| 1. |
- Eriksson, Fredrik, et al.
(författare)
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14.5% near-normal incidence reflectance of Cr/Sc x-ray multilayer mirrors for the water window
- 2003
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Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 28:24, s. 2494-2496
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Tidskriftsartikel (refereegranskat)abstract
- Cr/Sc multilayer mirrors, synthesized by ion-assisted magnetron sputter deposition, are proved to have a high near-normal reflectivity of R = 14.5% at a grazing angle of 87.5degrees measured at the wavelength A = 3.11 nm, which is an improvement of more than 31% compared with previously published results. Elastic recoil detection analyses show that the mirrors contained as much as 15 at. % of N and traces of C and O. Soft x-ray reflectivity simulations reveal interface widths of sigma = 0.34 nm and an exceptionally small layer thickness drift of similar to1.6 X 10(-5) nm/multilayer period throughout the stack. Simulations show that a reflectivity of R = 25.6% is attainable if impurities and layer thickness drift can be eliminated. The abrupt interfaces are achieved with ion assistance with a low ion energy of 24 eV and high ion-to-metal flux ratios of 7.1 and 23.1 during Cr and Se sputter deposition, respectively. In addition, a near-normal incidence reflectivity of 5.5% for the C VI emission line (lambda = 3.374 nm) from a laser plasma source was verified.
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| 2. |
- Greczynski, G., et al.
(författare)
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Electronic structure of pristine and sodium doped poly(p-pyridine)
- 2001
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 114:9, s. 4243-4252
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Tidskriftsartikel (refereegranskat)abstract
- Ultraviolet spectroscopy (UPS) and x-ray photoelectron spectroscopy (XPS) were used to study the valence electronic structures of pristine and sodium doped poly (p-pyridine) (PPY). The UPS spectra were analyzed by studying the density-of-valence-states (DOVS) derived from quantum chemical calculations. The electronic band structure of the PPY chains was also theoretically investigated using the valence effective Hamiltonian (VEH) method. The theoretical approach was found to be more accurate in describing the electronic structure of PPY.
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| 3. |
- Johansson, Elisabeth, et al.
(författare)
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Methane emissions from a constructed wetland treating wastewater : Seasonal and spatial distribution and dependence on edaphic factors
- 2004
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Ingår i: Water Research. - : Elsevier BV. - 0043-1354 .- 1879-2448. ; 38:18, s. 3960-3970
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Tidskriftsartikel (refereegranskat)abstract
- Constructed wetlands for wastewater treatment have many advantages. They can be used for several purposes, for example, to reduce levels of organic matter and nutrients, and to retain toxic metals. However, most wetlands are inherently net sources of gaseous compounds like methane and nitrous oxide, which are of environmental concern due to their rapid current accumulation in the atmosphere and their potent global warming capacity. In order to determine the flux of methane from a constructed wetland a study was conducted over two growth seasons on a pilot scale wetland constructed to reduce nutrient levels in secondary treated wastewater. The emissions for the spring to autumn period averaged 141 mg CH4 m-2 d-1 (S.D.=187), ranging from consumption of 375 mg CH4 m-2 d-1 to emissions of 1739 mg CH4 m-2 d-1. The spatial and temporal variations were large, but could be accounted for by measured environmental factors. Among these factors, sediment and water temperatures were significant in all cases and independent of the scale of analysis (r2 up to 0.88).
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| 4. |
- Johansson, G. A., et al.
(författare)
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Compact soft x-ray reflectometer based on a line-emitting laser-plasma source
- 2001
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 72:1, s. 58-62
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Tidskriftsartikel (refereegranskat)abstract
- We describe a compact soft x-ray reflectometer for in-house characterization of water-window multilayer optics. The instrument is based on a line-emitting, liquid-jet, laser-plasma source in combination with angular scanning of the studied multilayer optics. With a proper choice of target liquid and thin-film filters, one or a few lines of well-defined wavelength dominate the spectrum and multilayer periods are measured with an accuracy of 0.003 nm using a multi-line calibration procedure. Absolute reflectivity may also be estimated with the instrument. The typical measurement time is currently 10 min. Although the principles of the reflectometer may be used in the entire soft x-ray and extreme ultraviolet range, the current instrument is primarily directed towards normal-incidence multilayer optics for water-window x-ray microscopy, and is thus demonstrated on W/B4C multilayers for this wavelength range.
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| 5. |
- Birch, Jens, et al.
(författare)
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Recent advances in ion-assisted growth of Cr/Sc multilayer X-ray mirrors for the water window
- 2002
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Ingår i: Vacuum. - 0042-207X .- 1879-2715. ; 68:3, s. 275-282
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Tidskriftsartikel (refereegranskat)abstract
- Cr/Sc multilayer X-ray mirrors intended for normal incidence reflection in the water window wavelength range, lambda=[2.4-4.4 nm], have been grown by ion-assisted sputter deposition and characterized using soft and hard X-ray reflectivity. By extracting low-energy ions, with energies, E-ion, ranging from 9 to 113 eV and with ion-to-metal flux ratios, Phi, between 0.76 and 23.1, from the sputtering plasma to the growing film, the nano-structure of the multilayer interfaces could be modified. A significantly increased soft X-ray reflectivity, using lambda = 3.374 nm, for Cr/Sc multilayers with layer thicknesses in the range 0.4-2.8 nm, was obtained when high ion-to-metal flux ratios, Phi(Cr) = 7.1 and Phi(Sc) = 23.1, and low energy ions, E-ion = 9eV, were used. An experimental reflectivity of 5.5% was obtained at 76degrees for a multilayer with 400 bi-layers. Simulations of the reflectivity data showed that the interface widths are < 0.425 nm. It could be concluded that roughness of low spatial frequency is reduced at lower ion energies than the high spatial frequency which was eliminated at the expense of intermixing at the interfaces at higher ion energies. The predicted performance of normal incidence multilayer mirrors grown at optimum conditions and designed for lambda = 3.374 and 3.115 nm indicates possible reflectivities of 6.5% and 14%, respectively.
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| 6. |
- Eriksson, Fredrik, et al.
(författare)
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Enhanced soft x-ray reflectivity of Cr/Sc multilayers by ion-assisted sputter deposition
- 2002
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Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 41:11, s. 2903-2909
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Tidskriftsartikel (refereegranskat)abstract
- Cr/Sc multilayers have been grown on Si substrates using dc magnetron sputtering. The multilayers are intended as condenser mirrors in a soft x-ray microscope operating at the wavelength 3.374 nm. They were designed for normal reflection of the first and second orders, with multilayer periods of 1.692 and 3.381 nm, and layer thickness ratios of 0,471 and 0.237, respectively. At-wavelength soft-x-ray reflectivity measurements were carried out using a reflectometer with a compact soft-x-ray laser-plasma source. The multilayers were irradiated during growth with Ar ions, varying both in energy (9 to 113 eV) and flux, in order to stimulate the adatom mobility and improve the interface flatness. It was found that to obtain a maximum soft x-ray reflectivity with a low flux (Cr=0.76, Sc=2.5) of Ar ions a rather high energy of 53 eV was required, Such energy also caused intermixing of the layers. By the use of a solenoid surrounding the substrate, the arriving ion-to-metal flux ratio could be increased 10 times and the required ion energy could be decreased. A high flux (Cr=7.1, Sc=23.1) of low-energy (9 eV) Ar ions yielded the most favorable growth condition, limiting the intermixing with a subsistent good surface flatness.
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| 7. |
- Eriksson, Fredrik, et al.
(författare)
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Enhanced soft x-ray reflectivity of Cr/Sc multilayers by ion assisted sputter deposition
- 2001
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Ingår i: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 4506, s. 84-92
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Cr/Sc multilayers have been grown on Si substrates using DC magnetron sputtering. The multilayers are intended as condenser mirrors in a soft x-ray microscope operating at the wavelength 3.374 nm. They were designed for normal reflection of the first and second order with multilayer periods of 1.692 nm and 3.381 nm, and layer thickness ratios of 0.471 and 0.237, respectively. At-wavelength soft x-ray reflectivity measurements were carried out using a reflectometer with a compact soft x-ray laser-plasma source. The multilayers were irradiated during growth with Ar ions, varying both in energy (9-113 eV) and flux, in order to stimulate the ad-atom mobility and improve the interface flatness. It was found that to obtain a maximum soft x-ray reflectivity with a low flux (Cr=0.76, Sc=2.5) of Ar ions a rather high energy of 53 eV was required. Such energy also caused intermixing of the layers. By the use of a solenoid surrounding the substrate, the arriving ion-to-metal flux ratio could be increased 10 times and the ion energy could be decreased. A high flux (Cr=7.1, Sc=23.1) of low energy (9 eV) Ar ions founded the most favourable growth condition in order to limit the intermixing with a subsistent surface flatness.
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| 8. |
- Hertz, Hans M., et al.
(författare)
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Table-top X-ray microscopy : Sources, optics and applications
- 2003
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Ingår i: Journal de Physique IV. - : EDP Sciences. - 1155-4339 .- 1764-7177. ; 104, s. 115-119
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Tidskriftsartikel (refereegranskat)abstract
- We have developed the first operative compact sub-visible-resolution x-ray microscope for the water-window region (lambda = 2.3 - 4.4 nm). The microscope is based on a 100 Hz liquid-jet-target laser-plasma x-ray source, normal-incidence multilayer condenser optics, diffractive zone plate optics and CCD detection. In the present article we emphasize the system's aspects and summarize the recent progress on the components, all aiming at the reduction of the exposure time of a few seconds, i.e., similar to bending-magnet based microscopes. This primarily includes improved laser-plasma source, improved condenser optics using Cr/Sc multilayers, and improved image handling capability using wavelet algorithms. Such compact short-exposure time microscopes would significantly increase the applicability of the technology.
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| 9. |
- Johansson, Magnus, et al.
(författare)
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Standing wave instabilities, breather formation and thermalization in a Hamiltonian anharmonic lattice
- 2002
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Ingår i: European Physical Journal B. - : Springer Science and Business Media LLC. - 1434-6028 .- 1434-6036. ; 29:2, s. 279-283
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Tidskriftsartikel (refereegranskat)abstract
- Modulational instability of travelling plane waves is often considered as the first step in the formation of intrinsically localized modes (discrete breathers) in anharmonic lattices. Here, we consider an alternative mechanism for breather formation, originating in oscillatory instabilities of spatially periodic or quasiperiodic nonlinear standing waves (SWs). These SWs are constructed for Klein-Gordon or Discrete Nonlinear Schrödinger lattices as exact time periodic and time reversible multibreather solutions from the limit of uncoupled oscillators, and merge into harmonic SWs in the small-amplitude limit. Approaching the linear limit, all SWs with nontrivial wave vectors (0 < Q < p) become unstable through oscillatory instabilities, persisting for arbitrarily small amplitudes in infinite lattices. The dynamics resulting from these instabilities is found to be qualitatively different for wave vectors smaller than or larger than p/2, respectively. In one regime persisting breathers are found, while in the other regime the system thermalizes.
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| 10. |
- Morgante, A.M., et al.
(författare)
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Breather-phonon resonances in finite-size lattices : 'Phantom breathers'?
- 2002
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Ingår i: Journal of Physics A. - : IOP Publishing. - 0305-4470 .- 1361-6447. ; 35:24, s. 4999-5021
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the resonance mechanisms for discrete breathers in finite-size Klein-Gordon lattices, when some harmonic of the breather frequency enters the linear phonon band. For soft on-site potentials, the second-harmonic resonances typically result in the appearance of solutions with non-zero tails, phonobreathers. However, these tails may be very weak, and for small systems where the phonon frequencies are sparsely distributed, we identify 'phantom breathers' as being practically localized solutions, existing with frequencies in-between the phonon frequencies. For particular parameter values the tails completely vanish, and the phantom breathers decay exponentially over the whole system. We also describe briefly a first-harmonic resonance with a constant-amplitude wave and the generation of phonobreathers for hard potentials.
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