| 1. |
- Abrikosov, I. A., et al.
(författare)
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Multiscale approach to theoretical simulations of materials for nuclear energy applications : Fe-Cr and Zr-based alloys
- 2013
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Ingår i: Advances in materials for nuclear energy. - : Materials Research Society. - 9781605114910 ; , s. 3-14
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Konferensbidrag (refereegranskat)abstract
- We review basic ideas behind state-of-the-art techniques for first-principles theoretical simulations of the phase stabilities and properties of alloys. We concentrate on methods that allow for an efficient treatment of compositional and thermal disorder effects. In particular, we present novel approach to evaluate free energy for strongly anharmonic systems. Theoretical tools are then employed in studies of two materials systems relevant for nuclear energy applications: Fe-Cr and Zr-based alloys. In particular, we investigate the effect of hydrostatic pressure and multicomponent alloying on the mixing enthalpy of Fe-Cr alloys, and show that in the ferromagnetic state both of them reduce the alloy stability at low Cr concentration. For Zr-Nb alloys, we demonstrate how microscopic parameters calculated from first-principles can be used in higher-level models.
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| 2. |
- Allali, Naoual, et al.
(författare)
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Electrocatalytic effect towards NADH induced by HiPco single-walled carbon nanotubes covalently functionalized by ferrocene derivatives
- 2013
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Ingår i: 2012 MRS Fall Meeting. - : Cambridge University Press.
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Konferensbidrag (refereegranskat)abstract
- The present work reports the covalent functionalization of single-walled carbon nanotubes (SWCNTs) by ferrocene derivatives with polyethyleneglycol linkers. A very clean initial sample was chosen to avoid any residual catalyst and carbon impurities. Functionalized SWCNTs (f-CNTs) are deposited on the surface of a glassy carbon electrode (GCE) and this modified electrode is used for oxidizing the cofactor NADH (dihydronicotinamide adenine dinucleotide) in the presence of diaphorase. A clear electrocatalytic effect is evidenced, which can only be attributed to the f-CNTs.
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| 3. |
- Allali, Naoual, et al.
(författare)
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Few-wall carbon nanotubes covalently functionalized by ferrocene groups for bioelectrochemical devices
- 2012
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Ingår i: MRS Online Proceedings Library. - : Cambridge University Press. - 9781605114286
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Konferensbidrag (refereegranskat)abstract
- The present work reports the covalent functionalization of few-wall CNTs (FWCNTs) by ferrocene derivatives to i) improve their dispersion efficiency in water and ii) to graft electroactive chemical groups on their side-walls in order to promote electron transfer to biomolecules. The functionalized CNTs (f-CNTs) are used to modify a glassy carbon electrode and this modified electrode is used for oxidizing the cofactor NADH (dihydronicotinamide adenine dinucleotide).
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| 4. |
- 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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| 5. |
- Biswas, Anis, et al.
(författare)
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The effect of oxygen partial pressure during deposition in the magnetic properties of ZnO thin film
- 2011
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Ingår i: Mater Res Soc Symp Proc. - : Springer Science and Business Media LLC. - 9781605112695 ; , s. 117-122
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Konferensbidrag (refereegranskat)abstract
- We have studied the magnetic properties of 100 nm thick ZnO thin films prepared by magnetron sputtering in different oxygen partial pressures (ratio of oxygen pressure to total pressure in deposition chamber, P Oxy). Only the films fabricated at P Oxy below ∼ 0.5 show room temperature ferromagnetism. The saturation magnetization at room temperature is initially found to increase as P Oxy increases and reaches maximum value of ∼ 5 emu/gm at P Oxy ∼ 0.3 and then starts to decrease and becomes diamagnetic for P Oxy > 0.5. From small angle XRD study of structural properties of the films, we find that the lattice stress developed in the film along c-axis also exhibits a similar behavior with the variation of P Oxy. Thus, both the room temperature ferromagnetism and lattice stress appear to originate from the intrinsic defects present in the sample.
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| 6. |
- 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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| 7. |
- Dou, Maofeng, et al.
(författare)
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Nanostructured ZnO-X alloys with tailored optoelectronic properties for solar-energy technologies
- 2013
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Ingår i: Materials Research Society Symposium Proceedings. - : Materials Research Society.
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Konferensbidrag (refereegranskat)abstract
- Alloying ZnO with isovalent compounds allows tailoring the material's optoelectronic properties. In this work, we theoretically analyze the ZnO-based alloys ZnO-X ≡ (ZnO)1-x(X)x where X = GaN and InN, employing a first-principles Green's function method GW0 based on the density functional approach. Since the alloy compounds are isovalent to ZnO, we find relatively small distortion of the crystalline structure, however, nanocluster structures are expected to be present in the alloy. ZnO-X reveal intriguing optoelectronic properties. Incorporating GaN or InN in ZnO strongly narrows the energy gap. The band gap energy is reduced from Eg = 3.34 eV in intrinsic ZnO to ∼2.17 and ∼1.89 eV in ZnO-X by alloying ZnO with 25% GaN and InN, respectively. Moreover, clustering enhances the impact on the electronic structure, and the gap energy in ZnO-InN is further reduced to 0.7-1.5 eV if the 25% compound contains nanoclusters. The dielectric function - 2(ω) varies weakly in ZnO-GaN with respect to alloy composition, while it varies rather strongly in ZnO-InN. Hence, by properly growing and designing ZnO-X, the alloy can be optimized for a variety of novel integrated optoelectronic nano-systems.
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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. |
- Fang, Mej, et al.
(författare)
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'In-situ' preparation of metal oxide thin films by inkjet printing acetates solutions
- 2013
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Ingår i: Mater Res Soc Symp Proc. - : Springer Science and Business Media LLC. - 9781605115245 ; , s. 13-20
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Konferensbidrag (refereegranskat)abstract
- Direct printing of functional oxide thin films could provide a new route to low-cost, efficient and scalable fabrications of electronic devices. One challenge that remains open is to design the inks with long term stability for effective deposition of specific oxide materials of industrial importance. In this paper, we introduce a reliable method of producing stable inks for 'in-situ' deposition of oxide thin films by inkjet printing. The inks were prepared from metal-acetates solutions and printed on a variety of substrates. The acetate precursors were decomposed into oxide films during the subsequent calcination process to achieve the 'in-situ' deposition of the desired oxide films directly on the substrate. By this procedure we have obtained room temperature contamination free ferromagnetic spintronic materials like Fe doped MgO and ZnO films from their acetate(s) solutions. We find that the origin of magnetism in ZnO, MgO and their Fe-doped films to be intrinsic. For a 28 nm thick film of Fe-doped ZnO we observe an enhanced magnetic moment of 16.0 emu/cm3 while it is 5.5 emu/cm3 for the doped MgO film of single pass printed. The origin of magnetism is attributed to cat-ion vacancies. We have also fabricated highly transparent indium tin oxide films with a transparency >95% both in the visible and IR range which is rather unique compared to films grown by any other technique. The films have a nano-porous structure, an added bonus from inkjetting that makes such films advantageous for a broad range of applications.
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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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