Publications

2013

• Ab initio study of the effects of pressure and strain on electron-phonon coupling in IV and III-V semiconductors
  
  • Sjakste Jelena
  • Vast Nathalie
  • Jani Hariom
  • Obukhov Sergey
  • Tyuterev Valeriy
  physica status solidi (b), Wiley, 2013, 250 (4), pp.716-720. (10.1002/pssb.201200526)
  DOI : 10.1002/pssb.201200526
• Ab initio study of plasmons and electron-phonon coupling in bismuth: from free-carrier absorption towards a new method for electron energy-loss spectroscopy
  
  • Timrov Iurii
  , 2013. This work has been devoted to the theoretical study of bulk semimetallic bismuth with methods based on the density functional theory (DFT). Effects of spin-orbit coupling and of the exchange-and-correlation functionals in the local density (LDA) and generalized gradient approximation (GGA) have been systematically investigated. I have found that electron and hole pockets at the Fermi level are accurately reproduced, which has enabled me to successfully interpret the pump-probe experiments in the photoexcited bismuth performed in the Laboratoire des Solides Irradiés. The strong dependence on the electronic wave vector, of the calculated electronic coupling of the upper valence band with the zone-center A1g LO phonon, explains the observation of a strongly k-dependent oscillation amplitude of the upper valence band in time-resolved photoemission experiments upon activation of the coherent A1g phonon under photoexcitation. I have also shown that the presence of local extrema in the conduction and valence bands structure, where the carrier mass can be as large as 18 m0, favours an accumulation of photoexcited carriers in these extrema and contributes to the augmentation of the plasma frequency as a function of time after the photoexcitation, an effect which has no analogy in other materials (as yet). Finally, I have developed a new ab initio approach in the time-dependent density functional perturbation theory (TDDFPT), which allows us to calculate the electronic response of materials for any momentum transfer. This approach based on the Lanczos recursion method has enabled me to calculate for the first time the electron energy-loss spectrum of Bi in the 0-100 eV energy range, bridging the gap between valence and core losses. This method opens the way to the routine calculation of surface plasmons.
• Multifractal scaling of flux penetration in the Iron-based Superconductor Ba(Fe$_{0.925}$Co$_{0.075}$)$_{2}$As$_2$
  
  • Grisolia Mathieu
  • van Der Beek Cornelis Jacominus
  • Fasano Yanina
  • Forget Anne
  • Colson Dorothée
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2013, 87, pp.104517. The penetration of magnetic flux fronts in the optimally doped iron based superconductor Ba(Fe$_{0.925}$Co$_{0.075}$)$_{2}$As$_2$ is studied by means of high resolution magneto-optic imaging. The analysis of roughening and growth of the magnetic flux front reveals anomalous scaling properties. While higher-order spatial correlation functions reveal multifractal behavior for the roughening, the usual Kardar-Parisi-Zhang growth exponent is found. Both exponents are found to independent of temperature. We propose a scenario for vortex penetration based on 2D percolation and cluster aggregation in an inhomogeneously disordered superconductor. (10.1103/PhysRevB.87.104517)
  DOI : 10.1103/PhysRevB.87.104517
• Study of formation and sequential relaxation of paramagnetic point defects in electron-irradiated Na-aluminosilicate glasses: Influence of Yb
  
  • Pukhkaya V.
  • Charpentier Thibault
  • Ollier Nadège
  Journal of Non-Crystalline Solids, Elsevier, 2013, 364, pp.1-8. Paramagnetic defects in electron irradiated Yb-doped Na-aluminosilicate glasses were studied. In particular, we paid more attention to characterize the defects with Electron Paramagnetic Resonance in links with the glass structure which was analyzed by Raman spectroscopy and Magic Angle Spinning Nuclear Magnetic Resonance. Under e(-)-irradiation hole centers on non-bridging oxygens bonded to Si with close presence of Na+, peroxy radicals, hole centers on oxygens bonded to Al (Al-OHC) and E' centers were detected. Doping glasses with Yb gives rise to more Al-OHC defects. Formations of hole centers and Al-OHC defects as well as their sequential relaxation are linearly anticorrelated. After the end of irradiation, the total amount of paramagnetic defects decreases in 2 months and then remains stable. The relaxation curve presents 2 regions with different rates of defect recovery. We showed in particular that the presence of Yb-clusters in the glasses acts on the relaxation of paramagnetic point defects by decreasing significantly the recovery of defects. (C) 2013 Elsevier B.V. All rights reserved. (10.1016/j.jnoncrysol.2013.01.021)
  DOI : 10.1016/j.jnoncrysol.2013.01.021
• Disorder, critical currents, and vortex pinning energies in isovalently substituted BaFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$
  
  • Demirdis Sultan
  • Fasano Yanina
  • Kasahara Shigeru
  • Terashima Takahito
  • Shibauchi Takasada
  • Matsuda Yuji
  • Konczykowski Marcin
  • Pastoriza H.
  • van Der Beek Cornelis Jacominus
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2013, 87, pp.094506. We present a comprehensive overview of vortex pinning in single crystals of the isovalently substituted iron-based superconductor BaFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$, a material that qualifies as an archetypical clean superconductor, containing only sparse strong point--like pins [in the sense of C.J. van der Beek {\em et al.}, Phys. Rev. B {\bf 66}, 024523 (2002)]. Widely varying critical current values for nominally similar compositions show that flux pinning is of extrinsic origin. Vortex configurations, imaged using the Bitter decoration method, show less density fluctuations than those previously observed in charge-doped Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$ single crystals. Analysis reveals that the pinning force and -energy distributions depend on the P-content $x$. However, they are always much narrower than in Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$, a result that is attributed to the weaker temperature dependence of the superfluid density on approaching $T_{c}$ in BaFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$. Critical current density measurements and pinning force distributions independently yield a mean distance between effective pinning centers $\overline{\mathcal L} \sim 90$~nm, increasing with increasing P-content $x$. This evolution can be understood as being the consequence of the P-dependence of the London penetration depth. Further salient features are a wide vortex free ''Meissner belt'', observed at the edge of overdoped crystals, and characteristic chain-like vortex arrangements, observed at all levels of P-substitution. (10.1103/PhysRevB.87.094506)
  DOI : 10.1103/PhysRevB.87.094506
• Non-trivial surface-band dispersion on Bi(111)
  
  • Ohtsubo Yoshiyuki
  • Perfetti Luca
  • Goerbig Mark Oliver
  • Fèvre Patrick Le
  • Bertran François
  • Taleb-Ibrahimi Amina
  New Journal of Physics, Institute of Physics: Open Access Journals, 2013, 15 (3), pp.033041. (10.1088/1367-2630/15/3/033041)
  DOI : 10.1088/1367-2630/15/3/033041
• Mechanisms of femtosecond laser ablation of dielectrics revealed by double pump-probe experiment
  
  • Mouskeftaras Alexandros
  • Guizard Stéphane
  • Fedorov N.
  • Klimentov S.
  Applied physics. A, Materials science & processing, Springer Verlag, 2013, 110, pp.709-715. We study experimentally the electronic excitation mechanisms involved in the breakdown and ablation of wide band gap dielectrics. A femtosecond pump-probe interferometry technique, with 100 fs temporal resolution, allows measuring the modification of refractive index induced by ultra-short intense laser pulses. To get more information in the complex process of excitation and relaxation mechanisms involved during and after the interaction, we use a sequence of two excitation pulses: a first short pulse at 400 nm excites a controlled density of carriers, and a second one at 800 nm with variable pulse duration, from 50 fs to 10 ps, reaches an excited solid. In Al2O3, we show that the total density of carriers never exceeds the sum of the densities excited by the two pulses sent independently. This means that the second pulse deposits further energy in the material by heating the previously excited carriers, and that no electronic multiplication occurs. On the other hand, in SiO2, it is possible, under specific conditions, to observe an increase of carrier density due to impact ionization. All these results demonstrate that the avalanche process, which is often invoked in the laser breakdown literature, does not play a dominant role in optical breakdown induced by short pulses. (10.1007/s00339-012-7217-7)
  DOI : 10.1007/s00339-012-7217-7
• Non-trivial surface-band dispersion on Bi(111)
  
  • Ohtsubo Yoshiyuki
  • Perfetti Luca
  • Goerbig Mark Oliver
  • Fèvre Patrick Le
  • Bertran François
  • Taleb-Ibrahimi Amina
  New Journal of Physics, Institute of Physics: Open Access Journals, 2013, 15 (3), pp.033041. (10.1088/1367-2630/15/3/033041)
  DOI : 10.1088/1367-2630/15/3/033041
• Study of the physical mechanisms involved in the femtosecond laser optical breakdown of dielectric materials
  
  • Mouskeftaras Alexandros
  , 2013. We have carried out detailed time resolved experimental studies of the mechanism of electron excitation-relaxation, when an ultrashort (60 fs -1 ps) laser (UV and IR) pulse interacts with a wide band gap dielectric material.The studies cover a range of different dielectric materials and the investigated regimes span from nondestructive ionization of the material at the low power end (~TW/cm²) to ablative domain at a higher laser power (~10 TW/cm²).This gives fundamental insight into the understanding of the laser damaging process taking place under our irradiation conditions. The usage of time-resolved spectral interferometry technique allows to directlymeasurethe electron density of the irradiated material under different excitation conditions and hence leads to quantification of the process. The measurements, carried out at the optical breakdown threshold utilizing different pulse durations, raisequestions regarding the usage of critical excitation density as a universal ablation criterion. A new criterion related to the exchanged energy is proposed. Additionally, the use of an experimental setup implementing a double pump pulse allows the identification of different excitation mechanisms taking place at time scales of the order of the pulse duration used. Electronic avalanche is observed in some materials (SiO2,NaCl) while this is not the case for others (Al2O3,MgO). These differences are discussed in detail. Next, we measure the energy spectrum of excited electrons with a complementary technique: the photoemission spectroscopy. These results allow us on one hand to show a crossed effect between the two "pump" pulses and on the other hand to measure electron relaxation characteristic times, as a function of their kinetic energy. Finally, a morphological study of craters resulting from ablation in the case of a single pulse has been carried out for different irradiation parameters: number of shots, energy and pulse duration.This work has been extended to the case of double pulsedamage, with the relative delay being the studied parameter.
• First principles Second-Harmonic Generation in quantum confined silicon-based systems
  
  • Bertocchi Matteo
  , 2013. In this thesis I have dealt with the ab initio description of the second-harmonic generation (SHG) process, a nonlinear optical property of materials, focusing in particular on quantum confined, silicon-based systems. In the last decades, the accuracy and possibilities of ab initio studies have demonstrated a great relevance in both the interpretation and prediction of the materials properties. It is then mandatory to improve the knowledge of the nonlinear optical processes as well as the SHG first-principle description. Nowadays, due to nontrivial difficulties, nonlinear optics has not yet reached the accuracy and development of linear phenomena. In particular, the state of the art of ab initio SHG calculations is represented by the inclusion of many-body effects as crystal local fields (LF) and electron-hole interaction, but today, the mostly used approach is the independent particle approximation (IPA), the only one able to approach calculations of complex structures such as surfaces and interfaces. Whereas IPA can be a good approximation for bulk systems, in discontinuous materials other effects may be predominant. Hence their description is of great relevance although the lack of studies. My thesis tries to give a first analysis of the SHG process in more complex systems as the interfaces and the Si-confined systems, inferring new insights on the physical mechanism and its link with the nature of the system. I use an efficient formalism based on the Time Dependent Density Functional Theory (TDDFT) where many-body effects are included via an appropriate choice of the TDDFT kernels. Both the formalism and the code have been developed during the thesis work permitting the study complex materials. The research has been focused on the Si(111)/CaF2 (T4 B-type) interface case study. Convergence studies show the importance of the semiconductor material with respect to the insulator. The response is characteristic of a deep region beyond the Si interface whereas the CaF2 converges soon after the first interface layers. Moreover, the signal demonstrates to be sensitive to the electronic-states modifications that are induced far below the interface, and not to the Si ionic structure that recovers soon the bulk configuration. A normalization procedure to compare with the experiment has been proposed. The SHG spectra have been calculated in the IPA, introducing LF and excitonic interactions. New behaviors have been observed with respect to the SHG processes on strained silicon, GaAs or SiC showing in particular the importance of crystal local-field effects with respect to both the IPA and the excitons. Whereas IPA can describe the position of the SHG main peaks and the excitonic effects slightly modify the total intensity, only LF are able to correctly reproduce the spectral shape and the relative intensities of the peaks. This underlines how SHG and the different involved effects depends on the nature of the materials. New methods of analysis of the response have been proposed; actually, the direct link between the peaks position and the transition energies is lost in SHG calculations (i.e. the signal comes from a second order Dyson equation where linear and nonlinear response functions at different frequencies are mixed together). Furthermore, the complexity of the system allowed me to extend the study to a large variety of materials as the multilayers and the silicon confined slabs. The results show a good agreement with the experiment confirming the proposed T4 B-type interface structure. This underlines the accuracy of the formalism, the possibility of improving our knowledge on these complex materials going beyond the standard approaches, and confirms the possibility of SHG ab-initio simulations to be employed as a predictive technique, supporting and guiding experiments and technological developments. Preliminary results on Si/Ge superlattice are presented.
• Atomic and electronic properties of quasi-one-dimensional MoS2 nanowires
  
  • Fernandez Seivane Lucas
  • Barron Hector
  • Botti Silvana
  • Marques Miguel A. L.
  • Rubio Angel
  • López-Lozano Xóchitl
  Journal of Materials Research, Springer, 2013, 28, pp.240-249. The structural, electronic, and magnetic properties of quasi-one-dimensional MoS2nanowires (NWs), passivated by extra sulfur, have been determined using ab initio density functional theory. The nanostructures were simulated using several different models based on experimental electron microscopy images and theoretical literature. It is found that independently of the geometrical details and the coverage of extra sulfur at the Mo edge, quasi-one-dimensional metallic states are predominant in all the low-energy model structures despite their reduced dimensionality. These metallic states are localized mainly at the edges. However, the electronic and magnetic character of the NWs does not depend only on the S saturation but also on the symmetry configuration of the S edge atoms. Our results show that for the same S saturation, the magnetization can be decreased by increasing the pairing of the S and Mo edge atoms. In spite of the observed pairing of S dimers at the Mo edge, the NWs do not experience a Peierls-like metal–insulator transition. (10.1557/jmr.2012.355)
  DOI : 10.1557/jmr.2012.355
• Ultrafast filling of an electronic pseudogap in an incommensurate crystal
  
  • Brouet V.
  • Mauchain Julien
  • Papalazarou E.
  • Faure Jérôme
  • Marsi M.
  • H. Lin P.
  • Taleb-Ibrahimi A.
  • Le Fevre P.
  • Bertran F.
  • Cario Laurent
  • Janod Etienne
  • Corraze Benoît
  • Ta Phuoc V.
  • Perfetti L.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2013, 87 (4), pp.041106. We investigate the quasiperiodic crystal (LaS)1.196(VS2) by angle and time resolved photoemission spectroscopy. The dispersion of electronic states is in qualitative agreement with band structure calculated for the VS2 slab without the incommensurate distortion. Nonetheless, the spectra display a temperature dependent pseudogap instead of quasiparticles crossing. The sudden photoexcitation at 50 K induces a partial filling of the electronic pseudogap within less than 80 fs. The electronic energy flows into the lattice modes on a comparable timescale. We attribute this surprisingly short timescale to a very strong electron-phonon coupling to the incommensurate distortion. This result sheds light on the electronic localization arising in aperiodic structures and quasicrystals. (10.1103/PhysRevB.87.041106)
  DOI : 10.1103/PhysRevB.87.041106
• Ab Initio Electronic Gaps of Ge Nanodots: The Role of Self-Energy Effects
  
  • Marsili M.
  • Botti Silvana
  • Palummo M.
  • Degoli E.
  • Pulci O.
  • Weissker H.-C.
  • Marques M.A.L.
  • Ossicini S.
  • del Sole R.
  Journal of Physical Chemistry C, American Chemical Society, 2013, 117 (27), pp.14229−1423. Nanostructuring of a material leads to enormous effects on its excited state properties. This study, through the application of different state-of-the-art ab initio theoretical tools, investigates the effect of size on the electronic gap of germanium nanocrystals highlighting similarities and differences with respect to equivalent silicon nanostructures. We performed both GW and ΔSCF calculations for the determination of their electronic structure. While it is known that ΔSCF corrections to the Kohn–Sham gap vanish for extended systems, the two approaches were expected to be equivalent in the limit of small clusters. However, it has been recently found that for hydrogenated Si clusters the ΔSCF gaps are systematically smaller than the GW ones, while the opposite is true for Ag clusters. In this work we find that the GW gaps are larger than the ΔSCF ones for all the Ge dots, with the exception of the smallest one. Such crossing between the ΔSCF and the GW gap values was not expected and has never been observed before. Moreover, also for hydrogenated Si nanocrystals we found a similar behavior. The origin of this crossing might be found in the Rydberg character of the LUMO of the smallest clusters and can also explain the qualitative differences in the comparison between GW and ΔSCF found in the previous studies. (10.1021/jp3121269)
  DOI : 10.1021/jp3121269
• Imaging the Fine Structure of a Magnetic Domain Wall in a Ni Nanocylinder
  
  • Biziere Nicolas
  • Gatel Christophe
  • Lassalle-Balier Rémy
  • Clochard Marie-Claude
  • Wegrowe J.-E.
  • Snoeck Etienne
  Nano Letters, American Chemical Society, 2013, 13 (5), pp.2053-2057. We present the first experimental imaging of the internal DW structure in 55 and 85 nm diameter Ni nanocylinders, using electron holography combined with micromagnetic calculations. We demonstrate the magnetic transition from a hybrid magnetic state with both vortex and transverse DW in 85 nm diameter Ni nanocylinders to a pure transverse wall in thinner nanowires. This is particularly important as DWs in nanocylinders are model systems to go beyond the classical Walker limit. (10.1021/nl400317j)
  DOI : 10.1021/nl400317j
• Evidence of AlOHC responsible for the radiation-induced darkening in Yb doped fiber
  
  • Deschamps T.
  • Vezin H.
  • Gonnet C.
  • Ollier N.
  Optics Express, Optical Society of America - OSA Publishing, 2013, 21, pp.8382 - 8392. Using a combination of experimental techniques such as optical absorption, Raman scattering, continuous wave and pulse Electron Spin Resonance (ESR), we characterize a set of γ-irradiated Yb³⁺ doped silica glass preforms with different contents of phosphorous and aluminum. We demonstrate that when P is introduced in excess compared to Al, nearly no radiodarkening is induced by γ-rays. On the other hand, when Al>P, a large absorption band is induced by radiation. Thermal annealing experiments reveal the correlation between the decrease of the optical absorption band and the decrease of the Al-Oxygen Hole Center (AlOHC) ESR signal, demonstrating the main role of AlOHC defects in the fiber darkening. HYSCORE (HYperfine Sublevel CORElation) pulse-ESR experiments show a high Al-P nuclear spin coupling when P>Al and no coupling when Al>P. This result suggests that both AlOHC and POHC creation is inhibited by Al-O-P linkages. Confronting our data with previous works, we show that the well-known photodarkening process, meaning losses induced by the IR pump, can also be explained in this framework. (10.1364/OE.21.008382)
  DOI : 10.1364/OE.21.008382
• Improved ion acceleration via laser surface plasma waves excitation
  
  • Bigongiari Alessandra
  • Raynaud Michèle
  • Riconda Caterina
  • Héron Anne
  Physics of Plasmas, American Institute of Physics, 2013, 20 (5), pp.052701. The possibility of enhancing the emission of the ions accelerated in the interaction of a high intensity ultra-short (<100 fs) laser pulse with a thin target (<10 l0), via surface plasma wave excitation is investigated. Two-dimensional particle-in-cell simulations are performed for laser intensities ranging from 10^19 to 10^20 W/cm2.µm2. The surface wave is resonantly excited by the laser via the coupling with a modulation at the target surface. In the cases where the surface wave is excited, we find anenhancement of the maximum ion energy of a factor ~2 compared to the cases where the target surface is flat. (10.1063/1.4802989)
  DOI : 10.1063/1.4802989
• Powellite-Rich Glass-Ceramics: A Spectroscopic Study by EPR and Raman Spectroscopy
  
  • Taurines T
  • Neff Delphine D.
  • Boizot B
  Journal of the American Ceramic Society, Wiley, 2013, pp.1-7. The aim of this study is to better understand the incorporation of rare earth elements in glass-ceramics of nuclear interest. We synthesized glass-ceramics from glasses in the system SiO 2-B 2 O 3-Na 2 O-CaO-Al 2 O 3-MoO 3-Gd 2 O 3 by various heat treatments. Gadolinium is used both as a spectroscopic probe and as a minor actinide surrogate. Glass-ceramics contain only one crystalline phase in the bulk: powellite (CaMoO 4). This phase can incorporate Gd 3+ and Na + ions by substitutions on the Ca site. We demonstrated that the charge compensation by Na + favors the rare earth elements incorporation. Moreover, the incorporated elements do not seem to be randomly distributed into the powellite structure. (10.1111/jace.12401)
  DOI : 10.1111/jace.12401
• Evidence of Resonant Surface-Wave Excitation in the Relativistic Regime through Measurements of Proton Acceleration from Grating Targets
  
  • Ceccotti T
  • Floquet V
  • Sgattoni A
  • Bigongiari A
  • Klimo O
  • Raynaud M
  • Riconda C
  • Heron A
  • Baffigi F
  • Labate L
  • Gizzi L. A.
  • Vassura L
  • Fuchs J
  • Passoni M
  • Květon M
  • Novotny F
  • Possolt M
  • Prokůpek J
  • Proška J
  • Pšikal J
  • Stolcova L.
  • Velyhan A
  • Bougeard M
  • D 'Oliveira P
  • Tcherbakoff O
  • Réau F
  • Martin P
  • Macchi A
  Physical Review Letters, American Physical Society, 2013. The interaction of laser pulses with thin grating targets, having a periodic groove at the irradiated surface, is experimentally investigated. Ultrahigh contrast ($ 10 12) pulses allow us to demonstrate an enhanced laser-target coupling for the first time in the relativistic regime of ultrahigh intensity >10 19 W=cm 2. A maximum increase by a factor of 2.5 of the cutoff energy of protons produced by target normal sheath acceleration is observed with respect to plane targets, around the incidence angle expected for the resonant excitation of surface waves. A significant enhancement is also observed for small angles of incidence, out of resonance. (10.1103/PhysRevLett.111.185001)
  DOI : 10.1103/PhysRevLett.111.185001
• Magnetoresistance in magnetic nanoconstrictions: The role of structural defects Magnetoresistance in magnetic nanoconstrictions: The role of structural defects
  
  • Biziere Nicolas
  • Clochard M.-C
  • Do Pham
  • Wegrowe J.-E
  • Viret M
  Journal of Applied Physics, American Institute of Physics, 2013, pp.173910. The resistance of a ferromagnetic cylindrical Ni nano-constriction has been measured as a function of the external magnetic field. Typical profiles of the resistance versus external field are observed with irreversible jumps separated by stable plateaus, showing systematic slow relaxation effects. An interpretation in terms of magnetomechanical strain at the level of the constriction is proposed. This scenario allows the slow relaxation behaviour to be understood in terms of displacement of dislocations or similar metastable structural defects. V C 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4803702] (10.1063/1.4803702)
  DOI : 10.1063/1.4803702
• Growth of "moth-eye" ZnO nanostructures on Si(111), c-Al2O3, ZnO and steel substrates by pulsed laser deposition
  
  • Sandana Vinod E.
  • Rogers David J.
  • Teherani Ferechteh Hosseini
  • Bove Philippe
  • Troyon Michel
  • Largeteau Alain
  • Demazeau Gérard
  • Scott Colin Philip
  • Orsal Gaëlle
  • Drouhin Henri-Jean
  • Ougazzaden Abdallah
  • Razeghi Manijeh
  Physica Status Solidi C: Current Topics in Solid State Physics, Wiley, 2013, 10 (10), pp.1317-1321. Self-forming, vertically-aligned, arrays of black-body-like ZnO moth-eye nanostructures were grown on Si(111), c-Al2O3, ZnO and high manganese austenitic steel substrates using Pulsed Laser Deposition. X-ray diffraction (XRD) revealed the nanostructures to be well-crystallised wurtzite ZnO with strong preferential c-axis crystallographic orientation along the growth direction for all the substrates. Cathodoluminescence (CL) studies revealed emission characteristic of the ZnO near band edge for all substrates. Such moth-eye nanostructures have a graded effective refractive index and exhibit black-body characteristics. Coatings with these features may offer improvements in photovoltaic and LED performance. Moreover, since ZnO nanostructures can be grown readily on a wide range of substrates it is suggested that such an approach could facilitate growth of GaN-based devices on mismatched and/or technologically important substrates, which may have been inaccessible till present. (10.1002/pssc.201200975)
  DOI : 10.1002/pssc.201200975
• Les supraconducteurs ferromagnétiques
  
  • Lévy-Bertrand Florence
  • van Der Beek K.
  Reflets de la Physique, EDP sciences, 2013, 32, pp.4. (10.1051/refdp/201332004)
  DOI : 10.1051/refdp/201332004
• Low-temperature anharmonicity of barium titanate: A path-integral molecular-dynamics study
  
  • Geneste Grégory
  • Dammak Hichem
  • Hayoun Marc
  • Thiercelin Mickael
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2013, 87 (1). (10.1103/PhysRevB.87.014113)
  DOI : 10.1103/PhysRevB.87.014113