118 research outputs found
Electronic tuneability of a structurally rigid surface intermetallic and Kondo lattice: CePt / Pt(111)
We present an extensive study of structure, composition, electronic and
magnetic properties of Ce--Pt surface intermetallic phases on Pt(111) as a
function of their thickness. The sequence of structural phases appearing in low
energy electron diffraction (LEED) may invariably be attributed to a single
underlying intermetallic atomic lattice. Findings from both microscopic and
spectroscopic methods, respectively, prove compatible with CePt formation
when their characteristic probing depth is adequately taken into account. The
intermetallic film thickness serves as an effective tuning parameter which
brings about characteristic variations of the Cerium valence and related
properties. Soft x-ray absorption (XAS) and magnetic circular dichroism (XMCD)
prove well suited to trace the changing Ce valence and to assess relevant
aspects of Kondo physics in the CePt surface intermetallic. We find
characteristic Kondo scales of the order of 10 K and evidence for
considerable magnetic Kondo screening of the local Ce moments.
CePt/Pt(111) and related systems therefore appear to be promising
candidates for further studies of low-dimensional Kondo lattices at surfaces.Comment: 14 pages, 11 figure
Related RNAs in lepidopteran cells after in vitro infection with Hyposoter didymator virus define a new polydnavirus gene family
In the present study, we describe the isolation and the characterization of three different Hyposoter didymator virus (HdV) lepidopteran host-expressed genes, the products of which might interfere with the host physiology during parasitism. In this report, we study the expression of HdV genes in Sf9 cells infected with HdV since results indicate that the Sf9 model mimics to some extent the in vivo model and may be utilized to study expression of HdV genes in lepidopteran host cells. This system allowed us to isolate three HdV-specific cDNAs, termed M24, M27, and M40. cDNA nucleotide sequence analysis demonstrated significant regions of homology. The three cDNAs displayed repeated sequences arranged in tandem array that might have evolved through domain duplication. Similar to other previously described polydnavirus host-expressed genes, two intron positions have been found in the M24 leader region. The cDNAs corresponded to RNAs of 1.6, 1.6, and 2.3 kb that are also detected in parasitized Spodoptera littoralis larvae. They are encoded by different genes likely located on different HdV DNA molecules. Corresponding RNAs are detected early postinfection and remain detectable for at least 10 days postinfection. They encode secreted glycine- and proline-rich proteins. An antiserum raised against a baculovirus recombinant M24-encoded protein detected similar proteins in the culture medium of infected lepidopteran cells and in parasitized host hemolymph. We propose that the three cloned genes belong to an HdV gene family specifically expressed in parasitized lepidopteran hosts, (C) 1999 Academic Press
Structure of self-organized Fe clusters grown on Au(111) analyzed by Grazing Incidence X-Ray Diffraction
We report a detailed investigation of the first stages of the growth of
self-organized Fe clusters on the reconstructed Au(111) surface by grazing
incidence X-ray diffraction. Below one monolayer coverage, the Fe clusters are
in "local epitaxy" whereas the subsequent layers adopt first a strained fcc
lattice and then a partly relaxed bcc(110) phase in a Kurdjumov-Sachs epitaxial
relationship. The structural evolution is discussed in relation with the
magnetic properties of the Fe clusters.Comment: 7 pages, 6 figures, submitted to Physical Review B September 200
Oscillatory magnetic anisotropy in one-dimensional atomic wires
One-dimensional Co atomic wires grown on Pt(997) have been investigated by x-ray magnetic circular dichroism. Strong changes of the magnetic properties are observed as the system evolves from 1D- to 2D-like. The easy axis of magnetization, the magnetic anisotropy energy, and the coercive field oscillate as a function of the transverse width of the wires, in agreement with theoretical predictions for 1D metal systems
Determination of the cation site distribution of the spinel in multiferroic CoFe2O4 / BaTiO3 layers by X-ray photoelectron spectroscopy
International audienceThe properties of CoFe2O4/BaTiO3 artificial multiferroic multilayers strongly depend on the crystalline structure, the stoichiometry and the cation distribution between octahedral (Oh) and tetrahedral (Td) sites (inversion factor). In the present study, we have investigated epitaxial CoFe2O4 layers grown on BaTiO3, with different Co/Fe ratios. We determined the cation distribution in our samples by X-ray magnetic circular dichroism (XMCD), a well accepted method to do so, and by X-ray photoelectron spectroscopy (XPS), using a fitting method based on physical considerations. We observed that our XPS approach converged on results consistent with XMCD measurements made on the same samples. Thus, within a careful decomposition based on individual chemical environments it is shown that XPS is fully able to determine the actual inversion factor
Field-regulated switching of the magnetization of Co-porphyrin on graphene
Differentmagnetic couplingmechanisms have been identified for a fewmonolayers of Co-porphyrin molecules
deposited on a graphene-covered Ni(111) single crystal. A relatively strong antiferromagnetic coupling of the
first molecular layer via graphene to the Ni crystal in comparison to a weaker intermolecular coupling gives
rise to a complex field-dependent response of this hybrid system. By continuously increasing the magnetic field
strength, the net magnetization of the molecular system switches from antiparallel to parallel to the field direction
at 2.5 T. Utilizing x-ray absorption spectroscopy and x-ray magnetic circular dichroism, the element-specific
magnetization and field dependence was probed. The nature of the magnetic couplings is identified by means of
density functional theory and orbital-dependent susceptibilities
Magnetic Coupling and Single-Ion Anisotropy in Surface-Supported Mn-based Metal-Organic Networks
The electronic and magnetic properties of Mn coordinated to
1,2,4,5-tetracyanobenzene (TCNB) in the Mn-TCNB 2D metal-ligand networks have
been investigated by combining scanning tunneling microscopy and X-ray magnetic
circular dichroism (XMCD) performed at low temperature (3 K). When formed on
Au(111) and Ag(111) substrates the Mn-TCNB networks display similar geometric
structures. Magnetization curves reveal ferromagnetic (FM) coupling of the Mn
sites with similar single-ion anisotropy energies, but different coupling
constants. Low-temperature XMCD spectra show that the local environment of the
Mn centers differs appreciably for the two substrates. Multiplet structure
calculations were used to derive the corresponding ligand field parameters
confirming an in-plane uniaxial anisotropy. The observed interatomic coupling
is discussed in terms of superexchange as well as substrate-mediated magnetic
interactions.Comment: J. Phys. Chem. C 201
Atomic-Scale Study of Metal–Oxide Interfaces and Magnetoelastic Coupling in Self-Assembled Epitaxial Vertically Aligned Magnetic Nanocomposites
Vertically aligned nanocomposites (VANs) of metal/oxide type have recently emerged as a novel class of heterostructures with great scientific and technological potential in the fields of nanomagnetism, multiferroism, and catalysis. One of the salient features of these hybrid materials is their huge vertical metal/oxide interface, which plays a key role in determining the final magnetic and/or transport properties of the composite structure. However, in contrast to their well‐studied planar counterparts, detailed information on the structural features of vertical interfaces encountered in VANs is scarce. In this work, high resolution scanning transmission electron microscopy (STEM) and electron energy‐loss spectroscopy (EELS) are used to provide an element selective atomic‐scale analysis of the interface in a composite consisting of ultrathin, self‐assembled Ni nanowires, vertically epitaxied in a SrTiO3/SrTiO3(001) matrix. Spectroscopic EELS measurements evidence rather sharp interfaces (6–7 Å) with the creation of metallic NiTi bonds and the absence of nickel oxide formation is confirmed by X‐ray absorption spectroscopy measurements. The presence of these well‐defined phase boundaries, combined with a large lattice mismatch between the oxide and metallic species, gives rise to pronounced magnetoelastic effects. Self‐assembled columnar Ni:SrTiO3 composites thus appear as ideal model systems to explore vertical strain engineering in metal/oxide nanostructures
Tissue-specific inducible expression of antimicrobial peptide genes in Drosophila surface epithelia
The production of antimicrobial peptides is an important aspect of host defense in multicellular organisms. In Drosophila, seven antimicrobial peptides with different spectra of activities are synthesized by the fat body during the immune response and secreted into the hemolymph. Using GFP reporter transgenes, we show here that all seven Drosophila antimicrobial peptides can be induced in surface epithelia in a tissue-specific manner. The imd gene plays a critical role in the activation of this local response to infection. In particular, drosomycin expression, which is regulated by the Toll pathway during the systemic response, is regulated by imd in the respiratory tract, thus demonstrating the existence of distinct regulatory mechanisms for local and systemic induction of antimicrobial peptide genes in Drosophila
Ultralow-temperature device dedicated to soft X-ray magnetic circular dichroism experiments
A new ultralow-temperature setup dedicated to soft X-ray absorption spectroscopy and X-ray magnetic circular dichroism (XMCD) experiments is described. Two experiments, performed on the DEIMOS beamline (SOLEIL synchrotron), demonstrate the outstanding performance of this new platform in terms of the lowest achievable temperature under X-ray irradiation (T = 220 mK), the precision in controlling the temperature during measurements as well as the speed of the cooling-down and warming-up procedures. Moreover, owing to the new design of the setup, the eddy-current power is strongly reduced, allowing fast scanning of the magnetic field in XMCD experiments; these performances lead to a powerful device for X-ray spectroscopies on synchrotron-radiation beamlines facilities
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