Indentations have been performed on (001) faces of indium alloyed GaAs crystals in darkness and under infrared illumination. The Vickers hardness was measured and the dislocation microstructure around the indents observed by high voltage transmission electron microscopy. A softening effect of indium is evidenced by comparison with the Vickers hardness obtained in the same conditions on undoped GaAs. No significant influence of indium on the dislocation microstructure resulting from indentation in darkness is noted. Indentation under infrared illumination does not reveal any macroscopic photoplastic effect; however, a modification of dislocation microstructure is observed. Whatever the experimental conditions, dislocations appear to experience strong lattice friction. The softening effect of indium addition and the enhanced dislocation mobilities under infrared illumination are discussed in the framework of dislocation glide governed by the Peierls mechanism.

We present a Nuclear Quadrupole Resonance (NQR) study of Cu(2) (planes) and Cu(1) (chains) sites in two YBa2Cu3Oy≈7 powder samples with carbon concentration equal to 500 ppm and 3000 ppm, and in a free-carbon sample. By comparison with standard spectra in YBa2Cu3Oy, we show that a new NQR line appears at 30.90 MHz, the intensity of which is strongly correlated with the amount of carbon in the sample. Moreover, according to the spin-lattice relaxation rate 1/T1 measurements at different frequencies of the spectrum, we attribute this anomalous line to the formation of clusters in which the superconductivity is destroyed by the presence of carbonate groups, which substitute preferentially for copper chain site. Those results are in good agreement with those of Wang et al. [1], obtained by high resolution electron microscopy.

Long range ordering between chromium and thallium has been evidenced for the first time in copper oxychromate Tl3(CrO4)Sr8Cu4O16 using HREM, XRD and ND. This compound, which crystallizes in an orthorhombic cell with a = 3.7803(1) Å, b = 15.2573(2) Å and c = 17.6737(3) Å  derives from the "1201" TlSr2CuO5 structure by replacing one thallium oxygen polyhedra out of four by one CrO4 group in an ordered way. The Mayn features that characterize this original structure deal with the waving character of the [CuO2]∞ layers, and the absolute planar character of the [(Tl,Cr)O]∞ layers. In the [(Tl,Cr)O]∞ layers, the thallium and oxygen atoms form triple ribbons of edge-sharing TlO4 tetrahedra and TlO6 octahedra running along a, whereas the CrO4 tetrahedra are displayed in rows running along a, but are disconnected from each other and from the other polyhedra in the layer. Two kinds of CuO6 octahedra are observed, whose distortions originate from their connection with different polyhedra along c. This superconductor, whose Tc can be raised to 34 K after argon-hydrogen annealing, exhibits a rather high superconducting volume fraction (> 40%) compared to other "1201" thallium cuprates.

In situ elaboration of YBaCuO thin films, on polycrystalline yttria doped zirconia substrates, has been optimized. A reactive sputtering model has been developed and the electrical conductivity of the substrate has been studied as a function of temperature and doping. The Jc value of $\approx 3\times 10^4~{\rm A/cm}^2$ at 77 K, measured on microbridges, is among the best reported in the literature for this substrate type.

To understand the adhesion phenomena, we have studied the electric field effect on the gold thin films (< 100 Å) growth on ceramic substrate. Three parameters are studied in the too cases, with and without field: particles density, average size and substrate temperature. An electric field is applicated normaly to the surface and the adhesion is interpreted in terms of adhesion energy.

Industrial applications of the bulk superconducting YBa2Cu3O7 material imply to control the growth of large oriented monodomains in samples of big size (several centimeters). The laboratory EPM-Matformag is committed to produce such materials according to three different methods (zone melting, solidification controlled by a magnetic field, crystal growth from a seed). The results obtained show that it is possible by such methods to elaborate a material with high performances at the centimeter scale and to produce it in series. The availability of such materials allows the measure of physical properties on a large scale and the testing of prototypes for cryo-electrotechnical applications (magnetic bearing, flywheel, coupling device, current lead...).

The origin of the photoluminescence (PL) shifts in Porous Silicon (PS) is discussed according to a quantum confinement – based model, in which we modelize the PS layer as a mixture of quantum dots and wires. It was shown that a PL blueshift or redshift may occur during laser irradiation of PS, depending on preparation conditions. No PL shift was observed for some PS samples, even after a long ageing in air, due to the presence of an amorphous silicon phase detected from Raman spectroscopy measurements. It was found that the presence of the amorphous phase plays an important role in the PL behaviour of oxidised PS.

Un limiteur de courant supraconducteur pourrait être utilisé en haute tension. La plupart des matériaux à haute température critique existants actuels ont été testés en situation de limitation du courant. Les matériaux massifs sont classés par densité de courant critique croissante qui correspondent à des comportements différents. Le champ critique lors des transitions semble être de l'ordre de 1 kV/m.

Raman scattering can be used as an efficient probe with regard to the understanding of local structure in highly disordered films. This investigation is particularly fruitful if one takes into account Stokes, anti-Stokes and multiple-order processes. The interpretation is given in terms of the whole density of vibrational states. Some recent results obtained with amorphous Si, SiC and C films are presented. Comparison with other techniques, including numeric modelisations, are discussed.

SrTiO3 had been often tentatively used as an insulating barrier for HT superconductor/insulator heterostructures. Unfortunately, the deposition of SrTiO3 on the YBa2Cu3O7 inverse interface results in a poor epitaxial regrowth producing a high roughness dislocated titanate layer. Taking into account the good matching with YBa2Cu3O7 and LaAlO3, CeO2 and Ce1−xMxO2 (M = La, Zr), epitaxial layers were grown by pulsed laser deposition on LaAlO3 substrates and introduced into YBa2Cu3O7 based heterostructures as insulating barrier. After adjusting the growth parameters from RHEED oscillations, epitaxial growth is achieved, the oxide crystal axes being rotated by 45° from those of the substrate. The surface roughness of 250 nm thick films is very low with a rms value lower than 0.5 nm over 1 μm2. The YBa2Cu3O7 layers of a YBa2Cu3O7/CeO2 /YBa2Cu3O7 heterostructures grown using these optimized parameters show an independent resistive transition, when the thickness is larger than 25 nm, respectively at Tc1 = 89.6K and Tc2 = 91.4K.

Une méthode de synthèse simple, permettant de faire croître des monocristaux de composition ${\rm Hg}_{{\rm l}-x}{\rm M}_x{\rm Ba}_2{\rm Ca}_{n-1}{\rm Cu}_n {\rm O}_{2n+2+\delta}$ (n = 1, 2 et 3) sans utiliser de boîte à gants ou de techniques sous hautes pressions, a été developpée en substituant partiellement le mercure par un cation M (M = Bi, Cu, Ti). Des études par microscopie électronique couplées avec des analyses EDX ont confirmé les modes d'empilement et l'introduction de 1'é1ément M sous la forme de couches mixtes ${\rm Hg}_{0,8}{\rm M}_{0,2}$. Les études structurales réalisées par diffraction de rayons X sur monocristal ont mis en évidence un éclatement du site oxygène lié à la couche mercure. Ces monocristaux, bruts de synthèses, présentent des Tc comparables à celles observées dans les céramiques "tout mercure" correspondantes. L'étude des propriétés d'ancrage des vortex, menée sur les cristaux dopés au bismuth, confirme la position intermédiaire du terme n = 1 par rapport aux termes n = 2 et n = 3. De plus, une comparaison entre les cristaux de type 1223 (n = 3) dopés successivement au titane (${\rm Hg}_{0,6}{\rm Ti}_{0,4}{-}1223$) et au bismuth (${\rm Hg}_{0,8}{\rm Bi}_{0,2}{-}1223$) semble mettre en avant les valeurs du rapport Hg/M et du paramètre c sur ces propriétés.

We have studied the effect of the deposition conditions on the hydrogen incorporation modes and content and their effects on the optoelectronic properties of three different series of a-Si:H films prepared by R.F. magnetron sputtering at high substrate temperature (250 °C) and high deposition rates (~ 10 Å/s). We have correlated infrared absorption measurements with optical transmission and Photothermal Deflection Spectroscopy (PDS) experiments. The samples were characterized successively in their as-deposited state and after annealing at a temperature around 180 °C. The results indicate that the modes of H incorporation as well as the hydrogen content in the three series are completely different from those observed for the samples prepared by Plasma Enhanced Chemical Vapour Decomposition of pure silane (P.E.C.V.D.) at the same substrate temperature. The microstructure of the films is also different. The density of deep defects measured in the as-deposited is slightly higher in the former case. This density decreases significantly after annealing at 180 °C and becomes comparable to that obtained for a-Si:H samples prepared by P.E.C.V.D. at 250 °C at low deposition rates (~ 1 Å/s), with however a higher disorder in the R.F. sputtered films.

L'étude microstructurale des films minces supraconducteurs de formule générale : ${\rm (CaCuO_2)}_m{\rm (Ba_2CuO_2CO_3)}_n$, déposés à partir d'une seule cible, a montré qu'ils sont formés de nombreuses intercroissances. Ceci les rend pratiquement inutilisables pour des caractérisations physiques fines. Dans cet article sont présentées les étapes de la mise en oeuvre du système multicible nécessaire à la croissance d'un empilement régulier.

Les évolutions structurales développées dans un alliage à mémoire de forme du type Cu–Ni–Al (préalablement élaboré par fonderie, puis filé à chaud et finalement trempé à l'eau) ont été caractérisées par dilatométrie et analyse différentielle. La structure résultant de cette suite de traitements est du type martensite $\beta'_1$ ; elle présente une texture marquée, ce qui justifie qu'un effet mémoire se manifeste, sur la courbe dilatométrique au chauffage ($\rm 10~^\circ C/s$) – lequel se traduit par une contraction lors de la transition $\beta'_1\rightarrow\beta_1$. À température plus élevée, la phase $\beta_1$ se désordonne pour donner la phase β dont la structure est du type $\rm A_2$. Au refroidissement, la mise en ordre $\beta\rightarrow\beta_1$ se développe en deux étapes, quelle que soit la vitesse Vr mise en œuvre. Par contre, à plus basse température, les points Ms et Mf associés à la transformation martensitique $\beta_1\rightarrow\beta'_1$ évoluent en fonction de Vr ; en particulier, ils diminuent significativement quand cette vitesse devient suffisamment élevée. D'autre part, des essais par analyse enthalpique différentielle, effectués avec Vc = Vr = 2 °C min−1 sur l'alliage à l'état trempé, ont révélé que des processus de vieillissement se développaient, entre 200 et 350 °C, dans la phase $\beta_1$ ; des précipités de très faible taille sont alors formés, qui se dissolvent ensuite partiellement lorsque le chauffage est poursuivi entre 380 et 440 °C. À température encore plus élevée (500-560 °C), la phase $\beta_1$ se décompose pour donner les phases d'équilibre α et $\gamma_2$, lesquelles – à leur tour – se combinent pour former la phase β stable à haute température. Par refroidissement assez lent (2 °C min−1), l'alliage – préalablement porté à 620 °C – se retransforme en ($\alpha + \gamma_2$) selon la réaction eutectoïde prévue par le diagramme d'équilibre.

La densité de courant critique selon l'axe c (Jc) est mesurée à 77 K en transport et par des mesures magnétiques sur les mêmes échantillons texturés monodomaines d'YBaCuO. L'influence des plans de macles (TP) sur Jc et sur la ligne d'irréversibilité $B(T^*$) est étudiée en faisant tourner le champ dans les plans ab, perpendiculairement à l'axe c. Les résultats montrent que dans ces composés, Jc et $B(T^*$) sont fortement influencés par le piégeage par les TP. Divers comportements des lignes de flux résultant de l'influence de ces défauts corrélés sont proposés selon les gammes de température et de champ étudiées.

Afin de déterminer la capacité à limiter le courant du composé ${\rm Y}_1{\rm Ba}_2{\rm Cu}_3{\rm O}_{7-\delta}$ texturé, des études en courants de transport élevés, en régime pulsé et en régime permanent alternatif, ont été menées. Il en résulte que YBaCuO possède une forte capacité de transport du courant en régime pulsé (9000 A soit 23 000 $\ {\rm A} / {\rm cm}^2$ dans un barreau de 4 cm de long) et en régime permanent alternatif (3000 A soit 7800 $\ {\rm A} / {\rm cm}^2$) et que le retour à l'état normal par dépassement du courant critique est très abrupt.

A finite element method is presented to compute time harmonic microwave fields in three dimensional configurations. Nodal-based finite elements have been coupled with an absorbing boundary condition to solve open boundary problems. This paper describes how the modeling of large devices has been made possible using parallel computation. New algorithms are then proposed to implement this formulation on a cluster of workstations (10 DEC ALPHA 300X) and on a CRAY C98. Analysis of the computation efficiency is performed using simple problems. The electromagnetic scattering of a plane wave by a perfect electric conducting airplane is finally given as example.

We have performed experiments consisting to probe a multilayer material with a pulsed laser light flux and to measure the time dependent temperature at interfaces. A real time and high gray level imagery technique gives the backscattered flux at the entrance face of the composite and the incident heat flux entering in the slab. We further present an analytical model for studying transient diffusive phenomena in a one dimensional multilayer medium submitted to periodic external conditions. This approach uses a matricial formalism and the development of the incident thermal flux on an orthogonal complete base of rectangular functions called "Walsh functions". The use of the transfer matrix formulation then leads to a eigenvalues transcendental equation. The experimental method for steady or periodic heating of the slab together with the model predictions yields the thermo-physical parameters of the multilayer medium.

We have studied the effect of annealing on the structural and electrical properties of tin-doped indium oxyde, $\rm In _2O_3{:}Sn$ (ITO), thin films prepared by DC sputtering at different partial pressure of oxygen (ppo). Annealing experiments have been done in vacuum and in Ar atmosphere up to a temperature of 450 °C. A change of texture from $\langle 100\rangle $ to $\langle 111\rangle $ as the ppo was increased was noted in the as-deposited films. Annealing induced cristallinity and improved the texture of these films. The lattice constant decreased after annealing. The (222) grain size increased after vacuum annealing but was unaffected by annealing in Ar atmosphere; while the (400) grain size decreased for samples having the $\langle 100\rangle $ texture. The electrical resistivity decreases sharply after annealing to a minimum value of 87 × 10-4 Ω cm .