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2015 Fall

Nanomaterials,Nanostructures and Nano devices

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Deformation at small-scale: insights from experiments and simulations

Mechanical properties of crystalline micro or nano objects have recently drawn intensive attention, through their high achievable yield strength and ductility. They are thus considered as model samples to investigate elementary deformation processes (dislocations, twins) close to the atomic scale.

 

Scope

 

The goal of this symposium is to bring together experimentalists (in situ TEM, SEM mechanical testing, HRTEM, tomography) and computational modellers (ab initio, MD, DD) in order to improve our knowledge on small-scale deformation processes that govern the mechanical properties on certain length scales, with a focus to bridging scaled in order to understand architecturally-controlled structural materials in the future. The symposium will focus on recent and original studies dedicated to small-scale deformation analysis. While numerous studies have been dedicated to classic metals, investigations dedicated to other materials including complex alloys, ceramics, semi-conductors and oxides are welcome. As the main goal of the symposium is to enhance the interactions between experiments and simulations, interdisciplinary studies (e.g., HRTEM + atomistic simulations) are of great interest.

 

Hot topics to be covered by the symposium

 

  • Nano-mechanical testing
  • Size-effects on material properties
  • Deformation under extreme conditions
  • Characterization of defects
  • Dislocation structures in complex materials
  • Role of sample synthesis, growth and preparation
  • Defects-based deformation model on various length scales
  • Influence of interfaces and interaction with other defects
  • Experimental and numerical technical innovations
  • From small scale properties to applications

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09:00 Welcome    
09:15
Authors : E. Clouet, N. Chaari, D. Rodney, D. Caillard
Affiliations : SRMP, CEA Saclay, France; SRMP, CEA Saclay, France; ILM, Univ. Lyon 1, France; CEMES, CNRS Toulouse, France

Resume : Titanium and zirconium have a close plastic behaviour arising from their hexagonal close-packed crystallography and from their similar electronic structure. In particular, plasticity in these two transition metals is controlled by screw dislocations gliding in the prism planes, with cross-slip in the first-order pyramidal planes or in the basal planes activated at high enough temperature. However, in situ transmission electron microscopy straining experiments reveal differences in the plastic behaviour. In Ti, the motion of the screw dislocations is jerky, with long time periods where the dislocations appear immobile, separated by short escape events where the dislocations glide rapidly over several Peierls valleys in the prism planes. On the other hand, screw dislocations glide in the prism planes without any lattice friction in Zr. We use ab initio calculations and NEB method to study core properties of the screw dislocations and their mobility in both metals. These calculations show that screw dislocations may adopt different cores that are dissociated either in a prism or in a pyramidal plane, in agreement with the existence of stable stacking faults in these planes. The prismatic core easily glide in its habit plane, whereas the pyramidal core needs to overcome an important energy barrier to glide. An inversion of stability of these cores between Zr and Ti is at the origin of the different plastic behaviours.

N.1.5
09:45
Authors : W. Szewc (1), S. Brochard (1), E. Clouet (2), L. Pizzagalli (1)
Affiliations : (1) Institut Pprime, CNRS UPR 3346, Université de Poitiers, SP2MI, BP 30179, Boulevard Marie et Pierre Curie, 86962 Futuroscope Chasseneuil Cedex, France; (2) CEA, DEN, Service de Recherches de Métallurgie Physique, F-91191 Gif-sur-Yvette, France

Resume : We present an atomic-scale study of the emergence of plasticity in alpha-zirconium monocrystal through nucleation of dislocations. Zirconium is a material of immense importance to the nuclear industry, as it is used in fuel cladding. One of the factors potentially degrading its mechanical properties is the precipitation of zirconium hydrides ZrH_x. Through Zr/ZrH_x lattice mismatch, the growing precipitate exerts increasing strain on the zirconium matrix, eventually leading to nucleation of dislocations at the interface and thus to a plastic behaviour. The experimental investigation of this process is extremely difficult and complementary information can be drawn from computer simulations. Our method of choice was molecular dynamics with embedded atom model (EAM) potential applied to an increasingly strained Zr surface. We found that the onset of plasticity is controlled by heterogeneous nucleation of partial dislocations in the first-order pyramidal planes, immediately followed by partial dislocations in the basal plane. The apparent blocking of the prismatic-plane slip, which unquestionably dominates in bulk zirconium, follows from the loading conditions imposed by the precipitate. The elastic limit depends on the geometric features of the surface making contact to the precipitate. In particular, it is lowered by the presence of surface steps. In specific circumstances, it is possible to favour the basal slip over the pyramidal one.

N.1.7
10:00
Authors : Dongyoo Kim, Levente Vitos
Affiliations : Applied Material Physics, Department of Materials Science and Engineering, Ryoal Institute of Technology (KTH), Sweden

Resume : We investigated plastic deformation behavior of faced center cubic (FCC) Al with compressed volume and lattice distortion via first principles. Competition between slip and twin barriers is dealt as main mechanism of plastic deformation of FCC metals. Plastic deformation map (PDM), suggested by Jo and coworkers [1], provide simple understanding of intrinsic energy barrier competition and plastic deformation mode of FCC metals. Based on PDM and calculated generalized stacking fault energies, we find that change of volume and lattice distortion can induce twinning deformation. It may provide understanding to deformation twinning of the nanocrystal Al. [1] Jo et al., Proc. Natl. Acad. Sci. 111, 6560 (2014)

N.1.24
10:15 Coffee Break    
11:00
Authors : D. Kiener, J. Jeong, M. Alfreider, S.H. Oh
Affiliations : Department Materials Physics, Montanuniversität Leoben, Jahnstraße 12, 8700 Leoben, Austria; Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), San 31, Hyoja-dong, Nam-gu, Pohang 790-784, Korea; Department Materials Physics, Montanuniversität Leoben, Jahnstraße 12, 8700 Leoben, Austria; Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), San 31, Hyoja-dong, Nam-gu, Pohang 790-784, Korea

Resume : While the nanomechanical properties and deformation modes of face centered and body centered cubic metals have received broad interest in recent years, less attention was given to hexagonally close packed materials. For magnesium in particular, the literature is inconclusive in terms of the magnitude of size dependent strengthening and the occurrence of twinning as a governing deformation mode. Therefore, in this work we investigated the micron and sub-micron mechanical properties of single crystal Mg samples with different principal orientations. Specimens were produced by focused ion beam machining, subsequently annealed to remove the FIB related damage, and subsequently tested using quantitative in situ SEM and TEM approaches, respectively. From the in situ observations, in conjunction with the mechanical data and post characterization, we find a size dependent material strength for Mg, the scaling of which depends on the active deformation mode. For the <0001> direction, plasticity was governed by basal slip with a size scaling similar to fcc metals. Contrarily, both tensile twinning and pyramidal slip are observed over the investigated size regime in <2-1-10> compression tests. The contribution of the two mechanisms was found to depend on the strain rate of the experiment. This points to a rate dependent influence on the plastic deformation of single crystal Mg that was not considered in previous studies.

N.2.3
11:15
Authors : A. Jager, J. Bocan, J. Manak
Affiliations : Department of Advanced Structural Materials Institute of Physics Na Slovance 2 Prague Czech Republic

Resume : The anisotropic nanomechanical properties of hexagonal close packed 99.95% magnesium and AZ31 alloy (nominally 3 wt. % Al, 1 wt. % Zn, 0.3 wt. % Mn, balance Mg) were measured in situ via nanoindentation of individual grains with simultaneous observations using a scanning electron microscope (SEM). Values of the nanohardness, indentation size effect, elastic modulus, plastic work and yield strength were correlated with the crystallographic orientation provided by electron backscattering diffraction in a wide range of orientations. An attempt for quantification of indentation size effect, i.e. smaller-is-stronger, was also made. The nanohardness of AZ31 was found to be generally above that of pure Mg due to solid solution strengthening. The indentation size effect was stronger for AZ31 than for pure Mg, and its magnitude decreased as the angle between the lattice c-axis and the indentation direction increased. The AZ31 modulus remained nearly constant throughout the range of investigated orientations; the modulus of pure Mg followed a theoretical angular dependence but was generally lower than expected, which was likely due to the applied Ar+ ion etching. It is also shown that the amount of plastic deformation increased as the angle between c-axis and indentation direction increased.

N.2.16
11:30
Authors : R. Brunner 1, R. Treml 2, D. Kozic 1, R. Schöngrundner 1, D. Kiener 2, J. Zechner3, H.-P. Gänser
Affiliations : 1 Materials Center Leoben, Roseggerstr. 12, 8700 Leoben, Austria, 2 Department Materials Physics, Montanuniversität Leoben, Jahnstr.12, 8700 Leoben, Austria 3 EMPA Thun, Feuerwerkerstr. 39, 3602 Thun, Switzerland

Resume : The trend of miniaturization has revealed exciting novel material properties at small length scales. This demands miniaturized testing techniques to determine for instance the residual stresses and fracture properties in miniaturized systems such as thin films. In this presentation, we will review recent developments regarding the measurement of residual stresses and miniaturized fracture properties using in situ SEM experiments. In detail we will discuss challenges and benefits of the presented approach by examine the residual stresses and fracture properties of single layer and multilayer thin film systems. Further, we address possible limitations regarding the data analysis as well as the development of accompanied finite element modeling for the determination of crack driving forces. The presented work shall give an approach to understand novel material properties resulting due to the ongoing trend of miniaturization.

N.2.4
11:45
Authors : Ville Jansson, Ekaterina Baibuz, Flyura Djurabekova
Affiliations : Helsinki Institute of Physics and Department of Physics, University of Helsinki

Resume : Good mechanical and electrical properties place copper among the materials, which are the most frequently used for operation in extreme conditions. One of such application is to use copper as a construction material for high gradient accelerating structure in linear particle accelerators. A major problem in the design of such accelerators is that the high electric field causes electric discharges in form of arcs to appear inside the structures, despite an ultra high vacuum. One hypothesis for these arcs are that they are triggered by nano-sized tips on the copper (Cu) surface. In order to study the feasibility of the tip hypothesis, it becomes important to know under which conditions such tips are stable and for how long. We have for this purpose developed a new Kinetic Monte Carlo model designed especially for studying the surface evolution of metals and Cu in particular by considering the atom migration jumps, described by tabulated migration barriers calculated using the Nudged Elastic Band method. We have validated our model by comparing with Molecular Dynamics simulations of diffusion of Cu tips at different kinds of surfaces and different temperatures. We obtained good agreements. Using the model, we found a significant stability of 13 nm high tips at room temperature are stable for hours. At temperatures above 800 K, we found that the same tip will disappear in less than a microsecond, indicating a strong temperature dependence on the flattening mechanism.

N.2.22
12:00
Authors : Mihkel Veske, Stefan Parviainen, Vahur Zadin*, Flyura Djurabekova
Affiliations : Mihkel Veske - University of Helsinki & University of Tartu; Stefan Parviainen - University of Helsinki; Vahur Zadin - University of Tartu; Flyura Djurabekova - University of Helsinki

Resume : In aim to enhance the current and to broaden the future areas of research, CERN has initiated a new compact electron-positron linear collider CLIC project. One of the key issues in CLIC is to get under the control the electric breakdowns that are caused by high, up to 300 MV/m electric fields used to accelerate leptons. Breakdowns may via positive feedback effect be initiated by the small protrusions on the copper surface that cause local field enhancement. The resulting field currents are so far the main experimental evidence of protrusions, they have never seen directly. This may be due their tendency to collapse without external force. The aim of current study is to use computational techniques to investigate the stability of copper protrusions with and without external electric field applied to the system. The main simulation tool is the hybrid electrodynamics – molecular dynamics code HELMOD, where electric forces are added to classical interatomic interactions. In the study, the protrusion shape memory and pseudoelasticity caused by high electric fields and electromigration phenomenon are investigated with respect to the protrusion stability. As a result of the study it is found, that application of strong electric field to the system stabilizes the protrusions significantly and poses one possible mechanism for the lack of experimental observation of protrusions.

N.2.21
12:15 Lunch Break    
14:00
Authors : S. Queyreau (1), B. Devincre (2)
Affiliations : (1) LSPM-CNRS, UPR 3407, Universite Paris XIII, 93430 Villetaneuse, France | (2) LEM-CNRS/ONERA, UMR104, 29 av de la Division Leclerc, 92322 Chatillon, France

Resume : Bauschinger Effect (B.E.) is defined from simple forward and reverse loading tests, and is manifested by the reverse flow curve exhibiting a reduced elastic limit, a well-rounded appearance of the initial plastic portion and a permanent softening with respect to the forward hardening curve. Investigation of B.E. is of particular interest for the understanding of cyclic deformation and for the modeling of kinematic hardening in crystal plasticity. Today, existing interpretations and modelling of the B.E. are dominated by the concepts of Backstress and long range internal stresses, which at the elementary scale are justified by the accumulation of geometrically necessary dislocations in a deformed sample. Hewever, such interpretations are in many regards incompatible with the true B.E. observed in single crystals of pure metals. In this study, the B.E. of Ni single crystals is investigated with the help of 3D dislocation dynamics simulations. Among the different elementary features controlling the strain hardening, we show that the junction strength and the mobile dislocation mean free path are key physical parameters to understand the dislocation microstructure assymtries upon load path changes. A new model based on short-range properties observed in the simulations is proposed. This model, which neglects the possible influence of a Backstress and whose parameters are directly determined from DD simulation results, captures many details of the existing experimental data.

N.3.1
14:30
Authors : Osamu Waseda, Michel Perez, Julien Morthomas, Roberto Veiga
Affiliations : Laboratoire MATEIS INSA de Lyon, Departamento de Engenharia Metalúrgica e de Materiais, Universidade de Saõ Paulo

Resume : Despite the intensive studies of ageing of steels over the course of years, the structure of Cottrell atmospheres, the kinetics of their creation, as well as the pinning force exerted on the dislocation are not well understood. In our study, we develop a Monte Carlo (MC) simulation framework, that searches for the energetically best configuration of carbon atoms in bcc crystal iron in a small simulation box containing an edge dislocation. Then in regular MC steps, it is incorporated into a larger simulation box to allow the boundaries of the small simulation box to attain a stress-free configuration. This eventually leads to the creation of Cottrell atmospheres in different development levels. Subsequently, the behaviour of the dislocation as well as the Cottrell atmosphere is scrutinized in various stress fields to understand the effect of Cottrell atmospheres on the stress-strain relation.

N.3.2
14:45
Authors : Adrien Gola, Peter Gumbsch, Lars Pastewka
Affiliations : Karlsruher Institut für Technologie (KIT) Institut für Angewandte Materialien - Computational Materials Science (IAM- CMS)

Resume : We used a combination of Monte Carlo (MC) and molecular dynamics MD to study Cu(x)Ag(1-x)|Ni multilayers with 5 nm and 25 nm layer width. We find that Cu-Ni multilayers form a semi-coherent interface with a network of partial dislocations arranged in a regular triangular pattern. Silver is then alloyed to the copper layers in order to tune the lattices misfit in a controlled way. A combination of MC and MD was used to equilibrate Cu(x)Ag(1-x)|Ni with x=0%, 5% and 10% towards the thermodynamic equilibrium. We find segregation of Ag within the Cu layers at 300 K and 600 K and mixing of Cu and Ni at 600 K in good agreement with the experimental binary phase diagrams of the Cu-Ag and Cu-Ni systems. Ag segregates preferentially at the nodes of the triangular misfit pattern. The equilibrated structures were then sheared parallel and perpendicular to the normal of the bilayer interface. We generally find (1) initial sliding at the Cu|Ni interface within the dislocation network, (2) followed by emission of partial dislocations into the Cu layer, and finally (3) an increase of yield stress with increase of interface roughness and silver content.

N.3.17
15:00
Authors : Dr M. M RAJATH HEGDE 1, Dr TENZIN PASANG 2, N. B PRADEEP KUMAR 3
Affiliations : 1-PROFESSOR DEPARTMENT OF MECH ENGG JNNCE SHIMOGA & VISITING PROFESSOR CENT-SCEM ADYAR MANGALORE KARNATAKA INDIA, 2-RESEARCH SCIENTIST CENT-SCEM ADYAR MANGALORE KARNATAKA INDIA, 3-RESEARCH SCHOLAR DEPARTMENT OF MECHAICAL ENGINEERING JNNCE SHIMOGA KARNATAKA INDIA

Resume : Mixture of elemental powders of Al, Cu and Fe are mechanically alloyed in a planetary ball mill. The initial composition of the powder selected was Al70Fe20Cu10 atomic percent. Ball milling induces the formation of ternary alloy (Al(Cu,Fe) of orthorhombic structure) as well as binary alloy (AlCu of monoclinic structure) solid solutions at 15 hours of ball milling time. Further, intermetallic phase (Al4Cu9) of cubic structure is formed at the end of 30 hours of ball milling time. Solubility of Fe in Al is limited to a large extent compared to the solubility of Cu in Al. Thus, due to increased onslaught of plastic deformation by ball milling, Fe rebounds back to elemental form at the end of 30 hours of ball milling time. Ball milled powders have been characterized by SEM and TEM and the analysis has been correlated with that of XRD. Magnetization decreases with increase in ball milling time. However, transition of solid solution to intermetallic phase with increase in temperature causes ferromagnetic to paramagnetic transition. Key words: ball milling; mechanical alloying; Al-Cu-Fe; nanostructured; magnetization

N.3.8
15:15 Coffee Break    
16:00
Authors : Oleg Kovalenko, Dor Amram, Eugen Rabkin
Affiliations : Department of Materials Engineering, TechnionIsrael Institute of Technology, 32000 Haifa, Israel

Resume : We demonstrate that Au, Fe and Mo nanoparticles obtained by solid state dewetting of thin metal films on non-wetting substrate exhibit defect-free atomic structure. As a result, their compressive strength is approaching the theoretical shear strength of respective metal. The paucity of crystalline defects in the faceted single crystalline particles results in metastable particle shapes different from the equilibrium crystal shape. The shape evolution toward equilibrium is impeded by a prohibitive energy barrier associated with the nucleation of a new atomic layer on a flat facet. We demonstrate that the presence of a grain boundary in the particle results in much faster equilibration as compared with single crystalline particles. Also, a controlled injection of dislocations in single crystalline Au and Fe nanoparticles by nanoindentation technique results in their fast equilibration at elevated temperatures. Moreover, we demonstrate that the defect-free structure of the Fe nanoparticles results in high energy barrier for the nucleation of the face centered cubic phase above 912 °C, thus allowing superheating of the body centered cubic Fe nanoparticles up to 200 °C above the transformation temperature. This underlines a deep analogy between plasticity and phase transformations at the nanoscale.

N.4.10
16:30
Authors : Simon Vigonski, Vahur Zadin*, Stefan Parviainen, Alvo Aabloo, Flyura Djurabekova
Affiliations : Vigonski: University of Tartu, Helsinki Institute of Physics and University of Helsinki; Zadin: University of Tartu; Parviainen: Helsinki Institute of Physics and University of Helsinki; Aabloo: University of Tartu; Djurabekova: Helsinki Institute of Physics and University of Helsinki

Resume : Localized electric field enhancement near metal surfaces plays an important role in high-gradient applications such as particle accelerators. The planned new Compact Linear Collider (CLIC) at CERN uses surface electric fields up to 300 MV/m, leading to frequent electrical breakdowns in the copper accelerating structures. The field enhancement leading to the breakdowns is presumably caused by nanoscale field emitters appearing on the surface during normal operation. We investigate the effects such emitters can have on the material and the field near the surface. In the current study, we use the molecular dynamics-electrodynamics code HELMOD in conjunction with a FEM based electric field and material deformation model to investigate the enhanced field distribution around the emitter. By using HELMOD, we verify the applicable range of the FEM material model. The results of HELMOD and FEM simulations are compared to understand the behavior of the system over a wide range of length and time scales. As a result, these two methods are used to simulate the final stages of emitter formation by analyzing a rising tip as the external field is increased. The HELMOD method can be used to determine the field enhancement factors, as well as for detailed analysis of specific deformation mechanisms of nanoscale surface defects. The FEM simulations can give important insight into steady-state configurations and stress in the material with the possibility to estimate the stability conditions.

N.4.11
16:45
Authors : Doriane Djomani (1), Gilles Patriarche(3), Géraldine Hallais (1,2), Alexandre Jaffre (4), Charles Renard(1,2), Daniel Bouchier(1,2), Laetita Vincent (1,2).
Affiliations : (1) Université Paris-Sud, Institut d'Electronique Fondamentale, UMR 8622, Orsay, F-91405; (2) CNRS, Orsay, F-91405; (3) CNRS, Laboratoire de Photonique et de Nanostructures, UPR20, Marcoussis, F-91460 ; (4) Génie électrique et électronique de Paris, UMR 8507, 11, rue Joliot Curie, Plateau de Moulon, F-91192 Gif sur Yvette.

Resume : Nanowires show unique deformation behaviour resulting from the nanoscale size effect. This specific behaviour can cause unexpected structural reorganizations of atoms inducing the creation of novel functional materials as well as innovative heterostructures. We report on a stress induced martensitic phase transformation in Ge nanowires attributed to the size effect.<111>-oriented Ge nanowires with standard diamond structure (3C) undergo plastic deformation under external stress leading to a phase transformation toward the hexagonal 2H-allotrope. The obtained nanostructures exhibit Ge-2H nano-domains heterogeneously embedded along their length. This polytypism was successfully achieved from both bottom-up and top-down fabrication approaches with diameters ranging from 40 to 230 nm. Uncommon phases of Ge have been of high interest for researchers for the past two decades. Theoretical studies predict in particular a direct small gap in Ge-2H. Thereby, this novel heterostructure 2H/3C in Ge nanowires can pave the way to exciting applications of group-IV material for next-generation devices. For instance, the periodic formation of phase boundaries could induce a strong reduction of thermal conductivity while the electronic conductivity is conserved therefore enhanced thermoelectric properties are expected. Understanding the origin of this metastable phase formation is critical to evaluate the potential of those technological applications. The generation of the 2H allotrope was observed in both silicon and germanium upon hot indentation. The cubic to hexagonal diamond phase transformation was assigned to a martensitic phase transformation where a mechanism of local relaxation stress in the region of twin intersection was proposed. Structural (HRTEM) and physical characterizations have been performed in our transformed nanowires. We have studied various key parameters such as the diameters of the nanowires and the temperature of the transformation. A strain-induced martensitic transformation could account for the transformation in nanowires with a threshold temperature of 300° C; below this temperature the stress induces plastic deformation. In the case of nanowires twin-twin interaction seems yet not to be a relevant mechanism. Raman shift evidence both a residual stress within the nanostructures and the presence of the 2H phase.

N.4.12
17:00
Authors : Firas Abed El Nabi, Laurent Pizzagalli, Sandrine Brochard, Julien Godet
Affiliations : Pprime Institute – CNRS – University of Poitiers, FRANCE

Resume : While bulk silicon is brittle at temperatures below 600-700K, the compression of nanopillars has shown that a decrease of the diameter below few hundreds of nanometers could change the silicon behavior from brittle to ductile [1]. As silicon is free of initial defect, this size effect should be controlled by the cracks and/or the dislocations nucleation from the surface. The identification of the parameters governing the brittle to ductile transition in size and the understanding of the mechanisms are the key points to prevent the failure of microelectronic components based on the silicon strained technology. Nowadays the respective improvements in simulations and experiments allow to investigate the mechanical properties of objects of similar sizes, close to hundreds of nanometers. We considered atomistic simulations based on two different semi-empirical potentials fitted to better reproduce the ductile and brittle properties of bulk silicon. The simulations under tensile load show the nucleation of perfect dislocations from the surface that can lead to cavity opening when they interact [2]. We first observe that the height of the nanopillars must be higher than 20 nm to allow the cavity opening. Second, we show that the brittle to ductile transition is controlled by the diameter of the nanopillars, as observed experimentally in compression. The underlying mechanisms will be detailed. [1] F. Oestlund et al. AFM 19 (2009) 1 [2] F. Abed El Nabi et al MSMSE 23 (2015) 025010

N.4.13
 
Poster session : Ph. Carrez
17:30
Authors : M. M. Aish
Affiliations : MENOUIA UNIVERSITY, EGYPT

Resume : Molecular Dynamics (MD) simulations have been carried out on pure Nickel (Ni) crystal with face-centered cubic (FCC) lattice upon application of uniaxial tension at nanolevel with a speed of 20 m/s. The deformation corresponds to the direction <001>. To the calculated block of crystal - free boundary conditions are applied in the directions <100>, <010>. A many-body interatomic potential for Ni within the second-moment approximation of the tight-binding model (the Cleri and Rosato potentials) was employed to carry out three dimensional molecular dynamics simulations. A computer experiment is performed at a temperature corresponding to 10K, 300Kand 1000K. MD simulation used to investigate the effect of long of Ni nanowire on the nature of deformation and fracture. The feature of deformation energy can be divided into four regions: quasi-elastic, plastic, flow and failure. The nature of deformation, slipping, twinning and necking were studied. Stress decreased with increasing volume. The results showed that breaking position depended on the nanowire length.

N.N.1
17:30
Authors : Kovalyuk B., Nikiforov Yu., Mocharskyi V., Onisimchuk V., Popovych D.,
Affiliations : Ternopil Ivan Puluj National Technical University, Pidstryhach Institute for Applied Problems of Mechanics and Mathematics

Resume : Nowadays, laser shock waves (LSW) for modification of nanomaterials are widely used. In the presented research the back side of 100 microns copper screen which was in contact with the treated by LSW surface of ZnO nanopowder and polished steel is investigated. LSW were generated by Q-switched Nd-glass laser. The laser radiation was carried out in transparent condensed medium. Findings: damages are located on the back side of copper foil. The shapes and dimensions depend on type of material and conditions of experiments. The mechanism of damage after LSW passing through the sandwich: copper screen- acoustic lay-specimen is discussed. Moreover, the importance of scratches on the foil surface in damage forming is estimated. The system of periodical dents (holes) on the back side of copper foil is observed as the result of LSW treatment of ZnO nanopowder. The holes are oval, the dimensions range from 800 nm to 2-3 microns, the distance between them within 3-6 microns. Some of the holes are of sharp shapes. Besides, the tracks of steel strips on the back surface of copper are observed after LSW treatment. It testifies that LSW treatment of materials results in simultaneous processes: stamping and coil pulse action. The stamping is expected to be induced by the presence of transparent condensed medium and coil effect by the interference between incident and reflected LSW. This assumption is testified by experiments with suspended copper foil conducted additionally.

N.N.3
17:30
Authors : Anna Kosinova1, Ruth Schwaiger2, Oliver Kraft2, Eugen Rabkin1
Affiliations : 1 Department of Materials Engineering, Technion-Israel Institute of Technology, 32000 Haifa, Israel; 2 Karlsruhe Institute of Technology, Institute for Applied Materials, PO Box 3640, 76021 Karlsruhe, Germany

Resume : A wide application of thin metal films in the microelectronics industry requires smooth and defect-free surfaces. Therefore, their thermal and mechanical stability are of great importance. Surface defects can serve as nucleation sites for the onset of solid state dewetting upon heating. Here we present the results of dewetting studies of Au-Fe bi-layer films modified by nanoindentation. Au-Fe thin films (48 nm thick Au film on a 2 nm thick Fe underlayer) were deposited on sapphire substrates using electron beam deposition. The Au layer was bi-crystalline, exhibiting a [111] out-of-plane orientation and two twinning-related in-plane orientations. The arrays of nanoimprints (array size 100×100 m) were produced on the film surfaces with a Berkovich tip at applied loads of 0.1-0.4 mN. The samples were annealed in a forming gas flow (Ar + 10% H2) at 700 °C for different annealing times up to 24 h. After each treatment they were characterized by optical and atomic force microscopies. Upon heating the initially triangular imprints round off and evolve to a more rounded shape. Thermal treatment results in overgrowing of the imprints made at the applied loads of 0.2-0.1 mN, while at higher applied loads (0.4-0.3 mN) the hole formation at the imprints is observed. This fact is due to the higher penetration depth for higher loads, which facilitates the imprints to reach the substrate and to form a hole. Once the holes form, they grow laterally upon subsequent heat treatments without accumulation of material at the hole edges. We revealed that the probability of the hole formation increases with the distance between nanoimprints. The hole nucleation occurs preferentially at the edges of the array of nanoimprints, which is due to the stress gradient between the indented area and the rest of unperturbed film.

N.N.4
17:30
Authors : Xiao-Yu Sun, Vincent Taupin, Claude Fressengeas, Patrick Cordier
Affiliations : Unite Materiaux et Transformations, UMR 8207 CNRS/Universite Lille1, Villeneuve d?Ascq, France;Laboratoire d'Etude des Microstructures et de Mecanique des Materiaux (LEM3), Universite de Lorraine/CNRS, Ile du Saulcy, 57045 Metz Cedex, France

Resume : A crossover between atomistic description and continuous representation of grain boundaries in polycrystals is set-up to model the periodic arrays of structural units by using dislocation and disclination dipole arrays along grain boundaries. Continuous modelling of the boundary is built by bottom-up processing, meaning that the strain, rotation, curvature, disclination and dislocation density fields are calculated by using the discrete atomic positions generated by molecular dynamics simulations. Continuous modelling of a 18.9? symmetric tilt boundary in copper is presented. By linking the atomistic description with continuum mechanics representations, they provide new insights into the structure of the grain boundary.

N.N.5
17:30
Authors : Julien Godet, Clarisse Furgeaud, Michael J. Demkowicz
Affiliations : Pprime Institute – CNRS – University of Poitiers, FRANCE; Pprime Institute – CNRS – University of Poitiers, FRANCE; MIT - Dept. of Materials Science and Engineering, 77 Massachusetts Avenue, Cambridge, MA 02139-4307 USA

Resume : MIT - Dept. of Materials Science and Engineering, 77 Massachusetts Avenue, Cambridge, MA 02139-4307 USA

N.N.6
17:30
Authors : Shubhankar Majumdar, Rahul Kumar, Subhashis Das, Mihir Mahata, Dhrubes Biswas
Affiliations : Advanced Technology Development Centre, Indian Institute of Technology, Kharagpur, West Bengal, India

Resume : A numerical approach is employed to determine the optimum operating temperature of III-arsenide (As) alloys, at which the figure of merit, i.e. the product of sheet carrier concentration and mobility, is highest. From the material perspective, variation in optimum operating temperature is due to defect states. For this type of growth constrained problem support vector machine (SVM) is a viable candidate, because it is material system insensitive and efficient classifier. To the best of authors’ knowledge, for the first time, SVM is employed for the exact determination of performance variation, of grown epi-structure, with temperature. III-As alloys are grown by molecular beam epitaxy on GaAs (001) substrate, for demonstrating the SVM capability. Reflection high energy electron diffraction system (15 keV and 1.52 Amp) is employed for real-time growth monitoring, which shows a streaky 2 × 4 pattern that confirms the arsenic-rich surface reconstruction. Temperature dependent Hall measurements are performed by Vander-Pauw method with a 0.5T magnetic field, and the temperature varies from 90° K to 500° K in Accent HL5500 Hall measurement system. Indium-Tin alloy is utilized to form ohmic contact on the samples. Hall measurements generate a linearly separable data set that consist of mobility and sheet carrier concentration with respect to temperature variation. SVM model utilizes optimization of hyperplane equation to separate the dataset. The optimum operating temperatures for three samples, i.e. GaAs/GaAs, AlGaAs/GaAs and AlGaAs/InGaAs/GaAs, were calculated as, 207K, 243K, and 235K, respectively, via SVM model. At validation phase, the model shows an excellent match with experimental results.

N.N.8
17:30
Authors : Catherine Ainsworth, Brian Derby, William Sampson
Affiliations : School of Materials, University of Manchester, Manchester, United Kingdom

Resume : Silver nanowire (Ag NW) networks are an attractive substitute for ITO as a transparent conducting electrode material because Ag NWs are highly conductive and the network allows good transmittance of light. Ag NW networks however, unlike ITO, have also been shown to retain their conductivity after many bending cycles, meaning that the networks can be used in flexible TCE applications such as bendable touch screens. We would expect Ag NWs to exhibit tensile strengths greater than those of bulk Ag, in line with numerous studies of the strength of metal nanowires and micropillars measured in compression. Due to the difficulty in performing tensile tests on such a small area, there are a limited number of techniques currently being used, most of which utilise AFM to deform the nanowires. We are measuring the tensile properties of individual nanowires in-situ using a tensile stage in the SEM. With the NW secured by Pt deposition using a FIB, Load-Displacement data is collected allowing NW mechanical properties to be determined. Preliminary results indicate a yield strength of 1.8GPa for a nanowire with diameter 200nm.

N.N.10
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09:00
Authors : H. Idrissi1,2*, B. Amin-Ahmadi1, M.S. Colla2, C. Bollinger3, F. Boioli4, J.P. Raskin5, P. Cordier4, T. Pardoen2, D. Schryvers1
Affiliations : 1. Electron Microscopy for Materials Science (EMAT), Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium; 2. Institute of Mechanics, Materials and Civil Engineering, Université catholique de Louvain, Place Sainte Barbe 2, B-1348 Louvain-la-Neuve, Belgium; 3. Bayerisches GeoInstitut, University of Bayreuth, Bayreuth, Germany; 4. Unité Matériaux et Transformations, UMR 8207 CNRS/Université Lille1, Villeneuve d’Ascq, France ; 5. Information and Communications Technologies, Electronics and Applied Mathematics (ICTEAM), Microwave Laboratory, Université catholique de Louvain, Place Sainte Barbe 2, B-1348 Louvain-la-Neuve, Belgium

Resume : Recently, the development of a new generation of advanced instruments for in-situ TEM nanomechanical testing has allowed establishing a one-to-one relationship between load-displacement characteristics and stress-induced microstructure evolution in the transmission electron microscope. In the present work, it will be demonstrated that a step forward in the investigation of the small-scale plasticity mechanisms in crystalline and amorphous materials can be made by combining commercial [1] and in-house developed lab-on-chip [2] micro/nanomechanical testing techniques with advanced TEM techniques including high resolution aberration corrected TEM, Angstrom-beam-electron-diffraction as well as automated crystallographic orientation and phase mapping in TEM. These techniques have been used to reveal the fundamental plasticity mechanisms activated in nanocrystalline metallic thin films, metallic glass thin films and, more recently, the minerals of the Earth’s mantle. [1] H. Idrissi, A. Kobler, B. Amin-Ahmadi, M. Coulombier, M. Galceran, J-P Raskin, S.Godet, C. Kübel, T. Pardoen, D. Schryvers. Appl. Phys. Lett. 104 (2014) 101903 [2] H. Idrissi, B. Wang, M.S. Colla, J.P. Raskin, D. Schryvers, T. Pardoen. Adv. Mater. 23 (2011) 2119

N.5.14
09:30
Authors : Wei-Ting Liu, Lih-Juann Chen
Affiliations : National Tsing Hua University

Resume : Metal oxide nanowires have attracted considerable attention during past decades. The fundamental physical and chemical properties of these nanostructures have been widely investigated. Furthermore, the interfacial reactions of these nanostructures and metals also affect the performance of electronic devices that are one of the main applications of nanomaterials. With in situ transmission electron microscopy (TEM), we could provide essential information for the interface dynamics and phase transformation of nanomaterials. In the present work, we demonstrate the in situ TEM observation of the interfacial dynamics with In metal/SnO2 nanowire and Sn metal/In2O3 nanowire. Both metal oxide nanowires are fabricated by vapor-liquid-solid (VLS) method. The nanowires are dispersed on the grids with a 50 nm thick Si3N4 window. Afterwards, different metals with thicknesses of 10 to 25 nm were deposited directly by thermal deposition. The thermal treatment of the sample is carried out with the heating element built in the double tilt heating holder (JEOL EM-21240) and calibrated by the infrared pyrometer. Furthermore, we also use scanning electron microscopy and photoluminescence to analyze these diffusion phenomena and dynamics transformations. A number of efforts have been devoted to obtain fundamental information on the interfacial reaction of metal/metal oxide nanowires. The present experiments have been able to investigate in detail the mechanism of the interfacial dynamics of these nanostructures. Several different kinetic phenomena have been observed through ultra high vacuum (UHV) - in situ TEM system, such as reverse VLS process, metal oxide compound formation and diffusion with metal atoms. The diverse phenomena are correlated to the variation in temperature, structure size and vapor pressure.

N.5.15
09:45
Authors : Guilherme S. Fabris, Chad E. Junkermeier, Ricardo Paupitz
Affiliations : Departamento de Fisica, IGCE, Universidade Estadual Paulista, 13506-900, Rio Claro, SP, Brazil; Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park PA 16802, USA; Departamento de Fisica, IGCE, Universidade Estadual Paulista, 13506-900, Rio Claro, SP, Brazil

Resume : Inspired by the interest raised by Porous Graphene (recently synthesized) and other structures, like the theoretically predicted two-dimensional carbon allotrope Biphenilene Carbon (BPC) and by the topological relation between Graphene and Carbon nanotubes, we propose and investigate a new class of structures, the Porous Nanotubes. They are based on carbon nanotubes architecture and constructed by rolling up Porous Graphene (or BPC membrane) in order to form a Nanotube like structure with an organized porous pattern. We investigate structural and electronic properties of this class of quasi-one-dimensional materials using complementary methodologies. The Reactive Force Field (ReaxFF), used for structural stability and thermal properties calculations and the so called Density Functional Tight Binding (DFTB) method, for electronic structure calculations. Taking into account the possibility of tailoring some physical properties of these materials by geometrical modifications, electronic structure calculations were carried at equilibrium geometry and under mechanical stress, caused by small-scale deformations. Two classes of "Porous Nanotubes" were considered, one derived from Porous Graphene membranes and the second one constructed by rolling up BPC membranes. Calculations were carried for several diameter sizes and chiralities. We investigate also the possible use of these Porous Nanotubes as molecular sieves for selective separation of diatomic gases, like H2 from a mixture.

N.5.25
10:00
Authors : Marco Deluca (a), Jozef Keckes (b), René Hammer (a), Jochen Kraft (c), Sara Carniello (c), Stefan Defregger (a)
Affiliations : (a) Materials Center Leoben Forschung GmbH; (b) Erich Schmid Institute; (c) AMS AG;

Resume : Through silicon vias (TSV) are affected by high residual stresses due to processing and thermal mismatch between adjacent layers. A careful analysis and control of residual stresses around TSVs is mandatory to ensure mechanical and electrical stability of interconnect devices. Micro-Raman spectroscopy (µ-RS) is well-known for the study of residual stresses in Si-based devices. The greatest challenge in applying µ-RS is the identification of the stress tensor components contributing to the observed Raman signal for each experimental configuration. We used µ-RS and synchrotron X-ray microdiffraction (µ-XRD) to analyse strains in silicon in function of the distance from the wall of a tungsten-based TSV. To interpret the Raman results, a finite elements (FE) calculation of the strain tensor was performed, and then the Raman shift was reverse-calculated using the deformation potentials formalism. This is necessary since the observed Raman shift is a function of multiple strain tensor components. By comparing calculated and observed Raman shifts, a tuning of the FE model was possible. Strains obtained from the combined FE-Raman approach were then compared with the strain tensor from µ-XRD, providing good correspondence. These results confirm that µ-RS is a powerful, easy-to-use method that can complement or replace µ-XRD analyses for the study of TSVs. The main difficulties in Raman data interpretation can be overcome if suitable FE simulations are coupled with µ-RS.

N.5.9
10:15 Coffee Break    
11:00
Authors : I. Issa (1,2), J. Amodéo (1), L. Joly-Pottuz (1), J. Réthoré (2), C. Esnouf (1), J. Morthomas (1), J. Chevalier (1), K. Masenelli-Varlot (1)
Affiliations : (1) Université de Lyon, INSA-Lyon, MATEIS, UMR CNRS 5510, F-69621 Villeurbanne Cedex, France; (2) Université de Lyon, INSA-Lyon, LaMCoS, UMR CNRS 5259, F-69621 Villeurbanne Cedex, France

Resume : Nano-objects are attracting large attention nowadays due to their amazing mechanical properties in comparison to their bulk counterparts. In particular, they can exhibit far larger and size-dependent elastic limits [1]. Several mechanisms have been proposed, among which dislocation nucleation at the surfaces. Large numbers of studies have been dedicated to plastic deformation of metals at the nano-scale. On ceramic materials, previous works showed that these materials can exhibit significant plastic deformation, whereas the corresponding bulk materials are brittle. A better comprehension of the mechanisms involved in the deformation of ceramics at the nanoscale could help optimizing their fabrication process. The mechanical properties of ceramic nano-objects of a few tens of nanometers can be studied using in situ compression tests in TEM. This technique will be applied on MgO nanocubes. Deformation mechanisms will be proposed from the contrasts in the images and Molecular Dynamics simulations [4]. An experimental mechanical behavior law will be identified from the images and the force-displacement curves using Digital Image Correlation. The parameters (Young modulus, yield stress) will be discussed in function of the observation conditions as well as the nanocube size. [1] Kraft O. et al. Annu.l Rev. Mater. Res. 40 (2010) 293 [2] Korte S. et al. Acta Mater. 59 (2011) 7241 [3] Calvié E. et al. JECS 32 (2012) 2067 [5] Issa I. et al. Acta Mater. 86 (2015) 295

N.6.18
11:15
Authors : Pierre Hirel, Philippe Carrez, Patrick Cordier
Affiliations : UMET, Bat. C6, Université de Lille 1, 59655 Villeneuve d'Ascq, France

Resume : Bulk crystalline materials can often be sorted in two categories: on one hand metallic materials that are ductile in a broad range of conditions, and on the other hand materials like semiconductors, ceramics and minerals, which are brittle at ambient conditions. However some oxides, although referred to as ceramics, are known to show some ductility even at ambient temperature, like magnesium oxide (MgO). More surprisingly strontium titanate (SrTiO3) not only has a usual ductile-to-brittle transition when cooled below 1300 K, but it becomes ductile again below 1000 K. This inverse transition, quite unusual for a ceramic, raises questions about the mechanisms responsible for the plastic deformation in this class of materials. Recent experimental and theoretical studies allow for a better understanding of the mechanical behavior of perovskite materials, emerging from the atomic-scale structure and mobility of dislocations. We will present three examples: strontium titanate (SrTiO3) which is cubic at all temperatures; potassium niobate (KNbO3), a ferroelectric perovskite that exists in four different phases depending on temperature; and magnesium silicate (MgSiO3), a mineral that is stable only at very high pressure. The slip systems, dislocations properties, and mechanical behavior of these materials will be presented and compared. It will be shown that although all these materials belong to the same structural family, they do not form an isomechanical group and each perovskite has specific properties of its own.

N.6.19
11:30
Authors : James A. Wollmershauser, Boris N. Feigelson, Edward P. Gorzkowski, Kathryn J. Wahl
Affiliations : Naval Research Laboratory, Washington, DC USA

Resume : The application of modified slip-distance theory to observations of size effects in annealed polycrystalline copper suggests that hardness varies significantly with indent size when the indent size and grain size are within an order of magnitude of each other. However, simulations based on this theory also predict that small grained materials will appear to have a constant hardness and no indentation size effect (ISE) when the indentations are large. Extrapolating this result implies that nanocrystalline materials will only demonstrate ISE during nanoindentation and will not exhibit ISE during microindentation. The present paper explores these concepts with new nanocrystalline ceramics fabricated by recently developed Enhanced High Pressure Sintering. The nanocrystalline ceramics fabricated by this novel technique have average grain sizes as small as 28nm and demonstrate increasing hardness with decreasing grain size upon microindentation hardness measurements (i.e. the Hall-Petch relationship). Nanoindentation ISE studies of microcrystalline ceramics and these new nanocrystalline ceramics reveal similar ISE trends when the indent size is similar-to or smaller than the crystallite size. However, the mechanical response of the nanocrystalline ceramic becomes distinct when the indent size is orders of magnitude larger than the grain size. Effects of surface finish, such as mechanical and ion polishing, on the elasto-plastic transition are also explored.

N.6.20
11:45
Authors : Alexandre MUSSI 1, Patrick CORDIER 1, Sylvie DEMOUCHY 2
Affiliations : 1 University Lille 1, 2 University Montpellier 2

Resume : The deformation associated with convection flow from our cooling Earth is the driving force for plate tectonics. The study of the lithospheric mantle rheology (the uppermost mantle) is thus essential to understand plate tectonic dynamics and the coupling with the underlying convective mantle. Olivine, the upper mantle major silicate, deforms in the lithosphere at high pressure (>1GPa) relatively low temperatures (at c.a. 0.5Tm). Nevertheless, the plastic deformation mechanisms of olivine are not perfectly known in this temperature conditions yet. The previous studies have shown that, in this temperature range, plasticity is controlled by the screw [001] dislocation glide. These dislocations are mostly straight-line due to the high lattice friction of screw dislocations. Consequently, it is difficult to characterize the olivine slip systems near 0.5Tm. Dislocation electron tomography is a perfectly adapted tool for this study. It enables an access to the dislocation microstructure in 3D for a high dislocation number. In this study, we have used and we have optimized the electron tomography technique to identify the slip systems of olivine deformed at 0.5Tm. The new [001]{120}, [001]{130}, [001]{140} and [100]{041} slip systems have been determined. We have also characterized collinear annihilation mechanisms. Finally, the dislocation populations of olivine single crystals have been compared, with two different orientations, to understand the plastic deformation near 0.5Tm.

N.6.6
12:00
Authors : A. Gómez-Núñez, C. López, S. Alonso-Gil, A. Vilà
Affiliations : Department of Electronics, University of Barcelona, Martí i Franquès 1, E-08028-Barcelona, Spain. ; Departament of Inorganic Chemistry, University of Barcelona, Martí i Franquès 1. E-08028-Barcelona, Spain. ; Department of Organic Chemistry, University of Barcelona, Martí i Franquès 1, E-08028-Barcelona, Spain. ; Department of Electronics, University of Barcelona, Martí i Franquès 1, E-08028-Barcelona, Spain.

Resume : Printed electronics is a large-area low-price technology compatible with a wide variety of materials and substrates. In particular, inkjet printing is a non-contact green, on-demand, scalable and low-waste process with excellent capabilities to realize printed circuits on flexible substrates. However, sometimes organic-based metal-oxide precursors cannot be stabilized in solvent (such as ink) which is of particular importance in drop-on-demand systems. Thus, an adequate stabilizer is required. Previous work identified the molecular nature of the ZAD-EA precursor complex that constitutes the sol-gel film. Moreover, some particular volatiles were detected by EGA experiments on this precursor at various decomposition stages. Using the fundamental laws of quantum mechanics, Gaussian software predicts the energies, molecular structures, vibrational frequencies and reactions in a wide variety of chemical environments. In addition with the Car-Parinello approach, CPMD software is designed for ab-initio molecular dynamics and predicts molecular structures and their evolution over the free energy surface at specific temperatures. The present work uses these tools to computationally compare the effects of using some EA-equivalent aminoalcohols as stabilizers in ZnO sol-gel precursors and to compare and understand their optical and thermal degradation. This information is crucial to enhance the design of the ink, its thermal decomposition conditions and, ultimately, the ZnO properties.

N.6.23
12:15 Lunch Break    
14:00 round-table discussion    
15:15 Conclusion Symposium N    
18:00 Best Student Presentation Awards Ceremony and Reception (Main Hall)    

No abstract for this day


Symposium organizers
Philippe CARREZUniversity of Lille

Lab. UMET UMR/CNRS 8207 59655 Villeneuve d’Ascq France

+33 320 434861
philippe.carrez@univ-lille1.fr
Daniel KIENER Department Materials Physics Montanuniversität Leoben

Jahnstr. 12 8700 Leoben Austria

+43 3842 804 412
daniel.kiener@unileoben.ac.at
Jonathan AMODEO Lab. MATEIS UMR/CNRS 5510

25 avenue Jean Capelle 69621 Villeurbanne Cedex France

+33 4 72 43 82 35
jonathan.amodeo@insa-lyon.fr
Karsten DURSTMaterials Science, Physical Metallurgy (PhM) | Technische University Darmstadt

Alarich-Weiss-Straße 2 D-64287 Darmstadt Germany

+49(0)6151-16-76132
k.durst@phm.tu-darmstadt.de