Search

H. Klym thanks to the Ministry of Education and Science of Ukraine for support and Dr. P. Demchenko for the assistance in XRD experiments., Crystallization transformation in the 80GeSe2-20Ga2Se3 chalcogenide glasses caused by annealing at 380 °C during different duration (25, 50, 80 and 100 hours) are studied using X-ray diffraction and atomic force microscopy methods. It is established that GeGa4Se phase of low- and high-temperature modification, Ga2Se3 phase (α- and γ-modification) and GeSe2 phases are crystallized during this process. It is shown that annealing duration over 50 h does not lead to further internal structural crystallization, while annealing for 80 h result in processes of surface crystallization., Ministry of Education and Science of Ukraine; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²

Within the general goal of reaching high operating temperature while maintaining strong requirements on infrared photodetector performances, the pressure on HgCdTe material quality is increasingly growing. In particular, careful attention is now being paid to stress and stress relaxation within HgCdTe photodiodes. While recent studies have focused on the lattice mismatch induced strain over areas in the order of the wafer, no experimental investigation has been able to resolve the strain at the micrometer level.The typical millimetric spatial resolution limit of standard diffraction can be overtaken using a focused synchrotron X-ray white beam. Indeed, by performing Laue microdiffraction measurements, we can map with a sub-micrometer resolution both the local deviatoric strain and lattice orientation. This thesis focuses on the analysis of etched trenches inside HgCdTe layers with variations on passivation and annealing steps. We are able to investigate a precise mapping around the etching and appreciate the local effects of the processing steps. Diffraction peak displacement mapping evidences bending of the crystal planes around etched trenches, with strong dependence upon the processing steps.Then, we focus on the relative position of all the peaks which are measured simultaneously. Assuming a bi-axial strain between layer and substrate, the slope of the peak relative displacement as a function of their position directly provides the strain value undergone by the material. Thus, we measure the strain through the entire sample with a precision of 3.10-5 and map it with a sub-micronic position precision.Finally, we show how the use of a three point calibrated bending set-up leads to the experimental determination of the plasticity threshold in HgCdTe/CdZnTe epitaxial structures together with the spatial distribution of the applied strain. The dynamics from elastic to plastic regime and the layer behavior once the plastic threshold is reached are investigated. Furthermore, the etching step creates abrupt edges inside the layer, leading to a modification of the strain field by concentrating it on the angles of the trench.; Dans le but d'atteindre une température de fonctionnement élevée tout en conservant de fortes exigences sur les performances des photodétecteurs infrarouges, la pression sur la qualité du matériau HgCdTe augmente de plus en plus. En particulier, une attention spéciale est maintenant portée aux contraintes et à leur relaxation des photodiodes HgCdTe. Bien que de récentes études se soient concentrées sur la déformation induite par un désaccord paramétrique sur des surfaces de la taille d'un plaque, aucune étude expérimentale n'a été capable de résoudre la déformation au niveau micrométrique.La limite de résolution spatiale millimétrique typique de la diffraction standard peut être dépassée en utilisant un faisceau synchrotron de rayons X focalisés. En effet, en effectuant des mesures de microdiffraction Laue, nous pouvons cartographier, avec une résolution submicronique, à la fois la contrainte déviatorique locale et l'orientation de la maille. Cette thèse se concentre sur l'analyse de tranchées gravées à l'intérieur des couches de HgCdTe avec des variations sur les étapes de passivation et de recuit. Nous sommes en mesure d'étudier une cartographie précise autour de la gravure et d'apprécier les effets locaux des étapes de traitement. La cartographie de déplacement des pics de diffraction montre la courbure des plans cristallins autour des tranchées gravées, avec une forte dépendance aux étapes technologiques.Ensuite, nous nous concentrons sur la position relative de tous les pics, qui sont mesurés simultanément. En supposant une contrainte bi-axiale entre la couche et le substrat, la pente du déplacement relatif du pic en fonction de leur position fournit directement la valeur de contrainte subie par le matériau. Ainsi, nous mesurons la déformation à travers l'ensemble de l'échantillon avec une précision de 3.10-5 et la cartographions avec une précision de position submicronique.Enfin, nous montrons comment l'utilisation d'un système de flexion 3 points conduit à la détermination expérimentale du seuil de plasticité dans les structures épitaxiées HgCdTe / CdZnTe ainsi qu'à la distribution spatiale de la contrainte appliquée. La dynamique du régime élastique au régime plastique et le comportement de la couche une fois que le seuil plastique est atteint sont étudiés. De plus, l'étape de gravure crée des bords abrupts à l'intérieur de la couche, conduisant à une modification du champ de contrainte en la concentrant sur les angles de la tranchée.

Within the general goal of reaching high operating temperature while maintaining strong requirements on infrared photodetector performances, the pressure on HgCdTe material quality is increasingly growing. In particular, careful attention is now being paid to stress and stress relaxation within HgCdTe photodiodes. While recent studies have focused on the lattice mismatch induced strain over areas in the order of the wafer, no experimental investigation has been able to resolve the strain at the micrometer level.The typical millimetric spatial resolution limit of standard diffraction can be overtaken using a focused synchrotron X-ray white beam. Indeed, by performing Laue microdiffraction measurements, we can map with a sub-micrometer resolution both the local deviatoric strain and lattice orientation. This thesis focuses on the analysis of etched trenches inside HgCdTe layers with variations on passivation and annealing steps. We are able to investigate a precise mapping around the etching and appreciate the local effects of the processing steps. Diffraction peak displacement mapping evidences bending of the crystal planes around etched trenches, with strong dependence upon the processing steps.Then, we focus on the relative position of all the peaks which are measured simultaneously. Assuming a bi-axial strain between layer and substrate, the slope of the peak relative displacement as a function of their position directly provides the strain value undergone by the material. Thus, we measure the strain through the entire sample with a precision of 3.10-5 and map it with a sub-micronic position precision.Finally, we show how the use of a three point calibrated bending set-up leads to the experimental determination of the plasticity threshold in HgCdTe/CdZnTe epitaxial structures together with the spatial distribution of the applied strain. The dynamics from elastic to plastic regime and the layer behavior once the plastic threshold is reached are investigated. Furthermore, the etching step creates abrupt edges inside the layer, leading to a modification of the strain field by concentrating it on the angles of the trench.; Dans le but d'atteindre une température de fonctionnement élevée tout en conservant de fortes exigences sur les performances des photodétecteurs infrarouges, la pression sur la qualité du matériau HgCdTe augmente de plus en plus. En particulier, une attention spéciale est maintenant portée aux contraintes et à leur relaxation des photodiodes HgCdTe. Bien que de récentes études se soient concentrées sur la déformation induite par un désaccord paramétrique sur des surfaces de la taille d'un plaque, aucune étude expérimentale n'a été capable de résoudre la déformation au niveau micrométrique.La limite de résolution spatiale millimétrique typique de la diffraction standard peut être dépassée en utilisant un faisceau synchrotron de rayons X focalisés. En effet, en effectuant des mesures de microdiffraction Laue, nous pouvons cartographier, avec une résolution submicronique, à la fois la contrainte déviatorique locale et l'orientation de la maille. Cette thèse se concentre sur l'analyse de tranchées gravées à l'intérieur des couches de HgCdTe avec des variations sur les étapes de passivation et de recuit. Nous sommes en mesure d'étudier une cartographie précise autour de la gravure et d'apprécier les effets locaux des étapes de traitement. La cartographie de déplacement des pics de diffraction montre la courbure des plans cristallins autour des tranchées gravées, avec une forte dépendance aux étapes technologiques.Ensuite, nous nous concentrons sur la position relative de tous les pics, qui sont mesurés simultanément. En supposant une contrainte bi-axiale entre la couche et le substrat, la pente du déplacement relatif du pic en fonction de leur position fournit directement la valeur de contrainte subie par le matériau. Ainsi, nous mesurons la déformation à travers l'ensemble de l'échantillon avec une précision de 3.10-5 et la cartographions avec une précision de position submicronique.Enfin, nous montrons comment l'utilisation d'un système de flexion 3 points conduit à la détermination expérimentale du seuil de plasticité dans les structures épitaxiées HgCdTe / CdZnTe ainsi qu'à la distribution spatiale de la contrainte appliquée. La dynamique du régime élastique au régime plastique et le comportement de la couche une fois que le seuil plastique est atteint sont étudiés. De plus, l'étape de gravure crée des bords abrupts à l'intérieur de la couche, conduisant à une modification du champ de contrainte en la concentrant sur les angles de la tranchée.

The CuxNi1−xFe2O4 (x = 0.0, 0.2, 0.5, 0.8, 1.0) nanoferrite powder were synthesized through chemical co-precipitation method using only (FeCl3, 6H2O), (NiCl2, 6H2O), (CuCl2, 4H2O), NaOH and acid oleic as raw materials. The synthesized powder was characterized by X-ray diffraction (XRD); it was used to determine the structural properties. The transmission electron microscopy and the scanning electron microscopy were used to determine the morphology and particle size. The Fourier Transform Infra-Red (FT-IR) spectroscopy is used to deduce the structural investigation and confirmation of ferrite. Raman spectroscopy is used to verify that we have synthesized CuxNi1−xFe2O4 and determines their phonon modes. The thermo gravimetric analysis findings allow the thermal cycle determination of samples whereas differential thermal analysis findings allow the phase transition temperature identification. The optical study UV–Visible is used to calculate the band gap energies. The vibrating sample magnetometer was used to obtain the hysteresis parameters. In conclude, the XRD confirmed the single phase spinel structure. The lattice constant increased with the increased copper contents. The size of nanoparticles decreased with the increased copper contents. The magnetic property of the CuxNi1−xFe2O4 shows remarkable changes with change of Cu2+.The variation of copper substitution has a significant influence on the optical, grain size and magnetic properties. The mean crystalline size of the synthesized ferrite was in the range of 14–43 nm., The present work was supported by the Research Funds of Electrochemistry, Materials and Environment Research Unit UREME (UR17ES45), Faculty of Sciences Gabes University, Tunisia and Structures, Properties and Modeling of Solids (SPMS) Laboratory, Ecole Centrale Paris, France.

cited By 0; Conference of 11th IEEE Nanotechnology Materials and Devices Conference, NMDC 2016 ; Conference Date: 9 October 2016 Through 12 October 2016; Conference Code:125383; International audience; We demonstrated the high throughput production of ultra-thin SiNWs by the innovative Inductively Coupled Plasma (ICP) approach. Our investigations revealed that the vast majority (∼95%) of the ICP produced SiNWs grew according to the Oxide Assisted Growth mechanism, and the 5% through the Vapor-Liquid-Solid mechanism. These SiNWs present an intriguing internal nanostructure, that provides a new kind of nanocomposite, where quantum confinement effects are expected. Indeed, an intense photoluminescence emission in the near infra-red was observed. These results prove the ICP as a genuinely bulk process, which can be exploited for large scale production of thin SiNWs to be integrated into attractive large-area and flexible optoelectronic devices.

cited By 18; International audience; Third-generation TiO2 photocatalysts were prepared by implantation of C+ ions into 110nm thick TiO2 films. An accurate structural investigation was performed by Rutherford backscattering spectrometry, secondary ion mass spectrometry, X-ray diffraction, Raman-luminescence spectroscopy, and UV/VIS optical characterization. The C doping locally modified the TiO2 pure films, lowering the band-gap energy from 3.3eV to a value of 1.8eV, making the material sensitive to visible light. The synthesized materials are photocatalytically active in the degradation of organic compounds in water under both UV and visible light irradiation, without the help of any additional thermal treatment. These results increase the understanding of the C-doped titanium dioxide, helpful for future environmental applications.

International audience; This work focuses on the structural and electrical characterization of La-Ni-O coatings deposited by reactive magnetron sputtering using Plasma Emission Monitoring (PEM) which allows high deposition rate. The optimal regulation setpoint for lanthanumdeposition is determined and then the current dissipated on the nickel target is adjusted to obtain the convenient La/Ni ratio to achieve the K2NiF4 structure. After an appropriate annealing treatment, all coatings exhibit crystalline structures that depend on the La/Ni ratio. Some cracks appear on samples deposited on alumina substrates depending to the argon flow rate and influence their electrical behavior.

International audience; A rational approach for the construction of multistranded artificial beta-sheets based not on hydrogen bonding, but on pi-pi aromatic stacking is presented. Using 4,6-dinitro,3,5-phenylenediamine units, rigid turns were designed that allow face-to-face pi-pi interactions between appended linear aromatic segments to be strong enough for folding in an organic solvent, but weak enough to prevent aggregation and precipitation. Solution and solid state studies on a series of turn units showed that the desired degree of rigidity, resulting from hindered bond rotation, could be fine tuned by the inclusion of additional methyl substituents on the aromatic rings. The high degree of preorganization afforded by these qualities further allowed the facile preparation of macrocyclic sheet structures from their non cyclic precursors. These macrocycles were shown to have slow internal dynamics and defined conforma-tional preferences. Using this background three and five-stranded artificial beta-sheets were synthesized and their folded conformations extensively characterized in solution by NMR. The solid state structures of the three and five-stranded sheets were also elucidated in the solid state by x-ray crystallography and confirmed intramolecular pi-pi aromatic stacking.

Thermally grown amorphous SiO2 was implanted at room temperature with heavy noble gases Kr and Xe in order to create cavities in the oxide and increase its porosity. The implantation energies were chosen in order to have the same implantation depth for both ions. Although both ions induce bubbles in amorphous SiO2, bubble size and spatial distribution depend upon the ion mass. Moreover, Xe implantation leads to the additional formation of "nanoclusters". Thermal stability of bubbles/cavities depends on the implanted ion. The nucleation of bubbles and nanoclusters in amorphous SiO2 is discussed in terms of ion mobility, gas-defect interactions, and chemical interaction. Bubble growth is shown to occur by a migration and coalescence process.