Publications

2018

• Cumulant Green's function calculations of plasmon satellites in bulk sodium: Influence of screening and the crystal environment
  
  • Zhou Jianqiang Sky
  • Gatti Matteo
  • Kas J. J.
  • Rehr J.
  • Reining Lucia
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2018, 97 (3). (10.1103/PhysRevB.97.035137)
  DOI : 10.1103/PhysRevB.97.035137
• Conservation of the piezoelectric response of PVDF films under irradiation
  
  • Melilli G.
  • Lairez D.
  • Gorse D.
  • Garcia-Caurel E.
  • Peinado A.
  • Cavani O.
  • Boizot B.
  • Clochard M.-C.
  Radiation Physics and Chemistry, Elsevier, 2018, 142, pp.54-59. (10.1016/j.radphyschem.2017.03.035)
  DOI : 10.1016/j.radphyschem.2017.03.035
• Conservation of the piezoelectric response of PVDF films under irradiation
  
  • Melilli G.
  • Lairez D.
  • Gorse D.
  • Garcia-Caurel E.
  • Peinado A.
  • Cavani O.
  • Boizot B.
  • Clochard M.-C.
  Radiation Physics and Chemistry, Elsevier, 2018, 142, pp.54-59. As opposed to piezo-ceramics (i.e PZT), flexibility and robustness characterize piezoelectric polymers. The main advantage of a piezoelectric polymer, such as Poly (vinylidene fluoride) (PVDF), is an electric power generation under large reversible elastic deformation. Starting from polarized PVDF, we have shown that, despite the fact that irradiation is known to structurally modify the PVDF by introducing defects (radicals, chain scission and crosslinks), the electro-active properties were not affected. At doses lower than 100 kGy, a comparison between swift heavy-ion (SHI) and e-beam irradiations is presented. A homemade device was realized to measure the output voltage as a function of the bending deformation for irradiated and non-irradiated PVDF film. DSC and FT-IR techniques give new insights on which crystalline part or structural change contributes to the conservation of the output voltage. Results suggest that despite the material after irradiation is composed of smaller crystallites, the β-phase content remains stable around 36%, which explains the remarkable preservation of the piezoelectric response in irradiated polarized PVDF films. (10.1016/j.radphyschem.2017.03.035)
  DOI : 10.1016/j.radphyschem.2017.03.035
• Strain engineering of photo-induced phase transformations in Prussian blue analogue heterostructures
  
  • Adam Adeline
  • Poggi Mélanie
  • Larquet Eric
  • Cortès Robert
  • Martinelli Lucio
  • Coulon Pierre-Eugène
  • Lahera Eric
  • Proux Olivier
  • Chernyshov Dmitry
  • Boukheddaden Kamel
  • Gacoin Thierry
  • Maurin Isabelle
  Nanoscale, Royal Society of Chemistry, 2018, 10 (34), pp.16030-16039. Heterostructures based on Prussian blue analogues (PBA) combining photo- and magneto-striction have shown a large potential for the development of light-induced magnetization switching. However, studies of the microscopic parameters that control the transfer of the mechanical stresses across the interface and their propagation in the magnetic material are still too scarce to efficiently improve the elastic coupling. Here, this coupling strength is tentatively controlled by strain engineering in heteroepitaxial PBA core–shell heterostructures involving the same Rb0.5Co[Fe(CN)6]0.8·zH2O photostrictive core and isostructural shells of similar thickness and variable mismatch with the core lattice. The shell deformation and the optical electron transfer at the origin of photostriction are monitored by combined in situ and real time synchrotron X-ray powder diffraction and X-ray absorption spectroscopy under visible light irradiation. These experiments show that rather large strains, up to +0.9%, are developed within the shell in response to the tensile stresses associated with the expansion of the core lattice upon illumination. The shell behavior is, however, complex, with contributions in dilatation, in compression or unchanged. We show that a tailored photo-response in terms of strain amplitude and kinetics with potential applications for a magnetic manipulation using light requires a trade-off between the quality of the interface (which needs a small lattice mismatch i.e. a small a-cubic parameter for the shell) and the shell rigidity (decreased for a large a-parameter). A shell with a high compressibility that is further increased by the presence of misfit dislocations will show a decrease in its mechanical retroaction on the photo-switching properties of the core particles. (10.1039/C8NR03597K)
  DOI : 10.1039/C8NR03597K
• Variational approach to the stationary spin-Hall effect
  
  • Wegrowe J.-E.
  • Déjardin P.-M.
  EPL - Europhysics Letters, European Physical Society / EDP Sciences / Società Italiana di Fisica / IOP Publishing, 2018, 124 (1), pp.17003. The Kirchhoff-Helmholtz principle of least heat dissipation is applied in order to derive the stationary state of the spin-Hall effect. Spin-accumulation due to spin-orbit interaction, spin-flip relaxation, and electrostatic interaction due to charge accumulation are treated on an equal footing. A nonlinear differential equation is derived, that describes both surface and bulk currents and spin-dependent chemical potentials. It is shown that if the ratio of the spin-flip relaxation length over the Debye-Fermi length is small, the stationary state is defined by a linear spin-accumulation potential and zero pure spin-current. (10.1209/0295-5075/124/17003)
  DOI : 10.1209/0295-5075/124/17003
• Enhanced Piezoelectric Response in Nanostructured Ni/PVDF Films
  
  • Melilli M
  • Gorse D
  • Galifanova A
  • Oral O
  • Balanzat E
  • Doaré Olivier
  • Tabellout M
  • Bechelany Mikhael
  • Lairez D
  • Wegrowe Je
  • Clochard Mary Claude
  Journal of Materials Science and Engineering, Hilaris Publisher, 2018, 07 (02). Poly(vinylidene fluoride) (PVDF) composites have recently emerged as excellent candidates to fabricate flexible and small piezoelectric generators for portable devices. Among various techniques used to nanostructure polarized PVDF, the track-etching represents a new route for manufacturing nanostructured composite thin films. The moderate influence of irradiation on the piezoelectric response of polarized PVDF makes possible the use of this technique. In this way, a nanostructured composite based on polarized thin PVDF films comprising embedded nickel nanowires (Ni NWs) was fabricated. The nanostructured PVDF/Ni NWs composites were tested under bending conditions using a homemade pressure cell. Due to the presence of NWs, an increase of five-fold the initial dielectric permittivity, in the low-frequency range, was observed. It suggested the presence of an interfacial polarization at the PVDF/Ni interface. With respect to the etched PVDF, the nanostructured PVDF/Ni NWs composites exhibited a non-negligible enhancement by 2.5 times the piezoelectric efficiency. This result was attributed to the increased Au/Ni NWs electrode surface. (10.4172/2169-0022.1000444)
  DOI : 10.4172/2169-0022.1000444
• On the optimal basis set for electron dynamics in strong laser fields: The case of molecular ion H2+
  
  • Labeye Marie
  • Zapata Felipe
  • Coccia Emanuele
  • Véniard Valérie
  • Toulouse Julien
  • Caillat Jérémie
  • Taïeb Richard
  • Luppi Eleonora
  Journal of Chemical Theory and Computation, American Chemical Society, 2018, 14 (11), pp.5846-5858. A clear understanding of the mechanisms that control the electron dynamics in strong laser field is still a challenge that requires to be interpreted by advanced theory. Development of accurate theoretical and computational methods, able to provide a precise treatment of the fundamental processes generated in the strong field regime, is therefore crucial. A central aspect is the choice of the basis for the wave-function expansion. Accuracy in describing multiphoton processes is strictly related to the intrinsic properties of the basis, such as numerical convergence, computational cost, and 1 representation of the continuum. By explicitly solving the 1D and 3D time-dependent Schrödinger equation for H2+ in presence of an intense electric field, we explore the numerical performance of using a real-space grid, a B-spline basis, and a Gaussian basis (improved by optimal Gaussian functions for the continuum). We analyze the performance of the three bases for high-harmonic generation and above-threshold ionization for H2+. In particular, for high-harmonic generation, the capability of the basis to reproduce the two-center interference and the hyper-Raman phenomena is investigated. (10.1021/acs.jctc.8b00656)
  DOI : 10.1021/acs.jctc.8b00656
• Towards Thermal Reading of Magnetic States in Hall Crosses
  
  • Xu Y.
  • Petit-Watelot S.
  • Polewczyk V.
  • Parent G.
  • Montaigne F.
  • Wegrowe J.-E.
  • Mangin S.
  • Lacroix D.
  • Hehn M.
  • Lacour D.
  Physical Review Applied, American Physical Society, 2018, 9, pp.034028. The 3ω method is a standard way to measure the thermal conductivity of thin films. In this study, we apply the method to read the magnetic state of a perpendicularly magnetized CoTb ferrimagnetic Hall cross using a thermal excitation. In order to generate the thermal excitation, an oscillating current at an ω frequency is applied to the Hall cross using different geometries. The magnetic signals oscillating at ω, 2ω, and 3ω are probed using a lock-in technique. From the analysis of the power dependence, we can attribute the 3ω response to the temperature oscillation and the 2ω to the temperature-gradient oscillation. Finally, the frequency dependence of the magnetic signals can be understood by considering the heat diffusion in a two-dimensional model (10.1103/PhysRevApplied.9.034028)
  DOI : 10.1103/PhysRevApplied.9.034028
• Combined EPR and photoluminescence study of electron and proton irradiated 3C-SiC
  
  • Al Atem Abdul Salam
  • Bratus Victor
  • Canut Bruno
  • Lefèvre Jérémie
  • Guillot G
  • Bluet Jean-Marie
  , 2018. In past few years, point defects in silicon carbide (SiC) have been identified as promising for applications in quantum technologies [1]. A variety of point defects in hexagonal SiC [2], including VSi and VSiVC have been optically isolated and used as single defect-based spin qubits with long coherence time [3-5]. All of this, proves that these point defects allow the SiC to be a very favorable candidate for quantum applications especially, solid state quantum bits (Qubits) and single photon source (SPS). Most of these studies were carried out on the hexagonal polytypes 4H-SiC and 6H-SiC, although the 3C-SiC polytype presents the unique advantage of integration possibility on standard Si wafer. This is due to the amount of defects (dislocation mainly) in the 3C-SiC heteroepitaxy on Si which are detrimental for long coherence time considering Qubit application. Consequently, the goal of the present study is the investigation of point defects formation after implantation by proton H + (300 keV) and irradiation by electron e-(0.8 and 2 MeV) in 3C-SiC (respectively 3C-SiC<p> and 3C-SiC<e>) for SPS application purpose. Toward this end, we have combined two characterization techniques, the photoluminescence (PL) and the electron paramagnetic resonance (EPR). PL (12K) and EPR (70-300K) measurements will be presented in order to analyze precisely the signatures of point defects generated after these two types of irradiations. The effects of the thermal annealing (500-1000°C) were also investigated. PL spectra both for 3C-SiC<p> and 3C-SiC<e> are presented in figure 1 for the annealing temperatures giving the highest PL signal (1000°C for 3C-SiC<p> and 750°C for 3C-SiC<e>). We notice first that the whole PL signal is higher for 3C-SiC<p>. In this case the spectrum is dominated by the DI defect line (possibly related to antisite pair [6]) and the E line (attributed to Si vacancy [7, 8]) while in electron irradiated sample the  line (attributed to CSiVC in a 3C-SiC nanocrystal [8]) dominates as previously reported [9]. A strong zero phonon line at 1.6 eV also appears for 3C-SiC<p> with its phonon replica. This line was previously observed also for neutron and proton irradiated 3C-SiC and at present is of unknown origin [10, 11]. In the infrared range, the proton implantation is also more efficient to produce the VcVsi PL line with an optimum luminescence for 750°C annealing. All together, these results show that, even if the energy transferred to the host atoms during electron irradiation is quite above the displacement thresholds for both C and Si, defects involving Si vacancy are more pronounced in 3C-SiC<p> samples. EPR spectra for 3C-SiC<p> for isochronal annealing (30 min.) at different temperatures are presented in figure 2. The spin-three-half negatively-charged Si vacancy (the T1 center) is a dominant defect in 3C-SiC<p> epitaxial layers corresponding to the E line in the PL spectra. Similar to neutron irradiated 3C-SiC crystals the as-implanted not annealed 3C-SiC<p> samples demonstrate an isotropic spectrum with the g-value of 2.0029 and a superhyperfine doublet with a splitting typical to the T1 center (10.4028/www.scientific.net/MSF.963.301)
  DOI : 10.4028/www.scientific.net/MSF.963.301
• Corbino magnetoresistance in ferromagnetic layers: Two representative examples Ni 81 Fe 19 and Co 83 Gd 17
  
  • Madon B
  • Wegrowe J.-E
  • Hehn Michel
  • Montaigne F
  • Lacour D
  Physical Review B, American Physical Society, 2018, 98. The magnetoresistance of Ni 81 Fe 19 and Co 83 Gd 17 ferromagnetic thin films is measured in Corbino disk geometry, and compared to the magnetoresistance of the same films measured in the Hall-bar geometry. The symmetry of the magnetoresistance profiles is drastically modified by changing the geometry of the sample, i.e., by changing the boundary conditions. These properties are explained in a simple model, showing that the Corbino magnetoresistance is defined by the potentiostatic boundary conditions while the Hall-bar magnetoresistance is defined by galvanostatic boundary conditions. The Hall effect was first measured in 1879 by Hall [1] by applying a magnetic field to a conducting slab contacted to an electric generator at the extremities. Later on, Corbino [2] found a similar effect by applying a magnetic field on a disk geometry with two concentric electrodes. Quickly the question arose on whether the effect measured by Corbino (the so-called Corbino effect) in a disk and by Hall in a bar have the same origin. In 1914, Adams and Chapman measured the Corbino effect in many different metals [3] by using an oscillating current flowing from the center of the disk to its outer. Adams concluded in 1915 that "the Corbino effect is, essentially, the same as the Hall effect" [4]. However, the question remains about the exact meaning of the adverb "essentially." In the 1950's, the Hall effect in the Corbino geometry was studied for its practical applications. The magnetoresistance of InSb slabs was shown to depend strongly on the shape of the samples [5]. The reason is that near the current injection edge, the Hall electric field is shorted and a transverse electric current appears which causes an increase of the resistance as in the Corbino geometry [6-9]. Accordingly, one can see the Corbino geometry as the extreme scenario where the Hall electric field is zero everywhere and a Hall current is flowing, or, in other terms, one can view the Corbino disk as a Hall bar in which the electrostatic charge accumulation is reduced to zero everywhere. The system cannot generate a voltage between the edges so that a Hall current is flowing and the Joule heating is higher than in the Hall bar for an equivalent volume [10-12]. The mechanism responsible for both the Hall effect and the Corbino effect is indeed the same, but the Corbino disk is a device that is more constrained than the Hall bar, due to the change of the boundary conditions. At the turn of the last century, the emergence of spintronics has shown the possibility of exploiting spin-polarized currents * jean-eric.wegrowe@polytechnique.edu and spin-dependent potentials, and has paved the way to the realization of new electronic devices. Recently, various developments about the spin-Hall effects (anomalous Hall effect, spin-Hall effect, spin-pumping effect, spin-Seebeck effects, etc. [13,14]) tend to show that the usual Hall-bar conditions with spin relaxation could be turned into "Corbino-like boundary conditions," in the sense that the electric charge accumulation drops to zero at the edges and a pure spin current can be generated instead of a Hall voltage [11]. In this context, the goal of this Rapid Communication is to study NiFe and GdCo ferromagnetic Corbino disks and Hall bars, in order to understand the behavior of the magnetoresistance [13,15-17] when the boundary conditions are switched (by changing the geometry) from spin current to spin-dependent voltage. The alloys Ni 81 Fe 19 and Co 83 Gd 17 are chosen for their maximum contribution to the anisotropic magnetoresistance and the anomalous Hall magnetoresistance (that defines the anomalous Hall angle), respectively. First, we will present our measures of Corbino magne-toresistance performed on NiFe and CoGd rings. The results are then analyzed in the framework of the generalized Ohm's law by defining the Corbino magnetotransport coefficients C as a function of the usual Hall-bar coefficients [see Eq. (12) below]. The consistency of the proposed explanation is checked independently, by measuring the magnetotransport coefficients of the Hall bar. The samples studied are 20-nm-thick layers of Ni 81 Fe 19 and Co 83 Gd 17 sputtered on glass substrates. The magnetic layers are sandwiched between 5-nm-thick Ta buffers and 3-nm-thick Pt caps. The magnetic properties of the thin layers have been previously studied [18] (see Supplemental Material [19]). The sample magnetization is uniform for quasistatic states, although nonuniform states could take place at low magnetic fields (this regime is, however, not considered in the present study). The NiFe is textured with small uniaxial anisotropy lying in the sample plane. The coercivity field in the in-plane geometry is of the order of 1 mT. The out-2469-9950/2018/98(22)/220405(5) 220405-1 (10.1103/PhysRevB.98.220405)
  DOI : 10.1103/PhysRevB.98.220405
• Editorial (IRaP 2016 Proceedings)
  
  • Yvette Ngono-Ravache
  • Marie-Claude Clochard
  • Muriel Ferry
  Radiation Physics and Chemistry, Elsevier, 2018, 142, pp.1. This issue of Radiation Physics and Chemistry contains selected papers presented at the 12th Ionizing Radiation and Polymers conference (IRaP 2016) that was held from September 25 to September 30, 2016 at Belambra “Les Criques” in Giens, France. IRaP has the particularity to focus on the effect of ionizing radiations on polymers. This biennial conference was initiated with the three-fold objective to 1) bring together scientists from research centers, universities and industry, 2) provide a forum to exchange knowledge and information in this field and , 3) to promote innovative applications. IRaP 2016 was attended by 125 scientists and 10 accompanying persons from 20 countries. The scientific program consisted of 15 plenary sessions (21 invited and 40 selected lectures), two poster sessions (68 posters), 1 course and 1 keynote. The course, delivered by Emmanuel Balanzat (Caen, France), gave young scientists the opportunity to enlarge their knowledge on the influence of the nature of the projectile on polymer modification, i.e. the specificity of Swift Heavy Ions. The keynote, presented by Pr. Vladimir Feldman (Moscow, Russia), gave a great overview on radiation damage mechanisms at cryogenic temperatures. IRaP2016 in France gave the opportunity to honor the memory of Dr. Natacha Betz, one of the founders of the IRaP conference, for the tenth anniversary of her passing away. In a dedicated tribute, Dr. Serge Bouffard (Caen, France) offered a wealth of insights on her scientific career, testimonials of memorable moments and messages to the polymer irradiation community. IRaP2016 was also the occasion to acknowledge some senior scientists’ contributions. Especially, a special session on gels, devoted to Pr. Janusz Rosiak (Lodz, Poland), was hosted to mark his upcoming retirement. This was an opportunity for his colleagues and friends to congratulate him and to highlight his valuable and remarkable input on the development of hydrogels. Traditional IRaP symposium topics such as fundamental processes, radiation-induced chemical modifications (ageing, degradation, resulting physical properties modification) and their application in the fabrication of advanced materials were addressed. Notably, the nanostructures of polymer thin films through ion-track technology allows the fabrication of interesting advanced polymer-based new materials for sensoring purposes. Radiation-induced grafting technique is still widely developed, using up-to-date polymerization mechanisms (eg. RAFT mechanism), and applied to various industrial fields of interest among which flame retardant materials, energy harvesting or drug delivery systems. It is worth noting that drug delivery devices, combining various radiation-based strategies such as the synthesis of crosslinked nanogels, were widely represented. In addition to synthetic polymers, bio-based and biopolymers were presented as base materials of growing interest. Due to an increasing environmental concern, numerous studies aimed notably at improving the biodegradability of polymers. New sessions (Radiolysis and Lifetime prediction) and new trends (Monte-Carlo calculations for the study of polymer ageing and the association of metal/polymer hybrid nanoparticles for medical applications) have entered the topic list of the 12th IRaP. The present special issue of Radiation Physics and Chemistry gathers the selected articles, peer reviewed by independent referees, among the manuscripts submitted for publication after the conference. The organizing committee gratefully acknowledges all the contributors. We thank the referees for their critical reading of the manuscripts and the associated detailed reviews, ensuring the required standard for RPC. The three guest editors would also like to thank Pr. Laszlo Wojnarovits for his help during the editing process. The success of this 12th edition of the IRaP conference is first assigned to the attendees and the contributors. On behalf of the organizing committee, we would like to thank them for this special issue, the scientific and steering committees for their valuable help in the organization and the local organizing committee (the green team and L. De Baeremaker included) for all the hours of hard work they have pulled to make this conference a great success. We address a special and personal thanks to Dr. Caroline Aymes-Chodur for her precious help all along the conference organization, despite her knowing that she wouldn’t attend the conference. We also thank the staff of the Belambra “Les Criques“ resort, especially Ms. Céline Lacommère for her friendliness and her dedication. All this, added to the gorgeous location and the sunny weather, certainly contributed in the enjoyment of IRaP2016. We would like to acknowledge the institutions, organizations and companies that supported the IRaP 2016: IAEA, IIA (International Irradiation Association), CEA, Andra, CNRS, Université de Caen, Caen la Mer and Ionisos. Thanks to the support of the IAEA and IIA, eight young scientists, selected on the basis of their scientific work, have been granted to attend the IRaP2016 conference. Finally, we would like to address special thanks to the companies who funded an exhibition booth: AERIAL, NIST, Steris and Thermo Scientific. (10.1016/j.radphyschem.2017.10.010)
  DOI : 10.1016/j.radphyschem.2017.10.010
• Colossal electromagnon excitation in the non-cycloidal phase of TbMnO3 under pressure
  
  • Aupiais Ian
  • Mochizuki Masahito
  • Sakata Hideaki
  • Grasset Romain
  • Gallais Yann
  • Sacuto Alain
  • Cazayous Maximilien
  Npj Quantum Materials, Nature publishing, 2018, 3. The magnetoelectric coupling, i.e., cross-correlation between electric and magnetic orders, is a very desirable property to combine functionalities of materials for next-generation switchable devices. Multiferroics with spin-driven ferroelectricity presents such a mutual interaction concomitant with magneto-active and electro-active excitations called electromagnons. TbMnO 3 is a paradigmatic material in which two electromagnons have been observed in the cycloidal magnetic phase. However, their observation in TbMnO 3 is restricted to the cycloidal spin phase and magnetic ground states that can support the electromagnon excitation are still under debate. Here, we show by performing Raman spectroscopy measurements under pressure that the lower-energy electromagnon (4 meV) disappears when the ground state enters from a cycloidal phase to an antiferromagnetic phase (E-type). On the contrary, the magneto-electric activity of the higher-energy electromagnon (8 meV) increases in intensity by one order of magnitude. Using microscopic model calculations, we demonstrate that the lower-energy electromagnon, observed in the cycloidal phase, originates from a higher harmonic of the magnetic cycloid, and we determine that the symmetric exchange-striction mechanism is at the origin of the higher-energy electromagnon which survives even in the E-type phase. The colossal enhancement of the electromagnon activity in TbMnO 3 paves the way to use multiferroics more efficiently for generation, conversion and control of spin waves in magnonic devices. (10.1038/s41535-018-0130-3)
  DOI : 10.1038/s41535-018-0130-3