Publications

2016

• Optimized virtual orbital subspace for faster GW calculations in localized basis
  
  • Bruneval Fabien
  The Journal of Chemical Physics, American Institute of Physics, 2016, 145 (23), pp.234110. The popularity of the GW approximation to the self-energy to access the quasiparticle energies of molecules is constantly increasing. As the other methods addressing the electronic correlation, the GW self-energy unfortunately shows a very slow convergence with respect to the basis complexity, which precludes the calculation of accurate quasiparticle energies for large molecules. Here we propose a method to mitigate this issue that relies on two steps: (i) the definition of a reduced virtual orbital subspace, thanks to a much smaller basis set; (ii) the account of the remainder through the simpler one-ring approximation to the self-energy. We assess the quality of the corrected quasiparticle energies for simple molecules, and finally we show an application to large graphene chunks to demonstrate the numerical efficiency of the scheme. (10.1063/1.4972003)
  DOI : 10.1063/1.4972003
• Exciton band structure in two-dimensional materials
  
  • Cudazzo Pierluigi
  • Sponza Lorenzo
  • Giorgetti Christine
  • Reining Lucia
  • Sottile Francesco
  • Gatti Matteo
  Physical Review Letters, American Physical Society, 2016, 116. Low-dimensional materials differ from their bulk counterpart in many respects. In particular, the screening of the Coulomb interaction is strongly reduced, which can have important consequences such as the significant increase of exciton binding energies. In bulk materials the binding energy is used as an indicator in optical spectra to distinguish different kinds of excitons, but this is not possible in low-dimensional materials, where the binding energy is large and comparable in size for excitons of very different localization. Here we demonstrate that the exciton band structure, which can be accessed experimentally, instead provides a powerful way to identify the exciton character. By comparing the ab initio solution of the many-body Bethe-Salpeter equation for graphane and single-layer hexagonal BN, we draw a general picture of the exciton dispersion in two-dimensional materials, highlighting the different role played by the exchange electron-hole interaction and by the electronic band structure. Our interpretation is substantiated by a prediction for phosphorene. (10.1103/PhysRevLett.116.066803)
  DOI : 10.1103/PhysRevLett.116.066803
• The concept of entropic rectifier facing experiments
  
  • Lairez D.
  • Clochard M.-C.
  • Wegrowe J.-E.
  Scientific Reports, Nature Publishing Group, 2016, 6 (1), pp.38966. The transport of molecules in confined media is subject to entropic barriers. So theoretically, asymmetry of the confinement length may lead to molecular ratchets with entropy as the only driving force for the biased transport. We address experimentally this question by performing alternative ionic current measurements on electrolytes confined in neutral conical nanopores. In case anions and cations widely differ in size, we show that rectification of ionic current can be obtained that depends on ions size and cycle frequency, consistently with the entropic ratchet mechanism. (10.1038/srep38966)
  DOI : 10.1038/srep38966
• Large area fabrication of self-standing nanoporous graphene-on-PMMA substrate
  
  • Clochard M.-C.
  • Melilli G.
  • Rizza G.
  • Madon B.
  • Alves M.
  • Wegrowe J.-E.
  • Toimil-Molares M.-E.
  • Christian M.
  • Ortolani L.
  • Rizzoli R.
  • Morandi V.
  • Palermo V.
  • Bianco S.
  • Pirri F.
  • Sangermano M.
  Materials Letters, Elsevier, 2016, 184, pp.47-51. We report a new fabrication strategy to obtain large area continuous NPGs-on-substrate combining graphene-on-substrate industrial techniques and swift-ion beam irradiation (SHI). Graphene membranes were synthesized on the Cu substrate and afterwards a 600 nm layer of PMMA was spin-coated on the surface to complete the PMMA-Graphene-Cu stack. The PMMA-graphene-Cu trilayer was exposed to a flow of Au heavy ions that penetrate through the entire thickness of both polymer layer and the graphene sheet creating ion-tracks and damages. A consecutive track-etching technique is used with an adequate revealing agent for PMMA, IsoPropyl Alcohol (IPA), to selectively dissolve the latent tracks and damages created during SHI irradiation in the insulating material and the graphene sheet. Resulting from SHI irradiation and track-etching, the graphene nanopores are thus perfectly aligned to the PMMA nanopores, providing, after cupper dissolution, a composite that features both well-defined and truly 2-dimensional nanopores in the graphene layer but that can be handled as a normal polymer film. (10.1016/j.matlet.2016.07.133)
  DOI : 10.1016/j.matlet.2016.07.133
• The concept of entropic rectifier facing experiments
  
  • Lairez D.
  • Clochard M.-C.
  • Wegrowe J.-E.
  Scientific Reports, Nature Publishing Group, 2016, 6 (1). The transport of molecules in confined media is subject to entropic barriers. So theoretically, asymmetry of the confinement length may lead to molecular ratchets with entropy as the only driving force for the biased transport. We address experimentally this question by performing alternative ionic current measurements on electrolytes confined in neutral conical nanopores. In case anions and cations widely differ in size, we show that rectification of ionic current can be obtained that depends on ions size and cycle frequency, consistently with the entropic ratchet mechanism. (10.1038/srep38966)
  DOI : 10.1038/srep38966
• Electronic Transport: Electrons, Phonons and Their Coupling within the Density Functional Theory
  
  • Vast Nathalie
  • Sjakste Jelena
  • Kané Gaston
  • Trinité Virginie
  , 2016, pp.31-96. (10.1002/9781118761793.ch2)
  DOI : 10.1002/9781118761793.ch2
• Fabrication of Ion-Shaped Anisotropic Nanoparticles and their Orientational Imaging by Second-Harmonic Generation Microscopy
  
  • Slablab Abdallah
  • Isotalo Tero
  • Mäkitalo Jouni
  • Turquet Léo
  • Coulon Pierre-Eugène
  • Niemi Tapio
  • Ulysse Christian
  • Kociak Mathieu
  • Mailly Dominique
  • Rizza Giancarlo
  • Kauranen Martti
  Scientific Reports, Nature Publishing Group, 2016, 6 (1), pp.37469. Abstract Ion beam shaping is a novel and powerful tool to engineer nanocomposites with effective three-dimensional (3D) architectures. In particular, this technique offers the possibility to precisely control the size, shape and 3D orientation of metallic nanoparticles at the nanometer scale while keeping the particle volume constant. Here, we use swift heavy ions of xenon for irradiation in order to successfully fabricate nanocomposites consisting of anisotropic gold nanoparticle that are oriented in 3D and embedded in silica matrix. Furthermore, we investigate individual nanorods using a nonlinear optical microscope based on second-harmonic generation (SHG). A tightly focused linearly or radially-polarized laser beam is used to excite nanorods with different orientations. We demonstrate high sensitivity of the SHG response for these polarizations to the orientation of the nanorods. The SHG measurements are in excellent agreement with the results of numerical modeling based on the boundary element method. (10.1038/srep37469)
  DOI : 10.1038/srep37469
• Atomistic simulation of fatigue in face centred cubic metals
  
  • Fan Zhengxuan
  , 2016. Fatigue is one of the major damage mechanisms of metals. It is characterized by strong environmental effects and wide lifetime dispersions which must be better understood. Different face centred cubic metals, Al, Cu, Ni, and Ag are analyzed. The mechanical behaviour of surface steps naturally created by the glide of dislocations subjected to cyclic loading is examined using molecular dynamics simulations in vacuum and in air for Cu and Ni. An atomistic reconstruction phenomenon is observed at these surface steps which can induce strong irreversibility. Three different mechanisms of reconstruction are defined. Surface slip irreversibility under cyclic loading is analyzed. All surface steps are intrinsically irreversible under usual fatigue laboratory loading amplitude without the arrival of opposite sign dislocations on direct neighbor plane.With opposite sign dislocations on non direct neighbour planes, irreversibility cumulates cycle by cycle and a micro-notch is produced whose depth gradually increases.Oxygen environment affects the surface (first stage of oxidation) but does not lead to higher irreversibility as it has no major influence on the different mechanisms linked to surface relief evolution.A rough estimation of surface irreversibility is carried out for pure edge dislocations in persistent slip bands in so-called wavy materials. It gives an irreversibility fraction between 0.5 and 0.75 in copper in vacuum and in air, in agreement with recent atomic force microscopy measurements.Crack propagation mechanisms are simulated in inert environment. Cracks can propagate owing to the irreversibility of generated dislocations because of their mutual interactions up to the formation of dislocation junctions.
• Interfacial skew tunneling in group III-V and group IV semiconductors driven by exchange and spin-orbit interactions; Study in the frame of an extended k.p theory
  
  • Dang Thi Huong
  , 2016. We report on theoretical, analytical and computational investigations and k.p calculations of electron and hole tunneling, in model systems and heterostructures composed of exchange-split III-V semiconductors involving spin-orbit interaction (SOI). We show that the interplay of SOI and exchange interactions at interfaces and tunnel junctions results in a large difference of transmission for carriers, depending on the sign of their incident in-plane wave vector (k//): this leads to interfacial skew-tunneling effects that we refer to as Anomalous Tunnel Hall Effect (ATHE). In a 2x2 exchange-split band model, the transmission asymmetry (A) between incidence angles related to +k// and -k// wave vector components, is shown to be maximal at peculiar points of the Brillouin zone corresponding to a totally quenched transmission (A = 100%). More generally, we demonstrate the universal character of the transmission asymmetry A vs. in-plane wavevector component, for given reduced kinetic energy and exchange parameter, A being universally scaled by a unique function, independent of the spin-orbit strength and of the material parameters. Similarly, striking tunneling phenomena arising in topological insulators have just been predicted. While they all are related to the spin-orbit directional anisotropy, ATHE differs from the tunneling Hall effect, spontaneous anomalous, and spin Hall effects, or spin-galvanic effect, previously reported for electron transport, by its giant forward asymmetry and chiral nature. These features have non-trivial connection with the symmetry properties of the system. All these results show that a new class of tunneling phenomena can now be investigated and experimentally probed.When valence bands are involved, we show (using 14x14 Hamiltonian and within a 2x2 toy model) that ATHE accurate calculations rely on a subtle treatment of the spurious (unphysical) states and we give an insight into the topology of the complex band structure. We introduce two numerical methods to remove spurious states and successfully, include them in 30-band codes able to describe indirect bandgap group-IV semiconductors. Calculations performed in the valence bands of model heterostructures including tunnel barriers, in both 6x6 and 14x14 k.p Hamiltonians without inversion asymmetry, more astonishingly highlight the same trends in the transmission asymmetry which appears to be related to the difference of orbital chirality and to the related branching (overlap) of the corresponding evanescent wave functions responsible for the tunneling current. Besides, we built an analytical model and developed scattering perturbative techniques based on Green’s function method to analytically deal with electrons and holes and to compare these results with numerical calculations. The agreement between the different approaches is very good. In the case of holes, the asymmetry appears to be robust and persists even when a single electrode is magnetic.
• Ultrafast photocurrents at the surface of the three-dimensional topological insulator Bi 2 Se 3
  
  • Braun Lukas
  • Mussler Gregor
  • Hruban Andrzej
  • Konczykowski Marcin
  • Schumann Thomas
  • Wolf Martin
  • Münzenberg Markus
  • Perfetti Luca
  • Kampfrath Tobias
  Nature Communications, Nature Publishing Group, 2016, 7, pp.13259. Three-dimensional topological insulators are fascinating materials with insulating bulk yet metallic surfaces that host highly mobile charge carriers with locked spin and momentum. Remarkably, surface currents with tunable direction and magnitude can be launched with tailored light beams. To better understand the underlying mechanisms, the current dynamics need to be resolved on the timescale of elementary scattering events (B10 fs). Here, we excite and measure photocurrents in the model topological insulator Bi 2 Se 3 with a time resolution of 20 fs by sampling the concomitantly emitted broadband terahertz (THz) electromagnetic field from 0.3 to 40 THz. Strikingly, the surface current response is dominated by an ultrafast charge transfer along the Se–Bi bonds. In contrast, photon-helicity-dependent photocurrents are found to be orders of magnitude smaller than expected from generation scenarios based on asymmetric depopulation of the Dirac cone. Our findings are of direct relevance for broadband optoelectronic devices based on topological-insulator surface currents. (10.1038/ncomms13259)
  DOI : 10.1038/ncomms13259
• SANS study of vortex lattice structural transition in optimally doped (Ba 1− x K x )Fe 2 As 2
  
  • Demirdiş S
  • van Der Beek C.
  • Mühlbauer S
  • Su Y
  • Wolf Th
  Journal of Physics: Condensed Matter, IOP Publishing [1989-....], 2016, 28 (42), pp.425701. (10.1088/0953-8984/28/42/425701)
  DOI : 10.1088/0953-8984/28/42/425701
• Zero-Point Energy Leakage in Quantum Thermal Bath Molecular Dynamics Simulations
  
  • Brieuc Fabien
  • Bronstein Yael
  • Dammak Hichem
  • Depondt Philippe
  • Finocchi Fabio
  • Hayoun Marc
  Journal of Chemical Theory and Computation, American Chemical Society, 2016, 12 (12), pp.DOI: 10.1021/acs.jctc.6b00684. The quantum thermal bath (QTB) has been presented as an alternative to path-integral-based methods to introduce nuclear quantum effects in molecular dynamics simulations. The method has proved to be efficient, yielding accurate results for various systems. However, the QTB method is prone to zero-point energy leakage (ZPEL) in highly anharmonic systems. This is a well-known problem in methods based on classical trajectories where part of the energy of the high-frequency modes is transferred to the low-frequency modes leading to a wrong energy distribution. In some cases, the ZPEL can have dramatic consequences on the properties of the system. Thus, we investigate the ZPEL by testing the QTB method on selected systems with increasing complexity in order to study the conditions and the parameters that influence the leakage. We also analyze the consequences of the ZPEL on the structural and vibrational properties of the system. We find that the leakage is particularly dependent on the damping coefficient and that increasing its value can reduce and, in some cases, completely remove the ZPEL. When using sufficiently high values for the damping coefficient, the expected energy distribution among the vibrational modes is ensured. In this case, the QTB method gives very encouraging results. In particular, the structural properties are well-reproduced. The dynamical properties should be regarded with caution although valuable information can still be extracted from the vibrational spectrum, even for large values of the damping term. (10.1021/acs.jctc.6b00684)
  DOI : 10.1021/acs.jctc.6b00684
• Anomalous and planar Righi-Leduc effects in Ni 80 Fe 20 ferromagnets
  
  • Madon B.
  • Pham Do Ch
  • Wegrowe J.-E.
  • Lacour Daniel
  • Hehn M.
  • Polewczyk V.
  • Anane A.
  • Cros V.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2016, 94 (14), pp.144423 (1-8). In this paper, we report experimental evidence of anomalous and planar Righi-Leduc effects on NiFe. The Righi-Leduc effect is the thermal analog of the Hall effect, in which the electric current is replaced by the heat current and the electric field by the temperature gradient. When the material is ferromagnetic, it is well known that there are two other contributions to the Hall voltage which depend on the orientation of the magnetization. These two extra contributions are called the anomalous Hall effect when the magnetization is out of the plane of the sample and the planar Hall effect when the magnetization is in the plane of the sample. In the same way, an anomalous and a planar Righi-Leduc effects are shown to appear when a transverse temperature gradient is generated by a heat current. (10.1103/PhysRevB.94.144423)
  DOI : 10.1103/PhysRevB.94.144423
• Radiolysis effect on oxide film of 316L stainless steel formed in PWR primary water under irradiation
  
  • Wang M.
  • Perrin S.
  • Corbel C.
  • Feron D.
  , 2016. This work is focused on the corrosion behaviour of austenitic 316L stainless steel in PWR primary water under the influence of radiolysis. The present approach uses a high energy proton beam to control the production of radiolytic species at a 316L/PWR solution interface in a high temperature and high pressure electrochemical cell working in the range. Previous work showed that the corrosion potential of 316L stainless steel was enhanced by the radiolysis causing by high energy proton beam. A high similarity of electrochemical behaviour was also observed under electron beam.The electrochemical oxidative response of the 316L/PWR solution interface under radiolysis is related to the surface characterization analysis (SEM, XPS, Raman spectroscopy, NRA) on the oxide layers of 316L which are formed under or without irradiation. The radiolysis effect on the oxide film includes micron scale cavities which were observed in a highly irradiated oxide film. The observation of Fe$_2$O$_3$ hematite on the outer oxide film where cavities were formed is in accordance with the electrochemical oxidative response.
• Rigamonti et al. Reply:
  
  • Rigamonti Santiago
  • Botti Silvana
  • Véniard Valérie
  • Draxl Claudia
  • Reining Lucia
  • Sottile Francesco
  Physical Review Letters, American Physical Society, 2016, 117 (15). (10.1103/PhysRevLett.117.159702)
  DOI : 10.1103/PhysRevLett.117.159702
• Photoemission spectra from reduced density matrices: The band gap in strongly correlated systems
  
  • Di Sabatino Stefano
  • Berger Arjan
  • Reining Lucia
  • Romaniello Pina
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2016, 94, pp.155141. (10.1103/PhysRevB.94.155141)
  DOI : 10.1103/PhysRevB.94.155141
• Energy gap evolution across the superconductivity dome in single crystals of (Ba 1−x K x )Fe 2 As 2
  
  • Cho Kyuil E
  • Kończykowski Marcin E
  • Teknowijoyo Serafim E
  • Tanatar Makariy E
  • Liu Yong E
  • Lograsso Thomas E
  • Straszheim Warren E
  • Mishra Vivek E
  • Maiti Saurabh E
  • Hirschfeld Peter J
  • Prozorov Ruslan E
  Science Advances, American Association for the Advancement of Science (AAAS), 2016, 2, pp.e1600807. The mechanism of unconventional superconductivity in iron-based superconductors (IBSs) is one of the most intriguing questions in current materials research. Among non-oxide IBSs, (Ba 1−x K x)Fe 2 As 2 has been intensively studied because of its high superconducting transition temperature and fascinating evolution of the superconducting gap structure from being fully isotropic at optimal doping (x ≈ 0.4) to becoming nodal at x > 0.8. Although this marked evolution was identified in several independent experiments, there are no details of the gap evolution to date because of the lack of high-quality single crystals covering the entire K-doping range of the superconducting dome. We conducted a systematic study of the London penetration depth, l(T), across the full phase diagram for different concentrations of point-like defects introduced by 2.5-MeV electron irradiation. Fitting the low-temperature variation with the power law, Dl ∼ T n , we find that the exponent n is the highest and the T c suppression rate with disorder is the smallest at optimal doping, and they evolve with doping being away from optimal, which is consistent with increasing gap anisotropy, including an abrupt change around x ≃ 0.8, indicating the onset of nodal behavior. Our analysis using a self-consistent t-matrix approach suggests the ubiquitous and robust nature of s ± pairing in IBSs and argues against a previously suggested transition to a d-wave state near x = 1 in this system. (10.1126/sciadv.1600807)
  DOI : 10.1126/sciadv.1600807
• Radiation hardening of sol gel-derived silica fiber preforms through fictive temperature reduction
  
  • Babu B. Hari
  • Lancry Matthieu
  • Ollier Nadege
  • Hamzaoui Hicham El
  • Bouazaoui Mohamed
  • Bertrand Poumellec
  Applied optics, Optical Society of America, 2016, 55 (27), pp.7455. The impact of fictive temperature (T f ) on the evolution of point defects and optical attenuation in non-doped and Er3-doped sol-gel silica glasses was studied and compared to Suprasil F300 and Infrasil 301 glasses before and after γ-irradiation. To this aim, sol-gel optical fiber preforms have been fabricated by the densification of erbium salt-soaked nanoporous silica xerogels through the polymeric sol-gel technique. These γ-irradiated fiber preforms have been characterized by FTIR, UV-vis-NIR absorption spectroscopy, electron paramagnetic resonance, and photoluminescence measurements. We showed that a decrease in the glass fictive temperature leads to a decrease in the glass disorder and strained bonds. This mainly results in a lower defect generation rate and thus less radiation-induced attenuation in the UV–vis range. Furthermore, it was found that γ-radiation “hardness” is higher in Er3+-doped sol-gel silica compared to un-doped sol-gel silica and standard synthetic silica glasses. The present work demonstrates an effective strategy to improve the radiation resistance of optical fiber preforms and glasses through glass fictive temperature reduction (10.1364/AO.55.007455)
  DOI : 10.1364/AO.55.007455
• Functional nano-structured tungsten based coatings for systems for energy production
  
  • Li Chenyi
  • Baldinozzi Gianguido
  • Pontikis V.
  • Maroutian Thomas
  • Lecoeur Philippe
  , 2016. The stability of heterophase interfaces between metal systems, their kinetic, structural, and thermomechanical properties are a matter of concern for high demanding applications involved in the development of technological coatings for the first wall materials in fusion reactors and their prototypes (ITER). We would like to discuss preliminary results of numerical simulations and X-ray experiments on model coatings made of tungsten, in particular the problems related to strain and adhesion of thin or thick metal films on heterophase substrates. This research is supported by a research grant of Investissements d’Avenir of LabEx PALM (ANR-10-LABX-0039-PALM).
• How to measure low doping concentrations by NMR spectroscopy
  
  • Maron Sébastien
  • Ollier Nadège
  • Gacoin Thierry
  • Dantelle Géraldine
  , 2016.
• Ab initio description of second-harmonic generation from crystal surfaces
  
  • Tancogne-Dejean Nicolas
  • Giorgetti Christine
  • Véniard Valérie
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2016, 94 (12). We propose an ab initio framework to derive the dielectric and the second-order susceptibility tensors for crystal surfaces. The single-surface response is extracted from a supercell scheme. We evaluate macroscopic quantities, taking into account the local fields. The first- and second-order susceptibilities are evaluated within time-dependent density functional theory, in the long-wavelength limit. We apply our formalism to the calculation of the second-harmonic generation for clean and hydrogenated silicon surfaces. The agreement with measured second-order susceptibility components is significantly better, illustrating the importance of local-field effects. (10.1103/PhysRevB.94.125301)
  DOI : 10.1103/PhysRevB.94.125301
• Influence of Adsorption on Proteins and Amyloid Detection by Silicon Nitride Nanopore
  
  • Balme Sébastien
  • Coulon Pierre-Eugène
  • Lepoitevin Mathilde
  • Charlot Benoit
  • Yandrapalli Naresh
  • Favard Cyril
  • Muriaux Delphine
  • Bechelany Mikhael
  • Janot Jean-Marc
  Langmuir, American Chemical Society, 2016, 32 (35), pp.8916 - 8925. (10.1021/acs.langmuir.6b02048)
  DOI : 10.1021/acs.langmuir.6b02048
• Atomistic simulation of surface cyclic slip irreversibility in FCC metals
  
  • Fan Z.
  • Hardouin Duparc O.
  • Sauzay M.
  • Diawara B.
  , 2016. The mechanical behaviour of surface steps created by the emergence at the free surface of gliding dislocations, subjected to cyclic loading is examined using molecular dynamics simulations. Different face centred cubic metals, Al, Cu, Ag and Ni are analysed. An atomistic reconstruction phenomenon is observed at these surface steps which can induce strong irreversibility. The irreversibility cumulates and a micronotch is produced whose depth increases cyclically. A rough estimation of surface irreversibility for pure edge dislocations gives an irreversibility fraction between 0.5 and 0.75 in copper. An analysis coupling surface mechanisms with the classical EGM bulk slip irreversibility model gives an irreversibility fraction of 0.62 in copper for pure screw dislocations, contrary to many sketches proposed in the past. It seems that oxygen molecules cannot lead to higher irreversibility as they have no major influence on different mechanisms linked to surface relief evolution.
• Enhanced photoemission from laser-excited plasmonic nano-objects in periodic arrays
  
  • Fedorov N
  • Geoffroy G.
  • Duchateau G.
  • Štolcová L
  • Proška J
  • Novotný F
  • Domonkos M
  • Jouin H.
  • Martin P.
  • Raynaud Michèle
  Journal of Physics: Condensed Matter, IOP Publishing [1989-....], 2016, 28 (31), pp.315301. The process of photoelectron emission from gold surfaces covered with nano-objects that are organized in the form of a periodic array is addressed in the short laser pulse regime ($\leqslant 50$ fs) at moderate intensities $\sim {{10}^{10}}$ W cm−2 and for various laser wavelengths. The emission spectrum from a gold single crystal measured under the same conditions is used for reference. The comparison of the photo-emission yield and the energy of the ejected electrons with their counterparts from the (more simple) reference system shows that the periodic conditions imposed on the target surface drastically enhance both quantities. In addition to the standard mechanism of Coulomb explosion, a second mechanism comes into play, driven by surface plasmon excitation. This can be clearly demonstrated by varying the laser wavelength. This interpretation of the experimental data is supported by predictions from model calculations that account both for the primary quantum electron emission and for the subsequent surface-plasmon-driven acceleration in the vacuum. Despite the fact that the incident laser intensity is as low as $\sim 5\times {{10}^{10}}$ W cm−2, such a structured target permits generating electrons with energies as high as 300 eV. Experiments with two incident laser beams of different wavelengths with an adjustable delay, have also been carried out. The results show that there exist various channels for the decay of the photo-emission signal, depending on the target type. These observations are shedding light on the various relaxation mechanisms that take place on different timescales. (10.1088/0953-8984/28/31/315301)
  DOI : 10.1088/0953-8984/28/31/315301
• Study of radiation effects on Er$^{3+}$-doped nanoparticles germano-silica fibers
  
  • Babu B. Hari
  • Ollier Nadege
  • Savelli Inna
  • Hamzaoui Hicham El
  • Pastouret A.
  • Poumellec Bertrand
  • Bouazaoui Mohamed
  • Bigot Laurent
  • Lancry Matthieu
  Journal of Lightwave Technology, Institute of Electrical and Electronics Engineers (IEEE)/Optical Society of America(OSA), 2016, 34 (21), pp.4981. The main goal of the present work is to study the impact of Er–SiO$_2$ and Er–Al$_2$O$_3$ nanoparticles on the radiation induced defects in germano-silica optical fibers with Al/Ge ranges over 0.1–150. These fibers are prepared by a modified chemical vapor deposition technique and are characterized by optical absorption and electron paramagnetic resonance spectroscopy. High amount of Ge, Er–SiO$_2$ nanoparticles-derived optical fibers exhibit lower radiation induced attenuation than those with a low Ge content undoped or doped with Al$_2$O$_3$ nanoparticles. Furthermore, the behavior of point defects namely GeE’, Ge(1), SiE’, nonbridging oxygen hole centers, and H(1) is reported according to the Al/Ge ratio. In contrast to the optical fiber preforms, no Al-related defects are found in the optical fibers. Therefore, the results evidence the strong radiation tolerance by the virtue of the nanoparticle doping, which is enabling technology for the development of the photonic and space applications in the radiation fields. (10.1109/JLT.2016.2599173)
  DOI : 10.1109/JLT.2016.2599173