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2020 Spring Meeting

Nanomaterials and advanced characterization


New developments in the modeling and analysis of radiation damage in materials II

Nowadays, it is common to find technological environments subject to irradiation with energetic particles, such as for instance materials in spintronics, semiconductors, space applications or nuclear reactors. This particle/matter interaction strongly affects the properties of the materials. This symposium will provide a forum to discuss the latest development in the characterization and modeling of particle/solid interactions.


The use of particle (ions, photons, neutrons, protons...) beams over a broad range of energies is a powerful tool to synthesize, test, and modify the properties of advanced materials. On the other hand, there also exist technological applications subject to undesired energetic particle fluxes that strongly degrade their performances. Research and applications of energetic particle beams encompass, among others, advanced electro-optical devices, nanostructures, strain engineering, nuclear materials, and space exploration. In most cases, particle beam modification of materials relies on the energy transfer from the energetic particles to atomic nuclei and/or electrons of the target. Usually, the deposited energy leads to defect generation and damage accumulation. These phenomena are sometimes desired, e.g., to simulate radiation environments such as those encountered in space and nuclear reactors; but they may also be a drawback, for instance in ion doping processes, or in the synthesis of nanostructures. In any case, understanding the mechanisms of damage formation and accumulation in materials as a result of energy deposition under irradiation is a crucial task to tackle.

This symposium is the follow-up of the 2018 edition which took place during the E-MRS Spring meeting and gathered ~ 60 scientists (speakers + posters) from more than 10 countries around the world. The aim of this symposium is therefore to provide a forum for researchers to present and discuss the developments and improvements of experimental characterization techniques, computational tools, theoretical models and codes for data fitting in the field of radiation damage. Special focus will be given to techniques, protocols, and methodologies allowing damage quantification. The coupling of experimental and computational characterizations will also receive particular attention. Finally, recent progress in in situ measurements, small-scale testing as well as improvements of conventional techniques to investigate radiation damage will also be addressed. To finish, this symposium is cross-disciplinary on a wide range of materials including metals, semiconductors, and iono-covalent materials with different dimensionality (e.g. 0D quantum dots, 1D nanowires or tubes, 2D thin film materials and 3D bulk materials) and on a broad range of irradiation conditions, experimental techniques and computational simulations.

Hot topics to be covered by the symposium:

The topics covered by the symposium include, but are not restricted to,
the following hot topics:

  • Time resolved measurements of phase transformations, micro-structural changes, and surface effects
  • High (time/space) resolution characterization of defects and disorder
  • Computer simulation and modeling of damage formation and evolution
  • Combination of computing and experimental approaches
  • Quantification of radiation disorder
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Microstructures and nanostructures I : Andrés Redondo Cubero
Affiliations : 1. Centre de Sciences Nucléaires et de Sciences de la Matière (CSNSM), Université Paris-Sud, CNRS/IN2P3, Université Paris-Saclay, 91405 Orsay, France 2. CEA, DEN, Service de Recherche de Métallurgie Physique (SRMP), Université Paris-Saclay, 91191 Gif-sur-Yvette, France 3. CEA, DEN, DPC, SCCME, Université Paris-Saclay, 91191 Gif-Sur-Yvette, France

Resume : Modification of materials using ion beams has become a widespread route to improve or design materials for advanced applications, from ion doping for microelectronic devices to emulation of nuclear reactor environments. Yet, despite decades of studies, some questions regarding irradiation-induced microstructural effects are not comprehensively addressed. One such question is the lattice-strain development process in irradiated crystals. To address this issue, we implemented a consistent approach that combines X-ray diffraction (XRD) measurements with molecular dynamics (MD) simulations, and applied that approach to study UO2, c-ZrO2 and MgO. We demonstrate that these materials exhibit a common behavior with respect to the strain development process1. In fact, strain build-up followed by strain relaxation is observed in the three investigated cases. The strain variation is unambiguously ascribed, thanks to MD simulation data, to a change in the defect configuration: strain development is first due to the clustering of interstitial defects into dislocation loops, while the strain release is associated with the disappearance of these loops through their integration into a network of dislocation lines. Another topic that is worth deeper investigation is the response of materials to irradiation at varying temperature. To address this question, we considered c-ZrO2 and MgO because, whereas these materials exhibit similar damage accumulation process under ion irradiation at fixed temperature, they, in contrast, display an unexpected opposite damaging rate to changes in the irradiation temperature. Combining XRD experiments with rate equation cluster dynamics (RECD) simulations, we showed that, with increasing temperature, defect clustering is favored over defect recombination in c-ZrO2, but the situation is reversed for MgO, explaining the observed opposite response to temperature of the two materials2. This contrasting behavior can be rationalized in terms of non-equivalent interstitial versus vacancy defect migration energies in MgO, behavior that is not present in c-ZrO2. In the two cases addressed in this presentation, the use of computational techniques allowed for unraveling the large quantity of experimental data and provided better insight into the basic irradiation-induced disordering processes. This methodology can be applied to any other insulating material, given some (sometimes strong) simplifying assumptions.

Authors : Laurence Luneville, Philippe Garcia, David Simeone
Affiliations : CEA Saclay 91191 Gif sur Yvette, France; CEA Cadarrache, St Paul-lez Durance, France; CEA Saclay 91191 Gif sur Yvette, France

Resume : In non miscible AcB1-c binary alloys, radiation-induced mixing acts in conjunction with purely thermodynamic effects to produce steady states associated with unexpected micro-structures. In this work, we provide an analytical solution to the minimization problem of the pseudo free-energy which predicts the appearance of all possible steady states in the continuum approach. Two distinct types of steady states result from the minimization of this pseudo free energy: a non periodic one similar to the one observed at equilibrium, and a periodic one. For a given periodic steady state, it appears that different values of the average composition c will lead to different microstructures. This result, corroborated by previously reported and newly acquired experimental data, extends analyzing the emergence of non periodic steady states using a dynamic phase diagram to periodic steady states via a structure diagram which goes beyond the temperature concept.

09:50 Coffee Break    
Characterization of damage and defects I : Alexandre Boulle
Authors : B. P. Uberuaga, S. Agarwal, M. O. Liedke, A. Jones, E. Reed, A. Kohnert, N. Li, Y. Wang, R. Auguste, P. Hosemann, L. Capolungo, J. Cooper, D. Kaoumi, D. Edwards, M. Butterling, A. Wagner and F. A. Selim
Affiliations : Los Alamos National Laboratory; Bowling Green State University; University of California, Berkeley; Helmholtz-Zentrum Dresden-Rossendorf

Resume : Understanding radiation damage in materials begins with knowing the defect content. Positrons are an ideal tool to quantify minute concentrations of vacancies and even provide detailed information about their size distributions. However, historically, as positron studies require bulk samples, they have been limited to neutron-irradiated materials. Recently, the advent of pulsed positrons beams can provide depth-resolved information of defect accumulation in ion beam irradiated materials in a non-destructive manner. Here, we demonstrate the use of such beams to examine ion-irradiation-induced damage in bcc Fe thin films. The as-grown films contain a high amount of porosity. Combined with transmission electron microscopy, the positron studies reveal that, upon irradiation to even small doses of only 0.06 displacements per atom, the original void structure is modified. While the number of larger voids remains constant, they tend to shrink. The positron studies show that this is accompanied by an increase in the concentration of small vacancy clusters, indicating a net flow of vacancy content from large defects to small defects. These results corroborate recent modeling efforts in the literature and highlight the potential of positrons to reveal novel phenomena in ion-beam irradiated materials.

Authors : Xin Jin, Alexandre Boulle, Alain Chartier, Jean-Paul Crocombette, Aurélien Debelle
Affiliations : Université Paris-Saclay, CNRS/IN2P3, IJCLab, 91405 Orsay, France; Institut de Recherche sur les Céramiques (IRCer), CNRS UMR 7315, Centre Européen de la Céramique,12 rue Atlantis, 87068 Limoges, France; CEA, DEN, Service de la Corrosion et du Comportement des Matériaux dans leur Environnement (SCCME), Université Paris-Saclay, 91191 Gif-sur-Yvette, France; CEA, DEN, Service de Recherche de Métallurgie Physique (SRMP), Université Paris-Saclay, 91191 Gif-sur-Yvette, France

Resume : Molecular Dynamics (MD) simulations can be an effective method to mimic irradiation damage in materials. Therefore, results of these simulations can constitute input data for computing characterization techniques signals, thereby allowing to interpret experimental data. In this paper, we implement this approach in the case of uranium dioxide (UO2). We performed MD simulations of damage accumulation and we used the MD cells we obtained as input data for computing Rutherford Backscattering Spectrometry in Channeling mode (RBS/C) and X-Ray Diffraction (XRD) signals. The damage in the UO2 MD cells, represented by displacements per Uranium atom (dpU), ranged from 0 to 10 dpU, which covers several defect evolution stages. Disordering kinetics were determined from the analysis of the computed RBS/C and XRD data. They exhibit qualitatively close agreements with those determined experimentally, indicating that the used methodology is valid. More importantly, each step of the disorder build-up can be ascribed to a perfectly identified microstructure through the detailed analysis of the MD cells. A modified cascade-overlap disorder accumulation model is proposed to fit the disorder kinetics in order to obtain insights on the contribution to the total disorder from each type of defects. This analysis allows for a quantitative description of the entire damage build-up process.

Authors : Cyprian Mieszczynski 1, Lech Nowicki 1, Kazimierz Skrobas 1,2, Jacek Jagielski 1,3
Affiliations : 1 National Centre for Nuclear Research, NOMATEN CoE MAB Division, A. Soltana 7, 05-400 Otwock, Poland; 2 Institute of High Pressure Physics PAS, ul. Sokolowska 29/37, 01-142 Warsaw Poland; 3 Institute for Electronic Materials Technology, Wolczynska 133, 01-926 Warsaw, Poland

Resume : The main purpose of the McChasy code is to reproduce RBS/C experimental spectra by simulating He-ions traveling inside the crystal structures. Nuclear-encounter-probability approach and Monte Carlo method are used to reproduce the spectra. The new version of the code (v.2.0) provides possibility to simulate channeling spectra in large samples of solid crystalline materials with ca. 108 atoms. Such samples can be created on the basis of crystallographic data or produced by Molecular Dynamic calculations. In this work McChasy code was used to study the local flux of ions passing through the crystal with extended structural defects (dislocations and dislocation loops) thermalized by using MD - LAMMPs code. Influence of such defects on the flux and on channeling backscattering spectra is shown and discussed.

Authors : Maik Lang, Eric O’Quinn, William Cureton, Alexandra Navrotsky, and Joerg Neuefeind
Affiliations : Maik Lang, Eric O’Quinn, and William Cureton: Department of Nuclear Engineering, University of Tennessee, Knoxville, TN, 37996, USA Alexandra Navrotsky: School of Molecular Sciences and Center for Materials of the Universe, Arizona State University, Temp AZ 85281 USA Joerg Neuefeind: Chemical and Engineering Materials Division, Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge, TN, USA

Resume : We present neutron total scattering with pair distribution function (PDF) analysis combined with high-temperature calorimetry as a new strategy for the characterization of radiation effects in materials. Irradiation experiments were performed at the UNILAC accelerator of the GSI Helmholtz Center with heavy ions of specific energy of 11.4 MeV/u. The use of swift heavy ions with a very high penetration depth (up to 100 µm) produces the sufficiently large irradiated sample mass (~150 mg) required for bulk structural and thermodynamic analysis. Structural characterization of the irradiated samples was performed at the Nanoscale Ordered Materials Diffractometer beamline at the Spallation Neutron Source (Oak Ridge National Laboratory). High temperature oxide melt solution calorimetry and differential scanning calorimetry was utilized to investigate the thermodynamic properties and energetic evolution using the same set of irradiated samples. We studied various ion-induced structural modifications, such as defect formation (CeO2 and ThO2), disordering (Er2Sn2O7), and amorphization (Dy2Ti2O7). This advanced analytical approach demonstrated that irradiation-induced structural modifications, and their thermal recovery, are much more complex than previously thought with distinct processes occurring over different length scales and temperature regimes. While radiation resistant simple oxides form low-energy defects that readily recover, amorphizable ternary oxides with a high degree of order form a local damage structure that persists structurally and energetically when subject to very high temperatures.

Authors : Solène Béchu, Damien Aureau, Nathalie Simon, Anne-Marie Gonçalves, Mathieu Frégnaux, Muriel Bouttemy, Arnaud Etcheberry
Affiliations : ILV, Université de Versailles Saint-Quentin en Yvelines, Université Paris-Saclay, 78035 Versailles, France

Resume : Bombardment of semi-conductors induces several perturbations, chemical (nature, network and stoichiometry), morphological, optical… This study focuses on the perturbation evaluation induced on InP by an Ar bombardment. Both Ar+ ionic sputtering performed directly inside the X-Ray photoemission spectroscopy (XPS) chamber using an ion gun by means of a plasma source through Glow Discharge Optical Emission Spectroscopy (GD-OES) set-up are considered. Electrochemistry is a very efficient probe and quantitative tool to provide information about bulk and surface properties of any electrode material. Its capabilities will be illustrated and associated to XPS analyses to get a better insight on the damages induced by those bombardment which can strongly impact the material properties and the integrity of the information collected during XPS sequential profiling for example. One of the possible investigations using the modified electrochemical response concerns the differential abrasion effect induced by the ions/surface interaction. Ionic bombardment of InP surfaces generates a surface stoichiometry loss, with an In enrichment. We will discuss how the XPS and electrochemical characterizations combination is able to provide complete and complementary diagnostic of the stoichiometry loss and its electrochemical reactivity. Those modifications will be compared to an electrochemistry cathodic decomposition of InP. Anodic dissolution will be also presented in order to recover the surface integrity of InP surface. Characterizations of the perturbations will be performed with XPS measurements, Scanning electronic microscopy (SEM) but mostly, with electrochemical measurements.

12:00 Lunch break    
Modelling of damage and defects I : Christophe J. Ortiz
Authors : Alain CHARTIER
Affiliations : DEN - Service de la Corrosion et du Comportement des Matériaux dans leur Environnement (SCCME), CEA

Resume : Molecular dynamics simulation of radiation damages in materials frequently refer to studies in which displacement cascades, threshold displacement energies and sometimes, thermal spikes are performed. Each of these techniques are meant to address the primary damage – i.e. single events – produced by electronic loss and/or ballistic interactions. Recent attempts have tried to explore the effect of the irradiation dose by accumulating these single events. However, this demarche is limited to low doses (0.1 dpa) since very cpu demanding. One may circumvent single events and access higher doses – in some specific cases – by shortcutting part of the story. Instead of repeating ‘single event’ one after the other to get the effect of dose, the final state can be used as a starting point. Here, we show that as long as single events end up with point defects or very small clusters, it is convenient to accumulate point defects to reach doses up to 10 dpa or more [1]. Such a simulation procedure opens highways for understanding complicated mechanisms at work when materials are in severe irradiation environments. For example, one can (i) identify the specific defect responsible for amorphization in titanate pyrochlores, (ii) shed light on the wrinkling responsible for the anisotropic swelling in graphite, (iii) exhibit Frank loops as part of the monitoring mechanism for UO2 swelling, or (iv) evidence that C15 clusters are seeds for both ½ <111> and <100> loops.

Authors : A. Platonenko, D. Gryaznov, A. I. Popov, E. K. Kotomin
Affiliations : Institute of Solid State Physics, University of Latvia, 8 Kengaraga Str., Riga, LV-1063, Latvia

Resume : Corundum (sapphire, α-Al2O3) is an important radiation-resistant material with potential applications for components of diagnostic windows and breeder blankets. Radiation-induced changes in structural and optical properties of radiation-exposed α-Al2O3 crystalline materials are mainly associated with aluminium and oxygen vacancies (VAl and VO). The vacancies in oxygen sublattice result in the formation of electronic defects after trapping one or two electrons (so called F+ and F-centers). The vast majority of the experiments on point defects were performed so far using the optical absorption and luminescence, while such rapidly developing techniques as Raman spectroscopy and neutron scattering methods were used only in very rare cases. Note that the optical absorption method does not work in the region of large defect concentrations due to the optical density saturation. Here we analyze by means of ab initio calculations the oxygen sublattice defect induced vibrational modes in corundum. The aim of this study is to find possible “fingerprint” modes for identification of the oxygen defects, such as the F, F+-centers, vacancies and interstitials, in various charge states. Using LCAO approach and hybrid B3PW functional as implemented in the CRYSTAL17 computer code, the structural and vibrational properties are evaluated for each defect, suggesting possible defect-specific modes for vibrational spectroscopy. Obtained results are compared with available experimental results.

Authors : Jean-Paul Crocombette
Affiliations : DEN, Service de Recherches de Métallurgie Physique, CEA, Université Paris-Saclay, F-91191 Gif-sur-Yvette, France

Resume : The analysis of ion irradiation experiments often starts with an estimation of the number of defects (the so-called primary damage) created by the irradiation. Binary Collision Approximation (BCA) calculations provide such an estimation. In this framework, two types of damage calculation exist: Full Cascade and Quick Calculations. Full Cascade calculations describe fully the cascades while in Quick Calculations, only the trajectory of the ion is followed, and effective formulas give an estimation of the damage resulting from each collision of the ion. We will briefly recall our implementation of Quick Calculations of damage in the Iradina code [1], which is a modern, fast and open source alternative to SRIM. Quick calculations were implemented for elemental and multi-component solids. Good agreement is obtained with SRIM. We will show that Quick Calculations are unphysical in multi-component systems. First, the predicted numbers of created defects per atomic species are illogical. In addition, the balance between ballistic and electronic losses is not correctly reproduced. We therefore advise to favour Full Cascade over Quick Calculation because it more grounded physically and applicable to all materials. Quick Calculations remain a good option for pure solids in the case of actual quantitative comparisons with neutron irradiations simulations in which damage levels are estimated with the NRT (Norgett-Robinson and Torrens) formulas. [1]: “Quick calculation of damage for ion irradiation: implementation in Iradina and comparisons to SRIM”, Jean-Paul Crocombette and Christian Van Wambekke, EPJ Nuclear Sci. Technol. 5, 7 (2019)

Authors : Satoru Yoshioka, Konosuke Tsuruta, Tomokazu Yamamoto, Kazuhiro Yasuda, Syo Matsumura, Norito Ishikawa, Eiichi Kobayashi
Affiliations : Kyushu University; Kyushu University; Kyushu University; Kyushu University; Kyushu University; Japan Atomic Energy Agency; Kyushu Synchrotron Light Research Center

Resume : Magnesium aluminate oxide (MgAl2O4) has a normal spinel structure in the ground state, although the disordering of MgAl2O4 at high temperature has been reported by experimental analysis and computational investigations. Under swift heavy ion (SHI) irradiation, trails of damage with diameters of several nanometers along the ion path has been observed in MgAl2O4. In this study, cation disordering in MgAl2O4 induced by SHI was investigated with a combination of XANES and density function theory calculation spectra, and the inversion degree of the spinel cation was quantitatively determined. The MgAl2O4 specimens were irradiated with 200 MeV Xe ions at the H1 beamline of the tandem ion accelerator facility at the Japan Atomic Energy Agency. Ion irradiation was performed on the specimens perpendicular to their surface at room temperature. Mg K-edge and Al K-edge XANES measurements were performed at the BL2A beamline of UVSOR, using the partial fluorescence yield method. To obtain correct theoretical XANES spectra, we used the full-potential linearized augmented plane wave plus local orbitals technique as implemented in WIEN2k code. The both Mg and Al K-edge spectral features of the MgAl2O4 sample irradiated with a high fluence are drastically different from those of the pristine sample. The calculated spectra indicated that the changes in the experimental spectra were due to cationic disorder between Mg in tetrahedral sites and Al in octahedral sites.

Authors : R. I. Eglitis, J. Purans, A. I. Popov
Affiliations : Institute of Solid State Physics, University of Latvia, 8 Kengaraga Str., Riga LV1063

Resume : By means of the hybrid exchange-correlation functionals, as it is implemented in the CRYSTAL computer code, ab initio calculations for main ABO3 perovskite (001) surfaces, namely SrTiO3, BaTiO3, PbTiO3, CaTiO3, SrZrO3, BaZrO3, PbZrO3 and CaZrO3 were performed. For ABO3 perovskite (001) surfaces, with a few exceptions, all atoms of the upper surface layer relax inward, all atoms of the second surface layer relax outward, and all third layer atoms, again inward. The relaxation of (001) surface metal atoms for ABO3 perovskite upper two surface layers for both AO and BO2-terminations, in most cases, are considerably larger than that of oxygen atoms, what leads to a considerable rumpling of the outermost plane. The ABO3 perovskite (001) surface energies always are smaller than the (011) and especially (111) surface energies. The ABO3 perovskite AO and BO2-terminated (001) surface band gaps always are reduced with respect to the bulk values. The B-O chemical bond population in ABO3 perovskite bulk always are smaller than near the (001) and especially (011) surfaces [1,2]. We performed comparative ab initio calculations for polar ReO3 and WO3 (001) surfaces, and compared the results with ABO3 perovskite (001) surfaces. The systematic trends in our ABO3 perovskite bulk and (001) surface F-center calculations are analyzed and compared with relevant experimental data [3]. References: [1] R. I. Eglitis and A. I. Popov, J. Saudi Chem. Soc. 22, 459-468 (2018) [2] R. I. Eglitis, J. Purans, J. Kleperis, A. I. Popov, R. Jia, Journal of Materials science 55, 203-217 (2020) [3] R. I. Eglitis and A. I. Popov, J. Nano-Electron. Phys. 11, 01001 (2019)

Authors : Vladimir Lipp, Beata Ziaja
Affiliations : Center for Free-Electron Laser Science CFEL at DESY, Hamburg, Germany; Center for Free-Electron Laser Science CFEL at DESY, Hamburg, Germany and Institute of Nuclear Physics, Polish Academy of Sciences, Krakow, Poland

Resume : We simulate the dynamics of silicon after its excitation by an X-ray laser in two-dimensional (2D) geometry. The approach combines classical Monte Carlo (MC) [1] with Two-Temperature-like model, nTTM [2]. The MC takes into account X-ray absorption and electron cascading and provides the initial conditions for the nTTM, which takes into account Auger recombination and impact ionization, band gap evolution, ambipolar carrier diffusion, electronic and atomic heat conduction, and electron-phonon coupling. To solve the nTTM system of equations in 2D, we developed a finite-difference integration algorithm based on Alternating Direction Implicit method with additional predictor-corrector algorithm, which takes care of the nonlinearities. We show the first results of the model and discuss its possible applications. In particular, the approach should be applicable also for metals, various radiation sources (e.g., heavy ion beams), and extendable to three dimensions. [1] V. Lipp, N. Medvedev, B. Ziaja, Proc. SPIE 10236, 102360H (2017). [2] H. van Driel, Phys. Rev. B 35, 8166 (1987).

Poster session : Chairman to be defined
Authors : Alexandre Boulle, Vincent Mergnac
Affiliations : Institut de Recherche sur les Céramiques - CNRS UMR 7315 - Limoges France, Université de Limoges - Direction des Systèmes d’Information - Limoges France

Resume : The determination of sub-surface strain and disorder profiles is an essential step in the characterization of ion irradiated materials. Among the few existing techniques that allow to reach this goal X-ray diffraction (XRD) has the advantage of being simultaneously sensitive to strain and disorder, while being a non-destructive technique that allows to determine these quantities on an absolute scale. The main obstacle on this path is that the determination of the depth-resolved strain/disorder profiles requires a careful modeling and simulation of experimental data, a task that is often restricted to experts of the XRD technique. In order to make the XRD determination of strain/disorder profiles more intuitive we previously developed the free and open-source software RaDMaX ( RaDMaX is written in Python and therefore requires the installation of a full Python development environment which can be a disincentive for a non-negligible amount of potential users. With this in mind, we rewrote RaDMaX in order to make it able to run in a web browser. This program, RaDMax-online, allows the users to upload XRD data, analyze and fit the data on the web, and download the simulation results. It can be found at: . The program entirely relies on free / open-source libraries related to the Python ecosystem (NumPy, SciPy, Jupyter, ipywidgets, bqplot, voila). The website is deployed using Docker containers.

Authors : B.L.Oksengendler*(1,2), A.F.Zatsepin(2), A.N.Kiryakov(2), N.N.Nikiforova(1), S.Suleymanov(3)
Affiliations : (1) Institute of Ion-Plasma and Laser Technologies (IPLT UAS), Tashkent, Uzbekistan; (2) Ural Federal University (UrFU), Yekaterinburg, Russia; (3) Materials Science Institute “Physics-Sun” (MSI UAS), Tashkent, Uzbekistan

Resume : A thorough analysis of the so-called hybrid objects made it possible to make a new classification of them and revealed a useful opportunity to distinguish them into the so-called complex systems. Their complexity can be described with very great commonality within the framework of five code concepts: nano, fractality, low dimensionality, chirality and synergetics. Applying the methods of radiation physics in series to each, and then in various combinations of the above features of hybrid media, it was possible to build models of basic atomic rearrangements such as radiation defect formation, radiation-stimulated diffusion, and basic radiation-stimulated quasi-chemical reactions. This allows you to outline a rough response of hybrid media to the effects of certain types of radiation, for example, fast electrons and ions, ordinary visible light and concentrated solar radiation. Particular attention is paid to electron-ion processes at interfaces with different curvatures. Cases of satisfactory agreement with experiment are discussed basing on various materials as examples.

Authors : I. Avetissov*, M. Zykova*, A. Chepurnov**, I. Nikulin***, R. Sayfutyarov*, M. Grishechkin*, R. Avetisov*
Affiliations : * D. Mendeleev University of Chemical Technology of Russia ** Lomonosov Moscow State University, Skobeltsyn Institute of Nuclear Physics *** Laboratory of Radiation Physics, Belgorod National Research University

Resume : One of the problems within the framework of Dark Matter search experiments is the creation of a neutron absorption system - VETO. One of the most effective known neutron absorbers is gadolinium nuclei. The VETO system requires the development of a constructionl material in which gadolinium or its compounds would be uniformly distributed in the volume of the polymer matrix with Gd- concentration ~ 1 wt%. and total content of radioactive impurities less than 1 mBq/kg. In terms of Gd compounds, the U and Th contents should not exceed 50 ppt. We found commercial gadolinium containing preparations with chemical purity of 4N-5N in which the content of radioactive components varied by 3 orders of magnitude. The procedure of reduction of U and Th content to 50 ppt level has been developed. Several polymer matrixes were used to incorporate Gd nuclei and to achieve the homogeneity distribution. The mechanical properties of hybrid materials within 77-300 K temperature range were studied. The research was financially supported by the Ministry of Science and High Education of Russian Federation by the project RFMEFI60419X0238

Authors : 1Marie-Noëlle de Noirfontaine, 2Enric Garcia – Caurel, 3Sandrine Tusseau – Nenez, 1,4Mireille Courtial,1Olivier Cavani, 5Ferenc Borondics,1Frédéric Dunstetter, 1Dominique Gorse – Pomonti
Affiliations : 1Laboratoire des Solides Irradiés, Ecole Polytechnique, CNRS UMR 7642, CEA-DSM-IRAMIS, IP Paris, F-91128 Palaiseau Cedex, France 2Laboratoire de Physique des Interfaces et des Couches Minces, UMR CNRS 7647, Ecole Polytechnique, IP Paris, F-91128 Palaiseau Cedex, France 3 Laboratoire de Physique de la Matière Condensée, UMR CNRS 7643, Ecole Polytechnique, IP Paris, F-91128, Palaiseau Cedex 4 Université d’Artois, 1230 Rue de l’Université, F-62408 Béthune, France 5 Synchrotron SOLEIL, F-91192, Gif - sur - Yvette Cedex, France

Resume : Portlandite Ca(OH)2 and brucite Mg(OH)2 are isomorphous. They belong to the family of CdI2 type compounds with a layered structure giving them interesting physico-chemical and electronic properties for a number of industrial applications. Commercial powders were electron-irradiated at 2.5 MeV, room temperature and high dose rate (of order 20kGy/s) using the accelerator NEC Pelletron of the SIRIUS platform. Portlandite and brucite are found stable up to doses as high as 10 GGy and even more. Some subtle differences exist between these two compounds, that were revealed and analyzed by X-ray diffraction and IR spectroscopy.

Authors : N. Daghbouja*, M . Callistib*, H. S. Sena*, , M. Karlikc,d, J. Čapeke, P. Minárikd T. Polcara, V. Havránekf
Affiliations : a Department of Control Engineering, Faculty of Electrical Engineering, Czech Technical University in Prague, Technická 2, 160 00 Prague 6, Czechia b Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge, CB3 0FS, United Kingdom c Department of Materials, Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Trojanova 13, 120 00 Prague 2, Czechia d Department of Physics of Materials, Faculty of Mathematics and Physics, Ke Karlovu 5, 121 16 Prague 2, Czechia e Department of Solid State Engineering, Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Trojanova 13, 120 00 Prague 2, Czechia f Nuclear Physics Institute CAS, v.v.i., Husinec - Řež 130, 250 68 Řež, Czech Republic

Resume : Sputter-deposited Zr/Nb nanoscale metallic multilayers (NMMs) with thin and thick periodicities were subjected to Cu+ irradiation with low and high fluences. Radiation-induced strain normally to interfaces was measured; the thinner layered exhibited a tensile strain in Nb layers, while a compressive strain applied in Zr layers. The thicker multilayer exhibited a compressive strain in both layers. The obtained results well supported by DFT calculations, which show that Cu trap at different positions depending on layer periodicities. For thin layers, Cu occupies tetrahedral site and basal plane of Nb and Zr respectively. For thick layers, Cu tends to form clusters.

Authors : D. Messou*(1, 2), S Béchu (2,1), S. Gaiaschi (3), M. Frégnaux (2,1), C. Eypert (3), P. Chapon (3), M. Bouttemy (2,1), A. Etcheberry (2,1)
Affiliations : (1) Institut Photovoltaïque d’Île de France (IPVF), 18 Boulevard Thomas Gobert, 91120 Palaiseau, France; (2) Institut Lavoisier de Versailles (UMR 8180), Université de Versailles-Saint-Quentin-en-Yvelines – CNRS, 45 avenue des États-Unis, 78035 Versailles, France ; (3) HORIBA Scientifique, 14 Boulevard Thomas Gobert - Passage Jobin Yvon CS 45002 91120 Palaiseau, France

Resume : Nowadays the development of tandem solar cells promotes the interest for III-V semiconductor materials. Such architecture evolutions of solar cells require an appropriate characterization strategy to accurately understand the chemical properties at the different interfaces constitutive of the heterojunction based device. Our methodology consists in reaching interfaces of interest quickly by Glow Discharge – Optical Emission Spectroscopy (GD-OES) and performing X-ray Photoelectron Spectroscopy (XPS) analyses directly inside the GD-OES crater. But the GD-OES profiling process and the Ar plasma sputtering stop lead to possible surface degradation of the explored material and re-deposition processes in the crater. The behavior of binary semiconductors (InP, GaAs and GaP) is compared to ternary ones (InGaAs, InGaP and AlGaAs). The GD-OES crater bottom is systematically studied to determine the possible perturbations of its surface chemistry, morphology, and optical signal (XPS, Auger, SEM-EBSD, ellipsometry). These techniques reveal the presence of a superficial damaged overlayer requiring to develop regeneration (chemical or physical) steps. Depending on the material, more or less pronounced modification of the crater roughness and composition are shown, as well as an amorphization. To complete this study, the surface chemical state obtained after GD-OES Ar plasma profiling is compared to the one obtained by ionic etching using Ar+ bombardment inside the XPS analysis chamber.

Authors : R.A. Redko a,b, G.V. Milenin a, V.V. Shynkarenko a, V.B. Neymash c, V.Y. Povarchuk c, S.M. Redko a
Affiliations : a V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine, 03680, Kyiv, Ukraine b State University of Telecommunications, 7, Solomenska str., 03680 Kyiv, Ukraine c Institute of Physics, NAS of Ukraine, Kyiv, 03028, Ukraine

Resume : The effect of 4 MeV electron irradiation on the photoluminescence (PL) properties of Si-doped GaN was investigated. MOCVD grown GaN thin films were irradiated at different doses 1·107, 2.5·107 and 1·108 rad (samples A, B and C, respectively). 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 with wavelength λ=315 nm and emittance of 5 μW/cm2. It was obtained that PL spectra from irradiated samples have been changed during long-term period after treatment. The shift positions for near band gap photoluminescence peak as well as its intensity change were detected. After electron irradiation, the shape of PL spectra for samples A-C is almost same. Integral PL intensities of samples B and C have been decrease due to electron irradiation but not dramatically. For Sample A an increase of the integral PL intensity was observed. Small radiation dose (107 rad) results in the increase of integral intensity while larger doses (2.5·107 and 108 rad) results in its decreasing. One can think that that electron irradiation with larger doses results in non-radiative recombination channel magnification. While the treatment with dose of 107 rad, on the contrary, results in its decrease. The last fact is well-known as low doses effect. It is meaning that low doses of external influences result in improvement of useful characteristics (i.e. structural perfection, emission properties, homogeneity and so on).

Authors : A. I. Popov and E. A. Kotomin
Affiliations : Institute of Solid State Physics, University of Latvia, Riga, Latvia E-mail:

Resume : Already about 60 years ago, Levi and Dienes performed first studies of radiation damage in Al2O3 crystals caused by fast neutrons, and almost fifty years ago, Compton and Arnold measured the threshold energy to displace atoms by incident energetic electrons. At the Second International Conference on Radiation Effects in Insulators (Albuquerque, 1983), J.H. Crawford summarized in his report the work done by that time and discussed what we still did not know at all or not enough [1]. In particular, he highlighted how scanty was our knowledge of interstitial defects. Since then, many attractive ideas have been suggested, and many precise experiments have been carried out. It is impossible to list all or even the most interesting and important of them in a single presentation (see, e.g., [2,3]). Therefore, in the present talk we will try to summarize only key results related to simple electron centers (F, F+ and their dimers, colloids) with a special attention to interstitial defects: their electronic structure, role and manifestations in the processes of thermal annealing of the F-type centers in Al2O3 [4] and several other ionic oxides, such as MgO, MgAl2O4, ZnO, BeO and Y3Al5O12. We will also discuss the possible solution of the second puzzle, mentioned by Crawford, namely why and how the so-called hole V-type centers could be formed under optical transformation of the electron centers F+→ F in α-Al2O3 and MgO single crystals. Finally, we will discuss the process of the intrinsic high-temperature migration/transformation of F centers in ionic oxides and demonstrate how F-type dimer centers and metallic colloids could be formed as a part of the process [5]. [1] J.H. Crawford, Nucl. Instrum. Meth. B 1 (1984) 159-165. [2] E.A. Kotomin and A.I. Popov, Nucl. Instrum. Meth. B 141 (1998) 1-15. [3] S.J. Zinkle and C. Kinoshita, J. Nucl. Mat. 251 (1997) 200-217. [4] A.I. Popov, A. Lushchik, et al. Nucl. Instrum. Meth. B 433 (2018) 93-97. [5] V.N. Kuzovkov, E.A. Kotomin, and A.I. Popov, J. Nucl. Mater., 502 (2018) 295-300.

Authors : Dechao Meng(1), Geng Li(2), Xiangyu Sun(1), Yu Song(1), Donghua Yue(3), Chenbowen Li(2), LiQiang Xu(4), Haoliang Huang(5), Feng Chen(4), Ke Wang(2), Yijia Du(1)
Affiliations : (1) Microsystem and Terahertz Research Center & Institute of Electronic Engineering, China Academy of Engineering Physics, Chengdu, 610200, China. (2) State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, P. R. China (3) Institute of Systematical Engineering, China Academy of Engineering Physics, Mianyang, 621900, China. (4) Department of Physics, University of Sciences and Technology of China, and High Magnetic Field Laboratory, Chinese Academy of Sciences (CAS), Hefei 230026, China (5) National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, China

Resume : Prior work on gamma ray irradiation of functional materials has shown a direct correlation between total ionic dose (TID) and degradation of functional properties. Generally, the gamma ray would lead to charge traps generation/accumulation, and result in more deterioration than enhancement of the properties. Various methods have attempted to elucidate such process at both micro and macro scales. Some phenomenological models [1] have been developed to quantify defect interactions. Though it was also used to manipulate the performance of functional materials, gamma ray is far beyond effective engineering method, which seems to only cause degradations. Achieving obvious promotion and relatively precise prediction seems to be the main drawback in application of gamma ray defect engineering. Similar to the dose dependent dielectric constant, almost all the remnant polarizations (Pr) follow the monotonous degradation model [1] well, with a few exceptions [2-6]. These “strange” Pr firstly increased and then decreased in TID experiments, which could be well modeled using a modified Weibull`s rule [1] as ΔPr/Pr=1-exp(-a*x^(1-b)) c*x, where x means the irradiation dose. These results mainly obtained from poled samples indicate that the pristine piezoelectric states might contribute to the additional linear part and significantly influence the defect interaction and promote the radiation hardness. It initializes our further work about gamma ray in ferroelectric materials. Then great efforts have been taken in manipulation of pristine states to promote gamma ray as an effective defect engineering method, achieving both piezoelectric enhancement and degradation. High performance PbZr0.52Ti0.48O3 (PZT) films have been selected and fabricated on silicon based substrate at several micrometers. A perovskite structured bufferlayer of a few nanometers was optimized to stabilize the structures. Obvious Pr enhancements were confirmed even at different dose rate, but absent in a bulk ceramics and these films in reference with even similar composition but lower textured structures. It means that the pristine structural states play the similar role to bias in these exceptions. XRD, pole figure and SEM results suggest the films to be 99% highly textured, which stabilized a large remnant polarization without electrical bias. EBSD and STEM reveal a gradient evolution of grain orientation along the thickness. It might cause another internal field across the film confirmed by KPFM, which acts as a bias field and actually poles the films. In summary, we eventually achieve gamma ray defect engineering in ferroelectric metal oxides by manipulating the pristine sates in highly textured films, and develop a modified degradation model to predict the performance. It provides a new method that forgoes chemical doping and might benefit further advances in microelectronics and micro-electro-mechanical systems. [1] Sci. Rep. 7, 5308 (2017); [2] Phys. Rev. 184, 476 (1969); [3] IEEE T. Nucl. Sci, 37, 1703(1990); [4] IEEE T. Nucl. Sci, 37, 1713(1990);[5] Thin Solid Films 562,185(2014); [6] J. Alloy. Compd., 152148 (2019)

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Materials I : Tiziana Cesca
Authors : C. Grygiel, A. Ribet, J. G. Mattei, H. Lebius, E. Balanzat, I. Monnet
Affiliations : CIMAP, Normandie Univ, ENSICAEN, UNICAEN, CEA, CNRS, 14000 Caen, France

Resume : Experiments at large-scale facilities as ion accelerators allow the simulations for materials of real working conditions such as radiative environments ranging from nuclear to space applications. Indeed, swift heavy ion irradiation leads mainly to the deposition of intense electronic excitations entailing defect formation and structural modifications that depend on material characteristics. Since few years the development of versatile laboratory X-Ray diffractometers allows high resolution in grazing geometry being suitable for the irradiated material characterizations where the upper irradiated part of samples might be strongly and non-homogeneously modified in depth. Damage depth profiles are thus established in irradiated materials by using combination of in-situ GIXRD, ex-situ HR-XRD, TEM and even UV-Vis absorption. In the presentation, an overview on defect formation and structural modifications (amorphization, strain, grain subdivision) associated to energy deposition processes (Se or Sn) induced by swift heavy ion irradiation in functional materials will be presented.

Authors : Matthew J. Lloyd, Robert G. Abernethy, Bethany Jim, Mark R. Gilbert, Ian Griffiths, Jack C. Haley, Paul A. J. Bagot, Enrique Martinez, Duc Nguyen-Manh, Michael P. Moody, David E. J. Armstrong
Affiliations : Department of Materials, University of Oxford and UKAEA; Department of Materials, University of Oxford and UKAEA; Department of Materials, University of Oxford; UKAEA; Department of Materials, University of Oxford; Department of Materials, University of Oxford; Department of Materials, University of Oxford; Theoretical Division, Los Alamos National Laboratory; UKAEA; Department of Materials, University of Oxford; Department of Materials, University of Oxford

Resume : The realisation of fusion energy is dependant on the development of resilient plasma facing materials that can withstand the combined effects of high energy neutron irradiation and high operating temperatures. Transmutation in these components leads to the production of Re and Os, and a composition that varies significantly with time [1]. The precipitation of Re and Os, observed experimentally in both ion and neutron studies is a potential life limiting factor [2]. In this research, neutron irradiated W was irradiated to 1.67dpa at 900oC, producing a post irradiation composition of W-1.4at.%Re-0.1at.%Os. Characterisation using a combination of Atom Probe Tomography (APT) and Scanning Tunnelling Electron Microscopy (STEM) found mostly voids decorated with both Re and Os, as well as smaller isolated precipitates. Grain boundaries were also decorated with both Re and Os. Experimental results were supported by a multicomponent, atomistic kinetic Monte Carlo model [3] incorporating both vacancy & interstitial defects, and solute concentration dependant interactions. [1] Gilbert, M.R. and Sublet, J.-C., Nuclear Fusion, 2011. [2] Lloyd, M.J., Abernethy, R.G., Gilbert, M.R., Griffiths, I., Bagot, P.A., Nguyen-Manh, D., Moody, M.P. and Armstrong, D.E., 2019. Scripta Materialia, 173, pp.96-100. [3] Lloyd, M.J., Abernethy, R.G., Armstrong, D.E., Bagot, P.A., Moody, M.P., Martinez, E. and Nguyen-Manh, D., 2019. The European Physical Journal B, 92(10), p.241.

Authors : 1Marie-Noëlle de Noirfontaine, 2Enric Garcia – Caurel, 2Daniel Funes-Fernando, 1,3Jihane Jdaini, 4Sandrine Tusseau – Nenez, 1,5Mireille Courtial, 1Frédéric Dunstetter, 3Céline Cau – dit –Coumes, 1Dominique Gorse – Pomonti
Affiliations : 1Laboratoire des Solides Irradiés, Ecole Polytechnique, CNRS UMR 7642, CEA-DSM-IRAMIS, IP Paris, F-91128 Palaiseau Cedex, France 2Laboratoire de Physique des Interfaces et des Couches Minces, UMR CNRS 7647, Ecole Polytechnique,IP Paris, F-91128 Palaiseau Cedex, France 3Laboratoire d’études des Ciments et Bitumes pour le Conditionnement (LCBC) - CEA-DEN, DE2D/SEAD/LCBC - Marcoule, F-30207 Bagnols-sur-Cèze, France 4 Laboratoire de Physique de la Matière Condensée, UMR CNRS 7643, Ecole Polytechnique, IP Paris, F-91128, Palaiseau Cedex 5Université d’Artois, 1230 Rue de l’Université, F-62408 Béthune, France

Resume : Brushite CaHPO4.2H2O (Dicalcium Phosphate Dihydrate: DCPD) is considered as a sorbent of strontium (90Sr2+) which is a contaminant present in some acidic effluents produced by cleaning operations during the dismantling of former nuclear facilities. The idea is to check how electron - radiation - sensitive is this material, since structural and chemical changes caused by irradiation might affect significantly its ion exchange capacity. The energy deposited by the projectile electron into the target is known to be approximated as the sum of two contributions, ballistic and electronic. But only their order of magnitude is supposed to be known. As a result, the structural damage caused by electron irradiation cannot be even reasonably estimated and the radiation sensitivity of brushite has to be checked experimentally. In this paper, powder X-ray diffraction and Raman spectroscopy are associated to analyze the damage effects to brushite following electron irradiation. The accelerator NEC Pelletron of the SIRIUS platform is used for electron irradiation at 2.5 MeV (dose rate of order 20 kGy/s). Amorphization of brushite is observed with increasing dose, and was found complete at 6 GGy. The Raman spectroscopy study tells us that the ultimate compound at the highest dose could be of type anhydrous pyrophosphate. Consequences regarding the damage mechanisms are considered.

Authors : Roger Smith
Affiliations : School of Science, Loughborough University, LE11 3TU, UK

Resume : Both borosilicate and iron phosphate glasses are used for the encapsulation of high level nuclear waste. A description of how atomistic models can be used, together with molecular dynamics simulations of radiation damage in these glasses to understand the damage processes and to explain why glasses are an especially good choice for waste encapsulation. In the case of crystals the amount of damage produced by an irradiation event is usually categorised by the number of Frenkel pairs produced but this cannot be used in the case of a glass. It will be shown that a useful concept instead is the change in atomic co-ordination induced by the collision cascade. It will also be demonstrated how some modern simulation techniques can be used to determine how the glasses relax over times scale longer than those generally accessible by molecular dynamics.

Authors : J.-F. Barbot, M.-F. Beaufort, A. Boulle, A. Declémy
Affiliations : Institut Pprime, Département Physique et Mécanique des Matériaux, CNRS-Université de Poitiers, ENSMA, TSA 41123, 86073 Poitiers Cedex 9 Institut de Recherche sur les Céramiques, CNRS UMR 7315, Limoges, France

Resume : Single crystals of 4H-SiC were implanted by noble gases under different conditions (fluence and temperature). The elastic strain buildup was particularly studied at elevated temperature for which the dynamical recombination prevents the amorphous transition. A phenomenological model based on Multi-Step-Damage Accumulation (MSDA) and cascade recovery (Gibbon's model) allows to fit the evolution of the maximal elastic strain according to the fluence and for different temperatures of implantation. In addition, with the help of transmission electron microscopy the evolution of the implantation related defects under annealing was studied. The formation of nanocavities was observed under severe implantation/annealing conditions of Xe implantation. These cavities are found of different nature according to the xenon and damage distribution as well as the related-strain profile (obtained by the simulations of the XRD curves). The surface swelling (step height) under implantation/annealing was also studied leading to different activation energies supporting the idea of different defects contributions to swelling.

11:50 Lunch break    
Modelling of damage and defects II : Chairman to be defined
Authors : Daniel Mason, Andrea Sand, Sergei Dudarev
Affiliations : CCFE, Culham Centre for Fusion Energy, Abingdon, Oxfordshire OX14 Q3DB, United Kingdom; Department of Physics, University of Helsinki, PO Box 43, FI-00014, Helsinki, Finland; CCFE, Culham Centre for Fusion Energy, Abingdon, Oxfordshire OX14 Q3DB, United Kingdom

Resume : The theoretical basis of object kinetic Monte Carlo, and many related methods, is that the current state of the system consists of set of spatially discrete objects- point defects, dislocation loops and voids - which may evolve and interact with each other with predefined rules. An object is typically described with a small number of parameters - for instance a void may be defined by the number of vacancies contained, but there is no reason why additional shape information should not be retained if such information is useful. The logical limit of the amount of information retained per object is a description of the atomic types and positions. We describe the development of a new object kinetic Monte Carlo code where the elementary defect objects are off-lattice atomistic configurations. An object evolves by internal rearrangements of the atoms, which can be found on-the-fly. Such rearrangements typically transform one object into another, but can also involve displacement of the centre-of-mass, or splitting one object into two. Elastic interactions are handled with interatomic potentials within an object, and with the dipole tensor formalism between objects. We track visited configurations to build up a relevant database of objects plus events. Once a good database is found we can evolve mobile interstitial clusters faster than the equivalent MD simulation, even at high temperature. We apply the model to the evolution of 20 keV PKA cascades in tungsten, and capture complex internal relaxations of sessile objects instigated by object collisions. These cascades are evolved to experimental timescales at technologically relevant temperatures 600-900 K. We discuss the lessons learnt and the challenges for modelling irradiation damage evolution with object kinetic Monte Carlo. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014–2018 and 2019–2020 under grant agreement No. 633053, and from the RCUK Energy Programme [grant number EP/P012450/1]. The views and opinions expressed herein do not necessarily reflect those of the European Commission. AES acknowledges support from the Academy of Finland through project No. 311472.

Authors : Pavlos Mouratidis, James McHugh, Kenny Jolley, Malcolm Heggie, Patrick Briddon
Affiliations : Loughborough University Department of Chemistry;Loughborough University Department of Chemistry;Loughborough University Department of Chemistry;Loughborough University Department of Chemistry;Newcastle University School of Engineering

Resume : Graphite has been the material of choice in construction of nuclear reactors for many years due to its low neutron absorption cross-section and high scattering cross-section. The physical properties of a graphite moderator can greatly influence the cost, safety and lifespan of a reactor. Neutron collision damage in graphite results in the formation of basal dislocations. The subsequent interaction of basal dislocations with each other and the surrounding lattice causes severe dimensional changes along the basal direction. There has been a lot of interest recently in AB and AC stacking grain boundaries in bilayer graphene. Transition from AB to AC stacking can be described by the glide of partial basal dislocations resulting in expansion of dislocation cores and buckling of the bilayer. Herein we present full ab initio and molecular dynamics calculations of basal dislocation network structures in bilayer graphene and few-layer graphene in large supercells of up to 100 nm.

Authors : Gonzalo Valles, Carlo L. Guerrero, Fernando Jiménez, Christophe J. Ortiz
Affiliations : Laboratorio Nacional de Fusión por Confinamiento Magnético-CIEMAT, Spain

Resume : Owing to their properties, reduced-activation ferritic/martensitic (RAFM) steels are proposed as structural materials for in-vessel components of future fusion reactors. Neutron irradiation produces defects in the material, leading to detrimental effects on its mechanical properties such as hardening and embrittlement. Dislocation mobility, which is related to the mechanical behaviour of the material, is highly influenced by the defects created due to neutron/ion irradiation. Moreover, it has been reported that dislocations have an influence on the spatial distribution of defects in bcc iron. Elastic interactions between dislocations and SIA clusters lead to dislocation decoration and to an inhomogeneous spatial distribution of SIA clusters. In this work, we present a study of the influence of spatial defect distribution on dislocation mobility in the case of self-ion irradiation on bcc iron. For this purpose, defect distribution in the presence of dislocations is calculated by MEGA code, an object kinetic Monte Carlo code based on GPU programming which allows the study of high irradiation doses, large spatial regions and elastic interactions between SIA clusters and dislocations. Dislocation mobility in the presence of defects, either placed at random positions or at those positions previously calculated by okMC, is studied by means of Dislocation Dynamics technique with MoDELib suit of codes.

Authors : Carlo L. Guerrero, Fernando Jimenez, Christophe J. Ortiz
Affiliations : Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT) Av. Complutense, 40, 28040 Madrid, Spain

Resume : In the study of the evolution of Fe microstructures and their alloys under irradiation, there is a large body of work focused on the defect formation energies calculated through ab initio simulations. In general, the minimum-energy configuration of defects is used in kinetic models to simulate the long-term evolution of the microstructure. In this work, our goal is to study the evolution of the Fe microstructure under irradiation when the presence of non-conventional configurations of interstitial clusters is taken into account. We calculated with ab initio the formation energies of several configurations of different interstitial and vacancy structures in Fe. Additionally, for each defect, the transformation energy between the two most stable configurations was calculated. In order to determine the influence of non-conventional configurations on the microstructure evolution, we reproduced a Resistivity Recovery (RR) experiment in electron-irradiated Fe using Object kinetic Monte Carlo (OkMC) with two different models. The first set of simulations uses the conventional configurations for interstitial clusters, which correspond to the most stable configurations. The second set of OkMC simulations takes the two most stable configurations for each cluster into consideration and the probability of transformation from one configuration to the other.

Authors : López, P.*(1), Aboy, M.(1), Muñoz, I.(1), Santos, I.(1), Marqués, L.A.(1), Couso, C.(2), Ullán, M.(2) & Pelaz L.(1)
Affiliations : (1) Departamento de Electricidad y Electrónica, Universidad de Valladolid, ETSI Telecomunicación, Paseo de Belén 15, 47011 Valladolid, Spain (2) Centro Nacional de Microelectrónica (IMB-CNM, CSIC), Campus UAB, 08193 Bellaterra, Barcelona, Spain

Resume : Si detectors built on p-type substrates are suitable for high energy physics applications due to their improved radiation hardness. However, they are still strongly affected by irradiation-induced displacement damage, as it alters the net space charge. It has been reported that the effective doping concentration (Neff) undergoes a fast decay for low neutron fluences, attributed to an acceptor removal process, and that the removal rate decreases as the initial dopant concentration increases. This process is associated to dopant deactivation by damage, but its microscopic origin and the reason for the rate dependence on resistivity are still unknown. We use atomistic simulations to analyze the acceptor removal process in samples with B concentrations ranging from 1013 to 1017 cm-3, irradiated up to 1016 cm-2 1-MeV neq fluences. Si recoils are simulated within a binary collision approximation scheme, following the energy distribution of primary knock-on atoms calculated with the SPECTRA-PKA code. The subsequent dopant-defect interactions are simulated with a kinetic Monte Carlo code with detailed models of defect and dopant diffusion, as well as dopant deactivation. The simulated Neff dependence on fluence and the obtained removal rates are consistent with experiments. Through the analysis of defect-dopant interactions we will shed light on the atomistic mechanisms responsible for the acceptor removal process, and will explain some intriguing features not understood until now.

15:50 Coffee Break    
Characterization of damage and defects II : Maik Lang
Authors : M-F BARTHE
Affiliations : CEMHTI, CNRS, Université d’Orléans (Orléans, FRANCE)

Resume : Positron annihilation spectroscopy (PAS) is a well-established technique for characterizing materials. It is based on the positron specific properties in matter. It can be trapped in vacancies and annihilates with electrons leading to the emission of gamma rays with energy depending on the momentum of the electron-positron annihilated pair. Two annihilation characteristics give the signature of the defects and allow determining some of their properties such as their nature, concentration, chemical environment : the positron lifetime related to the electron density experienced by positron before annihilating and the momentum distribution of the electron-positron annihilated pairs. By using slow positrons, the defects depth profile can be studied in thin layers. PAS has numerous advantages among them, it is non-destructive and can be used for conducting as well as insulating materials crystalline or amorphous. The annihilation characteristics can be predicted by first principle calculations and these data when available can help to identify defects. Sensitive to the single vacancy, PAS can allow to determine the size of the vacancy clusters up to a maximum of about 1 nm in the concentration range from 1015 to a few 1018 cm-3. In this talk the advantages of PAS an d its complementarity with other techniques and modelling will be illustrated with examples based on recent studies in the spintronic or nuclear (fusion, fission) applications.

Authors : Abner Velazco Torrejón, Armand Béché, Johan Verbeeck
Affiliations : EMAT, Antwerp University, Groenenborgerlaan 171, 2020 Antwerp, Belgium.

Resume : The current strategies to reduce beam damage in a transmission electron microscope (TEM) consists in reducing the electron dose, calculated in electrons per area (usually given in square angstrom), that is delivered to the sample either by decreasing the electron beam current or making fast acquisitions of images, resulting in low signal-to-noise ratio images. A new approach from the field of data compression has been proposed to overcome or alleviate the problem of beam damage in TEM. The so-called compressed sensing technique is based on a sub-sampling approach where the information can be retrieved from a reduced data acquisition [1]. In STEM (Scanning TEM) mode, with compressed sensing is possible to retrieve an image scanning a fewer number of pixels than with normal acquisition. This non-conventional method of dose reduction has been recently implemented in STEM [2,3] and it has showed the possibility of atomic-resolution imaging of beam sensitive materials [3]. As with this sub-sampling technique the sample is not irradiated consecutively, we proposed that a dissipation of a dynamic process of beam damage could be involved in damage reduction when the dose is accumulated at a slower rate than the diffusion of this process. Charging or heating of the sample would follow these model, for instance. In the conventional raster scanning where the probe is scanned across the sample line by line, the dose is accumulated in a consecutive order. If only the order of the scanning positions is modified, skipping a fixed number of pixels between two scanning positions in a line and scanning the missing pixels after completing all the scan lines, for instance, the dose in the surrounding area of a specific point in the sample would be accumulated at a different time rate than with the raster scanning. If any dynamic mechanism is involved, this strategy could dissipate or reduce damage on the sample. With the help of a programmable scan engine different alternative scanning strategies were tested on a beam sensitive sample (commercial Linde type A Zeolite) where the total electron dose was kept constant but its temporal distribution modified. Our results showed less damage when scanning in a different order than raster scanning. These findings demonstrate that the way how the dose is distributed plays an important role on beam damage which gave some insights about the mechanism which can be modelled by a diffusion process. Diffusion simulations can be useful to find a suitable scanning strategy according to the sample characteristics to outrun beam damage in STEM. [1] Candes E. J., Romberg J. K. and Tao T., Communications on Pure and Applied Mathematics, 59, 1207-1223 (2006). [2] Béché, A., Goris, B., Freitag, B., Verbeeck, J., Appl. Phys. Lett. 2016, 108, 093103. [3] A. Stevens, L. Luzi, H. Yang, L. Kovarik, B. Mehdi, A. Liyu, M. Gehm, and N. Browning, Appl. Phys. Lett. 112, 043104 (2018).

Authors : Z. Hu1, M-F. Barthe1, P. Desgardin1 C. Genevois1 J.joseph1 B. Decamps2, R. Schaublin3
Affiliations : 1 CNRS, CEMHTI UPR3079, Univ. Orléans, F-45071 Orléans, France 2 CSNSM/IN2P3/CNRS, Orsay University, France 3 Laboratory of Metal Physics and Technology, Dept. of Materials, ETH Zurich, Switzerland

Resume : Due to emerging challenges in the energy production, the thermonuclear fusion could be one of the key solutions in answering to the requirements of greenhouse effect limitations and the world increasing demand. Hence, after the ITER reactor building, we need to prepare the next step in the development of this technology, the Demonstration power plant (DEMO). Tungsten has been chosen to cover the divertor in ITER and is envisaged for first walls in DEMO. Such components must be able to suffer high heat flux and irradiations. It is already known that under such severe operational conditions materials properties could be degraded. To dimension the reactor components, we need to predict precisely their impact. Among the critical open questions, a better knowledge is required on the actions of radiation induced defects and their interactions with impurities. Theoretical studies show their potential impact on the evolution of the microstructure under irradiation and we propose to carry out experimental investigations. We attempt to combine Transmission electron microscopy (TEM) and Positron annihilation spectroscopy (PAS), especially adapted to characterize small voids (from single vacancy to vacancy clusters), and to study the effect of W purity on their formation and evolution under irradiation and post-annealing. We irradiated various W samples with different purities from 99.95% to 99.9999% and PAS and TEM analysis exhibited the effect of purity for irradiation at 500°C 0.02dpa.

Authors : M. Scepanovic, M. A. Auger, T. Leguey, V. de Castro
Affiliations : Universidad Carlos III de Madrid

Resume : One of the main structural candidate materials for advanced nuclear fusion reactors over the last decade are oxide dispersed strengthened reduced activation ferritic steels (ODS RAFS). A fine, homogeneous, dispersion of stable nanoparticles such as Y2O3 would allow increasing their upper operating temperatures and radiation damage resistance. However, currently available results require further research to clarify the effect of irradiation on these materials. The main objective of this work is to investigate the microstructural stability of different ODS RAFS with nominal composition Fe–14Cr–2W–0.3Ti–0.3Y2O3 (wt%) subjected to simultaneous dual (Fe3+, He+) ion irradiation at 400 °C to 30 dpa. The characterization of the steels has been accomplished using Transmission electron microscopy (TEM), Atom Probe Tomography (APT) and Positron Annihilation Spectroscopy (PAS). The stability of the nanoparticles has been investigated. The irradiation induced damage has been characterized, focusing in the study of open volume defects. There is a slight change in the chemical composition of nanoparticles after irradiation. The mean size and mean distance of nanoclusters is lower after the irradiation pointing to dissolution of larger nanoclusters and nucleation of new, smaller ones. PAS investigations show a limited increase of open volume defects after the irradiation suggesting a possible entrapment of all injected He ions into the open-volume defects simultaneously created by the Fe irradiation or/and recombination of vacancies and interstitials due to the intermediate temperature of the irradiation. CDB profiles show no clear relation between positron traps and He.

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Microstructures and nanostructures II : Clara Grygiel
Authors : A. Redondo-Cubero 1, K. Lorenz 2, F.J. Palomares 3, B. Galiana 4, D. Bahena 5, L. Vázquez 3
Affiliations : 1 Applied Physics Department, Universidad Autónoma de Madrid, 28049 Madrid, Spain 2 IPFN and INESC-MN, Instituto Superior Técnico, Universidade de Lisboa, 2695-066 Bobadela LRS, Portugal 3 Instituto de Ciencia de Materiales de Madrid, CSIC, 28049 Madrid, Spain 4 Departamento de Física, Universidad Carlos III de Madrid, Avenida de la Universidad 30, 28911 Leganés, Spain 5 Laboratorio Avanzado de Nanoscopia Electrónica (LANE), CINVESTAV, Av. IPN 2508, 07360 DF México, México

Resume : Self-organization mechanisms play an important role in the development of current low-dimensional structures. Ion beam erosion is a well-studied process leading to dot patterns at the nanoscale. In the case of silicon substrates, these dot patterns develop at normal incidence with the incorporation of metal impurities, which lead to the formation of silicides [1]. However, the exact control of those patterns in terms of the physical parameters is not fully understood. Here we report on the production of silicide nanodot patterns by medium-energy ion beam sputtering (IBS) of silicon targets with simultaneous and isotropic metal supply. The advantage of using medium-energy ions lies on the enhancement of the physical magnitudes of the nanodots, regarding both the structure and the surface metal content, when compared to those obtained at low energies [1,2]. This fact enables a better assessment of the structural and compositional properties of the patterns and their dependence with the different irradiation conditions. In order to further understand the metal-assisted IBS surface patterning, we have performed the irradiations under different conditions, by changing the ion species (Xe/Ar), the metal (Mo/Fe) and target temperature. The obtained patterns have been intensely characterized by transmission and scanning electron microscopies as well as by atomic and magnetic (for the Fe case) force microscopies, and X-ray photoelectron spectroscopy. From these analyses, it can be confirmed that the dots are silicide-rich structures, although the flat areas between them also contain silicides but in a lesser extent. The pattern ordering was analysed using the Voronoi tessellation [3]. It was found that ordering depends on the target temperature, ion species as well as in the local metal content. In particular, its change with the temperature depends also on the metal species. Likewise, the silicide distribution within the dot structure changed with the target temperature. Although some morphological features are similar to those found for low-energy IBS, IN the latter case their eventual correlations are difficult to assess because of the reduced dimensions and metal content. Thus, metal-assisted medium-energy IBS dot patterning could be a useful technique to advance the understanding of this interesting nanofabrication method. [1] R. Gago, A. Redondo-Cubero, F. J. Palomares and L. Vázquez, Nanotechnology 25 (2014) 415301. [2] A. Redondo-Cubero, B. Galiana, K. Lorenz, F.J. Palomares, D. Bahena, C. Ballesteros, I. Hernandez-Calderón and L. Vázquez, Nanotechnology 27 (2016) 444001. [3] A. Redondo-Cubero, K Lorenz, F. J. Palomares, A. Muñoz, M. Castro, J. Muñoz-García, R. Cuerno and L. Vázquez, J. Phys.: Condens. Matter. 30 (2018) 274001.

Authors : Parswajit Kalita1, Santanu Ghosh1*, Gaëlle Gutierrez2, Parasmani Rajput3, Vinita Grover4, Gaël Sattonnay5, Devesh K. Avasthi6
Affiliations : 1Dept. of Physics, Indian Institute of Technology Delhi, New Delhi – 110016, India 2CEA Saclay, DEN, SRMP, Labo JANNUS, 91191 Gif-sur-Yvette, France 4Chemistry Division, Bhabha Atomic Research Centre, Mumbai – 400085, India 5LAL, Université Paris-Sud, Bât 200 F-91405, Orsay, France 6Amity Institute of Nanotechnology, Amity University, Noida – 201313, India

Resume : We report here the effect of crystallite (grain) size on the radiation tolerance against simultaneous dual beam irradiations. Yttria stabilized zirconia pellets with two different crystallite sizes (nano-crystalline and bulk-like) are simultaneously irradiated with high energy 27 MeV Fe (electronic energy loss (Se) dominant) and low energy 900 keV I (nuclear energy loss (Sn) dominant) ions. XRD and Raman spectroscopy indicate that the nano-crystalline sample exhibits lesser radiation damage (viz. degradation in crystallinity) after the simultaneous irradiations i.e. the nanocrystalline sample is found to be more radiation tolerant, when compared with the bulk-like sample,under simultaneous irradiation with the high energy and low energy ions. This is interpreted within the frame-work of the thermal spike model after considering the fact that there is essentially no spatial and time overlap between the damage events of the two ‘simultaneous’ ion beams. The current work presents a keen interest for both fundamental understanding of ion-material interactions and the potential application of nano-crystalline materials in the nuclear industry. EXAFS measurements suggest a similar trend in the local disorder/damage as that in the long range (shown by XRD).

Authors : Lin JUN (1), Guillaume TOQUER (1), Sandrine DOURDAIN (1), Clara GRYGIEL (2), Xavier DESCHANELS (1)
Affiliations : (1) ICSM, CEA, CNRS, Univ Montpellier, Marcoule, France; (2) Centre de Recherche sur les Ions, les matériaux et la photonique, CEA-DSM-IRAMIS-CIMAP BP 5133 14 070 Caen Cedex 5, France

Resume : Mesoporous silicas have been proposed for the treatment of radioactive effluents by a new strategy called separation / conditioning. This strategy would allow both the separation of the radionuclide using a selective organic ligand, and its encapsulation after collapse of the porosity by “soft” way (sol-gel reaction, heating under stress or irradiation) to obtain a primary wasteform matrix. This low temperature process would be particularly interesting for the treatment of radioactive effluents containing volatile elements (Cs, I). The talk reports recent results on the dimensional change and the collapse of mesoporous silica pellets under electron beams (2MeV) representative of the beta decay of Cs. The irradiated samples were analyzed by density measurement, Small Angle X-Rays (SAXS), nitrogen adsorption-desorption isotherms to evaluate the evolution of the mesoporous network and Nuclear Magnetic Resonance (NMR), infrared spectroscopy (IR) for the silica network. A mechanism will be proposed to explain the evolution of the mesoporous structure under irradiation. P. Makowski, X. Deschanels, A. Grandjean, D. Meyer, G. Toquer and F. Goettmann, New J. Chem., 2012, 36, 531. Y. Lou, S. Dourdain, C. Rey, Y. Serruys, D. Siméone, N. Mollard, X. Deschanels, Micropor. Mesopor. Mater, 2017, 251, 146.

Authors : F. Bergner, M. Hernández-Mayoral, L. Malerba, M.J. Konstantinović, C. Pareige
Affiliations : Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, 01328 Dresden, Germany; Division of Materials, CIEMAT, Avenida Complutense 40, 28040 Madrid, Spain; SCK•CEN, Nuclear Material Science Institute, Boeretang 200, B–2400 Mol, Belgium; Groupe de Physique des Matériaux, Université et INSA de Rouen, UMR 6634 CNRS, Avenue de l’Université, BP 12, 76801 Saint Etienne du Rouvray, France

Resume : One of the open issues concerning the quantitative understanding of irradiation hardening in Cr steels is related to the spatial arrangement of irradiation-induced dislocation loops with respect to pre-existing dislocations and its consequences for irradiation hardening. In order to tackle this issue, a number of neutron-irradiated industrial-purity Fe-Cr alloys (Cr between 2.5 and 12%) was studied by means of TEM. Loops in irradiated Fe-Cr alloys of lower Cr content were found to arrange more homogeneously in the matrix. In contrast, loops tend to arrange preferentially along dislocation lines for higher Cr contents [Hernandez-Mayoral et al., JNM 474 (2016) 88]. At the same time, reported tensile stress-strain curves [Matijasevic et al., JNM 377 (2008) 147] exhibit trends from smooth elastic-plastic transitions towards yield drops for both increasing Cr and increasing neutron exposure with an exception to be discussed. The poster is aimed to rationalize both observations, namely dislocation decoration at the nm length scale and yield effects at the macroscale, on the basis of the source hardening model [Trinkaus et al., JNM 251 (1997) 172]. In particular, calculated unlocking stresses are found to correlate with measured values of the upper yield stress.

Authors : M. Roldán1*, F. J. Sánchez1, P. Galán2, A. Gómez-Herrero3.
Affiliations : 1National Fusion Laboratory. CIEMAT, Madrid, Spain. 2Centro de Microanálisis de Materiales, Universidad Autónoma Madrid, Madrid, Spain. 3Centro Nacional de Microscopía Electrónica, Universidad Complutense, Madrid, Spain.

Resume : Nowadays, a big effort is being done for the Scientific Community in order to understand the complex mechanisms that lie in the relationship between irradiation damage, stress and high temperature. That synergy is observed in the formation of dislocation loops, swelling, complex chemical changes such as chemical segregation or secondary phase transformations which modify completely the material. All the insight gain in this matter comes from experiments that sometimes are quite complex due to the technical requirements to be performed, but very impressive advances have been achieved in terms of characterization of such microstructural evolution and converted afterwards into models that would be able to predict the behaviour of materials subjected in such harsh environment. However unfortunately, a huge gap is found between the real structural steel microstructures and the computational models available today. Trying to move a bit forward, a set of experiments that combine strained samples, irradiation damage and high temperature are performed. Small specimens were subjected to a strain gradient (supported by a simple FEM analysis) during self-ion irradiation at high temperature to study the effect of a strain field and temperature on irradiation defects. Afterwards, specimens were extracted from the irradiated sample and a deep TEM characterization was carried out. In order to fully understand the evolution of the defects during such experiment, strain-free specimens were also irradiated and characterized to establish properly a starting point irradiated microstructure. The materials that were taken into consideration were both a model alloy such as EFDA Fe10Cr (because is the base of the complex promising structural RAFM materials) and an well known EUROFER97. In the beginning, since the lack of knowledge about the possible synergy between strain effect during irradiation in the defects fate, high irradiation damage was achieved, far from overlapping dose, to easily determine the possible effect or even if strain field act as bias for defect generation. So far, there is not extensive literature studying the issues concerning these experiments, for that reason, it is believed that this research is of a great interest to the Nuclear Fusion Community.

11:50 Lunch break    
Materials II : Chairman to be defined
Authors : K. Lorenz [1,2,3], M. C. Sequeira [1,3], D.R. Pereira [1,2,3], M. Peres [1,3], P. Jozwik [1,3], S. Magalhães [1,3], E. Alves [1,3]
Affiliations : [1] Instituto Superior Técnico (IST), University of Lisbon, Lisbon, Portugal; [2] INESC-MN, Lisbon, Portugal; [3] IPFN, IST, Lisbon, Portugal.

Resume : Wide bandgap semiconductors (WBS) such as group-III nitrides and metal oxides are generally considered very radiation-resistant. Indeed, nitride-based electronic devices are currently tested in satellites and are promising materials for radiation-hard electronic circuits for space or nuclear applications. However, radiation effects in these materials are usually very complex due to the diversity of lattice sites in compound crystals as well as the high mobility of point defects. Defect mobility allows, on the one hand, the annihilation of primary defects but can lead, on the other hand, to the formation of extended defects. The complexity of defect accumulation in WBS upon ion irradiation will be discussed using three case studies. The high stability of GaN upon irradiation with highly ionizing swift heavy ions is shown to be due to efficient in-track and inter-track recrystallization [1]. In the cases of MoO3 and Ga2O3 WBS, ion beams can be used to tune the electrical and optical properties by defect engineering. In the first, ion implantation allows controlling the electrical conductivity over several orders of magnitude [2]. In the latter, defects influence the behaviour of optical dopants such as rare earth and transition metals helping in some cases to stabilise optically active sites [3]. [1] M.C. Sequeira, et al.; to be published [2] D.R. Pereira, et al.; Acta Materialia 169 (2019) 15 [3] M. Peres, et al.; JPD 50 (2017) 325101

Authors : D. Aureau, M. Frégnaux, S. Béchu, N. Simon1,M. Bouttemy, A. Etcheberry, A-M. Gonçalves
Affiliations : ILV, Université de Versailles Saint-Quentin en Yvelines, Université Paris-Saclay, 78035 Versailles, France

Resume : Initially developed for surface analysis (Auger, XPS, SIMS), argon ion beams are commonly used for material depth profiling but the question of surface damage and modified reactivities remains unelucidated. With the objective of gaining a better control and understanding of the induced modifications, we will show some electrochemical and structural changes induced by ion bombardment on III-V semiconductors. An original approach to quantitatively estimate at nanoscale the thickness of the disturbed area using anodic dissolution will also be introduced. Interestingly, it appears that new attainable physico-chemical properties might be obtained. For instance, we observed in situ surface reconstruction of indium phosphide; i.e a progressive decrease of the disorder initially induced during monoatomic bombardment. By changing incidence angle and energy of ion beams, different morphologies and chemical composition will be presented and the reconstruction of surfaces with spontaneous dangling bond reactivity or in situ annealing will be investigated in details. The idea to promote surface activations thanks to dangling bonds reactivity or In enrichment of the surface as consequences of low-energy bombardments (1-8 KeV range) appear relevant for functionalization or passivation. Therefore, we will show preliminary results demonstrating the grafting coverage enhancement of indium rich surfaces with small thiolated molecules thanks to the affinity of sulfur groups with metallic atoms.

Authors : Matteo Vanazzi, Boris Paladino, Jing Hu, Wei-Ying Chen, Meimei Li, Marco G. Beghi, Fabio Di Fonzo.
Affiliations : Center for Nano Science and Technology @PoliMi, Istituto Italiano di Tecnologia, Via Pascoli 70/3, 20133 Milano (MI), Italy; Energy Department, Politecnico di Milano, Via Ponzio 34/3, 20133 Milano (MI), Italy; Nuclear Engineering Division, Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, Illinois, USA.

Resume : Future generation nuclear reactors present intrinsic benefits in terms of economics, safety and waste management. However, innovative material strategies must be designed. Recently, coatings have earned great attention in the nuclear field as a reliable cost-efficient solution. In this framework, amorphous/nano-crystalline oxides have been characterized as corrosion-resistant anti-diffusion barriers. Previously, oxide films have been tested under ion irradiation, proving high stability up to 150 dpa. This radiation tolerance has been related to the amorphousness of the pristine material, which evolves towards a crystalline structure under irradiation. To preserve the radiation tolerance and improve the range of operation, the amorphous state must be conserved as long as possible. In this work, the stabilization of traditional oxides by doping is discussed. Firstly, pure and doped materials have been compared by thermal annealing, showing a significant increase in the crystallization temperature of the mixed systems. Then, irradiation tests have been performed with in situ TEM. Samples have been irradiated with different ions, up to 20 dpa. Experiments have been conducted at 600 °C and at 800 °C, to observe the effects of temperature on the radiation induced crystallization. Dopants retard the crystallization threshold even under irradiation and stabilize the intermediate metastable phases, conserving partially the pristine characteristics. While pure systems suffer from voids formation after crystallization (a traditional phenome for bulk oxides), no swelling appears in the doped counterpart.

Authors : Shengli Chen (1,2,*), David Bernard (1), Léonie Tamagno (1,#) & Olivier Litaize (1)
Affiliations : (1) CEA, DEN, DER, SPRC, LEPh, 13108 Saint-Paul-Lez-Durance, France (2) Université Grenoble Alpes, I-MEP2, 38402 Saint Martin d'Hères, France (#) Current address at CEA, DEN, DTN, SMTA, LMN, 13108 Saint-Paul-Lez-Durance, France

Resume : The mechanical and thermal property change of materials under irradiation is an important challenge for nuclear materials. For a typical Pressurized Water Reactor (PWR), radiation damage of the Reactor Pressure Vessel (RPV) is one of the most important issues that determine the operating lifetime of a reactor. Accurate calculation with realistic uncertainty estimates of radiation damage is thus of great importance. In nuclear reactors, radiation damage of materials is mainly induced by energetic neutrons. The accurate uncertainty quantification of neutron radiation damage requires thus the complete covariance matrix of damage cross section and the covariance matrix of neutron flux spectrum. Covariance matrices of different Prompt Fission Neutron Spectra (PFNS) of 235U are propagated to the neutron flux spectra in a simplified PWR RPV (such as the examples shown in Ref. [1]). Covariance matrix of damage cross section is propagated from nuclear reaction model parameters and primary damage model parameters. The total uncertainties of neutron-induced displacement damage from both the uncertainties of PFNS and the uncertainty of damage cross section are deduced using the so-called “sandwich” formula. In addition to the calculation of total uncertainty of primary radiation damage in the RPV, Primary Knock-on Atom (PKA) spectra and the corresponding covariance matrices are obtained by considering the covariance matrix of neutron flux spectra (but without considering the uncertainties from nuclear reaction data). These PKA spectra and the associated covariance matrices can be used together with molecular dynamics or binary collision approximation simulations to accurately determine the radiation damage and the corresponding uncertainty. Using the standard Norgett-Robinson-Torrens formula, numerical results show that the complete covariance matrices of neutron flux (resulting from covariance matrices of PFNS) lead to about 4% relative uncertainty (depending on different PFNS) for the atomic displacement damage of the RPV, whereas only 1% uncertainty is obtained if the correlations of neutron flux spectra in the RPV at different energies are not considered for generating the PKA spectra. [1] L. Berge, “Contribution à la modélisation des spectres de neutrons prompts de fission. Propagation d’incertitudes sur un calul de fluence cuve,” PhD thesis, Université Grenoble Alpes, 2015.

Authors : R. E. Schäublin1,2, V. Vojtech1, S. Küchler1, S. S. A. Gerstl1,2, J. F. Löffler1
Affiliations : 1 Laboratory of Metal Physics and Technology, Department of Materials, ETH Zurich, 8093 Zurich, Switzerland 2 Scientific Center for Optical and Electron Microscopy, ETH Zurich, 8093 Zurich, Switzerland

Resume : Ferritic steel is one of the most promising candidate structural material of future fusion reactors. The extreme conditions when exposed to the fusion plasma, with high temperatures and 14 MeV fusion neutron irradiation, lead to a microstructural modification that impacts properties. Besides the generation of dislocation loops and cavities, there is Cr-rich α' precipitation, which leads to hardening and embrittlement, as well as changes in magnetic properties. In order to better understand and model its evolution a detailed description of its structure is needed. Fe-Cr model alloys are used to understand the fundamental mechanisms at play. Fe-20Cr (in wt.%) were considered in this work, with a thermally-driven decomposition induced by an anneal at 500 °C that leads to a high number density of α' precipitates that are few nanometers in diameter. The α' precipitates’ structure, composition and interface with the matrix were investigated using high-end transmission electron microscopy correlated to atom probe tomography and supported by molecular dynamics simulations.

15:50 Coffee Break    
Modelling of damage and defects III : Chairman to be defined
Authors : Kevin G. Field, Mingren Shen, Dane D. Morgan
Affiliations : University of Michgiran; University of Wisconsin; University of Wisconsin

Resume : Dislocation loop formation in body centered cubic (BCC) alloys are of interest for nuclear materials as their formation directly impacts material properties such as mechanical strength. The classic approach for the quantification of dislocation loops is to use transmission electron microscopy with specific two-beam imaging conditions followed by human counting and sizing. Recently, scanning transmission electron microscopy (STEM)-based techniques, such as on zone imaging where loop Burgers vector can be determined based on projected loop morphology, has been used to improve contrast and image interpretation. The reduced signal-to-noise in these STEM-based images are also idealized towards machine learning techniques to automatically count and size dislocation loops. Removal of the human element means a non-biased, community standard method for quantifying dislocation loops. Here, a framework based on STEM imaging and machine learning techniques will be outlined with results provided on irradiated FeCrAl alloys as an example.

Authors : T. Jourdan, C. Jacquelin, E. Meslin, M. Nastar
Affiliations : CEA, DEN, Service de Recherches de Métallurgie Physique, Université Paris-Saclay, F-91191 Gif-sur-Yvette, France

Resume : In thin foil irradiations, the point defect microstructure (voids, dislocation loops) can be modified by the presence of surfaces nearby. The magnitude of this effect is, however, not precisely known. If thin foil irradiations are used to reproduce bulk irradiations, this phenomenon must be assessed quantitatively to provide appropriate corrections to the cluster densities and sizes. In order to study in more detail surface effects on point defect cluster evolution, we have developed a object kinetic Monte Carlo code (OKMC) which includes elastic interactions between point defects and sinks. In particular, by coupling the OKMC code to a finite element solving of the elastic equilibrium in the presence of image traction forces, the correct elastic solution for a finite system is obtained. This enables us to simulate the evolution of microstructures in irradiated thin foils. We will show that elastic interactions between point defects and sinks can be significantly modified by the presence of surfaces, leading to different growth velocities from those observed in the bulk. Comparison with experiments of loop growth in aluminum thin foils will be discussed.

Authors : Juan Pablo Balbuena, Maria Jose Caturla
Affiliations : Department of Applied Physics, University of Alicante (SPAIN)

Resume : In a recent study we addressed the formation mechanisms of <100> loops in pure iron. In this model, the migration of the loops did not depend on the local environment. In fact, <100> loops were considered immobile while ½<111> loops migration followed an Arrhenius law using some predefined prefactors and migration barriers depending on their size. With the present study we want to move a step forward by considering long range interactions between dislocation loops of any size. Expressions for elastic interactions between dislocation loops derived from Dudarev et al. are included into our custom version of the kinetic Monte Carlo code MMonCa. Preliminary calculation show that, for high enough concentrations of loops, the mobility is biased by the presence of the other loops. We plan to perform simulations in irradiated pure iron to explore and evaluate the effects of such interactions into the one dimensional migration of ½<111> loops. In a last instance we plan to compare our results with those obtained by Arakawa et al. who obtained activation energies for loop diffusion of 1.3 eV, independent of the loop size, value that is one order of magnitude higher than that obtained with molecular dynamics simulations. This first approach in using elastic interactions are not accounting for thermally fluctuating small changes in the direction of the Burgers vector, as predicted by Boleininger e et al.

Authors : Karthik Guda Vishnu, Alejandro Strachan
Affiliations : School of Materials Engineering, Purdue University

Resume : Radiation hard microelectronic components are essential for aeronautics and space applications and the reduced feature sizes at advanced technology nodes make these devices more susceptible to failure due to irradiation. Our objective is to investigate the atomic-level mechanisms of irradiation-induced defect generation in semiconductor/dielectric heterostructures relevant for FinFETs and nanosheet transistors. We focus on the initial generation of radiation cascades and the annealing that takes place over the first tens of picoseconds using large-scale molecular dynamics simulations using accurate reactive interatomic potentials. We modeled Si/amorphous-SiO2 heterostructures and considered 10 keV Si and O primary knock-on atoms. A detailed analysis of the MD trajectories enabled us to characterize displaced atoms and defective ones. As could be expected, we find that the Si/SiO2 interfaces acts as sinks for O defects but, quite surprisingly, Si defects accumulate at interfaces and preferentially anneal in the bulk SiO2 and Si regions.

Authors : Santos, I., Aboy, M., Caballo, A., Marqués, L.A., López, P. & Pelaz, L.
Affiliations : Departamento de Electricidad y Electrónica, Universidad de Valladolid, ETSI Telecomunicación, Paseo de Belén 15, 47011 Valladolid, Spain

Resume : The emergence of alternative Si processes and devices has promoted applications outside the usual processing temperature window and the failure of traditional models of defect kinetics. They are based on Ostwald ripening mechanisms with parameters estimated by atomistic simulations, but generally pre-established defect configurations were assumed, formation energies were evaluated at 0 K and entropic contributions were neglected. We have carried molecular dynamics simulations of self-interstitial clustering in crystalline Si with no assumptions on preferential defect configurations. We have analyzed relevant defect configurations and we have characterized them in terms of their formation enthalpy and also their vibrational entropy calculated from their local vibrational modes. Our calculations illustrate that entropic terms are key to understand defect evolution in a wide temperature range. In addition, we show that, although different crystallographic planes favor specific defect symmetries and “magic numbers”, energy barriers make it difficult the transformation to the minimum energy configuration for each size. This allows the presence of non-expected small defects clusters that may lead to optical and electrical signals in low temperature processes. At very high temperatures, typical of sub-melting laser Si processing, we have found highly entropic liquid-like self-interstitial clusters embedded in the solid that dominate defect kinetics through a coalescence mechanism.

18:30 AWARD CEREMONY followed by SOCIAL EVENT    
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Symposium organizers
Alexandre BOULLENational Center for Scientific Research

Ceramics Research Institute - 12, rue Atlantis, 87068 Limoges, France

+33 5 87 50 23 82
Christophe ORTIZ (Main)CIEMAT

Laboratorio Nacional de Fusión por Confinamiento Magnético - Avenida Complutense, 40, 28040, Madrid, Spain

+34 914 96 25 82
Emmanuelle MARQUISUniversity of Michigan

Department of Materials Science and Engineering, 2300 Hayward St, Ann Arbor, MI 48109, USA

+1 734 764 8717
Tiziana CESCAUniversità di Padova

Dipartimento di Fisica e Astronomia "G. Galilei" - Via Marzolo, 8, I-35131 Padova, Italy

39 0498277044