Publications

2019

• Interplay between superconductivity and itinerant magnetism in underdoped Ba$_{1−x}$K$_x$Fe$_2$As$_2$ (x = 0.2) probed by the response to controlled point-like disorder
  
  • Prozorov Ruslan
  • Kończykowski Marcin
  • Tanatar Makariy A
  • Wen Hai-Hu
  • Fernandes Rafael M
  • Canfield Paul C
  Npj Quantum Materials, Nature publishing, 2019, 4 (1), pp.34. The response of superconductors to controlled introduction of point-like disorder is an important tool to probe their microscopic electronic collective behavior. In the case of iron-based superconductors, magnetic fluctuations presumably play an important role in inducing high-temperature superconductivity. In some cases, these two seemingly incompatible orders coexist microscopically. Therefore, understanding how this unique coexistence state is affected by disorder can provide important information about the microscopic mechanisms involved. In one of the most studied pnictide family, hole-doped Ba$_{1−x}$K$_x$Fe$_2$As$_2$ (BaK122), this coexistence occurs over a wide range of doping levels, 0.16 ≲ x ≲ 0.25. We used relativistic 2.5 MeV electrons to induce vacancy-interstitial (Frenkel) pairs that act as efficient point-like scattering centers. Upon increasing dose of irradiation, the superconducting transition temperature $T_c$ decreases dramatically. In the absence of nodes in the order parameter this provides a strong support for a signchanging s± pairing. Simultaneously, in the normal state, there is a strong violation of the Matthiessen's rule and a decrease (surprisingly, at the same rate as $T_c$) of the magnetic transition temperature T sm , which indicates the itinerant nature of the longrange magnetic order. Comparison of the hole-doped BaK122 with electron-doped Ba(Fe$_x$Co$-{1-x}$)$_2$As$_2$ (FeCo122) with similar $T_{sm}$$\sim$ 110 K, x = 0.02, reveals significant differences in the normal states, with no apparent Matthiessen's rule violation above $T_{sm}$ on the electron-doped side. We interpret these results in terms of the distinct impact of impurity scattering on the competing itinerant antiferromagnetic and s ± superconducting orders. (10.1038/s41535-019-0171-2)
  DOI : 10.1038/s41535-019-0171-2
• Reply to: Ultrafast evolution and transient phases of a prototype out-of-equilibrium Mott-Hubbard material
  
  • Boschetto D.
  • Weis M.
  • Zhang J.
  • Caillaux Jonathan
  • Nilforoushan N.
  • Lantz G.
  • Mansart B.
  • Papalazarou E.
  • Moisan N.
  • Grieger D.
  • Perfetti L.
  • Jacques V.
  • Bolloc’h D. Le
  • Laulhe C.
  • Ravy S.
  • Rueff J.-P.
  • Glover T.
  • Hertlein M.
  • Hussain Z.
  • Song S.
  • Chollet M.
  • Fabrizio M.
  • Marsi M.
  • Zaghrioui Mustapha
  Nature Communications, Nature Publishing Group, 2019, 10 (1). Replying to D. Moreno-Mencía et al. Nature Communications https://doi.org/10.1038/s41467-019-11743-3 (2019). (10.1038/s41467-019-11744-2)
  DOI : 10.1038/s41467-019-11744-2
• Artificial Solid Electrolyte Interphase Formation on Si Nanoparticles through Radiolysis: Importance of the Presence of an Additive
  
  • Bongu Chandra S.
  • Surble Suzy
  • Alper John
  • Boulineau Adrien
  • Martin Jean-Frederic
  • Demarque Alexandre
  • Coulon Pierre-Eugène
  • Rosso Michel
  • Ozanam Francois
  • Franger Sylvain
  • Herlin-Boime Nathalie
  • Le Caër Sophie
  Journal of Physical Chemistry C, American Chemical Society, 2019, 123 (47), pp.28550-28560. In the context of energy transition, irradiation is a powerful tool to mimic quickly the modification of electrode materials upon charge/discharge cycles in lithium-ion batteries. In this study, the evolution of the surface of silicon nanoparticles upon irradiation in two electrolytes, containing or not fluoroethylene carbonate (FEC), was studied. In the presence of FEC, irradiation leads to the formation of a homogeneous layer of a few nanometers thick, covering the whole surface of the nanoparticles. The formation of an artificial solid electrolyte interphase (SEI) layer through radiolysis is thus achieved. Without FEC, only patches of degradation products are formed on the nanoparticle surfaces for the same irradiation dose. In the absence of FEC, Li$_x$PF$_y$O$_z$ salts are formed. In the presence of FEC, Li$_x$PO$_y$, LiF, and Si–F bonds are generated. In both cases, the interphase contains Li$_2$CO$_3$ and a polymer containing ethylene carbonate units. Slightly different polymers are formed at the surface of nanoparticles in the presence or absence of FEC, i.e., more cross-linked in the former case. The elastomeric properties of the polymer formed in the presence of FEC are thought to be responsible for the formation of the homogeneous layer on the Si surfaces, leading to the generation of an artificial solid SEI through the radiolysis process. This SEI, however, prevents the efficient transfer of Li$^+$ ions, and more work is required to optimize its intrinsic (electro)chemical properties. (10.1021/acs.jpcc.9b07179)
  DOI : 10.1021/acs.jpcc.9b07179
• Highly Transparent Fluorotellurite Glass-Ceramics: Structural Investigations and Luminescence Properties
  
  • Laval Jean-Paul
  • Duclère Jean-René
  • Couderc Vincent
  • Allix Mathieu
  • Genevois Cécile
  • Sarou-Kanian Vincent
  • Fayon Franck
  • Coulon Pierre-Eugène
  • Chenu Sébastien
  • Dutreilh-Colas Maggy
  • Cornette Julie
  • Thomas Philippe
  • Delaizir Gaëlle
  Inorganic Chemistry, American Chemical Society, 2019, 58 (24), pp.16387-16401. Crystallization from glass can lead to the stabilization of metastable crystalline phases, which offers an interesting way to unveil novel compounds and control the optical properties of resulting glass-ceramics. Here, we report on a crystallization study of the ZrF4-TeO2 glass system and show that under specific synthesis conditions, a previously unreported Te0.47Zr0.53OxFy zirconium oxyfluorotellurite antiglass phase can be selectively crystallized at the nanometric scale within the 65TeO2-35ZrF4 amorphous matrix. This leads to highly transparent glass-ceramics in both the visible and near-infrared ranges. Under longer heat treatment, the stable cubic ZrTe3O8 phase crystallizes in addition to the previous unreported antiglass phase. The structure, microstructure, and optical properties of 65TeO2-35ZrF4Tm3+-doped glass-ceramics, were investigated in detail by means of X-ray diffraction, scanning and transmission electron microscopies, and 19F, 91Zr, and 125Te NMR, Raman, and photoluminescence spectroscopies. The crystal chemistry study of several single crystals samples by X-ray diffraction evidence that the novel phase, derived from α-UO3 type, corresponds in terms of long-range ordering inside this basic hexagonal/trigonal disordered phase (antiglass) to a complex series of modulated microphases rather than a stoichiometric compound with various superstructures analogous to those observed in the UO3–U3O8 subsystem. These results highlight the peculiar disorder–order phenomenon occurring in tellurite materials. (10.1021/acs.inorgchem.9b01955)
  DOI : 10.1021/acs.inorgchem.9b01955
• Unveiling the vortex glass phase in the surface and volume of a type-II superconductor
  
  • Aragón Sánchez Jazmín
  • Cortés Maldonado Raúl
  • Cejas Bolecek Néstor R
  • Rumi Gonzalo
  • Pedrazzini Pablo
  • Dolz Moira I
  • Nieva Gladys
  • Beek Cornelis J van Der
  • Konczykowski Marcin
  • Dewhurst Charles D
  • Cubitt Robert
  • Kolton Alejandro B
  • Pautrat Alain
  • Fasano Yanina
  Communications Physics, Nature Research, 2019, 2 (1), pp.143. Order-disorder transitions between glassy phases are common in nature and yet a comprehensive survey on the entailed structural changes is challenging since the constituents are in the micro-scale. Vortex matter in type-II superconductors is a model system where some of these experimental challenges can be tackled. Samples with point disorder present a glassy transition on increasing the density of vortices. A glassy yet quasi-crystalline phase, the Bragg glass, nucleates at low densities. The vortex glass stable at high densities is expected to be disordered, however its detailed structural properties remained experimentally elusive. Here we show that the vortex glass has large crystallites with in-plane positional displacements growing algebraically and short-range orientational order. Furthermore, the vortex glass has a finite and almost constant correlation length along the direction of vortices, in sharp contrast with strong entanglement. These results are important for the understanding of disorderdriven phase transitions in glassy condensed matter. (10.1038/s42005-019-0243-4)
  DOI : 10.1038/s42005-019-0243-4
• Single-step synthesis of vertically aligned carbon nanotube forest on aluminium foils
  
  • Nassoy Fabien
  • Pinault Mathieu
  • Descarpentries Jeremie
  • Vignal Thomas
  • Banet Philippe
  • Coulon Pierre-Eugène
  • Goislard de Monsabert Thomas
  • Hauf Harald
  • Aubert Pierre-Henri
  • Reynaud Cécile
  • Mayne-L'Hermite Martine
  Nanomaterials, MDPI, 2019, 9 (11), pp.1590. Vertically aligned carbon nanotube (VACNT) forests are promising for supercapacitor electrodes, but their industrialisation requires a large-scale cost-effective synthesis process suitable to commercial aluminium (Al) foils, namely by operating at a low temperature (<660°C). We show that Aerosol-Assisted Catalytic Chemical Vapour Deposition (CCVD), a single-step roll-to-roll compatible process, can be optimised to meet this industrial requirement. With ferrocene as a catalyst precursor, acetylene as a carbon source and Ar/H$_2$ as a carrier gas, clean and dense forests of VACNTs of about 10 nm in diameter are obtained at 615°C with a growth rate up to 5 $\mu$m/min. Such novel potentiality of this one-step CCVD process is at the state-of-the-art of the multi-step assisted CCVD processes. To produce thick samples, long synthesis durations are required, but growth saturation occurs that is not associated with a diffusion phenomenon of iron in aluminium substrate. Sequential syntheses show that the saturation trend fits a model of catalytic nanoparticle deactivation that can be limited by decreasing acetylene flow, thus obtaining sample thickness up to 200 $\mu$m. Cyclic voltammetry measurements on binder-free VACNT/Al electrodes show that the CNT surface is fully accessible to the ionic liquid electrolyte, even in these dense VACNT forests. (10.3390/nano9111590)
  DOI : 10.3390/nano9111590
• Direct Observation of Band Gap Renormalization in Layered Indium Selenide
  
  • Zhang Zailan
  • Chen Zhesheng
  • Bouaziz Meryem
  • Giorgetti Christine
  • Yi Hemian
  • Avila Jose
  • Tian Bingbing
  • Shukla Abhay
  • Perfetti Luca
  • Fan Dianyuan
  • Li Ying
  • Bendounan Azzedine
  ACS Nano, American Chemical Society, 2019, 13 (11), pp.13486-13491. (10.1021/acsnano.9b07144)
  DOI : 10.1021/acsnano.9b07144
• Radiative Recombination in Quadruple Cation Organic-Inorganic Mixed Halide Perovskite Layers: Electron Irradiation Induced Ageing Effects
  
  • Aversa Pierfrancesco
  • Öz Senol
  • Jung Eunhwan
  • Plantevin Olivier
  • Cavani Olivier
  • Ollier Nadège
  • Geffroy Bernard
  • Mathur Sanjay
  • Corbel Catherine
  , 2019.
• NaYF4 Microstructure, beyond Their Well-Shaped Morphology
  
  • Leménager Godefroy
  • Tusseau-Nenez Sandrine
  • Thiriet Maud
  • Coulon Pierre-Eugène
  • Lahlil Khalid
  • Larquet Eric
  • Gacoin Thierry
  Nanomaterials, MDPI, 2019, 9 (11), pp.1560. Lanthanide doped nanoparticles are widely investigated for their optical properties. However, the sensitivity of the lanthanide ions to the local symmetry, useful when investigating structural environments, becomes a drawback for optimized properties in the case of poorly controlled crystallinity. In this paper, we focus on β-NaYF4 nanorods in order to provide a detailed description of their chemical composition and microstructure. The combination of detailed XRD analysis and TEM observations show that strong variation may be observed from particles from a same batch of synthesis, but also when considering small variations of synthesis conditions. Moreover, also the nanorods observed by SEM exhibit a very nice faceted shape, they are far from being monocrystalline and present significant local deviation of crystalline symmetry and orientation. All these structural considerations, sensitively probed by polarized emission analysis, are crucial to be analyzed for the development of optimal systems toward the targeted applications. (10.3390/nano9111560)
  DOI : 10.3390/nano9111560
• Revealing the Nanoparticle-Protein Corona with a Solid-State Nanopore
  
  • Coglitore Diego
  • Coulon Pierre Eugene
  • Janot Jean-Marc
  • Balme Sébastien
  Materials, MDPI, 2019, 12 (21), pp.3524. Protein adsorption at the liquid–solid interface is an old but not totally solved topic. One challenge is to find an easy way to characterize the protein behavior on nanoparticles and make a correlation with its intrinsic properties. This work aims to investigate protein adsorption on gold nanoparticles and the colloidal properties. The protein panel was chosen from different structural categories (mainly-α, mainly-β or mix-αβ). The result shows that the colloidal stability with salt addition does not depend on the structural category. Conversely, using the single nanopore technique, we show that the mainly-α proteins form a smaller corona than the mainly-β proteins. We assign these observations to the lower internal energy of α-helices, making them more prone to form a homogeneous corona layer. (10.3390/ma12213524)
  DOI : 10.3390/ma12213524
• Multi magnetic states in Co/Cu multilayered cylindrical nanowires studied by combination of off-axis electron holography imaging and micromagnetic simulations
  
  • Biziere Nicolas
  • Reyes Vasquez David Fernando
  • Wade T. L
  • Warot-Fonrose Bénédicte
  • Gatel Christophe
  Journal of Applied Physics, American Institute of Physics, 2019, 126 (16), pp.163906. We report on a wide variety of magnetic states in Co/Cu multilayered nanocylinders grown by electrodeposition with different thicknesses of both elements. The remnant magnetic states in individual Co layers have quantitatively been determined at the nanoscale by micromagnetic reconstruction of the magnetic phase shift image obtained by electron holography. We demonstrate that the magnetization in the Co layers can present either uniform or vortex states. Also, different magnetic configurations can be observed within the same nanocylinder. In the case of vortices, the direction of the core can rotate almost at 90° from the nanocylinder axis for layers with aspect ratio close to 1. We show that the occurrence of each magnetic configuration depends on the aspect ratio of the layers, the direction of magnetocrystalline anisotropy and in some cases on the interlayer dipolar coupling. Such a wide variety of magnetic states are observed due to lower values of the Co magnetic constants (magnetization, exchange, anisotropy) with respect to bulk, typical of electrodeposition process in a single bath, and to the local geometrical variation of the layers. We also calculated the phase diagram of the remnant magnetic states in a single layer for various amplitudes and orientations of the magnetocrystalline anisotropy and different directions of the saturation field. In particular cases, these phase diagrams in addition to statistics of occurrence of each kind of magnetic configurations in the multilayer and the application of a saturation field in different directions allows recovering information on the preferential orientation of the crystalline anisotropy. (10.1063/1.5124620)
  DOI : 10.1063/1.5124620
• Vibrational and structural properties of P$_2$O$_5$ glass: Advances from a combined modeling approach
  
  • Shcheblanov N. S.
  • Giacomazzi L.
  • Povarnitsyn M. E.
  • Kohara S.
  • Martin-Samos L.
  • Mountjoy G.
  • Newport R. J.
  • Haworth R. C.
  • Richard N.
  • Ollier And N.
  Physical Review B, American Physical Society, 2019, 100, pp.134309. We present experimental measurements and ab initio simulations of the crystalline and amorphous phases of P2O5. The calculated Raman, infrared, and vibrational density of states (VDOS) spectra are in excellent agreement with experimental measurements and contain the signatures of all the peculiar local structures of the amorphous phase, namely, bridging and nonbridging (double-bonded or terminal) oxygens and tetrahedral PO4 units associated with Q2, Q3, and Q4 species (Qn denotes the various types of PO4 tetrahedra, with n being the number of bridging oxygen atoms that connect the tetrahedra to the rest of the network). In order to reveal the internal structure of the vibrational spectrum, the characteristics of vibrational modes in different frequency ranges are investigated using a mode-projection approach at different symmetries based on the Td symmetry group. In particular, the VDOS spectrum in the range from ∼600 to 870 cm−1 is dominated by bending (F2b) motions related to bridging oxygen and phosphorus (∼800 cm−1 band) atoms, while the high-frequency doublet zone (∼870–1250 cm−1) is associated mostly with the asymmetric (F2s) and symmetric (A1) stretching modes, and most prominent peak around 1400 cm−1 (exp. 1380 cm−1) is mainly due to asymmetric stretching vibrations supported by double-bonded oxygen atoms. The lower-frequency range below 600 cm−1 is shown to arise from a mixture of bending (E and F2b) and rotation (F1) modes. The scissors bending (E) and rotation (F1) modes are well localized below 600 cm−1, whereas the F2b bending modes spread further into the range ∼600–870 cm−1. The projections of the eigenmodes onto Q2, Q3, and Q4 species yield well-defined contributions at frequencies in striking correspondence with the positions of the Raman and infrared bands. (10.1103/physrevb.100.134309)
  DOI : 10.1103/physrevb.100.134309
• Theoretical study of the many-body electronic states of defects in diamond : the case of the NV center under high pressure
  
  • Romanova Mariya
  , 2019. The aim of this thesis is to study the influence of the pressure on the optical transitions between multi-determinant ground state and excited states of the NV center from the first-principles.In this work, I study both the neutral NV0 and negatively charged NV- centers.Long-range interactions have a crucial effect in such defects: first, elastic deformations have a long range and need to be accounted for; second, when the defect has a charge, it is important to avoid spurious charge-charge interactions between neighboring supercells caused by the use of periodic boundary conditions. Thus, I study the atomic structure of defect with large supercells by the density functional theory (DFT).The NV center is a deep-center defect, its optical and magnetic properties are related with localized levels in the electronic band-gap. These levels are believed to be built out of the localized orbitals of dangling bonds pointing towards the vacancy, providing strongly correlated electronic states. Thus, an accurate quantum mechanical treatment is needed.DFT is a powerful approach for the calculation of the ground state properties of defects. However, the single Slater determinant nature of the DFT wave function lacks the non-dynamical correlations, that characterize such defects, and does not allow for the calculation of many-body levels. Moreover, exchange and correlation (XC) functionals used in DFT add have a limited accuracy.Therefore, in this PhD work, I first develop a combined DFT + Hubbard model technique. I study the triplet-triplet transition both with the PBE XC functional and the HSE06 one. I confirm that the use of the hybrid XC functional HSE06 improves the description of correlations beyond DFT-PBE and allows for more accurate prediction of optical transitions.An exact diagonalization (or in quantum chemistry language full Configuration Interaction calculations) of the Hubbard Hamiltonian in the many-electron basis constructed of in-gap localized levels, allows to get access to multi-determinant ground and excited states. I benchmark this technique comparing it to the recent state of the art methods.Finally, I apply the developed technique in order to study the effect of the hydrostatic pressure on NV- and NV0 centers. Among many results of my work, I discovered a very interesting effect related to the singlet-singlet transition in the NV-center under hydrostatic pressure. The results I have obtained during my PhD have never been calculated nor observed experimentally. In order to validate the theoretical model, I have compared our results with the measurements that have been obtained by our experimental collaborators for the optical transition in the NV- and NV0. Last but not least, the effect of the electron-phonon interaction was discussed.As a perspective, I developed a new code that can be applied to study other defect systems of interest in the quantum technologies.
• Advanced k.p multiband methods for semiconductor-based spinorbitronics
  
  • To Duy-Quang
  , 2019. This thesis work is essentially devoted to the development of the tunneling theory k.p 14, 30 and 40 bands for a spinorbitronic application with semiconductor. Spinorbitronic combines the effects of spin and orbit, which via spin-orbit coupling, introduces new transport properties such as spin Hall and anomalous Hall effects. The latter is characterized by a deflection of the trajectory of polarized carriers in the transverse direction of their flow. Other characteristic effects concern i) the spin transfer mechanisms for switching angular momentum transfer magnetization, thus generalizing spin transfer as well as ii) spin-charge conversion mediated by the terms Rashba or Dresselhaus. In this context, our tunnel transport theory is adaptable to semiconductor heterostructures, magnetic or not, dealing with a simple interface or tunnel junctions. It allows to take into account in a fine way the spin-orbit interactions of heart and interface. It generally uses the introduction of additional high bands, called ghosts, to deal with the spurious states inherent in the multiband k.p theory. Apart from the introduction of the "spurious" states neither deforming the electronic structure nor the polarized transport, our approach uses the continuity of the components of the wave functions at each interface and the connection of the components of wave current according to symmetry interfaces either by 1) the continuity of the components of wave current (extension of Ben Daniel Duke theory), 2) the connection conditions obeying a C2v symmetry by mixing heavy holes cd / light in the valence band (conditions from Ivchenko) or 3) discontinuity of the 'high' bands. We also demonstrate the equivalence of the continuity conditions for the case of AlAs / GaAs / AlAs III-V quantum wells, which represents a generalization of previous results developed in 14 bands.The whole of this work of analytical and numerical thesis, include several important demonstrations. We show that our theory can be used to describe the spin transport of spin-orbit coupled states in growth axis (100) or (110) semiconductor heterostructures. These results are notably materialized by the calculations of the three components of the spin current in the III-V barriers (GaAs, AlAs) acting as spin phase-shifters. Calculations show that we develop in effect, as provided by the analytic theory, a vector rotation of the spin density matrix in the thickness of the barrier and as provided by the application of an effective spin-orbit field Dresselhaus parallel to the plane of the barrier.Our theory is also successfully compared to the multiband perturbation calculations using Green's transport functions to address the mechanisms of abnormal Hall tunnel effect in the conduction band and the valence band. The results are remarkable of fidelity which shows the power of the technique used. We also calculate spin current properties in GaMnAs-based ferromagnetic tunnel junctions to derive the spin transfer torque responsible for switching the fine ferromagnetic element. We show, for example, how the transverse spin components of the current are relevant to switch a magnetization. Finally, we adapted our transport theory to III-V structures to compute confined quantum well states in the conduction band and valence band. We successfully compare our state-of-the-art 6-band and 14-band multiband results on the optical anisotropy of absorption between the directions (110 and (1-10) of the electric field when the symmetry of the heterostructure is reduced to C2v symmetry.
• Functionalized track-etched PVDF membrane-electrodes for toxic metal determination in water
  
  • Pinaeva Uliana
  , 2019. Present work reports on radiation grafting of poly(acrylic acid) (PAA), poly(4-vinyl pyridine) (P4VP) and bis[2-(methacryloyloxy)ethyl] phosphate (B2MP) functional polymers inside nanoporous structure of track-etched poly(vinylidene fluoride) (PVDF) membranes for selective pre-concentration of Pb(II), Hg(II) and U(VI) from aqueous solutions. Track-etched PVDF membranes were made by means of swift heavy ion (SHI) irradiation followed by ion track revealing. The resulting nanoporous PVDF membranes were then functionalized through remained radicals at the nanopore walls. EPR spectroscopy was used to examine the amount and reactivity of the trapped radicals, notably towards a novel functionality inside the etched tracks, namely B2MP. It was found that these radicals, alkyl and peroxy ones, were sufficient to initiate free-radical polymerization in presence of the three studied vinyl monomers. FESEM, FTIR and a less conventional zeta-potential measurements were utilized for examination of functional group presence. In case of P4VP grafting, the measured nanopore surface charge versus pH demonstrated uniform and relatively dense grafting all along the nanopore channels. As the objective of this work is to develop innovative electrochemical sensors for toxic metal determination in water, adsorption experiments were performed confirming that efficient uptakes of the grafted track-etched PVDF membranes are due to the presence of functional groups that facilitate coordination reactions from pure inherent to PAA electrostatic interaction to chelating complexation with P4VP and B2MP complexation in between. The moderate interaction effect in case of U(VI) adsorption by B2MP is due to the co-existence of ion-exchange and chelating groups in B2MP. For electrochemical sensoring, membranes functionalized with abovementioned chelate polymers were converted into electrodes. The pre-concentration of toxic metal adsorbed inside the nanoporosity permit to below stripping voltammetry sensitivity limits to sub-ppb (μg/L) level. Time-resolved photoluminescence (TRPL) measurements accompanied with XPS were performed on uranyl adsorbed B2MP-g-PVDF membranes in order to understand deeper the U(VI)-B2MP coordination mechanism.
• Excitons on a microscopic level: The mixed dynamic structure factor
  
  • Reshetnyak Igor
  • Gatti Matteo
  • Sottile Francesco
  • Reining Lucia
  Physical Review Research, American Physical Society, 2019, 1 (3). The dynamic structure factor of materials is proportional to their linear electronic response and it displays their excitation spectra. Usually the response is measured on the same length scale as the perturbation. Here we illustrate that much can be gained by studying also the mixed dynamic structure factor, which connects different spatial components of perturbation and response. We extend state-of-the-art ab initio calculations to access the mixed dynamic structure factor, including excitonic effects. Using bulk silicon and lithium fluoride as prototype examples, we show that these effects play a crucial role above and below the quasi-particle gap, and are needed in order to explain coherent inelastic x-ray scattering experiments. Our approach also yields important information concerning the microscopic structure of time-dependent density functional theory. One of the key concepts in condensed matter theory is screening, the modification of a potential felt by a charge due to the rearrangement of other charges [1]. In many cases the dominant contribution to this phenomenon can be described in linear response [2]. This means that the knowledge of the response of a system to an external perturbation is entirely contained in the density-density response function χ,which is determined only by the material.The poles of χ in frequency space are the excitation energies of the system. The density-density response function is measured directly or indirectly in many spectroscopy experiments [3], such as electron energy loss spectroscopy (EELS) [4], optical absorption [5, 6], or inelastic x-ray scattering (IXS) [7], which yields the dynamic structure factor (DSF) that is proportional to the imaginary part of χ. Knowing χ can also help to understand or predict effects such as a significant local rearrangement of charges as response of the system to a perturbation, which can have dramatic effects on the structure, for example self-trapped excitons [8]. Finally, screening is also one of the fundamental processes that govern the behavior of all many-body systems. Therefore it appears naturally as a building block in the formulation of many-body perturbation theory [9], via the screened Coulomb interaction W = v c + v c χv c , where v c is the bare Coulomb interaction. The widely-used GW approximation (GWA) [10], for example, uses W as effective interaction. Some important features of the frequency-dependent screening are captured for the homogeneous electron gas by the Lindhard dielectric function [11] from the random phase approximation (RPA) [12], where only the classical electrostatic potential between charges is taken into account. For small momentum transfer this is sufficient to describe the long-range collective oscillations of the electron gas, called plasmons, even for simple metals and semiconductors (see, e.g., [13-17]). However, in many other cases this approximation yields unsatisfactory results. Prominent examples are materials with localized d-or f-states [18-21], or loss spectra for larger momentum transfer [22-25], where a shorter length scale is probed. Moreover, the RPA cannot yield bound ex-citons [26], which are most clearly seen in optical spectra [27, 28]. Such many-body effects are instead captured by the Bethe-Salpeter equation (BSE) [29], a two-body Dyson equation that correlates the excited electrons and holes [26, 30]. This equation has been successfully used to calculate optical spectra in the framework of semi-empirical calculations since the eighties [31-34], and in first principles calculations since the nineties [35-38]. Loss spectra for vanishing momentum transfer have been looked at more recently [39-41], and a few calculations exist for loss spectra at non-vanishing momentum transfer [42-50]. Optics, EELS and IXS probe the response of the system on the same length scale as the perturbation. Besides the spectroscopic information, this allows one also to reconstruct charge excitations as an averaged function of space and time from experimental IXS spectra [51-55]. However, in an inhomogeneous material even a spatially monochromatic perturbation creates a response on different length scales [56, 57], depending on the local structure of the material. Only when all these components of the response are known can one describe induced charges with spatial resolution, and can one determine important many-body effects that depend on all the components of W. For these reasons, it is highly desirable to extend state-of-the-art advanced theoretical and numerical approaches to the description of the full inhomogeneous response of materials including excitonic effects. This gives access to the mixed DSF (MDSF), which is a matrix in reciprocal space whose diagonal is the ordinary DSF [7]. The MDSF can be measured by coherent IXS (CIXS) [7]. On the theory side, some off-diagonal elements of the MDSF in silicon were calculated in the adiabatic local density approximation (ALDA) of time-dependent den (10.1103/PhysRevResearch.1.032010)
  DOI : 10.1103/PhysRevResearch.1.032010
• Hyperuniform vortex patterns at the surface of type-II superconductors
  
  • Rumi Gonzalo
  • Aragón Sánchez Jazmín
  • Elías Federico
  • Cortés Maldonado Raúl
  • Puig Joaquín
  • Cejas Bolecek Néstor René
  • Nieva Gladys
  • Konczykowski Marcin
  • Fasano Yanina
  • Kolton Alejandro B
  Physical Review Research, American Physical Society, 2019, 1 (3), pp.033057. A many-particle system must possess long-range interactions in order to be hyperuniform at thermal equilibrium. Hydrodynamic arguments and numerical simulations show, nevertheless, that a three-dimensional elastic-line array with short-ranged repulsive interactions, such as vortex matter in a type-II superconductor, forms at equilibrium a class-II hyperuniform two-dimensional point pattern for any constant-z cross section. In this case, density fluctuations vanish isotropically as ∼q$^α$ at small wave vectors q, with α = 1. This prediction includes the solid and liquid vortex phases in the ideal clean case and the liquid in presence of weak uncorrelated disorder. We also show that the three-dimensional Bragg glass phase is marginally hyperuniform, while the Bose glass and the liquid phase with correlated disorder are expected to be nonhyperuniform at equilibrium. Furthermore, we compare these predictions with experimental results on the large-wavelength vortex density fluctuations of magnetically decorated vortex structures nucleated in pristine, electron-irradiated, and heavy-ionirradiated superconducting Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ samples in the mixed state. For most cases, we find hyperuniform two-dimensional point patterns at the superconductor surface with an effective exponent α$_{eff}$ ≈ 1. We interpret these results in terms of a large-scale memory of the high-temperature line-liquid phase retained in the glassy dynamics when field cooling the vortex structures into the solid phase. We also discuss the crossovers expected from the dispersivity of the elastic constants at intermediate length-scales, and the lack of hyperuniformity in the x-y plane for lengths $q^{−1}$ larger than the sample thickness due to finite-size effects in the z direction. We argue these predictions may be observable and propose further imaging experiments to test them independently. (10.1103/PhysRevResearch.1.033057)
  DOI : 10.1103/PhysRevResearch.1.033057
• III-V on Si solar cells behavior at NIRT and LILT conditions for space applications
  
  • Medjoubi Karim
  • Cariou Romain
  • Lefevre Jeremie
  • Vauche Laura
  • Veinberg-Vidal Elias
  • Jany Christophe
  • Roasting Cedric
  • Amalbert Vincent
  • Boizot Bruno
  , 2019, pp.1-7. In this study, we review the potential of III-V/Si solar cell technology for space applications. We present here the experimental results of wafer bonded 2-terminal III-V/Si solar cells electron irradiation. The Begin-Of-Life (BOL) and End-Of-Life (EOL) electrical performances, after 1-MeV electron irradiations, are characterized under AM0 spectrum, and the radiation hardness is compared in Normal Irradiance Room Temperature (NIRT) and Low Irradiance Low Temperature (LILT) conditions. (10.1109/ESPC.2019.8932069)
  DOI : 10.1109/ESPC.2019.8932069
• Tuning Eu2+ amount and site symmetry in phosphate glasses under irradiation by electron energy and integrated dose
  
  • Mahfoudhi Mohamed
  • Ollier Nadège
  Optical Materials, Elsevier, 2019, 95, pp.109253. This paper relates the formation of Eu2+ under 700 keV and 2.5 MeV irradiation in meta and polyphosphate glasses. EPR and photoluminescence measurements evidenced the presence of two sites for Eu2+ ions corresponding to low-symmetry and high-symmetry sites. We highlighted that the glass composition and in particular the presence of ZnO favors the formation of high-symmetry sites. Moreover, we found out that 700 keV electron energy is much more efficient to produce Eu2+ ions compared to 2.5 MeV. This is probably linked to an enhancement of the alkaline migration generated under the charge depletion induced by the 700 keV electrons implentation. This migration depolymerizes the network structure and tends to favor the formation of Eu2+. The same tendency is observed at 2.5 MeV when the dose is higher than 1 GGy. (10.1016/j.optmat.2019.109253)
  DOI : 10.1016/j.optmat.2019.109253
• Eu3+ ion environment modification by Electron and femtosecond laser irradiation in metaphosphate and polyphosphate glasses
  
  • Mahfoudhi Mohamed
  , 2019. Rare Earth (RE) doped phosphate glasses are attractive materials in optic due to their low glass transition temperature and their high ability to dissolve rare earth ions compared to silicate glasses. In this work, we are interested in understanding the mechanisms leading to the structural modification of zinc polyphosphate and metaphosphate glasses under irradiation with the aim of controlling the environment of rare earth ions (in particular Eu3+ ions) by irradiation. We compared the effects obtained under electron and femtosecond laser irradiation by varying the dose and electron energy (700 keV and 2.5 MeV), the laser repetition rate as well as the glass compositions that contain different alkaline and alkaline earth ions (Na, Li, K and Mg) and Zn contents.We have demonstrated the decrease of the Eu3+ site symmetry, the increase of the sites dispersion as well as an effective reduction of Eu3+ to Eu2+ under electron irradiation.The presence of Zn attenuates the variation of the local order around the rare earth, while the vitreous network is less stable under irradiation. The formation of Eu2+ ions (under two types of high and low symmetry environments) is further enhanced in the presence of Zn and using 700 keV electrons. The femtosecond laser at 10 KHz gives causes crystallization of metaphosphate glasses without reduction of Eu3+ ions.
• Surface currents in Hall devices
  
  • Creff M
  • Faisant F
  • Rubì J M
  • Wegrowe Jean-Eric
  , 2019. A variational approach is used in order to study the stationary states of Hall devices. Charge accumulation, electric potentials and electric currents are investigated on the basis of the Kirchhoff-Helmholtz principle of least heat dissipation. A simple expression for the state of minimum power dissipated-that corresponds to zero transverse current and harmonic chemical potential-is derived. It is shown that a longitudinal surface current proportional to the charge accumulation is flowing near the edges of the device. Charge accumulation and surface currents define a boundary layer over a distance of the order of the Debye-Fermi length. arXiv:1908.06282v1 [cond-mat.mes-hall]
• Ab initio study of Silver chloride: Modelization of the dielectric function
  
  • Lorin Arnaud
  • Reining Lucia
  • Sottile Francesco
  • Gatti Matteo
  , 2019.
• One step synthesis of core@shell SiGe@Si nanoparticles and their use as active material in high capacity anodes for Li-ion batteries
  
  • Desrues Antoine
  • Alper John
  • Boismain Florent
  • Coulon Pierre-Eugène
  • Soloy Adrien
  • Haon Cédric
  • Herlin-Boime Nathalie
  , 2019. In the frame of energy transition, silicon is a material of interest to develop Li-ion batteries with increased energy density. Nevertheless, the important volume change upon cycling (280 %) and reactivity towards electrolytes lead to rapid degradation of performances. Designing silicon-germanium structures is an efficient strategy to obtain stable performances of Li-ion batteries anodes. The synergetic effect of alloying silicon and germanium was demonstrated by Duveau et al [1], using micrometric particles obtained by ball-milling. The stability of the alloys was better than the stability of pure silicon and its capacity was higher than the capacity of pure germanium.
• Best performing SiGe/Si core‐shell nanoparticles synthesized in one step for high capacity anodes
  
  • Desrues Antoine
  • Alper John
  • Boismain Florent
  • Dominguez Diana Zapata
  • Berhaut Christopher
  • Coulon Pierre-Eugène
  • Soloy Adrien
  • Grisch Frederic
  • Tardif Samuel
  • Pouget Stephanie
  • Lyonnard Sandrine
  • Haon Cédric
  • Herlin-Boime Nathalie
  Batteries & Supercaps, Wiley, 2019, 2, pp.970-978. Silicon-germanium nanostructures are promising anode materials for high stability, high capacity and fast cycling Li-ion batteries. In this work, we report on the outstanding performance of original SiGe/Si core@shell nanoparticle heterostructures synthetized in one step by laser pyrolysis of silane and germane. By tuning the silane to germane ratio, the composition of Si100-xGex alloy was readily adjusted. Nanoparticles with x = 0, 20, 47, 77, and 100 were investigated and the composition of each alloy (including internal mixed phases) was confirmed by X-ray diffraction and energy-dispersive X-ray spectroscopy. The electrochemical performances of the Si100-xGex alloys were evaluated by cycling half cell batteries from C/5 to 5C. The optimal trade-off between stability and capacity was obtained in Si53Ge47 core shell nanoparticles alloy. This material exhibits the best performance reported so far for SiGe compounds, with a reversible specific capacity of 1695 mAh.g-1 after 60 cycles (90 % of its initial value). The (de)alloying properties of this optimal Si53Ge47 heterostructure were followed by Operando synchrotron WAXS measurements, suggesting sequential lithiation of the various phases present in the material. The alloying process, combined with the realization of peculiar nanostructures composed of a Ge-rich core and a Si-rich shell, therefore allow to reach electrochemical properties suited for a practical application in energy storage device. (10.1002/batt.201900094)
  DOI : 10.1002/batt.201900094
• Bis[2-(methacryloyloxy)ethyl] phosphate radiografted into track-etched PVDF for uranium (VI) determination by means of cathodic stripping voltammetry
  
  • Pinaeva U.
  • Dietz T.C.
  • Al Sheikhly M.
  • Balanzat E.
  • Castellino M.
  • Wade T.L.
  • Clochard M.C.
  Reactive and Functional Polymers, Elsevier, 2019, 142, pp.77-86. We report the radiation grafting of bis[2-(methacryloyloxy)ethyl] phosphate (B2MP) through electron-beam onto PVDF films and through swift heavy ions (SHI) irradiations into the pores of track-etched PVDF membranes. Radiolytically produced radicals were studied using EPR. To adapt the radiation grafting protocol inside the nanopores of track-etched membranes, the electron-beam irradiated films at varying monomer concentrations, doses and solvent mixtures were first studied. It was found that track-etched membranes, even after 1 h of chemical treatment, do not require a post-etching irradiation to initiate free-radical polymerization of B2MP from remaining radiationinduced radicals. The presence of functional groups inside the nanopores of the membrane were examined using FTIR and XPS. After exposure of B2MP-g-PVDF membranes to a uranyl solution, XPS was also exploited to evidence of O2UO22+ trapping inside the membrane nanoporosity by tracking the presence of U 4f peak. The B2MP-g-PVDF membranes were converted into electrodes by depositing 35 nm of gold on each side through a mask. Detection of ppb concentrations (from 20 to 100 ppb) of uranyl by B2MP-g-PVDF membrane electrodes was demonstrated by means of square wave cathodic stripping voltammetry (SW-CSV). The limit of detection (LOD) was estimated to be 17 ppb (3σ−/ slope). (10.1016/j.reactfunctpolym.2019.06.006)
  DOI : 10.1016/j.reactfunctpolym.2019.06.006