Electronic structure and magnetism in two-dimensional hexagonal 5d transition metal carbides, Tan+1Cn (n=1,2,3)

Density functional calculations are used to investigate the electronic structure of two-dimensional 5d tantalum carbides with honeycomb-like lattice structures. We focus on changes in the low-energy bands near the Fermi level with dimensionality. We find that the Ta 5d states dominate, but the extended nature of the wavefunctions makes them weakly correlated. The carbide sheets are prone to long range magnetic order. We evaluate the stability of these states to enhanced electron--electron interactions through a Hubbard U correction. Lastly, we find spin orbit interactions strongly renormalize the band structure for n=2, but play a minor role in n=1 and 3.Comment: 4 pages, 4 figure

Ti3SiC2-formation during Ti–C–Si multilayer deposition by magnetron sputtering at 650 °C

Titanium Silicon Carbide films were deposited from three separate magnetrons with elemental targets onto Si wafer substrates. The substrate was moved in a circular motion such that the substrate faces each magnetron in turn and only one atomic species (Ti, Si or C) is deposited at a time. This allows layer-by-layer film deposition. Material average composition was determined to Ti0.47Si0.14C0.39 by energy-dispersive X-ray spectroscopy. High-resolution transmission electron microscopy and Raman spectroscopy were used to gain insights into thin film atomic structure arrangements. Using this new deposition technique formation of Ti3SiC2 MAX phase was obtained at a deposition temperature of 650 °C, while at lower temperatures only silicides and carbides are formed. Significant sharpening of Raman E2g and Ag peaks associated with Ti3SiC2 formation was observed

Glyceryl trinitrate inhibits hypoxia-induced release of soluble fms-like tyrosine kinase-1 and endoglin from placental tissues

Preeclampsia is associated with increased circulating levels of proinflammatory molecules, such as soluble fms-like tyrosine kinase 1 (sFlt-1) and soluble endoglin (sEng). On release by an inadequately perfused placenta into the maternal circulation, these molecules cause systemic endothelial dysfunction and the associated hypertension and proteinuria that characterize preeclampsia. We previously showed that glyceryl trinitrate (GTN) inhibits hypoxia/reoxygenation-induced apoptosis in the syncytiotrophoblast of term chorionic villi explants. Herein, we demonstrate that GTN inhibits the release of sFlt-1 and sEng from term chorionic villi explants exposed to hypoxia. Although transcript levels and secretion of sFlt-1 and sEng increased in explants exposed to hypoxia, low concentrations of GTN significantly inhibited the hypoxia-induced expression of these molecules at the mRNA and protein levels. Treatment of explants with GTN also prevented the hypoxia-induced accumulation of hypoxia-inducible factor-1α, a key mediator of cellular adaptations to hypoxia. Furthermore, knockdown of hypoxia-inducible factor-1α inhibited the hypoxia-induced secretion of sFlt-1 and sEng. This study provides evidence that hypoxia induces the release of sFlt-1 and sEng in the placenta via a mechanism that is inhibited by low concentrations of GTN. Our findings indicate that GTN may have potential applications in the treatment and/or prevention of preeclampsia. Copyright © 2011 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved

Synthesis and DFT investigation of new bismuth-containing MAX phases

The M(n + 1)AX(n) phases (M = early transition metal; A = group A element and X = C and N) are materials exhibiting many important metallic and ceramic properties. In the present study powder processing experiments and density functional theory calculations are employed in parallel to examine formation of Zr(2)(Al(1−x)Bi(x))C (0 ≤ x ≤ 1). Here we show that Zr(2)(Al(1−x)Bi(x))C, and particularly with x ≈ 0.58, can be formed from powders even though the end members Zr(2)BiC and Zr(2)AlC seemingly cannot. This represents a significant extension of the MAX phase family, as this is the first report of a bismuth-based MAX phase

Electronic structure investigation of Ti3AlC2, Ti3SiC2, and Ti3GeC2 by soft-X-ray emission spectroscopy

The electronic structures of epitaxially grown films of Ti3AlC2, Ti3SiC2 and Ti3GeC2 have been investigated by bulk-sensitive soft X-ray emission spectroscopy. The measured high-resolution Ti L, C K, Al L, Si L and Ge M emission spectra are compared with ab initio density-functional theory including core-to-valence dipole matrix elements. A qualitative agreement between experiment and theory is obtained. A weak covalent Ti-Al bond is manifested by a pronounced shoulder in the Ti L-emission of Ti3AlC2. As Al is replaced with Si or Ge, the shoulder disappears. For the buried Al and Si-layers, strongly hybridized spectral shapes are detected in Ti3AlC2 and Ti3SiC2, respectively. As a result of relaxation of the crystal structure and the increased charge-transfer from Ti to C, the Ti-C bonding is strengthened. The differences between the electronic structures are discussed in relation to the bonding in the nanolaminates and the corresponding change of materials properties.Comment: 15 pages, 8 figure

Electrical transport and percolation in magnetoresistive manganite / insulating oxide composites: case of La0.7Ca0.3MnO3 / Mn3O4

We report the results of electrical resistivity measurements carried out on well-sintered La0.7Ca0.3MnO3 / Mn3O4 composite samples with almost constant composition of the magnetoresistive manganite phase (La0.7Ca0.3MnO3). A percolation threshold (fc) occurs when the La0.7Ca0.3MnO3 volume fraction is ~ 0.19. The dependence of the electrical resistivity as a function of La0.7Ca0.3MnO3 volume fraction (fLCMO) can be described by percolation-like phenomenological equations. Fitting the conducting regime (fLCMO > fc) by the percolation power law returns a critical exponent t value of 2.0 +/- 0.2 at room temperature and 2.6 +/-0.2 at 5 K. The increase of t is ascribed to the influence of the grain boundaries on the electrical conduction process at low temperature.Comment: 7 pages, 3 figures, accepted for publication in Phys. Rev.