1. |
- Brennan, S. J., et al.
(författare)
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Photometric and spectroscopic evolution of the interacting transient AT 2016jbu(Gaia16cfr)
- 2022
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 513:4, s. 5642-5665
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Tidskriftsartikel (refereegranskat)abstract
- We present the results from a high-cadence, multiwavelength observation campaign of AT 2016jbu (aka Gaia16cfr), an interacting transient. This data set complements the current literature by adding higher cadence as well as extended coverage of the light-curve evolution and late-time spectroscopic evolution. Photometric coverage reveals that AT 2016jbu underwent significant photometric variability followed by two luminous events, the latter of which reached an absolute magnitude of MV ∼ −18.5 mag. This is similar to the transient SN 2009ip whose nature is still debated. Spectra are dominated by narrow emission lines and show a blue continuum during the peak of the second event. AT 2016jbu shows signatures of a complex, non-homogeneous circumstellar material (CSM). We see slowly evolving asymmetric hydrogen line profiles, with velocities of 500 km s−1 seen in narrow emission features from a slow-moving CSM, and up to 10 000 km s−1 seen in broad absorption from some high-velocity material. Late-time spectra (∼+1 yr) show a lack of forbidden emission lines expected from a core-collapse supernova and are dominated by strong emission from H, He I, and Ca II. Strong asymmetric emission features, a bumpy light curve, and continually evolving spectra suggest an inhibit nebular phase. We compare the evolution of H α among SN 2009ip-like transients and find possible evidence for orientation angle effects. The light-curve evolution of AT 2016jbu suggests similar, but not identical, circumstellar environments to other SN 2009ip-like transients.
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2. |
- Nyholm, R., et al.
(författare)
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ADSORPTION-SITE DETERMINATION OF ORDERED YB ON SI(111) SURFACES
- 1993
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 47:15, s. 9663-9668
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Tidskriftsartikel (refereegranskat)abstract
- Low-energy-electron-diffraction (LEED), scanning-tunneling-microscopy (STM), and photoelectron-spectroscopy measurements have been performed on the ordered submonolayer surface reconstructions of Yb on Si(111). Two of these reconstructions, namely, 3 X 1 and 2 X 1, have been studied in detail. STM and LEED revealed that what was considered to be the 3 X 1 reconstruction is actually a 3 X 2 reconstruction. By combining STM and photoelectron-spectroscopy results from the 3 X 2 and 2 X 1 reconstructions, we conclude that the Yb atoms are adsorbed in bridge sites.
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3. |
- Nyholm, R., et al.
(författare)
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ELECTRONIC AND STRUCTURAL-PROPERTIES OF THE CU-BI2CASR2CU2O8 INTERFACE
- 1991
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Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 180:1-4, s. 120-123
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Tidskriftsartikel (refereegranskat)abstract
- The formation of the Cu-Bi2CaSr2Cu2O8 interface has been studied by photoelectron spectroscopy using synchrotron radiation. Photon energies in the range 20-1000 eV were utilized in order to probe both the valence band and to monitor chemical changes upon Cu deposition, as revealed by the core-level shifts. A strong chemical reaction between Bi2CaSr2CuO8 and Cu is manifested by the formation of metallic Bi. From the intensity variations as a function of electron emission angle it is shown that the metallic Bi segregates to the top surface layer.
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4. |
- Nyholm, R., et al.
(författare)
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EPITAXIAL SILICIDE FORMATION IN THE MG/SI(111) SYSTEM
- 1993
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 289:3, s. 290-296
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Tidskriftsartikel (refereegranskat)abstract
- The silicide formation has been studied in the Mg/Si(111) system by IOW energy electron diffraction (LEED) and photoelectron spectroscopy. It has been found that an epitaxial Mg2Si silicide is responsible for the (2/3 square-root e x 2/3 square-root 3)R30-degrees reconstruction in this system. The thickness of the silicide is limited due to the very low formation temperature for this silicide. The Fermi level is positioned 0.59 +/- 0.06 eV above the valence band maximum in the Si substrate and the valence band maximum in the epitaxial silicide is positioned 0.3 +/- 0.1 eV below the Fermi level.
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5. |
- Nyholm, R., et al.
(författare)
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FORMATION OF SM SILICIDES ON SI(111) - COMPOSITION AND EPITAXY
- 1993
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Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 293:3, s. 254-259
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Tidskriftsartikel (refereegranskat)abstract
- The formation of Sm silicides on Si(111) by means of solid phase epitaxy has been studied with low energy electron diffraction, Auger electron spectroscopy and photoelectron spectroscopy of the Sm 4f level and Si 2p level. A limited reaction is found to occur already at room temperature whereas at higher temperatures a strongly intermixed Sm/Si layer showing some long range order is formed. The Sm atoms of this intermixed phase are found to be completely trivalent in accordance with expectations. The intermixed layer consists of two silicides with different compositions, one of them being SmSi2-x, the other being tentatively ascribed to SmSi.
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6. |
- Nyholm, R., et al.
(författare)
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PHOTOEMISSION-STUDY OF THE BI2CASR2CU2O8 SUPERCONDUCTOR WITH CU, AG AND AU OVERLAYERS
- 1993
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 218:1-2, s. 103-108
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present a photoemission study of the interaction of Cu, Ag and Au with clean single-crystal Bi2CaSr2Cu2O8 superconductor surfaces. Both the valence-band and the Bi 5d, O 1 s and Sr 3d core levels were monitored for all overlayers. Cu, Ag and Au were deposited as consecutively thicker layers starting with a third of a monolayer and progressing in steps up to a deposition in the range of eight monolayers. Comparing the results for the different overlayers reveals the Ag overlayer to be less reactive than Au which causes the formation of metallic Bi on cleaved Bi2CaSr2Cu2O8 surface. Cu is shown to be the most reactive of the three metals. The Au and Ag overlayers display an island-growth mode, while Cu grows in a layer-by-layer fashion.
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7. |
- Nyholm, R., et al.
(författare)
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SURFACE SCIENCE AT MAX-LAB
- 1989
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 282:2-3, s. 553-558
-
Tidskriftsartikel (refereegranskat)
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8. |
- Nyholm, R., et al.
(författare)
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SYNCHROTRON-RADIATION SOFT-X-RAY PHOTOEMISSION-STUDY OF LEAD ON BI2CASR2CU2O8
- 1992
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 46:10, s. 6488-6494
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we present a study of the interaction of Pb with a clean single-crystal Bi2CaSr2Cu2O8 superconductor surface based on photoemission and low-energy electron diffraction (LEED). Deposition of Pb on a Bi2CaSr2Cu2O8 Crystal kept at room temperature gives rise to the formation of metallic Bi and oxidized Pb at the interface. This behavior could not be observed when the crystal was kept at 100 K during Pb deposition. For all investigated Pb overlayers on a cold crystal (100 K), surface-sensitive photoelectron spectroscopy revealed the growth of a covering metallic Pb overlayer film. The growth at 100 K, contrary to the growth at room temperature, preserved the original LEED 5 X 1 pattern even for Pb depositions corresponding to a 24-angstrom thick overlayer indicating epitaxial growth. Furthermore, a rigid 0.4-eV shift of the valence band and the Bi 5d core levels is observed upon initial Pb deposition and is tentatively attributed to electron doping.
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9. |
- Pärna, R., et al.
(författare)
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FinEstBeaMS – A wide-range Finnish-Estonian Beamline for Materials Science at the 1.5 GeV storage ring at the MAX IV Laboratory
- 2017
-
Ingår i: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0168-9002. ; 859, s. 83-89
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Tidskriftsartikel (refereegranskat)abstract
- The FinEstBeaMS beamline is under construction at the 1.5 GeV storage ring of the MAX IV Laboratory at Lund, Sweden. It has been designed to cover an unusually wide energy range from ultraviolet (4.3 eV) to soft X-rays (1000 eV) but experiments will also be possible at the Mg and Al Kα energies. Instead of having two different insertion devices and optical schemes for low and high photon energy regions, we have based our design on a single long-period, elliptically polarizing undulator and a plane grating monochromator. This solution will provide very good conditions for planned experiments in the whole photon energy region. The beamline will have two branches: one will mainly be used to investigate free atoms, molecules and clusters with photoelectron/photoion coincidence spectroscopy as well as solids with photoluminescence spectroscopy whereas the other one will be dedicated to ultra-high vacuum studies of surfaces and interfaces, utilizing X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. This paper focuses on the optical design of the beamline and general design concepts of the gas phase and solid state end stations.
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10. |
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11. |
- Sandell, A., et al.
(författare)
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THE INNER VALENCE REGION OF CO ADSORBED ON PD(100)
- 1994
-
Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 26:19, s. 10659-10668
-
Tidskriftsartikel (refereegranskat)abstract
- The inner valence region of CO/Pd(100) p(2square-root2 x square-root2)R45-degrees has been studied by angular resolved photoemission at the Pd 4d Cooper minimum, and with resonant Auger spectroscopy at photon energies corresponding to the C 1s and O 1s x-ray absorption (XA) maxima of the unoccupied parts of the 2pi*-Pd 4d hybrid (2pi(un)). Previously unobserved inner valence states are revealed in the direct photoemission and are compared with resonant Auger results. The interpretation and assignment of the different spectral features to different main final state configurations are based on energy, symmetry and intensity arguments, as well as comparisons with previous results.
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12. |
- Taddia, Francesco, et al.
(författare)
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Analysis of broad-lined Type Ic supernovae from the (intermediate) Palomar Transient Factory
- 2019
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 621
-
Tidskriftsartikel (refereegranskat)abstract
- We study 34 Type Ic supernovae that have broad spectral features (SNe Ic-BL). This is the only SN type found in association with long-duration gamma-ray bursts (GRBs). We obtained our photometric data with the Palomar Transient Factory (PTF) and its continuation, the intermediate PTF (iPTF). This is the first large, homogeneous sample of SNe Ic-BL from an untargeted survey. Furthermore, given the high observational cadence of iPTF, most of these SNe Ic-BL were discovered soon after explosion. We present K-corrected Bgriz light curves of these SNe, obtained through photometry on template-subtracted images. We analyzed the shape of the r-band light curves, finding a correlation between the decline parameter Delta m(15) and the rise parameter Delta m-(10 ). We studied the SN colors and, based on g - r, we estimated the host-galaxy extinction for each event. Peak r-band absolute magnitudes have an average of -18.6 +/- 0.5 mag. We fit each r-band light curve with that of SN 1998bw (scaled and stretched) to derive the explosion epochs. We computed the bolometric light curves using bolometric corrections, r-band data, and g - r colors. Expansion velocities from Fen were obtained by fitting spectral templates of SNe Ic. Bolometric light curves and velocities at peak were fitted using the semianalytic Arnett model to estimate ejecta mass M-ej , explosion energy E-K and Ni-56 mass M( Ni-56) for each SN. We find average values of M-ej = 4 +/- 3 M-circle dot, E-K = (7 +/- 6) x 10(51) erg, and M( Ni-56) = 0.31 +/- 0.16 M-circle dot . The parameter distributions were compared to those presented in the literature and are overall in agreement with them. We also estimated the degree of Ni-56 mixing using scaling relations derived from hydrodynamical models and we find that all the SNe are strongly mixed. The derived explosion parameters imply that at least 21% of the progenitors of SNe Ic-BL are compatible with massive (>28 M-circle dot), possibly single stars, whereas at least 64% might come from less massive stars in close binary systems.
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13. |
- Bassler, M, et al.
(författare)
-
Beam line 1411 at MAX II - performance and first results
- 2001
-
Ingår i: NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT. - : ELSEVIER SCIENCE BV. - 0168-9002. ; 469:3, s. 382-393
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the characteristics and first results from the soft X-ray beam line I411, based on an undulator at the third generation synchrotron facility MAX II, Sweden. The beam line is designed for high-resolution, angle-resolved electron spectroscopy o
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14. |
- Bassler, M, et al.
(författare)
-
Soft X-ray undulator beam line I411 at MAX-II for gases, liquids and solid samples
- 1999
-
Ingår i: JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA. - : ELSEVIER SCIENCE BV. - 0368-2048. ; 103, s. 953-957
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We report on the build-up of the new undulator beam line I411 at the third-generation synchrotron radiation facility MAX II in Lund, Sweden. This beam line is based on an upgraded version of the modified SX700-monochromator and the end station which were
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15. |
- Bässler, M., et al.
(författare)
-
Beam line I411 at MAX II - Performance and first results
- 2001
-
Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - 0168-9002. ; 469:3, s. 382-393
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the characteristics and first results from the soft X-ray beam line I411, based on an undulator at the third generation synchrotron facility MAX II, Sweden. The beam line is designed for high-resolution, angle-resolved electron spectroscopy on gases, liquids and solids. Main components are the modified SX700 monochromator and the end station, both of which were previously used at beam line 51 at MAX I. The end station is equipped with a rotatable SES-200 hemispherical electron-analyser. Before the end station, a one-metre section is reserved for exchangeable experimental set-ups. The usable photon energy range is 50-1500 eV and the photon flux is two orders of magnitudes higher compared to beam line 51. At 400 eV a resolving power of about 5700 in the first order of the monochromator grating could be obtained. In gas phase, a total electron energy resolution of 16 meV has been achieved. Detailed results on the undulator performance, flux, photon and electron energy resolution as well as some technical details are presented here. As an example of the capabilities of the beam line I411, we present the fully vibrationally resolved Auger resonant Raman electron spectrum of gas-phase N 2.
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16. |
- Bässler, M., et al.
(författare)
-
Soft x-ray undulator beam line 1411 at MAX-II for gases, liquids and solid samples
- 1999
-
Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048. ; 101-103, s. 953-957
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the build-up of the new undulator beam line 1411 at the third-generation synchrotron radiation facility MAX II in Lund, Sweden. This beam line is based on an upgraded version of the modified SX700-monochromator and the end station which were installed previously at beam line 51 at MAX I. The end station is equipped with a rotatable Scienta hemispherical electron-analyser making angle-resolved high resolution electron spectroscopy possible for various kinds of samples. The beam line performance will be considerably improved on MAX II due to a new undulator and the superior light source properties, e.g. the small vertical electron beam size. Undulator spectra have been measured and estimates of the photon flux at the experiment and the expected energy resolution are presented. The parameters for a new refocusing mirror were defined by ray tracing using the beam waist of the undulator. The beam line length was extended by 1 m to offer additional space for exchangeable experimental chambers.
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17. |
- Denecke, R., et al.
(författare)
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Beamline 1511 at MAX II, capabilities and performance
- 1999
-
Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - 0368-2048. ; 101-103, s. 971-977
-
Tidskriftsartikel (refereegranskat)abstract
- The new undulator beamline 1511 at MAX-lab, now under commissioning, has been optimized for X-ray emission and photoelectron spectroscopies. Using an SX-700 high flux monochromator the accessible photon energy range is from 90 eV to about 1500 eV. The performance of the undulator agrees very well with the specifications, as shown by measurements using a photodiode. The energy resolution of the monochromator has been checked using absorption measurements in a gas cell. It was found to meet the expectations and exceeds a resolving power of 10 000 at 244 eV. The photon flux as a function of energy has been recorded as well and gives a maximum flux of 3×1013 photons/s/100 mA/0.1% BW. Beamlines 1511 and 1411 will be the first synchrotron beamlines making use of a so-called beam waist phenomenon, known from laser physics. We show results of ray-tracing calculations to determine the ultimate spot size on the sample location. The endstations to be used at this new beamline and their capabilities will be discussed as an example of the future use of this facility.
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18. |
- Denecke, R, et al.
(författare)
-
Beamline I511 at MAX II, capabilities and performance
- 1999
-
Ingår i: JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA. - : ELSEVIER SCIENCE BV. - 0368-2048. ; 103, s. 971-977
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The new undulator beamline I511 at MAX-lab, now under commissioning, has been optimized for X-ray emission and photoelectron spectroscopies. Using an SX-700 high flux monochromator the accessible photon energy range is from 90 eV to about 1500 eV. The per
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19. |
- Elango, M., et al.
(författare)
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Autoionization phenomena involving the 2p53d configuration of argonlike ions in ionic solids
- 1993
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Ingår i: Physical Review B (Condensed Matter). - 0163-1829. ; 47:18, s. 11736-11748
-
Tidskriftsartikel (refereegranskat)abstract
- The photon-induced Auger and photoelectron spectra of the argonlike ions Cl- (in NaCl), K+ (in KCl), Ca2+ (in CaCl2 and CaF2), and Sc3+ (in Sc2O3) have been measured in the vicinity of the L23 absorption edges of these ions. It is shown that at the 2p6→2p53d(4s) resonance a spectator structure appears in the L23M23M23 Auger spectra, which shifts to higher kinetic energies with increasing photon energy. This structure originates from the 3p-23d(4s) final configuration arising as a product of the Auger resonant-inelastic-scattering process of the incident photons. We demonstrate that the peculiarities of this process and the role of the collapsing 3d electron in it can be largely understood in terms of an atomic treatment. The solid-state effects, caused by the crystal field and the lattice polarization, may play an additional role.
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20. |
- Grepstad, J. K., et al.
(författare)
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As capping of MBE-grown compound semiconductors; novel opportunities to interface science and device fabrication
- 1994
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Ingår i: Physica Scripta. - 0031-8949. ; 1994:T54, s. 216-225
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Tidskriftsartikel (refereegranskat)abstract
- In situ condensation of an amorphous cap of the high vapour pressure element (i.e. As, Sb) has been found to provide effective protection of molecular beam epitaxy grown compound semiconductor surfaces against ambient contamination. Most work reported so far relates to arsenic-capped AlGaAs. Detailed investigation with surface sensitive structural (RHEED, LEED) and chemical (XPS) probes confirms that the protective cap is conveniently removed by annealing in ultrahigh vaccum environments at a temperature in excess of similar 350 °C. Clean AlxGa1-xAs(001) surfaces with different atomic reconstructions and corresponding (Al)Ga: As composition ratios are now routinely prepared by this technique, and thus offers an ideal testing ground for compound semiconductor surface and interface research. Reconstruction-dependent reactivity at metal/GaAs(001) interfaces is demonstrated, using surface sensitive synchrotron radiation photoelectron spectroscopy. Exploiting the protection offered by the As (Sb) cap for device fabrication purposes (e.g. in selective area epitaxy), demands a suitable method of pattern definition in the amorphous arsenic layer. The cap is shown to be chemically stable versus exposure to standard photolithographic processing chemicals, including photoresist, developer, and acetone (the photoresist solvent). However, the temperature required for thermal decapping is grossly inappropriate for photoresist curing. A novel technique of reactive decapping in a beam of hydrogen radicals (H‒) is shown to be effective at room temperature. This innovation makes pattern definition in the As cap compatible with standard photolithography, and test structures with similar 5 μm linewidth is demonstrated. Scanning electron micrographs unveil the presence of arsenic cap residues along the photoresist mask edges. Moreover, trace amounts of surface gallium oxide and carbon impurities were found with core-level photoelectron spectroscopy. The technique thus needs further refinement, before being useful in fabrication of compound semiconductor device structures.
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21. |
- Guo, J. H., et al.
(författare)
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Characterization of undulator radiation at MAXII using a soft X-ray fluorescence spectrometer
- 1999
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - 0168-9002. ; 431:1, s. 285-293
-
Tidskriftsartikel (refereegranskat)abstract
- A grazing-incidence grating spectrometer has been used for the investigation of the undulator radiation from beamline 411 at MAX-lab. The direct detection of undulator light is expected to obtain the information of the quality of the undulator. Regular undulator radiation and some higher harmonics were observed. The effects of electronic beam coupling and Landau cavities have been studied. The experiment presents an easy and quick method to characterize the undulator radiation before the permanent monochromator is installed.
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22. |
- Guo, JH, et al.
(författare)
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The characterization of undulator radiation at MAXII using a soft X-ray fluorescence spectrometer
- 1999
-
Ingår i: NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT. - : ELSEVIER SCIENCE BV. - 0168-9002. ; 431:1-2, s. 285-293
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- A grazing-incidence grating spectrometer has been used for the investigation of the undulator radiation from beamline 411 at MAX-lab. The direct detection of undulator light is expected to obtain the information of the quality of the undulator. Regular un
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23. |
- Halme, P., et al.
(författare)
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Challenges of ecological restoration : Lessons from forests in northern Europe
- 2013
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Ingår i: Biological Conservation. - : Elsevier BV. - 0006-3207 .- 1873-2917. ; 167, s. 248-256
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Forskningsöversikt (refereegranskat)abstract
- The alarming rate of ecosystem degradation has raised the need for ecological restoration throughout different biomes and continents. North European forests may appear as one of the least vulnerable ecosystems from a global perspective, since forest cover is not rapidly decreasing and many ecosystem services remain at high level. However, extensive areas of northern forests are heavily exploited and have lost a major part of their biodiversity value. There is a strong requirement to restore these areas towards a more natural condition in order to meet the targets of the Convention on Biological Diversity. Several northern countries are now taking up this challenge by restoring forest biodiversity with increasing intensity. The ecology and biodiversity of boreal forests are relatively well understood making them a good model for restoration activities in many other forest ecosystems. Here we introduce northern forests as an ecosystem, discuss the historical and recent human impact and provide a brief status report on the ecological restoration projects and research already conducted there. Based on this discussion, we argue that before any restoration actions commence, the ecology of the target ecosystem should be established with the need for restoration carefully assessed and the outcome properly monitored. Finally, we identify the most important challenges that need to be solved in order to carry out efficient restoration with powerful and long-term positive impacts on biodiversity: coping with unpredictability, maintaining connectivity in time and space, assessment of functionality, management of conflicting interests and social restrictions and ensuring adequate funding. © 2013 Elsevier Ltd.
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24. |
- Lunnan, Ragnhild, et al.
(författare)
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A UV resonance line echo from a shell around a hydrogen-poor superluminous supernova
- 2018
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Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 2:11, s. 887-895
-
Tidskriftsartikel (refereegranskat)abstract
- Hydrogen-poor superluminous supernovae (SLSN-I) are a class of rare and energetic explosions that have been discovered in untargeted transient surveys in the past decade(1,2). The progenitor stars and the physical mechanism behind their large radiated energies (about 1O(51) erg or 1O(44) J) are both debated, with one class of models primarily requiring a large rotational energy(3,4) and the other requiring very massive progenitors that either convert kinetic energy into radiation through interaction with circumstellar material (CSM)(5-8 )or engender an explosion caused by pair-instability (loss of photon pressure due to particle-antiparticle production)(9,10). Observing the structure of the CSM around SLSN-I offers a powerful test of some scenarios, although direct observations are scarce(11,)(12). Here, we present a series of spectroscopic observations of the SLSN-I iPTF16eh, which reveal both absorption and time- and frequency-variable emission in the Mg n resonance doublet. We show that these observations are naturally explained as a resonance scattering light echo from a circumstellar shell. Modelling the evolution of the emission, we infer a shell radius of 0.1 pc and velocity of 3,300 km s(-1), implying that the shell was ejected three decades before the supernova explosion. These properties match theoretical predictions of shell ejections occurring because of pulsational pair-instability and imply that the progenitor had a helium core mass of about 50-55 M-circle dot, corresponding to an initial mass of about 115 M-circle dot.
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25. |
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26. |
- Nyholm, D, et al.
(författare)
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Duodenal levodopa infusion monotherapy vs oral polypharmacy in advanced Parkinson disease
- 2005
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Ingår i: Neurology. - 0028-3878 .- 1526-632X. ; 64:2, s. 216-223
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: To compare daytime intraduodenal levodopa/carbidopa infusion as monotherapy with individually optimized conventional combination therapies in patients with advanced Parkinson disease (PD) for motor fluctuations and quality of life (QoL). Methods: Twenty-four patients with motor fluctuations and dyskinesia were studied in a randomized crossover design to compare individualized conventional treatment and intraduodenal infusion of a levodopa/ carbidopa gel for 3 + 3 weeks. Video scoring of motor function was assessed by blinded assessors on a global Treatment Response Scale from -3 to 0 to +3 (from severe "off" to "on" to "on" with severe dyskinesia). Patient self-assessment of motor performance and QoL was done using an electronic diary. Results: Median percentage of ratings in a functional "on" interval (-1 to +1) was increased from 81 to 100% by infusion therapy (p < 0.01). This improvement was accompanied by a decrease in "off" state (p < 0.01) and no increase in dyskinesia. Median Unified Parkinson's Disease Rating Scale score decreased from 53 to 35 in favor of infusion (p < 0.05). QoL was improved, using the two instruments: Parkinson's Disease Questionnaire-39 and 15D Quality of Life Instrument (p < 0.01). Adverse events were similar for both treatment strategies. Conclusions: Continuous intraduodenal infusion of the levodopa/carbidopa enteral gel as monotherapy is safe and clinically superior to a number of individually optimized combinations of conventional oral and subcutaneous medications in patients with motor fluctuations. Intraduodenal infusion of levodopa offers an important alternative in treating patients with advanced Parkinson disease.
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27. |
- Ruus, R., et al.
(författare)
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M4,5N4,5N4,5 Auger decay spectra of the resonantly excited 3d94f configuration of xenonlike ions in solids
- 1994
-
Ingår i: Physical Review B (Condensed Matter). - 0163-1829. ; 49:21, s. 14836-14844
-
Tidskriftsartikel (refereegranskat)abstract
- The synchrotron-radiation-induced Auger and photoelectron spectra of the xenonlike ions I- (in CsI), Cs+ (in CsI), Ba2+ (in BaF2), and La3+ (in LaF3) have been measured in the vicinity of the M4,5 absorption edges of these ions. It is shown that the spectra of La and Ba measured at 3d10→3d94f resonances exhibit a very intense 4f-spectator structure which changes its energy and intensity with the energy of the exciting photons. Calculation of the Auger decay of the 3d-14f configuration shows that this structure is due to transitions to the 4d-24f+4p-1 final ionic configuration, the high-energy part of which overlaps the 4d-2 continuum. In the case of Ba this structure coexists with the normal Auger structure which appears as a result of the M4M5N6,7 Coster-Kronig transitions. The spectra of I- contain only the normal M4,5N4,5N4,5 Auger structure related to the 3d-1→4d-2 transitions. The spectra of Cs+ are similar to those of I- with a small admixture of the 4f-spectator-like structure.
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28. |
- Schmidt-May, J., et al.
(författare)
-
Resonant electron and ion emission and desorption mechanism in rare earth oxides
- 1985
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 163:2-3, s. 303-314
-
Tidskriftsartikel (refereegranskat)abstract
- The resonant enhancement in photoelectron spectra at the 4d edges of rare earth atoms and metals is also found in yield spectra of desorbed ions from the surfaces of the oxides of Sm, Eu and Yb following the photon excitation. The analysis of the 4d → 4f resonance leads to a picture of an indirect mechanism of ion desorption which is mainly caused by the flux of energetic 4f photoelectrons from the bulk. In this case the dominant desorption through secondary processes limits the use of the photon-stimulated desorption (PSD) to determine to which type of atom the desorbing species was attached.
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29. |
- Smedh, M., et al.
(författare)
-
Vibrationally resolved C Is photoemission from CO absorbed on Rh(1 1 1) : The investigation of a new chemically shifted C Is component
- 2001
-
Ingår i: Surface Science. - 0039-6028. ; 491:1-2, s. 99-114
-
Tidskriftsartikel (refereegranskat)abstract
- High-resolution core-level photoemission at an energy resolution better than the intrinsic width of the C 1s level has been used to study the CO/Rh(1 1 1) overlayer system. C Is spectra have been measured in a large CO coverage range; from low coverages, where the CO molecules only adsorb in on-top positions, to saturation coverage, where CO molecules occupy both on-top and threefold hollow sites. Fine structure components due to vibrational excitation of the C-O stretch mode are clearly resolved in the emission peak from each site. The vibrational splittings and intensity ratios are found to be different for the different adsorption sites. A third C Is component, which has not been resolved earlier, is found at intermediate CO coverages. Some possible explanations for the origin of this extra component are discussed. In the light of its binding energy and vibrational energy in photoemission, together with supporting evidence from highresolution electron energy loss spectroscopy data and photoelectron diffraction, this is assigned to bridging CO species at intermediate coverages.
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30. |
- Urpelainen, S., et al.
(författare)
-
FINEST:A high performance branch-line for VUV photon energy range gas phase studies at MAX-lab
- 2010
-
Ingår i: AIP Conference Proceedings. - : AIP. - 0094-243X. - 9780735407824 ; 1234, s. 411-414
-
Konferensbidrag (refereegranskat)abstract
- We present a dedicated beamline branch for high flux and ultra-high resolution (R>100000) gas and vapor phase studies in the vacuum-ultra-violet (VUV) region of light on the undulator beamline I3, located on the 700 MeV MAX-III storage ring. The mechanical and optical design of the branch-line, the differential pumping setup as well as performance characteristics are presented.
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31. |
- Aksela, S., et al.
(författare)
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Study of different SX-700 monochromator designs for the undulator beamline (BL51) at MAX-lab
- 1992
-
Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 63:1, s. 1252-1255
-
Tidskriftsartikel (refereegranskat)abstract
- Different designs of the SX-700 plane grating monochromator have been investigated for the undulator beamline (51) by using analytical considerations and carrying out ray tracing calculations. The most important modifications of the original design are those where the ellipsoidal focusing mirror has been replaced by a plane elliptical or by a spherical mirror. A significant advantage of the spherical mirror is essentially better figure accuracies (±0.2 arcsec). This is partly compensated by the introduced coma aberration which, however, can be made small with rather long exit arm lengths (5-6 m). If the slope errors of the plane elliptical mirror can be made as small as 0.5 arcsec, the differences in the ultimate resolution are small between the plane elliptical and spherical designs and then the source size is the main factor.
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32. |
- Andersen, J. N., et al.
(författare)
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Alkali metal adsorption on Al(111)
- 1993
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 289:3, s. 307-334
-
Tidskriftsartikel (refereegranskat)abstract
- The submonolayer adsorption of Na, K, Rb, and Cs on the Al(111) surface at 100 K and at room temperature is investigated by high resolution core level spectroscopy and low energy electron diffraction. It is found that the first alkali atoms on the surface adsorb at surface defects. At higher coverages, up to approximately one third of the maximum submonolayer coverage, alkali atoms adsorbed at defects coexist with a dispersed phase. At higher coverages island formation is found to occur for the majority of the systems. It is argued that all of the ordered structures formed at room temperature involve a disruption of the Al(111) surface in contrast to the situation at 100 K where the alkali atoms adsorb as adatoms.
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33. |
- Andersen, J. N., et al.
(författare)
-
Changes in the local surface geometry with conserved adsorbate coverage and long-range order caused by annealing
- 1992
-
Ingår i: Physical Review B (Condensed Matter). - 0163-1829. ; 46:19, s. 12784-12787
-
Tidskriftsartikel (refereegranskat)abstract
- The ordered c(2×2) Na on Al(100) and (3 × 3) R30°K on Al(111) structures formed at either 100 K or at room temperature are studied by high-resolution core-level spectroscopy. For both systems equal alkali coverages are found at these two temperatures. The core-level spectra, however, show strong changes with temperature. This behavior leads to the surprising conclusion that annealing at room temperature causes an irreversible change in the local geometry, i.e., of the adsorption site, of the overlayer even though neither the long-range order nor the adsorbate coverage changes.
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34. |
- Andersen, J. N., et al.
(författare)
-
Differences in the Cs 4d and 5p surface and interface core-level shifts
- 1994
-
Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 226:1-2, s. 106-110
-
Tidskriftsartikel (refereegranskat)abstract
- Core-level binding energy shifts of Cs induced by changes in the surroundings of the Cs atoms are measured for two different Cs core levels, 5p and 4d, and are found to be different for these two levels. The surface core-level shift of Cs is found to differ by 25 meV between the two levels. In the case of the Cs core-level shifts between bulk Cs atoms and Cs atoms at an interface between Cs and an Al(111) surface the difference between the two levels is found to be as large as 60 meV. The implications of these results for the precision of the Z+1 approximation are discussed.
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35. |
- Andersen, J. N., et al.
(författare)
-
Intermixing in the Na on Al(111) system
- 1992
-
Ingår i: Physical Review Letters. - 0031-9007. ; 68:1, s. 94-97
-
Tidskriftsartikel (refereegranskat)abstract
- Ordered structures formed by Na adsorption on the Al(111) surface are investigated by high-resolution core-level spectroscopy. It is shown that, contrary to the common picture of alkali adsorption, two of the structures formed at room temperature consist of intermixed Na-Al layers. The results for the (3 ×)-rotated-30°structure are also consistent with intermixing although they do not provide any definite proof. For Na layers deposited at 100 K no intermixing is found.
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36. |
- Andersen, Jesper N, et al.
(författare)
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Photoemission Spectroscopy At Max-Lab
- 1991
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Ingår i: Synchrotron Radiation News. - : Informa UK Limited. - 0894-0886 .- 1931-7344. ; 4:4, s. 15-19
-
Tidskriftsartikel (refereegranskat)
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37. |
- Andersen, J. N., et al.
(författare)
-
Strong phonon replicas in Be 1s photoemission spectra
- 2001
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 86:19, s. 4398-4401
-
Tidskriftsartikel (refereegranskat)abstract
- Strong phonon replicas in Be 1s photoemission spectra were investigated. The fine structure caused by intrinsic excitation of a narrow band of optical phonons was discussed in the 1s photoemission proces. The excitations of the optical Be phonons in the photoemission process caused fine structures. It was found that the phonon replicas in Be metal were strong due to large size misfit between neutral and core-ionized Be.
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38. |
- Andersen, J. N., et al.
(författare)
-
Surface core-level shifts as a probe of the local overlayer structure : CO on Pd(100)
- 1991
-
Ingår i: Physical Review Letters. - 0031-9007. ; 67:20, s. 2822-2825
-
Tidskriftsartikel (refereegranskat)abstract
- The bonding energies of the Pd 3d and the C 1s core levels have been studied for the p(2 S 2 × 2) R45°, p(3 s2 × S2) R45°, and p(4 S 2 × S 2) R45°structures of CO on Pd(100). Adsorption of CO shifts the Pd 3d surface emission to higher binding energies with the magnitude of the shift depending almost linearly on the number of Pd to CO bonds; the measured shift per bond is close to 0.5 eV. A direct relation is established between the detailed geometry of the CO overlayer and the changes in the Pd 3d spectra.
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39. |
- Andersen, J. N., et al.
(författare)
-
Surface core-level shifts of some 4d-metal single-crystal surfaces : Experiments and ab initio calculations
- 1994
-
Ingår i: Physical Review B (Condensed Matter). - 0163-1829. ; 50:23, s. 17525-17533
-
Tidskriftsartikel (refereegranskat)abstract
- High resolution measurements are reported of the surface core-level shift of the 3d level for the Rh(111), Rh(110), Pd(111), Pd(110), and Ag(111) single-crystal surfaces. These measurements and earlier ones for the Mo(110), Rh(100), and Pd(100) surfaces are analyzed by ab initio calculations of the surface core-level shift. The calculations are found to reproduce well the trends of the experimental shifts with the 4d metal and with the crystal plane. The comparison between these experimental and theoretical results demonstrates the importance of proper inclusion of final-state effects for accurate calculations of surface core-level shifts. A core hole in a surface atom is found to be better screened than one in a bulk atom for the 4d metals to the left of Pd in the Periodic Table. The use of the Z+1 approximation to describe the core hole is investigated both by explicit use of this approximation and by performing calculations for 1s and 3d core holes, respectively. The Z+1 approximation is found to be well obeyed in the case of Ag whereas for the rest of the 4d transition metals it is less precise, introducing errors of typically 0.1 eV.
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40. |
- Andersen, J. N., et al.
(författare)
-
Vibrational fine structure in the C 1s core level photoemission of chemisorbed molecules : Ethylene and ethylidyne on Rh(111)
- 1997
-
Ingår i: Chemical Physics Letters. - 0009-2614. ; 269:3-4, s. 371-377
-
Tidskriftsartikel (refereegranskat)abstract
- The origin of fine structure in the core-level photoemission spectra of the C2H4, C2D4, C2H3 and C2D3 molecules chemisorbed on Rh(111) is probed in a careful high-resolution study showing that this structure arises from internal molecular vibrations rather than from other chemically-shifted carbon atoms. It is shown by comparison of the adsorbate and gas-phase spectra that the underlying features are the same despite differences arising from adsorption. This new approach to the investigation of adsorbed molecules may prove to be useful in further studies of other systems and the possibility that such effects may exist could lead to the reinterpretation of other adsorbate systems.
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41. |
- Arcavi, Iair, et al.
(författare)
-
Energetic eruptions leading to a peculiar hydrogen-rich explosion of a massive star
- 2017
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 551:7679, s. 210-213
-
Tidskriftsartikel (refereegranskat)abstract
- Every supernova so far observed has been considered to be the terminal explosion of a star. Moreover, all supernovae with absorption lines in their spectra show those lines decreasing in velocity over time, as the ejecta expand and thin, revealing slower-moving material that was previously hidden. In addition, every supernova that exhibits the absorption lines of hydrogen has one main light-curve peak, or a plateau in luminosity, lasting approximately 100 days before declining(1). Here we report observations of iPTF14hls, an event that has spectra identical to a hydrogen-rich core-collapse supernova, but characteristics that differ extensively from those of known supernovae. The light curve has at least five peaks and remains bright for more than 600 days; the absorption lines show little to no decrease in velocity; and the radius of the line-forming region is more than an order of magnitude bigger than the radius of the photosphere derived from the continuum emission. These characteristics are consistent with a shell of several tens of solar masses ejected by the progenitor star at supernova-level energies a few hundred days before a terminal explosion. Another possible eruption was recorded at the same position in 1954. Multiple energetic pre-supernova eruptions are expected to occur in stars of 95 to 130 solar masses, which experience the pulsational pair instability(2-5). That model, however, does not account for the continued presence of hydrogen, or the energetics observed here. Another mechanism for the violent ejection of mass in massive stars may be required.
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42. |
- Asfaw, Habtom Desta
(författare)
-
Multifunctional Carbon Foams by Emulsion Templating : Synthesis, Microstructure, and 3D Li-ion Microbatteries
- 2017
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Carbon foams are among the existing electrode designs proposed for use in 3D Li-ion microbatteries. For such electrodes to find applications in practical microbatteries, however, their void sizes, specific surface areas and pore volumes need be optimized. This thesis concerns the synthesis of highly porous carbon foams and their multifunctional applications in 3D microbatteries. The carbon foams are derived from polymers that are obtained by polymerizing high internal phase water-in-oil emulsions (HIPEs).In general, the carbonization of the sulfonated polymers yielded hierarchically porous structures with void sizes ranging from 2 to 35 µm and a BET specific surface area as high as 630 m2 g-1. Thermogravimetric and spectroscopic evidence indicated that the sulfonic acid groups, introduced during sulfonation, transformed above 250 oC to thioether (-C-S-) crosslinks which were responsible for the thermal stability and charring tendency of the polymer precursors. Depending on the preparation of the HIPEs, the specific surface areas and void-size distributions were observed to vary considerably. In addition, the pyrolysis temperature could also affect the microstructures, the degree of graphitization, and the surface chemistry of the carbon foams.Various potential applications were explored for the bespoke carbon foams. First, their use as freestanding active materials in 3D microbatteries was studied. The carbon foams obtained at 700 to 1500 oC suffered from significant irreversible capacity loss during the initial discharge. In an effort to alleviate this drawback, the pyrolysis temperature was raised to 2200 oC. The resulting carbon foams were observed to deliver high, stable areal capacities over several cycles. Secondly, the possibility of using these structures as 3D current collectors for various active materials was investigated in-depth. As a proof-of-concept demonstration, positive active materials like polyaniline and LiFePO4 were deposited on the 3D architectures by means of electrodeposition and sol-gel approach, respectively. In both cases, the composite electrodes exhibited reasonably high cyclability and rate performance at different current densities. The syntheses of niobium and molybdenum oxides and their potential application as electrodes in microbatteries were also studied. In such applications, the carbon foams served dual purposes as 3D scaffolds and as reducing reactants in the carbothermal reduction process. Finally, a facile method of coating carbon substrates with oxide nanosheets was developed. The approach involved the exfoliation of crystalline VO2 to prepare dispersions of hydrated V2O5, which were subsequently cast onto CNT paper to form oxide films of different thicknesses.
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43. |
- Asfaw, Habtom D., et al.
(författare)
-
Nanosized LiFePO4-decorated emulsion-templated carbon foam for 3D micro batteries : a study of structure and electrochemical performance
- 2014
-
Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 6:15, s. 8804-8813
-
Tidskriftsartikel (refereegranskat)abstract
- In this article, we report a novel 3D composite cathode fabricated from LiFePO4 nanoparticles deposited conformally on emulsion-templated carbon foam by a sot-gel method. The carbon foam is synthesized via a facile and scalable method which involves the carbonization of a high internal phase emulsion (polyHIPE) polymer template. Various techniques (XRD, SEM, TEM and electrochemical methods) are used to fully characterize the porous electrode and confirm the distribution and morphology of the cathode active material. The major benefits of the carbon foam used in our work are closely connected with its high surface area and the plenty of space suitable for sequential coating with battery components. After coating with a cathode material (LiFePO4 nanoparticles), the 3D electrode presents a hierarchically structured electrode in which a porous layer of the cathode material is deposited on the rigid and bicontinuous carbon foam. The composite electrodes exhibit impressive cyclability and rate performance at different current densities affirming their importance as viable power sources in miniature devices. Footprint area capacities of 1.72 mA h cm(-2) at 0.1 mA cm(-2) (lowest rate) and 1.1 mA h cm(-2) at 6 mA cm(-2) (highest rate) are obtained when the cells are cycled in the range 2.8 to 4.0 V vs. lithium.
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44. |
- Asfaw, Habtom Desta, 1986-, et al.
(författare)
-
Nanosized LiFePO4-decorated emulsion-templated carbon foam for 3D micro batteries : a study of structure and electrochemical performance
- 2014
-
Ingår i: Nanoscale. - Royal Society of Chemistry. - 2040-3364 .- 2040-3372. ; 6:15, s. 8804-8813
-
Tidskriftsartikel (refereegranskat)abstract
- In this article, we report a novel 3D composite cathode fabricated from LiFePO4 nanoparticles deposited conformally on emulsion-templated carbon foam by a sol–gel method. The carbon foam is synthesized via a facile and scalable method which involves the carbonization of a high internal phase emulsion (polyHIPE) polymer template. Various techniques (XRD, SEM, TEM and electrochemical methods) are used to fully characterize the porous electrode and confirm the distribution and morphology of the cathode active material. The major benefits of the carbon foam used in our work are closely connected with its high surface area and the plenty of space suitable for sequential coating with battery components. After coating with a cathode material (LiFePO4nanoparticles), the 3D electrode presents a hierarchically structured electrode in which a porous layer of the cathode material is deposited on the rigid and bicontinuous carbon foam. The composite electrodes exhibit impressive cyclability and rate performance at different current densities affirming their importance as viable power sources in miniature devices. Footprint area capacities of 1.72 mA h cm−2 at 0.1 mA cm−2 (lowest rate) and 1.1 mA h cm−2 at 6 mA cm−2(highest rate) are obtained when the cells are cycled in the range 2.8 to 4.0 V vs. lithium.
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45. |
- Ausmees, A., et al.
(författare)
-
Secondary photoelectron spectra of ionic solids as a function of the incident photon energy
- 1991
-
Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - 0168-9002. ; 308:1-2, s. 219-222
-
Tidskriftsartikel (refereegranskat)abstract
- Energy distributions of slow electrons (0-10 eV) emitted by thin layers of NaCl, KBr, CsBr, and CsI irradiated by monochromatic XUV photons with various energies in the interval of 50-300 eV are measured. The contributions of slow secondaries, hot secondaries and primary photoelectrons are obtained. It is shown that the higher the absorption coefficient for incident photons, the stronger the contribution of hot secondaries. The relationship between their contribution and the electron-phonon scattering process is discussed.
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46. |
- Ausmees, A., et al.
(författare)
-
Secondary photoelectron spectra of NaCl and KBr excited by XUV radiation : Experiments and computer simulations
- 1990
-
Ingår i: Solid State Communications. - 0038-1098. ; 76:12, s. 1383-1386
-
Tidskriftsartikel (refereegranskat)abstract
- Energy distributions of slow electrons (0 to 10eV) emitted by thin layers of NaCl and KBr irradiated by monochromatic XUV photons with various energies in the interval of 50 to 300 eV are measured. For all cases the photoelectron spectrum starts with an intense peak of slow secondaries and has a hot-secondary structure at the energies 1 to 5 eV. The smaller the photon absorption depth, the stronger is this structure. An attempt is made to reproduce such a behaviour of spectra by a Monte Carlo simulation of electron-electron and electron-phonon scattering sequences induced in solids by XUV photon absorption. It appears that for high-energy ( > 2 to 3 eV) conduction electrons the electron-phonon scattering is mainly due to acoustic phonons.
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47. |
- Berg, C., et al.
(författare)
-
Observation of a low-binding-energy peak in the 2p core-level photoemission from oxidized Al(111)
- 1993
-
Ingår i: Physical Review B (Condensed Matter). - 0163-1829. ; 47:19, s. 13063-13066
-
Tidskriftsartikel (refereegranskat)abstract
- High-resolution photoemission studies of oxidation of the Al(111) surface have been performed. The appearance of a component at lower binding energy than the metallic bulk Al emission in the Al 2p spectrum at oxygen exposures above ∼50 langmuir (1 L = 10-6 Torr s) is argued to be due to Al atoms which do not bond directly to oxygen atoms at the oxide-metal interface. Low-energy electron diffraction initially shows a 1×1 structure, which subsequently fades away at higher oxygen exposures, 400 L.
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48. |
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49. |
- Beutler, A., et al.
(författare)
-
Adsorption properties of a mixed surface studied by high resolution core level photoemission : CO/0.5 ML Pd/Rh(111)
- 1998
-
Ingår i: Surface Science. - 0039-6028. ; 411:1-2, s. 111-122
-
Tidskriftsartikel (refereegranskat)abstract
- The coverage-dependent adsorption properties of a laterally heterogeneous bimetallic surface have been investigated by high resolution core level photoemission and low energy electron diffraction. The specific system under study was CO adsorbed on a Rh(111) surface onto which 2D Pd islands (coverage 0.5 ML) were formed by vapor deposition. The CO adsorption properties of the heterogeneous surface were compared with CO adsorption on a Rh(111) surface covered with a full Pd monolayer and with previous results for the CO/Rh(111) system. For low exposures CO is only found on the Rh(111) patches which can be explained by diffusion of CO from the Pd islands onto Rh parts in the adsorption process. At higher exposures CO diffusion from Rh to Pd is indicated. The origin of the diffusion processes can be found in the different coverage-dependent CO adsorption energies on the two surface parts.
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50. |
- Beutler, A., et al.
(författare)
-
Coverage- and temperature-dependent site occupancy of carbon monoxide on Rh(111) studied by high-resolution core-level photoemission
- 1998
-
Ingår i: Surface Science. - 0039-6028. ; 396:1-3, s. 117-136
-
Tidskriftsartikel (refereegranskat)abstract
- High-resolution core-level photoemission is used to study structural aspects for the molecular adsorption of CO on the Rh(111) single-crystal surface, and in particular to derive the adsorption sites. The site sensitivity of the core-level binding energy and the fact that the core level photoemission signal is proportional to the adsorbate coverage make it possible to study quantitatively how the occupation of different sites changes with temperature and/or CO coverage. For the CO/Rh(111) adsorption system we find two sites (on-top and three-fold hollow) to be occupied by the CO molecules. At coverages up to 0.33 ML only on-top sites are occupied, whereas at higher coverages a mixture of three-fold hollow and on-top sites are found. The distribution between these two sites is found to depend strongly on temperature. Quantitative studies of these reversible, temperature-dependent site changes have been carried out for a number of CO coverages. For coverages between 0.33 and ∼0.54 ML, increasing the temperature results in part of the molecules moving from on-top to three-fold hollow sites. This change is strongest for a (4 × 4) structure formed at 0.5 ML where an order-disorder transition is observed at a temperature of 120 K. For coverages above ∼0.54 ML, increasing the temperature leads instead to a decrease of the relative occupation of the three-fold hollow sites. For coverages below 0.33 ML, the molecules occupy on-top sites at all temperatures.
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