Nanofils ferromagnétiques auto-assemblés en matrice d'oxyde : croissance, épitaxie verticale et propriétés magnétiques

In this PhD thesis, we study the growth and the properties of ferromagnetic nanowires made of cobalt, nickel and cobalt-nickel, embedded in a matrix made of of strontium and baryum titanate. The nanowires are grown taking advantage of self-assembly processes occurring during sequential pulsed laser deposition. First, we model the growth with a kinetic Monte-Carlo code to highlight the parameters that control the diameter and the density of the nanowires. Then, it is shown that the nanowires are strained along their axis, and relaxed perpendicular to it. The origin of the strained state is explained in the framework of the Frenkel-Kontorova model, and its inhomogeneities are described through analysis of mappings of the reciprocal space. Furthermore, it is shown that the strain is high enough to shift the magnetic easy axis of the nickel nanowires, through magneto-elastic coupling. Finally, for Co0.4Ni0.6 nanowires with a diameter greater than four nanometers, the blocking temperature of the assembly is above room temperature and the energy barrier for the magnetic reversal of the nanowires is of the order of one electronvolt. This is interesting for potential applications in data storage, for example.Cette thèse présente l'élaboration et l'étude de nanofils ferromagnétiques de cobalt, nickel et d'alliages cobalt-nickel épitaxiés en matrice de titanate de strontium et de baryum. Les fils sont élaborés par auto-assemblage lors de dépôts séquentiels par ablation laser pulsé. Tout d'abord, les paramètres de croissance permettant de contrôler le diamètre des fils et leur densité sont mis en évidence en modélisant la croissance de l'hétéro-structure par simulations Monte-Carlo cinétique. Ensuite, on montre que les fils sont dilatés axialement et relaxés radialement. L'origine de l'état dilaté est expliquée en adaptant le modèle de Frenkel-Kontorova à notre situation et les inhomogénéités de déformation des nanofils sont décrites en analysant des cartographies de l'espace réciproque. La dilatation crée une anisotropie magnétique, par couplage magnéto-élastique, qui, dans le cas du nickel, peut compenser l'anisotropie de forme des fils. Enfin, pour des fils de Co0.4Ni0.6 de diamètre supérieur à quatre nanomètres, la température de blocage de l'assemblée de fils est supérieure à la température ambiante et la barrière d'énergie du renversement magnétique est de l'ordre d'un électronvolt, ce qui est intéressant pour d'éventuelles applications, par exemple en enregistrement de données

The bidirectional tumor - mesenchymal stromal cell interaction promotes the progression of head and neck cancer

Introduction: Mesenchymal stromal cells (MSC) are an integral cellular component of the tumor microenvironment. Nevertheless, very little is known about MSC originating from human malignant tissue and modulation of these cells by tumor-derived factors. The aim of this study was to isolate and characterize MSC from head and neck squamous cell carcinoma (HNSCC) and to investigate their interaction with tumor cells. Methods: MSC were isolated from tumor tissues of HNSCC patients during routine oncological surgery. Immunophenotyping, immunofluorescence and in vitro differentiation were performed to determine whether the isolated cells met the consensus criteria for MSC. The cytokine profile of tumor-derived MSC was determined by enzyme-linked immunosorbent assay (ELISA). Activation of MSC by tumor-conditioned media was assessed by measuring cytokine release and expression of CD54. The impact of MSC on tumor growth in vivo was analyzed in a HNSCC xenograft model. Results: Cells isolated from HNSCC tissue met the consensus criteria for MSC. Tumor-derived MSC constitutively produced high amounts of interleukin (IL)-6, IL-8 and stromal cell-derived factor (SDF)-1α. HNSCC-derived factors activated MSC and enhanced secretion of IL-8 and expression of CD54. Furthermore, MSC provided stromal support for human HNSCC cell lines in vivo and enhanced their growth in a murine xenograft model. Conclusions: This is the first study to isolate and characterize MSC from malignant tissues of patients with HNSCC. We observed cross-talk of stromal cells and tumor cells resulting in enhanced growth of HNSCC in vivo

Search for eccentric black hole coalescences during the third observing run of LIGO and Virgo

Despite the growing number of confident binary black hole coalescences observed through gravitational waves so far, the astrophysical origin of these binaries remains uncertain. Orbital eccentricity is one of the clearest tracers of binary formation channels. Identifying binary eccentricity, however, remains challenging due to the limited availability of gravitational waveforms that include effects of eccentricity. Here, we present observational results for a waveform-independent search sensitive to eccentric black hole coalescences, covering the third observing run (O3) of the LIGO and Virgo detectors. We identified no new high-significance candidates beyond those that were already identified with searches focusing on quasi-circular binaries. We determine the sensitivity of our search to high-mass (total mass M>70 M⊙) binaries covering eccentricities up to 0.3 at 15 Hz orbital frequency, and use this to compare model predictions to search results. Assuming all detections are indeed quasi-circular, for our fiducial population model, we place an upper limit for the merger rate density of high-mass binaries with eccentricities 0<e≤0.3 at 0.33 Gpc−3 yr−1 at 90\% confidence level

Ultralight vector dark matter search using data from the KAGRA O3GK run

Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we present the result of a search for U(1)B−L gauge boson DM using the KAGRA data from auxiliary length channels during the first joint observation run together with GEO600. By applying our search pipeline, which takes into account the stochastic nature of ultralight DM, upper bounds on the coupling strength between the U(1)B−L gauge boson and ordinary matter are obtained for a range of DM masses. While our constraints are less stringent than those derived from previous experiments, this study demonstrates the applicability of our method to the lower-mass vector DM search, which is made difficult in this measurement by the short observation time compared to the auto-correlation time scale of DM

Self-assembled ferromagnetic nanowires embedded in an oxide matrix : growth, vertical epitaxy, magnetic properties

Cette thèse présente l'élaboration et l'étude de nanofils ferromagnétiques de cobalt, nickel et d'alliages cobalt-nickel épitaxiés en matrice de titanate de strontium et de baryum. Les fils sont élaborés par auto-assemblage lors de dépôts séquentiels par ablation laser pulsé. Tout d'abord, les paramètres de croissance permettant de contrôler le diamètre des fils et leur densité sont mis en évidence en modélisant la croissance de l'hétéro-structure par simulations Monte-Carlo cinétique. Ensuite, on montre que les fils sont dilatés axialement et relaxés radialement. L'origine de l'état dilaté est expliquée en adaptant le modèle de Frenkel-Kontorova à notre situation et les inhomogénéités de déformation des nanofils sont décrites en analysant des cartographies de l'espace réciproque. La dilatation crée une anisotropie magnétique, par couplage magnéto-élastique, qui, dans le cas du nickel, peut compenser l'anisotropie de forme des fils. Enfin, pour des fils de Co0.4Ni0.6 de diamètre supérieur à quatre nanomètres, la température de blocage de l'assemblée de fils est supérieure à la température ambiante et la barrière d'énergie du renversement magnétique est de l'ordre d'un électronvolt, ce qui est intéressant pour d'éventuelles applications, par exemple en enregistrement de données.In this PhD thesis, we study the growth and the properties of ferromagnetic nanowires made of cobalt, nickel and cobalt-nickel, embedded in a matrix made of of strontium and baryum titanate. The nanowires are grown taking advantage of self-assembly processes occurring during sequential pulsed laser deposition. First, we model the growth with a kinetic Monte-Carlo code to highlight the parameters that control the diameter and the density of the nanowires. Then, it is shown that the nanowires are strained along their axis, and relaxed perpendicular to it. The origin of the strained state is explained in the framework of the Frenkel-Kontorova model, and its inhomogeneities are described through analysis of mappings of the reciprocal space. Furthermore, it is shown that the strain is high enough to shift the magnetic easy axis of the nickel nanowires, through magneto-elastic coupling. Finally, for Co0.4Ni0.6 nanowires with a diameter greater than four nanometers, the blocking temperature of the assembly is above room temperature and the energy barrier for the magnetic reversal of the nanowires is of the order of one electronvolt. This is interesting for potential applications in data storage, for example

Huge metastable axial strain in ultrathin heteroepitaxial vertically aligned nanowires

International audienceStrain engineering is a powerful tool to tailor the physical properties of materials coherently stacked in an epitaxial heterostructure. Such an approach, applied to the mature field of planar heteroepitaxy, has yielded a variety of new phenomena and devices. Recently, heteroepitaxial vertically aligned nanocomposites have emerged as alternatives to planar structures. Owing to the peculiar geometry of such nanoarchitectures, efficient strain control can be achieved, opening the way to novel functionalities. In this paper, we report a very large tensile axial strain in epitaxial transition metal nanowires embedded in an oxide matrix. We show that axial strains in excess of 1.5% can be sustained over a large thickness (a few hundred nanometers) in epitaxial nanowires having ultrasmall diameters (∼3–6 nm). The axial strain depends on the diameter of the nanowires, reflecting its epitaxial nature and the balance of interface and elastic energies. Furthermore, it is experimentally shown that such strain is metastable, in agreement with the calculations performed in the framework of the Frenkel-Kontorova model. The diameter dependence and metastability provide effective ways to control the strain, an appealing feature for the design of functional nanoarchitectures

Large Orbital Magnetic Moment Measured in the [TpFe(III)(CN)3](-) Precursor of Photomagnetic Molecular Prussian Blue Analogues.

Photomagnetism in three-dimensional Co/Fe Prussian blue analogues is a complex phenomenon, whose detailed mechanism is not yet fully understood. Recently, researchers have been able to prepare molecular fragments of these networks using a building block synthetic approach from mononuclear precursors. The main objective in this strategy is to isolate the smallest units that show an intramolecular electron transfer to have a better understanding of the electronic processes. A prior requirement to the development of this kind of system is to understand to what extent electronic and magnetic properties are inherited from the corresponding precursors. In this work, we investigate the electronic and magnetic properties of the FeTp precursor (N(C4H9)4)[TpFe(III)(CN)3], (Tp being tris-pyrazolyl borate) of a recently reported binuclear cyanido-bridged Fe/Co complex. X-ray absorption spectroscopy and X-ray magnetic circular dichroism measurements at the Fe L2,3 edges (2p → 3d) supported by ligand field multiplet calculations have allowed to determine the spin and orbit magnetic moments. Inaccuracy of the spin sum rule in the case of low-spin Fe(III) ion was demonstrated. An exceptionally large value of the orbital magnetic moment is found (0.9 μB at T = 2 K and B = 6.5 T) that is likely to play an important role in the magnetic and photomagnetic properties of molecular Fe/Co Prussian blue analogues.Commutateur Photo-Magnétique UnimoléculaireAssociation Contrôlée de Molécules-Aimants pour une nouvelle Génération de Matériaux magnétiquesSynthèse et étude de chaines aimant photocommutable

Modulation of Biomarker Expression by Osimertinib: Results of the Paired Tumor Biopsy Cohorts of the AURA Phase I Trial

Introduction: Osimertinib is an oral, potent, irreversible EGFR tyrosine kinase inhibitor (TKI) selective for EGFR TKI and T790M resistance mutations. To enhance understanding of osimertinib's mechanism of action, we aimed to evaluate the modulation of key molecular biomarkers after osimertinib treatment in paired clinical samples from the phase I AURA trial. Methods: Paired tumor biopsy samples were collected before the study and after 15 plus or minus 7 days of osimertinib treatment (80 or 160 mg daily). Clinical efficacy outcomes were assessed according to whether viable paired biopsy samples could be collected; safety was also assessed. Immunohistochemical analyses assessed key pathway and tumor/immune-relevant markers (phospho-EGFR, phospho-S6, phospho-AKT, programmed death ligand 1, and CD8), with samples scored by image analysis or a pathologist blinded to treatment allocation. Results: Predose tumor biopsy samples were collected from 61 patients with EGFR T790M tumors; 29 patients had no viable postdose biopsy sample because of tumor regression or insufficient tumor sample. Evaluable predose and postdose tumor biopsy samples were collected from 24 patients. Objective response rate (ORR) and median progression-free survival (mPFS) were improved in patients from whom a postdose biopsy sample could not be collected (ORR 62% and mPFS 9.7 months [p = 0.027]) compared with those from whom paired samples were collected (ORR 29% and mPFS 6.6 months). Osimertinib modulated key EGFR signaling pathways and led to increased immune cell infiltration. Conclusions: Collection of paired biopsy samples was challenging because of rapid tumor regression after osimertinib treatment, highlighting the difficulties of performing on-study biopsies in patients treated with highly active drugs. (C) 2017 International Association for the Study of Lung Cancer. Published by Elsevier Inc. All rights reserved