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- Qviller, A. J., et al.
(författare)
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Thermal stability of photovoltaic a-Si:H determined by neutron reflectometry
- 2014
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 105:23, s. 231909-
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Tidskriftsartikel (refereegranskat)abstract
- Neutron and X-ray reflectometry were used to determine the layer structure and hydrogen content of thin films of amorphous silicon (a-Si:H) deposited onto crystalline silicon (Si) wafers for surface passivation in solar cells. The combination of these two reflectometry techniques is well suited for non-destructive probing of the structure of a-Si:H due to being able to probe buried interfaces and having sub-nanometer resolution. Neutron reflectometry is also unique in its ability to allow determination of density gradients of light elements such as hydrogen (H). The neutron scattering contrast between Si and H is strong, making it possible to determine the H concentration in the deposited a-Si:H. In order to correlate the surface passivation properties supplied by the a-Si:H thin films, as quantified by obtainable effective minority carrier lifetime, photoconductance measurements were also performed. It is shown that the minority carrier lifetime falls sharply when H has been desorbed from a-Si:H by annealing. (C) 2014 AIP Publishing LLC.
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| 7. |
- Valo, J., et al.
(författare)
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Nd substitution effects in YBa2Cu4O8 prepared using a conversion reaction from Y1-xNdxBa2Cu3O7-delta and CuO
- 2000
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Ingår i: International Journal of Inorganic Materials. - 1466-6049 .- 1878-5689. ; 2:2-3, s. 269-276
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Tidskriftsartikel (refereegranskat)abstract
- Synthesis, crystal structure and magnetic properties of samples with partial substitution of Nd for Y in YBa2Cu4O8 are considered. The samples with nominal composition Y1-xNdxBa2Cu4O8 (x=0.0-0.75) were prepared using a solid state conversion reaction from Y1-xNdxBa2Cu3O7-8 and CuO using LiF as a flux. The annealing was performed at 790 degrees C in a flowing oxygen atmosphere. The products with x=0.0-0.5 showed thermal stability up to 660 degrees C in N-2(g) atmosphere revealing a single phase composition. The success of the synthesis is considered in relation to the effective ionic size of the Nd3+ ion. The crystal structures of the compounds are described on the basis of powder neutron diffraction measurements. The T-c values of the Nd substituted samples were noticeably lower than for the pristine YBa2Cu4Odelta. Possible reasons for the decrease in T-c are discussed on the basis of calculated values for hole concentrations in the Cu-O-2 planes obtained via the BVS (bond valence sum) method, and on the basis of some Nd3+ ions being introduced at Ba2+ ion sites in the lattice.
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| 8. |
- Vidya, R., et al.
(författare)
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Tailor-made electronic and magnetic properties in one-dimensional perovskite-like oxides
- 2003
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Ingår i: Physical Review Letters. ; 91, s. 186404-
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Tidskriftsartikel (refereegranskat)abstract
- Full-potential density-functional calculations show that the electronic structure of one-dimensional ferrimagnetic Ca3Co2O6 varies from metal to half metal to insulator as its magnetic ordering changes from the ferrimagnetic through the ferromagnetic to the paramagnetic state. The present Letter is the first to establish the occurrence of half metallicity in one-dimensional oxides. Moreover, the electronic and magnetic properties of this material can be tuned by substitution of Y for Ca, as shown by our detailed study on Ca3–xYxCo2O6 (x = 0, 0.3, 0.75, and 1). The Co ions are in two different valence states [Co4+ (low-spin) and Co2+ (high-spin)], and hence the occurrence of charge ordering in addition to spin ordering is established. For specific Y concentrations we predict a rarely seen combination of ferromagnetic and insulating behavior.
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