27 research outputs found
Quantitative analysis of shadow X-ray Magnetic Circular Dichroism Photo-Emission Electron Microscopy
Shadow X-ray Magnetic Circular Dichroism Photo-Emission Electron Microscopy
(XMCD-PEEM) is a recent technique, in which the photon intensity in the shadow
of an object lying on a surface, may be used to gather information about the
three-dimensional magnetization texture inside the object. Our purpose here is
to lay the basis of a quantitative analysis of this technique. We first discuss
the principle and implementation of a method to simulate the contrast expected
from an arbitrary micromagnetic state. Text book examples and successful
comparison with experiments are then given. Instrumental settings are finally
discussed, having an impact on the contrast and spatial resolution : photon
energy, microscope extraction voltage and plane of focus, microscope background
level, electric-field related distortion of three-dimensional objects, Fresnel
diffraction or photon scattering
Transmission XMCD-PEEM imaging of an engineered vertical FEBID cobalt nanowire with a domain wall
Using focused electron-beam-induced deposition, we fabricate a vertical, platinum-coated cobalt nanowire with a controlled three-dimensional structure. The latter is engineered to feature bends along the height: these are used as pinning sites for domain walls, which are obtained at remanence after saturation of the nanostructure in a horizontally applied magnetic field. The presence of domain walls is investigated using x-ray magnetic circular dichroism (XMCD) coupled to photoemission electron microscopy (PEEM). The vertical geometry of our sample combined with the low incidence of the x-ray beam produce an extended wire shadow which we use to recover the wire''s magnetic configuration. In this transmission configuration, the whole sample volume is probed, thus circumventing the limitation of PEEM to surfaces. This article reports on the first study of magnetic nanostructures standing perpendicular to the substrate with XMCD-PEEM. The use of this technique in shadow mode enabled us to confirm the presence of a domain wall without direct imaging of the nanowire
Metabolic and Innate Immune Cues Merge into a Specific Inflammatory Response via the UPR
Erratum in : Metabolic and Innate Immune Cues Merge into a Specific Inflammatory Response via the UPR. [Cell. 2019]International audienceInnate immune responses are intricately linked with intracellular metabolism of myeloid cells. Toll-likereceptor (TLR) stimulation shifts intracellular metabolism toward glycolysis, while anti-inflammatorysignals depend on enhanced mitochondrial respiration. How exogenous metabolic signals affect theimmune response is unknown. We demonstrate that TLR-dependent responses of dendritic cells (DC)are exacerbated by a high fatty acid (FA) metabolic environment. FA suppress the TLR-inducedhexokinase activity and perturb tricarboxylic acid cycle metabolism. These metabolic changesenhance mitochondrial reactive oxygen species (mtROS) production and, in turn, the unfolded proteinresponse (UPR) leading to a distinct transcriptomic signature, with IL-23 as hallmark. Interestingly,chemical or genetic suppression of glycolysis was sufficient to induce this specific immune response.Conversely, reducing mtROS production or DC-specific deficiency in XBP1 attenuated IL-23expression and skin inflammation in an IL-23-dependent model of psoriasis. Thus, fine-tuning of innateimmunity depends on optimization of metabolic demands and minimization of mtROS-induced UPR