| 2. |
- Schmidt, Torsten, et al.
(författare)
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Radiative exciton recombination and defect luminescence observed in single silicon nanocrystals
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 86:12, s. 125302-
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Tidskriftsartikel (refereegranskat)abstract
- The role of quantum confinement (QC) and surface-related defect centers (DCs) on the photoluminescence (PL) of individual silicon nanocrystals (Si NCs) is investigated using confocal microscopy with radially and azimuthally polarized laser beams. It is shown that the multiple-peak PL spectra of single Si NCs revealing SiO 2 phonon side bands are associated with a linear transition dipole moment (TDM) and a short lifetime of 4 ns, indicating that the PL originates from defect centers. In a new study applied to free-standing single Si NCs obtained by Si cluster beam deposition, we could discriminate between PL centers with one- and more-dimensional TDM. Nanoparticles revealing a three-dimensional TDM are characterized by a significantly weaker and structureless Gaussian PL band at larger wavelengths and by ÎŒs lifetimes. These PL features are attributed to the radiative recombination of quantum-confined excitons generated in the Si cores. Within the same sample, we found coexistence of Si NCs exhibiting QC PL and others showing DC PL.
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| 3. |
- Kannisto, Hannes, 1979, et al.
(författare)
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Efficient low temperature lean NOx reduction over Ag/Al2O3-A system approach
- 2011
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 104:1-2, s. 74-83
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Tidskriftsartikel (refereegranskat)abstract
- This study focuses on lean NOx reduction (LNR) by n-octane using silver-alumina based catalysts, with the addition of hydrogen. The work takes a system approach, where parameters such as temperature, reformate gas composition, fuel penalty and realistic monolith samples are considered. The LNR catalyst samples were prepared by impregnation and sol-gel methods and the NOx reduction performance was characterized by flow-reactor experiments, where realistic engine-out gas compositions were used. The hydrogen feed over the LNR catalyst samples was determined via data achieved by autothermal reforming experiments over a rhodium based catalyst, using real diesel as feedstock. The LNR catalyst samples generally show an enhanced NOx reduction when hydrogen is added to the gas feed. In particular, a 2 wt% silver-alumina sample with the addition of minute amounts of platinum, shows a high increase in NOx reduction when hydrogen is added to the feed. The addition of CO, a potential poison in the reaction and a by-product from the reforming, did not show any significant effect on the LNR catalyst performance at the conditions used. This is beneficial, since it renders a CO clean-up step in the reformer system unneeded. Ammonia formation is discussed in terms of a possible dual-SCR system. Finally, the fuel penalty for hydrogen production and hydrocarbon addition is taken into consideration. It is found that an addition of 1000 ppm H-2 leads to unacceptable fuel penalties. (C) 2011 Elsevier B.V. All rights reserved.
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