Publications

2014

• Quasiparticle Self-Consistent GW Method for the Spectral Properties of Complex Materials
  
  • Bruneval Fabien
  • Gatti Matteo
  Topics in current chemistry, Springer, 2014, 347, pp.99-135. The GW approximation to the formally exact many-body perturbation theory has been applied successfully to materials for several decades. Since the practical calculations are extremely cumbersome, the GW self-energy is most commonly evaluated using a first-order perturbative approach: This is the so-called G 0 W 0 scheme. However, the G 0 W 0 approximation depends heavily on the mean-field theory that is employed as a basis for the perturbation theory. Recently, a procedure to reach a kind of self-consistency within the GW framework has been proposed. The quasiparticle self-consistent GW (QSGW) approximation retains some positive aspects of a self-consistent approach, but circumvents the intricacies of the complete GW theory, which is inconveniently based on a non-Hermitian and dynamical self-energy. This new scheme allows one to surmount most of the flaws of the usual G 0 W 0 at a moderate calculation cost and at a reasonable implementation burden. In particular, the issues of small band gap semiconductors, of large band gap insulators, and of some transition metal oxides are then cured. The QSGW method broadens the range of materials for which the spectral properties can be predicted with confidence. (10.1007/128_2013_460)
  DOI : 10.1007/128_2013_460
• Corrosion under argon irradiation of titanium in the low MeV range: A study coupling AFM and Spectroscopic Ellipsometry
  
  • Do Ngoc-Long
  • Garcia-Caurel Enric
  • Bérerd N.
  • Moncoffre N.
  • Gorse-Pomonti Dominique
  Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Elsevier, 2014, 327, pp.47-51. This paper reports on a recent study of the corrosion under argon ion irradiation of titanium in the low MeV range (1-9 MeV), associating AFM and Spectroscopic Ellipsometry. Irradiation with MeV Arn+ (n = 1, 3) ions produces damages on the titanium surface. Large craters form on the oxidized titanium surface whose characteristics vary as a function of the argon energy between 2 and 9 MeV. The superficial oxide grows thicker under irradiation over the same energy range, especially near 3 MeV. It is suggested that collisions cascades play a significant role in the overall damage process. (10.1016/j.nimb.2013.09.049)
  DOI : 10.1016/j.nimb.2013.09.049
• Tuning a Schottky barrier in a photoexcited topological insulator with transient Dirac cone electron-hole asymmetry
  
  • Hajlaoui Mahdi
  • Papalazarou E.
  • Mauchain Julien
  • Perfetti Luca
  • Taleb-Ibrahimi Amina
  • Navarin F.
  • Monteverde M.
  • Auban-Senzier P.
  • Pasquier C. R.
  • Moisan N.
  • Boschetto Davide
  • Neupane M.
  • Hasan M. Z.
  • Durakiewicz T.
  • Jiang Z.
  • Xu Y.
  • Miotkowski I.
  • Chen Y. P.
  • Jia S.
  • Ji H. W.
  • Cava R. J.
  • Marsi M.
  Nature, Nature Publishing Group, 2014, 5, pp.3003. The advent of Dirac materials has made it possible to realize two-dimensional gases of relativistic fermions with unprecedented transport properties in condensed matter. Their photoconductive control with ultrafast light pulses is opening new perspectives for the transmission of current and information. Here we show that the interplay of surface and bulk transient carrier dynamics in a photoexcited topological insulator can control an essential parameter for photoconductivity-the balance between excess electrons and holes in the Dirac cone. This can result in a strongly out of equilibrium gas of hot relativistic fermions, characterized by a surprisingly long lifetime of more than 50 ps, and a simultaneous transient shift of chemical potential by as much as 100 meV. The unique properties of this transient Dirac cone make it possible to tune with ultrafast light pulses a relativistic nanoscale Schottky barrier, in a way that is impossible with conventional optoelectronic materials. (10.1038/ncomms4003)
  DOI : 10.1038/ncomms4003
• Photoemission spectra and effective masses of n- and p-type oxide semiconductors from first principles: ZnO, CdO, SnO2, MnO, and NiO
  
  • Rödl Claudia
  • Schleife André
  Physica Status Solidi A (applications and materials science), Wiley, 2014, 2011, pp.74-81. While there is a persistent interest in oxides, e.g., for semiconductor technology or optoelectronics, it seems to be difficult to achieve n-type and p-type doping for one and the same material. At the same time, it is important to understand the electronic structure for both types of doping individually. In this work, we use modern electronic-structure calculations to compute the density of states as well as effective electron and hole masses for n-type (ZnO, CdO, SnO2) and p-type (MnO, NiO) oxide materials. We establish our ab initio electronic structures by comparison to photoemission experiments at various incident photon energies. Taking into account the photoionization cross-sections, we are able to analyze the contributions of different atomic states and to verify the results by comparison to measured data. Based on these electronic structures, we calculate free-electron and free-hole masses as well as their dependence on the concentration of free carriers in the system. For SnO2, we compare with experimental results from another article (see M. Feneberg et al., Phys. Status Solidi A, DOI 10.1002/pssa.201330147 (2013) ) in this special issue. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim (10.1002/pssa.201330181)
  DOI : 10.1002/pssa.201330181
• Determination of thicknesses of oxide films grown on titanium under argon irradiation by spectroscopic ellipsometry
  
  • Do Ngoc-Long
  • Garcia-Caurel Enric
  • Bererd Nicolas
  • Moncoffre Nathalie
  • Gorse-Pomonti Dominique
  Journal of Nuclear Materials, Elsevier, 2014, 447 (1-3), pp.197-207. In this article we present a study of the oxidation of pure titanium bulk samples under argon ion irradiation at 500°C under rarefied air. In particular we follow the dependence of the oxide thickness as a function of the energy of argon ions. The novelty of this study consists in the range of ion energy explored, from 1 to 9MeV. Until very recently it was commonly accepted that metal surfaces were transparent to ion beams in this low energy range (few MeV), and no surface modifications were expected. In a previous paper by the authors of this work, the formation of shallow craters in the surface of titanium was reported as a result of argon ion bombardment with energies of 2, 4 and 9MeV under the same environmental conditions. We show here that around 3MeV the oxide growth is unexpectedly enhanced. We think that an interplay of electronic excitations and nuclear ballistic collisions could possibly explain this enhanced oxide growth. We have used spectroscopic visible ultraviolet ellipsometry and XPS to determine the thickness of the oxide layers and characterize their optical properties. From the optical properties of the oxides we observed that for ion energies below 3-4MeV the oxides show a dielectric-like behavior, whereas for ion energies above 3-4MeV the oxides show a metal-like behavior. These findings indicate also that ion bombardment in this energy range may change substantially the oxygen-to-titanium ratio in the oxide films grown under irradiation leading to the formation of titanium sub-oxides. (10.1016/j.jnucmat.2014.01.010)
  DOI : 10.1016/j.jnucmat.2014.01.010
• Surface enhanced infrared absorption in dielectric thin films with ultra-strong confinement effects
  
  • Chalopin Yann
  • Hayoun Marc
  • Volz Sebastian
  • Dammak Hichem
  Applied Physics Letters, American Institute of Physics, 2014, 104 (1), pp.011905. By formulating a microscopic description of the non-local dielectric constant, we have investigated the mechanisms of infrared absorption in dielectrics thin films by molecular dynamics simulations. We found that light absorption in dielectric slabs does not occur predominantly at the polaritons resonances but through anomalous surface modes extremely confined in space. This demonstrate that any macroscopic description of electrodynamics in dielectrics breaks down at the nanoscale. (10.1063/1.4860989)
  DOI : 10.1063/1.4860989
• Multiphoton k -resolved photoemission from gold surface states with 800-nm femtosecond laser pulses
  
  • Sirotti Fausto
  • Beaulieu Nathan
  • Bendounan Azzedine
  • Silly Mathieu G.
  • Chauvet Christian
  • Malinowski Grégory
  • Fratesi Guido
  • Véniard Valérie
  • Onida Giovanni
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2014, 90 (3), pp.35401 - 35401. We measure direct multiphoton photoemission of the Au(111) surface state with 800-nm laser pulses. We observe the parabolic dispersion in the angular distribution of photoelectrons having absorbed between four and seven photons. The k dispersion we measure can be explained in terms of Shockley-state replicas, with a nascent hot electrons distribution at k above the Fermi level. Moderate laser power densities, of the order of 100 GW/cm 2 , resulted in large electron yields, indicating the importance of multiphoton excitations to define the electronic and magnetic properties of matter in the first hundred femtoseconds after laser excitation. (10.1103/PhysRevB.90.035401)
  DOI : 10.1103/PhysRevB.90.035401
• Microscopic work function anisotropy and surface chemistry of 316L stainless steel using photoelectron emission microscopy
  
  • Barrett N.
  • Renault O.
  • Lemaître H.
  • Bonnaillie P.
  • Barcelo F.
  • Miserque F.
  • Wang M.
  • Corbel C.
  Journal of Electron Spectroscopy and Related Phenomena, Elsevier, 2014, 195, pp.117 - 124. We have studied the variation in the work function of the surface of sputtered cleaned 316L stainless steel with only a very thin residual oxide surface layer as a function of grain orientation using X-ray photo-electron emission microscopy (XPEEM) and Electron Backscattering Diffraction. The grains are mainly oriented [1 1 1] and [1 0 1]. Four distinct work function values spanning a 150 meV energy window are measured. Grains oriented [1 1 1] have a higher work function than those oriented [1 0 1]. From core level XPEEM we deduce that all grain surfaces are Cr enriched and Ni depleted whereas the Cr/Fe ratio is similar for all grains. The [1 1 1] oriented grains show evidence for a Cr 2 O 3 surface oxide and a higher concentration of defective oxygen sites. (10.1016/j.elspec.2014.05.015)
  DOI : 10.1016/j.elspec.2014.05.015
• Strain-induced inverse magnetostriction measured on a single contacted Ni nanowire in a polymer matrix Strain-induced inverse magnetostriction measured on a single contacted Ni nanowire in a polymer matrix
  
  • Pham Do-Ch
  • Biziere Nicolas
  • Melilli G
  • Pajon R
  • Lacour D
  • Bouvot L
  • Tabellout M
  • Lairez D
  • Drouhin H-J
  • Clochard M-C
  • Wegrowe J-E
  Materials Research Express, IOP Publishing Ltd, 2014, pp.045017. The effects of the thermoelastic and piezoelectric strain exerted by an active polymer matrix on a Ni nanowire (NW) are studied at the nanoscale by measuring the inverse magnetostriction of single-contacted Ni NWs. The reorientation of the magnetization is measured by anisotropic magnetoresitance. In the absence of strain, the Ni NW exhibits a typical uniform rotation of the magnetization as a function of the external field. When piezoelectric or ther-moelelastic strain is present in the polymer matrix, the hysteresis loop becomes strongly modified by the inverse magnetostriction of Ni. It is shown that the ferromagnetic NW plays then the role of a mechanical probe that allows the effects of the mechanical strain to be characterized and described qualitatively and quantitatively. Moreover the stress exerted by the polycarbonate matrix on the NW is found to be isotropic while the one produced by the PVDF matrix is anisotropic. (10.1088/2053-1591/1/4/045017)
  DOI : 10.1088/2053-1591/1/4/045017
• FIRST-PRINCIPLES CALCULATIONS OF ELECTRON-PHONON SCATTERING
  
  • Sjakste Jelena
  • Timrov Iurii
  • Gava Paola
  • Mingo Natalio
  • Vast Nathalie
  , 2014, 17 (N/A), pp.333-383. (10.1615/AnnualRevHeatTransfer.2014007320)
  DOI : 10.1615/AnnualRevHeatTransfer.2014007320
• Evidence for anisotropic dielectric properties of monoclinic hafnia using high-resolution TEM valence electron energy-loss spectroscopy and ab initio time-dependent density-functional theory
  
  • Guedj C.
  • Hung L.
  • Zobelli A.
  • Blaise P.
  • Sottile F.
  • Olevano Valerio
  Applied Physics Letters, American Institute of Physics, 2014, 105 (22), pp.222904. The effect of nanocrystal orientation on the energy loss spectra of monoclinic hafnia (m-HfO2) is measured by high resolution transmission electron microscopy (HRTEM) and valence energy loss spectroscopy (VEELS) on high quality samples. For the same momentum-transfer directions, the dielectric properties are also calculated ab initio by time-dependent density-functional theory (TDDFT). Experiments and simulations evidence anisotropy in the dielectric properties of m-HfO2, most notably with the direction-dependent oscillator strength of the main bulk plasmon. The anisotropic nature of m-HfO2 may contribute to the differences among VEELS spectra reported in literature. The good agreement between the complex dielectric permittivity extracted from VEELS with nanometer spatial resolution, TDDFT modeling, and past literature demonstrates that the present HRTEM-VEELS device-oriented methodology is a possible solution to the difficult nanocharacterization challenges given in the International Technology Roadmap for Semiconductors. (10.1063/1.4903218)
  DOI : 10.1063/1.4903218
• Negative Hall coefficient of ultrathin niobium in Si/Nb/Si trilayers
  
  • Zaytseva I
  • Abal 'Oshev O
  • Dłuzewski P
  • Paszkowicz W
  • Zhu L.Y. L.Y.
  • Chien C.L.
  • Konczykowski M.
  • Cieplak Marta Z.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2014, 90, pp.5. Structural and transport properties of thin Nb layers in Si/Nb/Si trilayers with Nb layer thickness d from 1.1 nm to 50 nm have been studied. With decreasing thickness, the structure of the Nb layer changes from polycrystalline to amorphous at d 3.3 nm, while the superconducting temperature T c monotonically decreases. The Hall coefficient varies with d systematically but changes sign into negative in ultrathin films with d < 1.6 nm. The influence of boundary scattering on the relaxation rate of carriers, and band broadening in the amorphous films, may contribute to this effect. (10.1103/PhysRevB.90.060505)
  DOI : 10.1103/PhysRevB.90.060505
• Functionalization of nanochannels by radio-induced grafting polymerization on PET track-etched membranes
  
  • Soto Espinoza S.L.
  • Arbeitman C.R.
  • Clochard Marie-Claude
  • Grasselli M
  Radiation Physics and Chemistry, Elsevier, 2014, pp.72-75. Irradiated PET foils with swift-heavy ions were etched and grafted in a step-by-step process. Grafting polymerization was performed on the remaining active sites after etching. Track-etched PET membranes were fluorescently labeled by chemical functionalization. Functionalized track-etched PET membranes were analyzed by fluorescence and confocal microscopy. a b s t r a c t The application of swift-heavy ion bombardment to polymers is a well-established technique to manufacture micro-and nanopores onto polymeric films to obtain porous membranes. A few years ago, it was realized that, during ion bombardment, the high energy deposition along the ion path through the polymer reached cylindrical damage regions corresponding to the core trace and the penumbra. After the etching procedure, there are still enough active sites left in the penumbra that can be used to initiate a polymerization process selectively inside the membrane pores. In this study, we report the grafting polymerization of glycidyl methacrylate onto etched PET foils to obtain functionalized nanochannels. Grafted polymers were labeled with a fluorescent tag and analyzed by different fluorescence techniques such as direct fluorescence, fluorescence microscopy and confocal microscopy. These techniques allowed identifying and quantifying the grafted regions on the polymeric foils. & (10.1016/j.radphyschem.2013.05.043)
  DOI : 10.1016/j.radphyschem.2013.05.043
• Quantum-classical model for the surface plasmon enhanced photoemission process at metal surfaces
  
  • Jouin H
  • Raynaud M
  • Duchateau G
  • Geoffroy G
  • Sadou A
  • Martin Patrick
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2014. The main purpose of this work is to propose a theoretical description of the surface plasmon polariton stimulated electron emission process at metal surfaces in which the primary electron ejection from the conduction band is treated quantum mechanically in order to go beyond the approximate approaches used up to now to represent this first step. Our theoretical results are well supported by experimental energy spectra obtained for some tens of femtosecond laser pulses impinging on a gold grating target at various intensities in the GW/cm 2 range. The present model which allows us to discuss various features of the surface plasmon photoemission process such as the role of the surface plasmon phase is rather simple and could be applied with slight modifications to study the stimulated photoemission of metallic nanoparticles which has been a subject of growing interest during the past few years. (10.1103/PhysRevB.89.195136)
  DOI : 10.1103/PhysRevB.89.195136
• Effect of gamma rays absorbed doses and heat treatment on the optical absorption spectra of silver ion-exchanged silicate glass
  
  • Farah Khaled
  • Hosni Faouzi
  • Mejri Arbi
  • Boizot Bruno
  • Hafedh Ben
  • Hamzaoui Ahmed Hichem
  Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Elsevier, 2014, 323, pp.36-41. Samples of a commercial silicate glass have been subjected to ion exchange at 320 °C in a molten mixture of AgNO 3 and NaNO 3 with molar ratio of 1:99 and 5:95 for 60 min. The ion exchange process was followed by gamma irradiation in the dose range of 1–250 kGy and heating at the temperature of 550 °C for different time periods ranging from 10 to 582 min. The spectral absorption in UV–Vis range of the Ag–Na ion exchanged glass was measured and used to determine the states of silver prevailing in the glass during the ion exchange, the gamma irradiation and the heat treatment. The gamma irradiation induced holes and electrons in the glass structure leading to the creation of a brown colour, and silver ions trapped electrons to form silver atoms. We observed the first stage of aggregation after irradiation, as well as after heating. The silver atoms diffused and then aggregated to form nanoclusters after heating at 550 °C. A characteristic band at about 430 nm was induced. The surface Plasmon absorption of silver nanoclusters in the glass indicated that the nanoclusters radius grew between 0.9 and 1.43 nm with increasing of annealing time from 10 to 242 min and then saturated. We also found that the size of aggregates depends on the value of gamma radiation absorbed dose. Contrary to what was expected, we found that 20 kGy is the optimal absorbed dose corresponding to the larger size of the aggregates which decreases for absorbed doses above 20 kGy. (10.1016/j.nimb.2014.01.019)
  DOI : 10.1016/j.nimb.2014.01.019
• Colour centre production in yttria-stabilized zirconia by X-ray and electron irradiations: effect of yttria content
  
  • Costantini Jean-Marc
  • Fasoli Mauro
  • Beuneu François
  • Boizot Bruno
  Philosophical Magazine, Taylor & Francis, 2014, 94 (35), pp.4053. Yttria-stabilized zirconia (YSZ) single crystals (for 9.5 and 18 mol% yttria) were irradiated at room temperature (RT) by X-rays (W white spectrum) and 2.5-MeV electrons. The growth curves of the so-called T-centre (for trigonal centre, i.e. Zr3+ sitting in a trigonal symmetry site) were studied as a function of absorbed dose, or irradiation time, by UV–visible optical absorption (OA) spectroscopy and X-band electron paramagnetic resonance spectroscopy. The defect concentration at saturation and the production rate are increased by a factor around two for 18 mol% yttria with respect to 9.5 mol%. Defect decay was then followed after irradiation by OA spectroscopy as a function of ageing time at RT. Growth and decay curves of the T-centre are modelled on the basis of rate equations of charge-exchange reactions with the zirconium lattice ions. Increase in yttrium content is thought to decrease hole trapping on Zr3+ ions, thereby enhancing T-centre formation. (10.1080/14786435.2014.977369)
  DOI : 10.1080/14786435.2014.977369
• Differences in fundamental reaction mechanisms between high and low-LET in recent advancements and applications of ionizing radiation
  
  • Farahani Mahnaz
  • Clochard Marie-Claude
  • Gifford Ian
  • Barkatt Aaron
  • Al-Sheikhly Mohamad
  Radiation Physics and Chemistry, Elsevier, 2014, pp.39-47. Recent applications of high-LET radiation include boron neutron capture therapy. UV treatment of electron-irradiated UHMWPE impedes degradation caused by allyl radicals. Radiation synthesis of PVP nanogels above 55 1C leads to intra-molecular crosslinking. PCBs in contaminated sediments can be dechlorinated by reactions with hydrated electrons. a b s t r a c t Differences among the mechanisms of energy deposition by high-linear energy transfer (LET) radiation, consisting of neutrons, protons, alpha particles, and heavy ions on one hand, and low-LET radiation, exemplified by electron beam and gamma radiation on the other, are utilized in the selection of types of radiation used for specific applications. Thus, high-LET radiation is used for modification of carbon nanotubes, ion track grafting, and the synthesis of membranes and nanowires, as well as for characterization of materials by means of neutron scattering. Recent applications of low-LET irradiation include minimization of radiolytic degradation upon sterilization of ultra-high molecular weight polyethylene (UHMWPE), radiolytic synthesis of nanogels for drug delivery systems, grafting of polymers in the synthesis of adsorbents for uranium from seawater, and reductive remediation of PCBs. (10.1016/j.radphyschem.2014.05.032)
  DOI : 10.1016/j.radphyschem.2014.05.032
• Comparative study of the effects of electron irradiation and natural disorder in single crystals of SrFe 2 (As 1−x P x ) 2 superconductor (x = 0.35)
  
  • Strehlow C. P.
  • Konczykowski M.
  • Murphy J. A.
  • Teknowijoyo S.
  • Cho K.
  • Tanatar M. A.
  • Kobayashi T.
  • Miyasaka S.
  • Tajima S.
  • Prozorov R.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2014, 90, pp.5. The London penetration depth λ(T) was measured in single crystals of a SrFe 2 (As 1−x P x) 2 (x = 0.35) iron-based superconductor. The influence of disorder on the transition temperature T c and on λ(T) was investigated. The effects of scattering controlled by the annealing of as-grown crystals was compared with the effects of artificial disorder introduced by 2.5 MeV electron irradiation. The low-temperature behavior of λ(T) can be described by a power-law function λ(T) = AT n , with the exponent n close to one in pristine annealed samples, as expected for a superconducting gap with line nodes. Upon electron irradiation with a dose of 1.2 × 10 19 e/cm 2 , the exponent n increases rapidly, exceeding a dirty limit value of n = 2, implying that the nodes in the superconducting gap are accidental and can be lifted by the disorder. The variation of the exponent n with T c is much stronger in the irradiated crystals compared to the crystals in which disorder was controlled by the annealing of the growth defects. We discuss the results in terms of different influence of different types of disorder on intraband and interband scattering. (10.1103/PhysRevB.90.020508)
  DOI : 10.1103/PhysRevB.90.020508
• Magnetic nanoconstrictions made from nickel electrodeposition in polymeric bi-conical tracks: Magneto-transport behavior
  
  • Clochard M-C
  • El Jouad M
  • Biziere Nicolas
  • Do Pham
  • Drouhin H-J
  • Balanzat Emmanuel
  • Lairez D
  • Viret M
  • Wegrowe J-E
  International Journal for Radiation Physics and Chemistry, Elsevier, 2014, pp.173910. Single nanoconstriction per magnetic wire is obtained by bi-conical track etching and electrodeposition. Magnetoresistance measurements at various angles result in irreversible jumps. Resulting jumps of magnetization have been attributed to the pinning and depinning of a constrained magnetic domain wall. a b s t r a c t In a cylindrical magnetic nanowire, a magnetic domain wall (DW) can move along the wire when an applied magnetic field or a spin-polarized current is applied. We show that in a magnetic device composed of two conical nanowires connected by a nanosized constriction, a DW can be trapped and detrapped. The magnetoreistance and the relaxation processes of the DW exhibit a specific behavior. Such a device has been fabricating by Ni electrodeposition in bi-conical tracks polymer membrane made of Swift Heavy Ions bombarded poly(VDF-co-TrFE) copolymer and poly(ethylene terephtalate) PET thin films. The latter method allows to monitor the conicity of the bi-conical wires and to give access to a panel of very well-defined structures. & (10.1016/j.radphyschem.2013.06.016)
  DOI : 10.1016/j.radphyschem.2013.06.016
• Isolation of the CH3˙ rotor in a thermally stable inert matrix: first characterization of the gradual transition from classical to quantum behaviour at low temperatures
  
  • Buscarino G.
  • Alessi A.
  • Agnello S.
  • Boizot B.
  • Gelardi F. M.
  • Boscaino R.
  Physical Chemistry Chemical Physics, Royal Society of Chemistry, 2014, 16 (26), pp.13360-13366. Matrix isolation is a method which plays a key role in isolating and characterizing highly reactive molecular radicals. However, the isolation matrices, usually composed of noble gases or small diamagnetic molecules, are stable only at very low temperatures, as they begin to desegregate even above a few tens of Kelvin. Here we report on the successful isolation of CH3 radicals in the cages of a nearly inert clathrate–SiO2 matrix. This host is found to exhibit a comparable inertness with respect to that of most conventional noble gas matrices but it is characterized by a peculiar thermal stability. The latter property is related to the covalent nature of the host material and gives the opportunity to study the confined radicals from a few degrees of Kelvin up to at least room temperature. Thanks to this advantage we were able to explore with continuity for the first time the CH3 rotor properties by electron paramagnetic resonance spectroscopy, starting from the quantum rotations which are observable only at the lowest temperatures (T E 4 K), going through the gradual transition to the classical motion (4 K o T o 30 K), and ending with the properties of the fully classical rotor (T 4 30 K). The method of isolation presented here is found to be very effective and promising, as it is expected to be applicable to a large variety of different molecular radicals. (10.1039/c4cp01499e)
  DOI : 10.1039/c4cp01499e
• Multiple satellites in materials with complex plasmon spectra: From graphite to graphene
  
  • Guzzo Matteo
  • Kas Joshua J.
  • Sponza Lorenzo
  • Giorgetti Christine
  • Sottile Francesco
  • Pierucci Debora
  • Silly Mathieu G.
  • Sirotti Fausto
  • Rehr John J.
  • Reining Lucia
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2014, 89, pp.085425. The photoemission spectrum of graphite is still debated. To help resolve this issue, we present photoemission measurements at high photon energy and analyze the results using a Green's function approach that takes into account the full complexity of the loss spectrum. Our measured data show multiple satellite replicas. We demonstrate that these satellites are of intrinsic origin, enhanced by extrinsic losses. The dominating satellite is due to the π+σ plasmon of graphite, whereas the π plasmon creates a tail on the high-binding energy side of the quasiparticle peak. The interplay between the two plasmons leads to energy shifts, broadening, and additional peaks in the satellite spectrum. We also predict the spectral changes in the transition from graphite towards graphene. (10.1103/PhysRevB.89.085425)
  DOI : 10.1103/PhysRevB.89.085425
• Defects and strain enhancements of second-harmonic generation in Si/Ge superlattices
  
  • Bertocchi Matteo
  • Luppi E.
  • Degoli Elena
  • Véniard Valérie
  • Ossicini Stefano
  The Journal of Chemical Physics, American Institute of Physics, 2014, 140 (21), pp.214705. Starting from experimental findings and interface growth problems in Si/Ge superlattices, we have investigated through ab initio methods the concurrent and competitive behavior of strain and defects in the second-harmonic generation process. Interpreting the second-harmonic intensities as a function of the different nature and percentage of defects together with the strain induced at the interface between Si and Ge, we found a way to tune and enhance the second-harmonic generation response of these systems. (C) 2014 AIP Publishing LLC. (10.1063/1.4880756)
  DOI : 10.1063/1.4880756
• Supercritical carbon dioxide extraction of metals from sulphuric acid solutions
  
  • Hung L.
  • Hertz Audrey
  • Hatmann D.
  • Charton F.
  • Boutin Olivier
  , 2014. no abstract
• Troisième génération d’OLEDs
  
  • Marghad Ikbal
  • Renaud C.
  • Zissis Georges
  , 2014.