Strain mapping of ultrathin epitaxial ZnTe and MnTe layers embedded in CdTe

High-resolution electron microscopy is used to investigate the morphology of ultrathin pseudomorphic (001) ZnTe and MnTe strained layers grown in CdTe. Local distortions of the crystal lattice are measured directly on high-resolution images by use of image processing software. In the case of ZnTe/CdTe superlattices, the method yields the location of Zn within each place in the heterostructure and the total amount of Zn per period. For MnTe layers embedded in CdTe, one can deduce the atomic morphology of the interfaces which are shown to present a clear asymmetry

Analyse de PZT morphotropique par diffraction X haute température : influence du procédé d'élaboration sur la dispersion chimique

La solution solide PbZrxTi1-xO3, (PZT) présente à l'ambiante une zone morphotropique pour x voisin de 0,54 et pour laquelle coexistent deux phases de même composition chimique mais de structure différente (quadratique et rhomboédrique). Ces solutions sont classiquement obtenues par chamottage, réaction de synthèse souvent incomplète. Les deux phases constitutives du PZT présentent des variations de composition chimique autour de la composition moyenne et qui modifient de façon complexe le diffractogramme, empêchant son interprétation aisée. Nous présentons dans cet article une étude par diffraction X en température sur des PZT chamottés de façon différente. Les diffractogrammes sont enregistrés à 550°C, température pour laquelle il n'existe qu'une seule phase cubique. Les pics sont considérés comme résultant d'une solution cubique de composition moyenne déterminée par les positions des maxima. De la mesure des largeurs de raies, est calculée une fluctuation de paramètre de maille, puis une fluctuation chimique à l'aide d'une courbe d'étalonnage réalisée à partir d'un lot de PZT de compositions déterminées par fluorescence X, technique ayant fait l'objet d'une optimisation particulière.By means of temperature x-ray diffraction, we estimate the compositional fluctuation in morphotropic PbZrxTi1-xO3 (PZT) solid solutions. In these systems, near the morphotropic phase boundary (x≈ 0.54), the tetragonal and rhomboedral phases coexist at room temperature, with respective constant lattice parameters and with relative amounts according to the average law. Because of the overlapping and the broadening of the diffraction lines, the morphotropic PZT x-ray pattern is complex. A convenient method is to measure diagrams at 550°C, temperature above Curie temperature (490°C) for which the PZT had cubic symmetry. From the observed line broadening, a fluctuation of lattice spacing is calculated. The compositional fluctuation is then deduced from a calibration curve made out with some PZT samples whose compositions are determined by x-ray fluoresence

On the use of the automobile code of colors in the housing environment context for persons in loss of autonomy

International audienceThe persons in loss of autonomy have several sociological and psychological blockings in using the technologies aimed to reduce their dependence. Thus, it is important to offer non neither intrusive nor stigmatizing solutions. It becomes necessary to propose schemes to allow these people to appropriate more easily the home automation and information technologies equipments installed in their housing environment. In our approach, we consider that the potential users of these technologies already had an automobile. We thus proposed the transfer of technologies initially dedicated to the automobile domain to the housing of the persons in loss of autonomy with the following concept: can the principles of communication, safety and protection used for the automobile be transposed to the housing context? The car manufacturers have created an effective descriptive system thanks to a green/orange/red visual code having a universal meaning. These colors were chosen because of the ability of the brain to get them quickly. The dashboard of the car perfectly integrates a set of logos based on these three colors. The brief appearance of a logo using one of these colors activates an immediate reaction of the person. Red means an immediate danger, orange call a greater surveillance and green is indicative and tolerant. The color code now overcomes the frame of the automobile and becomes a way of perceiving the environment in the daily life. It is thus interesting to study the transposition of this code and related logos to reduce the loss of autonomy. A possible application concerns the elders and the people affected by the Alzheimer's disease using the chromatic perception. In a first step, the association of the color code with the perception of the space allows to guide and to insure the fragile persons within their own environment. A second step consists in integrating chromic materials in the design of technological objects and items for the persons in loss of autonomy. The col! or of these smart materials changes reversibly according to various stimuli applied (heat, humidity, pressure, electricity, light ...). The red/orange/green code can then be chosen here also for a wide range of applications

Caractérisation de poudres de zircone synthétisées par voie hydrothermale

A new process, based on the simultaneous gelling of alumina/zirconia precursors followed by hydrothermal treatment, may be used to produce mixed oxides composite powders with increased homogeneity. The aim of this paper is to present zirconia powders characteristics as a function of synthesis conditions. Crystallite sizes are determined by X-ray diffraction, specific surface area by B.E.T. method, density by helium pycnometry. Powders are observed by T.E.M..La synthèse hydrothermale permet la réalisation de poudres fines cristallisées et désagglomérées. Ces qualités sont appropriées à l'élaboration de composites fins oxyde/oxyde par synthèse simultanée des deux phases. Nous avons développé ce protocole pour la réalisation de nanocomposites alumine/zircone (Q). Nous présentons ici plus particulièrement le travail effectué sur la zircone. Les conditions de traitement hydrothermal et d'un traitement thermique modéré supplémentaire sont analysées en relation avec les caractéristiques des poudres synthétisées. Différentes techniques complémentaires sont utilisées pour ces poudres de zircone : diffraction des rayons X (% de la phase quadratique, taille des cristallites), B.E.T. (surface spécifique), pycnométrie hélium (densité), morphologie (observations M.E.T.)

Interdiffusion studies in CdTe/HgTe superlattices

SIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : RM 1386 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Structural and Optical Studies of CdTe/ZnTe Superlattices with Ultrathin ZnTe Layers

Spatially selective introduction of ultrathin ZnTe layers (1 to 3 mono-layers) into CdTe allows the study of special superlattice structure, corresponding to a monomolecular plane-host crystal system. Particular attention is given to the strain state control of the inserted ZnTe monolayer. High resolution electron microscopy is used to measure the local lattice distortion: the method yields the location and the total amount of Zn per period, and the results are compared with X-ray diffraction data. Optical properties of these superlattices are also presented. All results show the ability to control ultrathin pseudomorphic layers of ZnTc within CdTe, with limited Zn segregation, and of high crystalline and optical quality. In addition, they can be fitted within the framework of elasticity theory for the structural data, and of a finite quantum well model for the optical ones, even in the ultimate limit of only one nominal ZnTe monolayer