From metastable to stable modifications-in situ Laue diffraction investigation of diffusion processes during the phase transitions of (GeTe)(n)Sb2Te3 (6 < n < 15) crystals.

Temperature dependent phase transitions of compounds (GeTe)nSb2Te3 (n = 6, 12, 15) have been investigated by in situ microfocus Laue diffraction. Diffusion processes involving cation defect ordering at B300 8C lead to different nanostructures which are correlated to changes of the thermoelectric characteristics

Unraveling the strain state of GaN down to single nanowires

GaN nanowires (NWs) grown by molecular beam epitaxy are usually assumed free of strain in spite of different individual luminescence signatures. To ascertain this usual assumption, the c/a of a GaNNW assembly has been characterized using both X-ray diffraction and Raman spectroscopy, with scaling the measurement down to the single NW. Free-standing single NWs have been observed free of strain defined as [c/a-(c/a)o]/(c/a)o within the experimental accuracy mounting to 1.25 × 10-4. However, in the general case, a significant portion of the NWs is coalesced, generating an average tensile strain that can be partly released by detaching the NWs from their substrates. It is concluded that at the scale of the single NW, the free surface and the residual doping do not generate a significant strain and only coalescence does

Fundamental research using synchrotron X-rays on key technological materials

While writing this HDR manuscript, I took the opportunity to look back on my professional carrier to realise I had conducted numerous studies of fundamental research using different synchrotron techniques. I think I am fundamentally curious and therefore I like to discover new or emerging fields of research since it challenges my understanding and possesses a large exploration aspect. As a consequence, I am not a specialist dedicated to one field of research but I develop collaboration with various groups: I've been working on a wide range of research fields, each research field being linked to the problematic of the group I develop collaboration with. And looking back on those years, I noticed that in my collaborations, my contribution was always to provide understanding of key technological material under development, hence the title of this manuscript.Despite it will not be fully developed in this manuscript, there was also a very nice engineering aspect to my career since I have significantly contributed to the construction of two French beamlines at ESRF. From 1999 to 2003, I help built the forth French CRG beamline at ESRF named BM30B-FAME (French Absorption spectroscopy beamline in Material and Environmental sciences) with the complete definition of required beamline characteristics for EXAFS studies on diluted systems (<10 ppm), as well as its components tuning once operational. From 2004 to 2012, I help refurbish the historical first French CRG beamline at ESRF BM32-IF (InterFace) with full re-definition and construction of all beamline optical elements as well as the development of the first European whitebeam (4-40 keV) of submicronic size and its dedicated µLaue station for which I will give some details.Thanks to these two beamlines, I was able to become competent in two emblematic synchrotron techniques that are EXAFS and white beam Laue microdiffraction. Emblematic since they require a continuously adjustable and very bright X-ray energy on a very broad energy range, a challenge only synchrotron may take up.Among all my collaborations, two of them were really long-term collaborations and I choose to present them with some details. The first long-term collaboration is the object of chapter ‘I-Phase-change materials’, was dedicated to the study of phase-change materials, covers the 1999→2012 period and makes extensive use of the EXAFS technique. The second long-term collaboration is presented chapter ‘III-High-performance IR detection’, is dedicated to IR material, covers the 2006→2018 period, is still ongoing and makes extensive use of the white beam Laue microdiffraction detailed into part ‘II-‎The µLaue setup’.And finally, because research appears to me as an exciting never-ending journey into wonderland, I will expose in part ‘IV-Research perspectives’ some of my research perspectives

Diffraction de Laue sub-micronique à très haute résolution pour l’étude de la contrainte et de la plastification d’hétérostructures fragiles HgCdTe/CdZnTe

International audienceHigh resolution sub-micronic Laue diffraction used to study strain and plastification of HgCdTe/CdZnTe fragile heterostructuresDiffraction de Laue sub-micronique à très haute résolution pour l’étude de la contrainte et de la plastification d’hétérostructures fragiles HgCdTe/CdZnT

Diffraction de Laue sub-micronique à très haute résolution pour l’étude de la contrainte et de la plastification d’hétérostructures fragiles HgCdTe/CdZnTe

International audienceHigh resolution sub-micronic Laue diffraction used to study strain and plastification of HgCdTe/CdZnTe fragile heterostructuresDiffraction de Laue sub-micronique à très haute résolution pour l’étude de la contrainte et de la plastification d’hétérostructures fragiles HgCdTe/CdZnT

Extended x-ray absorption fine structure study of arsenic in HgCdTe: p-type doping linked to nonsubstitutional As incorporation in an unknown AsHg8 structure

International audienceAn extended x-ray absorption fine structure (EXAFS) investigation has been carried out on arsenic-doped Hg70Cd30Te samples. The incorporation of atomic arsenic has been achieved using a nonconventional radio-frequency plasma source in a molecular beam epitaxy reactor. Two samples from the same epitaxial wafer have been studied. One underwent a 400°C activation annealing under Hg pressure, leading to n to p-type conversion. In the commonly admitted scenario, this conversion is associated with the annealing-induced migration of As from a Hg site to a Te site. This study shows that this is not the case. Before annealing, As is found to be involved in noncrystalline structures: 50% inside an As2Te3 chalcogenide glass and 50% inside a new AsHg8 compact structure. After annealing, the As2Te3 chalcogenide glass disappears, 31% of As occupies Hg sites and 69% incorporates inside this new AsHg8 compact structure that occupies Te sites. The EXAFS results are in excellent agreement with 77K Hall-effect measurements. The new AsHg8 structure is found to have an acceptor behavior. Overall, this study provides an entirely new vision of extrinsic p-type doping of HgCdTe as well as the first experimental evidence of As site transfer induced by annealing

Sign of the nonlinear dielectric susceptibility of amorphous and crystalline SrTiO 3 films

International audienc

Using 2D integral breadth to study plastic relaxation in a quasi-lattice-matched HgCdTe/CdZnTe heterostructure

International audienceMicro-Laue diffraction has been used to record cross-section profiles on a quasi-lattice-matched HgCdTe/CdZnTe heterostructure as a function of the stress induced by a flexion machine. The heterostructure may be decomposed into four different regions according to depth. Sufficiently far from the interface, the CdZnTe substrate is undisturbed by the HgCdTe layer, while the region situated 10 µm beneath the interface presents an in-plane lattice parameter adjustment to the +0.02% mismatched layer. The layer has a 2 µm critical thickness and, beyond, misfit dislocations induce a large peak broadening whose main direction changes with depth. The same occurs over the whole heterostructure once flexion-induced plastification has started. Consequently, the usual full width at half-maximum or integral breadth is no longer relevant, and only a newly defined and rotationally invariant 2D integral breadth correctly measures the plastification-induced peak broadening. Taking into account only the critical thickness region, a 15.1 ± 0.7 MPa tensile HgCdTe elastic limit was measured, slightly overestimated because of the initial compressive layer stress. It was observed that the plastic onset of the substrate perfectly matches the elastic limit of the layer, despite the fact that the substrate elastic limit is expected to be four times higher: a striking demonstration of the propagation of threading dislocations. The `plastification easiness' is found to be 2.4 times smaller deep inside the substrate than in the layer critical thickness region, while in the substrate lattice adjustment region, the plastification easiness goes from the substrate to the layer value with a 22–25 MPa transition interval. This novel method using the 2D integral breadth allows for easy critical thickness measurement as well as precise plastic onset determination and plastification easiness assessment. It is a quite general method, since it may be applied to the vast class of epitaxial layers for which the critical thickness is larger than the micro-Laue beam size (currently 250 nm)

Investigations structurales haute-résolution de photodiodes infrarouges de nouvelle génération

Cette thèse concerne le domaine des détecteurs infrarouges HgCdTe utilisés pour la vision nocturne, pour lequel le Laboratoire Infrarouge du CEA-Leti-Minatec est un des leaders mondiaux. L'étudiant participera à l'élaboration complète d'un détecteur bi-spectral permettant de détecter simultanément plusieurs parties du spectre IR. La zone active est une superposition de couches nanométriques dopées lors de la croissance par épitaxie par jets moléculaires, qui est ensuite subdivisée en matrices de photodiodes de taille micrométrique par gravure avant passivation. Des techniques d'investigation tout à fait spécifiques et extrêmement sensibles, utilisant le rayonnement synchrotron et les faisceaux d'ions, seront utilisées pour étudier ces structures et déterminer les propriétés locales des matériaux processés. Notamment, l'environnement immédiat des dopants, les contraintes liées à la gravure et les déplacements atomiques induits par les procédés de fabrication seront déterminés.Cette thèse concerne le domaine des détecteurs infrarouges HgCdTe utilisés pour la vision nocturne, pour lequel le Laboratoire Infrarouge du CEA-Leti-Minatec est un des leaders mondiaux. L'étudiant participera à l'élaboration complète d'un détecteur bi-spectral permettant de détecter simultanément plusieurs parties du spectre IR. La zone active est une superposition de couches nanométriques dopées lors de la croissance par épitaxie par jets moléculaires, qui est ensuite subdivisée en matrices de photodiodes de taille micrométrique par gravure avant passivation. Des techniques d'investigation tout à fait spécifiques et extrêmement sensibles, utilisant le rayonnement synchrotron et les faisceaux d'ions, seront utilisées pour étudier ces structures et déterminer les propriétés locales des matériaux processés. Notamment, l'environnement immédiat des dopants, les contraintes liées à la gravure et les déplacements atomiques induits par les procédés de fabrication seront déterminés

Investigations structurales haute-résolution de photodiodes infrarouges de nouvelle génération

Cette thèse concerne le domaine des détecteurs infrarouges HgCdTe utilisés pour la vision nocturne, pour lequel le Laboratoire Infrarouge du CEA-Leti-Minatec est un des leaders mondiaux. L'étudiant participera à l'élaboration complète d'un détecteur bi-spectral permettant de détecter simultanément plusieurs parties du spectre IR. La zone active est une superposition de couches nanométriques dopées lors de la croissance par épitaxie par jets moléculaires, qui est ensuite subdivisée en matrices de photodiodes de taille micrométrique par gravure avant passivation. Des techniques d'investigation tout à fait spécifiques et extrêmement sensibles, utilisant le rayonnement synchrotron et les faisceaux d'ions, seront utilisées pour étudier ces structures et déterminer les propriétés locales des matériaux processés. Notamment, l'environnement immédiat des dopants, les contraintes liées à la gravure et les déplacements atomiques induits par les procédés de fabrication seront déterminés.Cette thèse concerne le domaine des détecteurs infrarouges HgCdTe utilisés pour la vision nocturne, pour lequel le Laboratoire Infrarouge du CEA-Leti-Minatec est un des leaders mondiaux. L'étudiant participera à l'élaboration complète d'un détecteur bi-spectral permettant de détecter simultanément plusieurs parties du spectre IR. La zone active est une superposition de couches nanométriques dopées lors de la croissance par épitaxie par jets moléculaires, qui est ensuite subdivisée en matrices de photodiodes de taille micrométrique par gravure avant passivation. Des techniques d'investigation tout à fait spécifiques et extrêmement sensibles, utilisant le rayonnement synchrotron et les faisceaux d'ions, seront utilisées pour étudier ces structures et déterminer les propriétés locales des matériaux processés. Notamment, l'environnement immédiat des dopants, les contraintes liées à la gravure et les déplacements atomiques induits par les procédés de fabrication seront déterminés