| 11. |
- Karim, Amir, 1976-, et al.
(författare)
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Characterization of Er/O-doped Si-LEDs with low thermal quenching
- 2005
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Ingår i: Material Research Society Symposium Proceedings. ; , s. 117-124
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Konferensbidrag (refereegranskat)abstract
- Electroluminescence studies of MBE-grown Er/O-doped Si-diodes at reverse bias have been done. For some devices there is much reduced thermal quenching of the emission at 1.54 µm. There are examples where the temperature dependence is abnormal in that the intensity for a constant current even increases with temperature up to e.g. 80 oC. These devices have been studied with cross-sectional transmission electron microscopy to see the microstructure of the Er/O-doped layers as well as the B-doped SiGe-layers that are used as electron emitters during reverse bias. Although there are defects in the layers there is no evidence for large thick precipitates of SiO2. While reduced thermal quenching often is attributed to having the Er-ions within SiO2 layers, this is not the case for our structures as evidenced by our TEM-studies. The origin of the abnormal temperature dependence is attributed to the two mechanisms of breakdown in the reverse-biased diodes. At low temperature the breakdown current is mainly due to avalanche resulting in low-energy electrons and holes that quenches the intensity by Auger de-excitation of the Er-ions. At higher temperature the breakdown current is mainly phonon-assisted tunnelling which results in a more efficient pumping with less de-excitation of the Er-ions. Finally at the highest temperatures the thermal quenching sets in corresponding to an activation energy of 125 meV, which is slightly lower than 150 meV that has been reported in other studies.
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| 12. |
- Kovacev, M, et al.
(författare)
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Extreme ultraviolet fourier-transform spectroscopy with high order harmonics
- 2005
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Ingår i: Physical Review Letters. - 1079-7114. ; 95:22
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a new scheme for extreme ultraviolet (xuv) Fourier-transform spectroscopy based on the generation of two phase-locked high-harmonic beams. It allows us to measure for the first time interferograms at wavelengths as short as 90 nm, and open the perspective of performing high-resolution Fourier-transform absorption spectroscopy in the xuv. Our measurements also demonstrate that a precise control of the relative phase of harmonic pulses can be obtained with an accuracy on an attosecond time scale, of importance for future xuv pump-xuv probe attosecond spectroscopy.
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| 13. |
- Lemel, Mikael, et al.
(författare)
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Quantification of the Formaldehyde Emissions from Different HCCI Engines Running on a Range of Fuels
- 2005
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Ingår i: SAE Transactions, Journal of Fuels and Lubricants. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0096-736X. ; 114:4, s. 1347-1357
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- In this paper, the formaldehyde emissions from three different types of homogenous charge compression ignition (HCCI) engines are quantified for a range of fuels by means of Fourier Transform Infra Red (FTIR) spectroscopic analysis. The engines types are differentiated in the way the charge is prepared. The characterized engines are; the conventional port fuel injected one, a type that traps residuals by means of a Negative Valve Overlap (NVO) and finally a Direct Injected (DI) one. Fuels ranging from pure n-heptane to iso-octane via diesel, gasoline, PRF80, methanol and ethanol were characterized. Generally, the amount of formaldehyde found in the exhaust was decreasing with decreasing air/fuel ratio, advanced timing and increasing cycle temperature. It was found that increasing the source of formaldehyde i.e. the ratio of heat released in the cool-flame, brought on higher exhaust contents of formaldehyde. The application of a standard three-way catalyst completely removed formaldehyde from the exhaust stream.
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| 14. |
- Lindau, Filip, et al.
(författare)
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Laser-accelerated protons with energy dependent beam direction
- 2005
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Ingår i: Physical Review Letters. - 1079-7114. ; 95:175002, s. 1-175002
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Tidskriftsartikel (refereegranskat)abstract
- The spatial distribution of protons, accelerated by intense femtosecond laser pulses interacting with thin target foils under oblique irradiation are investigated. Under certain conditions, the proton beams are directed away from the target normal. This deviation is towards the laser forward direction, with an angle that increases with the level and duration of the amplified spontaneous emission pedestal before the main laser pulse. In addition, for a given laser pulse, this beam deviation increases with proton energy. The observations are discussed in terms of different electron acceleration mechanisms and target normal sheath acceleration, in combination with a laser-controllable shock wave locally deforming the target rear surface.
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| 15. |
- LiU, Ya-Jun, et al.
(författare)
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Density functional theory study of NO adsorbed in A-zeolite
- 2005
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 109:16, s. 7948-7951
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Tidskriftsartikel (refereegranskat)abstract
- Density functional theory was employed to investigate the adsorption site and hyperfine interactions of nitric oxide adsorbed in Na-LTA (previous name NaA) zeolite. Three different cluster models of increasing complexity were used to represent the zeolite network: (1) a six-membered ring terminated by hydrogen atoms with one sodium ion above the ring, (2) as model 1 with the addition of three sodium ions located at the centers of three imagined four-membered rings adjacent to the six-membered ring, and (3) as model 2 with the addition of the three four-membered rings adjacent to the six-membered ring. Calculations on the largest system (model 3) showed very good agreement with measured electronic Zeeman interaction couplings, 14N hyperfine coupling tensors, and 23Na hyperfine and nuclear quadruple coupling tensors of the S = 1/2 Na+⋯N-O adsorption complex when the position of the sodium ion was relaxed. The optimized geometry of the complex agreed nicely with that estimated experimentally, except for the Na-N distance, where the present results indicate that the distance deduced from previous ENDOR experiments may be underestimated by as much as 0.5 Å. © 2005 American Chemical Society.
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| 16. |
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| 17. |
- Lopez, Rodrigo, et al.
(författare)
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Amplitude and phase control of attosecond light pulses
- 2005
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Ingår i: Physical Review Letters. - 1079-7114. ; 94:3
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Tidskriftsartikel (refereegranskat)abstract
- We report the generation, compression, and delivery on target of ultrashort extreme-ultraviolet light pulses using external amplitude and phase control. Broadband harmonic radiation is first generated by focusing an infrared laser with a carefully chosen intensity into a gas cell containing argon atoms. The emitted light then goes through a hard aperture and a thin aluminum filter that selects a 30-eV bandwidth around a 30-eV photon energy and synchronizes all of the components, thereby enabling the formation of a train of almost Fourier-transform-limited single-cycle 170 attosecond pulses. Our experiment demonstrates a practical method for synthesizing and controlling attosecond waveforms.
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| 18. |
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| 19. |
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| 20. |
- Melin, Jonas, et al.
(författare)
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Microreplication in a Silicon Processing Compatible Material
- 2005
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Ingår i: IEEE/LEOS Optical MEMS 2005: International Conference on Optical MEMS and Their Applications, Oulu, Finland, 1-4 August 2005. - 9780780392786 ; , s. 89-90
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Konferensbidrag (refereegranskat)abstract
- We present a novel fabrication process for the integration of polymer micro-optical elements on silicon. The process relies on a reverse order protocol based on embossing in an amorphous fluorocarbon polymer, Cytop™.
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