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Lee J.-S.,Brookhaven National Laboratory | Arena D.A.,Brookhaven National Laboratory | Yu P.,University of California at Berkeley | Nelson C.S.,Brookhaven National Laboratory | And 7 more authors.
Physical Review Letters | Year: 2010

We present an unreported magnetic configuration in epitaxial La 1-xSrxMnO3 (x∼0.3) (LSMO) films grown on strontium titanate (STO). X-ray magnetic circular dichroism indicates that the remanent magnetic state of thick LSMO films is opposite to the direction of the applied magnetic field. Spectroscopic and scattering measurements reveal that the average Mn valence varies from mixed Mn3⊃+/Mn4⊃+ to an enriched Mn3⊃+ region near the STO interface, resulting in a compressive lattice along the a, b axis and a possible electronic reconstruction in the Mn e g orbital (d3z2-r2). This reconstruction may provide a mechanism for coupling the Mn3⊃+ moments antiferromagnetically along the surface normal direction, and in turn may lead to the observed reversed magnetic configuration. © 2010 The American Physical Society.

Olivier J.-H.,University of Strasbourg | Harrowfield J.,ISIS | Ziessel R.,University of Strasbourg
Chemical Communications | Year: 2011

Synthetic routes for the construction of 3-substituted 2,4-pentadionate ligands are broadly surveyed. They involve sequential alkylation and arylation by numerous methods, including those based on reactions of coordinated ligands, and can provide access to various rationally designed ligands. Applications of such ligands in the synthesis of multichromophoric complexes are illustrated in some detail. Incorporation of 3-substituted 2,4-pentanedione units into mesomorphic and macromolecular structures is considered in relation to structural control of energy and electron transfer processes in photoactive systems. Aspects of the general supramolecular chemistry of complexes of 3-substituted-2,4-pentadionate ligands are briefly discussed to illustrate the utility of such species within the full range of 1,3-dionate chemistry. © 2011 The Royal Society of Chemistry.

Hall D.A.,University of Manchester | Evans J.D.S.,Atomic Weapons Establishment | Covey-Crump S.J.,University of Manchester | Holloway R.F.,University of Manchester | And 3 more authors.
Acta Materialia | Year: 2010

The hydrostatic pressure-induced martensitic transformation from the ferroelectric rhombohedral to antiferroelectric orthorhombic phase in PZT 95/5 ceramics has been studied using neutron diffraction. The transition to the orthorhombic phase initiates at a pressure of 260 MPa and is almost complete at 290 MPa. This stress range is much narrower than that observed in uniaxial loading, which starts at 200 MPa and is incomplete even at 400 MPa. The narrower stress range observed under hydrostatic loading is attributed to a lack of internal stress developed during the transformation. By contrast, the work required to start the transformation is approximately the same under both types of loading. The transformation progresses more gradually with increasing pressure when a static electric field is applied to a specimen in a pre-poled state. Tests carried out on porous specimens, having a relative density of approximately 90%, demonstrated that the transformation occurred over a narrow pressure range but with a lower transformation pressure of approximately 220 MPa. © 2010 AWE and Crown Copyright. Published by Elsevier Ltd. All rights reserved.

Shen H.-H.,Physical and Theoretical Chemistry Laboratory | Thomas R.K.,Physical and Theoretical Chemistry Laboratory | Penfold J.,ISIS | Fragneto G.,ILL
Langmuir | Year: 2010

The lipopeptide surfactin from Bacillus subtilis strains exhibits strong surface and biological activity, the latter probably because of its interaction with biological membranes. We have investigated the interaction of aqueous solutions of surfactin with supported bilayers of diphosphatidylcholine (DPPC) on silica using neutron reflectometry. We have also used small-angle neutron scattering (SANS) to study the solubilized aggregates formed as a result of the destruction of the supported membrane by surfactin. Although surfactin on its own does not attach to the silica supporting surface, it is taken up from solution by the membrane, confirming that there is an attractive interaction between DPPC and surfactin. The surfactin concentration in the layer can reach up to about 20 mol % relative to DPPC. The membrane is stable provided that the surfactin concentration is below its critical micelle concentration (cmc, 5×10-5 M). Above the cmc, however, the membrane is solubilized and removed from the surface, though not always completely, over a period of hours. There are signs that there is an induction period while the surfactin concentration builds up in the membrane. This would be consistent with the need for a threshold concentration of surfactin in the bilayer. The presence of a surfactin correlation peak in the SANS showed that in the bulk solution, at the same concentrations as used for the deposition, surfactin forms aggregates that must be localized in the DPPC multilamellar vesicles at a separation of about 160 Å. The structure could be fitted with an approximate model where the surfactin has an aggregation number of 50 ± 10 with a radius of about 27 Å. Given the very small water thicknesses in the DPPC lamellar aggregates, the surfactin must exist as aggregates in the phospholipid bilayer, and these structures are responsible for solubilizing the DPPC. © 2010 American Chemical Society.

George K.,University of Southampton | Jura M.,ISIS | Levason W.,University of Southampton | Light M.E.,University of Southampton | Reid G.,University of Southampton
Dalton Transactions | Year: 2014

The reaction of AlCl3 with Me2E (E = S, Se or Te) or nBu2E (E = Se or Te) in CH2Cl2 under rigorously anhydrous conditions gave the pseudo-tetrahedral complexes [AlCl3(R2E)]. The [AlX3(Me2E)] (X = Br or I, E = S; X = Br, E = Te) were made from toluene solution since attempted syntheses in CH2Cl2 resulted in substantial chloride incorporation. The synthesis of [(AlCl3)2{o-C 6H4(CH2SEt)2}], in which the ligand bridges two tetrahedral aluminium centres, and of the six-coordinate trans-[AlX2{MeE(CH2)2EMe}2][AlX 4] (X = Cl or Br, E = S, and X = Cl, E = Se) and cis-[AlI 2{MeS(CH2)2SMe}2][AlI4] are reported. The tripodal thioether forms [AlCl3{MeC(CH 2SMe)3}], which is a chain polymer with κ2-coordinated ligand and a tbp arrangement at Al(iii). Chalcogenoether macrocycle complexes [AlCl3([9]aneS3)], [AlCl2([14]aneS4)][AlCl4] and [AlCl 2([16]aneSe4)] [AlCl4] are also described. All complexes were characterised by microanalysis, IR and multinuclear NMR ( 1H, 27Al, 77Se or 125Te) spectroscopy as appropriate. In CH2Cl2 solution [AlCl 3(Me2S)] with added Me2S forms [AlCl 3(Me2S)2], and the [AlX2{MeS(CH 2)2SMe}2][AlX4] exist as mixtures of cis and trans isomers which undergo rapid exchange at ambient temperatures. X-Ray crystal structures are reported for [AlCl3(Me2Se], [AlX3(Me2Te)] (X = Cl or Br), trans-[AlCl 2{MeE(CH2)2EMe}2][AlCl4] (E = S or Se), cis-[AlI2{MeS(CH2)2SMe} 2][AlI4], [AlCl3{MeC(CH2SMe) 3}], and for the sulfonium salt [Me2SH][AlCl4]. The aluminium halide chalcogenoether chemistry is compared with the corresponding gallium and indium systems, and the relative Lewis acidities of the metals discussed. Attempts to use [AlCl3(nBu 2E)] (E = Se or Te) as LPCVD reagents to form aluminium chalcogenide films were unsuccessful. © 2014 The Royal Society of Chemistry.

De Groot C.H.,University of Southampton | Gurnani C.,University of Southampton | Hector A.L.,University of Southampton | Huang R.,University of Southampton | And 3 more authors.
Chemistry of Materials | Year: 2012

The distorted octahedral complexes [SnCl4{ nBuSe(CH2)nSenBu}] (n = 2 or 3), (1) and (2), obtained from reaction of SnCl4 with the neutral bidentate ligands and characterized by IR/Raman and multinuclear (1H, 77Se{1H} and 119Sn) NMR spectroscopy and X-ray crystallography, serve as very effective single source precursors for low pressure chemical vapor deposition (LPCVD) of microcrystalline, single phase tin diselenide films onto SiO2, Si and TiN substrates. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) imaging show hexagonal plate crystallites which grow perpendicular to the substrate surface in the thicker films, but align mostly parallel to the surface when the quantity of reagent is reduced to limit the film thickness. X-ray diffraction (XRD) and Raman spectroscopy on the deposited films are consistent with hexagonal SnSe 2 (P3̄m1; a = b = 3.81 Å; c = 6.13 Å), with strong evidence for preferred orientation of the crystallites in thinner (0.5-2 μm) samples, consistent with crystal plate growth parallel to the substrate surface. Hall measurements show the deposited SnSe2 is a n-type semiconductor. The resistivity of the crystalline films is 210 (±10) mω cm and carrier density is 5.0 × 1018 cm-3. Very highly selective film growth from these reagents onto photolithographically patterned substrates is observed, with deposition strongly preferred onto the (conducting) TiN surfaces of SiO2/TiN patterned substrates, and onto the SiO2 surfaces of Si/SiO2 patterned substrates. A correlation between the high selectivity and high contact angle of a water droplet on the substrate surfaces is observed. © 2012 American Chemical Society.

George K.,University of Southampton | Jura M.,ISIS | Levason W.,University of Southampton | E. Light .M.,University of Southampton | And 2 more authors.
Inorganic Chemistry | Year: 2012

Reaction of GaCl 3with 1 mol equiv of [14]aneS 4in anhydrous CH 2Cl 2gives the exocyclic chain polymer [GaCl 3([14]-aneS 4)] (1) whose structure confirms trigonal bipyramidal coordination at Ga with a planar GaCl 3unit. In contrast, using [16]aneS 4and GaCl 3or [16]aneSe 4and MCl 3(M = Ga or In) in either a 1:1 or a 1:2 molar ratio produces the anion-cation complexes [GaCl 2([16]aneS 4)][GaCl 4] (2) and [MCl 2([16]-aneSe 4)][MCl 4] (M = Ga, 3 and M = In, 4) containing transoctahedral cations with endocyclic macrocycle coordination. The ligand-bridged dimer [(GaCl 3) 2{o-C 6H 4(SMe) 2}] (5) is formed from a 2:1 mol ratio of the constituents and contains distorted tetrahedral Ga(III). This complex is unusually reactive toward CH 2Cl 2, which is activated toward nucleophilic attack by polarization with GaCl 3, producing the bis-sulfonium species [o-C 6H 4(SMeCH 2Cl) 2][GaCl 4] 2(6), confirmed from a crystal structure. In contrast, the xylyl-based dithioether gives the stable [(GaCl 3) 2{o-C 6H 4(CH 2SEt) 2}] (8). However, replacing GaCl 3with InCl 3with o-C 6H 4(CH 2SEt) 2preferentially forms the 4:3 In:L complex [(InCl 3) 4{o-C 6H 4(CH 2SEt) 2} 3] (9) containing discrete tetranuclear moieties in which the central In atom is octahedrally coordinated to six bridging Cl's, while the three In atoms on the edges have two bridging Cl's, two terminal Cl's, and two mutually trans S-donor atoms from different dithioether ligands. GaCl 3also reacts with the cyclic bidentate [8]aneSe 2to form a colorless, extremely air-sensitive adduct formulated as [(GaCl 3) 2([8]aneSe 2)] (10), while InCl 3gives [InCl 3([8]aneSe 2)] (14). Very surprisingly, 10 reacts rapidly with O 2gas to give initially the red [{[8]aneSe 2} 2][GaCl 4] 2(11) and subsequently the yellow [{[8]aneSe 2}Cl][GaCl 4] (12). The crystal structure of the former confirms a dimeric [{[8]aneSe 2} 2] 2+dication, derived from coupling of two mono-oxidized {[8]aneE 2} +·cation radicals to form an Se-Se bond linking the rings and weaker transannular 1,5-Se···Se interactions across both rings. The latter (yellow) product corresponds to discrete doubly oxidized {[8]aneSe 2} 2+cations (with a primary Se-Se bond across the 1,5-positions of the ring) with a Cl -bonded to one Se. Tetrahedral [GaCl 4] -anions provide charge balance in each case. These oxidation reactions are clearly promoted by the Ga(III) since [8]aneSe 2itself does not oxidize in air. The new complexes have been characterized in the solid state by IR and Raman spectroscopy, microanalysis, and X-ray crystallography where possible. Where solubility permits, the solution characteristics have been probed by 1H, 1Se{ 1H}, and 1Ga NMR spectroscopic studies. © 2012 American Chemical Society.

Dalgliesh R.M.,ISIS | Langridge S.,ISIS | Plomp J.,Technical University of Delft | De Haan V.O.,Technical University of Delft | Van Well A.A.,Technical University of Delft
Physica B: Condensed Matter | Year: 2011

OffSpec has been purposely built as a low background, polarised neutron reflectometer with spin-echo for Larmor labeling. The instrument received first neutrons in December 2008 and five of the intended seven modes of operation have now been tested and operated with peer reviewed user experiments. The technical performance of the instrument will be reviewed in each of the modes and future scientific possibilities discussed. Particular attention will be paid to results from spin-echo SANS (SESANS) and spin-echo resolved grazing incidence scattering (SERGIS), where the largest number of measurements have been performed. © 2010 Elsevier B.V. All rights reserved.

Barbagallo M.,University of Cambridge | Hine N.D.M.,University of Cambridge | Hine N.D.M.,Imperial College London | Cooper J.F.K.,University of Cambridge | And 7 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

We have carried out both experimental and theoretical studies of the magnetic properties of thin films of oxygen-deficient EuO. Accurate control of the oxygen vacancy concentration in these films was achieved by sputter codeposition of Eu and Eu2 O3. The films were characterized by superconducting quantum interference device, x-ray reflectometry and polarized neutron reflectometry and the magnetic moment was found to increase monotonically with oxygen vacancy concentration. The electronic structure of EuO1-x was calculated using density-functional theory (DFT+U). In agreement with previous studies, these calculations show that oxygen vacancies act as n -type dopants in EuO and that the excess electrons preferentially populate the majority spin branch of the spin-polarized conduction band. The observed increase in the magnetic moment originating from these excess electrons was accurately determined experimentally and found to be in good agreement with our quantitative predictions. © 2010 The American Physical Society.

The motivational interview helps nurses trained in this technique to optimise the motivational approach with the patient. This communication tool also gives them greater understanding of the resistance of people confronted with a chronic disease and to support them more effectively towards change. © 2014 Elsevier Masson SAS. All rights reserved.

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