Laboratoire des Matériaux et du Génie Physique

Materials Science Forum (MSF) is a peer-reviewed journal. The journal scope covers all aspects of theoretical, computational and experimental research in the area of materials science. It includes but is not limited to materials synthesis, analysis of materials properties,the technology of materials processing and materials application. Materials Science Forum is one of the largest periodicals in its field. Materials Science Forum specializes on the publication of thematically complete volumes as well as special topic volumes. Publication of stand-alone papers by individual authors is also considered. All published materials are archived with PORTICO and CLOCKSS. Authors retain the right to publish an extended and significantly updated version in another periodical. Note from the Honorary Editor Emeritus Professor Graeme Murch: I can recommend Materials Science Forum as an excellent location for authors to get their papers published in a fast and stream-lined fashion. Abstracted/Indexed in:SCOPUS www.scopus.com.REAXYS www.reaxys.com. Ei Compendex www.ei.org/. Chimica https://www.elsevier.com/solutions/engineering-village/content#chimica. Inspec (IET, Institution of Engineering Technology) www.theiet.org. Chemical Abstracts Service (CAS) www.cas.org. Google Scholar scholar.google.com. GeoRef www.americangeosciences.org/georef. NASA Astrophysics Data System (ADS) http://www.adsabs.harvard.edu/. INIS Atomindex (International Nuclear Information System) https://inis.iaea.org. Cambridge Scientific Abstracts (CSA) www.csa.com. ProQuest www.proquest.com. Ulrichsweb www.proquest.com/products-services/Ulrichsweb.html. EBSCOhost Research Databases www.ebscohost.com/. Zetoc zetoc.jisc.ac.uk. EVISA http://www.speciation.net/Public/Linklists/EVISA.html. Index Copernicus Journals Master List www.indexcopernicus.com. WorldCat (OCLC) www.worldcat.org.

Dans la première partie de ce Mémoire, on propose de considérer l'énergie magnétocristalline et magnétoélastique d'un corps ferromagnétique comme la somme de termes élémentaires relatifs chacun à une liaison, c'est-à-dire à un couple de deux atomes proches voisins. Sur cette base, on développe la théorie de la magnétostriction et de l'anisotropie magnétocristalline et, de sa comparaison avec les résultats expérimentaux, on déduit les valeurs des paramètres qui caractérisent l'énergie de liàison. Des mêmes prémices, on déduit qu'il doit exister dans les corps ferromagnétiques, une énergie d'anisotropie superficielle, dépendant de l'orientation de l'aimantation spontanée par rapport à la surface et ne présentant d'ailleurs aucun rapport avec le phénomène classique de champ démagnétisant de forme. Cette énergie de surface, de l'ordre de O, I à I erg/cm2, est susceptible de jouer un rôle important dans les propriétés des substances ferromagnétiques dispersées en éléments de dimensions inférieures à I00 Å. Dans la seconde partie, on montre, en adoptant le point de vue précédent, que dans les solutions solides ferromagnétiques à deux constituants au moins, traitées à chaud dans un champ magnétique, les atomes proches voisins d'un atome donné doivent se répartir d'une façon anisotrope autour de ce dernier et donner naissance à une surstructure d'orientation. Par trempe, cette surstructure est susceptible de se conserver en faux équilibre à basse température et se manifeste par l'apparition d'une anisotropie magnétique de caractère uniaxial. Les phénomènes sont précisés par le calcul, notamment le rôle de la concentration, dans le cas de différents réseaux cubiques simples et dans le cas d'une substance isotrope par compensation. L'anisotropie calculée est de l'ordre de I03 à I05 ergs/cm2, mais paraît dépasser largement ces valeurs dans des cas exceptionnels. Cette théorie rend compte des propriétés des ferronickels traités à chaud dans un champ magnétique et, en particulier, des monocristaux de permalloy. On suggère le rôle possible de ces effets dans l'alnico V et les ferrites de cobalt orientés. Dans une troisième partie, on montre que l'on peut créer une surstructure d'orientation dans une solution solide quelconque au moyen d'une déformation élastique à chaud et la conserver par trempe. Si la solution solide est ferromagnétique, les surstructures ainsi créées donnent naissance à une anisotropie magnétique de caractère uniaxial. En s'appuyant sur une théorie sommaire des propriétés élastiques des solutions solides développée à cet effet, le phénomène est soumis au calcul : on trouve des anisotropies de I04 ergs/cm3 pour des tensions de I0 kg/mm2 , dans le cas des ferronickels. On propose d'interpréter par la création de telles surstructures l'anisotropie magnétique uniaxiale des ferronickels quasi unicristallins laminés à froid, la déformation plastique permettant aux atomes de prendre la répartition d'équilibre correspondant au système des tensions appliquées. Dans les ferronickels polycristallins laminés ou étirés, l'anisotropie est de signe contraire à la précédente; on propose de l'expliquer selon le même mécanisme que les phénomènes de restauration après fluage.

International audience

Recent experiments have confirmed that coherent effects in the multiple scattering of light affect the angular dependence of the intensity reflected by disordered media. By considering the constructive interferences between time-reversed paths of light in a semi-infinite medium, we analyze the experimental line shape of the albedo within the diffusion approximation and explain the observed effects of polarization.

BACKGROUND: The exact overall incidence of sarcoma and sarcoma subtypes is not known. The objective of the present population-based study was to determine this incidence in a European region (Rhone-Alpes) of six million inhabitants, based on a central pathological review of the cases. METHODOLOGY/PRINCIPAL FINDINGS: From March 2005 to February 2007, pathology reports and tumor blocks were prospectively collected from the 158 pathologists of the Rhone-Alpes region. All diagnosed or suspected cases of sarcoma were collected, reviewed centrally, examined for molecular alterations and classified according to the 2002 World Health Organization classification. Of the 1287 patients screened during the study period, 748 met the criteria for inclusion in the study. The overall crude and world age-standardized incidence rates were respectively 6.2 and 4.8 per 100,000/year. Incidence rates for soft tissue, visceral and bone sarcomas were respectively 3.6, 2.0 and 0.6 per 100,000. The most frequent histological subtypes were gastrointestinal stromal tumor (18%; 1.1/100,000), unclassified sarcoma (16%; 1/100,000), liposarcoma (15%; 0.9/100,000) and leiomyosarcoma (11%; 0.7/100,000). CONCLUSIONS/SIGNIFICANCE: The observed incidence of sarcomas was higher than expected. This study is the first detailed investigation of the crude incidence of histological and molecular subtypes of sarcomas.

The entire zone-center phonon spectrum of the $R3c$ ferroelectric antiferromagnetic phase of bismuth ferrite is computed using a first-principles approach based on density functional theory. Two phonon modes exhibiting eigendisplacement vectors that strongly overlap with the atomic distortions taking place at the ferroelectric structural phase transition are identified and give support to a transition with displacive character. Both Raman and infrared reflectivity spectra are also computed, providing benchmark theoretical results for the assignment of experimental spectra.

Abstract Chalcogenide phase-change materials (PCMs), such as Ge-Sb-Te alloys, have shown outstanding properties, which has led to their successful use for a long time in optical memories (DVDs) and, recently, in non-volatile resistive memories. The latter, known as PCM memories or phase-change random access memories (PCRAMs), are the most promising candidates among emerging non-volatile memory (NVM) technologies to replace the current FLASH memories at CMOS technology nodes under 28 nm. Chalcogenide PCMs exhibit fast and reversible phase transformations between crystalline and amorphous states with very different transport and optical properties leading to a unique set of features for PCRAMs, such as fast programming, good cyclability, high scalability, multi-level storage capability, and good data retention. Nevertheless, PCM memory technology has to overcome several challenges to definitively invade the NVM market. In this review paper, we examine the main technological challenges that PCM memory technology must face and we illustrate how new memory architecture, innovative deposition methods, and PCM composition optimization can contribute to further improvements of this technology. In particular, we examine how to lower the programming currents and increase data retention. Scaling down PCM memories for large-scale integration means the incorporation of the PCM into more and more confined structures and raises materials science issues in order to understand interface and size effects on crystallization. Other materials science issues are related to the stability and ageing of the amorphous state of PCMs. The stability of the amorphous phase, which determines data retention in memory devices, can be increased by doping the PCM. Ageing of the amorphous phase leads to a large increase of the resistivity with time (resistance drift), which has up to now hindered the development of ultra-high multi-level storage devices. A review of the current understanding of all these issues is provided from a materials science point of view.

Metallic nanowire networks have huge potential in devices requiring transparent electrodes. This article describes how the electrical resistance of metal nanowire networks evolve under thermal annealing. Understanding the behavior of such films is crucial for the optimization of transparent electrodes which find many applications. An in-depth investigation of silver nanowire networks under different annealing conditions provides a case study demonstrating that several mechanisms, namely local sintering and desorption of organic residues, are responsible for the reduction of the systems electrical resistance. Optimization of the annealing led to specimens with transmittance of 90% (at 550 nm) and sheet resistance of 9.5 Ω sq(-1). Quantized steps in resistance were observed and a model is proposed which provides good agreement with the experimental results. In terms of thermal behavior, we demonstrate that there is a maximum thermal budget that these electrodes can tolerate due to spheroidization of the nanowires. This budget is determined by two main factors: the thermal loading and the wire diameter. This result enables the fabrication and optimization of transparent metal nanowire electrodes for solar cells, organic electronics and flexible displays.

Abstract Transparent heaters (TH) have attracted intense attention from both scientific and industrial sectors due to the key role they play in many technologies, including smart windows, deicers, defoggers, displays, actuators, and sensors. While transparent conductive oxides have dominated the field for the past five decades, a new generation of THs based on nanomaterials has led to new paradigms in terms of applications and prospects in the past years. Here, the most recent developments and strategies to improve the properties, stability, and integration of these new THs are reviewed.

On montre qu'il convient de distinguer au moins deux espèces de traînages magnétiques : le traînage réversible et le traînage irréversible dont on peut décrire les propriétés de la manière la plus simple, du point de vue formel, en introduisant deux champs magnétiques fictifs de traînage, dépendant du temps et superposés au champ magnétique appliqué. Le champ fictif de traînage réversible provient de la stabilisation progressive avec le temps de l'aimantation spontanée suivant la direction qu'elle occupe : cette stabilisation est liée à une diffusion matérielle à l'intérieur de la substance ferromagnétique. On remarque que les contraintes de magnétostriction ne suffisent pas à expliquer la stabilisation de diffusion et l'on suggère d'attribuer la stabilisation aux couplages magnétocristallins, selon un mécanisme qui est décrit. Quant au champ de traînage irréversible, il provient des fluctuations thermiques qui interviennent de différentes manières : l'effet le plus important paraît dû aux fluctuations du champ interne de dispersion provenant des fluctuations en direction de l'aimantation spontanée. Enfin, on a rassemblé quelques données numériques qui précisent les ordres de grandeur des deux espèces de traînage.

$\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_{3}$ ceramics were investigated by means of infrared reflectivity and time domain terahertz transmission spectroscopy at temperatures $20--950\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, and the magnetodielectric effect was studied at $10--300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ with the magnetic field up to $9\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. Below $175\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the sum of polar phonon contributions to the permittivity corresponds to the value of measured permittivity below $1\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$. At higher temperatures, a giant low-frequency permittivity was observed, obviously due to the enhanced conductivity and possible Maxwell-Wagner contribution. Above $200\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ the observed magnetodielectric effect is caused essentially through the combination of magnetoresistance and the Maxwell-Wagner effect, as recently predicted by Catalan [Appl. Phys. Lett. 88, 102902 (2006)]. Since the magnetodielectric effect does not occur due to a coupling of polarization and magnetization as expected in magnetoferroelectrics, we call it an improper magnetodielectric effect. Below $175\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ the magnetodielectric effect is by several orders of magnitude lower due to the decreased conductivity. Several phonons exhibit gradual softening with increasing temperature, which explains the previously observed high-frequency permittivity increase on heating. The observed noncomplete phonon softening seems to be the consequence of the first-order nature of the ferroelectric transition.

Regularly twinned domain structures are observed by scanning piezoforce microscopy on single crystalline grains of BiFeO3 ceramics being grown by a special low temperature sintering process. The domains are considerably larger than those observed in thin films. Their spontaneous polarization comes close to that predicted theoretically and overcomes restrictions hitherto being set to bulk single crystals. The observed ferroelastic twin domain structure resembles that of classic T domains in rhombohedrally distorted NiO, but is additionally superimposed by ferroelectric twin domain patterns.

Après avoir rappelé l'existence et la théorie du traînage de fluctuations (ou traînage irréversible), l'auteur développe une théorie du traînage magnétique de diffusion (ou traînage réversible) selon laquelle les atomes étrangers interstitiels, qui sont à l'origine du phénomène, agiraient par couplage magnétocristallin entre leur position et la direction de l'aimantation spontanée. Il montre que tout se passe comme s'il fallait ajouter aux termes ordinaires d'anisotropie magnétique une énergie, dite de stabilisation, susceptible d'atteindre des valeurs de l'ordre de 100 ergs/cm 3. Il en déduit l'expression générale de la pression subie, à un instant donné, par une paroi à 90° ou à 180°, du fait des phénomènes de diffusion des atomes étrangers, connaissant les positions antérieures de la paroi. Il donne une méthode approchée de calcul des effets de la diffusion, lorsque ceux-ci peuvent être assimilés à une petite perturbation du processus ordinaire d'aimantation. Quelques exemples simples d'application de la théorie sont alors donnés et permettent d'interpréter les expériences les plus classiques de désaccommodation ou de traînage, dans le cas de variations discontinues du champ appliqué ou dans le cas de champs alternatifs sinusoïdaux. L'auteur étudie ensuite des exemples plus compliqués et explique notamment le traînage anomal de Mitkewitch ainsi que les expériences de Webb et Ford relatives à la perméabilité en courant alternatif des tôles au silicium. Il montre comment on peut rendre compte des variations de cette perméabilité en fonction des temps écoulés depuis la désaimantation et depuis l'application du champ de mesure, ainsi que les variations de cette perméabilité en fonction du champ magnétique. La théorie paraît donner une interprétation qualitative satisfaisante des propriétés actuellement connues caractérisant le traînage de diffusion.

In the present work, the electronic and vibrational properties of both pristine ${\mathrm{V}}_{2}\mathrm{C}$ and fully terminated ${\mathrm{V}}_{2}\mathrm{C}{T}_{2}$ (where $T=\mathrm{F},$ O, OH) two-dimensional monolayers are investigated using density functional theory. First, the atomic structures of ${\mathrm{V}}_{2}\mathrm{C}$-based MXene phases are optimized, and their respective dynamical stabilities are discussed. Second, electronic band structures are computed indicating that ${\mathrm{V}}_{2}\mathrm{C}$ is metallic as well as all the corresponding functionalized systems. Third, the vibrational properties (phonon frequencies and spectra) of ${\mathrm{V}}_{2}\mathrm{C}$-based MXenes are computed with the density functional perturbation theory and reported. Both Raman-active (${E}_{g}$, ${A}_{1g}$) and infrared-active (${E}_{u}$, ${A}_{2u}$) vibrational modes are predicted ab initio with the aim to correlate the experimental Raman peaks with the calculated vibrational modes and to assign them to specific atomic motions. The effect of the terminal groups on the vibrational properties is emphasized, along with the effect on the presence and position of the corresponding Raman peaks. Our results provide insights for the identification and characterization of ${\mathrm{V}}_{2}\mathrm{C}$-based samples using Raman spectroscopy.

Medication non-adherence and the clinical implications in difficult-to-control asthma were audited. Prescription issue data from 115 patients identified sub-optimal adherence (<80%) in 65% of patients on inhaled corticosteroids (ICS) or combined ICS/long-acting β2 agonist (LABA). In those using separate ICS and LABA, adherence to LABA (50%) was significantly better than to ICS (14.3%). Patients with sub-optimal ICS adherence had reduced FEV(1) and higher sputum eosinophil counts. Adherence ratio was an independent predictor of previous ventilation for acute severe asthma (p=0.008). The majority of patients with difficult-to-control asthma are non-adherent with their asthma medication. Non-adherence is correlated with poor clinical outcomes.

Silver nanowire (AgNW) networks are efficient as flexible transparent electrodes, and are cheaper to fabricate than ITO (Indium Tin Oxide). Hence they are a serious competitor as an alternative to ITO in many applications such as solar cells, OLEDs, transparent heaters. Electrical and optical properties of AgNW networks deposited on glass are investigated in this study and an efficient method to optimize them is proposed. This paper relates network density, nanowire dimensions and thermal annealing directly to the physical properties of the nanowire networksusing original physical models. A fair agreement is found between experimental data and the proposed models. Moreover thermal stability of the nanowires is a key issue in thermal optimization of such networks and needs to be studied. In this work the impact of these four parameters on the networks physical properties are thoroughly investigated via in situ measurements and modelling, such a method being also applicable to other metallic nanowire networks. We demonstrate that this approach enables the optimization of both optical and electrical properties through modification of the junction resistance by thermal annealing, and a suitable choice of nanowire dimensions and network density. This work reports excellent optical and electrical properties of electrodes fabricated from AgNW networks with a transmittance T = 89.2% (at 550 nm) and a sheet resistance of Rs = 2.9 Ω □(-1), leading to the highest reported figure of merit.

This study investigated how substrate geometry influences in-vitro tissue formation at length scales much larger than a single cell. Two-millimetre thick hydroxyapatite plates containing circular pores and semi-circular channels of 0.5 mm radius, mimicking osteons and hemi-osteons respectively, were incubated with MC3T3-E1 cells for 4 weeks. The amount and shape of the tissue formed in the pores, as measured using phase contrast microscopy, depended on the substrate geometry. It was further demonstrated, using a simple geometric model, that the observed curvature-controlled growth can be derived from the assembly of tensile elements on a curved substrate. These tensile elements are cells anchored on distant points of the curved surface, thus creating an actin "chord" by generating tension between the adhesion sites. Such a chord model was used to link the shape of the substrate to cell organisation and tissue patterning. In a pore with a circular cross-section, tissue growth increases the average curvature of the surface, whereas a semi-circular channel tends to be flattened out. Thereby, a single mechanism could describe new tissue growth in both cortical and trabecular bone after resorption due to remodelling. These similarities between in-vitro and in-vivo patterns suggest geometry as an important signal for bone remodelling.

A previous study of the growth conditions has shown that single-phase BiFeO3 thin films can only be obtained in a narrow pressure–temperature window and that these films display a weak magnetic moment. Here, we study in more detail the structure and the magnetism of single-phase BiFeO3 films by means of reciprocal space mapping, Raman spectroscopy and neutron diffraction. X-ray and Raman data suggest that the BiFeO3 structure is tetragonal for 70 nm thick films and changes to monoclinic for 240 nm thick films, thus remaining different from that of the bulk (rhombohedral) structure. In the 240 nm monoclinically distorted film, neutron diffraction experiments allow the observation of a G-type antiferromagnetic order as in bulk single crystals. However, the satellite peaks associated with the long-wavelength cycloid present in bulk BiFeO3 are not observed. The relevance of these findings for the exploitation of the magnetoelectric properties of BiFeO3 is discussed.

On montre que le ferrite de cuivre prend par refroidissement lent; une structure quadratique à grand champ coercitif, à saturation magnétique plus faible et dont le rapport des axes c/α atteint 1,06. A chaque température correspond un état d'équilibre caractérisé par une valeur différente de c/a, comprise entre I et 1,06. L'étude aux rayons X, à l'aide du rayonnement Co K a, montre que les variétés cubiques et quadratiques sont proches de l'état de ferrite inverse, mais que la fraction λ des ions Fe+++ croit sur les sites tétraédriques au fur et à mesure de la décroissance de la température. On propose une surstructure. comportant une répartition ordonnée d'ions de Fe et Cu sur le sous-réseau des places octaédriques. Une telle surstructure, si elle existe, serait très difficile à mettre en évidence pour les autres ferrites, car les ions de Co, Ni, Mg, etc., déforment moins les réseaux que les ions de Cu++. La variation de c/a aurait alors deux causes, d'une part, l'établissement d'un ordre entre les ions Cu++ et Fe+++ dans le sous-réseau des sites octaédriques et, d'autre part, la variation de λ, c'est-à-dire les changements de concentration des ions du sous-réseau : on sait en effet que, pour toutes les surstructures, les paramètres varient en fonction du titre.

Abstract Three systems exhibiting ferromagnetic‐antiferromagnetic coupling, CoCoO, NiFeNiFeMn, NiFeCr 2 O 3 , are studied using uniaxial thin films. A new property of such systems is found, i.e., a concentration of the hysteresis loops as a function of the number of cycles traced ( n ). This contraction follows a 1/ \documentclass{article}\pagestyle{empty}\begin{document}$\sqrt n $\end{document} n law for the first 50 cycles and is related to the rotational hysteresis. This phenomenon is attributed to fluctuations in the ferromagnetic‐antiferromagnetic coupling, which modify the magnetic interactions between differently coupled regions with each reversal.