Tailoring tunnel magnetoresistance by ultrathin Cr and Co interlayers: A first-principles investigation of Fe/MgO/Fe junctions

We report on systematic ab-initio investigations of Co and Cr interlayers embedded in Fe(001)/MgO/Fe(001) magnetic tunnel junctions, focusing on the changes of the electronic structure and the transport properties with interlayer thickness. The results of spin-dependent ballistic transport calculations reveal options to specifically manipulate the tunnel magnetoresistance ratio. The resistance area products and the tunnel magnetoresistance ratios show a monotonous trend with distinct oscillations as a function of the Cr thickness. These modulations are directly addressed and interpreted by means of magnetic structures in the Cr films and by complex band structure effects. The characteristics for embedded Co interlayers are considerably influenced by interface resonances which are analyzed by the local electronic structure

Evaluation of conduction eigenchannels of an adatom probed by an STM tip

Ballistic conductance through a single atom adsorbed on a metallic surface and probed by a scanning tunneling microscope (STM) tip can be decomposed into eigenchannel contributions, which can be potentially obtained from shot noise measurements. Our density functional theory calculations provide evidence that transmission probabilities of these eigenchannels encode information on the modifications of the adatom's local density of states caused by its interaction with the STM tip. In the case of open shell atoms, this can be revealed in nonmonotonic behavior of the eigenchannel's transmissions as a function of the tip-adatom separation.Comment: 4.5 pages, 5 figures, REVTe

Bi2Te3Bi_2Te_3: Implications of the rhombohedral k-space texture on the evaluation of the in-plane/out-of-plane conductivity anisotropy

Different computational scheme for calculating surface integrals in anisotropic Brillouin zones are compared. The example of the transport distribution function (plasma frequency) of the thermoelectric Material \BiTe near the band edges will be discussed. The layered structure of the material together with the rhombohedral symmetry causes a strong anisotropy of the transport distribution function for the directions in the basal (in-plane) and perpendicular to the basal plane (out-of-plane). It is shown that a thorough reciprocal space integration is necessary to reproduce the in-plane/out-of-plane anisotropy. A quantitative comparison can be made at the band edges, where the transport anisotropy is given in terms of the anisotropic mass tensor.Comment: 7 pages, 6 figs., subm. to J. Phys. Cond. Ma

Impurity scattering and quantum confinement in giant magnetoresistance systems

Ab initio calculations for the giant magnetoresistance (GMR) in Co/Cu, Fe/Cr, and Fe/Au multilayers are presented. The electronic structure of the multilayers and the scattering potentials of point defects therein are calculated self-consistently. Residual resistivities are obtained by solving the quasi-classical Boltzmann equation including the electronic structure of the layered system, the anisotropic scattering cross sections derived by a Green's function method and the vertex corrections. Furthermore, the influence of scattering centers at the interfaces and within the metallic layers is incorporated by averaging the scattering cross sections of different impurities at various sites. An excellent agreement of experimental and theoretical results concerning the general trend of GMR in Co/Cu systems depending on the type and the position of impurities is obtained. Due to the quantum confinement in magnetic multilayers GMR can be tailored as a function of the impurity position. In Co/Cu and Fe/Au systems impurities in the magnetic layer lead to high GMR values, whereas in Fe/Cr systems defects at the interfaces are most efficient to increase GMR.Comment: 8 pages, 6 figure

Theory of real space imaging of Fermi surfaces

A scanning tunneling microscope can be used to visualize in real space Fermi surfaces with buried impurities far below substrates acting as local probes. A theory describing this feature is developed based on the stationary phase approximation. It is demonstrated how a Fermi surface of a material acts as a mirror focusing electrons that scatter at hidden impurities.Comment: 10 pages, 4 figure

Cruciate Ligament Cell Sheets Can Be Rapidly Produced on Thermoresponsive poly(glycidyl ether) Coating and Successfully Used for Colonization of Embroidered Scaffolds

Anterior cruciate ligament (ACL) cell sheets combined with biomechanically competent scaffolds might facilitate ACL tissue engineering. Since thermoresponsive polymers allow a rapid enzyme-free detachment of cell sheets, we evaluated the applicability of a thermoresponsive poly(glycidyl ether) (PGE) coating for cruciate ligamentocyte sheet formation and its influence on ligamentocyte phenotype during sheet-mediated colonization of embroidered scaffolds. Ligamentocytes were seeded on surfaces either coated with PGE or without coating. Detached ligamentocyte sheets were cultured separately or wrapped around an embroidered scaffold made of polylactide acid (PLA) and poly(lactic-co-ε-caprolactone) (P(LA-CL)) threads functionalized by gas-phase fluorination and with collagen foam. Ligamentocyte viability, protein and gene expression were determined in sheets detached from surfaces with or without PGE coating, scaffolds seeded with sheets from PGE-coated plates and the respective monolayers. Stable and vital ligamentocyte sheets could be produced within 24 h with both surfaces, but more rapidly with PGE coating. PGE did not affect ligamentocyte phenotype. Scaffolds could be colonized with sheets associated with high cell survival, stable gene expression of ligament-related type I collagen, decorin, tenascin C and Mohawk after 14 d and extracellular matrix (ECM) deposition. PGE coating facilitates ligamentocyte sheet formation, and sheets colonizing the scaffolds displayed a ligament-related phenotype

Multicenter performance evaluation of a second generation cortisol assay

Background: Untreated disorders of the adrenocortical system, such as Cushing's or Addison's disease, can be fatal, and accurate quantification of a patient's cortisol levels is vital for diagnosis. The objective of this study was to assess the analytical performance of a new fully-automated Elecsys (R) Cortisol II assay (second generation) to measure cortisol levels in serum and saliva. Methods: Four European investigational sites assessed the intermediate precision and reproducibility of the Cortisol II assay (Roche Diagnostics) under routine conditions. Method comparisons of the Cortisol II assay vs. liquid chromatography-tandem mass spectrometry (LC-MS/MS), the gold standard for cortisol measurement, were performed. Cortisol reference ranges from three US sites were determined using samples from self-reported healthy individuals. Results: The coefficients of variation (CVs) for repeatability, intermediate precision, and reproducibility for serum samples were <= 2.6%, <= 5.8%, and <= 9.5%, respectively, and for saliva were <= 4.4% and <= 10.9%, and <= 11.4%, respectively. Agreement between the Cortisol II assay and LC-MS/MS in serum samples was close, with a slope of 1.02 and an intercept of 4.473 nmol/L. Reference range samples were collected from healthy individuals (n = 300) and serum morning cortisol concentrations (5-95th percentile) were 166.1-507 nmol/L and afternoon concentrations were 73.8-291 nmol/L. Morning, afternoon, and midnight saliva concentrations (95th percentile) were 20.3, 6.94, and 7.56 nmol/L, respectively. Conclusions: The Cortisol II assay had good precision over the entire measuring range and had excellent agreement with LC-MS/MS. This test was found suitable for routine diagnostic application and will be valuable for the diagnosis of adrenocortical diseases