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2018 Spring Meeting



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

Energetic particles (including electrons, neutrons, ions and photons) are widely used to modify materials or to emulate extreme environments. Particle/solid interaction usually generates damage whose formation mechanisms and subsequent evolution must be precisely characterized. This symposium provides a forum to discuss recent progress in the modeling and analysis of radiation damage in materials.


Energetic-particle irradiations are widely used both in the industry and in academic research laboratories to tune the physical properties (e.g. by ion doping) and microstructure of materials (e.g. nanopatterning, thin film growth, phase change) or to emulate radiation environments such as those encountered in space and nuclear reactors. Particle/solid interactions usually lead to (micro-)structural and/or chemical changes. In the case of controlled irradiation-induced material modifications, part of these changes may be deleterious as they can degrade the material properties (although there exists irradiation-defect engineering) and they are therefore considered as damage. On the other hand, when energetic particles are used to reproduce specific radiation environments, changes are purposely generated to evaluate the radiation-resistance of materials. Yet, in both cases, i.e. whether the damage is desired or suffered, its accurate characterization and fine description is a mandatory issue to tackle for the development and optimization of advanced materials and irradiation processes.

In this framework, the recent years have seen the development and improvement of experimental characterization techniques, computational tools, theoretical models and codes for data fitting. In addition, new ways to generate, emulate and simulate damage, either via computational methods or using innovative platforms delivering particle beams, are constantly being developed. The aim of this symposium is therefore to provide a forum for researchers to present and discuss new developments and findings in the generation, observation, description, and modeling of irradiation-induced damage in materials. 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 ionocovalent 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:

Generation, description and quantification of the radiation damage in materials includes the following topics:

  • Phase transformations, micro-structural changes, and surface effects
  • Defects and disorder at different length, space, and time scales
  • Quantitative analysis of radiation disorder
  • Simulation and modeling of damage formation and evolution
  • Experimental techniques for particle irradiation, characterization techniques and data-fitting codes

List of invited speakers:

  • Alexandre Boulle (CNRS / Univ. Limoges, Limoges, France)
    Radiation damage in materials: coupling X-ray diffraction with multi-scale numerical simulations”
  • Tiziana Cesca (University of Padova, Padova, Italy)
    “Energy-transfer and radiation damage in rare-earth ion-implanted silica: a photoluminescence investigation”
  • Jean-Paul Crocombette (CEA/DEN/DMN/SRMP, Saclay, France)
    "Rate Equation Cluster Dynamics approach to defect evolution in irradiated ceramics"
  • Pui-Wai Ma (UK Atomic Energy Authority, Culham, Oxfordshire; University of Oxford, and Imperial College London, UK)
    “Simple manifestations and the multiscale complexity of radiation damage”
  • Nuria Gordillo García (Autonomous University of Madrid, Madrid, Spain)
    “Study of damage induced by focused MeV ions in Diamond and its recovery after annealing by means of µ‑Raman and photoluminescence”
  • Emmanuelle Marquis (University of Michigan, Ann Harbor (MI), USA)
    “Quantification of irradiated microstructures using atom probe tomography”
  • Christophe Ortiz (CIEMAT, Madrid, Spain)
    “A BCA-MD method to simulate high-energy collision cascades in irradiated materials: Application to materials for Fusion"
  • Bertrand Radiguet (Université de Rouen, France)
    "Radiation resistance of a FeCrW model alloy nanostructured by severe plastic deformation”
  • Gihan Velisa (Oak Ridge National Lab, TN, USA)
    “On the quantification of irradiation-induced damage evolution in concentrated solid-solution alloys" 
  • Elke Wendler (University of Jena, Jena, Germany)
    “Modelling of damage accumulation in ion implanted materials”

A joint session with symposium K "Defect-induced effects in nanomaterials" is foreseen on the following topics:

  • In situ TEM and atom probe tomography
  • Ab initio calculations and numerical simulations

List of scientific committee members:

  • Eduardo Alves, University of Lisbon, Lisbon, Portugal
  • Charlotte Becquart, University of Lille, Lille, France
  • Maria José Caturla, University of Alicante, Alicante, Spain
  • Flyura Djurabekova, University of Helsinki, Helsinki, Finland
  • Thomas Jourdan, CEA-Saclay, Saclay, France
  • Sergei Kucheyev, Lawrence Livermore National Laboratory, Livermore (CA), USA
  • Giovanni Mattei, University of Padova, Padova, Italy
  • Lionel Thomé, CNRS/IN2P3, Orsay, France
  • Christina Trautmann, GSI Helmholtzzentrum, Darmstadt, Germany
  • William J. Weber, University of Knoxville, Knoxville (TN), USA


Selected papers will be published as a special issue of the journal Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms (Elsevier).

On-line submission via Elsevier’s Editorial System (EES) at  is required. The format, letter‑type and lay‑out will be the same as for the regular issues of the Journal (see Guide for Authors). The first manuscript is expected to be submitted no earlier than 18th June 2018. The submission deadline of first draft is 18th July 2018. The complete manuscript will be submitted to the Publisher not later than 10th September 2018.The length of the paper should not exceed 6 journal pages (8 journal pages for invited speakers).

Submission of a manuscript implies that it represents original work not previously published and not considered for publication elsewhere. All previously published material shall be fully acknowledged in the manuscript. Material from third parties can only be incorporated in the manuscript if the authors have procured permission in writing from each copyright holder.  

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Modelling of irradiation effects I : K. Lorenz & A. Redondo-Cubero
Authors : Elke Wendler
Affiliations : Friedrich-Schiller-Universität Jena Institut für Festkörperphysik Max-Wien-Platz 1 07743 Jena Germany

Resume : Ion implantation is a well established technique for the production of electronic and optical devices. The radiation damage, which is inherently connected with this process, is often undesired and makes subsequent damage recovery necessary. Additionally, the optimum annealing conditions may strongly depend on kind and concentration of damage produced during the ion implantation process. That is why for any new material becoming a possible candidate for new devises or functionalities, some basic studies on ion implantation effects are of interest. Since the early studies of ion implantation, modelling of damage evolution as a function of the implantation conditions has been used for better understanding the mechanisms of damage formation. In this presentation, the most common models will be reviewed and compared with each other. It is shown that similar physical concepts always results in similar dependences even if different mathematical approaches were used. Most of the experimental data shown, result from Rutherford backscattering spectrometry in channelling configuration (RBS/C). This is a common experimental method for studying radiation effects in crystalline materials, because it allows for easy quantification damage. The modelling of the physical processes during ion implantation becomes even more profitable when combining data from different experimental techniques. Examples will be shown for combining RBS/C with sub-gap optical spectroscopy and X-ray diffraction.

Authors : E.A. Kotomin, V.N. Kuzovkov, A.I. Popov
Affiliations : Institute of Solid State Physics, University of Latvia, Riga

Resume : Al2O3 (sapphire, corundum) is a promising material for fusion reactors, e.g. for components such as diagnostic windows, fibers, cables, monitoring equipment. Another two important optical materials are MgO and MgF2. Thus, this is very important to predict/simulate the kinetics of defect accumulation in these materials under neutron irradiation as well as long-time defect structure evolution. There were numerous experimental measurements of the primary defect accumulation kinetics (first of all, F color centers). As is well known, the F center mobility is much smaller than that of the complementary Frenkel defects – interstitial oxygen ions. Thus, at moderate radiation doses and temperatures, the kinetics of the F center annealing is controlled by their diffusion-controlled recombination with mobile oxygen interstitials. Despite numerous experimental data, very few theoretical efforts were devoted so far to the quantitative analysis of available kinetics, in order to extract main kinetic parameters- interstitial migration energy Ea and diffusion pre-exponent Do, necessary for further prediction of the secondary defect kinetics and radiation stability of sapphire and related materials. Such a theory was developed and applied recently to irradiated insulators [1,2]. In this study, we analyzed carefully the annealing kinetics for neutron irradiated oxides available from literature. The extracted migration energies in different experiments are reduced considerably, as radiation dose increases. The pre-exponent D0 is also much smaller than the estimate for a regular diffusion in crystalline solids. Moreover, we have observed a strong correlation between the activation energy Ea and pre-exponent Do(Ea) which is no longer constant but fits very well to the exponential function of Ea. In fact, as radiation dose increases, both the migration energy Ea and Do decrease, as the result defect diffusion rate effectively grows. These results are analysed in terms of the Meyer-Neldel rule [4] observed earlier in glasses and disordered materials. [1] V.N. Kuzovkov, E.A. Kotomin, A.I. Popov, R.Villa, Nucl. Inst. Meth. B 374, 107 (2016). [2] V.N. Kuzovkov, A.I. Popov, E.A. Kotomin et al, Low Temp. Phys., 42, 748 (2016). [3] A. Platonenko, D. Gryaznov, S. Piskunov, E.A. Kotomin et al, Phys. Stat. Sol. C 13, 932 (2016) [4] W. Meyer, H. Neldel, Phys. Zeitschrift, 38, 1014 (1937).

Authors : Lokesh VERMA (1,2) ; Laurence NOIROT (1) ; Philippe MAUGIS (2) ;
Affiliations : 1: CEA, DEN, DEC, Cadarache, 13108 Saint-Paul-lez-Durance, France ; 2: Aix Marseille Univ, Univ Toulon, CNRS, IM2NP, Marseille, France

Resume : Fission gases, especially Xenon, produced during irradiation in a nuclear fuel, have very low solubility in the UO2 fuel matrix and precipitate into bubbles. These gas bubbles interact with point defects of the fuel (vacancies, self-interstitials, etc.) causing significant microstructural evolution which may eventually affect the overall performance of the fuel. Spatially resolved models are developed to predict and model the microstructural change at the mesoscale. We present a new model, which focuses on modeling the interaction between point defects and xenon gas bubbles. This new model overcomes the limitation of the existing cluster dynamics models as it can account for spatialization as well as the limitation of the spatially resolved phase-field models as it can also account for very small defect clusters, even below the individual grid spacing. The modeling of the phenomena of coalescence of two bubbles in a vacancy supersaturation and the vanishing of a small bubble in the presence of a larger bubble (Ostwald ripening) prove the credibility of the new model. 2-D analysis of a case depicting the movement and growth of bubbles in a vacancy concentration gradient is presented and is in good agreement with the associated physics.

Combined experimental and computational study, simulation work I : G. Velisa & J.-P. Crocombette
Authors : A. Boulle(1), A. Chartier(2), J. -P. Crocombette(3), T. Jourdan(3), S. Pellegrino(4), A. Debelle(5)
Affiliations : (1)Institut de Recherche sur les Céramiques, CNRS UMR 7315, Limoges, France (2)CEA, DEN, DPC, SCCME, Gif-Sur-Yvette, France. (3)CEA, DEN, SRMP, Gif-sur-Yvette, France. (4)CEA, DEN, SRMP, Laboratoire JANNUS, Gif-sur-Yvette, France. (5)Centre de Sciences Nucléaires et de Sciences de la Matière, Université Paris-Sud, CNRS/IN2P3, Université Paris-Saclay, Orsay, France.

Resume : The interaction of energetic particles with matter usually leads to the generation of atomic defects and, with increasing defect density, to substantial microstructural changes, ranging from the formation of extended defects to structural phase transitions or amorphization. One of the most important issue to deal with in the study of radiation damage is its multi-scale character: whereas the primary events occur at the atomic scale, their consequences affect macroscopic volumes of the materials. On the path towards a better understanding of irradiation-induced damage in materials, the combination of atomic scale calculations with macroscopic structural characterization techniques plays a central role. This requires developing new models to describe disorder, up-scaling the calculations, and increasing the spatial resolution of the characterization techniques while keeping statistical relevance and atomic-scale sensitivity. We will present our recent efforts in coupling high-resolution X-ray diffraction (XRD) with molecular dynamics and rate-equation cluster dynamics calculations. Irradiated SiC and ZrC single crystals will be used as representative examples of amorphizable, and non-amorphizable materials, respectively. In both cases, an excellent quantitative agreement between computed damage build-up scenarios and experimental results is obtained. Details concerning the methodology will be given, in particular regarding the interpretation of the XRD data.

Authors : Y. Li*, C. Robertson, M. Shukeir, L. Dupuy
Affiliations : DEN-Service de Recherches Métallurgiques Appliquées, CEA, Université Paris-Saclay, F-91191, Gif-sur-Yvette, France

Resume : Plastic strain spreading in post-irradiated ferritic materials takes the form of thin, wavy shear bands. Associated plasticity mechanisms imply pinned, mobile dislocations, in interaction with radiation-induced dispersed defect loop populations. In the first preliminary step, we examine the effect of cross slip on the dislocation/loop interaction using dislocation dynamics simulations. A “composite dislocation source” configuration is adopted which consists of two connected arms or segments: one gliding in the primary slip plane, another one gliding in the cross-slip plane. It is found that the cross-slipped segment fosters dislocation unpinning, no matter the involved irradiation defect type (with Burgers vector [1-11] or [111]). In present work, the emphasis is laid on the contribution of the defect induced stress field for the aforementioned interactions. In the second step, the radiation-induced loops are then replaced by hard, impenetrable platelets (or facets) without any associated stress field. For facet cases, the total reaction time is close to that obtained with actual loops (within 0.5%). Moreover, the corresponding relative total strain errors are less than 10% at the reaction completion time, regardless of the loop type. In conclusion, the quantitative results indicate that cross-slip is possibly the dominant strain rate limiting mechanism, during post-irradiation plastic straining.

Authors : Luis A. Marqués (1), María Aboy (1), Iván Santos (1), Pedro López (1), Fuccio Cristiano (2), Antonino La Magna (3), Karim Huet (4), Toshiyuki Tabata (4), Lourdes Pelaz (1).
Affiliations : (1) Departamento de Electricidad y Electrónica, Universidad de Valladolid, E.T.S.I. de Telecomunicación, 47011 Valladolid, SPAIN. (2) LAAS-CNRS, Université de Toulouse, CNRS, 7 av. Du Col. Roche, 31031 Toulouse, FRANCE. (3) CNR-IMM, VIII Strada 5, 95121 Catania, ITALY. (4) SCREEN Semiconductor Solutions, Co., Ltd., LASSE, 14-30 rue Alexandre, 92230 Gennevilliers, FRANCE.

Resume : Defects in semiconductors appear as a side effect of processing or operation, and their presence has important technological implications. It is now well accepted that dopant implantation in Si generates a large self-interstitial (I) supersaturation, and that Is tend to aggregate in defect clusters that follow an Ostwald Ripening (OR) process driven by the reduction of defect formation energies. For decades, models based on the OR mechanism have been able to describe and predict the evolution and morphology of I-clusters during conventional thermal annealing steps. However, in recent ultra-fast laser annealing experiments, where Si is heated at temperatures close to the melting point just for several nanoseconds, unexpectedly large {001} I-loops form in a time scale incompatible with the OR mechanism. Such {001} loops had not been found in Si before and indeed were not expected from an energetic point of view. In this work, we combine focused experiments with molecular dynamics and phase-field simulations to investigate in detail the formation of {001} loops in nanosecond laser-annealed Si. We demonstrate that at temperatures close to the melting point, self-interstitial rich Si is driven into dense liquid-like droplets that are highly mobile within the solid crystalline Si matrix. These liquid droplets grow by a coalescence mechanism and eventually transform into {001} loops through a liquid-to-solid phase transition in the nanosecond timescale.

Experimental techniques for defect characterization, joint session Y-K : N. Sobolev & A. Debelle
Authors : Lide Yao, Sampo Inkinen, Sebastiaan van Dijken
Affiliations : NanoSpin, Department of Applied Physics, Aalto University School of Science, Finland

Resume : Oxygen defects can have a profound effect on the physical properties of transition metal oxides. Electric-field driven migration of oxygen vacancies provides a viable mechanism for the formation, rupture and reconstruction of conducting filaments in insulating oxides, an effect that is used in nanoscale resistive switching devices [1,2]. In complex oxides where magnetic, ferroelectric and superconducting phases emerge from strong correlations between localized transition metal valence electrons, oxygen vacancies can radically alter a plurality of intrinsic properties via valance changes and structural phase transitions [3]. The ability to reversibly control the concentration and profile of oxygen vacancies in oxide nanostructures would thus open up comprehensive prospects for new functional ionic devices. Advancements in this direction require experimental techniques that allow for simultaneous measurements of oxygen vacancy dynamics, atomic-scale structural effects and macroscopic physical properties. Here, we use in situ transmission electron microscopy (TEM) to demonstrate reversible switching between three resistance states in epitaxial La2/3Sr1/3MnO3 films. Simultaneous high-resolution imaging and resistance probing indicate that the switching events are caused by the formation of uniform structural phases. Reversible horizontal migration of oxygen vacancies within the manganite film, driven by combined effects of Joule heating and bias voltage, predominantly triggers the structural and resistive transitions. [1] R. Waser and M. Aono, Nature Mater. 6, 833 (2007) [2] J.J. Yang, D.B. Strukov, and D.R. Stewart, Nature Nanotech. 8, 13 (2013) [3] S.V. Kalinin and N.A. Spaldin, Science 341, 858 (2013)

Authors : Djamel Kaoumi, Ce Zheng
Affiliations : North Carolina State University

Resume : Ion irradiation is widely used to emulate radiation damage that occurs in structural alloys in a nuclear reactor. When combined with in-situ TEM, it provides a unique way to follow the kinetics of the formation and evolution of irradiation induced dislocation loops as well as the synergy of the interactions with the surrounding microstructure features. In this study we follow the microstructure evolution of two F/M steels of interest for nuclear applications irradiated in-situ in a TEM in terms of dislocation loop number density and size distribution as a function of dose (up to 20 dpa) and temperature (between 400 and 470C) and compare the dislocation burgers vector type with the case of bulk irradiation of the same alloys. The in-situ observations also allow us to follow the fate and impact of the initial dislocation network on the forming defects. Such spatially resolved information obtained with in-situ characterization is important for modeling efforts.

Authors : Przemyslaw Jozwik 1), Sergio Magalhães 1), Renata Ratajczak 2), Cyprian Mieszczynski 2), Elzbieta Guziewicz 3), Andrzej Turos 4), Roman Böttger 5), Rene Heller 5), Katharina Lorenz 1), Eduardo Alves 1)
Affiliations : 1. IPFN, Instituto Superior Técnico, Universidade de Lisboa, Estrada Nacional 10, 2695-066 Bobadela, Portugal 2. National Centre for Nuclear Research, A. Soltana 7, 05-400 Otwock-Swierk, Poland 3. Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, Poland 4. Institute of Electronic Materials Technology, Wolczynska 133, 01-919 Warsaw, Poland 5. Helmholtz Zentrum Dresden-Rossendorf, Bautzner Landstraße 400, 01328 Dresden, Germany

Resume : ZnO implanted with Rare Earth (RE)-ions is an extensively examined material due to its promising application in optoelectronics or photovoltaics. Such a wide band gap semiconductor is especially interesting as a host material for dopants because it is expected to overcome the temperature quenching effect observed in other materials (e.g. Si). RE-implantation is a great tool for a quick and efficient crystal modification, however it creates distortion of the ZnO structure due to the ballistic nature of the process. Accumulation and transformation of defects in ZnO formed at different fluences of RE-ions have been thoroughly examined at RT using complementary techniques: ion channeling (RBS/C), X-Ray diffraction (XRD) and X-Ray reflectivity (XRR). Defect types and the kinetics of their accumulation have been evaluated using Monte Carlo simulations of RBS/C spectra in the McChasy computer software. The driving forces of defect transformation occurring at certain critical RE fluences have been determined using simulations of the X-Ray techniques based on dynamical theory of XRD (the RC software). Different character of damage build-up for bulk crystals and thin-films of ZnO obtained using atomic layer deposition on GaN/Al2O3 substrate has been also observed and investigated. Presented research helps to understand the interaction between the impurity RE-ions and target atoms during implantation process. Implantation conditions can be properly prepared based on the results presented.

Authors : Elaina Reese, Li-Jen Yu, Bob Odette, Emmanuelle Marquis
Affiliations : University of Michigan, Ann Arbor, MI; University of California Santa Barbara, CA;

Resume : Atom probe tomography (APT) has provided unique insights into the development of microstructures under irradiation, through its unique chemical sensitivity in three dimensions and at the nanoscale. Using systematic experiments and quantitative data analysis methods to address common APT artefacts, we will discuss several examples of nanoscale clustering and precipitation in alloys under irradiation where dose rate effects play an important role on the resulting microstructures. One key example is precipitation of the a? phase in Fe-Cr alloys where phase decomposition is affected by cascade ballistic mixing at high dose rate leading to steady-state microstructures under ion irradiation that differ from those observed under neutron irradiation.

Authors : Elaina Reese, Li-Jen Yu, Bob Odette, Emmanuelle Marquis
Affiliations : University of Michigan, Ann Arbor, MI; University of California Santa Barbara, CA;

Resume : Atom probe tomography (APT) has provided unique insights into the development of microstructures under irradiation, through its unique chemical sensitivity in three dimensions and at the nanoscale. Using systematic experiments and quantitative data analysis methods to address common APT artefacts, we will discuss several examples of nanoscale clustering and precipitation in alloys under irradiation where dose rate effects play an important role on the resulting microstructures. One key example is precipitation of the a? phase in Fe-Cr alloys where phase decomposition is affected by cascade ballistic mixing at high dose rate leading to steady-state microstructures under ion irradiation that differ from those observed under neutron irradiation.

Authors : Sara D. Costa,1 Johan Ek Weis,1 Otakar Frank,1 Ossi Lehtinen,2 Arkady V. Krasheninnikov,2 Juhani Keinonen,2 and Martin Kalbac,1
Affiliations : 1)J. Heyrovsky Institute of Physical Chemistry of the AS CR, v.v.i., Dolejskova 2155/3, CZ-182 23 Prague 8, Czech Republic 2) Department of Physics University of Helsinki P.O. Box 43, FI-00014 Helsinki

Resume : Quantification of defects in carbon nanostructures is crucial for both fundamental science and practical applications. Raman spectroscopy is widely used to determine the number of defects in these materials, because it is non-destructive, fast and relatively easy to analyse. Here we used oxygen plasma or argon ions to induce specific amount of defects in graphene samples composed of monolayer, bilayer with Bernal stacked layers and bilayer with randomly stacked (turbostratic) layers. We applied isotopic labelling of graphene layers by 13C, which allowed us to address the Raman bands from the top and bottom graphene layers. Our results suggest that the phonons of the AB stacked bottom graphene layer are scattered by defects in the top graphene layer. Considering this effect we found that monolayer graphene and the top layer of turbostratic bilayer contains similar number of defects, while the top graphene layer of AB stacked bilayer contains fewer defects after a given time of oxygen plasma treatment. This result confirms that the behaviour of the top layer of turbostratic graphene is almost independent on the bottom layer, while the reactivity of the top layer in AB stacked graphene is significantly reduced by interactions with the bottom layer. Moreover,the phonon ‘scattering efficiency’ by the defects in neighbouring graphene layer seems to be dependent on the interactions between graphene layers, which results in the variation of the intensity of the D mode. While in the case of the turbostratic graphene samples this effect leads only to slight increase of the D mode intensity, for the AB stacked bilayer is the intensity of the D mode increased by almost 100%. Consequently, the relation between the Raman signatures of defects and the actual amount of defects in graphene is significantly influenced by a presence of defects in another graphene layer and by the stacking order of these graphene layers. The obtained thus results have a strong impact on the quantification of the number of defects in carbon nanostructures. References 1)M. Kalbac,Y-P. Hsieh, H. Farhat, L. Kavan, M. Hofmann, J. Kong, and M.S. Dresselhaus: Nanoletters, 10 (11),4619-4626 (2010). 2)Martin Kalbac, Ossi Lehtinen, Arkady V. Krasheninnikov and Juhani Keinonen: Adv Mat. 25 (7), 1004-1009 (2013). 3)Sara D. Costa, Johan Ek Weis, Otakar Frank, Martin Kalbac : Carbon 98, 592-598 (2016).

Authors : T. Calligaro(a), L. Beck(b), L. Bertrand(c), M. Chiari(d), V. Corregidor(e), F. Djurabekova(f) R. Freitas(g), S. Hageraats(h,c), I. Joosten(i), J. Kadissy(c), K. Keune(h), L. Maldanis(g), A. Mazzinghi(d), S. Siano(j), A. Simon(k), M. Stols-Witlox(h), Z. Szikszai(l), S. Webb(m)
Affiliations : (a) Centre de recherche et de restauration des musées de France C2RMF, Paris, France (b) Comissariat à l?énergie Atomique, CEA Jannus, Saclay, France (c) IPANEMA synchrotron SOLEIL, Gif-sur-Yvette, France (d) Laboratorio di Tecniche Nucleari per i Beni Culturali LABEC, Florence, Italy (e) Campus Tecnológico e Nuclear CTN, Bobadela, Portugal (f) University of Helsinki, Helsinki, Finland (g) Laboratório Nacional de Luz Síncrotron LNLS, Campinas, Brasil (h) Rijksmuseum, Amsterdam, The Netherlands (i) Cultural Heritage Agency, Amsterdam, The Netherlands (j) Institute of Applied Physics CNR IFAC, Rome, Italy (k) International Atomic Energy Agency, Vienna, Austria (l) Institute for Nuclear Research, Hungarian Academy of Sciences ATOMKI, Debrecen, Hungary (m) Stanford Synchrotron Radiation Light Source SSRL, Menlo Park, USA

Resume : Artworks and archaeological objects are commonly analyzed using energetic ions and X-rays produced by particle accelerators and synchrotrons. If such analytical methods are considered non-destructive, the highly focused radiation beams and long exposures can induce visible or non-visible modifications in the most fragile materials. Heritage stakeholders and scientists wish to investigate those effects rarely addressed till now. Developed under the umbrella of the IAEA, the present international research program targets the mechanism of modifications and their long-term evolution, and aims at determining thresholds and guidelines for a safer analysis using radiations. We report here the protocols and the first outcomes of a round-robin program on the effects of ionizing beams in two highly sensitive materials often present in historical paintings: lead white and lake pigments. Lead white paint layers were made from hydrocerussite and cerussite pigments in lipid and protein media (linseed oil and egg yolk) and lake layers from an organic dye precipitated on a metallic salt (mordant) in an organic media. The samples were exposed to ionising beams under classical conditions employed to characterise heritage materials: MeV protons, deuterons and helium ions from electrostatic accelerators, keV X-ray beams from synchrotrons. The induced modification were characterised using optical (UV-vis, luminescence), mechanical (3D microscopy and OCT) and chemical methods (µ-IRTF, GC-MS, HP-LC, SEM-EDX, ESR).

Computational methods for damage description, joint session Y-K : F. Djurabekova & P.-W. Ma
Authors : Jean-Paul crocombette
Affiliations : DEN-Service de Recherches de Métallurgie Physique, CEA, Université Paris-Saclay, F-91191 Gif sur Yvette, France

Resume : Recent progress in the modeling of irradiation primary damage The evolution of materials under irradiation depends on many factors. Its simulation involves multi-scale approaches both in space and time. At the smallest time scale, it starts by the modeling of the damage directly created by the atomic displacement cascades initiated by the fast moving neutrons or ions. This so-called primary state of damage pilots the subsequent number and nature of point and extended defects. The diffusion, recombination, clustering, etc. of these defects drive the evolution of the material under irradiation. The modelling of primary irradiation events of realistic energies is a difficult task especially when one wishes to describe ion irradiation. Several strategies exist. First, Binary Collision Approximation (BCA) calculations are very fast but approximate. Second, Molecular Dynamics (MD) simulations are more accurate but much heavier. I will present recent progress which has been made in these two approaches. As far as BCA calculations are concerned, the community relies almost entirely on the SRIM code[]. This code, while easy to use, suffers from severe drawbacks: it seems to be no longer maintained and it is not open-source so that no one really knows what is really coded in it. Some research groups have recently tried to design modern BCA codes. I will focus on what I believe to be a promising alternative to SRIM, the Iradina [] code. The coding of Kinchin-Pease (SRIM so-called “quick calculation of damage) in Iradina shed light on what could be called nasty little secrets of SRIM KP calculations. MD simulations enable a much more precise description of the displacement cascades. However they are quite heavy which strongly limits the energy of calculated cascades and number of cascades that are performed in a given study. This gives poor statistics on the nature and amount of damage at high energies and forbids in practice the direct comparison with experimental irradiations. In particular it is not possible to describe with MD the complete trajectory of an incoming external ion and the induced atomic displacements in the target. To reproduce such complete ion cascade, we have designed a modified MD simulation of cascades: Cell Molecular Dynamics for Cascades (CMDC)[ 1 2]. The goal of this code is to accelerate as much as possible the calculation of cascades by MD without loss of accuracy on the results. CMDC is based on the specificities of the cascade unfolding. The idea is to build the simulation box as the cascade develops. More and more atoms are added as the cascade unfolds. Symmetrically, the parts of the materials where the cascade is over, i.e. when the local structure does not evolve anymore on the MD scale (after the ballistic and thermal phases), are removed from the dynamic simulation. I will present validations of the CMDC code compared to standard MD simulations in the cases of Fe PKA in iron and U PKA in UO2. I shall then turn to results of cascade simulations in two ordered alloys (Ni3Al and UO2) for energies ranking between 0.1 and 580keV for both light and heavy constituents. The average number of subcascades and average number of defects per subcascades as a function of ballistic energy exhibit an unexpected variety of behaviors above the threshold for subcascade formation. Finally modeling of irradiations corresponding to real irradiations, (390 keV Xe and 4 MeV Au irradiations in UO2) will be presented with some emphasis on the differences between thin lamellas and bulk samples. [1] : [2] : [3] : J.-P. Crocombette and T. Jourdan, Nucl. Instrum. Methods Phys. B 352, 9 (2015). [4] J. P. Crocombette, L. Van Brutzel, D. Simeone, and L. Luneville, J. Nucl. Mater. 474, 134 (2016).

Authors : F. Granberg, K. Nordlund, A. Lehtinen, L. Laurson, and M. J. Alava
Affiliations : University of Helsinki, Helsinki, Finland; Aalto University, Espoo, Finland

Resume : Plastic deformation of crystalline materials is governed by the features of stress-driven motion of dislocations. In the case of irradiated steels subject to applied stresses, small dislocation loops as well as nanosized precipitates are known to interfere with the dislocation motion, leading to an increased yield stress as compared to pure crystals. We study the combined effect of nanosized precipitates and interstitial glissile 1/2 111 dislocation loops on the mechanical properties of iron, using largescale three-dimensional discrete dislocation dynamics simulations. Precipitates are included in the simulations using our recent multi-scale implementation [A. Lehtinen et al., Phys. Rev. E 93 (2016) 013309], where the strengths and pinning mechanisms of the precipitates are determined from molecular dynamics simulations. In the simulations we observe dislocations overcoming precipitates with an atypical Orowan mechanism which results from pencil-glide of screw segments in iron. Even if the interaction mechanisms with dislocations are quite different, our results suggest that in relative terms, precipitates and loops of similar sizes contribute equally to the yield stress in multi-slip conditions.

Authors : Denise Carpentier, Thomas Jourdan, Yann Le Bouar, Mihai-Cosmin Marinica
Affiliations : DEN-Service de Recherches de Métallurgie Physique, CEA, Université Paris-Saclay, F-91191, Gif-sur-Yvette, France ; DEN-Service de Recherches de Métallurgie Physique, CEA, Université Paris-Saclay, F-91191, Gif-sur-Yvette, France ; LEM CNRS/ONERA, Châtillon, France ; DEN-Service de Recherches de Métallurgie Physique, CEA, Université Paris-Saclay, F-91191, Gif-sur-Yvette, France

Resume : The behavior of materials under irradiation crucially depends on the microstructure evolution, which is driven by the absorption of point defects by the sinks (dislocations, cavities and loops). Cluster dynamics is a noteworthy theoretical tool of material science that can predict the microstructure evolution over long physical time. In this approach, the absorption kinetics of point defects depends on the values of sink strengths. An accurate evaluation of sink strengths is therefore necessary to obtain a reliable prediction of the materials evolution under irradiation. This work aims at computing accurate sink strength values by explicitly simulating the diffusion of point defects using Object Kinetic Monte-Carlo simulations. This study emphasizes the importance of elasticity on the diffusion of point defects. More precisely, elastic interactions between sinks and point defects are taken into account, and defects are described by their elastic dipoles and polarizabilities at stable and saddle points, which are computed by ab initio calculations. Our study of point defect migration to single sinks reveals that the anisotropy of point defects at saddle points is a key parameter in sink strength calculations, as it strongly affects the migration paths of point defects. We have also analyzed the migration of point defects in microstructures containing several sinks to investigate the effect of the neighboring clusters on sink strengths.

Authors : Graeme W. Watson, Aoife K. Lucid
Affiliations : School of Chemistry and CRANN, Trinity College Dublin, The University of Dublin

Resume : The doping of ceria with trivalent ions is known to enhance the O2- conductivity of ceria in the intermediate temperature range, which is important for a number of applications including energy storage and conversion. In this work, we consider the doping of ceria and its effect on diffusion in bulk and multicrysalline materials (grain boundaries). DFT simulations are used to investigate (i) the formation of charge compensating vacancies and their role in O2- conductivity and (ii) their effect on the reducibility of bulk CeO2. Here we consider both the position of the dopant ions and vacancies, which shows a clear relationship between the dopant ionic radius and its position and the impact on the reduction energy which is directly correlated with the defect structure. A state of the art force field derived from ab-initio data is derived and used to perform molecular dynamics simulation of bulk CeO2 and the Σ3(111) grain boundary. Segregation of the O vacancies to the boundary is observed along with enhanced diffusion of O2- parallel to the GB.

Authors : J. P. Balbuena, L. Malerba, N. Castin, G. Bonny, M. J. Caturla
Affiliations : Dept. Fisica Aplicada, Facultat de Ciencies, Universitat d'Alacant, Alacant, E-03960, Spain; SCK-CEN, Belgium

Resume : In this work we describe a diffusion model for large scale simulations of concentrated alloys. The simulation domain in this model is divided into small cells of the order of the lattice parameter. A migration rate is calculated for each migrating particle attending to the solute concentration of the cell containing the migrating point defect (i.e. vancacies and self-intersititials) and the concentration of its neighbouring cells. A bias in the activation energy of particle migration is calculated using the free enthalpy expressions developed by M. Levesque and co-workers for FeCr alloys [1], using an effective solute concentration for each involved cell from I. Dopico and co-workers [2]. Chromiun-enriched precipitates are achieved after an annealing treatment at 500ºC starting from a homogeneous Cr distribution of Fe20at%Cr, as it is experimentally determined by S. Novy and co-workers [3]. References [1] M. Levesque, E. Martinez, C-C. Fu, M. Nastar, F. Soisson. "Simple concentration-dependent pair interaction model for large-scale simulations of FeCr alloys", Physical Review B 84, 184205 (2011). [2] I. Dopico, P. Castrillo, I. Martin-Bragado. "Quasi-atomistic modeling of the microstructure evolution in binary alloys and its application to the FeCr case", Acta Materialia 95 (2015) 324-334. [3] S. Novy, P. Pareige, C. Pareige. "Atomic scale analysis and phase separation understandings in a thermally aged Fe-20at%Cr alloy", J. Nucl. Mat. 384 (2009) 96-102.

Authors : A. Platonenko, Yu. Zhukovskii, D. Gryaznov, E.A. Kotomin
Affiliations : Institute of Solid State Physics, University of Latvia, Riga, Latvia

Resume : Spinel-structured magnesium aluminate (MgAl2O4) possesses high optical transparency, from visible to infrared wavelength range, enhanced strength and melting temperature, as well as excellent chemical and radiation resistance. Combination of these properties makes it suitable for a number of technological applications, including windows for fusion reactors and inert matrices for nuclear fuels, where spinel demonstrates remarkable resistance to radiation damage from neutrons and light ions. Radiation induces in spinel Frenkel pairs of neutral or charged vacancies and interstitials O¬i, as well as numerous anti-site defects. We present the results of periodic ab initio simulations on the atomic, electronic structure and mobility of oxygen interstitials in MgAl2O4 spinel using DFT-LCAO method implemented in the CRYSTAL14 computer code. Defect calculations were performed within conventional (56 atoms) cells and 112 atom supercells, for both neutral and charged interstitials. The energetically favorable configuration for Oi were obtained using so-called site symmetry approach. Defect geometries, charge distribution, density of states and vibrational frequencies for both types of defects were analysed and compared. The interstitials form dumbbells with regular O atoms. The O-O distances are 1.42 Å for neutral, and 1.95 Å for charged Oi, respectively. Mobility of both type of defects was evaluated by simulation of Oi diffusion from the O-O dumbbell to another nearest regular oxygen atom. Estimated diffusion barriers are ~1.1 eV for neutral and ~0.8 eV for charged oxygen interstitial. Our results were compared with other calculations and available experimental data.

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Irradiation effects in metal alloys I : B. Radiguet & Ch. Ortiz
Authors : P.-W. Ma1, M.Y. Lavrentiev1, J.B.J. Chapman1, J.S. Wrobel2, D. Nguyen-Manh1, S. L. Dudarev1
Affiliations : 1CCFE, UK Atomic Energy Authority, Culham Science Centre, Oxfordshire OX14 3DB, UK; 2Division of Materials Design, Faculty of Materials Science and Engineering, Warsaw University of Technology, Wołoska 141, 02-507 Warsaw, Poland

Resume : The properties of iron alloys and steels significant to the use of these materials in magnetic fusion technology and engineering are their high temperature structural stability, allowing for the high thermal efficiency of operation of a fusion power plant, and magnetic properties that are expected to be compatible with the requirements of magnetic plasma confinement. Magnetism of iron alloys influences their phase stability, for example the position of the gamma-loop in the FeCr phase diagram [1], the solubility of chromium, and the relative stability of high temperature alpha and gamma phases [1,2]. Of particular interest is the effect of microstructure on magnetic properties, where simulations, confirmed by experimental observations, show that magnetism of iron is enhanced by vacancies produced by irradiation. The Curie temperature of FeCr alloys varies over a broad temperature range as a function of microstructure, increasing rapidly because of Cr precipitation [3]. We investigate the dynamics of magnetism in FeCr and FeNi alloys, relating it to the alloy microstructure, using dynamic magnetic cluster expansion models, parameterized using databases of DFT-generated atomic configurations. Dynamic magnetic cluster expansion simulations provide valuable information about the response of alloys to fluctuating magnetic field and temperature on a million atom scale, necessary for exploring structural and magnetic properties of steels under realistic plasma confinement conditions. [1] M.Y. Lavrentiev et al., Magnetic cluster expansion model for bcc-fcc transitions in Fe and Fe-Cr alloys, Phys. Rev. B 81, 184202 (2010); [2] P.-W. Ma et al., Dynamic simulation of structural phase transitions in magnetic iron, Phys. Rev. B 96, 094418 (2017); [3] M.Y. Lavrentiev et al., Magnetic cluster expansion model for high-temperature magnetic properties of iron and iron–chromium alloys, Journ. Appl. Phys. 109, 07E123 (2011)

Authors : B. Kaiser¹, E. Gaganidze¹, C. Dethloff¹, D. Brimbal², L. Beck² and J. Aktaa¹
Affiliations : ¹Karlsruhe Institute of Technology, Institute for Applied Materials, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany; ²CEA, DEN, Service de Métallurgie physique, Laboratoire Jannus, F-91191 Gif-sur-Yvette, France

Resume : For the design of future fusion devices radiation damage caused by high energy neutrons in structural materials of the first wall is a critical issue. In this context we investigate irradiation induced damage evolution in the European reduced activation ferritic martensitic steel EUROFER97 by means of a rate model for helium bubble nucleation and growth and Fe³⁺/He⁺ dual ion beam irradiation. The irradiation was carried out at the Jannus laboratory, CEA Saclay, introducing a damage of 15 dpa and a helium content up to 260 appm. The samples were irradiated at temperatures of 330 °C, 400 °C and 500 °C. In the post-irradiation analysis TEM bright-field and weak-beam-dark-field imaging modes are applied. Homogeneously distributed bubbles are observed in the matrix at all temperatures. At the highest irradiation temperature of 500 °C, heterogeneous formation of bubbles at grain boundaries and line dislocations is found in addition. With rising irradiation temperature the density of bubbles decreases and the bubble diameter increases. Dislocation loops with mean diameters of 4.2 nm and 6.1 nm were found at 330 °C and 400 °C, but not at 500 °C. The characterization of the Burgers vectors showed a domination of ½ a0 <111> orientation. A kinetic rate model is applied for nucleation and growth of helium bubbles determining the size and density of bubbles. The temperature dependence of these quantities is in good qualitative agreement with the experimental observation.

Authors : William Asplet , Marie-France Barthe, Pierre Desgardin , Francois Jomard
Affiliations : CNRS, CEMHTI UPR3079, Univ. Orleans, F-45071 Orléans, France ; GEMaC, 45 avenue des Etats Unis 78035 Versailles cedex, France

Resume : In the perspective of the development of the new generations of nuclear reactors based on fission or fusion one of the main challenges is to find new materials with more and more specific properties. Oxide-dispersion strengthened (ODS) steels are the main candidate for the structural materials of blanket/first-wall in fusion reactors as well as fuel cladding in advanced fast reactors. So they will be submitted to hard conditions : high temperatures (500°C-1000°C) and also high level of damage (200dpa)[1,2]. Based on a Fe-Cr ferritic or ferritic-martensitic matrix (Cr content from 9 to 18%) ODS steels demonstrate excellent properties (good high temperature creep resistance, irradiation resistance to swelling) due to their bcc structure and to the fine dispersion of oxides nanoparticles (Y,Ti,O). These ODS alloys are obtained by mechanical alloying of steel and oxide powders[3]. Their properties depend on the composition, size and dispersion into the matrix of nanometric oxides particles. The formation mechanism of these nanoparticles is not yet cleared and vacancies have been considered to be of most importance in the nanoparticles formation and nucleation. Strong interactions between vacancies and Yttrium and Oxygen have been already detected by Positron Annihilation Spectroscopy experiments and also by DFT calculations [4, 5]. By combining the techniques of positron annihilation spectroscopy (PAS) and secondary ion mass spectrometry (SIMS), we aim to obtain information about the interaction between vacancy defects and solutes such as Y, Ti, and O in Fe. For these studies, solutes (Yttrium and/or Oxygen) have been introduced within vacancies by using implantation performed at room temperature (300K) into high purity Fe samples (99,99%). Single or co-implantations with Yttrium at 1.2MeV and Oxygen at 285keV have been realized in order to introduce both elements at the same depth. . Doppler broadening spectroscopy performed in a slow positron accelerator allows to probing the possible vacancy type defects including pure or complexed vacancy clusters in the implanted layers. Their profiles are compared with solutes (Yttrium, Oxygen) depth profiles measured by SIMS. The effect of annealing temperature on these profiles is studied up to 550°C. Some extra experiments have been made with EXAFS (Extended X-Ray Absorption Fine Structure ), to check the formation of precipitates. [1] S.J. Zinkle and J.T. Busby, Materials Today 12 (2009) 12. [2] J. Knaster, A. Moeslang, T. Muroga Materials research for fusion Nat. Phys., 5 (2016), pp. 424–434 [3]. D.T. Hoelzer, J. Bentley, M.A. Sokolov, et al., J. Nucl. Mater. 367–370 (2007) 166–172. [4] Thesis C He ,2014 ,CEMHTI ,University of Orleans [5] Thesis C Barouh ,2015,CEA-CEMHTI,Unversity of Orleans

Authors : Martin Owusu-Mensah (I), Stéphanie Jublot-Leclerc (I), Aurélie Gentils (I), Vladimir A. Borodin (II), Joël Ribis (III)
Affiliations : (I) CSNSM, Univ Paris-Sud, CNRS/IN2P3, Paris-Saclay, Orsay, France; (II) NRC “Kurchatov Institute” and NRNU MEPhI, Moscow, Russia; (III) CEA, DEN, DMN, SRMA, Paris-Saclay, Gif-sur-Yvette, France

Resume : The combination of radiation damage and incorporation of elemental species in a material during ion implantation is a recognized technique of nanostructure production. Ion implantation allows de-correlating the contributions of individual experimental parameters and, when accompanied by appropriate modeling, gives better understanding of the mechanisms involved in nano-oxide particle nucleation and growth, including, in particular, role of defects. This report presents the results of ion-beam synthesis of Ti oxide nano-particles by the implantation of low energy (keV) Ti+ and O+ ions into a high purity Fe-10wt%Cr alloy at room temperature, followed by high-temperature thermal annealing. The micro-structural changes induced by ion implantation have been characterized by conventional, energy-filtered and high resolution Transmission Electron Microscopy (TEM), as well as Time-of-Flight Secondary Ion Mass Spectroscopy. The nucleation of Ti oxide nano-particles via the ion beam synthesis was clearly demonstrated. Both in situ TEM annealing and bulk specimens annealing results will be presented in terms of the size, chemical composition and crystallographic structure of the nano-oxide particles.

Combined experimental and computational study, simulation work II : E. Wendler & A. Redondo-Cubero
Authors : Gihan Velişa1, Shijun Zhao1, Mohammad W. Ullah1, Elke Wendler2, Haizhou Xue2, Ke Jin1, Miguel L. Crespillo3, Hongbin Bei1, WilliamJ. Weber3,1, and Yanwen Zhang1
Affiliations : 1Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA 2Friedrich-Schiller-Universität Jena, Institut für Festkörperphysik, Max-Wien-Platz 1, 07743, Jena, Germany 3Department of Materials Science & Engineering, University of Tennessee, Knoxville, TN 37996, USA

Resume : The chemical complexity in concentrated solid solution alloys (SP-CSAs) can be modified by varying the number, type, and concentration of the constituent elements. Studying the effects of chemical complexity has advanced understanding and revealed some incredible physical properties, including excellent mechanical properties, good corrosion resistance, and enhanced radiation performance. Disentangling the role of chemical complexity on defect dynamics and microstructure evolution may provide new paradigms for designing structural materials for next-generation nuclear power systems. A specially selected set of SP-CSAs with different type and number of alloying elements (Ni80Fe20, Ni80Cr20 and Ni40Fe40Cr20) are investigated under Mn ion irradiation at room temperature. Considerable improvement in radiation resistance is observed in the ternary alloy, as compared to the binary alloys and elemental Ni in the low fluence regime. The results from ion channeling measurements and MD simulations suggest that an effective way to improve radiation performance is to suppress defect production and enhance recombination at early stages. Besides irradiation studies at room temperature, experimental and computational approaches are also used to investigate the damage accumulation in elemental Ni, binary NiFe, and quaternary NiFeCoCr irradiated at 16 K. Our results show that the defect evolution is delayed with increasing compositional complexity from elemental Ni to binary NiFe, and to the quaternary NiFeCoCr alloy, which is attributed to sluggish diffusion and dynamic annealing of simple defects at early stages during irradiation. The 16 K results demonstrate that the enhanced radiation resistance in complex SP-CSAs is an intrinsic property that is not a thermally activated process. Moreover, we show that the radiation response is not simply dependent on the number of alloying elements, but can be also tuned by altering the concentrations of specific elements. This work was supported by the Energy Dissipation to Defect Evolution, an EFRC funded by the U.S. DOE, BES.

Authors : A.I.Titov1, P.A.Karaseov1, K.V.Karabeshkin1, V.B.Shilov2, G.M.Ermolaeva2, M. W. Ullah3, F. Djurabekova3, A. Kuronen3, K.Nordlund3
Affiliations : 1 Peter the Great Polytechnic University, St.Petersburg, Russia 2 Vavilov State Optical Institute, St. Petersburg, Russia 3 Helsinki University, Helsinki, Finland

Resume : GaN has attracted considerable interest due to the wide range of its applications in high power electronics, microwave and optoelectronic devices. Ion bombardment is an attractive choice in GaN-based device fabrication. This contribution will describe the results of investigation of mechanisms of irradiation?induced damage formation in GaN. We used keV monatomic and molecular ions. Ion-implantation-induced effects in wurtzite GaN bombarded with F, P, PF2, PF4, and Ag ions at room temperature are studied experimentally and by cumulative MD simulation in the correct irradiation conditions. In the low dose regime, damage formation is correlated with a reduction in photoluminescence decay time. In the high dose regime, it is associated with the thickness of the amorphous/disordered layer formed at the sample surface. In all the cases studied, an increase in the collision cascade density remarkably enhances the damage accumulation rate. The cumulative MD simulations do not reveal any significant difference in the total amount of both point defects and small defect clusters produced by light monatomic and molecular ions. On the other hand, increased production of large defect clusters by molecular PF4 ions is clearly seen in the vicinity of the surface. Ag ions produce almost the same number of small, but more large defect clusters compare to the others. This findings show that the higher probability of formation of a large defect clusters is important mechanism of the enhancement of stable damage formation in GaN under molecular, as well as under heavy monatomic ion irradiation. Work was supported by RFBR grant 18-08-01213.

Authors : Serge MAILLARD
Affiliations : DEN/DEC/SESC/LM2C, CEA Cadarache

Resume : In-pile irradiation of UO2 fuel material produces a large amount of fission gas atoms (mostly xenon) that may either precipitate or be released outside the material, thus increasing the fuel pin breakdown probability. Since irradiation defects are known to be very abundant and to strongly interact with the gas atoms, a Cluster Dynamics (CD) modelling approach was developed (among other techniques such as phase field related models) because it naturally allows one to account for both gas and defects using relatively rapid calculations. Nevertheless, because of the coupled behavior between xenon and defect, it is quite difficult to extract the relevant diffusion coefficients from gas release (i.e. annealing of samples implanted at a very low xenon dose). For this reason, a multi-scale approach based on atomistic calculations was developed to evaluate the various parameters of the CD model, i.e. defect or xenon production rates and formation or migration energies. A complete CD model in UO2 would require 3 dimensions (one for each component U, O, Xe) which would yield intractable calculations. We will present our model emphasizing the way 1) we reduced the model dimension and 2) we took into account the sensitivity of the mobile defect parameters to the local oxygen potential in UO2 as determined by the irradiation damage. We will also show the assessment of the model through a comparison with release experiments.

Authors : G. Roma, F. Bruneval, L. Martin-Samos
Affiliations : G. Roma and F. Bruneval: DEN-Service de Recherches de Métallurgie Physique, CEA, Université Paris-Saclay, F-91191 Gif sur Yvette, France ; L. Martin-Samos: CNR-Demokritos, Trieste, Italy

Resume : Polyethylene (PE), one of the simplest and most used aliphatic polymers, is generally provided with a number of additives, in particular antioxidants, because of its tendency to get oxidized. Carbonyl defects, a product of the oxidation of PE, are occurring in various forms, in particular saturated ones, known as ketones, where a C=O double bond substitutes a CH$_2$ group, and various unsaturated ones, i.e., with further missing hydrogens. Many experimental investigations of the optical properties in the visible/UV range mainly attribute the photoluminescence of PE to one specific kind of unsaturated carbonyls, following analogies to the emission spectra of similar small molecules. However, the reason why saturated carbonyls should not be optically detected is not clear. We investigated the optical properties of PE with and without carbonyl defects using perturbative GW and the Bethe-Salpeter equation in order to take into account excitonic effects. We discuss the calculated excitonic states in comparison with experimental absorption/emission energies and the stability of both saturated and unsaturated carbonyl defects. We conclude that the unsaturated defects are indeed the best candidate for the luminescence of oxidized PE, and the reason is mainly due to oscillator strengths.

Authors : H. Vazquez[1], M. Schleberger[2] and F. Djurabekova[1]
Affiliations : 1. Affiliation Helsinki Institute of Physics and Physics Department, University of Helsinki 2. Fakultät für Physik and CENIDE, Universität Duisburg-Essen, Duisburg, Germany

Resume : Previous studies have shown that in layered crystals such as SrTiO3 or Mica, SHI irradiation under grazing incidence can produce chains of hillocks/grooves on the surface of the material. These structures have length scales of tens of nanometers and were associated with the local electron density along the ion track [1, 2, 3]. We develop a new approach to simulate SHI grazing incidence irradiation in order to reveal the underlying mechanism of hillock and groove formation. The new method calcualtes the energy locally deposited by the ion based on the electronic density along the trajectory and simulates the electronic energy redistribution and transfer to the lattice according to the two-temperature model. This energy is added to the atoms and simulated with Molecular Dynamics (MD), producing structural changes in the material such as hillocks or grooves. The simulated hillocks show similar length, interdistance and height as in the experiments, supporting the hypothesis that the hillocks appear due to the variation of the local electron density along the ion track. In the simulation, the hillocks and grooves observed on the surface are associated to molten and sublimated material respectively. Finally we study the dependence of the hillock separation on the irradiation angle and crystal orientation and search for characteristic features which could be observable in future experiments. References: -[1] Akcöltekin, Ender, et al. "Creation of multiple nanodots by single ions." Nature Nanotechnology 2.5 (2007): 290-294. -[2] Gruber, Elisabeth, et al. "Swift heavy ion irradiation of CaF2?from grooves to hillocks in a single ion track." Journal of Physics: Condensed Matter 28.40 (2016): 405001. -[3] Aumayr, Friedrich, et al. "Single ion induced surface nanostructures: a comparison between slow highly charged and swift heavy ions." Journal of Physics: Condensed Matter 23.39 (2011): 393001.

Characterization methods for investigating radiation damage : T. Cesca & A. Boulle
Authors : N. Gordillo, R.J. Jiménez-Riobóo, A. de Andrés, M. A. Ramos, and M.D.Ynsa
Affiliations : Departamento de Física Aplicada, Universidad Autónoma de Madrid (UAM), Spain; Centro de Micro-Análisis de Materiales, Universidad Autónoma de Madrid (CMAM-UAM), Spain; Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC), Spain; Departamento de Física de la Materia Condensada and IFIMAC, Universidad Autónoma de Madrid (UAM), Spain; Instituto Nicolás Cabrera (INC-UAM), Madrid, Spain

Resume : Diamond is a well-known electrical insulator (with a bandgap of 5.45 eV) with a high industrial and technological value because of its exceptional hardness, very high thermal conductivity and high charge-carrier mobility. Moreover, its electrical and optical properties can be significantly modified by introducing charge-carriers by ion implantation [1?3]. Nevertheless, the lattice is frequently affected due to the damage inherent to the ion implantation [4?6]. This damage can be later healed with thermal treatments, but in diamond it can lead to graphitization, which is the most stable phase at room temperature, above a certain graphitization threshold [7]. However, graphitization can be avoided for buried layers above the amorphization threshold [8,9]. In this work, we have used micro Raman and photoluminescence spectroscopy in order to study the damaged lattice of irradiated diamond and its recovery after high-temperature annealing. In particular, (100) diamond crystals were irradiated with highly-focused 9 MeV B and C ions with fluences in the range 1e15 ? 1e17 ions/cm2. In order to heal the irradiation damage, the samples were annealed at 1000 ºC during 1h. The lattice damage was studied by micro Raman and photoluminescence before and after annealing as a function of fluence and layer-depth. Our results show in which particular conditions amorphized diamond, produced by deeply-buried ion implantations, can be returned to crystalline diamond, avoiding graphitization. [1] J.F. Prins, Diam. Relat. Mater. 10 (2001) 1756?1764. [2] T. Vogel, J. Meijer, A. Zaitsev, Diam. Relat. Mater. 13 (2004) 1822?1825. [3] A. Lohrmann, S. Pezzagna, I. Dobrinets, P. Spinicelli, V. Jacques, J.-F. Roch, J. Meijer, A.M. Zaitsev, Appl. Phys. Lett. 99 (2011) 251106. [4] M.D. Ynsa, F. Agulló-Rueda, N. Gordillo, A. Maira, D. Moreno-Cerrada, M.A. Ramos, Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. At. (2017). [5] F. Agulló-Rueda, M.D. Ynsa, N. Gordillo, A. Maira, D. Moreno-Cerrada, M.A. Ramos, Diam. Relat. Mater. 72 (2017) 94?98. [6] F. Agulló-Rueda, N. Gordillo, M.D. Ynsa, A. Maira, J. Cañas, M.A. Ramos, Carbon 123 (2017) 334?343. [7] C. Uzan-Saguy, C. Cytermann, R. Brener, V. Richter, M. Shaanan, R. Kalish, Appl. Phys. Lett. 67 (1995) 1194?1196. [8] J.O. Orwa, K.W. Nugent, D.N. Jamieson, S. Prawer, Phys. Rev. B 62 (2000) 5461. [9] P. Olivero, S. Rubanov, P. Reichart, B.C. Gibson, S.T. Huntington, J.R. Rabeau, A.D. Greentree, J. Salzman, D. Moore, D.N. Jamieson, S. Prawer, Diam. Relat. Mater. 15 (2006) 1614?1621.

Authors : Yann Mazel(1), Jean-Paul Barnes(1), Sébastien Legendre(2), Emmanuel Nolot(1), Céline Bout(1), Agnès Tempez(2)
Affiliations : (1) Univ. Grenoble Alpes, CEA, LETI, MINATEC Campus; (2) HORIBA FRANCE SAS

Resume : Secondary ion mass spectrometry (SIMS) is the technique of reference for measuring depth distribution of ion implants. SIMS offers high sensitivity and high depth resolution but quantification is usually complex and requires matrix matched reference samples. In addition SIMS instrumentation is a metrology tool only accessible to a limited number of operators. The plasma sputtering based technique, Plasma Profiling Time of Flight Mass Spectrometry (PP-TOFMS), provides similar composition versus depth information as SIMS but much faster (typically a factor 10). This is due to not only the fast erosion rate of the high density and low energy plasma source but also the fact that sample does not need to be transferred to a high vacuum chamber and thanks to the ultra-fast and quasi-simultaneous TOFMS detection of all mass-to-charge ratios of the ions from the sample. Furthermore the separation between sputtering and ionisation processes makes this technique much less matrix dependent than SIMS. A calibration free semi-quantification can be performed by simply rationing the amount of ions detected from a given layer. PP-TOFMS data of boron implanted Si and SiGe will be shown. Results will be compared to TOF-SIMS measurements and aspects of analytical performance with regards to sensitivity, quantification, depth resolution, repeatability and sample throughput will be discussed. Other examples in microelectronics and nanotechnology will also be presented. [1]A. Tempez, S. Legendre, J.-P. Barnes, E. Nolot, Combining plasma profiling TOFMS with TOF-SIMS depth profiling for microelectronic applications, J. Vac. Sci. Technol. B 34, 03H120 (2016).

Authors : M. Lang1, E. O?Quinn1, R.I. Palomares1, W. Cureton1, C.L. Tracy2, J. Neuefeind3, C. Trautmann4,5, and R.C. Ewing2
Affiliations : 1Department of Nuclear Engineering, University of Tennessee, Knoxville, TN, 37996, USA; 2Department of Geological Sciences, Stanford University, Stanford, CA, 94305, USA; 3Chemical and Engineering Materials Division, Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge, TN, USA; 4GSI Helmholtzzentrum für Schwerionenforschung, 64291 Darmstadt, Germany; 5Technische Universität Darmstadt, 64287 Darmstadt, Germany

Resume : We present neutron total scattering with pair distribution function (PDF) analysis as a new strategy for the characterization of radiation effects in materials. Key to this approach is the use of swift heavy ions with a very high penetration depth to produce sufficiently large irradiated sample mass (~150 mg). Irradiation experiments were performed at the UNILAC accelerator of the GSI Helmholtz Center with ions of specific energy of 11.4 MeV/u. The irradiated samples were characterized at the Nanoscale Ordered Materials Diffractometer (NOMAD) beamline at the Spallation Neutron Source (Oak Ridge National Laboratory). We investigated various ion-induced structural modifications, such as defect formation (CeO2 and ThO2), disordering (Er2Sn2O7), and amorphization (Dy2TiO5). Neutrons scatter strongly from low-Z elements, permitting a detailed analysis of both cation and anion defect behavior. PDF analysis elucidates the local defect structure, including changes in site occupation, coordination, and bond distance. This is particularly important for characterizing radiation effects in oxides, as structural modifications induced by ion-beam irradiation are seldom ordered over long length scales and in extreme cases result in complete loss of long-range order (i.e., amorphization). Initial results demonstrate that irradiation-induced structural modifications are much more complex than previously thought with distinct processes occurring over different length scales.

Authors : A.Ribet, I.Monnet and C.Grygiel
Affiliations : Centre de recherche sur les Ions, les Matériaux et la Photonique (CIMAP-GANIL) Boulevard Henri Becquerel BP 5133 14070 Caen cedex 5, France

Resume : Sapphire is a common substrate for a broad variety of materials due to its optical transparency, insulating property and its hexagonal structure allowing often an easy epitaxial growth. During the use in real world conditions, such materials can be exposed to extreme environments and their intrinsic properties can thereafter be modified. Thus it is necessary to study under ion irradiation the behaviour of sapphire substrate and its potential influence on the features of the epitaxial top layer. In this work, defect formation and structural modifications of a-Al2O3 induced by swift heavy ion irradiation are investigated. (0001)-Al2O3 single crystals have been irradiated along the c-direction by 92 MeV Xe at room temperature. The irradiation experiments have been performed at GANIL facility (Caen). High resolution X-ray diffraction and in-plane diffraction are mainly used to characterize samples. Using different fluences, the mechanisms of structural modifications are investigated. In the communication, the evolution of the X-Ray patterns recorded in different configurations for several reflections will be discussed. A careful study of the reflection characteristics will be detailed to highlight the material damaging through strain and amorphization. The kinetics of these evolutions with the ion fluence will be discussed. We will show how much the c-parameter (parallel to ion beam) and the a-parameter (perpendicular to ion beam) are affected by irradiation in the MeV range. A depth profile will be suggested as an explanation for the structural behaviour of Al2O3 under 92 MeV Xe irradiation. Complementary RBS/c, Raman spectroscopy and TEM results will be shown and discussed for a better understanding of these modifications under irradiation.

Authors : J.G. Mattei1, X. Portier1, F. Moisy1, M.C. Sequeira2, D. Levasseur1, E. Gardes1, A. Ribet1, C. Grygiel1, K. Lorenz2, C. Wetzel3, Mota-Santiago4, P. Kluth4 and I. Monnet1
Affiliations : 1 CIMAP, CEA-CNRS-ENSICAEN-Normandie Université BP5133 F-14070 Caen cedex5 France; 2 IPFN, Instituto Superior Técnico, Campus Tecnológico e Nuclear, Bobadela LRS, Portugal; 3 Department of Physics and Future Chips Constellation, Rensselaer Polytechnic Institute, Troy, New York, USA; 4 Department of Electronic Materials Engineering, Research School of Physics and Engineering, Australian National University, Canberra ACT 2601, Australia

Resume : The nitride semiconductors, (Al,Ga,In)N, display optical and electronic properties which can provide useful applications such as light-emitting diode devices. Swift heavy ions are well known to induce structural and chemical changes in the materials which can modify these properties [1]. InN and GaN specimens were irradiated at GANIL facility with 950 MeV Pb while InGaN quantum well samples were irradiated at the Australian National University with 185 MeV Au. Transmission electron microscopy (TEM) instrument was used to describe the disorder induced in the InN, GaN and InGaN Quantum Wells irradiated samples [2]. High resolution TEM investigations were performed to identify the structural order along the ion tracks and the strain induced in the lattice neighboring the ion tracks. Chemical investigations were carried out by STEM - Energy Dispersive X-ray Spectroscopy and Electron Energy Loss Spectroscopy techniques to analyze the fluctuation rate of each element across an ion track and to describe their chemical environment within the track. STEM HAADF analysis reveals the presence of discontinuous tracks in GaN samples and a density fluctuation around the track. Chemical profiles plotted across ion tracks show a decrease of gallium rate within the ion path while higher density of gallium is clearly observed outside the track. Furthermore, the nitrogen K near-edge fine structure investigation reveals the encapsulation of nitrogen bubbles inside the ion tracks. [1] Ackermann J., Angert N., Neumann R., et al. Nucl Instrum Methods Phys ResB, 1996, vol. 107, no 1-4, p. 181-184. [2] Sall, M., Monnet I., Moisy, F. et al. Journal of Materials Science, 2015, vol. 50, no 15, p. 5214-5227.

Irradiation-induced modification of physical properties : N. Gordillo & K. Lorenz
Authors : T. Cesca, B. Kalinic, N. Michieli, C. Maurizio, C. Scian, G. Mattei
Affiliations : Department of Physics and Astronomy, NanoStructures Group (NSG), University of Padova, via Marzolo 8, I-35131 Padova, Italy

Resume : Ion implantation is the technique of election for the local doping of substrates in out-of-equilibrium conditions. In the last years, this capability was efficiently exploited to incorporate optical rare-earth emitters in silica, as Er3+ ions emitting at 1.54 microns at room temperature, and to couple them with specific plasmonic nanostructures, to control and enhance their excitation and emission efficiency. To this regard, ion implantation is of paramount importance for controlling the early stages of nucleation in the synthesis of noble metal quantum clusters, which proved to be very efficient broadband sensitizers for the Er3+ excitation, and to get the incorporation of both optical emitters and sensitizing species on predefined patterns. In this presentation, we will report on the results of systematic photoluminescence (PL) characterizations aimed at investigating the mechanisms of energy-transfer between metallic quantum clusters and rare-earth ions incorporated in silica by ion implantation and subsequent thermal treatments. Moreover, the role of irradiation-induced defects on the luminescent emission properties and the cluster growth was investigated in order to decouple any detrimental effect due to implantation damage from the efficient sensitization process.

Authors : A.Sveshnikova, A.Akbulatov, S.Tsarev, S.Luchkin, K. Stevenson, V.Petrov, P.Troshin
Affiliations : Skolkovo Institute of Science and Technology; Lomonosov Moscow State Universit; Institute of Problems of Chemical Physics, Russian Academy of Science

Resume : Solar cells based on complex lead halides with the perovskite structure have attracted particular attention of material scientists and engineers all over the world. Rapid improvement in terms of power conversion efficiencies, which exceeded 22% in combination with potentially low fabrication costs of perovskite solar cells might accomplish a revolution on the PV market. Perovskite solar cells can also be fabricated on ultrathin and lightweight substrates, which makes them particularly attractive for both terrestrial and space applications. Conventional solar cells based on silicon, gallium arsenide or A3B5 type absorbers are usually installed on the satellites. However, these materials rapidly degrade under severe radiation exposure in space. While high-energy particles can be blocked efficiently by the solar cell encapsulation layers, the degradation induced by gamma irradiation from random Sun flares can hardly be avoided. Therefore, development of novel PV materials and solar cell architectures capable of sustaining significant gamma irradiation represents a highly relevant task. In this paper, we will report an experimental evaluation of the gamma radiation tolerance of perovskite solar cells. The effects of the light absorber (MAPbI3 vs. triple cation MA(x)FA(y)Cs(z)PbBrnI3-n) formulation and the electron transport materials on the device stability will be discussed in detail. The proposed pathways of the radiation-induced degradation will be presented with a particular focus on the self-healing effects revealed in these experiments. Finally, we will conclude on the potential of the perovskite photovoltaics with respect to the space applications.

Authors : Valentina Bonino1,2, Lorenzo Mino3, Daniele Torsello2,4, Angelo Agostino3, Carmelo Prestipino5, Carlo Lamberti1, Matteo Fretto6, Marco Truccato1,2
Affiliations : 1 Department of Physics, Interdepartmental Centre NIS, University of Torino, via Giuria 1, 10125, Torino, Italy 2 I.N.F.N., Sezione di Torino, via Giuria 1, I-10125 Torino Italy 3 Department of Chemistry, Interdepartmental Centre NIS, University of Torino, via Giuria 7, 10125, Torino, Italy 4 Department of Applied Science and Technology, Politecnico di Torino, Corso Duca degli Abruzzi 24, I-10129 Torino, Italy 5 Institut Sciences Chimiques de Rennes, UMR-CNRS 6226, Campus de Beaulieu, Université de Rennes 1, 35042, Rennes, Cedex, France 6 Nanofacility Piemonte INRiM (Istituto Nazionale di Ricerca Metrologica), Strada delle Cacce 91, 10135, Torino, Italy

Resume : The recent advent of nanofocused hard X-ray beams and of their high power densities has raised the point of synchrotron-induced material damage. In the case of the high temperature superconductors Bi2Sr2CaCu2O8+? (Bi-2212) and YBa2Cu3O7-? (Y-123), whose properties highly depend on the non-stoichiometric oxygen content ?, photon damage has been studied and controlled for the purpose of X-ray nanopatterning (XNP). Indeed, Josephson devices have been fabricated out of Bi-2212 by means of 50 nm beams at 17.5 keV, also allowing device on-line monitoring during fabrication [1]. Although the microscopic mechanism for defect formation is not fully understood, Monte Carlo simulations have proved that photogenerated electrons can knock on the Bi-2212 interstitial oxygen atoms and significantly modify their amount ? [2]. Moreover, nano-XRD maps have revealed the formation of mosaic domains showing a misalignment that increases with increasing the irradiation dose. XNP has been recently demonstrated also in a more conventional oxide like TiO2 by means of directly writing conducting channels via nanobeam irradiation. These findings represent a potential breakthrough for the whole class of oxide materials, paving the way to the fabrication of novel devices via XNP, which could be advantageous in terms of device heat dissipation and of its native 3D structure. 1. L. Mino, et al., Scientific Reports, 2017, 7(1), 9066 2. D. Torsello, et al., Physical Review Materials, 2018, 2(1), 014801

Authors : L. Basiricò1, A. F. Basile1, P. Cosseddu2, S. Gerardin3, T. Cramer1, M. Bagatin3, A. Ciavatti1, A. Paccagnella3, A. Bonfiglio2 and B. Fraboni*1
Affiliations : 1Department of Physics and Astronomy, University of Bologna, Italy 2Department of Electrical and Electronic Engineering, University of Cagliari, Italy 3Department of Information Engineering, University of Padova, Italy

Resume : Organic electronic devices fabricated on flexible substrates are promising candidates for applications in environments where flexible, light-weight and radiation hard materials are required1. In this work, we have recently reported on how flexible devices based on 6,13-Bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) can be used as real-time, direct ionizing radiation detectors2, opening unprecedent perspectives for space applications of organic electronics. We monitored the device parameters as threshold voltage, charge mobility and trap density of TIPS-pentacene based OTFTs, before and after irradiation by high-energy protons3. The observed reduction of charge carrier mobility following irradiation can be only partially ascribed to the increased trap density. Indeed, Atomic Force Microscopy reveals morphological defects occurring in the organic dielectric layer induced by the impinging protons, which, in turn, induce a strain on the TIPS-pentacene crystallites lying above. The effects of this strain are investigated by Density?Functional?Theory simulations of two model structures, which describe the TIPS-pentacene crystalline films at equilibrium and under strain. The two different density of states distributions in the valence band have been correlated with the Photo-Current spectra acquired before and after proton irradiation. We conclude that the degradation of the dielectric layer and the organic semiconductor sensitivity to strain are the two main phenomena responsible for the reduction of OTFT mobility after proton irradiation.

Authors : Ph. Bolz1,2, A. Prosvetov1,2, C. Trautmann1,2, M.Tomut1
Affiliations : 1 GSI Helmholtzzentrum für Schwerionenforschung, Germany; 2 TU Darmstadt, Germany

Resume : Radiation-induced hardening and dynamic mechanical properties changes of isotropic graphite are analyzed by nano- and micro-indentation. The samples were exposed to C, Ca, Xe, Sm, Au and U ion beams in the GeV energy regime. The irradiations were performed at the M-branch facility at the UNILAC accelerator at GSI achieving fluences between 1e11 ions/cm² and 5e13 ions/cm². For graphite, a general increase of Young?s modulus and surface hardness with increasing ion fluence is observed. For fluences larger than 1e13 ions/cm2 and energy-loss values larger than 20 keV/nm, the hardness and Young?s modulus increased up to 500%. Investigations by Raman spectroscopy indicate that the steep increase in hardness is associated with an irradiation-induced allotropic transformation of graphite to a glassy carbon structure. In contrast to amorphization by keV-MeV ion energies, this type of transformation is related to specific structural defects created by ions with electronic energy-loss above a certain threshold. In addition, we investigated beam-induced embrittlement by repetitive nano-impact measurements that show an earlier failure of the material in high strain rate fatigue tests. The damping coefficient is decreased in irradiated samples indicating a reduction in crystallite size and an evolution towards a stiffer structure by cross-linking of the basal planes in graphite.

Authors : Chandan Sharma,Ajay Visvkarma,Robert Laishram,Ashok K Kapoor,DS Rawal,Seema Vinayak,Rajendra Singh
Affiliations : Indian Institute of Technology Delhi, Hauz Khas, New Delhi, India Solid State Physics Laboratory, Lucknow Road,Delhi, India

Resume : We report on the effect of gamma (γ) radiation on epitaxially grown AlGaN/GaN heterostructure using metal organic chemical vapor deposition (MOCVD) technique and the high electron mobility transistor (HEMT) devices fabricated on same structure separately. The layer structure has been irradiated cumulatively with γ-ray dose of the order of 10kGy. HR-XRD analysis of irradiated sample shows the reduction in defect density due to lowering in FWHM in comparison to that of pristine sample. While edge dislocations remain unaffected, a decrease in screw dislocation density along (0002) plane has been observed. Hall measurement shows an improvement in the mobility post irradiation which can be attributed to the reduction in defect density. The reduction in defect density is also supported by CL imaging. Electrical characterization of HEMT devices post γ irradiation shows a negative shift in the threshold voltage with a trend of improvement in the drain current. Simultaneously, transfer length measurement (TLM) characterization shows reduction in the contact resistance due to the local thermal heating effect after irradiation. Further, SEM imaging corroborates TLM analysis where the increase in local thermal heating is due to reduced perimeter to area ratio of metal-semiconductor contact. Hence this study infers that initial dose of γ irradiation enhances the quality of GaN material and improves the metal-semiconductor interface in the devices.

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Modelling of irradiation effects II : P. Karaseov & A. Debelle
Authors : Christophe J. Ortiz
Affiliations : Laboratorio Nacional de Fusión por Confinamiento Magnético - CIEMAT Avenida Complutense, 40 28040 Madrid, Spain

Resume : Since decades Molecular Dynamics (MD) and the Binary Collision Approximations (BCA) are used to simulate collision cascades in solids under irradiation. MD algorithm uses interatomic potentials and integrates the equations of motion of all atoms in the system. It is thus well-suited to study complex phenomena at the atomistic level and many-body effects. However, simulation boxes become very large as the initial energy of the projectile increases, resulting in a large number of atoms in the system and hence, a prohibitive computing time to solve all the Newton's equations. Using MD when the energy of the projectile is high (~ MeV) is thus not realistic. On the other hand, Binary Collision Approximation (BCA) is much more efficient than Molecular Dynamics (MD) to simulate collision cascades in solids as it only follows displaced atoms. The BCA is thus preferred over MD when simulating high-energy collision cascades in solids . However, though the BCA is accurate in the high-energy regime, it is not able to accurately predict last stages of cascades, i.e. when atoms have a low kinetic energy, since it does not take into account the long-range potential between atoms and neither solves for the equations of motion of each atom as MD does. As a consequence, the BCA cannot account for mechanisms such as the recombination of defects or the formation of clusters during the cooling phase of the cascade. In this work we combine the BCA and the MD, which results in a significant speedup of MD calculations. In order to demonstrate the accuracy of the BCA-MD method, we shall focus on the case of Fe under irradiation, a material of high importance for future fusion reactors. We shall show that the results obtained with the BCA-MD are in excellent agreement with those obtained with full MD calculations. We shall demonstrate that collision cascades for initial projectile energies in the order of MeV and that would be prohibitive for full MD calculations, can be simulated in a reasonable computational time with the BCA-MD.

Authors : J. P. Balbuena, A. Sand, C. Björkas, K. Nordlund, R. Schäublin, M. J. Caturla
Affiliations : Dept. Fisica Aplicada, Facultat de Ciencies, Universitat d'Alacant, Alacant, E-03960, Spain; University of Helsinki, Finland; ETH, Zurich, Switzerland

Resume : Future nuclear power plants will have to cope with severe harsh radiation environments generating defects in their structural materials that will undergo changes in their mechanical properties. Both experimental and simulation investigations are being carried out to observe which defects are being formed in such materials as well as to understand their formation mechanisms. Ferritic iron alloys are proposed, among others, as structural materials for such nuclear power plants, so this work is focused in such materials. Ion beam irradiation experiments using Fe ions are a prolific source of current data that is aimed to be reproduced and explained using simulation codes. In order to validate our simulation results we are using two experiments in which samples of UHP Fe at different temperatures are being irradiated with Fe ions of two different energies: 1) 0.5 MeV Fe ions toward UHP Fe samples at room temperature in the experiment of Prokhodtseva and co-workers [1], and 2) 2.0 MeV Fe ions toward UHP Fe samples at 500ºC from the experiment of Brimbal and co-workers [2]. We determine the cascades of vacancies and self-interstitials using a combination of codes. First we use SRIM [3] as well as MDRANGE [4] to calculate the deposited energy as a function of depth. With this information, we generate the initial distribution of defects (vacancies and self-interstitials) using a database of collision cascades generated by molecular dynamics simulations. Then, this defect distribution is used as the input data to study the evolution of microstructures with the OKMC code MMonCa [5]. Two different models for the formation of immobile self-interstitial (SIA) dislocation loops <100> are introduced (and separately evaluated) in this code. One of the mechanisms allows the formation of such loops as the interaction result of two 1/2<111> SIA loops under certain conditions [6,7], and the other one establishes that it can be rarely produced during the cascade collisions [8]. One important component on the microstructure evolution in Fe, carbon, is also included in these calculations. References [1] A. Prokhodtseva, B. Décamps, A. Ramar, R. Schäublin, Acta. Mat. 61, 6647-7034 (2013) [2] D. Brimbal, B. Décamps, J. Henry, E. Meslin, A. Barbu, Acta. Mat. 64, 391 (2014) [3] SRIM, J.F. Ziegler, M.D. Ziegler, J.P. Biersack, Nucl. Instrum. Meth. B 268, 1818-1823 (2010) [4] K. Nordlund, F. Djurabekova, G. Hobler, Phys. Rev. B 94, 214109 (2016) [5] I. Martin-Bragado, A. Rivera, G. Valles, J.L. Gomez-Selles, M.J. Caturla, Computer Physics Communications 184, 2703-2710 (2013) [6] J. Marian et al. PRL 88, 25 (2002) [7] H. Xu, R. Stoller, Y. Osetsky, D. Terentyev, PRL 110, 265503 (2013) [8] M.C. Marinica, F. Williaime, J.P. Crocombette, PRL 108, 025501 (2012)

Authors : Igor Milov (1), Igor Makhotkin (1), Ryszard Sobierajski (2), Nikita Medvedev (3,4), Vladimir Lipp (5), Nail Inogamov (6,7), Vasily Zhakhovsky (6,7), Viktor Khokhlov (7), Viacheslav Medvedev (8,9), Eric Louis (1), Fred Bijkerk (1)
Affiliations : 1) MESA+ Institute for Nanotechnology, University of Twente, Drienerlolaan 5, 7522 NB Enschede, The Netherlands; 2) Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, PL-02-668 Warsaw, Poland; 3) Institute of Physics, Czech Academy of Sciences, Na Slovance 2, 182 21 Prague 8, Czech Republic; 4) Institute of Plasma Physics, Czech Academy of Sciences, Za Slovankou 3, 182 00 Prague 8, Czech Republic; 5) Center for Free-Electron Laser Science CFEL, Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, 22607 Hamburg, Germany 6) Dukhov Research Institute of Automatics, Rosatom, Moscow 127055, Russia; 7) Landau Institute for Theoretical Physics, Russian Academy of Sciences, Chernogolovka 142432, Russia; 8) Institute for Spectroscopy RAS, Fizicheskaya str. 5, Troitsk, Moscow, Russia 108840; 9) ISTEQ BV, High Tech Campus 9, 5656AE Eindhoven, The Netherlands;

Resume : We present theoretical studies of single-shot damage of ruthenium thin films induced by femtosecond extreme ultraviolet (EUV) free-electron laser (FEL). Previous experimental analysis of the damaged spots with different types of microscopy (SEM, TEM and AFM) revealed the nature of the induced damage to be melting of the Ru surface with subsequent spallation of the top Ru layer. A combined model is used to simulate the interaction of the EUV fs pulse with the Ru film: (i) Photoabsorption and nonequilibrium electron kinetics are described with the Monte Carlo code XCascade-3D [1], which enables to calculate the time-space evolution of electron cascades induced by the EUV pulse. We show that since the electron cascading practically ends within a femtosecond, the EUV-induced electronic distribution in Ru may be considered as thermalized at all times. (ii) Diffusion of thermalized electrons into the depth of the material and heating of the lattice via electron-phonon interaction are described with the two-temperature model [2]. (iii) Finally, the lattice dynamical effects such as melting and spallation are modeled with the two-temperature hydrodynamics code [3] and the classical molecular dynamics approach. The simulations show that heating of Ru by the FEL EUV pulse occurs in the stress confinement regime. Large stresses develop inside the material during the heating process, leading to spallation of the top Ru layer, which is in agreement with the mentioned experimental observations. [1] V. Lipp, N. Medvedev, and B. Ziaja, SPIE Optics+ Optoelectronics, International Society for Optics and Photonics, 102360H, 2017. [2] Anisimov, S. I., B. L. Kapeliovich, and T. L. Perelman. Zh. Eksp. Teor. Fiz 66.2 (1974): 375-377. [3] Inogamov, N. A., et al. Applied Surface Science 255.24 (2009): 9712-9716.

Authors : Peter Hähner, Ana Ruiz Moreno
Affiliations : European Commission, Joint Research Centre, Directorate G: Nuclear Safety and Security, Westerduinweg 3, 1755 LE Petten, The Netherlands

Resume : Nano- and micromechanical testing is important for assessing damage induced by neutron irradiation (minimized volume of activated material) and ion irradiation (limited penetration depth) the latter being of interest for the emulation of neutron irradiation damage. Besides validated experimental methods a robust analytical framework is required. A modification to the Nix–Gao framework is introduced to describe the breakdown of the scaling regime of the indentation size effect (ISE) at small indentation depths. The modification consists in accounting for the spatial profile of the density of geometrically necessary dislocations (GNDs). The model sheds new light on the role of GNDs and statistically stored dislocations, thereby rationalizing a material's propensity to developing pile-up or sink-in behaviour, respectively, and elucidating the effect of residual stresses. The model is applied to a quantitative analysis of the ISE of the ferritic-martensitic steels T91 and Eurofer97, here investigated in the non-irradiated reference state, but envisaged as structural materials for nuclear fission and fusion applications, respectively. Depth-controlled single cycle measurements at various final indentation depths, force-controlled single cycle, force-controlled progressive multi-cycle measurements, and continuous stiffness measurements (CSM) all using a Berkovich tip at room temperature have been combined to assess the ISE. The present model captures the extremely high dislocation density associated with martensitic lath boundary misorientation. While the quasi-static methods show good agreement, CSM gives somewhat different results; hence breakdown of the scaling regime is sensitive to the test mode.

Irradiation effects in metal alloys II : E. Marquis & J.-P. Balbuena
Authors : B. Radiguet, X. Sauvage, A. Etienne, C. Pareige, N. Enikeev, M. Abramova, Andrey Mazilkin, J. Ivanisenko
Affiliations : Normandie Univ, UNIROUEN, INSA Rouen, CNRS, Groupe de Physique des Matériaux, 76000 Rouen, France Institute for Nanotechnology, Karlsruhe Institute for Technology (KIT), D-76021 Karlsruhe, Germany Ufa State Aviation Technical University, Ufa, Russia

Resume : The origin of the microstructural changes under irradiation is the super-saturation of point defects that can agglomerate in the form of loops or voids and can enhance or modify solute atom diffusion, resulting in enhanced or induced precipitation or segregation. In ultrafine grain (UFG) alloys, the volume fraction of grain boundaries is dramatically higher than in coarse grain (CG) materials. Since grain boundaries act as point defect sinks, a large part of irradiation induced defects can be annihilated. Therefore, a limitation of radiation damage is expected. The objective of the work presented here is to investigate the stability of a nanostructured FeCrW alloy under irradiation. A Fe-14%Cr-1%W model alloy was nanostructured by high pressure torsion in order to get grains of several tens of nanometers. Both CG and UFG alloys were ion irradiated at 400°C in JANNUS facilities. Their microstructures were characterized by transmission electron microscopy and atom probe tomography. Nanoindentation tests were performed to estimate irradiation hardening in both CG and UFG alloys. This talk will describe experimental results. The effect of nanostructuration on the stability of the microstructure and the hardening will be discussed.

Authors : M.Roldán (1)*, P. Fernández (1,) C. Ortiz (1), A. Gómez-Herrero (2) and D. Jiménez-Rey (1).
Affiliations : (1) CIEMAT. National Fusion Laboratory. Technology Division. Avda. Complutense, 40. 28040. Madrid. Spain. (2) National Center for Electronic Microscopy. Av. Complutense s/n.28040 Madrid.

Resume : Nowadays, one of the most important challenges in the development of fusion energy is to predict and mitigate the effects of large levels of transmuted gas atoms (He and H) along with high displacement damage produced by high energy neutrons that affect the mechanical properties of the structural materials and gives rise to phenomena like swelling. In fact, many issues related to the irradiation defects are still unknown. The understanding of the macroscopic effects of loops due to irradiation on the structural materials requires further research at different levels: experimental observations by TEM in basic and simple metals (model alloys) as a backup to modelling. Computational modelling of radiation damage in fusion materials may help to predict the damage effects and how could mitigate it and contribute also to design of DEMO (DEMOnstration fusion power plant) in the medium term. Modelling would help to understand the underlying physical mechanisms of the damage and to predict its evolution along the reactor's lifetime. In order to achieve a sturdy computational approach, the models and computational codes must be validated with experiments. In the present research, we have performed some validation experiments in order to evaluate the formation of dislocation loops in pure Fe when the loops have been created far away from the surface since the Fe ions are highly energetic (20 MeV) in bulk. This would prevent the generated dislocation loops from migration and disappearance at the surface of the well-known surface effect acting as defect sink. Understanding dislocation loop formation and interaction mechanisms are the main objectives of this research, given that this interaction is suspicious of being responsible for embrittlement of structural steels in fusion reactors. On the other hand, we carried out as well the same irradiations on thin films (electropolished TEM discs), in which the ions get through them, and the effect of free surfaces should be enhanced. The irradiations were as follows: 5 and 10 dpa (in peak, being lower on thin films) at different irradiation temperatures 350 and 450 ºC. After irradiations, the damaged areas were observed under transmission electron microscopy (TEM). Bulk specimens were prepared by means of lift-out technique and their surface will be polished with low Ar kV. The lamellae contained all the irradiation depth, so a deep characterization correlating depth and dpa level was achieved. However, thin films were studied directly by TEM after irradiation maintaining a constant dpa level within the thickness. The defects that were taken into consideration are only dislocation loops of the types ½ a0 <111> and a0 <100> since those are the only ones that form in ferritic materials, in agreement with the literature are considered. A swelling phenomenon produced by the loops (depending on their nature, vacancy or interstitials) was calculated comparing between thin films and bulk irradiation. The microstructure was completely different comparing the thin film thickness with the first 150 nm of the bulk irradiation, even having the same PKA profile calculated by MARLOWE. Large <100> loops of hundreds of nanometers were detected on thin films, and a few of them belong to <111> too. In contrast, in bulk irradiation very few embryos-like loops were discovered at the beginning of the lamella, the maximum loop density was found in the bulk, but even though the size was much smaller than the found ones on thin films. Complex modelling studies corroborate these experimental observations, which mean the validation was successful.

Authors : B. Gómez-Ferrer a, C. Heintze b, C. Dethloff c, E. Gaganidze c, M. J. Konstantinović d, L. Malerba d, P.Pareige a, C. Pareige a
Affiliations : a Normandie Univ, UNIROUEN, INSA Rouen, CNRS, Groupe de Physique des Matériaux, 76000 Rouen, France; b Helmholtz-Zentrum Dresden-Rossendorf e.V., Institute of Resource Ecology, Bautzner Landstraße 400, 01328 Dresden, Germany; c Karlsruhe Institute of Technology, Institute for Applied Materials (IAM), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany; d SCK•CEN, NMS institute, Boeretang 200 – 2400 Mol, Belgium

Resume : Among other effects, neutron irradiation hardens ferritic/martensitic (F/M) nuclear steels; this hardening is suspected to be due to the formation of dislocation loops, α’ phase and solute-rich clusters (SRCs). In neutron irradiated FeCr model alloys the SRCs—which are made of unavoidable impurities such as P—are likely to be the main contributors to the yield strength increase, together with the presence of α’ precipitates, if any [1,2]. Ion irradiation is an extended tool used to investigate the creation and evolution of radiation damage. Since the experiments are fast they offer the possibility to tune the parameters to design model-oriented experiments. Their use is also oriented to reproduce the effects of neutrons for nuclear applications. However, the characteristics of the nano-sized features (solute concentration, density, size and size distribution) are difficult to reproduce using ions with respect to neutrons, since the increase of the sink strength due to injected interstitials [3,4] and the high values of damage rate [5] influence defect production and evolution. Atom probe tomography (APT) is used in the present work to investigate the hardening nanofeatures in irradiated materials. First, an Fe14CrNiSiP model alloy has been irradiated with both Fe+ ions and neutrons up to a dose of 0.1 dpa at 300°C. At such low doses some features, such as SRCs or Cr-rich regions, are formed, thus a direct comparison can be made to highlight differences and commonalities between the two kinds of irradiation; these results can also be used for the development of models. Second, a similar investigation has been made on neutron irradiated EUROFER97 up to 15 dpa at 300°C. The presence of radiation induced segregation (RIS) and radiation enhanced features can be correlated to the model alloy providing some insights on the nature of the hardening in F/M steels. [1] F. Bergner, C. Pareige, M. Hernández-Mayoral, L. Malerba, C. Heintze, Application of a three-feature dispersed-barrier hardening model to neutron-irradiated Fe–Cr model alloys, J. Nucl. Mater. 448 (2014) 96–102. doi:10.1016/j.jnucmat.2014.01.024. [2] G. Monnet, Multiscale modeling of precipitation hardening: Application to the Fe–Cr alloys, Acta Mater. 95 (2015) 302–311. doi:10.1016/j.actamat.2015.05.043. [3] F. Soisson, T. Jourdan, Radiation-accelerated precipitation in Fe?Cr alloys, Acta Mater. 103 (2016) 870–881. doi:10.1016/j.actamat.2015.11.001. [4] O. Tissot, C. Pareige, E. Meslin, B. Décamps, J. Henry, Influence of injected interstitials on α′ precipitation in Fe–Cr alloys under self-ion irradiation, Mater. Res. Lett. 5 (2016) 117–123. doi:10.1080/21663831.2016.1230896. [5] E.R. Reese, N. Almirall, T. Yamamoto, S. Tumey, G. Robert Odette, E.A. Marquis, Dose rate dependence of Cr precipitation in an ion-irradiated Fe 18Cr alloy, Scr. Mater. 146 (2018) 213–217. doi:10.1016/j.scriptamat.2017.11.040.

Authors : Mariana M. Timm [1], Ítalo M. Oyarzabal [1], Francine Tatsch [1], Lívio Amaral [1], Paulo F. P. Fichtner [1,2].
Affiliations : [1] Instituto de Física, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil, [2] Escola de Engenharia, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil

Resume : Ion irradiation experiments give important insight about the mechanisms that govern the nucleation and growth of defects in materials exposed to a nuclear environment. In this contribution, we report on Au and Ag ion irradiation effects in a solubilized AISI 316L alloy to investigate the influence of ions of different masses on the development of irradiation induced precipitate reactions. Mechanically polished AISI 316L samples were implanted with Ar ions and then, along with control samples without Ar, were irradiated at 550 ºC with 5 MeV Au ions and with 3.5 MeV Ag ions reaching fluences of 20 and 40 dpa. The samples were analyzed via transmission electron microscopy. The Au irradiation caused the formation of small Ar bubbles (d≈2nm) and of precipitates identified as M23C6 and MC phases only in the samples implanted with Ar; the control samples are free from precipitates and it is observed the presence of typical radiation-induced defects. Differently, the Ag irradiation experiment triggered the formation of precipitates and small Ar bubbles/cavities in both samples, with and without Ar. The mechanisms of defect formation are discussed considering the density of collision cascades induced by each ion/matrix-atom interaction and the consequent number of vacancies produced by the cascades. The evolution of the precipitate system is also discussed considering the diffusion controlled supply of C atoms from the matrix and the efficiency of the Ar gas as a vacancy attractor.

Authors : Marcin Roland Zemła 1, Jan Wróbel 1, Marek Muzyk 2, Tomasz Wejrzanowski 1, Duc Nguyen-Manh 3, Par Olsson 4, Luca Messina 5, Christophe Domain 6,7
Affiliations : [1] Faculty of Materials Science and Engineering, Warsaw University of Technology, Wołoska 141, 02-507 Warsaw, Poland [2] Faculty of Mathematics and Natural Sciences, Cardinal Stefan Wyszynski University in Warsaw, Wóycickiego 1/3, 01-938 Warsaw, Poland [3] CCFE, Culham Science Centre, Abingdon, Oxon OX14 3DB, United Kingdom [4] KTH Royal Institute of Technology, Reactor Physics, Roslagstullsbacken 21, SE-10691 Stockholm, Sweden [5] DEN-Service de Recherches de Métallurgie Physique, CEA, Université Paris-Saclay, F-91191 Gif-sur-Yvette, France [6] EDF-R&D, Département Matériaux et Mécanique des Composants (MMC), Les Renardières, F-77818 Moret sur Loing Cedex, France [7] Laboratoire commun EDF-CNRS Etude et Modélisation des Microstructures pour le Vieillissement des Matériaux (EM2VM), France

Resume : Point defects as interstitial atoms and vacancies play an important role in controlling properties of materials and their kinetic evolution. As a consequence, a proper understanding and modelling of properties of materials require a precise knowledge of point defect properties, in particular their formation and migration energies. In alloys as Fe-Cr alloys, the investigation of point defects is complicated, because the properties of point defects can be dependent on the various parameters such as: Cr composition, short-range ordering of the alloy and the local environment of a defect. The DFT simulations performed within this study showed that the properties of interstitials in concentrated Fe-Cr alloys may fluctuate significantly as a function of Cr concentration, short-range ordering and the local environment of a defect. These fluctuations are observed to a lesser or greater extend for all investigated properties: lattice parameters, chemical potentials, bulk moduli, relaxation volumes, magnetic moments, and migration energies of dumbbells. Moreover, the most stable directions of Fe-Fe, Fe-Cr and Cr-Cr dumbbells were investigated. The formation energy of dumbbells depends on Cr content and on the number of Cr atoms in the local environment of a defect. The trends in the mean values of investigated properties are observed. The mean migration energies of Cr atoms are significantly smaller than those of Fe atoms. The relaxation volumes of dumbbells increase in the ordered and decrease in the disordered structure with the increase of number of Cr atoms in the local environment of a defect.

Poster session : N. Gordillo, E. Wendler, G. Velisa
Authors : Byung-Hyuk Jun, In-Hwan Cho, Chan-Joong Kim
Affiliations : Neutron Utilization Research Division, Korea Atomic Energy Research Institute (KAERI), Republic of Korea

Resume : The Li doped-ZnSnO (ZTO) thin films were fabricated on a SiO2 (100 nm)/p+-Si substrate using a spin coating method. The Zn:Sn ratio and concentration of Li-ZTO solution were 1:2 and 0.5 M, respectively, and the Li content was 3 at.%. Particle irradiation can change the properties by forming defects. Neutron irradiation on Li-ZTO thin films was conducted using a cyclotron (MC-50 in KIRAMS). A fast neutron was generated through 30 MeV proton irradiation on a Be target. The neutron flux was about E8 n/cm2 s, and the dose was varied by changing irradiation time from 10 to 2000 s. To fabricate thin film transistor (TFT), a patterned Al electrode was deposited after the neutron irradiation. The saturation mobility of Li-ZTO TFT increased to 11.3 cm2/Vs at a neutron dose of 2×E11 n/cm2. The X-ray photoelectron spectroscopy (XPS) analysis showed that the chemical bonding states such as O 1s, Zn 2p and Sn 3d were not changed regardless of the neutron dose. From the XPS and spectroscopic ellipsometer (SE) results, it was shown that the Fermi level of the sample irradiated for 1000 s (1×E11 n/cm2) was located at the closest position to the conduction band minimum from the band gap alignment. The increase in saturation mobility and the variation in Fermi level for the samples irradiated above 1×E11 n/cm2 were due to the electrons exited easily toward the conduction band by increasing the D1 state (carrier generating state) at the conduction band edge.

Authors : Xin Jin, Aurélien Debelle, David Simeone, Frederico Garrido, Laurence Luneville
Affiliations : Centre de Sciences Nucléaires et de Sciences de la Matière, CNRS/IN2P3, France

Resume : An approach to emulate neutron irradiation with ion irradiation with Ni and MgO as test-case materials is conducted. The neutron irradiation and ion irradiation properties are compared through weighted recoil spectra obtained by computational simulations using the DART code. The weighted recoil spectrum provides the relation between the Primary Knock-on Atom (PKA) energy and target atoms displacements. The 300 keV Bi-209 and 600 keV Ni-58 ion irradiations on Ni and the 1 MeV Cl-35 ion irradiation on MgO are determined to represent neutron irradiations reported in papers available in the literature. The X-Ray Diffraction (XRD) technique is used to examine if the strain induced in the post irradiation sample matches that in the neutron irradiation.

Authors : GAN Ming Xuan, WONG Chee How
Affiliations : Singapore Centre for 3D printing, School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore. SLM Solutions Singapore Pte Ltd, 25 International Business Park #02-15/17, German Centre, Singapore 609916, Singapore.

Resume : Additive manufacturing has presented several potentials in the engineering industries. However, the limited material range has slowed down the progress of this technology despite its rapid adoption and implementation in industries. For instance, the development of processes to additive manufacture ceramics is still an on-going challenge. Moreover, due to the nature of layerwise manufacturing, new standards are needed for part qualification and characterisation. This work focuses on the density measurement of a lithium aluminosilicate glass-ceramic. The most common method in the community for quantifying the relative density of additively manufactured parts is by the use of Archimedes method. In this method, a relative density of 100 % implies that the manufactured part is fully dense without porosity. However, the use of this method is not appropriate for characterising additively manufactured materials which undergo phase changes accompanied by a drastic change in material density. An example of such a material is spodumene. A transformation from the α-phase to β phase reduces the density of the material from 3.15 kg/m3 to 2.4 kg/m3 after heat-treatment.3 However, the physical dimensions of the printed part does not change. Therefore, the use of Archimedes method for this material results in an increase in relative density, providing false information on the internal porosity. For better qualification of such materials in future, this work proposes the use of computer tomography (CT) scan.4 The preference of this method over the others is the prevention of possible confusion between part density and material density. In addition, CT scan is able to provide visualisation of the internal structure of the printed parts, enabling defects such as porosity to be located.

Authors : Parikshit Phadke, Jacobus Sturm, Robbert van de Kruijs, Fred Bijkerk
Affiliations : MESA Institute for Nanotechnology, University of Twente, Drienerlolaan 5, 7522 NB Enschede, The  Netherlands

Resume : Low energy charged particle damage requires attention in various areas like ion thrusters, fusion reactors, lithography optics etc. Models involving binary collision approximations break down at low energies due to a linear increase in collision cross-section below 100eV, and thus making predictability questionable and necessitating experimental verification. We report the physical and chemical modification of ruthenium under the influence of noble gas and nitrogen ions near the sputter threshold. Measuring frequency changes in an AT-cut quartz crystal microbalance coated with ruthenium, allowed us to measure thickness losses with nanometer level precision. Comparing the obtained yields to the semi-empirical model by Yamamura showed that the model overestimates yields for argon by 10% for 300eV while nitrogen shows larger discrepancies from model predictions which can be explained by the formation of a nitride.

Authors : K. Lorenz [1], D.N. Faye [1], M. Peres [1], E. Alves [1], X. Biquard [2], E. Nogales [3], B. Méndez [3], B. Daudin [4], L.H.G. Tizei [5], M. Kociak [5], P. Ruterana [6]
Affiliations : 1. IPFN, Instituto Superior Técnico, Universidade de Lisboa, Campus Tecnológico e Nuclear, Estrada Nacional 10, 2695-066 Bobadela LRS, Portugal 2. Univ. Grenoble Alpes, CEA, INAC-MEM, 38000 Grenoble, France 3. Departamento de Física de Materiales, Universidad Complutense, 28040 Madrid, Spain 4. Univ. Grenoble Alpes, CEA, INAC-Pheliqs, 38000 Grenoble, France 5. Laboratoire de Physique des Solides, Université Paris-Sud, CNRS-UMR 8502, Orsay 91405, France 6. Centre de recherche sur les Ions les Matériaux et la Photonique (CIMAP) ENSICAEN, Boulevard Maréchal Juin 14050 Caen France

Resume : Rare earth doped GaN is a promising material for light emitters and optical sensors. In particular, doping with Eu offers temperature stable red emission. In this study, GaN nanowires, grown by Molecular Beam Epitaxy, were implanted with Eu to different fluences. Strain introduced by implantation defects in nanowires remains considerably lower than in thin films. Surface degradation is observed for high fluences, consistent with increased sputtering in nanowires. Nevertheless, the nanowire core remains of high crystalline quality. Moreover, no formation of extended defects (e.g. stacking faults) is seen, in contrast to GaN thin films. After post-implant rapid thermal annealing, the typical Eu3+ intra-ionic transitions were observed in all samples. X-ray absorption spectroscopy (XAS) shows the coexistence of two different charge states (2+ and 3+) and gives information on the coordination of Eu in GaN nanowires and thin films. A similar local environment was found in both structures: for low fluences, Eu is mainly incorporated on substitutional Ga-sites while for high fluences XAS points at the formation of a EuN-like next neighbour structure.

Authors : Qiushuo Sun, Xudong Liu, Jie Cao, Rayko I.Stantchev, Edward P.J. Parrott, Ni Zhao, Emma Pickwell- MacPherson
Affiliations : Department of Electronic Engineering, The Chinese University of Hong Kong & Department of Physics, The University of Warwick

Resume : Perovskite solar cells (PSCs) have emerged and been developed quickly over the past a few years as a promising low cost and highly efficient solution of renewable energy: some PSCs have reached an efficiency of higher than 20% [1]. However, the understanding of the lattice changes under illumination is still lacking. In this work, we propose a novel terahertz (THz) thin film total internal reflection (TF-TIR) spectroscopy to characterize the perovskite thin films. We show that TF-TIR spectroscopy enhances sensitivity compared to transmission geometry. The light induced spectral change and partial recovery process of two single halide perovskites (MAPbI3, MAPbBr3) and two mixed halide perovskites (MAPbI2.5Br0.5, MAPbI2Br1) were recorded with the proposed THz TF-TIR spectroscopy method. The effects of the moisture and oxygen were also included. The measured TF-TIR spectra were analyzed with Lorentz oscillator model (LOM) and the resonance frequency and oscillation strengths were examined physically. The X-ray diffraction (XRD) and Photoluminescence (PL) of the perovskite thin film samples under the same situation were also measured to verify the degradation and the phase segregation in the perovskites. From the THz TF-TIR spectral results, we presume there was two-step structural change in the perovskite thin films under illumination. Firstly, we showed that the intensity of the second THz phonon mode was enhanced after 5 minutes of illumination, which was attributed to the rotational vibration of the MA cations and the coupling between the cations and inorganic octahedra; Secondly, the long-term light soaking induced a decrease in the intensity of both THz phonon modes. In particular, the strength of the first phonon mode rapidly decreased to zero (within 30 minutes for MAPbI3) in the presence of moisture, which corresponds to the decreased bending strength of the halide-lead-halide bond. Our results match with the assumption proposed by Gottesman et al that inorganic octahedra would realign to adapt to the rotated MA cations induced by photo illumination [2]. Moreover, based on the experimental results, we are able to give the time scales of the two-step structural change. The rotation of the MA cations occurred within the first 5 minutes of illumination. In the presence of moisture, the halide-lead-halide bond bending strength remained stable for the first 10 minutes of illumination and then rapidly decreased to zero within the next 20 minutes. Without moisture, this bond bending strength was modified at a much slower rate. We also elaborate on the details of changes in the octahedra under illumination: the bending and stretching strength of the lead halide bond decreased; and in the presence of moisture and oxygen the vibrational resonance frequency of the halide-lead-halide bond bending had a blue shift. We demonstrate that our technique could give information about photo-induced structural changes in the perovskite crystal structure and our conclusions are reinforced by XRD and PL measurements. The proposed THz TF-TIR spectroscopy breaks the limitations of the traditional THz transmission TDS and ATR spectroscopy techniques, as it is able to capture features of weekly-absorbing materials without photoexcitation. Using this TF-TIR geometry we are potentially able to characterize materials that are too thin to be characterized in transmission geometry. This is very helpful for studying the dynamics of the carriers in materials. This method is also potentially able to examine the film quality of perovskite samples, which is an essential factor to determine the performance of the perovskite solar cell devices [3]. Reference [1] J.-P. Correa-Baena, M. Saliba, T. Buonassisi, M. Grätzel, A. Abate, W. Tress, et al., "Promises and challenges of perovskite solar cells," Science, vol. 358, pp. 739-744, 2017. [2] R. Gottesman, L. Gouda, B. S. Kalanoor, E. Haltzi, S. Tirosh, E. Rosh-Hodesh, et al., "Photoinduced reversible structural transformations in free-standing CH3NH3PbI3 perovskite films," The journal of physical chemistry letters, vol. 6, pp. 2332-2338, 2015. [3] U. Mehmood, A. Al-Ahmed, M. Afzaal, F. A. Al-Sulaiman, and M. Daud, "Recent progress and remaining challenges in organometallic halides based perovskite solar cells," Renewable and Sustainable Energy Reviews, vol. 78, pp. 1-14, 2017.

Authors : A. Redondo-Cubero (1), J. Rodrigues (2), L. Vázquez (3), D. Jalabert (4), T. Monteiro (2), K. Lorenz (5), and N. Ben Sedrine (2)
Affiliations : (1) Departamento de Física Aplicada, Universidad Autónoma de Madrid, 28049 Madrid, Spain (2) Departamento de Física e I3N, Universidade de Aveiro, 3810-193 Aveiro, Portugal 3) Materials Science Factory, Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas, 28049 Madrid, Spain (4) Université Grenoble Alpes, INAC-SP2M, LEMMA, F-38000 Grenoble, France ; CEA, INAC-SP2M, LEMMA, F-38000 Grenoble, France (5) IPFN, INESC-MN, Universidade de Lisboa, Campus Tecnológico e Nuclear, Estrada Nacional 10, 2695-066 Bobadela LRS, Portugal

Resume : Ion beam sputtering is a well-established technique for the production of nanopatterns in a large range of materials [1], but the formation of patterns in some binaries, such as GaN or ZnO, has been proven difficult to achieve [2,3] due to their high radiation hardness. In this work, we present the results on modeling and analysis of radiation damage in ZnO bulk substrates. We study the role of the energy (20 and 40 keV) and the fluence (from 1016 to 2·1018 cm-2) when samples are irradiated with Ar+ ions at oblique incidence (60º). We successfully create ripple patterns with an asymmetric shape and an uncorrelated direction with the beam. A detailed study of the damage-induced changes on the near-band-edge is carried out by photoluminesence and the evolution of both the damage and the roughness vs. the fluence are analyzed by spectroscopic ellipsometry. The results are contrasted with atomic force microscopy and Rutherford backscattering spectrometry in channeling mode and medium energy ion scattering measurements. With these methods we can confirm that the irradiation causes: i) a decrease of the refractive index, ii) a broadening of the excitonic transitions, and iii) an enhanced absorption below bandgap. [1] Muñoz-García et al. Mater. Sci. Eng. R-Rep. 86, 1 (2014). [2] Qian et al. J. Phys. D: Appl. Phys. 42, 105304 (2009). [3] Bhattacharjee et al. Appl. Surface Science 257, 6775 (2011).

Authors : O.M.Sydor, O.A.Sydor
Affiliations : Chernivtsi Department of the Institute of Materials Science Problems, the National Academy of Sciences of Ukraine

Resume : Investigations of radiation effects in III–VI semiconductors are promising from practical point of view for creation of photoconverters for use in photo-, opto- and quantum electronics, radiation hardness of which substantially exceeds that of silicon one. Layered crystal structure of III–VI compounds enables both to obtain their plates with atomically smooth surface by cleaving the ingot in air and to apply simple techniques (thermal oxidation and direct optical contact) for the preparation of device structures. In this work the influence of 10 MeV electron irradiation within a wide fluence range 10^13–10^15 cm-3 on the parameters of intrinsic oxide–p-InSe:Cd heterojunctions and p-InSe:Cd–n-InSe homojunctions is established. Current-voltage (dark and light), capacitance-voltage and load characteristics of the junctions, charge transfer mechanisms through the potential barriers, photoresponse spectra, open-circuit voltage, short-circuit current, current and voltage monochromatic sensitivities as well as solar energy conversion coefficient are investigated before and after radiation. The detected insignificant changes in the electrical and photoelectric characteristics for the diode InSe-based structures even at the maximum irradiation fluence showed a high resistance of the investigated photoconverters to high-energy electron irradiation. Its influence leads to the appearance of simple radiation-induced point defects located preferably in the interlayer spaces.

Authors : T. Hristova-Vasileva1, P. Petrik2, D. Nesheva1, Z. Fogarassy2, J. Lábár2, B. Kalas2, S. Kaschieva1, S. N. Dmitriev3, K. Antonova1
Affiliations : 1-Institute of Solid State Physics, Bulgarian Academy of Sciences,72 Tzarigradsko Chaussee Blvd,1784 Sofia, Bulgaria 2-Centre for Energy Research, Hungarian Academy of Sciences, H-l12l Budapest, Konkoly-Thege u. 29-33, Hungary 3-Joint Institute for Nuclear Research, Flerov Laboratory of Nuclear Reactions, Dubna, Moskow region 141980, Russia

Resume : Electron or ion irradiation of solids may result in irradiation-induced amorphization, recrystallization and annealing and may induce changes of electrical properties of solid-state materials and devices. Irradiation may also cause formation of amorphous nanosized domains and nanocrystals by decomposition of the target material. Therefore during the last few decades there was significant activity to explore such alterations in various types of semiconductor devices, in particular in those based on metal-oxide-silicon structures. Homogeneous films from SiOx (x=1.3) and composite a-Si-SiOx films, containing amorphous Si nanoparticles (a-Si) were prepared on crystalline Si substrates by evaporation of silicon monoxide. The nanoparticles were grown by post-deposition annealing at 700 °C. The samples were irradiated by 20-MeV electrons at fluencies of around 1015 el/cm2. The film thicknesses and optical constants were explored by spectroscopic ellipsometry. The development of the films’ structure caused by the electron-beam irradiation was studied by transmission electron microscopy. It has been shown that the SiOx films are optically homogeneous and the electron irradiation has led to small changes in the optical constants. The irradiation of the a-Si-SiOx composite films caused a decrease of the effective refractive index and, at the same time, an increase of the refractive index of the oxide matrix. Irradiation induced increase of the optical band gap and decrease of the absorption coefficient of the thermally grown amorphous Si nanoparticles has also been observed. The obtained results are discussed in terms of formation of small amorphous silicon nanoclusters in the homogeneous layers and electron irradiation induced nanoparticle size reduction in the composite films. The conclusion for the nanoparticle size reduction is supported by infrared transmittance results.

Authors : M.I.Rusu a *, C.R. Stefan a, Y. Addab b, C. Martin b, C. Pardanaud b, D. Savastru a,, C. E.A. Grigorescu a
Affiliations : a National Institute of R&D for Optoelectronics INOE 2000, 409 Atomistilor, Magurele, PO Box MG-5, 77125, Ilfov, Romania b Aix-Marseille Université, CNRS, PIIM UMR 7345, 13397, Marseille, France

Resume : Thin films of WO3 were grown at 400 °C under 5 and 590 Torr oxygen pressure by thermal oxidation of tungsten substrates with different grain size. Two samples were exposed to helium plasma in order to mimic the conditions of ITER diverter W-plasma facing components and to explore the effects on their properties. Ellipsometry measurements and modelling on the obtained samples were performed in order to determine the thicknesses of the films, thus consolidating the thickness values estimated previously between 20 and 270 nm by the FIB cross-section method [1]. The film thicknesses are influenced by the substrate grain size. Specular reflectance of the WO3 thin films in the 190-2100 nm range measured by spectroscopic ellipsometry shows that the minimum of the reflectance is shifted to lower wavelengths when the thickness of the films decreases. The substrate grain size does not significantly influence the reflectance spectra of the films. The reflectance spectra of the virgin tungsten, regardless the substrate grain size, does not present a sharply defined minimum. The modeled n and k dependencies of wavelength were compared with their measured counterparts. For the He exposed samples n and k have higher values than the unexposed ones. [1] Y. Addab et. al, Formation of thin tungsten oxide layers: characterization and exposure to deuterium, Phys. Scr. T167 (2016) 014036.

Authors : Ashish Kumar1, R. Singh2, D. Kanjilal1, P.A. Karaseov3, A.I. Struchkov3, and A.I. Titov3
Affiliations : 1) Inter-University Accelerator Center, Aruna Asaf Ali Road, Vasantkunj, New Delhi, India 2) Department of Physics, Indian Institute of Technology Delhi, Hauzkhas, New Delhi, India, 3) Department of Physical Electronics, Peter the Great Polytechnic University, St.Petersburg, Russia

Resume : Well known high radiation hardness makes GaN the material of interest for electronic applications where systems are exposed to fluxes of ionizing radiation like cosmic rays. Understanding of the processes affecting irradiation damage formation is extremely important to design technologically improved and radiation hard GaN devices. In this work investigation of radiation hardness of GaN epitaxial layers under irradiation with swift O, Ni, Ag and Au ions has been carried out by employing in-situ electrical resistivity measurements and study of microstructure of irradiated samples. Un-intentionally doped and Si-doped n-GaN epitaxial layers grown by MOCVD on sapphire were used for SHI irradiation. Irradiation with light O ions has very weak effect on the sample resistivity. On the other hand, the resistivity sharply increases for more than 6 orders of magnitude under bombardment with other ions. Interestingly, shape of the experimental curves is very similar to one obtained in the case of much lower (few MeV) energy ion irradiation. Formation of aligned chains of defect clusters was found by XTEM after Ag irradiation. Estimation of total amorphized area gives ~3% after target irradiation to highest experimental fluence of 2×10^11 ?m^-2. Such a low value will not significantly affect sample resistivity. On the other hand, nuclear energy loss can generate enough simple point defects to determine the effect observed. The mechanism of resistivity increase is formation of complexes consisting of a doping atom and a simple point defect generated by stopping ion. Corresponding model will be presented. Work was partly supported by the State Assignment for Higher Education Institutions (basic part), project ? 3.5469.2018

Authors : Irmak Sargin, Scott P. Beckman
Affiliations : Washington State University; Washington State University

Resume : Insulation cabling is an essential engineering component in nuclear power plants. The insulation around these wires is made of ethylene-propylene rubber and crosslinked polyethylene that is subjected to environmental and radiation damage. For the purpose of maintenance and reactor recertification, it is necessary to develop a non-destructive approach to test the impact of damage on the insulation. Accelerated aging experiments are used to develop these methods, although it is unclear how to relate these experimental results to in situ aged specimen. Here we use a kinetic rate model to investigate the impact of radiation dose rate and total dose on the crosslinking and chain scission of polyethylene. Analytical expressions for the concentration of crosslinking and scission sites as a function of time and radiation rate both for during and post radiation and crossover point between these two are presented in terms of radiation rate and time. The scission reaction rate is significantly slower than crosslinking for lower total doses whereas the situation is changed for higher total doses causing the ambiguity between the accelerated aging and in-situ aging methods. Also, chain scission forming reactions can continue for months or years during storage after being radiated, whereas crosslink forming ones end almost immediately after the radiation is turned off.

Authors : Michael Saleh(1,2)*, Dhriti Bhattacharyya(1), Paul Munroe(2)
Affiliations : (1) Australian Nuclear Science and Technology Organisation (ANSTO), Locked Bag 2001, Kirrawee DC, NSW 2232, Australia (2) School of Materials Science and Engineering, University of New South Wales, NSW, 2052, Australia * (corresponding author)

Resume : In determining the effects of neutron irradiation on structural reactor materials, the author have utilised both light, He at 1-3 MeV, and heavy ion, Au at 12 MeV, irradiation to examine the hardening behaviour of SS 316 and Duplex steel. Utilising two nano-indentation techniques (top-down and inclined indentation methods) and TEM analysis of the dislocation distribution the authors were able to observe the depth dependent hardening of these materials as a function of ion and indenter penetration depth. The usefulness and veracity of each technique were contrasted with numerical models that evaluated the growth and distribution of the complex plastic zones below the Berkovich indenter. Through a combination of an Orowan based hardening model and SRIM outputs, the authors were able to relate the dpa dose with an increased hardening response at an FE scale. The simulation results were qualitatively and quantitatively in good agreement with the experimentally derived results and proved a robust and predictive capability in broadly examining layered structures, of which ion irritated materials form an interesting subset group.


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Symposium organizers
Andrés REDONDO-CUBEROUniversidad Autonoma de Madrid

Facultad de Ciencias, Campus de Cantoblanco, 28049 Madrid, Spain

+34 914978607
Aurélien DEBELLE CSNSM, Univ. Paris-Sud, CNRS/IN2P3, Université Paris-Saclay

CSNSM, Univ. Paris-Sud, Bât. 108, 91405 Orsay Cedex, France

+33 1 69 15 35 95
Izabela SZLUFARSKAUniversity of Wisconsin

242 MS&E, 1509 University Ave, University of Wisconsin, Madison WI 53706-1595, USA

+1 608 265 5878
Katharina LORENZInstituto Superior Técnico, Universidade de Lisboa

Campus Tecnológico e Nuclear, Estrada Nacional 10, 2695-066 Bobadela LRS, Portugal

+351 21 9946052