NONE-No attached Diamond beamline
Theoretical Physics
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Abstract: From the dawn of modern electromagnetism it has been known that a magnetic field is not handed (chiral). Arima and Saito (2009 J. Phys.: Condens. Matter 21 498001) persist with unwisdom in their repeated claim to have observed control of chirality using a magnetic field by and in itself. In our reply to their claim, we demonstrate damning errors in all challenges in the comment levelled at our analysis of the observation reported by Saito et al (2008 Phys. Rev. Lett. 101 117402) and made on a crystal of copper metaborate.
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Dec 2009
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NONE-No attached Diamond beamline
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Abstract: Biologically synthesized magnetite (Fe 3 O 4 ) nanoparticles are studied using x-rayabsorption and x-raymagnetic circular dichroism following exposure to hexavalent Cr solution. By examining their magnetic state, Cr cations are shown to exist in trivalent form on octahedral sites within the magnetite spinel surface. The possibility of reducing toxic Cr(VI) into a stable, nontoxic form, such as a Cr 3+ -spinel layer, makes biogenic magnetite nanoparticles an attractive candidate for Cr remediation.
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Oct 2009
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NONE-No attached Diamond beamline
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Abstract: We present resonant magnetic X-ray scattering (RMXS) measurements in an applied magnetic field on a single crystal of Ca3Co2O6Ca3Co2O6. We focus our attention on the transition from an incommensurate partially disordered antiferromagnetic state to a ferrimagnetic state: a lock-in and a divergence of the magnetic correlation length at the transition shed light on the nature of the ground state and on the c-axis vs. in-plane exchange couplings in this system.
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Oct 2009
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NONE-No attached Diamond beamline
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Abstract: Epitaxially grown magnetic tunnel junctions (MTJs) with a stacking structure of Co2MnSi/MgO/CoFe were fabricated. Their tunnel magnetoresistance (TMR) effects were investigated. The TMR ratio and tunnelling conductance characteristics of MTJs were considerably different between those with an MgO barrier prepared using sputtering (SP-MTJ) and those prepared using EB evaporation (EB-MTJ). The EB-MTJ exhibited a very large TMR ratio of 217% at room temperature and 753% at 2?K. The bias voltage dependence of the tunnelling conductance in the parallel magnetic configuration for the EB-MTJ suggests that the observed large TMR ratio at RT results from the coherent tunnelling process through the crystalline MgO barrier. The tunnelling conductance in the anti-parallel magnetic configuration suggests that the large temperature dependence of the TMR ratio results from the inelastic spin?flip tunnelling process.
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Oct 2009
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NONE-No attached Diamond beamline
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Abstract: Spin-polarized neutron-reflectivity measurements have been performed on superconducting Pb films. For fields applied in the plane of the film we are able to determine the magnetic field profile across the thickness of the film in the superconducting state. This allows the direct observation of distinct mesoscopic ground states in this geometry, from Meissner expulsion to a double row of vortices, which occur as a function of film thickness and external magnetic field. The data can be compared directly with solutions of the time-dependent Ginzburg-Landau equations, where we demonstrate good agreement between data and simulation. This provides a powerful demonstration of this widely applicable experimental technique to study mesoscopic ground states and a useful validation of this theoretical approach.
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Oct 2009
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NONE-No attached Diamond beamline
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Abstract: Synchrotron surface X-ray diffraction has been used to investigate in situ the morphology and epitaxy of monolayer amounts of copper electrodeposited from aqueous electrolyte onto ultra-high vacuum prepared, smooth, Ga- or As-terminated GaAs(0 0 1) surfaces. The fcc lattice of the epitaxial Cu islands is rotated by ?5° and tilted by about ?9° with respect to the GaAs substrate lattice, leading to eight symmetry equivalent domains of Cu islands terminated by {1 1 1} facets.
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Sep 2009
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NONE-No attached Diamond beamline
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Abstract: This study investigated Zn adsorption to an extracellular polymeric substance (EPS)-producing bacterial strain, Bacillus licheniformis S-86. Batch metal adsorption experiments and spectroscopic (EXAFS) analysis were conducted using both native (EPS-covered) cells and EPS-free cells in order to assess the contribution made by EPS to metal adsorption by this strain. Thermodynamic modelling of the macroscopic adsorption data indicated that Zn complexation to both native and EPS-free cells was predominantly to carboxyl and phosphate functional groups, but with some adsorption to phosphodiester groups also evident. EXAFS analysis shows Zn-carboxyl complexation, but possibly with a significant contribution from a second, phosphate functional group. Apparently, EPS removal does not affect the metal adsorption capacity at the metal: biomass ratios used here. As the concentration of carboxyl and phosphate functional groups is only slightly affected by EPS extraction, complexation to these functional groups explains why EPS removal does not reduce the amount of Zn adsorbed by the cells. It was also observed that EPS production induces aggregation of cells in suspension. This may reduce the cell surface area available for metal adsorption, thus counteracting any greater availability of metal-complexing ligands in the EPS layer compared to an EPS-free cell surface. Furthermore, the EPS layer appears to be the major source of dissolved organic carbon (DOC) released to solution during the metal adsorption experiments. This DOC may reduce metal binding to the cell surfaces by acting as a competing complexing ligand. These observations have implications for industrial application of biofilms and suggest that over-production of EPS in bio-reactors may reduce the metal removal efficiency of the biomass.
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Sep 2009
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NONE-No attached Diamond beamline
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Abstract: The hole confinement in Ge dots fabricated on a wetting layer in Stranski-Krastanov (S-K) growth was directed by an applied bias. At medium bias voltage, the holes overflowed from the small dots, indicating a moderate potential barrier without a notch at the boundary. The electrostatic force of the confined holes attracted excessive holes to the wetting layer. The system was energetically stabilized by the formation of a "virtual dot" in an open space enclosed by dots. At a high bias voltage, the virtual dot disappeared since the holes in the wetting layer were emitted from the surface.
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Aug 2009
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NONE-No attached Diamond beamline
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Abstract: We report the doping dependence of the ground state of A-site ordered manganites below and above half doping. Energy and polarization dependence of the orbital reflection, taken by resonant soft-x-ray powder diffraction, at both Mn L2,3 and O K edges, provides direct evidence for orbital order at Mn3+ and oxygen sites and absence of Zener polaron formation. For x?0.2 anomalous melting of the orbital order is observed, which is coupled neither to magnetic ordering nor to a structural transition, indicating a two-dimensional character of the interactions.
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Aug 2009
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NONE-No attached Diamond beamline
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Abstract: The longitudinal coherence function at the Advanced Photon Source beamline 34-ID-C has been measured by a novel method and the coherence length (?L) determined to be, ?L = 0.66 ± 0.02µm. Three dimensional Coherent X-ray Diffraction (CXD) patterns were measured for multiple Bragg reflections from two Zinc Oxide (ZnO) nanorods with differing aspect ratios. The visibility of fringes corresponding to the 002 crystal direction for each reflection were found to be different and used to map the coherence function of the incident radiation. Partial coherence was found to be associated with amplitude ‘hot’ spots in three dimensional reconstructions of the crystal structure.
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Aug 2009
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