Publications

2005

• Anomalous electron spin resonance behavior of single-walled carbon nanotubes
  
  • Beuneu Francois
  • Salvetat J.-P.
  • Fehér T.
  • L'Huillier C.
  • Forró L.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2005, 72, pp.075440. We have studied the electron spin resonance ESR of single-walled carbon nanotubes SWNTs both in their pristine state and after irradiation with fast electrons in order to detect the signal of conduction electrons. No metallic Pauli contribution was observed in the global spin susceptibility, the ESR signal of the conduction electrons is undetectable because it is broadened by magnetic impurities. We measured a paramagnetic contribution from localized states, with an effective Curie constant decreasing when the temperature increases, following a deactivation law of the type A-B exp-Ea /kBT. This behavior is supposed to be characteristic of semiconducting SWNTs interacting with metallic impurities from the catalyst. (10.1103/PhysRevB.72.075440)
  DOI : 10.1103/PhysRevB.72.075440
• Thermodynamics of the vortex liquid in heavy-ion-irradiated superconductors
  
  • van Der Beek Cornelis
  • Konczykowski Marcin
  • Fruchter Luc
  • Brusetti René
  • Klein Thierry
  • Marcus Jacques
  • Marcenat C.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2005, 72 (214504), pp.1-9. 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 TirrH. 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.
• Comment on “Quantum Confinement and Electronic Properties of Silicon Nanowires”
  
  • Bruneval Fabien
  • Botti Silvana
  • Reining Lucia
  Physical Review Letters, American Physical Society, 2005, 94, pp.219701. A Comment on the Letter by Xinyuan Zhao et al., Phys. Rev. Lett. 92, 236805 (2004). The authors of the Letter offer a Reply. (10.1103/PhysRevLett.94.219701)
  DOI : 10.1103/PhysRevLett.94.219701
• Photopolymerization of epoxy coatings containing silica nanoparticles
  
  • Sangermano M.
  • Malucelli G.
  • Amerio E.
  • Priola A.
  • Billi E.
  • Rizza G.
  Progress in Organic Coatings, Elsevier, 2005, 54, pp.134. Silica nanoparticles, were employed to obtain organic-inorganic hybrid coatings via UV curing of an epoxy based system. The influence of the presence Of SiO2 on the rate of polymerization was investigated by real time FT-IR. The silica nanofiller induced both a bulk and a surface modification of UV cured coatings with an increase on T-g, modulus and surface hardness by increasing the amount of silica into the photocurable resin. TEM investigations confirmed that silica filler has a size distribution range between 5 and 50 nm without formation of aggregates. The strong decrease on water uptake in the presence of SiO2 makes these nanocomposites materials particularly interesting for gas-barrier coatings applications
• TDDFT from molecules to solids: The role of long-range interactions
  
  • Sottile F.
  • Bruneval F.
  • G. Marinopoulos A.
  • K. Dash L.
  • Botti Silvana
  • Olevano Valério
  • Vast N.
  • Rubio A.
  • Reining L.
  International Journal of Quantum Chemistry, Wiley, 2005, 102, pp.684. Classical Hartree effects contribute substantially to the success of time-dependent density functional theory, especially in finite systems. Moreover, exchange-correlation contributions have an asymptotic Coulomb tail similar to the Hartree term, and turn out to be crucial in describing response properties of solids. In this work, we analyze in detail the role of the long-range part of the Coulomb potential in the dielectric response of finite and infinite systems, and elucidate its importance in distinguishing between optical and electron energy loss spectra (in the long wavelength limit q 0). We illustrate numerically and analytically how the imaginary part of the dielectric function and the loss function coincide for finite systems, and how they start to show differences as the distance between objects in an infinite array is decreased (which simulates the formation of a solid). We discuss calculations for the model case of a set of interacting and noninteracting beryllium atoms, as well as for various realistic systems, ranging from molecules to solids, and for complex systems, such as superlattices, nanotubes, nanowires, and nanoclusters. (10.1002/qua.20486)
  DOI : 10.1002/qua.20486
• Plasmon channels in the electronic relaxation of diamond under high-order harmonics femtosecond irradiation.
  
  • Belsky Andrei
  • Esnouf Stéphane
  • Garnov Serguei V.
  • Gaudin Jérôme
  • Geoffroy Ghita
  • Guizard Stéphane
  • Klimentov Serguei M.
  • Martin Patrick
  • Olevano Valério
  • Petite Guillaume
  • Pivovarov Pavel A.
  Laser Physics, MAIK Nauka/Interperiodica, 2005, Letters 2, pp.292-296. We used high order harmonics of a femtosecond titanium-doped sapphire system (pulse duration 25 fs) to realise Ultraviolet Photoelectron Spectroscopy (UPS) measurements on diamond. The UPS spectra were measured for harmonics in the range 13 to 27. We also made ab initio calculations of the electronic lifetime of conduction electrons in the energy range produced in the UPS experiment. Such calculations show that the lifetime suddenly diminishes when the conduction electron energy reaches the plasmon energy, whereas the UPS spectra show evidence in this range of a strong relaxation mechanism with an increased production of low energy secondary electrons. We propose that in this case the electronic relaxation proceeds in two steps : excitation of a plasmon by the high energy electron, the latter decaying into individual electron-hole pairs, as in the case of metals. This process is observed for the first time in an insulator and, on account of its high efficiency, should be introduced in the models of laser breakdown under high intensity. (10.1002/lapl.200510001)
  DOI : 10.1002/lapl.200510001
• New 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.36-40. 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
• Optical properties of Si and Ge nanocrystals: Parameter-free calculations
  
  • E. Ramos L.
  • Weissker H.-Ch.
  • Furthmüller J.
  • Bechstedt F.
  physica status solidi (b), Wiley, 2005, 242, pp.3053-3063. An overview is given on the electronic and optical properties of Si and Ge nanocrystals. We model freestanding Si and Ge nanocrystals passivated with H, with up to 363 group-IV atoms and 276 H and oxidized nanocrystals with additional silicon oxide shells, e.g. Si41(O60Si42)(O108Si64)H148. The results discussed are based on parameter-free calculations for relaxed atomic structures. The electronic states and the many-body effects are considered within the density-functional theory and the supercell method. Energy gaps are described within the Kohn–Sham independent-particle picture and within the independentquasiparticle picture, whereas electronic excitations are treated within the delta self-consistent method by pair excitation energies. The projector-augmented wave method allows the calculation of optical matrix elements, oscillator strengths, optical spectra, and radiative lifetimes. We discuss quantum confinement, structural relaxation, oxidation, and the role of defects in oxidized Si NCs.
• Use of ion beam analysis techniques to characterise iron corrosion under water radiolysis
  
  • Lapuerta S.
  • Moncoffre N.
  • Millard-Pinard N.
  • Mendes E.
  • Corbel C.
  • Crusset D.
  Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Elsevier, 2005, 240, pp.288. The aim of this paper is to study the effect of water radiolysis under 12 MeV proton irradiation on the corrosion behaviour of pure iron. Oxygen and hydrogen playing a crucial role during the corrosion process have been specifically investigated. Heavy desaerated water ( enriched at 99.9% in D) was also used to determine the origin of hydrogen at the iron surface. Proton irradiations were performed at the CERI cyclotron in Orleans. Both sides of the Fe foil (respectively in contact with air and with water) were analysed with ion beam techniques: alpha Rutherford backscattering spectrometry was used to profile oxygen, elastic recoil detection analysis has allowed to profile hydrogen. The use of D2O gives evidence that the hydrogen concentration present on the water face could originate from wet air. In addition, in case of the aerated deionised H2O media, it is shown that the irradiation process induces a strong corrosion. Scanning electron microscopy experiments confirm the formation of oxide precipitates
• Effect of external gamma irradiation on dissolution of the spent UO2 fuel matrix
  
  • Jegou C.
  • Muzeau B.
  • Broudic V.
  • Peuget S.
  • Poulesquen A.
  • Roudil D.
  • Corbel C.
  Journal of Nuclear Materials, Elsevier, 2005, 341, pp.62. Leaching experiments were performed on UO2 pellets doped with alpha-emitters (Pu-238/239) and on spent fuel, in the presence of an external gamma irradiation source (A(60)Co = 260 Ci, D gamma = 650 Gy h(-1)). The effects of alpha, beta, gamma radiation, the fuel chemistry and the nature of the cover gas (aerated or Ar + 4%H-2) on water radiolysis and on oxidizing dissolution of the UO2 matrix are quantified and discussed. For the doped UO2 pellets, the nature of the cover gas clearly has a major role in the effect of gamma radiolysis. The uranium dissolution rate in an aerated medium is 83 mg m(-2) d(-1) compared with only 6 mg m-2 d-1 in Ar + 4%H-2. The rate drop is accompanied by a reduction of about four orders of magnitude in the hydrogen peroxide concentrations in the homogeneous solution. The uranium dissolution rates also underestimate the matrix alteration rate because of major precipitation phenomena at the UO2 pellet surface. The presence of studtite in particular was demonstrated in aerated media; this is consistent with the measured H2O2 concentrations (1.2 x 10(-4) mol L-1). For spent fuel, the presence of fission products (Cs and Sr), matrix alteration tracers, allowed us to determine the alteration rates under external gamma irradiation. The fission product release rates were higher by a factor of 5-10 than those of the actinides (80-90% of the actinides precipitated on the surface of the fragments) and also depended to a large extent on the nature of the cover gas. No significant effect of the fuel chemistry compared with UO2 was observed on uranium dissolution and H2O2 production in the presence of the 6 Co source in aerated conditions. Conversely, in Ar + 4%H-2 the fuel self-irradiation field cannot be disregarded since the H2O2 concentrations drop by only three orders of magnitude compared with UO2
• Creation of high energy electronic excitations in inorganic insulators by intense femtosecond laser pulses
  
  • Yatsenko B.N.
  • Bachau H.
  • Belsky A.N.
  • Gaudin J.
  • Geoffroy G.
  • Guizard S.
  • Martin P.
  • Petite G.
  • Philippov A.
  • Vasil'Ev A.N.
  Physica Status Solidi C: Current Topics in Solid State Physics, Wiley, 2005, 2, pp.240. We measured photoemission spectra for a number of insulators (CsI, Diamond, SiO2, CeF3) excited by femtosecond Ti-Sapphire laser pulses at peak intensities, from 0.5 to 6 TW/cm2, which are at least one order of magnitude below the optical breakdown threshold. An intense and pronounced plateau of high energy electrons appears in the photoelectron spectra in this intensity range, which extends up to 30-40 eV at the highest intensities, which we used. The excitation of electrons at high energies is treated in terms of direct interbranch transitions in the conduction band of insulator. These processes are described using calculations based on numerical solution of time dependant Schrödinger equation (TDSE) for Bloch electrons in electric fields
• Anomalous electron spin resonance behavior of single-walled carbon nanotubes
  
  • Salvetat J.P.
  • Feher T.
  • L'Huillier C.
  • Beuneu François
  • Forro L.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2005, 7207, pp.5440. We have studied the electron spin resonance (ESR) of single-walled carbon nanotubes (SWNTs) both in their pristine state and after irradiation with fast electrons in order to detect the signal of conduction electrons. No metallic Pauli contribution was observed in the global spin susceptibility, the ESR signal of the conduction electrons is undetectable because it is broadened by magnetic impurities. We measured a paramagnetic contribution from localized states, with an effective Curie constant decreasing when the temperature increases, following a deactivation law of the type A-B exp(-E-a/k(B)T). This behavior is supposed to be characteristic of semiconducting SWNTs interacting with metallic impurities from the catalyst
• Strong light-matter coupling at room temperature in simple geometry GaN microcavities grown on silicon.
  
  • Semond F.
  • Sellers I.R.
  • Natali F.
  • Byrne D.
  • Leroux M.
  • Massies J.
  • Ollier N.
  • Leymarie Joël
  Applied Physics Letters, American Institute of Physics, 2005, pp.3.
• Alfred Wilm et les débuts du Duralumin
  
  • Hardouin-Duparc O.
  Cahiers de l'histoire de l'aluminium, 2005, 34, pp.62-76. Loin d'être la découverte " romantique " parfois décrite, la mise au point du Duralumin se fit de façon volontariste, au début du siècle, dans un contexte militaro-industriel. L'invention d'un alliage conservant les qualités de légèreté de l'aluminium, mais lui adjoignant la dureté nécessaire à la production d'armes, fut obtenue par l'ingénieur Wilm dans le cadre d'un laboratoire militaire prussien. Le Duralumin – baptisé par jeu de mots – s'imposa d'autant plus rapidement aux autres pays industrialisés que ceux-ci menaient en parallèle des recherches similaires (ce qui entraina d'ailleurs des rivalités autour de la paternité du matériau). L'ensemble de ces recherches contribua à la compréhension progressive des mécanismes fondamentaux du durcissement des alliages par maturation
• Photoconductivité et photoémission de diamant(s) sous irradiation XUV femtoseconde
  
  • Petite Guillaume
  • Gaudin Jérôme
  • Geoffroy Ghita
  • Guizard Stéphane
  • Esnouf Stéphane
  • Olevano Valério
  • Klimentov Serguei M.
  • Pivovarov Pavel A.
  • Garnov Serguei V.
  • Carre Bertrand
  • Martin Patrick
  • Belsky Andrei
  Journal de Physique IV Proceedings, EDP Sciences, 2005, 127, pp.219. We report à study of the photoconductivity (PC) induced in different types of diamonds (type IIa single crystals and CVD) by femtosecond XUV pulses (high order harmonics - up to 19th - of a titanium doped laser). We also reprot UPS spectras obtained with harmonics 13 to 29. Depending on the harmonic's order, the PC signal first increases (orders 9 to 13) and then decreases. If the increase is easily interpreted as resulting from a carrier multiplication process, the further decrease has not yet received an explanation. The UPS measurements also suggest a strong effect of the plasmon relaxation on the carrier multiplication process. Finally, we performed a preliminary GW ab-initio calculation of the carriers lifetime, acounting for electron-electron interactions. In the near-bandgap region, it behaves approximatively according to the Fermi-liquid model, from which it strongly departs at higher energies, which is attributed to band-structure effects and to plasmon excitations.
• Effect of alpha irradiation on UO2 surface reactivity in aqueous media
  
  • Jegou C.
  • Muzeau B.
  • Broudic V.
  • Poulesquen A.
  • Roudil D.
  • Jorion F.
  • Corbel C.
  Radiochimica Acta, Oldenbourg Wissenschaftsverlag, 2005, 93, pp.35. The option of direct disposal of spent nuclear fuel in a deep geological formation raises the need to investigate the long-term behavior of the UO2 matrix in aqueous media subjected to alpha-beta-gamma radiation. The beta-gamma emitters account for most of the activity of spent fuel at the moment it is removed from the reactor, but diminish within a millennial time frame by over three orders of magnitude to less than the long-term activity. The latter persists over much longer time periods and must therefore be taken into account over a geological disposal time scale. Leaching experiments with solution renewal were carried out on UO2 pellets doped with alpha emitters (Pu-238 and Pu-239) to quantify the impact of alpha irradiation on UO2 matrix alteration. Three batches of doped UO2 pellets with different alpha flux levels (3.30 x 10(4), 3.30 x 10(5), and 3.2 x 10(6) alphacm(-2) s(-1)) were studied. The results obtained in aerated and deaerated media immediately after sample annealing or interim storage in air provide a better understanding of the UO2 matrix alteration mechanisms under alpha irradiation. Interim storage in air Of UO2 pellets doped with alpha emitters results in variations of the UO2 surface reactivity, which depends on the alpha particle flux at the interface and on the interim storage duration. The variation in the surface reactivity and the greater uranium release following interim storage cannot be attributed to the effect of alpha radiolysis in aerated media since the uranium release tends toward the same value after several leaching cycles for the doped UO2 pellet batches and spent fuel. Oxygen diffusion enhanced by alpha irradiation of the extreme surface layer and/or radiolysis of the air could account for the oxidation of the surface UO2 to UO2+x. However, leaching experiments performed in deaerated media after annealing the samples and preleaching the surface suggest that alpha radiolysis does indeed affect the dissolution, which varies with the flux at the UO2/water interface
• Mécanismes fondamentaux de l'ablation laser femtoseconde en "flux intermédiaire
  
  • Petite Guillaume
  , 2005, pp.319. This chapter aims at identifying what is specific to femtosecond laser ablation. It reviews the essential basic processes which contribute to femtosecond laser ablation of various materials : energy absorption by the material's electrons, electronic relaxation processes involving either electron-electron or electron-lattice interactions. A number of widely used models are briefly discussed, as well as some pending questions.
• Comment on "Sound Modes broadening in Quasicrystals
  
  • Coddens Gerrit
  , 2005. Recently de Boissieu et al. proposed an explanation for the broadening of acoustic modes observed in quasicrystals (QC). It is the transcription of a well-known model used for glasses. We raise two fundamental objections against applying it to QC.
• Ferromagnetic domain structure of La0.78Ca0.22MnO3 single crystals
  
  • Jung G.
  • Markovich V.
  • van Der Beek C.J.
  • Mogilyansky D.
  • Mukovskii M.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2005, 72 (134412), pp.1-6. The magneto-optical technique has been employed to observe spontaneous ferromagnetic domain structures in La0.78Ca0.22MnO3 single crystals. The magnetic domain topology was found to be correlated with the intrinsic twin structure of the investigated crystals. With decreasing temperature the regular network of ferromagnetic domains undergoes significant changes resulting in apparent rotation of the domain walls in the temperature range of 70–150 K. The apparent rotation of the domain walls can be understood in terms of the Jahn-Teller deformation of the orthorhombic unit cell, accompanied by additional twinning.
• Spin-induced forbidden evanescent states in III-V semiconductors
  
  • Rougemaille N.
  • Drouhin H.J.
  • Richard S.
  • Fishman G.
  • Schmid A.K.
  Physical Review Letters, American Physical Society, 2005, 9518, pp.6406. 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 center dot p 14x14 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
• 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