribution of elastic strain in the variation of the probabilities of diffusion transitions of atoms on the growth surface. This offers the opportunity to study the growth of ordered nanostructures on nonplanar substrates (prepared with nanoimprint or electron lithography) and on substrates with preliminarily induced strained regions (by ion irradiation, multilayer heterostructures). The strain field distribution at the surface of a multilayer structure with disklike SiGe nanomounds formed by molecular beam epitaxy is exploited to arrange the symmetric quantum dot molecules (QDM). The mechanisms underlying the formation of lateral QDM was studied by using scanning tunneling microscopy and numerical calculations of the strain energy distribution on the top of disklike SiGe nanomounds. The modelling of inhomogeneous strain fields in multilayer of Ge QDs heterostructures with variable Si interlayers show the increasing of Si tension strain near apex of the pyramidal shape Ge QDs due to overlapping of strains of Ge QDs multilayers as reduction of Si interlayers takes place. The experiments reveal the increasing of the electron binding energy was found by photocurrent spectroscopy technique. The work was funded by Russian Scientific Foundation (grant 14-12-00931).

Resume : Nanotwinned Cu possesses many spectacular physical and chemical properties that are dictated by twin boundary (TB) spacing. Herein, we report the experimental and theoretical investigation of Cu nanowires (NWs) with long-period twinning structures. The Cu NWs were electrochemically deposited in anodic alumina oxide (AAO) templates by pulsed electroplating. Bright-field images and selected area electron diffraction (SAED) patterns of three different twinning structures with periodic TB spacing ranging from a few to tens nanometers were recorder by transmission electron microscopy (TEM). The SAED patterns show an increasingly diffusive and streaky feature with decreasing TB spacing. The effect of TB periodicity on the SAED feature of nanotwinned Cu is successfully simulated using CaRIne crystallography software by adapting a non-primitive hexagonal close-packed (HCP) superlattice cell. The observed SAED patterns also agree with the structure-factor calculation results for the superlattice cell with different TB periodicity.

Resume : The structure and properties of nanoscale ion tracks created by fast ions in complex oxides with the pyrochlore structure are investigated. High angle annular dark field imaging, complemented with molecular dynamics simulations, show that the atoms in the shell structure surrounding the amorphous core of the track are disordered and can have relatively larger cation-cation interspacing, suggesting the presence of tensile strain. Static pair-potential calculations show that planar tensile strain lowers the oxygen vacancy migration barriers, leading to enhanced oxygen ion conductivity in the strained shell structure. Subsequent irradiation of ion tracks in the pyorchlores with a nanoscale electron beam can induce local restructuring of the ion tracks, indicating that locally controlled electron beam irradiation can be used to further modify the strain and properties of the ion tracks. These results suggest that strain engineering could be used to the tailor transport properties of ion tracks. This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.

Resume : As compared to conventional Reduced Activation Ferritic-Martensitic (RAFM) steels, Oxide Dispersion Strengthened (ODS) steels demonstrate much higher mechanical strength, as well as the high-temperature creep resistance. Y2O3 precipitates effectively hinder dislocation motion, making ODS steels a promising material for fission and future fusion reactors. Radiation resistance of the material strongly depends on the parameters of ODS nanoparticle ensembles, such as size, shape, and spatial distribution. A deep understanding of the ODS particle formation process at the atomistic level is essential for the successful production of ODS steels [1]. The shape of ODS nanoparticle is quite sensitive to the bonds, created between Y and O solute atoms at the very early stages of the particle formation process. We report the results of ab initio modelling of small nY/mO nanoclusters. Energetic stability of each particular configuration of defects in the host matrix is calculated with respect to single isolated defects, which allows us to compare stability of nanoclusters of different composition. The most energetically stable configurations of small nY/mO nanoclusters are described in details and collected in an ample database. This information provides a reliable basis for analysis of the ODS particle formation process, serving as input data for kinetic Monte Carlo simulations. [1] A. Gopejenko, Yu.F. Zhukovskii, P.V. Vladimirov, E.A. Kotomin, and A. Möslang, J. Nucl. Mater., 416, p. 40-44, 2011

Resume : The aim of this report is to compare the morphology of swift (167 and 230 MeV) Xe ion induced tracks in Y2Ti2O7 nanoparticles during post-irradiation heat treatment and after irradiation at different temperatures in pre-thinned TEM foils and TEM targets prepared from several hundred micron thick irradiated ODS steel. No difference in track parameters was found in room temperature irradiated nanoparticles in pre-thinned and conventional samples. Microstructural data gathered from pre-thinned foils irradiated in the temperature range 350-650 °C or annealed at similar temperatures suggest that amorphous latent tracks interact with the surrounding matrix, changing the track and nanoparticle morphology, while such effects are not observed in bulk ODS material treated at the same conditions. The fact that pre-thinned specimens exhibit different behavior than bulk material has major implications for the design of reliable experiments. High energy heavy ion induced radiation damage in bulk ODS material cannot reliably be simulated by pre-thinned targets.

Resume : Over the last decades, the development of ab initio molecular dynamics methods (AIMD), which offer a path that mixes the advantages of both classical MD and ab initio methods, has made it possible to elucidate the role of electrons during the dynamic process, and contributed significantly to advance the understanding of material properties and behaviors under extreme conditions. In this talk, I will discuss the application of AIMD method in simulation of the radiation responses of SiC, TiC and ZrC. Our calculations reveal that the existence of stacking faults (SFs) influences greatly the response of SiC to low energy irradiation. The C and Si atoms around the SFs are generally more difficult to be displaced than those in unfaulted SiC, and the corresponding threshold displacement energies for them are generally larger. As compared with the unfaulted state, more localized point defects are generated in faulted SiC. Also, the efficiency of damage production for Si recoils is generally higher than that for C recoils. By simulation of low energy recoil events in carbides, we find that carbon displacements occur more easily in SiC than TiC and ZrC. Another finding is that a number of antisite defects are observed in SiC, whereas few antisite defects are generated in TiC and ZrC under low energy irradiation. The different radiation tolerance between SiC and MC (M=Ti and Zr) may be mainly resulted from the discrepancy in the resistance to C disorder and antisite defects, which eventually induce structural amorphization in SiC. The defect distribution and the micromechanism for defect generation, as well as the effects of point defects on the mechanical and thermophysical properties of carbide materials, will all be presented. Overall, our simulations demonstrate that the AIMD method is a valuable tool for uncovering new phenomena, and predicting novel mechanisms for defect generation and new defective states.

Resume : In this work, we report on electrochemical porosification of GaN single crystals grown by metal organic chemical vapor deposition (MOCVD) and hydride vapor phase epitaxy (HVPE) techniques. It is shown that MOCVD-grown samples can be uniformly porosified, the transverse dimensions of pores depending upon the applied voltage and electrolyte concentration. The pores, parallel to each other, are oriented perpendicular to the top surface in contact with the electrolyte. At the same time photoelectrochemical (PEC) etching of HVPE-grown GaN evidenced the formation of self-organized three-dimensional nanostructured architectures including quasi-ordered concentric hexagonal structures. The study of as-grown samples by using Kelvin Probe Force Microscopy shows that the formation of self-organized architectures can be attributed to fine modulation of doping related to the spatial distribution of impurities and host lattice defects. We show that the formation of self-organized spatial architectures in the process of HVPE is caused by the generation of V-pits and their subsequent overgrowth accompanied by the spatial modulation of doping. It is demonstrated that the electrical and luminescence properties of HVPE-grown GaN are spatially modulated throughout, including islands between overgrown V-pit regions. The obtained results are indicative of new possibilities for defect engineering in gallium nitride and for three-dimensional spatial nanostructuring of this important electronic material. This work was supported by the Academy of Sciences of Moldova under the Grant no 15.817.02.29A, and by the Swiss National Science Foundation and EPFL under the SCOPES Grant no IZ73ZO_152273/1. Support from the Australian Microscopy & Microanalysis Research Facility at UNSW is acknowledged.

Resume : Although the irradiation with an e-beam is known to induce a structural damage in nanostructures, in some particular circumstances it may induce several unexpected benefits that allow tailoring of the morphology and structure of the material at the nanoscale. In this work we demonstrate how the interaction of e-beam with metal oxide nanotubes created by means of the Kirkendall effect [1], resulting in the generation of defects, can be employed usefully to manipulate matter at the nanoscale [2]. In our strategy, a focused electron beam, extracted from a transmission electron microscope source, is used to site-selectively heat the oxide material in order to generate and steer a metal ion diffusion flux inside nanotubes. The metal ion flux generated inside the nanotube is a consequence of the reduction of the oxide phase occurring upon exposure to the e-beam. We further show that the directional migration of the metal ions inside the nanotubes can be achieved by creating local defects in the oxide shell serving as a channel for matter diffusion. This allows sculpting organized metal nanoparticles inside the nanotubes with various sizes, shapes, and periodicities. This nanomanipulation technique is very promising since it enables creating unique nanostructures that, at present, cannot be attained by an alternative classical synthesis route. [1] El Mel et al., Small 2013, 9, 2838 [2] El Mel et al., ACS Nano 2014, 8, 1854

Resume : The breakthrough in electronics and information technology is anticipated by the development of emerging memory and logic devices, artificial neural networks and brain-inspired computing on the basis of memristive nanomaterials represented in a particular case by a simple metal–insulator–metal (MIM) structure. Oxides with high mobility of oxygen ions/vacancies are often used as the insulators. The present report is focused on the comparative analysis of MIM devices based on oxides with ionic (ZrOx, HfOx) and covalent (SiOx) bonding of various composition and geometry deposited by the methods of magnetron sputtering. The memristive devices demonstrate reproducible change in their resistance (resistive switching – RS) originated from the formation and rupture of conductive pathways (filaments) in oxide film due to the electric-field-driven migration of oxygen vacancies or mobile oxygen ions. The filamentary nature of the observed bipolar RS is supported by the kinetic Monte-Carlo computer simulation of the redox processes for different oxide structures. The effect of irradiation with ions of medium energies (up to 150 keV) is also analyzed and shown to simulate the impact of energetic particles, such as protons (10-15 MeV) or fission neutrons (0.2-1 MeV). The high tolerance of the device resistance state to radiation-induced defects is demonstrated and is very important for atomic energy and space applications of the developed memristive devices.

Resume : With the high ductility, electrical conductivity, heat dissipation and more requirements for electronic circuits, copper (Cu) nanowire has been the general interconnect material in electronic circuits for several decades. Owing to rapid shrinkage of size in electronic devices, the synthetic approach of Cu nanowire has become one of the most popular research topics. Here, we prepared the Cu nanowire by catalyst-free methods with a simple one-step procedure, at which twin boundaries played the most important role on the atomic nucleation for the growth of Cu nanowire. By annealing the Cu grid in an ultrahigh vacuum environment (5×〖10〗^(-8) pa), Cu atoms were found to diffuse through carbon film and evaporate under 700 oC. The kinetic studies of Cu atomic transportation were carried out on the basis of growth of Cu nanocrystals with various architectures. With the high resolution transmission electron microscope (HRTEM) image analysis, the atomic transportations could be observed by the motions of monomolecular layers. Those interactions resulted in the Cu nanowire growth upon supersaturation. Based on the observation by in situ TEM, we expect our study to be a starting point on the mass transportation mechanisms underlying the interaction between Cu precursor concentration and pathway of thermomigration. These findings lead to tentative conclusions about the preventions for Cu as microcomponent in integrated circuit (IC).

Resume : Good mechanical and electrical properties place copper among the materials, which are the most frequently used for operation in extreme conditions. One of such application is to use copper as a construction material for high gradient accelerating structure in linear particle accelerators. A major problem in the design of such accelerators is that the high electric field causes electric discharges in form of arcs to appear inside the structures, despite an ultra high vacuum. One hypothesis for these arcs are that they are triggered by nano-sized tips on the copper (Cu) surface. In order to study the feasibility of the tip hypothesis, it becomes important to know under which conditions such tips are stable, for how long, and which mechanism could possible create such tips. We have for this purpose developed a new Kinetic Monte Carlo model designed especially for studying the surface evolution of metals (Cu, Fe, W, Au) under electric fields. The model uses tabulated migration barriers that are modified by the electric field, obtained by solving Laplace's equation. Using our model, we found a significant stability of tips with high aspect ratios at room temperature, were the tips can be stable for hours. At temperatures above 800 K, we found that the same tip will disappear in less than a microsecond, indicating a strong temperature dependence on the flattening mechanism. We have also explored possible mechanisms for formations of surface tips under electric fields.

Resume : Controlling defects during the growth of materials is crucial to tailor their properties. Although the presence of defects is in general considered as a drawback, in some particular cases it can be of real benefit for a desired application. In this contribution we show how the presence of defects during the growth of metal nanowires can be extremely interesting to design the surface of these tailor-made nanomaterials. More precisely, during the growth of metal nanowires (copper, gold, silver, and alloys) by magnetron sputtering over a nanopatterned silicon substrate, the presence of defects results in the formation of periodic nano-hillocks. The key requirements to grow such nano-hillocks are i) the dimension of the silicon nanogratings serving as a physical template and ii) the rotation speed of the substrate during the deposition. The origin of such defects is attributed to the presence of compressive stress during the growth of the material that can be relaxed by reducing the dimension of the nanograted template structures. Such nanostructured metal nanowires can be considered as potential candidates for the development of advanced sensors and actuators.

Resume : Growing in the magnetron sputtering inert gas condensation chamber iron nanoparticles in some cases turn out to be cubes, which is counter-intuitive from the surface minimization consideration viewpoint. Although a spherical or close-to-spherical shape is energetically the most favorable one, we show that by tuning dc power of a dc-magnetron sputtering system, stable iron nanocubes can be obtained. We address this question by applying the combination of three different techniques: experiment, Molecular Dynamics and Kinetic Monte Carlo simulations. Our experiments as well as computer simulations indicate that the cubic shape of iron nanoparticles is explained by the difference in the kinetic growth modes of (100) and (110) surfaces, rather than the surface formation energetics. Our results are in good agreement between the different methods, showing that the final shape is defined by condensation temperature in combination with deposition rate. We present also the full deposition rate--temperature diagram of iron nanocluster shapes as well as an analytical model predicting the temperature and deposition rate evolution in nanoparticles. Combined together, the diagram and the model can be used to tune the desired final shape of the grown iron nanoparticles.

Resume : Graphene, being a monolayer of carbon atoms, is a great material for studying the atomic structure of defects, their dynamics, and the correlation between the exact disorder structure and macroscopic properties. At the same time, purposefully created defects can be used to control the mechanical, electronic and thermal properties of graphene, which can lead to new applications in a variety of different fields. However, to do this in a controlled manner, very good control over the creation of disorder is needed. One way to achieve this is to use energetic particles to introduce defects and to study in detail the resulting atomic structure. While this has been attempted to some extend, most of the structural analysis has relied on indirect spectroscopic data. In this presentation, I will present an enhanced theoretical model to describe electron beam knock-on damage in graphene with a high enough predictive power to determine isotope ratios from experimental graphene samples, describe large scale structural modification of graphene using electron and ion irradiation, as well as present results on implantation of foreign atoms into the graphene lattice using low-energy ions. Finally, I will present our new experimental setup that combines low-energy ion irradiation of graphene with subsequent observation of the atomic structure with a scanning transmission electron microscope in the same vacuum to protect the sample from contamination.

Resume : In this presentation we show how individual atomic defects and linear mirror twin boundaries in 2-D MoSe2, identified with super resolution atomic force microscopy, alter the electronic wave function, imaged via Scanning Tunneling Spectroscopic mapping, leading in the mirror twin boundaries to charge density waves and solitons. Electronic and Optoelectronic processes in matter are governed by the quantum mechanically determined electronic structure and are well understood for most bulk material systems. Even individual nano building blocks made from these materials are reasonably well characterized. However, heterogeneous nano building block assemblies, and specifically their electronic and optoelectronic properties, are largely uncharted territory. Herein lies the key to controlling electronic wave functions at their native length scale, enabling the improvement of current material functionality or the discovery of entirely new material properties. Hierarchically ordered defects or adsorbents in two dimensional transition metal dichalcogenides (TMDs - MoS2, WS2, MoSe2, etc…) enable the direct visualization of electron wave tuning using heterostructures, which are on a comparable length scale as the electronic wave function. 2D-TMDs are a unique class of materials, where electron confinement leads to high electron/hole mobility similar to graphene, but with an intrinsic direct bandgap in the visible/near-IR, enabling a wide range of optoelectronic applications. We employed low temperature scanning tunneling/atomic force microscope to correlate the precise local atomic morphology to the local electronic structure. We can identify individual Se vacancies – on both, the SPM facing and the substrate facing side. Both result in particular wave function distribution related to charges located at the atomic defect. The additional states created at the defect are energetically located in the band gap of pristine MoSe2, creating atomic type I heterojunctions. Along Mirror Twin Boundaries (MTB), where Se vacancies are aligned in one dimension, we directly observe the existence of charge density waves. These MTBs first create one atomic wide metallic wires embedded in this direct band gap semiconducting materials. Directly at the Fermi level however a bandgap of 100meV opens up. For the frontier states directly at the new band gap we observe a periodic modulation in the density of states along, with a wavelength of approximately three lattice constants. The modulations in the density of states above and below the Fermi level are spatially out of phase, consistent with charge density wave order. By charging up the charge density wave we observe the creation of solitons – a self-reinforcing wave - and are able to measure its’ energetic dispersion. These results demonstrate how defect can not only modify the local electronic wave function but directly alter the material properties and opens up a large playground for us to study the effects of linear defects, hierarchically ordered defects or adsorbents (which can be spatially manipulated by the STM itself) or how the electron wave functions are modulated at a 2-D/2-D heterojunction such as MoSe2/WSe2.

Resume : Since the discovery of carbon nanotubes the quasi 1D materials attract high interest as a possible base of future nanoelectronics. Still, to obtain atomic scale single-crystal structure is difficult and very limited examples were presented. Indeed, there are many groups of materials that are highly anisotropic in their bulk crystal structure with bonding strength differs significantly. This makes it possible that one can mechanically separate the bulk into high quality low dimensional crystals directly. Here, we will show that, by avoiding chemical synthesis, a new 1D single crystal material Ta2Pd3Se8, can be exfoliated using simple mechanical exfoliation technique. TEM study clearly shows that the diameter of TPS crystal can be reduced down to lower than 2 nm and preserve good crystal quality. The trend of expanding band gap was found when the diameter decreasing from bulk crystal to single ribbon along with the changing of the band gap type from indirect to direct one. Fabricated FETs with TPS crystal ranges from 10 nm to 30 nm perform best with an on/off ratio reaching 10^4 and mobility near 80 cm^2V^-1s^-1.Our results demonstrate a truly one dimensional atomic chain material which presents opportunities in areas including low dimensional physics, optoelectronics and energy harvesting. P.B.S. acknowledges the financial support of the Ministry of Education and Science of the Russian Federation in the framework of Increase Competitiveness Program of NUST «MISiS»(№ K2-2015-033).

Resume : This study investigated effects of vacancy defects on tensile behaviors of open-tip carbon nanocones (CNCs) by molecular dynamics simulations. To examine the effects of vacancy defects, a perfect and three vacancy-defect CNCs (including the upper-vacancy, the middle-vacancy, and the lower-vacancy CNCs) were inspected. Some findings were obtained. It was noticed that the upper-vacancy CNC has the greatest degradation in the failure strain and the failure load among the three vacancy-defect CNCs, and the lower-vacancy CNC has the smallest degradation in the failure strain and the failure load. Degradation in the failure load is larger than degradation in the failure strain. Moreover, no apparent yielding was observed before failure of the studied CNCs. All the vacancy-defect CNCs were broken near the top end rather than near the vacancy location of the CNCs. The behaviors of the vacancy-location-dependent degradation and the near top-end breaking of the vacancy-defect CNCs are quite different from those of vacancy-defect CNTs (carbon nanotubes). These particular behaviors are ascribed to non-uniform diameters along the cone axes of the CNCs.

Resume : Infrared wavelength range light-emitted diodes (further IR-LEDs) operate under conditions of various ionizing radiation which leads to combined action of ionizing radiation and long operating time factors limited their efficiency. Hence the purpose of this paper is research the influence of 60Co gamma-quanta preliminary irradiation on degradation processes development during long operating time. Matter of research is IR-LEDs based on double AlGaAs heterostructures. Irradiation has realized by 60Co gamma-quanta in passive power mode. Long operating time conditions have simulated step-by-step test on the assumption of operating current stepped increase from stage to stage and permanent ambient temperature by 65 оС. The main control parameter has been value of LEDs radiant power with operating current by 50 mA. Two characteristic radiation doses have chosen for preliminary irradiation. The first dose corresponds to first phase of radiant power decrease of LEDs irradiated by gamma-quanta (radiation-stimulated reconfiguration of present defect structure LEDs chip before irradiation). The second irradiation dose corresponds to second phase of radiant power decrease (radiant power reduction due to establishment of purely radiation defects. Consequently the research was determined that preliminary 60Co gamma-quanta irradiation has increased useful lifetime. At the same time severable radiation defects annealing is observed. Probable causes of observable results are discussed.

Resume : The sputtering and possible enhancement of sputtering yields from nanoparticles have been subject to several simulation studies, while experimental data has been scarce. We have set up an experimental system of an array of Au nanoparticles on a substrate, and measured their size changes due to sputtering by 25 keV Ga ion irradiation. However, the size change in such an experiment does not directly give the sputtering yield, since a significant fraction of the sputtered atoms will redeposit on other nanoparticles. To enable comparing the experiments with simulations, we develop a Monte Carlo model of the redeposition process, which takes as input the sputtering yield from either molecular dynamics or binary collision approximation simulations of different-sized nanoparticles. The results show that the molecular dynamics sputtering yield lead to better agreement with the experiments, pointing to the importance of heat spike effects on sputtering yields from nanoparticles.

Resume : ZnO bulk (3.3 eV band gap) is found to be attractive material for fabrication of water-splitting photocatalysts because of low cost, non-toxicity and electron mobility. Although this material has a wider band gap than required for visible-light photocatalytic applications (1.3-2.5 eV) and suffers from photocorrosion under UV irradiation, both drawbacks can be overcome. Alternative, nanoscale ZnO crystalline structures possess higher photostability and specific area as compared to bulk. Using a hybrid exchange-correlation functional for ab initio DFT-LCAO calculations, we have found that ZnO nanowires (NWs) possess narrower band gaps than bulk. Still, the tendency of band gap narrowing along with nanowire diameter growing is not sufficient, and its further modification is required. There exist various approaches to enhance photocatalytic efficiency of ZnO NWs, for example, their doping. It is reported that, in particular, N and Co mono- and co-dopants upon ZnO NWs improve their photocatalytic performance. While experimental studies of doped nanomaterials are rather complicated and expensive, there is a possibility to make reliable predictions of doping effect on the electronic structure of photocatalyst employing ab initio calculations. Results of simulations on a number of doped ZnO NWs are analyzed. It is shown that at certain concentration and location of dopants in nanowires the water splitting can be shifted to visible solar light diapason with a promising efficiency.

Resume : Recent investigations of the effects of radiation on nanostructured films found differences with respect to results obtained for large grains/polycrystalline films. The absence of a long distance order in these films allows for much shorter diffusion distances of the created defects before encountering sites in the network that act as sinks. Therefore, their properties could be less affected by exposure to radiation than those of single crystal or large grains materials. To investigate the effect of gamma and X-ray radiation on transparent and conductive oxides we used the Pulsed Laser Deposition (PLD) technique, which is very suitable to grow nanocrystalline or amorphous thin films of almost any materials starting from inexpensive targets. By simply changing the deposition parameters, films possessing different chemical compositions and/or structures could be easily obtained. In addition, the surface morphology of the deposited films is very smooth, allowing for the use of characterization techniques such as X-ray reflectivity, grazing incidence X-ray diffraction, X-ray diffusive scattering, or nanoindentation that all possess depth resolutions of the order of few nm. The effect of gamma and X-ray irradiation on the structure, desity, surface morphology, optical and electrical properties of the main TCO films used today in the industry, IZO and IGZO with various In, Zn and Ga compositions, were investigated and compared with those obtained on polycrystalline films

Resume : Pulsed laser ablation in liquid is a versatile method to synthesize high-purity nanomaterials such as ZnO nanoparticles, currently the subject of a large scientific interest stimulated by their applications in several fields. Their optical properties are characterized by two emission bands both excited above the energy gap (3.4 eV): 1) exciton related emission at 3.3 eV; 2) defect related emission at 2.2 eV, whose origin is not conclusively settled yet. This work studies nanomaterials produced by ablation with a pulsed Nd:YAG laser of a Zn plate in H2O. Microscopy (TEM, HRTEM, AFM) images and Raman spectra evidence the formation of ZnO nanocrystals with sizes of tens of nm, the distance between the crystalline planes and the vibrational modes being consistent with the wurtzite structure. Basing also on our previous work [App. Phys. Lett. 107, 013103 (2015)], the defect emission at 2.2 eV is proposed to originates from a light excited hole in the valence band recombining with a electron in a singly ionized oxygen vacancy. Thermal annealing at 300°C in O2 and He atmosphere, produces a reduction of the A1(LO) Raman mode at 562 cm-1, which is related to the oxygen vacancies, and a consequent decrease of the defect luminescence, while the excitonic luminescence increases. These results indicate that the ZnO emissions can be controlled by thermal annealing, and are promising in view of optoelectronic applications.

Resume : The results of degradation research of volt-ampere characteristics of light emitting diodes based on AlGaInP heterostructures with multiple quantum wells with wavelength λ =624 nm and λ = 590 nm are presented under irradiation by gamma-rays and fast neutrons in passive powering mode. An resistance increasing in in the high current field is shown. It can not be explained by an increase in resistance associated with the transition of the metal - semiconductor. Because the doped layers of the contact, which are directed from both sides of the diode and significantly reduces the potential barrier, effectively allow the flow of electrons to pass through the thickness of the material. Presumably the increase in resistance is associated with increased resistance of the contact areas as a result of changes in the mobility of the charge carriers, which changes as a result of increasing the number of defects and other imperfections in the structure of the solid.

Resume : Experimental research of structural and phase components states under the influence of γ-rays on powder mixture of Ti Al after preliminary mechanical activation is performed. Cylindrical samples were produced by powder mixtures compacting on standard equipment. After compaction irradiation has realized by stationary source 60Co γ-quanta during normal conditions. Then the samples are heated. Fine structure parameters have investigated using X-ray diffraction, X-ray and phase analysis at different stage of samples manufacture. The influence of γ-irradiation on the components structural condition of mechanically activated mixture has experimentally established. It is determined that γ-irradiation promotes the release of energy stored in the preliminary mechanically activated powder mixture Ti Al and it actually is a stimulant of structural and phase changes of the powder mixture even at room temperature. Application of preliminary irradiation by γ-quanta on mechanically activated powder mixture of Ti Al is allowed to realize synthesis at temperatures lower then typical temperature of SH-synthesis without the characteristic features of ignition phenomena. The possible mechanisms of γ-irradiation action on the processes of SH-synthesis are discussed.

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 (PL) measurements were carried out at room temperature in the 350–650 nm wavelength range using a Perkin-Elmer LS55 PL spectrometer, with an error below 0.5 nm. A source of excitation was light of wavelength λ = 315 nm. The treatment with super high frequency (SHF) radiation at regime with p=7.5 W/cm2 was chosen as efficiently method of defect structure modification. The initial sample (i.e., not subjected to SHF treatment) served as reference. It was kept under the same conditions between the measurements as the treated samples. All measurements were repeated during the time that was needed to reaching some equilibrium state with non-changed PL spectra. It was obtained, that modification of PL spectrum occurs during several days after end of treatment. It was found optimal regime of treatment, result in increasing of intensities of all observed PL bands (edge and "yellow"). We suppose that microwave radiation treatment leads to decrease of non-radiative recombination channel, resulted to observed features. Physical mechanism of observed transformation is based on non-thermal interaction or electromagnetic waves of SHF region with semiconductor material.

Resume : Nanosized structures created on the surface and in the surface region of semiconductor and dielectric films are the prospects in the creation of new instruments micro-, opto-and nanoelectronics. In particular, the increased interest in Nanoscale structure CoSi2 primarily due to their use in creating metal-dielectric-semiconductor, semiconductor-dielectric-semiconductor nanofilm structures, barrier and ohmic contacts, magneto-memory devices, and others. In this paper, a method of measuring the intensity of the transmitted light through the test samples of different frequencies are determined band gap Eg nanocrystalline phases NaSi2 and CoSi2 created in different depths Si by ion implantation in combination with annealing. It is found that the Eg of nanocrystalline metal silicides phases depending on their size may vary within 0.6 - 1 eV. The volume of each of the nanocrystalline phase, created at the same dose of the ions in the surface layer and in the surface layer will be approximately the same. At a dose D = 1015 cm-2 to this volume CoSi2 averaged ~ (1.5 - 2) • 10-18 cm3 (number of atoms in the nanocrystal ~ 20000). By varying the ion dose in the range of ~ 5•1014 - 5•1015 cm-2 can be controlled to vary the volume of nanocrystalline phase between ~ 10-19 - 5•10-18 cm3.

Resume : We have presented experimental data and the theoretical basis for the extraction of silver ions from aqueous solutions, using metal sulfides (PbS, ZnS, MnS, CuS, FeS) in the form of nanocrystals in gel matrices. A mathematical model, taking into account the sorption of Ag(I) due to a two-stage ion exchange in the occurence of solid-liquid phase contact. This model was applied in the technology of equipment design.

Resume : Due to high stable emission characteristics within the wide range of temperature the metal silicides on the boundary with Si have been used in the modern microelectronics widely. There are a number of advantages of the epitaxyal growth of silicides under the low energy ion beams in comparison with other methods of thin film microelectronics. The formation of silicides have been found on the Si (111) surface under the bombardment by alkali Li+, Na+, Rb+, ions in energy range of 50-1100 eV. The dose, energy and temperature conditions of silicide growth and existence on the surface have been determined by low-energy electron diffraction method and measuring the reflection/background ratio in the diffraction images. Alkali metal silicides with the surface structures Si(111)-(4x4)Li, Si(111)-(1x1)Na, Si(111)-(2x2)Rb have been identified and the probable models of their formation have been proposed. The contrast and the redistribution of diffraction and background intensity of LEED patterns in the Si(111)–(1×1)→Si(111)–(1×1)Na, Si(111)–(1×1)→Si(111)–(4×4)Li, Si(111)–(1×1) → Si(111)–(2×2)Rb, and transitions were measured automatically in irradiating the surface with low_energy ions. The initial structure vanished gradually, and a new low_intensity pattern emerged with an angle displacement in the direction of reflection. Experimental research demonstrated the possibility of modifying the near_surface regions of silicon bombarded with low_energy ions and stimulating the growth of submonolayer epitaxial films. In according to Van der Marve model all the reflections of the superlattices in the case of Li and Rb have been explained by defects of mismatch along both axeses of two-dimensional atomic lattices.

Resume : The behavior of the diffraction and background intensities in low energy electron diffraction (LEED) have been investigated depending on the energy and irradiation doze of Na+ ions with the energy of 50-1100 eV for the Si (111) surface up to the moment of its complete amorphization. The least destructive, simple and universal method of such investigations in situ is the low energy electron diffraction simultaneously in variants of electron diffraction and the dynamics of the reflex and background intensities (LEED R/B). Therefore the dependence of the relation between the reflex and background currents on the irradiation doze takes the form: Ir/Ib = ( Iri/Ibi ) exp (-ad) where Iri/Ibi is the meaning of the relation between the reflex and background currents before irradiation; a is an average area of disturbance per one bombarding ion; d is irradiation doze. It is seen, that a varies non-monotonically depending on the energy, the maxima being at ~200 eV and ~950 eV and minimum - at ~600 eV. For Ei < 100 eV the gradual, almost complete restoration of initial intensity is observed in 1-2 minutes after interruption of the bombardment without additional thermal treatment.The obtained non-monotone dependencies are explained by complex contribution to general amorphization of many factors; they are the implantation of ion beam substance, radiation displacement, self-annealing, crystallization of new Si1-Na1 phase, etc. At Еi < 100eV the complete destruction of the order on a surface does not occur even at long-term irradiation due to the formation of an equilibrium covering with a film of alkaline metal kept at the expense of self-sputtering.

Resume : Were studied the absorption spectra in the region of the absorption band edge and the photoluminescence (PL) in the 80-300K temperature range of ε-GaSe crystals doped with Eu in concentrations from 0.025 at.% to 3.0 at.%, grown by Bridgman method. At dopant concentrations of 0.05-1.0 at.% the absorption bands of excitons in the state n = 1 and n = 2 decrease in intensity. At Eu concentration of 3.0 at.% the excitonic bands disappear and as a result of light absorption on Eu3+ centers the absorption band edge shifts to higher energies. At temperatures of 80-300K the Eu doped GaSe crystals have an intense PL in the red-orange region of the spectrum. The PL of GaSe crystals doped with Eu in concentrations greater than 0.05 at.% is determined by the radiative annihilation of direct excitons, electronic transitions in Eu3+ luminescence centers and donor-acceptor emission in GaSe. The intensity of donor-acceptor PL band increases at Eu atoms concentration increasing. This can be a result of donor levels presence created in the band gap of GaSe compound by Eu atoms. The concentration of these levels is rising with the concentration of the dopant. The recombination levels and recombination mechanism were determined from the measurements of PL relaxation and PL intensity dependence on temperature and excitation intensity.

Resume : In this work are investigated the structural properties of GaSe single crystals doped with Eu in concentrations from 0.025 to 3.0 at.%. The undoped and Eu doped GaSe compounds were synthesized of elementary components Ga (5N), Se (5N) and Eu (5N) and grown by Bridgman method. The XRD patterns of undoped crystal contain intense lines of the (0 0 2), (0 0 4), (1 0 11) and (1 0 13) planes characteristic for ε-GaSe single crystals. GaSe crystals doping with low Eu concentrations (0.025-0.05 at. %) leads to the appearance of some XRD lines characteristic for δ-GaSe modification. Thus, we can admit that Eu located in the Van der Waals space moves the Se-Ga-Ga-Se packs resulting with δ-GaSe polytype formation. This phase transformation is amplified by Eu atoms concentration increase up to 1.0 at. %. At Eu concentrations of 1.0-3.0 at. % at the same time with the intensity amplification of XRD lines characteristic for δ-GaSe a compositional change occurs with formation of Ga2Se3 crystallites. Their volume density increases at dopant concentration increase. The structural defects introduced by Eu in GaSe crystals are also investigated by Raman spectroscopy. From the Raman spectra analysis result that Eu atoms at concentrations of 1.0 at. % and 3.0 at. % along with structural and phase changes form individual clusters with inhomogeneous volume density.

Resume : The difference in track parameters registered in some oxides at the same energy loss and different ion beam energy, the so called “velocity effect”, have been evidenced by a number of experimental methods. Most of the corresponding data on damage cross-section and then on the track radii were found by means of Channeling Rutherford Backscattering Spectroscopy or X-ray diffraction while the contribution of TEM results in the whole data array still remains very limited. In this report we present an analysis of existing TEM results related to the “velocity effect” and consider how the conical shape of latent tracks observed in the subsurface region of swift heavy ion irradiated oxides may affect the correct determination of the track size as well as the critical electronic energy loss for track formation. The discussion is based on our cross-sectional TEM studies of high energy Bi and Xe ion induced latent tracks in TiO2 and Al2O3 single crystals.

Resume : In this work, photothermal deflection techniques have been used to characterize the opto-thermal properties of porous GaAs samples. In particular, those layers are formed on heavily doped p-type GaAs substrates using electrochemical anodization process at different current densities (6, 12 and 24 mAcm-2). Photothermal deflection spectroscopy was used to determine the optical absorption spectra and the band gap energy of both porous layer and substrate. An estimation of the average mean size of the GaAs nanocrystals obtained from the effective mass theory and based on photothermal data is of about 8 nm. Spectral Reflectance was employed in the wavelength range of 250 to 800 nm, which served to exclude an important decrease in the optical loss with anodization current density. From the dependence of the photothermal deflection signal on the excitation light modulation frequency, thermal conductivity of the porous layers was evaluated. It was found that the increase of the current density causes a huge decrease in the thermal conductivity of the porous GaAs layers. This reduction is mainly due to phonon boundary scattering at the increased amount of interfaces. The obtained results reveal porous GaAs as an interesting candidate for both thermoelectric and photovoltaic applications in which thermal transport is a crucial issue.

Resume : Ion beam sputtering (IBS) is a universal phenomenon that can be used for the production of nanopatterns in a wide range of materials and scales. Many semiconductor systems are suitable for this kind of processing, but Si is certainly the most studied one due to its technological relevance, flatness, and mono-elemental nature [1]. In the last years, the key role of metal impurities for the initial formation of the pattern has been clearly established [2], changing the field in a significant way. Still, several questions remain open, such as the roles of metal silicides segregation [3] and the preferential sputtering for the different metal species [4], as well as the threshold metal concentration needed for nanopatterning at given experimental conditions. Most of these works are restricted to low energetic beams (0.5-5 keV) produced with conventional ion guns and different set-ups to induce indirect metal co-deposition [5]. However, in order to have an appropriate control of the metal species more dedicated systems, where metal could be also directly incorporated, are becoming essential. In this communication, we will present our recent experimental works on IBS nanopatterning of Si at medium energies (40 keV) with simultaneous metal incorporation [6]. In order to understand the influence of the metal on the pattern formation we study three different experimental systems produced with (a) direct metal implantation, (b) indirect metal co-deposition, i.e., with simultaneous irradiation of a metallic plate adjacent to the target, and (c) with non-metal implantation (used as a reference). In all cases, irradiation was carried out in a high-flux ion implanter using an incidence angle of 60º with respect to the target surface normal and for different ion fluences. The dynamics of the pattern is studied using atomic force microscopy (AFM) to characterize the pattern morphology, and particularly to quantify the surface roughness and pattern wavelength. Metal content was determined with Rutherford backscattering spectrometry and the formation of silicides mapped with conventional X-ray and hard X-ray photoelectron spectroscopy (performed at ESRF-BM25b). In addition, we performed current sensing AFM as well as transmission electron microscopy analysis of the metal containing samples in order to disclose the formation of any compositional pattern and its eventual correlation with the morphological one. We will discuss the main differences arising from the different metal incorporation paths, paying special attention to effects such as geometrical shadowing, the threshold contents required to trigger the pattern in every case and the formation of metal silicides. 1. J. Muñoz-García et al., Mater. Sci. Eng. R-Rep. 86, 1 (2014) 2. C. Madi et al., Phys. Rev. Lett. 101, 246102 (2008) 3. M. Engler et al., Nanotechnology 25, 115303 (2014) 4. R. Gago et al., Nanotechnology 25, 415301 (2014) 5. K. Zhang et al., Nanotechnology 25, 085301 (2014) 6. A. Redondo-Cubero et al. Phys. Rev. B 86, 085436 (2012)

Resume : Luminescent nanomaterials have been investigated due their potential application in optical bioimaging, development of LED and ultraviolet (UV) laser and others. The ZnO has a bandgap of 3.37 eV, high bond energy (60 MeV) making nanoparticles of zinc oxide (ZnO NPs) very stable; also these nanoparticles have a good biocompatibility. In addition the ZnO NPs are able to generate fluorescence in different emissions (UV, violet, blue, green, yellow, and orange-red) allowing us to have a wide range of dyes, making it possible to detect different cell lines simultaneously. Various luminescent mechanisms of ZnO NPs have been suggested either by direct exaction transition (band-edge emission at approximately 370 nm), size of the nanoparticle (quantum confinement effect) and surface defects responsible to the visible emission. These defects and sizes of ZnO NPs can be regulated by the synthesis conditions. There are many forms for synthesized ZnO NPs. However the Laser Ablation of Solids in Liquids (LASL) is a method experimentally simple and has been used to obtain metal oxides based colloidal solutions like ZnO. This technique successfully demonstrated the synthesis of colloidal ZnO NP, however the study of the behavior of these Np after production by this method has not been reported. Since the generation of fluorescence is a phenomenon little studied from dynamic point .It has considered this study to understand because it originates and changes in fluorescence generated by synthesized ZnO. In this work we present results on the characterization of the fluorescence of colloidal ZnO NPs obtained by the LASL technique at different times after of synthesis ablation times. Colloidal solutions of ZnO nanomaterials were synthesized by pulsed laser ablation of highly pure (99.99%) zinc metal target on the bottom of an open glass vessel filled with 10 mL of Acetone (from Fermont) at room temperature. The zinc target was ablated during 10 min by first harmonic (1064 nm) of a Nd:YAG laser (Minilite TM Continuum® ) operated at 15 Hz with pulse width of 7ns and laser intensity of 50 mJ/pulse. The second harmonic of a nanosecond pulsed Nd-YAG laser (532 nm), a metallic Zinc disk and acetone were used to prepare the colloidal ZnO NPs. Samples were characterized by UV-Vis, fluorescence, Raman spectroscopy and TEM. Results show that the first day of synthesis there was an increase in absorbance compared to liquid medium, however the characteristic band of ZnO wasn’t observe (360 nm). The nest day after ablation, the sample show that band in 360 nm and it remains, but that decreases to 22% passing some days. Fluorescence spectroscopy was very different to UV-Vis as the fluorescence emission increase. For the first day after synthesis only one band covering the region UV and visible regions, the simple didn’t show band or defined peak. In three day after of synthesis begin to observe four peaks, 370 nm 370 corresponding to the normal transition of band gap of ZnO, 406 nm, 447 nm and 570 nm corresponding to the visible region emission. As for the physical characteristics of the nanoparticle solution is passage of a coffee to be almost transparent colour. Raman spectroscopy throw one peak at 440 cm-1 corresponding to the transition E2 of ZnO and a band at 560 cm-1 corresponding to the transition A1, however this is more intense against the peak of 440 cm-1, which we would indicate that the material is in nanometer size, thrown by TEM images show the nanometric character of the particles having a morphology mostly spheres with an average size of 5 nm in diameter, plus it was observed a second morphology bars. Thereby we can conclude that the generation of fluorescence is a dynamic phenomenon because there was a considerable change in the fluorescence spectra from the initial to others this phenomenon contributes to a rafter morphology since it is UV-Vis spectrum suffers spectral changes.

Resume : Thin MoS2 samples suitable for Transmission Electron Microscopy (TEM) are irraidated by swift-heavy ions (209Bi ions with energies of 1.27 and 0.48 GeV). The latent tracks are observed and shown in figure 1 with circular shape under normal incidence. The dimension of the tracks is quite identical with diameter of about 5 nm. In figure 1 (b), the lattice structure remains in un-irradiated region. However, the lattice structure becomes disordered inside the tracks. It is worth noting that lattice is only partially disordered. The Raman spectra are measured and analyzed to further understand defects inside the latent tracks. Fig. 1 Bright field image of MoS2 irradiated with 209Bi ions. The specimens are irradiated under normal incidence. (a) 1.27 GeV 209Bi ions irradiated MoS2 under 1×1011 ions/cm2, (b) 0.48 GeV 209Bi ions irradiated MoS2 under 5×1011 ions/cm2 with higher magnification than (a).

Resume : A new phenomenon called SNEEL (Synergy between Nuclear and Electronic Energy Losses) was very recently discovered to occur in solids irradiated with a dual low- and high-energy ion beam [1-2]. This process leads to a strong decrease of the damage induced by ballistic collisions generated by slow ions (Sn) via a self-healing mechanism due to ionization from the electronic energy loss of swift ions (Se). This effect could be used to control at a nanoscale the nature of defects and then the properties of the materials. This paper reports RBS/C, Raman and TEM experiments dedicated to the understanding of the SNEEL phenomenon occurring in the particular case of SiC. Results show that dual-beam irradiation of SiC induces a dramatic change in the final sample microstructure with a substantial decrease of radiation damage as compared to single-beam irradiation. Actually, a defective layer containing dislocations is formed upon dual-beam irradiation (Sn&Se), whereas single low-energy irradiation (Sn alone) or even sequential (Sn+Se) irradiations lead to full amorphization. These results present a crucial interest for both fundamental issues and industrial applications. In nuclear reactors of the next generation, expected synergetic Sn/Se effects may lead to a strong reduction of the damage production allowing the preservation of the physical integrity of materials submitted to severe irradiations. [1] L. Thomé et al, Appl. Phys. Lett. 102, 141906 (2013). [2] L. Thomé et al, J. Appl. Phys. 117, 105901 (2015).

Resume : A transition border between macroscopic and nanoscale states of solids associated with change of its physical properties is certain to exist. The change of mechanical, magnetic, thermal and other properties of nanoparticles may be due to the surface tension, decrease in coordinate number in the top-surface layer, rebuilding of the electron shell structure, change of the symmetric group and the binding energy. Different defects of the structure can also have significant influence on the physical properties of nanoparticles. A deviation form the Neumann principle with decrease of the crystal sized is constant discussed in the literature. In the present work the dependence of elastic module, Debye’s temperature, melting point, thermal expansion coefficient, magnetic structure on a size of metal nanoparticles (first of all iron nanoparticles) is discussed. On the basis of the obtained results the scale border between nano- and macroscopic states is justified. In the present work the peculiarity of the physical processes (melting, diffusion, defects complexes formation) occurring in nanoparticles and nanomaterials during the irradiation is also discussed.

Resume : In the present work the distribution of implanted Xe in nanoscale multilayered ZrN/SiNx coatings depending on the thickness of ZrN (from 5 to 40 nm) and SiNx (from 0.4 to 20 nm) elementary layers was investigated. The multilayered ZrN/SiNx films were deposited onto Si (001) wafers by a reactive unbalanced magnetron sputtering method at the temperature of 300°C. Zr and Si3N4 targets were sequentially sputtered under mixed Ar N2 plasma discharges. The thickness of elementary layers was varied by altering the sputtering duration of Zr and Si targets. According to TEM and XRD analysis the multilayered films consist of nanocrystalline ZrN and X-ray amorphous SiNx layers. While pure ZrN films are characterized by (111) preferred orientation, the presence of SiNx layers results in its change to (200). It was found that the irradiation by Xe ions (180 keV) up to the dose of 5x1016 cm-2 does not influence on the elemental and phase composition of the films. As it follows from RBS spectra, the increase in the number of ZrN/SiNx layers leads to the shift of implanted Xe profile closer to the coating surface. The irradiation by Xe ions causes the reduction of the compressive stress with the dose increase due to accumulation of the implanted Xe. The basic mechanisms of segregation of the initial and radiation-induced defects at ZrN/SiNx interfaces as well as the influence of the interfaces density on the defects flow are discussed.

Resume : ZrN is a candidate-inert-matrix-fuel-host (IM) for the burn-up of plutonium and minor actinides. In particular ZrN with a nanocryatlline microstructure also potentially offers higher radiation tolerance to fission fragments. One of the main hazards for IMs is the accumulation of He due to alpha particle radiation resulting from the burn-up of the minor actinides. In this study we therefore investigate the thermal evolution of nc-ZrN irradiated with low energy He. As for many other materials nc-ZrN is prone to blister formation following He irradiation and thermal treatment. The microstructure of nc-ZrN layers irradiated with He up to flueces of 1×1016 cm-2 was investigated with transmission electron microscopy (TEM) preceding and after thermal treatment at temperatures between 700 and 900 °C. The results of the TEM analysis suggests that, the doping of nc-ZrN with helium up to a high concentration results in the formation of helium porosity, swelling and blistering after thermal treatment, but the porosity is annealed out at temperatures T < 0.3Tmelt. Helium is soluble both in nc-ZrN, and polycrystalline ZrN, therefore its desorption is possible from both these microstructures. The doping of nc-ZrN with helium results in its transformation from a nanocrystalline state into a polycrystalline state during thermal treatment. It has also been shown that the He induced swelling, porosity and blistering in nc-ZrN can be suppressed though irradiation with swift heavy ions.

Resume : Recently the nanocrystalline α-Zn2SiO4 phase formation in silica glass subsurface layer was observed under pulsed zinc ion implantation and annealing [1]. However, the mechanism of bright green photoluminescence (PL) for such a structure is still a matter of debate having hypotheses of either intrinsic defect or uncontrolled impurity as emission center. In present study the temperature-dependent photoluminescence (PL) and PL excitation spectra of Zn2SiO4 nanocrystalline phases formed in glassy and thin-film SiO2 matrices by means of ion implantation and annealing. Pure willemite ceramics was used as reference. Green and yellow light emission observed is associated with point defects inside α- and β-Zn2SiO4 nanoparticles. Different PL excitation mechanisms were distinguished for implanted silica. The electronic states of point defects are localized to dimensions much smaller than the nanocrystal size, so the PL band positions are similar to that of bulk material [1]. Contrary, the vibrational states are extended and therefore subjected to the effects of confinement, surface defects and disorder of host matrix [2]. Hence, the PL intensity quenching (Street law for α-phase vs. Mott law for β-phase) and line broadening (linear vs. exponential law) allowed to identify the PL emission mechanism and revealed the influence of amorphous silica matrix. The results obtained may be used to tailor the optical properties of the nanocomposite in wide temperature range.

Resume : The rich phenomena in the magnetic anisotropy of diluted ferromagnetic semiconductors (DFS) have opened new concepts for spintronics beyond conventional electronic logic devices [1]. As an example, the magnetic anisotropy of (Ga,Mn)(As,P) can be changed from in-plane to out-of-plane by low temperature annealing [2, 3]. In this work, we demonstrate another flexible approach to tune the magnetic anisotropy by He ion irradiation, which is a well-developed chip-technology. For the as-prepared (Ga,Mn)(As,P), the low-temperature long-time annealing suppresses the compensation from Mn interstitials, resulting in a higher carrier concentration and the switching of the magnetic easy axis from the in-plane [100] to the out-of-plane [001] direction [3]. By He irradiation, we can turn the magnetic easy axis gradually back to the out-of-plane direction. Therefore, ion irradiation combined with low-temperature long-time annealing boosts the prospects of flexible tailoring of the magnetic anisotropy of DFS material, allowing for the development of new concepts for spintronic devices. [1] T. Dietl and H. Ohno, Rev. Mod. Phys. 86, 187-251 (2014). [2] M. Sawicki et al., Phys. Rev. B 70, 245325 (2004). [3] A. Casiraghi et al., Appl. Phys. Lett. 97, 122504 (2010).

Resume : Synthesis of silicon-nanoparticles (SiNPs) by ion implantation has many advantages, although post-implantation processing (e.g. thermal annealing) is required to form Si-nanoparticles and remedy implantation damage. Another way to anneal defects and form or modify SiNPs is irradiation by swift heavy ions [1]. We recently studied the effects of irradiation of SiNPs by heavy MeV ions followed by thermal annealing, and found that defect luminescence was reduced at high irradiation fluence [2]. In this work, we investigate annealing effect of defects in SiNPs, synthesized by ion implantation, in SiO2 by heavy ion irradiation after the thermal annealing process. The 100 nm-thick SiO2 films are implanted by 40 keV Si at corresponding fluences of 1-10 atomic percent), directly followed by thermal annealing in N2-atmosphere at 1100 oC. The effects of heavy ion irradiation using 30-50 MeV I-ions at varying fluence, flux and irradiation temperature is now being investigated by photoluminescence (PL) spectroscopy. As a result, it is found that the PL of SiNPs increases at higher irradiation flux and defect-related luminescence increases for higher fluence and/or flux. The results are discussed in terms of a combination of electronic and nuclear stopping powers. References: [1] G.A. Kachurin et al., Appl. Phys. A, 98 (2010) 873. [2] T. Chulapakorn et al., Phys. Status Solidi C, 12 (2015) 1301.

Resume : Gallium nitride is the promising III-V semiconductor for the application in hybrid photonic devices compatible with current CMOS infrastructure. In this work, the possibility of ion synthesis of GaN nanoclusters by co- implantation of Ga and N ions in Si and Si-compatible SiO2, Si3N4, Al2O3, HfO2 films has been studied. Various technological routes with different conditions and sequence of implantation and annealing are implemented. The data of comprehensive experimental investigation by various techniques are analyzed to establish the chemical, phase and defect composition of implanted layers. Certain conditions are realized to preserve high enough concentration of implanted Ga and its bonding to nitrogen. One of the most exciting results is the observation of visible PL at around 500 nm in the Ga and N co-implanted Si and SiO2 layers related probably to the defect-impurity radiative centers. Theoretical calculation of electronic spectra and interband transitions in GaN nanocrystals is used to determine the radiative rates and internal quantum efficiency of photoresponse in visible to near-UV spectral range. Si3N4 and HfO2 appear to be the most suitable dielectric matrices for GaN nanocrystals and provide high blue shift of interband transition and the highest values of photosensitivity. The study is supported by the Ministry of Education and Science of the Russian Federation (RFMEFI58414X0008) and the Department of Science and Technology, India (INT/RUS/RMES/P-04/2014).

Resume : Resistive switching in metal-insulator-metal memristive nanostructures based on SiOx films is known to be associated with the field-induced transformation of local defect structure of dielectric due to the migration of oxygen ions. In this work, it has been experimentally shown for the memristive nanostructures deposited by the method of magnetron sputtering that the stoichiometry (SiO2 vs. SiO) and thickness of SiOx film (ranging from 20 to 60 nm), as well as the area (from 1∙10-3 to 1∙10-2 cm2) of gold top electrode don’t significantly affect the current-voltage characteristics and switching parameters. These results evidence in favor of the filamentary model of switching and confirm the key role of redox reactions inthe partial destruction/recovery of conductive silicon filaments. Resistive switching phenomenon in the structures subjected to the implantation of low-energy ions (when ion range is much smaller than film thickness) and medium-energy ions (when ions pass through the entire thickness of SiOx film) have been investigated as well. The variation of ion kind, energy and dose allows manipulating the resistive switching parameters in the considered types of memristive nanostructures by producing radiation damage in the local regions of dielectric film. The work is supported by the grants of the President of the Russian Federation (МК-3714.2015.2) and Russian Foundation for Basic Research (№ 16-37-00360).

Resume : Metal-oxide particles are used in advanced ferritic-martensitic steels to improve their performance in the high-temperature environment of Generation IV fission and future fusion facilities. The need to use oxide-dispersion (ODS) steels in radiation environment puts forth the question of radiation stability of oxide particles. A better fundamental understanding of the mechanisms providing the oxide particle resistance to cascade-forming irradiation can be helpful in clarifying often controversial experimental observations. The report summarizes the results of molecular dynamics simulations of collision cascade interaction with aluminum-oxide clusters in bcc iron. The selection of aluminum oxide instead of more common yttrium or titanium oxides is due to both the practical applicability for recent experiments on Al2O3 precipitation by ion implantation [1] and the availability of a reasonably good interaction potential for the ternary system Fe-Al-O [2]. The results are in many aspects compatible with the earlier predictions for Y2O3 performance under the effect of collision cascades [3], but provide also new insights on the cluster stability at higher recoil energies. In particular, high chemical selectivity of oxide particle destruction by collision cascades is demonstrated. . [1] C.Zheng et al., Philos. Mag. 94, 2937 (2014). [2] X.W. Zhou, H.N.G. Wadley, J. Phys.: Condens. Matter 17, 3619 (2005). [3] T. Lazauskas et al. J. Nucl. Mater. 437, 317 (2013).

Resume : The production of nanocrystals based on compound III - V semiconductors embedded in a semiconductor matrix with higher band gap is of great interest for optoelectronic devices since the pronounced quantum confinement effects of such materials allows to tune their light emission by controlling the size of the nanocrystals. Although the molecular beam epitaxy (MBE) is the most used technique to process such nanostructures, the combination of ion implantation and thermal annealing has proved to be an interesting alternative. In recent years there has been a lot of activity towards the properties of III – V quantum dots made by MBE or MOCVD but relatively few works were dedicated to the study of these objects when they are synthesized by ion beam technique. The aim of the present work is to investigate the structural and optical properties of InAs nanoclusters obtained through sequential implantations of As and In ions in single crystalline Si followed by a rapid thermal annealing (RTA) treatment. To that end, <100> Si wafers were implanted at 500°C with 30 keV As ions and 35 keV In ions with different fluences (up to 5x1015 cm-2). The samples were annealed at different durations, using temperatures ranging from 700°C up to 1000°C. Due to the low implantation energy, the formation of InAs will occur near the surface (≈ 30 nm) which allows to characterize the targets with medium energy ion scattering (MEIS) analysis. Different other techniques like photoluminescence (PL), Rutherford backscattering spectrometry in channeling geometry (RBS-C) and transmission electron microscopy (TEM) were employed to investigate the optical and structural properties of the samples. It was observed that significant out-diffusion of As and In species occurs after annealing at the highest temperatures. We will show that this effect can be avoided by performing ion implantations at higher energies through a thermal SiO2 film previously grown at the surface of the Si wafer.

Resume : The disordering of the crystal lattice of silicon by high-energy ion self-implantation allows one to improve dramatically the efficiency of thermoelectric generators which are considered to be as an alternative to more expensive devices produced from less earth-abundant materials such as, e.g., bismuth telluride [1]. This improvement is resulted from forming the vacancy-rich disordered regions (DR) and, in order to gain insight into their open vacancy volume, we have undertaken the positron probing of these defects: for the first time the emission of two gamma-quanta has been studied by measuring the angular correlation of annihilation radiation (ACAR). High resolution of the set up has allowed us to probe with positrons the electron density of both the bonding and subvalent ion core electrons. Necessary concentration of DR was created by irradiating the material with the fast reactor neutrons. /// At rather high dose ~ 2•E18 fast neutrons per square cm) positrons are captured by DR, and the emission of the annihilation radiation from the vacancy-rich open volume dominates. The averaged electron density contacting the annihilating positron, n(e)' ≈ 3{r(s)'}(–3)/4π, is estimated to correspond to r(s)' ≈ 2.178±0.035 a.u.; a certain correction for the high-momentum annihilation of positron with subvalent ion core electrons has been made. The results obtained suggest that this numeral value of r(s)' characterizes, mainly, the electron density of the interatomic bonds in the vacancy-rich open volume of DR. The estimated positron annihilation lifetime tau {r(s)'} ≈ 223 to 229 picoseconds is close to the one known from ab-initio calculations for an unrelaxed vacancy (≈254–261 ps) or for the relaxed inward divacancy (246–263 ps); see [2] and references therein (when estimating the positron lifetime tau {r(s)'} value the electron-positron correlations have been taken into account)./// These positron traps of a vacancy type demonstrate high thermal stability in the course of the isochronal annealing up to ~ 600 ºC; then the annealing of these defects begins and proceeds to ~ 850 ºC: at this annealing temperature ACAR parameters are becoming to be very close to the ones for initial non-irradiated material. The preceding three annealing stages demonstrate clearly a dominance of the thermally stable vacancy radiation defects in forming ACAR spectra. /// Defects are known to introduce the spatially-localized vibrational modes which trap thermal phonons and influence on the flow of heat [3]. On an atomic scale information about this influence may be obtained by the positron probing of DR. In this connection strong temperature dependency of the positron trapping rate, ~T(–3), to be observed for both the divacancies and the phosphorus-vacancy complexes is discussed in terms of the cascade phonon-assisted positron trapping [2, 4]. We also shortly consider the ways of non-destructive characterization of the materials of thermoelectric generators by techniques based on using slow positron beams [5]. ----References----- [1] ---N. M. Wight and N. S. Bennett, Solid State Phenomena Vol. 242 (2016) pp 344-349./// [2] ---N. Yu. Arutyunov, M. Elsayed, R. Krause-Rehberg, V.V. Emtsev, G.A. Oganesyan and V.V. Kozlovski, ibid., pp 296-301./// [3] ---S. K. Estreicher, T. M. Gibbons, M.B. Bebek and A.L. Cardona, ibid., pp 335-343./// [4] ---N.Yu. Arutyunov, V.V. Emtsev, R. Krause-Rehberg, C. Kessler, M. Elsayed, G.A. Oganesyan and V.V. Kozlovski, AIP Conf. Proc. 1583 (2014) 41–45./// [5] ---T. T. Trinh, M. O. Liedke, W. Anwand, A. Wagner, K. Potzger and R. Krause-Rehberg, 28th Int. Conf. on Defects in Semiconductors (July 27-31, 2015, Helsinki, Finland), Book of Abstracts, 364_a(2pp).///

Resume : It is widely known that boron and phosphorus atoms in crystalline Si are the main impurities of silicon microelectronics. Revealing nanosilicon opens a big opportunity to transite from micro- to nanoelectronics. However, at the same time the role of these impurities in nanosized silicon is so far not fully understood. Here an electronic and spatial structures of the hydrogenated nanosized silicon clusters Si29H36, containing boron and phosphorus atoms have been studied in the frame of DFT BLYP approximation. The results obtained for geometrically optimized clusters Si28H36:B and Si28H36:P show that the silicon cluster with the substituted B or P impurities saves tetrahedral symmetry. Binding energies of the impurity B and P atoms in the Si cluster are more than ones for the case of ideal cluster. The calculations show that the location of the negative charged phosphorus impurity atom at the center position of the cluster Si28H36:P(-) broke the tetrahedral symmetry and increase the cluster diameter and it's also observed for the cluster Si28H36:B(-). Substituted phosphorus atoms near the surface is more energetically favorable than for the central position. The most stable position of the impurity atoms found to be in subsurface coordination sphere. But localization of the boron impurity in silicon cluster is not so sensitive as for phosporus because a positive charge region is forming around boron atom.

Resume : III-V semiconductors based quantum dots (QDs) have gained in popularity over the years. The advantages of normal incident absorption, high temperature operation, longer life time of excited state carriers etc. are associated with QDs based devices. However, S-K growth mode has disadvantage of formation of 2D-wetting layer just below the active QDs layer. Sub-monolayer (SML) QDs are being proposed as better alternative suppressing the formation of wetting layer. We report the impact of high energy protons on the optical properties of SML QDs. The SML heterostructure was grown by solid state molecular beam epitaxy (SSMBE), containing 10-stacks of InAs QDs. The samples were implanted with high energy protons with varying energies between 2 - 4.5 MeV, keeping the fluence constant at 2E12 ions/cm2. Low temperature (15K) photoluminescence (PL) plot demonstrated the highest PL intensity at 2.5 MeV; beyond that a steady drop was noticed for all energies. The optimum energy of proton (2.5 MeV) could be explained as: the defects (interstitial) in the system possibly created during the heavily strained QDs growth process required some amount of energy to occupy the original lattice positions, and this requisite energy was probably provided by proton implantation. As passivation of the defects is complete, increasing the implantation energy higher than optimum value possibly led to the creation of additional defects that can trap photo-generated carriers in the systems resulting drop in PL efficiency. All implanted samples exhibited a consistent PL peak shift from 1110 nm to ~1093 nm. This PL peak shift is probably because of In-Ga intermixing between the dots and capping layer resulted from implantation. All implanted samples exhibited rise in activation energy with respect to as-grown (238.8meV) while highest activation energy (434 meV) was showed by 2.5 MeV sample confirming that proton irradiation improved the overall optical quality of the SML QD material. We thank the Department of Science and Technology (DST), Government of India, and Riber, France for financial support.

Resume : Atoms surrounding defect shift from the sites of ideal lattice, e.g. defect atomic structure changes with respect to an ideal one, that in turn leads to changes in interaction energy of neighbor atoms and defect characteristics. Generally displacement fields in the vicinity of voids were determined by the equations of theory of elasticity. Such a description has its disadvantages as it doesn’t take into account the discrete atomic structure of materials. Results of elasticity theory are expected to be valid at distances from a defect that are much larger than the lattice parameter, therefore atom displacements in the vicinity of such defects as vacancies and nanovoids should significantly differ from the predictions of mentioned theory. In our recent works a new approach was developed. In particular in this approach an iterative procedure was used in which the atomic structure in the vicinity of point defect and constant, determining the displacement of atoms embedded into an elastic continuum are obtained in a self-consistent manner. The vacancy features (including formation volumes) obtained for a number of cubic metals agreed well with experimental values. In this work we use our approach for investigation of the atomic structure in the vicinity of nanovoids of different sizes. Analysis of simulation results shows that the displacements are significantly different for variant crystallographic directions and these differences are particularly large in metals with bcc structure.

Resume : The Sr(2)FeMoO(6–d) (SFMO) metal-oxide compound is a promising spintronic material possessing an advantageous combination of magnetic and magnetoresistive characteristics: a high Curie temperature (Tc = 400–450 K), large values of negative magnetoresistance (MR) (up to ~50% at 4.2 K) and almost 100% degree of spin polarization. In the present work SFMO thin films have been obtained by the ion-beam deposition technique at various substrate temperatures (Ts) and deposition rates (v). The SFMO films obtained at optimal conditions (Ts = 923 K and v = 7 nm/min) still contain a small amount of the SrFeO(3–d) antiferromagnetic phase (SFMO-1). Single-phase and homogeneous films having superstructural ordering of the iron and molybdenum cations were formed after an additional thermal treatment at 1173 K for 1 h in a continuous stream of 5%H2/Ar (SFMO-2). Results of the magnetization field dependences evidence a substantial influence of the degree of the superstructural ordering of cations and grain/cluster dimensions on the coercivity. It is characteristic of the both types of films that MR is negative in the entire range of temperatures and magnetic fields. By its nature this is the giant MR, and it is concerned with the presence of ferrimagnetic regions in the SFMO films, when the electron spins with different directions in two different magnetic regions become parallel to each other in magnetic fields exceeding the saturation magnetization value. Correspondingly, the contribution of magnetic scattering lowers, and electrical resistivity of the films becomes smaller. The presence of MR lower values in the SFMO-1 films is concerned with a smaller degree of Fe and Mo cations superstructural ordering, and a corresponding increase of the contribution of electronic scattering on the antistructural defects in the overall value of the electrical resistivity. The study was supported by RFBR (project № 16-38-50018 mol_nr), FCT of Portugal (project UID/CTM/50025/2013) and NUST “MISiS” (grant no. K3-2015-003).

Resume : Cu2ZnSnS4 (CZTS) is a very promising absorber layer in photovoltaic technology. The performance of CZTS-based solar cells has increased but not to the values presently achieved for Cu(In,Ga)Se2, or even silicon. The identification of radiative transitions in the complete solar cell structure and influence of the growth parameters on the electronic levels structure is crucial for the improvement of the devices. This level structure is crucially influenced by the density of defects, i.e. the intrinsic defects formed during growth. In this work we compare the electronic properties of solar cells with CZTS absorber layers prepared in two different ways: i) metallic precursors sulphurized in a tubular furnace by direct exposed to a sulphur vapor ; ii) metallic precursors sulphurized in a graphite box where sulphur pellets have been evaporated. Structural characterization reveals a dominant CZTS crystalline phase in both samples. The photoluminescence (PL) of the samples sulphurized in the tube furnace corresponds to a single, broad, and asymmetric band whereas for the other set of samples, a second component is identified at a higher energy. With the increase of the excitation power, a huge blueshift is observed which clearly shows the influence of fluctuating potentials on the electronic levels structure of CZTS, in accordance with high doping and strong compensation levels, typical in this material. An acceptor level with ionization energy of 78 meV is tentatively identified.

Resume : In this work we present a new computing technology which allowed us to carry out predictive modeling of possible structural, luminescent, and electronic properties of silicon structures with defects based on the developed original algorithms and first-principles calculations. The developed software with application of high-performance computing resources, based on supercomputers, allowed us to visualize the formation processes of defects in silicon structures. The study of these defects clearly showed a direct link between their structural peculiarities and luminescent properties of silicon. Besides that, we carried out computing experiments to study the formation processes of point defects and their transformation into extended ones in silicon by means of the computing technologies developed for multiscale modeling on supercomputers.

Resume : Point defects play a crucial role in tailoring the optical properties of a wide class of nanosized materials including insulators and semiconductors. Silica nanoparticles are systems of choice for this issue since they exhibit a strong emissivity, surprising if compared to their bulk counterpart, that is mainly related to the high specific surface area (~100 m^2 /g) that favors the formation of luminescent defects. The emission properties are influenced by the environment since the defect structure may change after light interaction and/or reaction with atomic and molecular species of the surrounding atmosphere that can easily access the surface sites. This work deals with the combined effects induced by UV exposure of a ns pulsed Nd:YAG laser in a vacuum or in controlled atmosphere (O2, N2, CO2,H2O) on a bright emission centered at 2.8 eV peculiar to silica nanoparticles. Spectral and lifetime changes were investigated by time-resolved spectroscopy under a tunable laser excitation. The reported results evidence that UV photons induce the bleaching of this emission, this effect being more pronounced when the silica surface is in contact with the atmosphere. These findings are useful to address the structural properties of the luminescent defect and its interaction with the molecules.

Resume : Silicon nanocrystals (NC-Si) in a SiO2 matrix are actively studied due to the intensive luminescence in infrared and visible spectral range at room temperature and their application as the base for optoelectronic and photovoltaic devices. The short-wave edge of exciton emission from silicon nanocrystals in SiO2 matrix observed at ≈ 2 eV is associated with the important role of self-trapped excitons (STE) on silicon nanocrystal surface [1]. Surface Si-Si dimers [2], as well as other surface defects (Si=O, Si-O) [3], can capture free excitons on the self-trapped states. The resonant STE state associated with Si-O bonds has been observed previously in the induced absorption experiments [4]. We present the theoretical model based on [2] and the experimental evidence obtained by time-resolved and excitation luminescence spectroscopy for the exciton self-trapped at surface Si-Si dimer. Multilayer periodical nanostructures (SiO2/NC-Si/…) have been prepared by the method described in [5]. The intensive luminescence band corresponding to the STEs at surface Si-Si dimers has been obtained for the structures with the average nanocrystal diameters from 2.5 to 3.5 nm. The STE photoluminescence band has a maximum at 1.06 um (1.17 eV) that does not depend on the nanocrystal size. The decay times of the PL band are long: 5.9 and 5.3 ms for the nanocrystal size of 2.5 and 3.5 nm, correspondingly. 1. M.V. Wolkin et al, Phys. Rev. B 82, 198 (1999). 2. G. Allan et al, Phys. Rev. B 76 2961 (1996). 3. M. Luppi and S. Ossicini Phys. Rev. B 71, 035340 (2005). 4. W.D.A.M. de Boer et al, Phys. Rev. B 85 161409 (2012). 5. A.V. Ershov, Semiconductors 47, 481 (2013).

Resume : A large variety of luminescent surface defects arises in SiO2 nanoparticles (np-SiO2) due to the constrains imposed by the reduction to nanoscale. An exception respect to the usual broad emission bands is observed in a vacuum and consists of a structured photoluminescence (PL), between 3.0 eV and 3.5 eV, whose sharp spectral features resemble those of a molecular-like system. Its quenching in air indicates that the interaction of the defects with the molecules of the ambient strongly affects the emission properties. This pronounced sensitivity to the atmosphere, in combination with the advantageous spectral features, is promising for the use of np-SiO2 as luminescent sensors of molecules. To this aim, the understanding of the fundamental mechanisms of the quenching is mandatory. By using time resolved PL technique in controlled atmosphere, we have carried out a detailed investigation of the spectral and decay properties of the structured emission in O2, N2, CO2 and H2O, thus singling out the effects induced by the interaction of the defect with such a species. PL quenching and lifetime decrease are observed, the extent of which depends on the specific molecular species. The results allow to address the quenching mechanisms, relating them to collisional- and/or reaction-limited processes.

Resume : An important problem of silicon photonics is the creation of efficient light emitters for the wavelength range around 1.5 um, which would be fully compatible with the modern CMOS technology. A possible solution to the problem is the formation with application of ion beams of silicon dislocation structures with a D1 luminescence line in the required wavelength range. The improvement of dislocation-related luminescence is a challenge from the practical viewpoint. Recently, we have studied the effect of additional ion doping on the luminescent properties and structure of silicon subjected to self-ion implantation and subsequent oxidizing annealing to generate the dislocation-related D1 emission centers. At some conditions, boron ion doping can lead to the increase in luminescence intensity [Semiconductors 48, 199 (2014); Phys. Status Solidi C 12, 84 (2015)]. This phenomenon is believed to be caused by the change in defect-impurity atmospheres of dislocations. In this report, the effect of doping and annealing conditions is analyzed in detail over a wide range of annealing temperatures, different annealing ambient and different types of intrinsic impurities (B, P). The results can be implemented in the technology of optoelectronics and silicon photonics integrated circuits as well they are useful for understanding the origin of D1 emission line. The work is supported by the Ministry of Education and Science of the Russian Federation (State Assignment No. 3.285.2014/K).