Publications

2005

• PHOTOCONDUCTIVITY AND PHOTOEMISSION OF DIAMOND UNDER FEMTOSECOND VUV IRRADIATION
  
  • Gaudin Jérôme
  • Geoffroy Ghita
  • Guizard Stéphane
  • Olevano Valério
  • Esnouf Stéphane
  • Klimentov Serguei M.
  • Pivovarov Pavel A.
  • Garnov Serguei V.
  • Martin Patrick
  • Belsky Andrei
  • Petite Guillaume
  , 2005. In order to gain some insight on the electronic relaxation mechanisms occuring in diamond under high intensity laser excitation and/or VUV excitation, we studied experimentally the pulsed conductivity induced by femtosecond VUV pulses, as well as the energy spectra of the photoelectrons released by the same irradiation. The source of irradiation consists in highly coherent VUV pulses obtained through high order harmonic generation of a high intensity femtosecond pulse at a 1.55 eV photon energy (titanium-doped sapphire laser). Harmonics H9 to H17 have been used for photoconductivity (PC) and harmonics H13 to H27 for photoemission experiments (PES). As the photon energy is increased, it is expected that the high energy photoelectrons will generate secondary e-h pairs, thus increasing the excitation density and consequently the PC signal. This is not what we observe : the PC signal first increases for H9 to H13, but then saturates and even decreases. Production of low energy secondary e-h pairs should also be observed in the PES spectrum. In fact we observe very few low energy electrons in the PES spectrum obtained with H13 and H15, despite the sufficient energy of the generated free carriers. At the other end (H21 and above), a very intense low energy secondary electron peak is observed. As a help to interprete such data, we realized the first ab initio calculations of the electronic lifetime of quasiparticles, in the GW approximation in a number of dielectrics including diamond. We find that the results are quite close to a simple "Fermi-liquid" estimation using the electronic density of diamond. We propose that a quite efficient mechanism could be the excitation of plasmons by high energy electrons, followed by the relaxation of plasmons into individual e-h pairs.
• Characterization of carbon and iron nanostructures synthesized by the DC arc discharge method: influence of the location in the reactor and of the pressure
  
  • Fnidiki Abdeslem
  • Lemarchand Dany
  • Talbot Etienne
  • Pascard H.
  European Physical Journal: Applied Physics, EDP Sciences, 2005, 32 (3), pp.177-185. X-ray diffraction, Mössbauer spectroscopy, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) techniques were used to characterize the Fe-C phases in the soots synthesized by the DC arc discharge method. Various equilibrium and non-equilibrium Fe-C compounds were identified, with fractions depending on both the location in the reactor and the helium gas pressure. The soots obtained are composed of the same five phases (C-graphite, α-Fe, γ-Fe, Fe3C and Fe5C2) whatever the helium gas pressure and wherever they are situated in the reactor. However, the location in the reactor has a considerable influence on the size of the particles in the nanostructure. The Fe-C compounds in the Pyrex vessel samples (CL) seem only to be present in the form of nanoparticles embedded in an amorphous gangue, while the water-cooled copper cylinder samples (RS) contain, in addition to these nanoparticles, large composite crystalline particles. (10.1051/epjap:2005094)
  DOI : 10.1051/epjap:2005094
• Thermodynamics of the vortex liquid in heavy-ion-irradiated superconductors
  
  • J. van Der Beek Cornelis
  • Konczykowski Marcin
  • Fruchter Luc
  • Brusettii René
  • Klein Thierry
  • Marcus Jacques
  • Marcenat C.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2005, 72, pp.214504. It is shown that the large effect of heavy ion irradiation on the thermodynamical properties of the anisotropic superconductor YBa2Cu3O7− extends well into the superconducting fluctuation regime. The presence of the induced amorphous columnar defects shifts the specific-heat maximum at the normal-to-superconducting transition. This effect is similar to that recently put into evidence in cubic KxBa1−xBiO3 x 0.35 . In both compounds, vortex pinning manifests itself as a sharp angular dependence of the equilibrium torque. In YBa2Cu3O7− , pinning by the defects appears at the temperature TCp max of the specific-heat maximum, well above the magnetic irreversibility line Tirr H . In isotropic KxBa1−xBiO3, the onset of the pinning-related torque anomaly tracks the onset of the specific-heat anomaly and the irreversibility line. In YBa2Cu3O7− , fluctuations of the amplitude of the order parameter and not vortex line wandering are ultimately responsible for the vanishing of pinning. In KxBa1−xBiO3, vortex pinning disappears only at the superconducting-to-normal transition. The results indicate that in both compounds, the pinning energy at the "Bose-glass" transition is large with respect to the total free energy gain in the superconducting state. By implication, the mechanism of this latter transition should be reconsidered. (10.1103/PhysRevB.72.214504)
  DOI : 10.1103/PhysRevB.72.214504
• Processus électroniques d'excitation et de relaxation dans les solides diélectriques excités par des impulsions ir et xuv ultracourtes
  
  • Gaudin Jerome
  , 2005. Nous avons étudiés l'excitation d'un solide diélectrique par une impulsion laser femtoseconde (fs) intense dans le domaine visible où XUV. Ce type d'irradiation produit des électrons excit és avec des énergies initiales qui vont de quelques eV à quelques dizaines d'eV au dessus du bas de la bande de conduction. La relaxation de ces électrons est à l'origine de nombreux phénomènes tels que l'ablation laser, le claquage optique ou le transport des électrons " chauds " dans les matériaux à intérêt technologique (SiO2 et diamant). L'objectif de ce travail de thèse est d'étudier de façon directe et de mieux comprendre ces mécanismes de relaxation électroniques. Deux techniques expérimentales complémentaires, utilisant les impulsions XUV ultrabrèves, issues de la génération d'harmoniques d'ordres élevés, ont été mises oeuvre pour mener à bien ces études. Tout d'abord, les expériences de photoémission ont permis de mettre en lumière un nouveau mécanisme d'absorption du rayonnement par les électrons de la bande de conduction : les transitions multiphotoniques interbandes. Nos résultats montrent que ce processus est le mécanisme dominant d'échauffement des électrons. Cette conclusion est de plus corroborée par les résultats d'un modèle théorique basé sur la résolution de l'équation de Schrödinger dépendante du temps. D'autre part, des expériences " pompe/sonde " de photoémission résolue en temps ont eu pour but de sonder la population d'électrons excités par une impulsion XUV et de suivre son évolution temporelle sur une échelle de temps fs à ps. Les temps de décroissance mesurés sont de l'ordre de quelques ps pour des électrons de 30 eV. L'interprétation des ces durées de vie longue est problématique. Nous suggérons un modèle de relaxation en deux étapes, tout d'abord purement électronique et rapide, puis d'interaction avec le réseau plus lente, pour expliquer ces résultats expérimentaux. Le second type d'expériences porte sur une spectroscopie de photoconduction sur du diamant. En utilisant les harmoniques d'ordres élevés comme source d'excitation nous avons mesuré le courant de déplacement induit qui permet d'accéder au nombre d'électrons excités en fonction de l'énergie des photons incidents. Cette information permet d'étudier l'efficacité de l'ionisation par impact (collision inélastique électron/électron). Nos résultats peuvent s'interpréter par la structure particulière du diamant qui comporte une deuxième bande interdite 10 eV au dessus du bas de la bande de conduction. Des simulations Monte-Carlo permettent de confirmer cette interprétation.
• Echange et Corrélation dans la Structure Electronique des Solides, du Silicium à l'Oxyde Cuivreux: Approximation GW et au-delà
  
  • Bruneval F.
  , 2005. La structure électronique des cristaux est un nom polymorphe qui couvre une large gamme de propriétés des électrons dans les solides périodiques. Par exemple, il peut se référer à la probabilité de trouver un électron au point r de l'espace, en d'autres termes, à la densité électronique. Il peut faire référence à l'énergie nécessaire pour extraire un électron du matériau, l'énergie d'ionisation, ou encore, le gain énergétique lorsqu'un électron est ajouté au système, l'affinité électronique. Il peut aussi se lire la réponse des électrons du solide à une perturbation externe (un photon ou un électron rapide). Toutes ces propriétés caractérisent la structure électronique du solide. Ils décrivent les aspects bien différents. Certains d'entre eux sont propriétés de l'état, d'autres correspondent à des états excités. Certains d'entre eux de conserver le nombre de particules, d'autres pas. En conséquence, les propriétés qui sont généralement appelés «structure électronique» sont mesurées avec différentes configurations expérimentales, par exemple photoémission directe et inverse, l'absorption optique, de l'énergie d'électrons de perte ... Et de manière analogue, la description théorique et la prévision de ces propriétés requièrent cadres distincts. Ce travail de thèse se chargera de la question de la structure électronique de l'oxyde cuivreux, Cu2O. Par conséquent, différentes méthodes théoriques seront utilisées et les résultats seront comparés à un large éventail de techniques expérimentales.
• Peptide immobilization onto radiation grafted PVDF-g-poly(acrylic acid) films
  
  • Clochard M.-C
  • Betz N
  • Goncalves M
  • Bittencourt C
  • Pireaux J.-J
  • Gionnet K
  • Déléris G
  • Le Moël A
  Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Elsevier, 2005, 236, pp.208. Introducing hydrophilic functions on poly(vinylidene fluoride) (PVDF) films surface allows the covalent immobili-zation of peptides. Therefore radiation grafting of acrylic acid (AA) in pre-irradiated PVDF films was achieved to allow surface functionalization with linear and cyclic peptides. Peptides were bound via spacer molecules using EDC as a coupling agent. The reactions were followed by Fourier Transform Infrared (FTIR) spectroscopy in attenuated total reflection (ATR) mode. The amount of immobilized peptides was determined by UV spectroscopy. As well, an uncommon method for PVDF characterization and reactions quantification was used: high-resolution-magic angle spinning nuclear mass spectroscopy (HR-MAS NMR). Spacer saturation of the film surface corresponded to 25 mol% yield meaning that one spacer on 4 carboxylic acids was covalently bound. XPS experiments were also performed to deepen analysis of the surface composition. Peptide density is governed by steric hindrance. ELISA tests showed that the peptidesÕ activity is maintained. (10.1016/j.nimb.2005.04.029)
  DOI : 10.1016/j.nimb.2005.04.029
• Conformal anodic oxidation of aluminum thin films
  
  • Cojocaru C. S.
  • Padovani J.M.
  • Wade T.
  • Mandoli C.
  • Jaskierowicz G.
  • Wegrowe J. -E.
  • Morral A.F.I.
  • Pribat Didier
  Nano Letters, American Chemical Society, 2005, 5 (4), pp.675-680. 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. (10.1021/nl050079b)
  DOI : 10.1021/nl050079b
• Analysis of molecular oxygen formation in irradiated glasses: a Raman depth profile study
  
  • Ollier N.
  • Boizot B.
  • Reynard Bruno
  • Ghaleb D.
  • Petite G.
  Journal of Nuclear Materials, Elsevier, 2005, 340 (2-3), pp.209-213. Depth profiles experiments have been performed by Raman spectroscopy on three alkali (Na, Li, K) borosilicate glasses irradiated with 1.8 MeV electrons at 1 and 3 GGy. These experiments show that molecular oxygen produced under β irradiation is concentrated near the glass surface according to a depth depending on the irradiation dose. Moreover, we observed that the polymerisation increase is the same in the entire volume sample. The average Si–O–Si angle decrease under irradiation is also homogeneous in the whole irradiated glass volume. From all results, we demonstrate that oxygen migrates up to the glass surface during irradiation without strong interaction with the glass network. Migration of oxygen and probably alkalis takes place through percolation channels with a possible departure of oxygen in some cases. (10.1016/j.jnucmat.2004.11.011)
  DOI : 10.1016/j.jnucmat.2004.11.011
• 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
• Comparison of the intergranular segregation for eight dilute binary metallic systems in the Σ 11′ {332} tilt grain boundary
  
  • Hardouin Duparc Olivier
  • Larere A.
  • Lezzar B.
  • Khalfallah O.
  • Paidar V.
  Journal of Materials Science, Springer Verlag, 2005, 40, pp.3169-3176. Intergranular segregation is studied in the limit of infinitely diluted solution for eight dilute metallic systems made of four face centred cubic metals, one transition metal, nickel, and three noble metals, copper, silver and gold. The grain boundary (GB) chosen is the symmetrical tilt Σ = 11′ {332} 〈110〉 GB with its characteristic “zigzag” structural pattern as numerically calculated and experimentally observed by high resolution transmission electronic microscopy in nickel. The metallic interactions are modelled with Finnis-Sinclair like potentials. The atomic sites are characterised by a geometrical parameter defined with their exact Voronoï' volumes and the tensor of the stresses locally exerted. The {332} GB presents the most diversity of sites in these respects. The segregation energies are computed and analysed versus the only two ‘driving forces' which can play a role in metallic intergranular segregation, viz. the elastic size effect and the excess cohesion energy effect. The elastic size effect calculated by the method of virtual impurity represents the main segregation driving force in most cases of the considered systems. It is worth noting however that the excess cohesion energy effect is important for non hydrostatic or compressive sites. It can even be predominant, as in the case of Ni(Cu).
• Template synthesis of nanomaterials
  
  • Wade T.L.
  • Wegrowe J.-E.
  European Physical Journal: Applied Physics, EDP Sciences, 2005, 29, pp.3. We present an overview of template synthesis as it applies to our nanomaterials research. This bottom-up approach is motivated by our desire to find an alternative to the big, top-down approaches to nanoscience, such as clean-rooms and X-ray lithography. Using universally available templates and materials, and very modest synthesis techniques, we have created a variety of interesting and useful structures. Starting with homogeneous ferromagnetic nanowires, we were able to study and manipulate spin-dependent transport. Next, we branched into multi-layer GMR and spin-valve structures for spintronics. As a side trip, we put carbon-encapsulated fullerene nanoparticles into nanopores for ballistic magnetoresistance studies. Carbon nanotube molecules were grown in templates by CVD self assembly. The carbon nanotubes grown using a cobalt catalyzer show spin-valve, ballistic transport, and Coulomb blockade effects. Very recently, we have started to study templated semiconductor nanorods with the amazing result that their behaviour is very similar to that of the carbon nanotubes and can be reduced to a scaling law. Essentially, the template acts as a skeleton for the nanoscale synthesis and macroscale contact of an infinite variety of materials and structures. It is our hope that by the following examples we demonstrate that high quality nanoscience research is available to everybody
• Second-generation quantum-well sensors for room-temperature scanning Hall probe microscopy
  
  • Pross A.
  • Crisan A.I.
  • Bending S.J.
  • Mosser V.
  • Konczykowski M.
  Journal of Applied Physics, American Institute of Physics, 2005, 97, pp.96105. Scanning Hall probe microscopy is a noninvasive magnetic imaging technique with potential for having a major impact in the data storage industry if high-resolution Hall effect sensors can be developed with sufficiently low-noise figures at room temperature. To meet this requirement, we have developed a series of second-generation quantum-well Hall probes whereby the careful design of an AlGaAs/InGaAs/GaAs pseudomorphic heterostructure, chip layout, metal interconnects, and passivation layers has allowed a dramatic reduction of low-frequency noise sources. In addition, the Johnson noise-limited minimum detectable fields of these sensors are more than an order of magnitude lower than those used in early microscopes. The key figures-of-merit of the sensors are presented and their performance illustrated in an imaging study of a yttrium-iron-garnet thin film at room temperature. (C) 2005 American Institute of Physics
• Relaxation of internal stress field and hydrogen ordering on YHx. Journal of Alloys and compounds
  
  • Garces J.
  • Gervasoni J.L.
  • Vajda P.
  Journal of Alloys and Compounds, Elsevier, 2005, 404, pp.126. Although there have been several theoretical efforts in the past to calculate both the best structure of H-H pairs in Y and the total energies as well as electronic structures, there exist no studies of the relation between hydrogen ordering and the shape of the Fermi surface. We use the FLAPW method, as implemented in the Wien2k code, focusing our research on the relation between chain ordering of H, the relaxation of internal coordinates and the electronic properties for hypothetical alpha-YH1/3 and alpha-YH2/3. In addition to the relaxed atomic positions in the cell, we obtain information on the negligible role of the H Is state contribution near E-F and the shape of the Fermi surface
• Influence of the pH on molecular hydrogen primary yields in He2+ ion tracks in liquid water. A Monte Carlo study
  
  • Cobut V.
  • Corbel C.
  • Patau J.P.
  Radiation Physics and Chemistry, Elsevier, 2005, 72, pp.207. Monte Carlo calculations are performed to investigate how the acidity of aqueous solutions at room temperature affects the molecular hydrogen (H-2) yield as a function of time in 20 MeV-He2+ ion track segments. For pH value, varying from 1 to 13, the time dependence of the calculated yields is nearly independent of pH in (he time ranee 10(-12)-10(-8) s and only weakly dependent in the time range 10(-8)-10(-6) s. To understand this behaviour. the kinetic mechanisms governing H-2 formation are examined as a function of time. It is found that the main reaction.; responsible for the H-2 yield as a function of time are strongly pH-dependent at low and high pH values. The pH-dependences of the reaction yields are however such that the variations in the yields compensate each other. This is why the time dependence of the H-2 yield is only weakly pH-dependent