Publications

2008

• Titanium reduction processes in oxide glasses under electronic irradiation
  
  • Ollier N.
  • Lombard P.
  • Farges F.
  • Boizot B.
  Journal of Non-Crystalline Solids, Elsevier, 2008, 354 (2-9), pp.480-485. Borosilicate and disilicate glasses doped with 0–2 mol% of TiO2 have been irradiated with 2 MeV electrons. Reduction of Ti4+ is attested by the presence of an intense electronic paramagnetic resonance (EPR) signal around g = 1.92 corresponding to Ti3+, not observed in samples that were not irradiated. Moreover, two distinct sites of Ti3+ have been detected in each glass composition. Ti–K-edge X-ray absorption near edge structure (XANES) experiment and more precisely the pre-edge analysis of non-irradiated samples indicates the presence of four, five and six coordinated Ti(IV) in borosilicate glass compositions. In contrast, the average Ti(IV) coordination in DS composition is a mixture between fivefold and sixfold. In irradiated glasses, the Ti–K-edge energy (as well as the pre-edge position) shows a shift to smaller energies, which we suggest is caused by Ti3+. Comparison between EPR, Raman and XANES results in a coherent description of Ti4+ reduction process in the glass samples
• IR and Raman spectroscopies, a way to understand how the Roman window glasses were made?
  
  • Raffaëlly L.
  • Champagnon Bernard
  • Foy Danièle
  • Ollier N.
  Journal of Non-Crystalline Solids, Elsevier, 2008, 354, pp.780-786. Two processes are known to make panes in West Europe during the Roman period: they may be cast on a flat surface or manufactured by the cylinder-blown process. The aim of our research is to give physico-chemical arguments to distinguish between both methods by using IR and Raman spectroscopies to determine the fictive temperature Tf of the archaeological samples. The position of the 1050 cm-1 band in the IR reflection spectra of annealed samples versus Tf has been studied, giving a calibration curve to determine the Tf of the archaeological sample. The position of the 1100 cm-1 Raman band and the ratio of the Q2/Q3 Raman bands intensities are also studied versus Tf for annealed samples. The Tf of both sides are found to be different, which is an argument in favor of the cast method (10.1016/j.jnoncrysol.2007.07.077)
  DOI : 10.1016/j.jnoncrysol.2007.07.077
• X-RAY DIFFRACTION STUDY OF THE DAMAGE INDUCED IN YTTRIA-STABILIZED ZIRCONIA BY SWIFT HEAVY ION IRRADIATIONS
  
  • Costantini Jean-Marc
  • Guillet François
  • Lambert Sébastien
  • Grébille Dominique
  • Beuneu François
  • Trautmann Christina
  Journal of Applied Physics, American Institute of Physics, 2008, 104, pp.073504. The lattice damage was investigated by x-ray diffraction techniques in yttria-stabilized zirconia single crystals with the (100) or (110) orientation upon irradiation with swift heavy ions (from 100-MeV C to 2.6-GeV U) in a broad electronic stopping power range (from about 0.3 to 48 keV nm−1). The -2 scans show that no amorphization or change to a new crystalline phase occurs regardless of the ion and crystal features. However, the rocking curves ( scans) and reciprocal space mappings show evidence of the mosaicity of the crystals, which is produced above a threshold electronic stopping power between 18 and 27 keV nm−1. This threshold is in agreement with our previous Rutherford backscattering spectroscopy/channeling spectroscopy data. Two kinds of damage phenomena are found: (i) nuclear-collision induced clusters of point defects which generate Bragg peak shifts and broadening in the 2- and -2 scans, and (ii) electronic-excitation induced lattice damage yielding broad peaks in the scans above the stopping power threshold at high fluences
• MOCVD growth of ZnO nanostrutures using Au droplets as catalysts
  
  • E. Sandana V.
  • J. Rogers D.
  • Hosseini Teherani F.
  • Mcclintock R.
  • Razeghi M.
  • Drouhin H.-J.
  • Clochard M.C.
  • Sallet V.
  • Garry G.
  • Fayoud F.
  Proceedings of the Society of Photo-Optical Instrumentation Engineers, 2008, 6895, pp.Z8950-Z8950. ZnO nanostructures were synthesised by Metal Organic Chemical Vapor Deposition growth on Si (100) and c-Al2O3 substrates coated with a 5nm thick layer of Au. The An coated substrates were annealed in air prior to deposition of ZnO so as to promote formation of Au nanodroplets. The development of the nanodroplets was studied as a function of annealing duration and temperature. Under optimised conditions, a relatively homogeneous distribution of regular An nanodroplets was obtained. Using the An nanodroplets as a catalyst, MOCVD growth of ZnO nanostructures was studied. Scanning electron microscopy revealed nanostructures with various forms including commonly observed structures such as nanorods, nanoneedles and nanotubes. Some novel nanostructures were also observed, however, which resembled twist pastries and bevelled-multifaceted table legs. (10.1117/12.775632)
  DOI : 10.1117/12.775632
• Emission of molecular fragments synthesized in hypervelocity nanoparticle impacts
  
  • Guillermier C.
  • Della-Negra S.
  • Schweikert E.A.
  • Dunlop A.
  • Rizza G.
  International Journal of Mass Spectrometry, Elsevier, 2008, 275, pp.86-90. We report on experiments with Aun nanoparticles (100 ≤ n ≤ 400) at velocities of 10–60 km/s. They are implanted virtually intact via hydrodynamic penetration. The products of the extreme pressure transient are observed by mass analyzing the ionized ejecta. Targets of labeled molecules (13C-, 15N-glycine) reveal fragmentation–recombination processes, producing CN− and OCN− with high efficiency (45%). This value is over two orders of magnitude larger than that obtained with atomic and small cluster projectiles. The experiments could simulate collisions of nanosized dust particles in interstellar space. (10.1016/j.ijms.2008.05.023)
  DOI : 10.1016/j.ijms.2008.05.023
• Theoretical Study of Superficial Segregation of Infinitely Dilute Binary Alloys made of Nickel, Copper, Silver and Gold.
  
  • Lezzar B.
  • Hardouin Duparc Olivier
  • Khalfallah O.
  • Larere A.
  • Paidar V.
  Physical and Chemical News, Best Edition, 2008, 41, pp.46-49. The behavior of the surface segregation in infinitely diluted bimetallic alloys is addressed by calculating the segregation energy, local pressure and relative changes in the volume of atomic sites. The atomic interactions are described by a Finnis-Sinclair semi-empirical N-body potential derived from the second moment approximation of the tight binding theory. The segregation energies by plane parallel to the surface are calculated by numerical simulation soaked in molecular dynamics. It models the surface segregation at the atomic scale in order to identify the physical phenomena that govern and so-called traditional driving forces. These different driving forces at the surface have been identified in the metals as a size effect, an effect of excess cohesion and an alloy effect. Surface segregation is studied in the limit of infinitely dilute solution for Ni(Ag), Cu(Ag), Ni(Cu), Au(Ag), as well as their opposite, Ag(Ni), Ag(Cu), Cu(Ni), Ag(Au). The study's main objective is the verification of the model of the driving forces involving the contributions of the size effect, the effect of excess cohesion and the alloy effect. The (110) surface is the surface which has the highest segregation in all systems among the three simple surfaces. Surface segregation is mainly localized on the surface. It is favoured for direct systems and is no longer for Inverse Systems. The results for the surface show that the energy of segregation is well reproduced by the sum the three effects: size, excess cohesion and alloy.
• Ab initio study of electron-phonon coupling and excitonic linewidth in GaAs under pressure and in GaP
  
  • Sjakste J.
  • Vast N.
  • Tuyterev V.
  Journal of Luminescence, Elsevier, 2008, 128 (5-6), pp.1004 - 1006. Interactions between excited electrons and short-wavelength (intervalley) phonons are the major source for the broadening of the excitonic line in GaAs under pressure and in GaP. We have studied the intervalley scattering deformation potential using density functional theory for the conduction bands, and density functional perturbation theory for phonon frequencies and for the matrix elements of the electronphonon interaction. We have calculated the electronphonon scattering time due to intervalley scattering t, integrating the scattering probabilities over all possible final states in the Brillouin zone without any ad hoc assumption about the behavior of the electronphonon matrix elements nor the topology of the conduction band. We compare our theoretical results with time-resolved photoluminescence experiment in GaAs, and with spectroellipsometry measurements in GaAs under pressure and in GaP. We show that our ab initio method also allows the evaluation of effective deformation potentials
• One and two dimensional 2D NMR spectra in LaD2.85
  
  • Zogal O.J.
  • Vajda P.
  • Massiot D.
  Polish Journal of Chemistry, Polish Chemical Society, 2008, 82, pp.1905-1910.
• New stabilized VK-type center in electron-irradiated sodium fluoride observed by electron paramagnetic resonance
  
  • Beuneu François
  • Vajda Peter
  Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Elsevier, 2008, 266, pp.2754. Sodium fluoride crystals were bombarded with MeV electrons near room-temperature or at 21 K and their EPR spectra measured. While after RT-irradiation one observes the spectrum of the classical cubic F-center, the low-T irradiation introduces a new low-symmetry defect which transforms reversibly into the F-center above 200K. We suggest for the new center a triplet VK-type defect stabilized during irradiation by the nearby created F-center. While the ordinary VK-center as observed after low-T X-ray and c-irradiation vanishes at 200 K the present electron-induced defect is stable and reappears upon cooling; it is still discernible after anneals up to 200 C.
• EPR study of Yb-doped irradiated glasses
  
  • Ollier N.
  • Planchais R.
  • Boizot B.
  Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Elsevier, 2008, 266 (12-13), pp.2854-2858. Yb3+ reduction under β and γ irradiation has been studied in aluminoborosilicate glasses by EPR spectroscopy. From the Yb3+ EPR line variation, we demonstrate that more than one Yb3+ sites coexist in the pristine Yb-doped glasses. Reduction of Yb3+ into Yb2+ is observed for all integrated doses and Yb doping contents. For doses higher than 108 Gy, an Yb3+ ion environment change occurs, this change is correlated with a stabilization of the reduced Yb2+ state. The paramagnetic defect concentration displays a linear variation as a function of the logarithm of the dose. The glass doping with Yb2O3 leads to a substantial decrease of the defect concentration as well as a modification in the relative proportion of the defects produced. In particular, Yb doping tends to increase the relative content of Oxy defects
• Behaviour of scintillators under XUV free electron laser radiation
  
  • Kirm M.
  • Babin V.
  • Feldbach E.
  • Guizard S.
  • de Grazia M.
  • Nagirnyi V.
  • Vasil'Ev A.
  • Vielhauer S.
  Journal of Luminescence, Elsevier, 2008, 128 (5-6), pp.732-734. Free electron lasers (FEL) are new generation accelerator-based short wavelength light sources providing high pulse intensity and femtosecond pulse duration, which enable investigation of interaction of elementary excitations in solids under extreme conditions. Using the FLASH facility of HASYLAB at DESY (Hamburg, Germany), we investigated the response of different materials with scintillating properties based on intrinsic emissions to the 25.6 and 13.8 nm FEL radiation by means of time-resolved luminescence spectroscopy. FLASH delivered single pulses of 25 fs duration having energy per pulse up to 30 μJ resulting in power densities of 1012 W/cm2 on crystals. As a function of excitation density we observed the shortening of lifetime and non-exponential behaviour of emission decays in CaWO4, while the emission spectra recorded are comparable to those obtained at conventional excitation sources
• Cluster-surface and cluster-cluster interactions: Ab initio calculations and modeling of asymptotic van der Waals forces
  
  • Botti Silvana
  • Castro Alberto
  • Andrade Xavier
  • Rubio Angel
  • A. L. Marques Miguel
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2008, 78, pp.035333. We present fully ab initio calculations of van der Waals coefficients for two different situations: (i) the interaction between hydrogenated silicon clusters and (ii) the interactions between these nanostructures and a nonmetallic surface (a silicon or a silicon carbide surface). The methods used are very efficient and allow the calculation of systems containing hundreds of atoms. The results obtained are further analyzed and understood with the help of simple models. These models can be of interest for molecular-dynamics simulations of silicon nanostructures on surfaces, where they can give a very fast yet sufficiently accurate determination of the van der Waals interaction at large separations. (10.1103/PhysRevB.78.035333)
  DOI : 10.1103/PhysRevB.78.035333
• Migration and correlation in highly defective systems: Fast-diffusion in lithium oxide
  
  • Hayoun Marc
  • Meyer Madeleine
  Acta Materialia, Elsevier, 2008, 56 (6), pp.1366-1373. The high-temperature superionic phase of lithium oxide is characterized by a high concentration of Frenkel defects and a diffusion mechanism involving several types of atomic jumps. We have calculated the tracer-correlation factor and analyzed the migration paths of the Li ions obtained by molecular dynamics (MD). A kinetic Monte Carlo code, simulating the lithium vacancy diffusion, has been developed and used to predict the correlation factor as a function of the atomic fraction of defects. There is a good agreement with the result directly obtained by MD. The analysis of the jump paths shows that the direct exchange between a vacancy and a migrating atom is the main part of the diffusion mechanism. The other atomic jumps, although complex, mostly imply vacancies. The Li+ fast-diffusion proceeds by a vacancy mechanism involving several jump types
• Materials Issues for Generation IV Systems. Satus, Open Questions and Challenges.
  
  • Ghetta V.
  • Gorse D.
  • Mazière D.
  • Pontikis V.
  , 2008, pp.586 p..
• Effect of the localization of the semicore density on the physical properties of transition and noble metals
  
  • Trinité Virginie
  • Vast Nathalie
  • Hayoun Marc
  Journal of Physics: Condensed Matter, IOP Publishing [1989-....], 2008, 20, pp.235239. We use density functional theory to study the density of the 3sp semicore states in transition and noble metals. The first objective is to understand how semicore states influence cohesive properties which mainly depend on the valence density. We define a localization radius for the semicore density which is found to be a crucial parameter and to heavily influence the cohesive properties. The localization radius is found to be controlled by the occupation numbers of the 3d states. This offers the possibility of setting criteria for the construction of accurate large core pseudopotentials freezing the semicore states, and to a posteriori control the use of large core pseudopotentials in the modeling. We illustrate our findings with the examples of copper and titanium