| 1. |
- Rehammar, Robert, 1980, et al.
(författare)
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Carbon nanofiber-based photonic crystals – fabrication, diffraction and ellipsometry investigations
- 2011
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Ingår i: Carbon-Based Electronic Devices - Processing, Performance and Reliability. - : Materials Research Society. - 0272-9172. - 9781618394996 ; , s. 28-33
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Konferensbidrag (refereegranskat)abstract
- Carbon nanofibers were used as building blocks for two-dimensional photonic crystal slabs. Electron beam lithography and chemical vapor deposition were used to fabricate regular arrays and random patterns of nanofibers. The optical properties of the samples were investigated using a diffraction measurement setup, as well as reflection ellipsometry. We find that carbon nanofiber regularity has a strong effect on both diffractive and specular optical properties. This shows that ellipsometry can be a valuable tool to study properties of carbon nanofiber arrays. It also shows that carbon nanofibers provide an interesting candidate as building blocks for nanostructured optical components.
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| 2. |
- Andersson, Henrik C. M., et al.
(författare)
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Creep testing of thick-wall copper electron beam and friction stir welds
- 2004
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Ingår i: Materials Research Society Symposium Proceedings. - 0272-9172 .- 1946-4274. - 1558997741 ; 824, s. 51-56
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Tidskriftsartikel (refereegranskat)abstract
- Thick section copper canisters are planned to be used as a corrosion protection of nuclear waste disposal containers for long term underground deposal in Sweden. The copper canisters will have the top and possibly the bottom lid welded to the canister walls using electron beam or friction stir welding. Due to the high external hydrostatic pressure and the relatively high temperature of the waste during the first one hundred years the copper will creep. The creep process will close the manufacturing gap between the cast iron container and the copper canister. The creep ductility must be sufficient to avoid cracking of the weld. Specimens cut from the friction stir welds and the electron beam welds have been creep tested at temperatures ranging from 75 to 175 degreesC. Cross-weld specimens were used for both friction stir and electron beam welds. Weld metal, heat affected zone and base metal were also studied for friction stir welds. The results for the electron beam welds show that the main creep deformation is concentrated to the weld metal where the failure takes place. Weld metal and most cross-weld tests of friction stir weld material show similar creep lives and ductility as base metal tests. Ductility at rupture was found to exceed 30% for friction stir weld specimens, and the Norton power law exponent was determined to be between 30 and 50.
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| 3. |
- Bader, Thomas K., 1980-, et al.
(författare)
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From lignin to spruce : Poromechanical upscaling of wood strength
- 2011
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Ingår i: 2010 MRS Fall Meeting. - Warrendale, Pennsylvania, USA : Materials Research Society. - 9781605112787 ; , s. 75-80
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Wood strength is highly anisotropic, due to the inherent structural hierarchy of the material. In the framework of a combined random-periodic multiscale poro-micromechanics model, we here translate compositional information throughout this hierarchy into the resulting anisotropic strength at the softwood level, based on “universal” elastic properties of cellulose, hemicelluloses, and lignin, and on the shear strength of the latter elementary constituent. Therefore, derivation of the elastic energy in a piece (representative volume element – RVE) of softwood, stemming from homogeneous macroscopic strains prescribed in terms of displacements at the boundary of the RVE and from pressure exerted by water filling the nanoporous space between the hemicelluloses-lignin network within the cell walls, with respect to the shear stiffness of lignin, yields higher order strains in the lignin phase, approximating micro-stress peaks leading to local lignin failure. Relating this (quasi-brittle) failure to overall softwood failure (or strictly speaking, elastic limit of softwood) results in a macroscopic microstructure-dependent failure criterion for softwood. The latter satisfactorily predicts the biaxial strength of spruce at various loading angles with respect to the grain direction. The model also predicts the experimentally well-established fact that uniaxial tensile and compressive strengths, as well as the shear strength of wood, depend quasi-linearly on the cell water content, but highly nonlinearly on the lumen porosity.
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| 4. |
- Boosalis, Alexander, et al.
(författare)
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Spectroscopic Mapping Ellipsometry of Graphene Grown on 3C SiC
- 2012
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Ingår i: MRS Proceedings Volume 1407. - : Springer Science and Business Media LLC. ; , s. aa20-43
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Konferensbidrag (refereegranskat)abstract
- Spectroscopic mapping ellipsometry measurements in the visible spectrum (1.25 to 5.35 eV) are performed to determine the lateral variations of epitaxial graphene properties as grown on 3C SiC. Data taken in the visible spectrum is sensitive to both the Drude absorption of free charge carriers and the characteristic exciton enhanced van Hove singularity at 5 eV. Subsequent analysis with simple oscillator models allows the determination of physical parameters such as free charge carrier scattering time and local graphene thickness with a lateral resolution of 50 microns.
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| 5. |
- Butorin, S. M., et al.
(författare)
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Resonant inelastic soft X-ray scattering studies of U(VI) reduction on iron surfaces
- 2004
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Ingår i: Materials Research Society Symposium Proceedings. - 0272-9172 .- 1946-4274. ; 807:Scientific Basis for Nuclear Waste Management XXVII, s. 113-118
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Tidskriftsartikel (refereegranskat)abstract
- The authors report on the spectroscopic anal. of several samples relevant to the processes governing the behavior of oxidized U species in groundwater solns. under anoxic conditions. Both Fe samples with different times of exposure to the U(IV) soln. and Fe metal-soln. interfaces in the liq. cell ex-situ and in-situ, resp. Resonant inelastic soft x-ray scattering is sensitive to the chem. state of U. The measurements were performed at a no. of energies of the primary photon beam across the U 5d absorption edge. The results unambiguously indicate the redn. of U(VI) to U(IV) on the Fe surface. [on SciFinder(R)]
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| 6. |
- Cui, Daqing, et al.
(författare)
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Surface mediated processes in the interaction of spent fuel α-doped UO2 with H2
- 2008
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Ingår i: Materials Research Society Symposium Proceedings. - 0272-9172. - 9781605110745 ; 1104, s. 87-99
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Konferensbidrag (refereegranskat)abstract
- In most deep disposal concepts, large amounts of hydrogen are expected to be produced by the anoxic corrosion of massive iron containers. At repository temperatures, hydrogen is quite inert and is not expected to contribute to the redox capacity of the deep groundwaters. In several recent works, a large impact of dissolved hydrogen on the dissolution of the LWR or MOX fuel and UO 2(s) doped with 233U or 238Pu has been observed. For hydrogen concentrations above a certain limit, the dissolution rates of these highly radioactive materials drop to very low values. A discussion of the results obtained with spent fuel or ?-doped UO 2 in the presence of a range of hydrogen concentrations is presented. Typical for all measurements under such conditions are the very low long term concentrations of uranium and other redox-sensitive radionuclides, such as Tc and the minor actinides. The concentrations of U are systematically lower than the values measured during UO2(s) solubility measurements carried out in the presence of strong reducing agents. Measurements of the radiolytic oxygen after long leaching periods result in values below detection limit. The investigation of the surface of spent fuel or UO2(s) pellets doped with 233U by XPS after long periods of testing shows absence of oxidation. The kinetics of the release of non-redox sensitive elements such as Sr and Cs, used to estimate fuel matrix dissolution rates, is also discussed. An attempt is made to propose potential mechanisms responsible for the observed behaviour, based mainly on data from studies on the interaction of water adsorbed on the surfaces of metal oxides or actinide oxides with radiation. Another important effect observed in recent studies is the existence of a threshold for the specific alpha activity below which no measurable influence of the alpha radiolysis on the uranium release from UO2 is observed. The importance of such a threshold for the behaviour of spent fuel under repository conditions encompassing very long time scales will be discussed, as well as the necessity to better investigate the mechanisms of recombination reactions in a thin water layer on the surface of actinide oxides affected by ?- radiolysis.
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| 7. |
- Di Luccio, Tiziana, et al.
(författare)
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Synthesis of CdS nanocrystals in polymeric films studied by in-situ GID and GISAXS
- 2015
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Ingår i: Insights for Energy Materials Using In-Situ Charaterization. - : Springer Science and Business Media LLC. - 0272-9172. - 9781510826625 ; 1810, s. 9-14
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Konferensbidrag (refereegranskat)abstract
- In this work, we describe the synthesis of CdS nanocrystals in thin polymeric films by in-situ Grazing Incidence Diffraction (GID) and Grazing Incidence Small Angle Scattering (GISAXS). The 2D GISAXS patterns indicate how the precursor structure is altered as the temperature is varied from 25°C to 300°C. At 150°C, the CdS nanocrystals start to arrange themselves in a hexagonal lattice with a lattice parameter of 27 A. The diffraction intensity from the hexagonal lattice reaches a maximum at 170"C and decreases steadily upon further heating above 220°C indicating loss of symmetry. Correspondingly, the GID scans at 170°C show strong crystalline peaks from cubic CdS nanocrystals that are about 2 nm size. The results indicate that a temperature of 170°C is sufficient to synthesize CdS nanocrystals without degradation of the polymer matrix (Topas) in thin films (about 30nm).
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| 8. |
- El Daif, O., et al.
(författare)
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Silver nanodiscs for light scattering in thin epitaxial silicon solar cells: Influence of the disc radius
- 2011
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Ingår i: Materials Research Society Symposium Proceedings. - : Springer Science and Business Media LLC. - 0272-9172. - 9781627482110 ; 1391, s. 75-80
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Konferensbidrag (refereegranskat)abstract
- The effect of silver nanoparticles showing localised plasmonic resonances on the efficiency of thin film silicon solar cells is studied. Silver (Ag) nanodiscs were deposited on the surface of silicon cells grown on highly doped silicon substrates, through hole-mask colloidal lithography, which is a low-cost and bottom-up technique. The cells have no back reflector in order to exclusively study the effect of the front surface on their properties. Cells with nanoparticles were compared with both bare silicon cells and cells with an antireflection coating. We optically observe a resonance showing an absorption increase controllable by the disc radius. We also see an increase in efficiency with respect to bare cells, but we see a decrease in efficiency with respect to cells with an antireflection coating due to losses at wavelengths below the plasmon resonance. As the material properties are not notably affected by the particles deposition, the loss mechanism is an important absorption in the nanoparticles. We confirm this by numerical simulations.
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| 9. |
- Ericsson, Torsten, 1938-, et al.
(författare)
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Studies of residual stress, microcracks, hardness and microstructure of cold compacted metallic green bodies
- 2003
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Ingår i: Materials Research Society Symposium Proceedings. - 0272-9172 .- 1946-4274. ; 759, s. 53-64
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Tidskriftsartikel (refereegranskat)abstract
- The residual stresses have been measured by X-ray and neutron diffraction on PM green bodies manufactured by conventional and high speed compaction of iron powder with and without added copper and brass powder. Compressive residual stresses are present in a thin layer in both top and side surfaces. They are largest in the side surfaces due to plastic deformation of the surface material caused by the friction forces during ejection out of the die. In the interior of the green body residual stresses exist with certain region under compression (periferical regions) and other under tension (more central regions). It is unclear whether mixing iron powder with brass or copper powder leads to considerable phase stresses between the two phases.
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| 10. |
- Fang, Mei, 1984-, et al.
(författare)
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Room temperature ferromagnetism of Fe-doped ZnO and MgO thin films prepared by ink-jet printing
- 2012
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Ingår i: MRS Proceedings. - : Springer Science and Business Media LLC. - 0272-9172 .- 1946-4274.
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Konferensbidrag (refereegranskat)abstract
- Room temperature magnetic properties of un-doped, as well as 10 at.% Fe-doped ZnOand MgO single-pass layer of ink-jet printed thin films have been investigated to obtain insightinto the role of the band gaps and mechanisms for the origin of ferromagnetic order in thesematerials. It is found that on doping with Fe, the saturation magnetization is enhanced by severalfoldin both systems when compared with the respective un-doped thin films. For a ~28 nm thickfilm of Fe-doped ZnO (Diluted Magnetic Semiconductor, DMS) we observe an enhancedmoment of 0.465 μB/Fe atom while it is around 0.111μB/Fe atom for the doped MgO (DilutedMagnetic Insulator, DMI) film of comparable thickness. Also, the pure ZnO is far moreferromagnetic than pure MgO at comparable low film thicknesses which can be attributed todefect induced magnetism originating from cat-ion vacancies. However, the film thicknessdependence of the magnetization and the defect concentrations are found to be significantlydifferent in the two systems so that a comparison of the magnetism becomes more complex forthicker films.
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