Publications

2016

• Dedicated Tool for Irradiation and Electrical Measurement of Large Surface Samples on the Beamline of a 2.5 Mev Pelletron Electron Accelerator: Application to Solar Cells
  
  • Lefevre Jeremie
  • Le Houedec Patrice
  • Losco Jerome
  • Cavani Olivier
  • Boizot Bruno
  , 2017, 16. (10.1051/e3sconf/20171616003)
  DOI : 10.1051/e3sconf/20171616003
• Interpretation of monoclinic hafnia valence electron energy-loss spectra by time-dependent density functional theory
  
  • Hung L.
  • Guedj C.
  • Bernier N.
  • Blaise P.
  • Olevano V.
  • Sottile F.
  Physical Review B, American Physical Society, 2016, 93 (16), pp.165105. We present the valence electron energy-loss spectrum and the dielectric function of monoclinic hafnia (m-HfO$_2$) obtained from time-dependent density-functional theory (TDDFT) predictions and compared to energy-filtered spectroscopic imaging measurements in a high-resolution transmission-electron microscope. Fermi's Golden Rule density-functional theory (DFT) calculations can capture the qualitative features of the energy-loss spectrum, but we find that TDDFT, which accounts for local-field effects, provides nearly quantitative agreement with experiment. Using the DFT density of states and TDDFT dielectric functions, we characterize the excitations that result in the m-HfO$_2$ energy loss spectrum. The sole plasmon occurs between 13-16 eV, although the peaks $\sim$28 and above 40 eV are also due to collective excitations. We furthermore elaborate on the first-principles techniques used, their accuracy, and remaining discrepancies among spectra. More specifically, we assess the influence of Hf semicore electrons (5$p$ and 4$f$) on the energy-loss spectrum, and find that the inclusion of transitions from the 4$f$ band damps the energy-loss intensity in the region above 13 eV. We study the impact of many-body effects in a DFT framework using the adiabatic local-density approximation (ALDA) exchange-correlation kernel, as well as from a many-body perspective using a $GW$-derived electronic structure to account for self-energy corrections. These results demonstrate some cancellation of errors between self-energy and excitonic effects, even for excitations from the Hf $4f$ shell. We also simulate the dispersion with increasing momentum transfer for plasmon and collective excitation peaks. (10.1103/PhysRevB.93.165105)
  DOI : 10.1103/PhysRevB.93.165105
• Status of Solar Generator Related Technology Development Activities Supporting the Juice Mission
  
  • Baur Carsten
  • Khorenko Victor
  • Siefer Gerald
  • Inguimbert Virginie
  • Park Seonyong
  • Boizot Bruno
  • Bourgoin Jacques C.
  • Casale Mariacristina
  • Campesato Roberta
  • Schnell Hans-Georg
  • Gerhard Andreas
  • Zanella Pietro
  • Ferrando Emanuele
  • Reutenauer Xavier
  • Bongers Ed
  • Gras Ana
  , 2017, 16. (10.1051/e3sconf/20171604005)
  DOI : 10.1051/e3sconf/20171604005
• Molecular dynamics simulation of surface step reconstruction and irreversibility under cyclic loading
  
  • Fan Zhengxuan
  • Hardouin Duparc Olivier
  • Sauzay Maxime
  Acta Materialia, Elsevier, 2016, 102, pp.149-161. The mechanical behaviour of surface steps naturally created by the glide of dislocations subjected to cyclic loading is examined using molecular dynamics simulations. Three face centred cubic metals, Al, Cu and Ag are analysed. An atomistic reconstruction phenomenon is observed at these surface steps which can induce strong irreversibility. Three different mechanisms of reconstruction are defined. They induce different reconstruction rates and various relief evolutions depending on the temperature. Surface slip irreversibility under cyclic loading is analysed. All surface steps are intrinsically irreversible under usual fatigue laboratory loading amplitude without the arrival of opposite sign dislocations. A surface step is reversible only when an opposite sign dislocation subsequently glides on a nearby atomic plane. Steps created by opposite sign dislocation glides on non neighbouring planes are irreversible. The irreversibility cumulates cycle by cycle and a micro-notch is produced whose depth increases cyclically. A rough estimation of surface irreversibility is carried out for pure edge dislocations in persistent slip bands in wavy materials. This gives an irreversibility fraction between 0.5 and 0.75 in copper. An analysis coupling surface mechanisms with the classical bulk slip irreversibility model proposed by Differt, Essmann and Mughrabi in 1986 and applied to pure screw dislocations gives an irreversibility fraction of 0.62 in copper. Similar estimations in nickel give irreversibility fractions around 0.6 and 0.8 for pure edge and screw dislocations respectively. These values are in agreement with recent atomic force microscopy measurements. (10.1016/j.actamat.2015.09.013)
  DOI : 10.1016/j.actamat.2015.09.013
• Direct measurement of ambipolar diffusion in bulk silicon by ultrafast infrared imaging of laser-induced microplasmas
  
  • Mouskeftaras Alexandros
  • Chanal Margaux
  • Chambonneau Maxime
  • Clady Raphael
  • Uteza Olivier
  • Grojo David
  Applied Physics Letters, American Institute of Physics, 2016, 108 (4). Carrier kinetics in the density range of N = 10(17) - 10(20) cm(-3) is investigated inside the bulk of crystalline silicon. Most conventional experimental techniques used to study carrier mobility are indirect and lack sensitivity because of charging effects and recombination on the surface. An all optical technique is used to overcome these obstacles. By focusing 1.3-mu m femtosecond laser pulses in the volume, we inject an initial free-carrier population by two-photon absorption. Then, we use pump-and-probe infrared microscopy as a tool to obtain simultaneous measurements of the carrier diffusion and recombination dynamics in a microscale region deep inside the material. The rate equation model is used to simulate our experimental results. We report a constant ambipolar diffusion coefficient D-a of 2.5 cm(2) s(-1) and an effective carrier lifetime tau(eff) of 2.5 ns at room temperature. A discussion on our findings at these high-injection levels is presented. (C) 2016 AIP Publishing LLC. (10.1063/1.4941031)
  DOI : 10.1063/1.4941031
• Ionizing Radiation Effects in Polymers
  
  • Ferry M.
  • Ngono-Ravache Y.
  • Aymes-Chodur C.
  • Clochard M.C.
  • Coqueret Xavier
  • Cortella L.
  • Pellizzi E.
  • Rouif S.
  • Esnouf S.
  , 2016. Compared to other materials such as steels or ceramics, polymers are quite sensitive to radiations, from UV to gamma-rays, and to particles beams (electrons, ions). Ionizing radiations induce chemical modifications that can be detrimental but also beneficial from a technological point of view. Since the discovery of these potentialities, the number of studies has not ceased to increase, on the fundamental effects of ionizing radiations on polymers, and more particularly on their application to the design new materials. In this article, we present an overview of the state of knowledge on the effects of ionizing radiations on polymers, on the related technological applications and their recent evolution. (10.1016/B978-0-12-803581-8.02095-6)
  DOI : 10.1016/B978-0-12-803581-8.02095-6
• Magnetic Configurations in Co/Cu Multilayered Nanowires: Evidence of Structural and Magnetic Interplay
  
  • Reyes Vasquez David Fernando
  • Biziere Nicolas
  • Warot-Fonrose Bénédicte
  • Wade T.
  • Gatel Christophe
  Nano Letters, American Chemical Society, 2016, 16, pp.1230-1236. Off-axis electron holography experiments have been combined with micromagnetic simulations to study the remnant magnetic states of electrodeposited Co/Cu multilayered nanocylinders. Structural and chemical data obtained by transmission electron microscopy have been introduced in the simulations. Three different magnetic configurations such as an antiparallel coupling of the Co layers, coupled vortices, and a monodomain-like state have been quantitatively mapped and simulated. While most of the wires present the same remnant state whatever the direction of the saturation field, we show that some layers can present a change from an antiparallel coupling to vortices. Such a configuration can be of particular interest to design nano-oscillators with two different working frequencies. (10.1021/acs.nanolett.5b04553)
  DOI : 10.1021/acs.nanolett.5b04553
• A transmission electron microscopy study of radiation damages to β-dicalcium (Ca2SiO4) and M3-tricalcium (Ca3SiO5) orthosilicates
  
  • de Noirfontaine Marie-Noëlle
  • Dunstetter Frederic
  • Courtial Mireille
  • Signes-Frehel Marcel
  • Wang Guillaume
  • Gorse-Pomonti Dominique
  Journal of Nuclear Materials, Elsevier, 2016, 468, pp.113-123. In this paper, we present results of a first study of electron radiation damages to β-dicalcium silicate (Ca2SiO4:C2S) and M3-tricalcium silicate (Ca3SiO5:C3S) in a Transmission Electron Microscope. Electron irradiation is used here as a means to bring to light a difference of reactivity under the electron beam between these two complex ceramic oxides, keeping in mind that C3S reacts faster with water than C2S and that this property remains unexplained, owing to the complex structural characteristics of these ceramics which have not yet been fully elucidated. The following results were obtained by coupling TEM imaging and EDS analysis: i) Rapid decomposition of both silicate particles into CaO nano-crystals separated by (presumably SiO2-rich) amorphous areas at low flux for both silicates; ii) once reached a threshold electron flux, formation of an amorphous crater in both silicates, fully calcium-depleted in C3S but never in C2S; iii) significant post-mortem structural evolution of the craters that at least partially recrystallize in C2S, to be compared to the quasi frozen damaged area in C3S; iv) hole drilling at high flux but only in C3S once reached a threshold flux, ϕth ∼ 7.9 × 1021 e− cm−2 s−1, of the same order of magnitude than previously estimated in a number of ceramic materials, whereas C2S still amorphizes under the electron beam for a flux as high as 2.2 × 1022 e− cm−2 s−1. The radiation damages and their post–mortem evolution differ largely between C2S and C3S. We attempted to relate the obtained results, and especially the evolution of the Ca content in the damaged areas under the electron beam to the available structural characteristics of these two orthosilicates.
• From network depolymerization to stress corrosion cracking in sodium-borosilicate glasses: Effect of the chemical composition
  
  • Barlet Marina
  • Delaye Jean-Marc L
  • Boizot Bruno
  • Bonamy Daniel
  • Caraballo Richard L
  • Peuget Sylvain L
  • Rountree Cindy L.
  Journal of Non-Crystalline Solids, Elsevier, 2016, 450, pp.174 - 184. The study herein examines how chemical composition impacts sub-critical stress corrosion cracking (SCC) in sodium borosilicate glasses. The crack speed versus stress intensity factor (v vs. K$_I$) curves were obtained for seven ternary SiO$_2$-Na$_2$ O-B$_2$ O$_3$ (SBN) glasses of selected chemical compositions. Na$_2$O plays an interesting role in the SCC behavior. First, increasing the Na$_2$O concentration yields an increase in the environmental limit (K$_e$). Second, increasing the Na$_2$O concentration affects how fast SCC occurs as K$_I$ increases (i.e. the slope in region I SCC). This second effect is highly nonlinear: it is insignificant for Na$_2$O < 20% but it becomes increasingly important above 20%, when sodium acts as a network modifier. Raman spectroscopy and Molecular Dynamics (MD) simulations aid in revealing the structural variations which arise from increasing concentrations of Na$_2$O. Na$_2$O causes the relative proportions of the different chemical bonds accessible in SBN glasses to vary. For this series of glasses, the Si–O–Si bond does not dominate the SCC properties. SCC variations originate in the mesoscale structure where sodium ions act as network modifiers on both the silica and borate units, thus yielding a partial depolymerization (i.e. a decrease in the reticulation level) of the network. This second effect reveals itself to be the one responsible for the SCC chemical dependency. Poisson's ratio increases approximately linearly with increasing Na$_2$O concentration , and thus, it is also not simply proportional to the slope in region I SCC. Partial depolymerization of the glass provides a novel prospective on the controlling factors in the sub-critical crack growth. (10.1016/j.jnoncrysol.2016.07.017)
  DOI : 10.1016/j.jnoncrysol.2016.07.017
• Electron radiation damages to dicalcium (Ca2SiO4) and tricalcium (Ca3SiO5) orthosilicates
  
  • de Noirfontaine Marie-Noëlle
  • Dunstetter Frederic
  • Courtial Mireille
  • Signes-Frehel Marcel
  • Wang Guillaume
  • Gorse-Pomonti Dominique
  Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Elsevier, 2016, 374, pp.111-115. Electron radiation damages to dicalcium silicate (Ca2SiO4) and tricalcium silicate (Ca3SiO5) are reported for the first time in this paper. With increasing flux, between 2.7 x 1017 and 2.2 x1022 e- cm-2 s-1, decomposition into nanodomains of crystalline CaO plus an amorphous silica rich phase is first observed for both silicates, then amorphization at higher flux always for both silicates, and finally hole drilling but only for Ca3SiO5. These structural modifications are accompanied by a net reduction of Ca content under the electron beam depending on the silicate species. These radiation effects occur for values of flux and dose larger than in previously studied orthosilicates (like olivines), and much larger than in all tectosilicates.
• Nanoscale mechanisms for the reduction of heat transport in bismuth
  
  • Markov Maxime
  • Sjakste Jelena
  • Fugallo Giorgia
  • Paulatto Lorenzo
  • Lazzeri Michele
  • Mauri Francesco
  • Vast Nathalie
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2016. Hand-on routes to reduce lattice thermal conductivity (LTC) in bismuth have been explored by employing a combination of Boltzmann's transport equation and ab initio calculations of phonon-phonon interaction within the density functional perturbation theory. We have first obtained the temperature dependence of the bulk LTC in excellent agreement with available experiments. A very accurate microscopic description of heat transport has been achieved and the electronic contribution to thermal conductivity has been determined. By controlling the interplay between phonon-phonon interaction and phonon scattering by sample boundaries, we predict the effect of size reduction for various temperatures and nanostructure shapes. The largest heat transport reduction is obtained in polycrystals with grain sizes smaller than 100 nm. (10.1103/PhysRevB.93.064301)
  DOI : 10.1103/PhysRevB.93.064301
• Electron Acceleration by Relativistic Surface Plasmons in Laser-Grating Interaction
  
  • Fedeli L.
  • Sgattoni A.
  • Cantono G.
  • Garzella D.
  • Réau F.
  • Prencipe I.
  • Passoni M.
  • Raynaud Michèle
  • Květoň M.
  • Proska J.
  • Macchi A.
  • Ceccotti T.
  Physical Review Letters, American Physical Society, 2016, 116 (1). The generation of energetic electron bunches by the interaction of a short, ultraintense (I > 10 19 W=cm 2) laser pulse with "grating" targets has been investigated in a regime of ultrahigh pulse-to-prepulse contrast (10 12). For incidence angles close to the resonant condition for surface plasmon excitation, a strong electron emission was observed within a narrow cone along the target surface, with energy spectra peaking at 5-8 MeV and total charge of ∼100 pC. Both the energy and the number of emitted electrons were strongly enhanced with respect to simple flat targets. The experimental data are closely reproduced by three-dimensional particle-in-cell simulations, which provide evidence for the generation of relativistic surface plasmons and for their role in driving the acceleration process. Besides the possible applications of the scheme as a compact, ultrashort source of MeV electrons, these results are a step forward in the development of high-field plasmonics. Surface plasmons [1,2], also named surface waves, are electromagnetic (EM) modes localized at the interface of different media which allow local field confinement and enhancement. Surface plasmons are the core of the vibrant research field of plasmonics [3], with applications ranging from light concentration beyond the diffraction limit [4], to biosensors [5] and plasmonic chips [6]. The extension of plasmonics into the regime of high fields, where nonlinear and relativistic effects arise, is largely unexplored. An example is provided by the multiterawatt laser-driven excitation of unipolar surface plasmons by transient charge separation [7,8], with potential application to the generation of intense THz pulses [8,9]. In the optical or near-infrared frequency range, surface plasmons can be excited by laser light incident on a sharp material interface having a periodic modulation, e.g., a grating, to allow phase matching. However, most experiments so far have been restricted to intensities below 10 16 W=cm 2 [10] because of the prepulses inherent in high-power laser systems which can lead to an early disruption of the target structuring. The development of devices for ultrahigh contrast pulses [11,12] now allows us to explore the interaction with targets structured on a submicrometric scale at laser intensities high enough for the electron dynamics to become relativistic [13,14]. In particular, a strong increase of the cutoff energy of protons accelerated from the rear surface of grating targets was observed and related to surface plasmon-enhanced absorption [15]. While a detailed theory is still lacking for nonlinear and relativistic surface plasmons, numerical simulations also showed surface plasmon-related effects in this regime [16,17], including electron acceleration at weakly relativistic intensities [18] and, more recently, surface plasmon-enhanced high harmonics [19] and synchrotron radiation [20] in gratings. In this Letter, we demonstrate that relativistic surface plasmons accelerate high-energy electrons along a grating surface. The acceleration process is related to two basic surface plasmon properties, i.e., the subluminal phase velocity and the longitudinal field component. The energy and number of electrons in gratings irradiated at an incidence angle close to the resonant value for surface plasmon excitation are strongly enhanced with respect to flat targets. At intensities I ¼ 5 × 10 19 W=cm 2 , corresponding to a relativistic parameter a 0 ≃ 5 [where a 0 ¼ ðIλ 2 =10 18 W cm −2 μm 2 Þ 1=2 and λ isthelaserwavelength]theelectronemissionwasconcentrated in a narrow cone with energy spectra peaking at 5-8 MeVand reaching up to ∼20 MeV. The basics of surface plasmon generation and electron acceleration may be described as follows. At high laser intensities (I > 10 18 W=cm 2) a solid target is ionized within one laser cycle, thus the interaction occurs with a dense plasma. Assuming a dielectric function εðωÞ ¼ 1 − ω 2 p =ω 2 ≡ 1 − α (where ω p is the plasma frequency) the phase velocity of a surface plasmon is v p ¼ ω=k ¼ cðα − 2Þ 1=2 =ðα − 1Þ 1=2 where k is the surface plasmon wave vector PRL 116, (10.1103/physrevlett.116.015001)
  DOI : 10.1103/physrevlett.116.015001
• BOL and EOL Characterization of Azur 3G Lilt Solar Cells for ESA Juice Mission
  
  • Khorenko Victor
  • Baur Carsten
  • Siefer Gerald
  • Schachtner Michael
  • Park Seonyong
  • Boizot Bruno
  • Bourgoin Jacques C.
  • Casale Mariacristina
  • Campesato Roberta
  , 2017, 16. (10.1051/e3sconf/20171603011)
  DOI : 10.1051/e3sconf/20171603011