| 1. |
- Brockstedt, Sara, et al.
(författare)
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Vertical field MR imaging of upper thorax and spine in small children. Evaluation of a new surface coil
- 1993
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Ingår i: Acta Radiologica. - 1600-0455. ; 34:6, s. 549-553
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Tidskriftsartikel (refereegranskat)abstract
- To improve image quality in a vertical field MR imaging unit, operating at low field strength (0.3 T), we have designed a half-elliptical coil for use in the upper thoracic region of small children. Our intention was also to shorten the examination time, which until now has been long, because several scans with different coils have been necessary to cover the thoracic region. The experimental coil is designed so that a child's shoulders fit into the central region. The coil consists of 2 serially connected cable-loops, mounted on a foam rubber vest. The coil performance was tested in a phantom and improvements relative to standard coils were demonstrated in in vivo studies. The results indicate that by using the half-elliptical coil, the signal-to-noise (S/N) ratio can be improved by a factor of 2 to 3 in the thoracic region of a child.
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| 2. |
- Malmgren, Sara, 1985-, et al.
(författare)
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Anomalous diffusion of ions in electrochromic tungsten oxide films
- 2017
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Ingår i: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 247, s. 252-257
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Tidskriftsartikel (refereegranskat)abstract
- Amorphous tungsten oxide thinfilms were deposited by sputtering at different O2/Ar ratios onto conducting substrates. Ion intercalation and diffusion in thefilms was studied by electrochemical impedance spectroscopy measurements in the frequency range 10 mHz–100 kHz and for potentials between 1.0 and 3.2 V vs. Li/Li+, using the film as working electrode in a Li+ containing electrolyte. The impedance data were in very good agreement with anomalous diffusion models. Different models were found to be applicable at potentials >1.8 V and <1.8 V. At high potentials ion intercalation was found to be reversible and an anomalous diffusion model describing ion hopping was favored. At low potentials ion intercalation was found to be irreversible and ion trapping takes place. In this latter range an anomalous diffusion model for the case of non-conserved number of charge carriers gave the best fit to experimentaldata. We obtained potential dependent diffusion coefficients in the range from 109 to 1011cm2/s, and anomalous diffusion exponents in the range 0.1 to 0.4, with the films deposited at lower O2/Ar ratios exhibiting the higher values.
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| 3. |
- Niklasson, Gunnar A., 1953-, et al.
(författare)
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Ageing of electrochromic tungsten oxide thin films studied by impedance spectroscopy.
- 2016
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Konferensbidrag (refereegranskat)abstract
- Tungsten oxide is the most widely used cathodic electrochromic material for smart window applications and a major challenge is to ensure the durability over a service life of more than 20 years. Hence, the degradation under operating conditions must be better understood and preferably prevented. Recent progress in this field includes studies of the power-law kinetics of the degradation process [1] as well as the possibility to rejuvenate degraded films, thereby restoring them to their initial state [2]. In this paper we use impedance spectroscopy to investigate electrochemical ageing of sputter deposited tungsten oxide thin films. Impedance spectroscopy measurements were carried out in a Li+-containing electrolyte, from the open circuit potential at about 3.2V vs. Li down to (1) 2.2 V, which is in the reversible intercalation range; (2) 1.5 V and (3) 1.0 V; at these latter voltages Li intercalation has been found to be irreversible. Subsequently, measurements were carried out for increasing voltages up to the starting point at 3.2 V vs. Li. The intercalated charge capacity was unaffected when potentials below 2.0 V were avoided, while it decreased drastically on the return path from 1.5 V and 1.0 V vs. Li. We interpret this ageing behaviour as an effect of trapping of Li ions irreversibly in the film. Secondly, after the films had been subjected to the low potentials known to induce degradation, the charge transfer resistance in the usual operating range above 2.0 V vs. Li showed a marked increase. This is interpreted as a signature of the development of a solid-electrolyte interface. In conclusion, our measurements suggest that the development of the solid-electrolyte interface may be responsible for the slow degradation observed under normal operating conditions, while Li ion trapping is mainly responsible for severe degradation at potentials significantly below 2.0 V vs. Li. [1] R.-T. Wen, C. G. Granqvist, and G. A. Niklasson: Cyclic voltammetry on sputter-deposited films of electrochromic Ni oxide: Power-law decay of the charge density exchange. Appl. Phys. Lett. 105 163502 (2014) [2] R.-T. Wen, G.A. Niklasson and C.G. Granqvist: Eliminating degradation and uncovering ion-trapping dynamics in electrochromic WO3 thin films. Nature Materials 14 996-1002 (2015)
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| 4. |
- Niklasson, Gunnar A., et al.
(författare)
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Determination of electronic structure by impedance spectroscopy
- 2010
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Ingår i: Journal of Non-Crystalline Solids. - : Elsevier BV. - 0022-3093 .- 1873-4812. ; 356:11-17, s. 705-709
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Tidskriftsartikel (refereegranskat)abstract
- We present a novel method, based on electrochemical intercalation and impedance spectroscopy, to determine the electronic density of states of disordered transition metal oxides. Specifically, we have determined the "electrochemical density of states" of tungsten and iridium oxide thin films over energy ranges as wide as 1-2 eV. Our experimental results show a number of qualitative features exhibited by state-of-the-art band structure computations. Differences in details are probably due to the disordered, porous and sometimes amorphous nature of our films. The results suggest that the impedance spectroscopy method can be used to obtain the density of states only if the conduction band states are localized. The electrochemical density of states is often smaller than the computed one due to kinetic effects, i.e. very slow relaxations of the charge carriers. Nevertheless, our sensitive method opens new vistas for studying the electronic structure of disordered materials.
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| 5. |
- Bocchetta, Carlo, et al.
(författare)
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Project Status of the Polish Synchrotron Radiation Facility Solaris
- 2011
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Ingår i: Proceedings of IPAC2011. - 9789290833666 ; , s. 3014-3016
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Abstract in Undetermined The Polish synchrotron radiation facility Solaris is being built at the Jagiellonian University in Krakow. The project is based on an identical copy of the 1.5 GeV storage ring being concurrently built for the MAX IV project in Lund, Sweden. A general description of the facility is given together with a status of activities. Unique features associated with Solaris are outlined, such as infrastructure, the injector and operational characteristics.
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| 8. |
- Ciosek Högström, Katarzyna, et al.
(författare)
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The Influence of PMS-Additive on the Electrode/Electrolyte Interfaces in LiFePO4/Graphite Li-Ion Batteries
- 2013
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:45, s. 23476-23486
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Tidskriftsartikel (refereegranskat)abstract
- The influence of a film-forming additive, propargyl methanesulfonate (PMS), on electrochemical performance and electrode/electrolyte interface composition of LiFePO4/graphite Li-ion batteries has been studied. Combined use of in-house X-ray photoelectron spectroscopy (XPS) and soft and hard X-ray photoelectron spectroscopy (PES) enabled nondestructive depth profiling at four different probing depths in the 2-50 nm range. Cells cycled with PMS and LiPF6 in ethylene carbonate/diethyl carbonate (EC/DEC) were compared to a reference sample cycled without PMS. In the first cycle, PMS cells showed a higher irreversible capacity, which is explained by formation of a thicker solid electrolyte interphase (SEI). After three cycles, the SET thicknesses were determined to be 19 and 25 nm for the reference and PMS samples, respectively. After the initial cycling, irreversible losses shown by the PMS cells were lower than those of the reference cell. This could be attributed to a different SET composition and lower differences in the amount of lithium between lithiated and delithiated electrodes for the PMS sample. It was suggested that PMS forms a triple-bonded radical on reduction, which further reacts with the electrolyte. The PMS additive was shown to influence the chemical composition at the positive electrode/electrolyte interface. Thicker interface layers with higher C-O and smaller LiF contributions were formed on LiFePO4 cycled with PMS.
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