Hyper-domains in exchange bias micro-stripe pattern

A combination of experimental techniques, e.g. vector-MOKE magnetometry, Kerr microscopy and polarized neutron reflectometry, was applied to study the field induced evolution of the magnetization distribution over a periodic pattern of alternating exchange bias (EB) stripes. The lateral structure is imprinted into a continuous ferromagnetic/antiferromagnetic EB bilayer via laterally selective exposure to He-ion irradiation in an applied field. This creates an alternating frozen-in interfacial EB field competing with the external field in the course of the re-magnetization. It was found that in a magnetic field applied at an angle with respect to the EB axis parallel to the stripes the re-magnetization process proceeds via a variety of different stages. They include coherent rotation of magnetization towards the EB axis, precipitation of small random (ripple) domains, formation of a stripe-like alternation of the magnetization, and development of a state in which the magnetization forms large hyper-domains comprising a number of stripes. Each of those magnetic states is quantitatively characterized via the comprehensive analysis of data on specular and off-specular polarized neutron reflectivity. The results are discussed within a phenomenological model containing a few parameters, which can readily be controlled by designing systems with a desired configuration of magnetic moments of micro- and nano-elements

A Role for the Unfolded Protein Response (UPR) in Virulence and Antifungal Susceptibility in Aspergillus fumigatus

Filamentous fungi rely heavily on the secretory pathway, both for the delivery of cell wall components to the hyphal tip and the production and secretion of extracellular hydrolytic enzymes needed to support growth on polymeric substrates. Increased demand on the secretory system exerts stress on the endoplasmic reticulum (ER), which is countered by the activation of a coordinated stress response pathway termed the unfolded protein response (UPR). To determine the contribution of the UPR to the growth and virulence of the filamentous fungal pathogen Aspergillus fumigatus, we disrupted the hacA gene, encoding the major transcriptional regulator of the UPR. The ΔhacA mutant was unable to activate the UPR in response to ER stress and was hypersensitive to agents that disrupt ER homeostasis or the cell wall. Failure to induce the UPR did not affect radial growth on rich medium at 37°C, but cell wall integrity was disrupted at 45°C, resulting in a dramatic loss in viability. The ΔhacA mutant displayed a reduced capacity for protease secretion and was growth-impaired when challenged to assimilate nutrients from complex substrates. In addition, the ΔhacA mutant exhibited increased susceptibility to current antifungal agents that disrupt the membrane or cell wall and had attenuated virulence in multiple mouse models of invasive aspergillosis. These results demonstrate the importance of ER homeostasis to the growth and virulence of A. fumigatus and suggest that targeting the UPR, either alone or in combination with other antifungal drugs, would be an effective antifungal strategy

Parameterization of a coarse-grained model of cholesterol with point-dipole electrostatics

© 2018, Springer Nature Switzerland AG. We present a new coarse-grained (CG) model of cholesterol (CHOL) for the electrostatic-based ELBA force field. A distinguishing feature of our CHOL model is that the electrostatics is modeled by an explicit point dipole which interacts through an ideal vacuum permittivity. The CHOL model parameters were optimized in a systematic fashion, reproducing the electrostatic and nonpolar partitioning free energies of CHOL in lipid/water mixtures predicted by full-detailed atomistic molecular dynamics simulations. The CHOL model has been validated by comparison to structural, dynamic and thermodynamic properties with experimental and atomistic simulation reference data. The simulation of binary DPPC/cholesterol mixtures covering the relevant biological content of CHOL in mammalian membranes is shown to correctly predict the main lipid behavior as observed experimentally

Silicon oxide nanolayers for soft X-ray optics produced by plasma enhanced CVD

We have studied the suitability of Plasma Enhanced Chemical Vapor Deposition (PECVD) to produce ultrasmooth silicon oxide layers ranging in thickness from some nanometers to some 10 nm. A tight process control of the layer thickness, layer density and microroughness of the growing film is required. We deposited silicon oxide on silicon wafers, float glass and superpolished quartz substrates. In a remote plasma enhanced CVD process, we used tetraethylorthosilicate (TEOS, Si(OC2H5)4) as precursor. Films with a thickness of some 10 nm were produced at different deposition parameters and characterized by in-situ soft X-ray reflectivity, hard X-ray diffraction and auger electron spectroscopy. Best results could be found for the deposition using TEOS in oxygen plasma. In case of SiO2 layers deposited on standard glass substrates signifcant roughness smoothing was obtained

Silicon oxide nanolayers for soft X-ray optics produced by plasma enhanced CVD

Hamelmann F, Aschentrup A, Schmalhorst J-M, et al. Silicon oxide nanolayers for soft X-ray optics produced by plasma enhanced CVD. JOURNAL DE PHYSIQUE IV. 2001;11(PR3):431-436.We have studied the suitability of Plasma Enhanced Chemical Vapor Deposition (PECVD) to produce ultrasmooth silicon oxide layers ranging in thickness from some nanometers to some 10 nm. A tight process control of the layer thickness, layer density and microroughness of the growing film is required. We deposited silicon oxide on silicon wafers, float glass and superpolished quartz substrates. In a remote plasma enhanced CVD process, we used tetraethylorthosilicate (TEOS, Si(OC2H5)(4)) as precursor. Films with a thickness of some 10 nm were produced at different deposition parameters and characterized by in-situ soft X-ray reflectivity, hard X-ray diffraction and auger electron spectroscopy. Best results could be found for the deposition using TEOS in oxygen plasma. In case Of SiO2 layers deposited on standard glass substrates signifcant roughness smoothing was obtained

Magnetic Tunneling Junctions — Materials, Geometry and Applications

Reiss G, Koop H, Meyners D, et al. Magnetic Tunneling Junctions — Materials, Geometry and Applications. In: Aktas B, Tagirov L, Mikailov F, eds. Magnetic Nanostructures. Springer Series in Materials Science. Vol 94. Berlin, Heidelberg: Springer; 2007: 147-165

Hyper-domains in exchange bias micro-stripe pattern

A combination of experimental techniques, e.g. vector-MOKE magnetometry, Kerr microscopy and polarized neutron reflectometry, was applied to study the field induced evolution of the magnetization distribution over a periodic pattern of alternating exchange bias (EB) stripes. The lateral structure is imprinted into a continuous ferromagnetic/antiferromagnetic EB bilayer via laterally selective exposure to He-ion irradiation in an applied field. This creates an alternating frozen-in interfacial EB field competing with the external field in the course of the re-magnetization. It was found that in a magnetic field applied at an angle with respect to the EB axis parallel to the stripes the re-magnetization process proceeds via a variety of different stages. They include coherent rotation of magnetization towards the EB axis, precipitation of small random (ripple) domains, formation of a stripe-like alternation of the magnetization, and development of a state in which the magnetization forms large hyper-domains comprising a number of stripes. Each of those magnetic states is quantitatively characterized via the comprehensive analysis of data on specular and off-specular polarized neutron reflectivity. The results are discussed within a phenomenological model containing a few parameters, which can readily be controlled by designing systems with a desired configuration of magnetic moments of micro- and nano-elements

Metal oxide/silicon oxide multilayer with smooth interfaces produced by in situ controlled plasma-enhanced MOCVD

Hamelmann F, Haindl G, Schmalhorst J-M, et al. Metal oxide/silicon oxide multilayer with smooth interfaces produced by in situ controlled plasma-enhanced MOCVD. THIN SOLID FILMS. 2000;358(1-2):90-93.Molybdenum oxide/silicon oxide and tungsten oxide/silicon oxide: multilayer with 24 periods and a period thickness of 9.2 nm were fabricated with plasma-enhanced MOCVD. The layer thickness was controlled by an in situ soft X-ray reflectivity measurement. For the deposition of the SiO2 layers, a new silicon organic precursor, pentamethylcyclopentadienyldisilane (Me5C5Si2H5) was used in an O-2 remote: plasma process. The high quality of multilayer interfaces was observed by cross-section transmission electron microscopy (TEM), the interface toughness was measured by hard X-ray reflectivity and diffuse scattering at grazing incidence experiments to be about 0.1 nm. Auger electron spectroscopy (AES) gives the information, that the silicon oxide is practically carbon free, and the carbon content of the metal oxides is low (<5%). (C) 2000 Elsevier Science S.A. All rights reserved

Polarized neutron reflectometry study on a magnetic film with an ion beam imprinted stripe pattern

Theis-Broehl K, Toperverg BP, Westphalen A, et al. Polarized neutron reflectometry study on a magnetic film with an ion beam imprinted stripe pattern. In: Superlattices and Microstructures. SUPERLATTICES AND MICROSTRUCTURES. Vol 41. ACADEMIC PRESS LTD ELSEVIER SCIENCE LTD; 2007: 104-108.We used polarized neutron reflectometry for a quantitative study of the field dependent arrangement of the magnetization vector in the different regions of an ion beam imprinted stripe pattern in a magnetic film. For the magnetic patterning of the Co70Fe30 film we took advantage of the exchange bias to an antiferromagnetic Mn83Ir17 layer which was changed locally by He-ion bombardment. The exchange bias was set to be antiparallel in the two different striped regions. We found that after magnetization reversal of half of the stripes the magnetization in neighbouring regions is periodically canted with respect to the stripe axis so that the net magnetization of the ferromagnetic film tums almost perpendicular to the stripes. At the same time the projection of the magnetization vector onto the stripe axis has a periodically alternating sign. (c) 2007 Published by Elsevier Lt