Home
Symposium : D
Nano-scale energetic materials: fabrication, characterization and molecular modeling
| start at | Subject | Num. |
|---|---|---|
| Multi-scale molecular modeling and simulation : To be defined | ||
| 09:00 | Atomic-Scale Studies of Fundamental Properties and Processes in Shock Loaded Energetic Materials Authors : Thomas D. Sewell Department of Chemistry University of Missouri-Columbia Columbia, MO 65211 USA Resume : We have recently undertaken large-scale non-equilibrium molecular dynamics studies to aid our understanding of dynamical processes in the cyclic nitramine high explosives HMX and RDX, in particular the inelastic, anisotropic response of crystals of those materials subjected to quasi-static and shock loading. The same force field used by Sewell and co-workers in preceding simulations of HMX equilibrium properties is employed for the present research. The overarching goal of this work is to provide information that can serve as a foundation in basic science for the formulation of improved mesoscale constitutive models for the constituent materials in selected energetic formulations. The medium-term scientific challenge that stands as a prerequisite to this larger objective is to carefully identify, characterize, and quantify the dominant mechanisms of localization and dissipation in such materials, under a variety of prescribed quasi-static and dynamic loading scenarios that lead to inelastic deformation of the crystals. The focus of the present talk will be the shock response of structurally perfect, but properly thermalized, HMX and RDX crystal; shock localization in RDX crystals containing 20 nm defects (voids); and dynamics at RDX grain boundaries oriented parallel to the direction of shock wave propagation. Time permitting, additional topics including recent simulation studies of TATB and PETN physical properties and the development of a method for extending the time scales for which shocked materials can be studied using molecular dynamics will also be presented. | 5 1 |
| 09:25 | Al/Ni intermetallic energetic system: ab initio computational approach Authors : M. Petrantoni 1,2, A. Hemeryck 1,2, JM. Ducéré 1,2, A. Estève 1,2, C. Rossi 1,2, M. Djafari Rouhani 1,2, D. Estève 1,2, G. Landa 1,2 1 CNRS ; LAAS ; 7 avenue du colonel Roche, F-31077 Toulouse, France 2 Université de Toulouse ; UPS, INSA, INP, ISAE ; LAAS ; F-31077 Toulouse, France Resume : An approach based on Density Functional Theory (DFT) is developed to better understand the behaviour of nanostructured energetic materials and to predict their properties. We investigate a simple bimetallic model-system (Al/Ni) showing exothermic reaction.
During deposition, the formation of an alloy barrier layer between Al and Ni species stabilizes the system. In order to integrate this type of materials into micro or nanosystems, it is crucial to control the formation of this barrier layer because of its effects on the physical properties and the overall energetic characteristics: ignition and energy release.
We here detail possible adsorption and diffusion mechanisms using DFT calculations to provide the kinetic and thermodynamic parameters of the reaction mechanisms. We compare both periodic and cluster approaches. A systematic comparison is performed to reveal and avoid undesirable constraints and/or long range effects that could impact severely the system interactions. The set up of adequate constraints, to reach a good compromise between periodic and cluster techniques, is presented.
We observe that Ni atoms diffuse into the top layer of Al during deposition of a Ni layer because of the low activation energy (0.06 eV). Al diffusion into Ni layer needs higher activation energy (2.5 eV). So, Ni diffuses preferentially in Al layer during Ni layer deposition. The Al diffusion in Ni is possible at higher temperatures than usual conditions. | 5 2 |
| 09:45 | Metascalable Atomistic Simulations of Nano-mechano-chemistry on Petaflops Computers Authors : Aiichiro Nakano, Professor Collaboratory for Advanced Computing and Simulations Department of Computer Science Department of Physics & Astronomy Department of Chemical Engineering & Materials Science University of Southern California 3651 Watt Way, VHE 610 Los Angeles, CA 90089-0242 Resume : We have designed a metascalable (or \\\\\\\\\\\\\\\"design once, scale on
new architectures\\\\\\\\\\\\\\\") simulation framework for large spatiotemporal-
scale (multibillion atoms for nanoseconds) simulations of nano-mechano-
chemistry on petaflops computers. The framework has achieved parallel
efficiency as high as 0.99 on 212,992 IBM BlueGene/L processors for
218 billion-atom molecular dynamics simulation and 1.68 trillion
electronic degrees-of-freedom quantum-mechanical calculation in the
framework of the density functional theory. Simulation results reveal
atomistic mechanisms of: (1) enhanced reaction in nanoenergetic
materials (e.g., nanojet-catalyzed reaction in a defected energetic
crystal and a concerted metal-oxygen flip mechanism at the metal/oxide
interface in thermites); and (2) sulfur-induced grain boundary
amorphization and embrittlement of nickel. | 5 3 |
| 10:15 | COFFEE BREAK | |
| 10:30 | Multimillion Atom Simulations of Reactive Nanosystems Authors : Priya Vashishta, Rajiv K. Kalia and Aiichiro Nakano Collaboratory for Advanced Computing and Simulations (CACS) Departments of Chemical Engineering & Materials Science, Physics & Astronomy, and Computer Science University of Southern California, Los Angeles, CA 90089-0242, USA Resume : Advanced materials and devices with nanometer grain/feature sizes are being developed to achieve higher strength and toughness in ceramic materials and greater speeds in electronic devices. Below 100 nm, however, continuum description of materials and devices must be supplemented by atomistic descriptions. Current state of the art atomistic simulations involve 10 million – 1 billion atoms. MD simulations are performed to study critical issues in the area of structural and dynamical correlations, and reactive processes in nanostructured materials under extreme conditions. We report the results of MD simulations of atomistic mechanisms of the oxidation of a Core (Aluminum)-Shell (Alumina) nanoparticle (ANP) are investigated using multimillion-atom molecular dynamics simulations. We find a thermal-to-mechanochemical transition of oxidation mechanism at elevated temperatures. The transition from thermal diffusion to mechanically enhanced diffusion to ballistic transport of atoms is accompanied by a change of intermediate reaction products from aluminum-rich to oxygen-rich clusters. Higher initial temperature of the Al core causes catastrophic fracture of the alumina shell during the expansion of the ANP, which provides direct oxidation pathways for core Al atoms, resulting in faster oxidation reaction and thus faster energy release. Initiation of chemical reactions at shock fronts prior to detonation and dynamic transition in the shock structure of an energetic material (RDX) will also be discussed. | 0 |
| 10:55 | Oxidation of nanocrystalline Aluminum by variable charge molecular dynamics. Authors : A. Perron, S. Garruchet, O. Politano, G. Aral* and V. Vignal ICB, UMR 5209 CNRS-Université de Bourgogne 9 AV. Alain Savary, 21000 Dijon, FRANCE *Institut of Physics, Izmir Institut of Technology, Gulbahce Campus, TR-35437, Urla, Izmir, Turkey Resume : We investigate the oxidation of nanocrystalline aluminum surfaces using molecular dynamics (MD) simulations with the variable charge model that allows charge dynamically transfer among atoms [1-3]. The interaction potential between atoms is described by the electrostatic plus (Es+) potential model, which is composed of an embedded atom method potential and an electrostatic term.
The simulations were performed from 300 to 750K on nanocrystalline samples with a mean grain size of 5 nanometers. We mainly focused on the effect of the temperature parameter on the oxidation kinetic. The results show that, beyond a first linear regime, the kinetics follow a direct logarithmic law (governed by diffusion process) and tend to a limiting value corresponding to a thickness of ~3nm. We also characterized the microstructure and the chemical composition of the oxide films obtained by using different oxygen pressures, temperatures and external applied strains. The present work permits to characterize for the first time by MD the growth of a partially crystalline oxide layer. We will also show a correlation between the crystallinity of the oxide film and the oxidation temperature.
[1] F.H. Streitz and J.W. Mintmire, Phys. Rev. B 50 (1994) 11996.
[2] A. Hasnaoui, O. Politano, J.M. Salazar and G. Aral, Phys. Rev. B 73 (2006) 035427.
[3] T.J. Campbell, G. Aral, S. Ogata, R. Kalia, A. Nakano, P. Vashishta, Phys. Rev. B 71 (2005) 205413. | 5 4 |
| 11:20 | Predictive modelling of the premixing interface layer in nanoenergetic materials using a large scale mesoscopic tool Authors : A. Hemeryck1, M. Petrantoni1, A. Estève1, C. Rossi1, M. Djafari Rouhani1,2, G. Landa1 and D. Estève1 1CNRS ; LAAS ; 7 avenue du colonel Roche, F-31077 Toulouse, France 2Université de Toulouse ; UPS, INSA, INP, ISAE, LAAS ; F-31077 Toulouse, France Resume : The main technological processes used for multilayer energetic materials fabrication are based on deposition techniques (ALD, PVD…). These processing conditions lead to an interface premixing layer between the constituents of the nanoenergetic materials to be further ignited. The premixing layer, in which both composition and structure are unknown, is shown to be one of the major sources of the decrease in performance of the overall energetic materials. Controlling this interface structure and its formation become crucial in order to get tailored energetic materials in terms of ignition rate and the amount of released energy.
This limitation for energetic materials applications can be overcome by developing virtual predictive tools able to predict the evolution of the system at each step of their life, particularly design, fabrication and utilization phases. The present work provides an atomistic picture of the diffusion mechanisms linked to the interface rearrangement during the deposition process. The multi-scale model combines DFT calculations, for the characterization of the elementary mechanisms, and a kinetic macroscopic tool, able to reproduce the formation of the premixing interface and its evolution under realistic processing conditions. Results are reported as a function of temperature, pressure, deposition time and layer thicknesses for a Ni/Al multilayer model system. | 5 5 |
| 11:40 | Simulation of Thermolysis Decomposition Mechanisms for Bicomponent Nanosystems Authors : Tatyana S. Pivina*, Tatyana V. Petukhova**, Boris L. Korsunsky***, and Victor P. Ivshin** *Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Leninsky Prospect 47, Moscow 119991, RUSSIA **Mari State University, Lenin square 1, Yoshkar-Ola, 424000, Mari El Republic, RUSSIA *** Semenov Institute of Chemical Physics, Russian Academy of Sciences, 117977 Kosygin Str. 4, Moscow, RUSSIA Resume : Earlier, we simulated the mechanisms of both Arrhenius (purely thermal) and mechanochemical (non-thermal) decomposition for individual energetic materials (EMs), because our approach makes it possible to generate the complete spectrum of reactions that are formally possible during thermolysis of organic compounds from various chemical classes. We believe that this approach can be extended to binary systems, thus proceeding to simulation of thermal decomposition mechanisms for nanoparticles and then to analysis of interactions between different substances.
Owing to high specific surface area of nanosystems, efficient contact between different solids and interactions between them become possible. The specificity of nano-EMs is manifested in the fact that the characteristic times of matter and energy transfer are significantly shorter, and reactions that are not characteristic of macrokinetic decomposition become possible. Therefore, computer-aided simulation of thermolysis mechanisms for multicomponent systems in the form of a complete spectrum of formally possible reactions within thermal decomposition may be quite helpful for predicting the thermolysis mechanisms for nano-EMs.
Since no computer simulations of decomposition of multicomponent systems have been performed by now, we started development of our approach from studies of possible interactions between simple model compounds belonging to different classes of EMs. The results of this study are presented in this investig | 5 6 |
| 12:00 | LUNCH | |
| new energetic material and synthesis process : to be defined | ||
| 14:00 | Studies of the reaction between iron carbide dispersed in a carbon matrix and water vapour with hydrogen generation Authors : Ewa Ekiert, Walerian Arabczyk West Pomeranian University of Technology, Institute of Chemical and Environment Engineering, Pułaskiego Street 10, 70-322 Szczecin, Poland Resume : A classic procedure of hydrogen generation with Steam Iron Method, in which the metallic iron obtained by reducing with mixture of hydrogen and carbon monoxide from coal gasification is subsequently oxidized by steam to produce iron oxide and hydrogen, is performed at temperatures as high as 800oC.
The interaction of water vapour and iron carbide dispersed in a carbon matrix, which was produced by catalytic decomposition of methane on the nanocrystalline iron, was investigated by thermogravimetric analysis with a mass spectrometer. It was observed that iron carbide dispersed in a carbon matrix starts to react with water vapour from as low as 300oC in temperature with simultaneously generation of hydrogen. The concentration of hydrogen increased with rising of temperature. The maximum temperature was estimated as 450oC. Above this value a carbon matrix starts to react with water vapour with generation of carbon monoxide. This effect is very undesirable because the carbon matrix accelerates the oxidation of iron carbide and the rate of iron carbide oxidation is linearly dependent on iron carburization degree.
Acknowledgement: The work has been co-financed by European Union within the framework of European Social Fund and the Country\\\'s Budget, Human Capital Operational Programme of Priority VIII, systemic project implemented by the provincial job centre in Szczecin \\\"Investment in knowledge stimulates innovation in the region\\\". | 6 1 |
| 14:20 | Phosphorus based nanothermites: a new generation of energetic materials Authors : Marc COMET, Vincent PICHOT, Benny SIEGERT, Denis SPITZER comet@isl.tm.fr, pichot@isl.tm.fr, siegert@isl.tm.fr, spitzer@isl.tm.fr Resume : Thermites are energetic materials which are classically made of a transition metal oxide mixed with a reducing metal . Contrary to explosives, thermites do not detonate because their combustion is relatively slow and their decomposition by-products are often solid or liquid. The use of nanoparticles to prepare superthermites is very promising. The dramatic changes observed in their reactivity were reported by numerous recent papers. Up to now, most of the studies dealing with nanothermites relate to compositions in which aluminium is used as a fuel.
Red phosphorus is widely used in pyrotechnic devices . Highly explosive compositions are classically obtained by mixing this substance with strong oxidizers such as potassium chlorate, silver nitrate or potassium permanganate. But to our knowledge, the idea to prepare P-nanothermites with metallic oxide nanoparticles was never reported before. In order to illustrate this new concept of energetic formulations, P-nanothermites were prepared from iron oxide (Fe2O3), nickel oxide (NiO) and copper oxide (CuO). The reactivity of these compositions was studied by thermogravimetric analysis, impact and friction tests and high speed cinematography. P-nanothermites are very insensitive to thermal and impact stress. They possess combustion rates which strongly depend on the nature of the oxide (NiO < Fe2O3 << CuO). The SEM observation of the microstructure of the metallic residues produced by the combustion clearly indicates that they were formed by the solidification of molten phases. In other words, P-thermite reactions release large amounts of energy which provoke the gasification of P4O10 formed by the combustion. For this reason, P-thermites can be considered gas generating materials. | 6 2 |
| 14:40 | Temperature induced nanoparticle assembly Authors : Philip Born, Eoin Murray, and Tobias Kraus Leibniz Institute for New Materials (INM), Saarbrücken Resume : We form superstructures from monodispersed nanoparticles that have complex, regular structures, which we hope to exploit for materials engineering. These materials have potential applications in many fields including electronics, photonics, catalysis and thermoelectrics.
The assembly of nanoparticles into ordered supercrystals has been previously demonstrated by increasing the particles’ interaction potential or decreasing the available volume. Here, we show how temperature variations at constant interparticle potential and average spacing effects structure formation in sterically stabilized, nanosized colloids. The colloids are chosen such that their interaction potentials lead to particle aggregation below some critical temperature near room temperature at moderate concentrations.
We vary the interparticle potential (with its attractive part mainly due to van der Waals interaction) by the choice of nanoparticle material and self-assembled capping monolayers. From metallic through semiconducting to insulating particles, the Hamaker coefficient could be varied over two orders of magnitude. In our experiments, Au, CdSe, and SiO-particles were used with stabilizing alkyl ligands. The chain length of the alkyls was varied from 6 to 18 C-atoms (forming self-assembled monolayers with thicknesses ranging from 0.5 to 2 nm). The particle assembly was monitored in-situ using dynamic light scattering and the resulting structures were characterized by bright field transmission electron microscopy and electron diffraction.
Sharp transitions from the stable colloidal state to agglomeration were observed. The temperature of the transition depended strongly on particle concentration and solvent polarity. By varying the temperature, the growth rate of the nanoparticle superstructures was modified, influencing the ordering and packing density of the particles in the structures. We hypothesize that this transition can be understood similarly to atomic crystallization or amorphous solidification. The results of this study further the understanding of the behaviour of colloids during temperature and concentration changes, from drying ink and wall paint to the formation of functional nanoparticle superstructures. | 6 3 |
| 15:00 | Nanometric tungsten oxide synthesis and thermite characterization Authors : N. Le Houx1, G. Pourroy1, M. Comet2, D. Spitzer2, F. Lacroix2, O. Muller2 1- Institut de Physique et Chimie des Matériaux, UMR 7504 CNRS-ULP, 23, rue du Loess, BP 43, 67034 Strasbourg cedex 2, France 2- Laboratoire des Nanomatériaux pour Systèmes Sous Sollicitations Extrêmes, NS3E, UMR ISL-CNRS 3208, Institut franco-allemand de Saint-Louis (ISL), 5, rue du général Cassagnou, 68301 Saint-Louis, France Resume : Non hydrolytic sol gel syntheses have been under investigation for several years now, and benzyl alcohol has proved to be an interesting route to obtain nanoparticles of various shapes and sizes , . Our study has focused on the synthesis of tungsten trioxide through a solvothermal process in benzyl alcohol, using tungsten hexachloride as precursor. Many experimental conditions were studied: experiments were carried out in different types of equipment, mostly in an automated autoclave and in a microwave furnace, and synthesis parameters such as reaction volume, experiment duration and concentration were studied, while keeping a focus on the effects of final synthesis temperature and heating rate. In the end, the resulting nanoparticles showed a wide variety of shapes – from spheres to platelets, sizes – from 6 to 50 nm, and crystal structures – from finely structured monoclinic tungsten oxide to slightly amorphous substoichiometric tungsten oxide.
Subsequent tests on thermite reactivity were carried out by mixing with aluminum nanoparticles in hexane, drying the thermite and pressing it into pellets, and using laser ignition with time-resolved cinematography to determine combustion rates and ignition delay times. The incidence of size and shape of the particles on the thermite reactivity will be discussed. | 6 4 |
| 15:20 | Nitrogen Rich Doped Carbon Nanotubes as Novel Nanoscale High Energetic Materials: Modeling and Experiments Authors : Hakima Abou-Rachid a, Mounir Jaidann a, Louis-Simon Lussier a, Yanfeng Songb , Yu Zhongc, Hao Liu c, Mihnea Ionescu c, Ruying Li c, Xueliang Sun c Resume : Recently, we have proposed nanoscale confinements to stabilize polynitrogen and polymeric nitrogen with carbon nanotubes. Nitrogen armchain and cubane N8 encapsulated inside carbon nanotubes, [1] and 1,2,3-triazine-like N4 doping onto carbon nanotubes, nanoscale polynitrogen and polymeric nitrogen systems, have been studied using first-principles simulations in the framework of density functional theory in condensed phases. Here, we present our theoretical simulations on several nitrogen rich energetic materials confined inside a carbon nanotube. These molecules have been received a great attention as an example of a cyclo-aromatic energetic material without a nitro-group as an oxidizing group. The structure properties, electronic structures, and heats of formation of this system have been studied in one hand. On the other hand, the experimental work of nitrogen doping into carbon nanotubes (N-doped CNTs) also was carried out. Floating catalyst chemical vapor deposition method was used. Melamine as carbon and nitrogen sources and ferrocene as catalyst result in 10 at% nitrogen in carbon nanotubes. The N-doped CNTs show bamboo-like structure (Fig.1). | 6 5 |
| 15:40 | COFFEE BREAK | |
| 16:00 | Les nanomatériaux et les besoins futures pour les matériaux énergétiques Authors : Jean-Yves KERMARREC DET/CEP/MAN/PE, DGA, BAGNEUX, FRANCE Resume : Les nanomatériaux et les besoins futures pour les matériaux énergétiques | 1 2 |
| POSTER : ... | ||
| 16:00 | DEVELOPMENT OF AL/NIO NANO ENERGETIC MATERIAL ON SILICON SUBSTRATE Authors : Ludovic Salvagnac, Kaili Zhang, Carole Rossi, Pierre Alphonse, Christophe Tenailleau LAAS-CNRS, Université de Toulouse, 7 ave du colonel Roche, 31077 Toulouse cedex 4, France b CIRIMAT, 118 route de Narbonne, 31062 Toulouse cedex 04, France Resume : In this work, the authors propose a way to synthesize an Al/NiO nano energetic material (nEM), which is fully compatible with microsystem. Two-dimensional (2D) NiO nano honeycomb is achieved by thermally annealing Ni film deposited onto silicon substrate by thermal evaporation. Then the NiO nano honeycomb is integrated with Al that is deposited by thermal evaporation to realize an Al/NiO nEM. This approach has advantages over previous investigations including lower ignition temperature, enhanced contact, reduced impurities, tailored dimensions, and easier integration into microsystem.X-ray diffraction shows the entire Ni film is oxidized into pure NiO after annealing. The deposited thickness of Al is 0.21 µm. It can be seen that Al is intimately integrated with the nano honeycomb, thus enhancing the interfacial contact area between Al and the NiO nano honeycomb.
The exothermic reaction of the Al/NiO nEM is characterized by differential scanning calorimetry and differential thermal analysis. The results suggest that nano Al reacts with NiO nano honeycomb with an onset temperature as low as 400 oC. The total heat of reaction is about 2200 J/g. The realized Al/NiO nEM has enhanced contact, lowered ignition temperature, reduced impurities, and tailored dimensions. Most interestingly, the nEM is realized onto silicon, a basic material for microelectronics and microsystem. Therefore, this will open the door to integrate the nEM into microsystem, thus leading to functional devices, | 6 6 |
| 16:00 | Dynamic Properties of Cantilevered Carbon Nanotube Resonator Encapsulating Copper Nanocluster Authors : Sun-Young Jung, Jeong-Won Kang* Chungju National Unversity, Republic of Korea Resume : Ultrahigh frequency carbon nanotube resonator encapsulating nanocluster was investigated via classical molecular dynamics simulations. Although primary frequencies for nanotube resonator encapsulating copper nanocluster were less than frequency of bare nanotube resonator, ultrahigh harmonic frequencies, which were impossible to be achieved from bare CNT resonator, could be achieved from controlling nanocluster’s position inside nanotube resonator. Such phenomena were due to the migration of the encapsulated copper nanocluster by the centrifugal force induced by vibrating nanotube resonator. Nanotube resonators encapsulating movable nanocluster has much potential to develop an ultrahigh frequency generator, tuner or band pass filter, ultrahigh fast supercomputer or quantum computing, ultra sensitive nanoscale inertia measurement unit, data storage media, ultrahigh resolution magnetic force microscope, gigahertz electromagnetic field source, and bio-nanoelectromechanical system. | 6 7 |
| 16:00 | Structural and thermal characterisation of mechanically alloyed Ni-Co powder mixture Authors : N. Bensebaa1*, N. Loudjani1, L. Bouras1, J.J. Suñol2, S. Alleg1 and J.M. Grenèche3 1Laboratoire de Magnétisme et de Spectroscopie des Solides (LM2S), Département de Physique, Faculté des Sciences, Université de Annaba, B.P. 12, 23000 Annaba, Algérie. 2 Dep. De Fisica, Universitat de Girona, Campus Montilivi, Girona 17071, Spain. 3 Laboratoire de Physique de l’état condensé – URM A 6087, Université du Maine, 72085, Le Mans Cedex 9, France. Resume : The aim of the present work is to follow the alloying process progresses of the Ni20Co80 (wt%) alloy prepared by high energy ball milling. The starting materials are crystalline powders of Ni and Co with purity of 99.9%. High-energy ball milling was performed in a planetary ball mill (Fritsch, P7) under argon atmosphere. The ball to powder weight ratio was 35/4 and the milling intensity was 8. Morphological changes of powder particles, structural and thermal properties of the milled powders were followed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC), respectively, as a function of the milling time. Structural and microstructural parameters (lattice parameters, microstrains, crystallite size, atomic positions and phase percentages) were deduced from the Rietveld refinement of XRD patterns, by using the MAUD program, and discussed as a function of milling time. The best refinement of the XRD patterns reveals the formation of the Ni(Co) solid solution with a fcc structure. The crystallite size refinement down to the nanometer scale is accompanied by an increase in the interval level strain. DSC results show a broad exothermic reaction indicating a recovery process. | 6 8 |
| 16:00 | Kinetic processes and confinement effects on the growth of one-dimensional Cu chains on the Pt vicinal surfaces Authors : H.Garbouj a *, F.Picaud b, M.Said a and C.Ramseyer b a Département de Physique, Université de Monastir, Faculté des Sciences de Monastir, UR1319, 5019 Monastir, Tunisie b Laboratoire de Physique Moléculaire, Université de Franche-Comté, 25030 Besançon, France Resume : Heteroepitaxial growth of the Cu-Pt system is investigated by using a Kinetic Monte Carlo simulations based on semi-empirical description of metal-metal interactions to interpret recent experiments devoted to the formation of copper wires on the steps of the vicinal Pt surface. We show that step decoration on the Pt (997) vicinal surface occurs for the narrow temperature range [275, 300] K in agreement with growth experiments. An exchange mechanism leading to interlayer diffusion at step edges is shown to influence the temperature range for which the perfect Cu wires are observed. An activation barrier higher than 0.6 eV for this exchange processes is found to be adequate to reproduce the experimental features observed by K.Kuhnke and K.Kern. We show at 350 K a detachment of Cu adatoms from Pt steps, whish strongly hinders the wire formation at step feet, this result is in accord with experiment observed by Gambardella. We have also studied the role of the confinement of Pt vicinal surface on the growth of one-dimensional Cu chains for T=200 K. | 6 9 |
| 16:00 | Study of infrared profile and inhomogeneous broadenings of CO adsorbate on MgO surface Authors : H. Zorgatia, M. Saida, C. Ramseyerb and C. Girardetb a UR physique des solides, Département de Physique, Université de Monastir, Faculté des Sciences de Monastir, 5019 Monastir, Tunisia b UTINAM, Laboratoire de Physique Moléculaire, UMR 6213, Université de Franche-Comté, 25030 Besançon, France zorgati_hanen@yahoo.fr Resume : The control of the quality of a surface at the nanoscopic scale has become a challenge in modern technology. The presence of point and / or extended defects on a physical surface is at the origin of disturbances in the properties of the surface or, on the contrary, it can help self-organisation of adsorbates. In both cases, probing the surface to detect the nature, size and location of the defects is required. We study the infrared response of CO molecules deposited on a physical ionic surface of MgO containing dipolar defects in various concentrations and distributions. More precisely, we consider that the molecules are randomly deposited at low coverage on a square surface containing itself randomly distributed dipolar defects. The Monte Carlo process is used to describe their radial and orientational distribution functions depending on the temperature in the canonical ensemble. As the coverage of adsorbates increases, the main peak frequency of the infrared profile significantly broadens but does not appreciably shift. However, when dipolar defects are present on the surface, the later peak is shifted and broadened when the coverage of defects increases. We conclude that dipolar molecules deposited on a physical ionic surfaces act as probes of dipolar defects. | 6 10 |
| 16:00 | Modeling of step decoration of Ni/Pt surfaces Authors : W. Essolaania, M. Saida and C. Ramseyerb a UR physique des solides, Département de Physique, Université de Monastir, Faculté des Sciences de Monastir, 5019 Monastir, Tunisia b UTINAM, Laboratoire de Physique Moléculaire, UMR 6213, Université de Franche-Comté, 25030 Besançon, France wafaess_fsm@yahoo.fr Resume : Nickel is known to exhibit specific properties at the nanometer scale. A lot of experiments and ab initio calculations are devoted of Ni wires formed at the step feet of vicinal surfaces on a large range of temperature. However, the wire formation is still misunderstood. We have performed a semi – empirical potential calculation in order to extract the diffusion barriers responsible for the growth process of Ni wires on the Pt surfaces. To investigate the wire formation at step edges, Kinitic Monto Karlo (KMC) simulations have been performed.
To study the role of the neighborhood in the process of growth of Ni adatom on step surface, two kinds of simulations are investigated. In the first simulations, we take into account only the first neighbors around the departure and the arrival sites of diffusion. The complete filling of the first row in the step is obtained at T around 500K for the two cases of steps (step A and B). This value is quite different from the common experimental temperature observed to grow nanowires on metal surfaces (typically 300K). The second simulation takes in to account of the next nearest neighbors, leads to a complete filling near 350K in agreement with growth experiments. | 6 11 |
| 16:00 | The influence of the quantum dot shape on the quantum confinement energy levels Authors : A.-M. Lepadatu(1), E. Rusnac(1), I. Stavarache(1), V. S. Teodorescu(1), M L Ciurea(1), and V Iancu(2) (1)National Institute of Materials Physics, 105 bis Atomistilor Street, Magurele 077125, Romania (2)“Politehnica” University of Bucharest, 313 Splaiul Independentei, Bucharest 060042, Romania Resume : We have studied the influence of the shape on the quantum confinement energy levels for silicon quantum dots embedded in an amorphous silica matrix. For this, we have analyzed the case of prolate spheroidal dots in the infinite quantum well (hard spheroid) approximation. The model is referred to the microstructure investigations and to the experimental energies for Si dots embedded in a-SiO2 (deduced from the Arrhenius behaviour of the I – T curves). From the microstructure investigations it resulted that part of the dots are not spherical, but prolate spheroids (ellipsoids with the axes a = b ≤ c, with c/a = 1.3 ± 0.2, the equivalent diameter d being calculated from the condition of equal volume)). From the I – T curves, three activation energies, representing the differences between consecutive quantum confinement energies, were obtained (E1 = 0.22 ± 0.02 eV, E1 = 0.32 ± 0.02 eV, E1 = 0.44 ± 0.02 eV). For transitions under high electric field (eU >> kT), the selection rules are Δl = Δm = 0 (l and m are the orbital and magnetic quantum numbers). For the simplified hard sphere model, the energy is degenerated over m and we obtain l = 1, d = 5.2 ± 0.4 nm. For the hard spheroid model, the three experimental activation energies can be simultaneously fitted only for l = 1, m = 0. Then c/a = 1.15 ± 0.03 and d = 5.26 ± 0.02 nm, in good agreement with the results obtained from both the microstructure investigations and the hard sphere model. | 6 12 |
| 16:00 | Structural study of mechanically alloyed Fe-P Authors : W. Tebib (a), S. Alleg (a), and J. M. Grenèche (b). (a) Laboratoire de Magnétisme et de Spectroscopie des Solides ( LM2S), Faculté des Sciences, Université de Annaba, B. P. 12, Annaba 23000, Algérie. (b) Laboratoire de Physique de l’Etat Condensé – UMR 6087, Université du Maine, Le Mans Cedex 9, 72085 France. Resume : Nanostructred materials have attracted considerable scientific and technological interest during the last decades since they show high potential for various engineering applications due to their interesting structural, magnetic and thermal properties. Elemental Fe and red phosphorus powders with a composition close to Fe-xP wt. % (x = 10, 15, 20) were mechanically alloyed in a planetary ball mill under an argon atmosphere. The structural changes were studied using X-ray diffraction (XRD). Mechanical alloying leads to a complete dissolution of the elemental powders forming an -Fe solid solution and different iron phosphides, after 3 h of milling, through a self-sustaining reaction. Detailed analyses of the X-ray spectra using the Maud program which is based on the Rietveld method reveal the dependence of the structural parameters on P concentration. | 6 13 |
| 16:00 | Effects of the surrounding medium on the photoexcited electron and phonon dynamics of Au nanoparticles characterized using transient grating technique Authors : Q. Shen (a), K. Katayama (b), T. Sawada (c) and T. Toyoda (a) (a) Department of Applied Physics and Chemistry, The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan (b) Department of Applied Chemistry, Faculty of Science and Technology, Chuo University, 1-13-27 Kasuga, Bunkyo, Tokyo 112-8551, Japan (c) Japan Science and Technology Agency, Kawaguchi Center Building, 4-1-8, Honcho, Kawaguchi-shi, Saitama 332-0012 Japan Email: shen@pc.uec.ac.jp; toyoda@pc.uec.ac.jp Resume : Metal nanoparticles have attracted much attention because they show interesting optical, electronic and chemical properties. In particular, they have a characteristic feature of localized surface plasmon resonance (LSPR). Such metal nanoparticles have potential applications in biological sensors and optoelectronic devices. Recently, it is found that photoinduced charge separation based on LSPR is possible between the interface of Au nanoparticles and TiO2 electrodes. Thus, a new type of metal nanoparticle-sensitized solar cells is promising. For these applications, photoexcited electron dynamics are very important. Especially, the issue of how the environment affects the electron and phonon dynamics is significant. In this study, we investigate photoexcited electron dynamics of Au nanoparicles (average size: 20 nm) with different environment, i.e., (a) in ethanol, (b) adsorbed onto mesoporous TiO2 films, by using a transient grating (TG) technique [1]. From the TG responses, two decay processes are observed. For the samples (a) and (b), the decay times of the fast decay processes are 2.4 and 1.3 ps, and the decay times of the slow ones are 125 ps and 410 ps, respectively. The fast and slow decay processes are attributed to the electron-phonon coupling and phonon-phonon coupling, respectively. Our experimental results indicate that the surrounding medium affects the electron and phonon dynamics greatly.
[1] K. Katayama et al., Appl. Phys. Lett. 82 (2003) 2775. | 6 14 |
| 16:00 | Double Complex Salts [M(NH3)4][Co(C2O4)2(H2O)2]•2H2O (M = Pt, Pd) – single-sourse precursors of nanoalloys Authors : E. Filatov, A. Zadesenets, P. Plyusnin, S. Korenev Nikolaev Institute of Inorganic Chemistry SB RAS, 630090 Novosibirsk, Lavrentyev Ave.3, Russia Novosibirsk State University, 630090 Novosibirsk, Pirogov St.2, Russia Resume : Ultradisperse bimetallic powders attract great interest among large sections of researchers. These systems possess outstanding physicochemical properties, which are not typical for bulk or single-component materials. The considerable quantity of works is devoted to systems containing noble and ignoble metals. Among them the systems platinum–cobalt and palladium cobalt often occur. This is attributed not only to their catalytic properties but also to magnetic characteristics of such phases.
Currently, a great variety of synthetic approaches for obtaining nanoalloys exist. We suggest a thermal decomposition of double complex salts (DCS), i.e. salts which consist of complex cation of one metal and complex anion of another. Thermolysis of these compounds in noble gas or hydrogen atmosphere leads to formation of bimetallic solid solution or intermetallic. Also we have noticed there, that the most suitable for our purposes is to use available ligands with reducing properties such as ammonia and oxalates, and metals in low oxidation states. In aggregate these facts cause complex compound to be thermally unstable and yield entirely reduced metallic product.
Thus, this work is investigation of DCS [M(NH3)4][Co(C2O4)2(H2O)2]•2H2O (M=Pd, Pt). The most important within the framework of our investigation: structure, thermal properties, metallic products composition and its dependence on temperature mode. | 6 15 |
| 16:00 | Size-selective Nanoparticles Stabilized by Dialkylmorpholinium Ionic Liquids Authors : SungHee Kim, GaYoung Gwon, Ari Kim, Sanghyun Kim, Jong-Ho Cha, Jeong Won Kang, Sunyoung Jung, Huen Lee, Ki-Sub Kim Resume : In this study, we have successfully synthesized metal nanoparticles (NPs) protected by dialkylammonium ionic liquids (ILs) via chemical reduction. ATR-FTIR, UV, and NMR spectroscopies, and transmission electron microscopy (TEM) were employed for characterization of the NPs. The ILs effectively stabilized the Pd NPs and the particle sizes were precisely controlled by the alkyl chain length of the cation in the ILs. The produced particles had a highly crystalline structure with a face centered cubic (fcc) lattice. Broadening of the (111) plane in the XRD patterns was observed and the particle sizes calculated by Scherrer’s equation were in good agreement with the TEM results. Additionally, UV, IR, and NMR spectra indicated that nano-sized particles were produced and ILs were bound to the surface of the NPs, thereby protecting the particles from aggregation | 6 16 |
| 16:30 | COFFEE BREAK | |
| 16:30 | Facile one-pot synthesis of metal nanoparticles using ionic liquids Authors : Ari Kim, GaYoung Gwon, SungHee Kim, Sanghyun Kim, Jong-Ho Cha, Jeong Won Kang, Sunyoung Jung, Huen Lee, Ki-Sub Kim Resume : A novel synthesis of Au nanoparticles was developed using alcohol ionic liquids. The alcohol ionic liquids simultaneously served as both reductants and protective agents, thereby significantly simplifying the process of nanoparticle preparation | 6 17 |
| Back | ||
| Une réalisation advisa.fr |  |