231 research outputs found
Hydrogen-induced reversible spin-reorientation transition and magnetic stripe domain phase in bilayer Co on Ru(0001)
Imaging the change in the magnetization vector in real time by spin-polarized
low-energy electron microscopy, we observed a hydrogen-induced, reversible
spin-reorientation transition in a cobalt bilayer on Ru(0001). Initially,
hydrogen sorption reduces the size of out-of-plane magnetic domains and leads
to the formation of a magnetic stripe domain pattern, which can be understood
as a consequence of reducing the out-of-plane magnetic anisotropy. Further
hydrogen sorption induces a transition to an in-plane easy-axis. Desorbing the
hydrogen by heating the film to 400 K recovers the original out-of-plane
magnetization. By means of ab-initio calculations we determine that the origin
of the transition is the local effect of the hybridization of the hydrogen
orbital and the orbitals of the Co atoms bonded to the absorbed hydrogen.Comment: 5 figure
Oxidation of graphene on metals
We use low-energy electron microscopy to investigate how graphene is removed
from Ru(0001) and Ir(111) by reaction with oxygen. We find two mechanisms on
Ru(0001). At short times, oxygen reacts with carbon monomers on the surrounding
Ru surface, decreasing their concentration below the equilibrium value. This
undersaturation causes a flux of carbon from graphene to the monomer gas. In
this initial mechanism, graphene is etched at a rate that is given precisely by
the same non-linear dependence on carbon monomer concentration that governs
growth. Thus, during both growth and etching, carbon attaches and detaches to
graphene as clusters of several carbon atoms. At later times, etching
accelerates. We present evidence that this process involves intercalated
oxygen, which destabilizes graphene. On Ir, this mechanism creates observable
holes. It also occurs mostly quickly near wrinkles in the graphene islands,
depends on the orientation of the graphene with respect to the Ir substrate,
and, in contrast to the first mechanism, can increase the density of carbon
monomers. We also observe that both layers of bilayer graphene islands on Ir
etch together, not sequentially.Comment: 15 pages, 10 figures. Manuscript revised to improve discussion,
following referee comments. Accepted for publication in Journal of Physical
Chemistry C, Feb. 11, 201
Evidence for Surface Effects on the Intermolecular Interactions in Fe (II) Spin Crossover Coordination Polymers
From X-ray absorption spectroscopy (XAS) and X-ray photoemission spectroscopy (XPS) it is evident that the spin state transition behavior of Fe(II) spin crossover coordination polymer crystallites at the surface differs from the bulk. A comparison of four different coordination polymers reveals that the observed surface properties may differ from bulk for a variety of reasons. There are Fe(II) spin crossover coordination polymers with either almost complete switching of the spin state at the surface or no switching at all. Oxidation, differences in surface packing, and changes in coordination could all contribute to making the surface very different from the bulk. Some Fe(II) spin crossover coordination polymers may be sufficiently photoactive so that X-ray spectroscopies cannot discern the spin state transition
Localization of Dirac electrons by Moire patterns in graphene bilayers
We study the electronic structure of two Dirac electron gazes coupled by a
periodic Hamiltonian such as it appears in rotated graphene bilayers. Ab initio
and tight-binding approaches are combined and show that the spatially periodic
coupling between the two Dirac electron gazes can renormalize strongly their
velocity. We investigate in particular small angles of rotation and show that
the velocity tends to zero in this limit. The localization is confirmed by an
analysis of the eigenstates which are localized essentially in the AA zones of
the Moire patterns.Comment: 4 pages, 5 figure
Electronic structure and direct observation of ferrimagnetism in multiferroic hexagonal YbFeO3
The magnetic interactions between rare-earth and Fe ions in hexagonal rare-earth ferrites (h-RFeO3), may amplify the weak ferromagnetic moment on Fe, making these materials more appealing as multiferroics. To elucidate the interaction strength between the rare-earth and Fe ions as well as the magnetic moment of the rare-earth ions, element-specific magnetic characterization is needed. Using x-ray magnetic circular dichroism, we have studied the ferrimagnetism in h-YbFeO3 by measuring the magnetization of Fe and Yb separately. The results directly show antialignment of magnetization of Yb and Fe ions in h-YbFeO3 at low temperature, with an exchange field on Yb of about 17 kOe. The magnetic moment of Yb is about 1.6ÎĽB at low temperature, significantly reduced compared with the 4.5 ÎĽB moment of a free Yb3+. In addition, the saturation magnetization of Fe in h-YbFeO3 has a sizable enhancement compared with that in h-LuFeO3. These findings directly demonstrate that ferrimagnetic order exists in h-YbFeO3; they also account for the enhancement of magnetization and the reduction of coercivity in h-YbFeO3 compared with those in h-LuFeO3 at low temperature, suggesting an important role for the rare-earth ions in tuning the multiferroic properties of h-RFeO3
Probing Mechanical Properties of Graphene with Raman Spectroscopy
The use of Raman scattering techniques to study the mechanical properties of
graphene films is reviewed here. The determination of Gruneisen parameters of
suspended graphene sheets under uni- and bi-axial strain is discussed and the
values are compared to theoretical predictions. The effects of the
graphene-substrate interaction on strain and to the temperature evolution of
the graphene Raman spectra are discussed. Finally, the relation between
mechanical and thermal properties is presented along with the characterization
of thermal properties of graphene with Raman spectroscopy.Comment: To appear in the Journal of Materials Scienc
“Avoiding or approaching eyes”? Introversion/extraversion affects the gaze-cueing effect
We investigated whether the extra-/introversion personality dimension can influence processing of others’ eye gaze direction and emotional facial expression during a target detection task. On the basis of previous evidence showing that self-reported trait anxiety can affect gaze-cueing with emotional faces, we also verified whether trait anxiety can modulate the influence of intro-/extraversion on behavioral performance. Fearful, happy, angry or neutral faces, with either direct or averted gaze, were presented before the target appeared in spatial locations congruent or incongruent with stimuli’s eye gaze direction. Results showed a significant influence of intra-/extraversion dimension on gaze-cueing effect for angry, happy, and neutral faces with averted gaze. Introverts did not show the gaze congruency effect when viewing angry expressions, but did so with happy and neutral faces; extraverts showed the opposite pattern. Importantly, the influence of intro-/extraversion on gaze-cueing was not mediated by trait anxiety. These findings demonstrated that personality differences can shape processing of interactions between relevant social signals
Genome Wide Transcriptome Analysis of Dendritic Cells Identifies Genes with Altered Expression in Psoriasis
Activation of dendritic cells by different pathogens induces the secretion of proinflammatory mediators resulting in
local inflammation. Importantly, innate immunity must be properly controlled, as its continuous activation leads to the
development of chronic inflammatory diseases such as psoriasis. Lipopolysaccharide (LPS) or peptidoglycan (PGN)
induced tolerance, a phenomenon of transient unresponsiveness of cells to repeated or prolonged stimulation,
proved valuable model for the study of chronic inflammation. Thus, the aim of this study was the identification of the
transcriptional diversity of primary human immature dendritic cells (iDCs) upon PGN induced tolerance. Using SAGESeq
approach, a tag-based transcriptome sequencing method, we investigated gene expression changes of primary
human iDCs upon stimulation or restimulation with Staphylococcus aureus derived PGN, a widely used TLR2 ligand.
Based on the expression pattern of the altered genes, we identified non-tolerizeable and tolerizeable genes. Gene
Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (Kegg) analysis showed marked enrichment of
immune-, cell cycle- and apoptosis related genes. In parallel to the marked induction of proinflammatory mediators,
negative feedback regulators of innate immunity, such as TNFAIP3, TNFAIP8, Tyro3 and Mer are markedly
downregulated in tolerant cells. We also demonstrate, that the expression pattern of TNFAIP3 and TNFAIP8 is
altered in both lesional, and non-lesional skin of psoriatic patients. Finally, we show that pretreatment of immature
dendritic cells with anti-TNF-α inhibits the expression of IL-6 and CCL1 in tolerant iDCs and partially releases the
suppression of TNFAIP8. Our findings suggest that after PGN stimulation/restimulation the host cell utilizes different
mechanisms in order to maintain critical balance between inflammation and tolerance. Importantly, the transcriptome
sequencing of stimulated/restimulated iDCs identified numerous genes with altered expression to date not associated
with role in chronic inflammation, underlying the relevance of our in vitro model for further characterization of IFNprimed
iDCs
Autophagy mediates degradation of nuclear lamina
Z.D. is supported by a fellow award from the Leukemia & Lymphoma Society. B.C.C. is supported by career development awards from the Dermatology Foundation, Melanoma Research Foundation, and American Skin Association. S.L.B., P.D.A. and R.M. are supported by NIA P01 grant (P01AG031862). S.L.B. is also supported by NIH R01 CA078831. R.D.G. is supported by R01 GM106023 and the Progeria Research Foundation
Nonvolatile Voltage Controlled Molecular Spin-State Switching for Memory Applications
Nonvolatile, molecular multiferroic devices have now been demonstrated, but it is worth giving some consideration to the issue of whether such devices could be a competitive alternative for solid-state nonvolatile memory. For the Fe (II) spin crossover complex [Fe{H2B(pz)2}2(bipy)], where pz = tris(pyrazol-1-yl)-borohydride and bipy = 2,2′-bipyridine, voltage-controlled isothermal changes in the electronic structure and spin state have been demonstrated and are accompanied by changes in conductance. Higher conductance is seen with [Fe{H2B(pz)2}2(bipy)] in the high spin state, while lower conductance occurs for the low spin state. Plausibly, there is the potential here for low-cost molecular solid-state memory because the essential molecular thin films are easily fabricated. However, successful device fabrication does not mean a device that has a practical value. Here, we discuss the progress and challenges yet facing the fabrication of molecular multiferroic devices, which could be considered competitive to silicon
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