Publications

2005

• Many-body perturbation theory using the density-functional concept: beyond the GW approximation
  
  • Bruneval Fabien
  • Sottile Francesco
  • Olevano Valério
  • del Sole Rodolfo
  • Reining Lucia
  Physical Review Letters, American Physical Society, 2005, 94, pp.186402. We propose an alternative formulation of Many-Body Perturbation Theory that uses the densityfunctional concept. Instead of the usual four-point integral equation for the polarizability, we obtain a two-point one, that leads to excellent optical absorption and energy loss spectra. The corresponding three-point vertex function and self-energy are then simply calculated via an integration, for any level of approximation. Moreover, we show the direct impact of this formulation on the timedependent density-functional theory. Numerical results for the band gap of bulk silicon and solid argon illustrate corrections beyond the GW approximation for the self-energy.
• Classical versus ab initio structural relaxation: electronic excitations and optical properties of Ge nanocrystals embedded in an SiC matrix
  
  • Cappellini G.
  • Weissker H-Ch
  • de Salvador D.
  • Furthmüller J.
  • Bechstedt F.
  • Satta G.
  • Casula F.
  • Colombo L.
  Journal of Physics: Condensed Matter, IOP Publishing [1989-....], 2005, 17, pp.643. We discuss and test a combined method to efficiently perform ground-state and excited-state calculations for relaxed structures using both a quantum first-principles approach and a classical molecular-dynamics scheme. We apply this method to calculate the ground state, the optical properties, and the electronic excitations of Ge nanoparticles embedded in a cubic SiC matrix. Classical molecular dynamics is used to relax the large-supercell system. First-principles quantum techniques are then used to calculate the electronic structure and, in turn, the electronic excitation and optical properties. The proposed procedure is tested with data resulting from a full first-principles scheme. The agreement is quantitatively discussed between the results after the two computational paths with respect to the structure, the optical properties, and the electronic excitations. The combined method is shown to be applicable to embedded nanocrystals in large simulation cells for which the first-principles treatment of the ionic relaxation is presently out of reach, whereas the electronic, optical and excitation properties can already be obtained ab initio. The errors incurred from the relaxed structure are found to be non-negligible but controllable
• Spin-Induced Forbidden Evanescent States in III-V Semiconductors
  
  • Rougemaille1 H.-J. Drouhin2 S. Richard3 G. Fishman3 And A. K. Schmid1 N.
  Physical Review Letters, American Physical Society, 2005, 95, pp.186406. Within the band gap of a semiconductor no electronic propagating states are allowed, but there exist evanescent states which govern charge transport such as tunneling. In this Letter, we address the issue of their spin dependence in III-V semiconductors. Taking into account the spin-orbit interaction, we treat the problem using a k p 14 14 Hamiltonian that we numerically compute for GaAs. Our results show that the removed spin degeneracy in the band gap can lead to giant energy splittings and induces forbidden zones in k space where evanescent states are suppressed. (10.1103/PhysRevLett.95.186406)
  DOI : 10.1103/PhysRevLett.95.186406
• On the problem of the correct interpretation of phason elasticity in quasicrystals
  
  • Coddens Gerrit
  , 2005. Recently Francoual et al. claimed to have observed the dynamics of long-wavelength phason fluctuations in i-AlPdMn quasicrystals. We will show that the data reported call for a more detailed development of the elasticity theory of Jaric and Nelsson in order to determine the nature of small phonon-like atomic displacements with a symmetry that follows the phason elastic constants.
• Wave propagation in highly inhomogeneous thin films : exactly solvable models
  
  • Petite Guillaume
  • Shvartsburg Alexander
  , 2005, pp.59890M-1. We present an exact treatment of wave propagation in some inhomogeneous thin films with highly space-dependent dielectric constant. It is based on a space transformation which replaces the physical space by the optical path. In the new space, the dispersion equation is that of a normal progressive wave. We will show that the dispersion properties of such films are plasma- or waveguide-like, the characteristic frequency being determined by the spatial characteristics of the dielectric constant's variations only. The theory is scalable, so that it can be applied in any wavelength range : optical, IR, radiofrequency, etc. depending only on the characteristic space scales. Several applications will be presented, concerning the reflection properties of such films (broadband anti-reflection, or dichroic coatings) or to the propagation and transmission through the film. We will show that depending on the type of space dependence, an incident wave can either propagate or tunnel through such films. We will investigate the behaviour of the light group-velocity and tunneling time inside or through such films. Though we can reproduce the phase-time saturation corresponding to the Hartman effect, analysis of the group velocity in the tunneling case shows no sign of superluminal propagation. A strong frequency dependence can be obtained in some situations, which allows to anticipate a strong reshaping of brodband laser pulses. (10.1117/12.632046)
  DOI : 10.1117/12.632046
• Characterization of swift heavy ion tracks in CaF2 by scanning force and transmission electron microscopy
  
  • Khalfaoui N.
  • Rotaru C.C.
  • Bouffard S.
  • Toulemonde M.
  • Stoquert J.P.
  • Haas F.
  • Trautmann C.
  • Jensen J.
  • Dunlop A.
  Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Elsevier, 2005, 240, pp.819. Single crystals of fluorite (CaF2) were exposed to various swift heavy ions (Ca up to U) of energy 1-11.1 MeV per nucleon, covering a large range of electronic stopping power S-e between 4.6 and 35.5 keV/nm. The irradiated (I 1 1) cleaved surfaces were investigated by means of scanning force microscopy in tapping mode. Nanometric hillocks produced by the ion projectiles were analyzed in terms of creation efficiency E-eff, diameter and height values, and diameter-height correlation. Hillock formation appears with a low efficiency above a Se threshold of similar to 5 keV/nm. The mean height of these hillocks is approximately constant (similar to 1 nm) between 5 and 10 keV/nm and increases linearly with Se above 10 keV/nm reaching 12.5 nm for the largest Se value investigated. Similarly, the efficiency grows versus Se achieving 100% for S-e > 13 keV/nm where each projectile produces an individual hillock. Above 13 keV/nm, the hillock height and diameter are strongly correlated. The diameter was deduced by graphical deconvolution of the scanning-tip curvature that is determined experimentally for each set of measurements. In the entire Se regime, the mean diameter exhibits a constant value of similar to 13 nm, which is significantly larger than 6 nm wide tracks observed by transmission electron microscopy
• Electron emission from solids under electron irradiation: a Monte Carlo study
  
  • Hakala M.
  • Corbel C.
  • Nieminen R.M.
  Journal of Physics D: Applied Physics, IOP Publishing, 2005, 38, pp.711. We have implemented a Monte Carlo simulation method to study electron emission from solid surfaces under electron irradiation at energies of up to 100 keV. Calculations are performed for the yields and energy distributions of the emitted electrons in backscattering and transmission geometries for Al and Au metals. For transmission studies the film thicknesses range from a few nanometres to micrometres. The method is demonstrated to predict correctly the electron backscattering and transmission properties, and gives a qualitatively reasonable description of the low-energy (E < 50 eV) secondary electron emission. For the exit surface of thin films we predict a universal behaviour according to which the maximum low-energy secondary electron yield is obtained when similar to 50-70% of the incident electrons are transmitted through the film. This corresponds to film thicknesses of similar to 0.75 times the mean depth of penetration of the electron with the same kinetic energy in a bulk target
• Effect of self-consistency on quasiparticles in solids
  
  • Bruneval Fabien
  • Vast Nathalie
  • Reining Lucia
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2005, 74, pp.045102. We have evaluated the self-energy of solids within different self-consistent approximations, from bare and screened exchange to screened exchange plus Coulomb hole !COHSEX" and GW approximations. Our calculations for silicon, aluminum, and argon assess the quality of the local-density approximation !LDA" valence wave functions and density with respect to their GW counterparts. The LDA conduction wave functions are shown to be of significantly poorer quality, in particular for not highly symmetric points of the Brillouin zone. Comparing the different approaches we show that screened exchange alone is not reliable and we propose to combine a self-consistent COHSEX with a subsequent perturbative GW calculation that gives a reasonable estimate of the self-consistent GW results, at a much lower computational cost. The calculations are based on the pseudopotential method; they confirm its reliability.
• Modification of N-doped carbon induced by 30 MeV C60 ions
  
  • Wang Z.G.
  • Dunlop A.
  • Zhao Z.M.
  • Song Y.
  • Jin Y.F.
  • Zhang C.H.
  • Sun Y.M.
  • Liu J.
  Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Elsevier, 2005, 230, pp.262. In the present work, 120 keV N-ion doped and 30 MeV C60 ion irradiated graphite-like-carbon samples were characterized by RBS, micro-FTIR, micro-Raman, XPS spectroscopy and the variation of the properties of the samples with the N-dopant and/or C60 irradiation fluence have been studied. The RBS spectra showed that C60 irradiation can induce a partial diffusion of N atoms to the surface and the amount of the diffused N atoms increases slightly with increasing C60 irradiation fluence. The FTIR and Raman spectra exhibit characteristic bands of carbon nitrogen bonds showing that the C and N atoms are chemically bonded. The amount of chemically bonded C and N atoms increases with increasing N-dopant. By deconvolution of the XPS spectra, the atomic concentration of N and C atoms were obtained and it was identified that the samples mainly consist of three phases, namely, C3N4, CNx and tetrahedral amorphous carbon. The effect of N-dopant and C60 irradiation fluence on the modification of the properties of the samples is also discussed.
• A brief introduction to the ABINIT software package
  
  • Gonze X.
  • Rignanese G.M.
  • Verstraete M.
  • Beuken J.M.
  • Pouillon Y.
  • Caracas R.
  • Jollet F.
  • Torrent M.
  • Zerah G.
  • Mikami M.
  • Ghosez P.
  • Veithen M.
  • Raty J.Y.
  • Olevano Valério
  • Bruneval F.
  • Reining L.
  • Godby R.
  • Onida G.
  • Hamann D.R.
  • Allan D.C.
  Zeitschrift für Kristallographie, De Gruyter, 2005, 220, pp.558. A brief introduction to the ABINIT software package is given. Available under a free software license, it allows to compute directly a large set of properties useful for solid state studies, including structural and elastic properties, prediction of phase (meta)stability or instability, specific heat and free energy, spectroscopic and vibrational properties. These are described, and corresponding applications are presented. The emphasis is also laid on its ease of use and extensive documentation, allowing newcomers to quickly step in
• Structure of spin-split evanescent states in the fundamental gap of zinc-blende-type semiconductors
  
  • Richard S.
  • Drouhin H.J.
  • Rougemaille N.
  • Fishman G.
  Journal of Applied Physics, American Institute of Physics, 2005, 97, pp.83706. We calculate evanescent waves in GaAs throughout the forbidden band gap, taking into account both the absence of inversion symmetry and the spin-orbit coupling. In this case, the energy bands are spin split. We find that the evanescent wave functions only exist in limited energy and wave-vector domains. We show that no evanescent state associated with a purely imaginary wave vector exists in some simple directions such as [110], which has implications concerning the tunneling mechanism itself. Finally, we show that a GaAs tunnel barrier can be used as a spin injector in solid-state devices
• High pressure studies of the erbium-hydrogen system
  
  • Palasyuk T.
  • Tkacz M.
  • Vajda P.
  Solid State Communications, Elsevier, 2005, 135, pp.226. High-pressure X-ray diffraction investigations up to 25 GPa using diamond anvil cell techniques (DAC) have been carried out on erbium and a series of erbium hydrides. The equations of state have been evaluated for ErH1.95, ErH2.091 (in the beta-phase) and for gamma-ErH3. For comparison, the compressibility of pure erbium metal has also been determined in the same pressure range. A rapid drop of lattice volume at a pressure of about 14.5 GPa has been observed for ErH2.091 accompanied by a color change of reflected light. This phenomenon was not observed in ErH1.95 where the molar volume varied smoothly up to the highest pressure. A pressure-induced transformation from hexagonal to cubic phase has been detected for erbium trihydride. For pure erbium metal, a transition from hexagonal to samarium structure has been revealed, confirming previously reported behavior
• Oxidation of Sm2+ in beta-irradiated Sm-doped borosilicate glasses under laser illumination
  
  • Malchukova E.
  • Boizot B.
  • Petite G.
  • Ghaleb D.
  Journal of Luminescence, Elsevier, 2005, 111, pp.53. Borosilicate glasses doped with samarium have been prepared. Samples exposed to 4 x 10(9) Gy of beta-irradiation have been investigated by fluorescence measurements, showing a strong reduction process of SM3+ to SM2+ ions in the irradiated samples. Oxidation of Sm2+ was observed in this glass as a result of frequency-doubled cw Nd:YAG laser irradiation, but not when using a pulsed titanium-doped sapphire laser. Influence of laser intensity was studied, showing that an increase of the laser intensity could induce complete oxidation of SM2+ ions. Such effect is not observed at low temperature nor using ultra short laser pulses. The conclusion is that the effect is of thermal origin
• VNew high field state of flux line lattice in CeCoIn5
  
  • Kasahara Y.
  • Watanabe T.
  • Izawa K.
  • Sakakibara T.
  • van Der Beek C.J.
  • Hanaguri T.
  • Nohara M.
  • Takagi H.
  • Shishido H.
  • Settai R.
  • Onuki Y.
  • Matsuda Y.
  Physica C: Superconductivity and its Applications, Elsevier, 2005, 426, pp.36. We have measured the ultrasound velocity of quasi-two-dimensional superconductor CeCoIn5 with extremely large Pauli paramagnetic susceptibility. The results indicate that the new high field superconducting phase, which is revealed by the recent heat capacity measurements, is characterized by the unusual softening of flux line lattice. The softening is most likely due to the collapse of the flux line lattice tilt modulus and transition to quasi-two-dimensional vortex state. These results provide a strong evidence that the high field phase is the Fulde-Ferrell-Larkin- Ovchinnikov phase, in which the order parameter is spatially modulated and has planar nodes aligned perpendicularly to the vortices
• Vortex correlations in the liquid states of Bi2Sr2CaCu2O8+y with tilted columnar defects
  
  • Kameda N.
  • Shibauchi T.
  • Tokunaga M.
  • Ooi S.
  • Tamegai T.
  • Konczykowski M.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2005, 7206, pp.4501. The interlayer and intralayer vortex correlations are studied in Bi2Sr2CaCu2O8+y with tilted and nontilted columnar defects (CDs) by the Josephson plasma-resonance experiments under various field angles. The interlayer correlation is enhanced at the recoupling field, near which we observe clear triple-resonance peaks. The recoupling field is determined only by the density of CDs in the superconducting layer, irrespective of CD angles from the c axis. In the low-field decoupled liquid state, we observe an increase of the interlayer correlations due to increased pinning by enlarged defects. By contrast, scaling analysis shows little effect of the pinning strength on the interlayer and intralayer correlations in the high-field recoupled liquid state
• Degradation kinetics of poly(ether-urethane) Estane((R)) induced by electron irradiation
  
  • Dannoux A.
  • Esnouf S.
  • Begue J.
  • Amekraz B.
  • Moulin C.
  Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Elsevier, 2005, 236, pp.488. Radiation effects on a segmented aromatic poly(ether-urethane) induced by electron beam irradiation under oxygen atmosphere were investigated using Fourier transform infrared spectroscopy (FTIR) and electron paramagnetic resonance (EPR) in order to determine the degradation mechanisms. Thin films have been irradiated under a dose rate of 1 MGy/h with absorbed doses varying from 25 to 1000 kGy under O-2. FTIR spectra have shown the formation of hydroperoxides, carboxylic acids, primary amines, alcohols, esters and formates. Moreover, the decrease of urethane and ether absorbances revealed the degradation of both soft and hard segments. Spin-trapping technique was used to monitor the evolution of short-lived peroxy and alkyl radicals at room temperature. Finally, a mechanism of degradation for electron irradiated polyurethane is proposed
• Optical properties of pristine and γ-rradiated Sm doped borosilicate glasses
  
  • Malchukova Evguenia
  • Boizot Bruno
  • Petite Guillaume
  • Ghaleb Dominique
  Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Elsevier, 2005, 537, pp.411. The structural evolution of simplified nuclear waste glasses under beta-irradiation (2.5 MeV) has been studied up to cumulated doses of the order of 3.109 Gy. A rapid saturation of the point defect creation is observed at a very low level (in large contrast with what is observed on pure silica). At large doses, we also observe an increase of the polymerisation of the vitreous lattice, and the appearance of dissolved molecular oxygen, which however does not coalesce into bubbles. These evolutions can be linked with the diffusion of alkaline ions in the material. The effects of the glass composition (mixed alkali-effect, specific role of some particular cations, which are shown to block the structural evolution) have also been investigated by spectroscopic methods (Nuclear Magnetic Resonance, Electronic Paramagnetic Resonance and Raman diffusion). Finally, lanthanides have been introduced in the glass composition (as simulant of the actinides) and their valence changes under irradiation are studied using photoluminescence
• Conformal anodic oxidation of aluminum thin film
  
  • Cojocaru C.S.
  • Padovani J.M.
  • Wade T.
  • Mandoli C.
  • Jaskierowicz G.
  • Wegrowe J.E.
  • Morral A.F.I.
  • Pribat D.
  , 2005. Membrane-based synthesis, also called template synthesis, is a very general approach used to prepare arrays of nanomaterials with monodispersed geometrical features. The most commonly used porous templates are track-etched polycarbonate and porous anodic alumina membranes. Common to all these templates is the fact that the pores are perpendicular to the surface of the membrane. Here, a novel approach is presented, where the pores are synthesized parallel to the surface of the membrane. For the first time, the anodic oxidation of an aluminum thin film is performed laterally, i.e., parallel to the surface of the substrate, instead of perpendicular as usually done. For low anodic oxidation voltages (between 3 and 5 V) we obtain highly regular and ordered pore arrays, at least over a few hundred nanometers length, with a minimum pore size of similar to 3 to 4 nm. With such porous alumina structures, the controlled in-plane organization of arrays of template-grown nanowires and carbon nanotubes for reproducible device fabrication should be much easier
• Energy dependence of the exchange-correlation kernel of time-dependent density functional theory: A simple model for solids
  
  • Botti Silvana
  • Nguyen F.
  • Roca I Cabarrocas Lucia
  • Sottile Francisco
  • Fourreau A.
  • Renault Y.O.
  Physica B: Condensed Matter, Elsevier, 2005, 72, pp.125203 - 1/9. Time-dependent density functional theory faces an important problem when it comes to extended systems: The long-range component of the exchange-correlation kernel fxc is completely absent from local density or generalized gradient approximations, but it is believed to be present in the “exact” fxc. Several attempts have been made to solve this issue, the simplest of them being the use of a model static long-range kernel of the form −astatic /q2. In this paper, we propose and motivate a dynamical extension of this model of the form −(a+Bw2)/q2. The dynamical model is then used to calculate the dielectric function of a large variety of semiconductors and insulators. The absorption spectra of large gap insulators are remarkably improved with respect to calculations where the kernel is taken to be static. This approach is valid also for energies in the range of plasmons, and hence it yields, e.g., good electron energy loss spectra. Finally, we present some simple theoretical arguments that relate the parameters of the model to physical quantities, like the dielectric constant and the plasmon frequency. (10.1103/PhysRevB.72.125203)
  DOI : 10.1103/PhysRevB.72.125203
• Alfred Wilm and the beginnings of Duralumin
  
  • Duparc O. Hardouin
  Zeitschrift fur Metallkunde, 2005, 4, pp.398-404. Aluminium is a fairly recent metal (XIXth century). Investigations of its alloys developed in a military-industrial context. Duralumin was, thus, discovered at the beginning of the last century in Prussian Germany by the Metallurgist Engineer Alfred Wilm (1869–1937) who had been explicitly mandated to look for an improved aluminium alloy in a military-owned research centre located in Neubabelsberg, just south-west of Berlin. The name Duralumin is as much due to the fact that it is hard as to the fact it has first been industrially produced in Düren. International connections, as well as harsh competition, accompanied the first research on this alloy in the beginning of the twentieth century
• Native and artificial radiation-induced defects in montmorillonite. An EPR study
  
  • Sorieul S.
  • Allard Thierry
  • Morin G.
  • Boizot Bruno
  • Calas G.
  Physics and Chemistry of Minerals, Springer Verlag, 2005, 32, pp.1-7. A natural montmorillonite containing radiation-induced defects was studied with Electron Paramagnetic Resonance (EPR) spectroscopy (X- and Q-band). A first dominant native defect, namely native defect 1, is identified. It gives rise to an orthorhombic spectrum with g(x) = 2.004 +/- 0.005 g(y) = 2.010 +/- 0.003, g(z) = 2.065 +/- 0.002. Simulation of the EPR spectrum at X- and Q-band reveals a second native defect with isotropic spectrum at g = 2.019 +/- 0.005. Both are electron holes trapped on oxygen atoms of the structure. The native defect 1 is located on an oxygen-silicon bond or a non-bonding orbital parallel to the c* axis. These defects are annealed at 500 degrees C and the half-life determined for native defect 1 is circa 3,000 years. Irradiations with beta rays produced two additional hole centers of lower stability and distinct EPR parameters. Artificial irradiations show that montmorillonite can be used as a dosimeter in a large dose range (10.1007/s00269-004-0427-6)
  DOI : 10.1007/s00269-004-0427-6
• Irradiation effects in simplified nuclear waste glasses
  
  • Boizot Bruno
  • Ollier Nadège
  • Petite Guillaume
  • Ghaleb D.
  • Olivier Florent
  • Malchukova Evguenia
  Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Elsevier, 2005, 240, pp.146-151. The structural evolution of simplified nuclear waste glasses under b-irradiation (2.5 MeV) has been studied up to cumulated doses of the order of 109 Gy. A rapid saturation of the point defect creation is observed at a very low level (in large contrast with what is observed on pure silica). At large doses, we also observe an increase of the polymerization of the vitreous lattice, and the appearance of dissolved molecular oxygen, which however does not coalesce into bubbles. These evolutions can be linked with the diffusion of alkaline ions in the material. The effects of the glass composition (mixed alkali effect, specific role of some particular cations, which are known to block the structural evolution) have been also investigated in order to study the possibility of decreasing alkaline mobility under irradiation. (10.1016/j.nimb.2005.06.105)
  DOI : 10.1016/j.nimb.2005.06.105