| 1. |
- Carlsson Tedgren, Åsa, et al.
(författare)
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Comparison of high-dose-rate Ir-192 source strength measurements using equipment with traceability to different standards
- 2014
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Ingår i: Brachytherapy. - : Elsevier. - 1538-4721 .- 1873-1449. ; 13:4, s. 420-423
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE:According to the American Association of Physicists in Medicine Task Group No. 43 (TG-43) formalism used for dose calculation in brachytherapy treatment planning systems, the absolute level of absorbed dose is determined through coupling with the measurable quantity air-kerma strength or the numerically equal reference air-kerma rate (RAKR). Traceability to established standards is important for accurate dosimetry in laying the ground for reliable comparisons of results and safety in adoption of new treatment protocols. The purpose of this work was to compare the source strength for a high-dose rate (HDR) (192)Ir source as measured using equipment traceable to different standard laboratories in Europe and the United States.METHODS AND MATERIALS:Source strength was determined for one HDR (192)Ir source using four independent systems, all with traceability to different primary or interim standards in the United States and Europe.RESULTS:The measured HDR (192)Ir source strengths varied by 0.8% and differed on average from the vendor value by 0.3%. Measurements with the well chambers were 0.5% ± 0.1% higher than the vendor-provided source strength. Measurements with the Farmer chamber were 0.7% lower than the average well chamber results and 0.2% lower than the vendor-provided source strength. All of these results were less than the reported source calibration uncertainties (k=2) of each measurement system.CONCLUSIONS:In view of the uncertainties in ion chamber calibration factors, the maximum difference in source strength found in this study is small and confirms the consistency between calibration standards in use for HDR (192)Ir brachytherapy.
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| 2. |
- Fallberg, Anna, 1980-
(författare)
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Chemical Vapour Deposition of Undoped and Oxygen Doped Copper (I) Nitride
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In science and technology there is a steadily increased demand of new materials and new materials production processes since they create new application areas as well as improved production technology and economy. This thesis includes development and studies of a chemical vapour deposition (CVD) process for growth of thin films of the metastable material copper nitride, Cu3N, which is a semiconductor and decomposes at around 300 oC. The combination of these properties opens for a variety of applications ranging from solar cells to sensor and information technology. The CVD process developed is based on a metal-organic compound copper hexafluoroacetylacetonate, Cu(hfac)2 , ammonia and water and was working at about 300 oC and 5 Torr. It was found that a small amount of water in the vapour increased the growth rate considerably and that the phase content, film texture, chemical composition and morphology were strongly dependent on the deposition conditions. In-situ oxygen doping during the CVD of Cu3N to an amount of 9 atomic % could also be accomplished by increasing the water concentration in the vapour. Oxygen doping increases the band gap of the material as well as the electrical resistivity and changes the stability. The crystal structure of Cu3N is very open and contains several sites which can be used for doping. Different spectroscopic techniques like X-ray photoelectron spectroscopy, Raman spectroscopy and near edge X-ray absorption fine structure spectroscopy were used to identify the oxygen doping site(s) in Cu3N. Besides the properties, the oxygen doping also affected the morphology and texture of the films. By combining thin layers of different materials several properties can be optimized at the same time. It has been demonstrated in this thesis that multilayers, composed of alternating Cu3N and Cu2O layers, i.e. a metastable and a stable material, could be grown by CVD technique. However, the stacking sequence affected the texture, morphology and chemical composition. The interfaces between the different layers were sharp and no signs of decomposition of the initially deposited metastable Cu3N layer could be detected.
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| 3. |
- Fallberg, Anna, et al.
(författare)
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Phase stability and oxygen doping in the Cu-N-O system
- 2010
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Ingår i: Journal of Crystal Growth. - North Holland : Elsevier. - 0022-0248 .- 1873-5002. ; 312:10, s. 1779-1784
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Tidskriftsartikel (refereegranskat)abstract
- A growth stability diagram for the system Cu-N-O has been determined in the temperature range 250-500°C for a thermally activated CVD process, based on copper (II) hexafluoroacetylacetonate (Cu(hfac)2), NH3 and H2O. Without any addition of water only Cu3N was obtained. Addition of water introduces oxygen into the Cu3N structure to a maximum amount of 9 atomic % at a water/nitrogen molar ratio of 0.36 at 325 °C. Above this molar ratio Cu2O starts to deposit in addition to an oxygen doped Cu3N phase. Only Cu2O is deposited at a large excess of water. XPS and Raman spectroscopy indicated that the additional oxygen in the doped Cu3N structure occupies an interstitial position with a chemical environment similar to oxygen in Cu2O. The oxygen doping of the Cu3N phase did not influence the lattice parameter which was close to the bulk parameter of 3.814 Å. The film morphology varied markedly with both deposition temperature and water concentration in the vapour during deposition. Increasing the water concentration results in less faceted and textured films with smoother and more sphere like grains. The resistivity of the Cu3N films increased with increased oxygen content of the film and varied between 10-100 Ωcm (0 to 9 atomic% O). The optical band gap increased from 1.25 to 1.45 eV as the oxygen content increased (0 to 9 atomic %).
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| 4. |
- Lindahl, Erik, et al.
(författare)
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Gas-Pulsed CVD for Film Growth in the Cu-Ni-N System
- 2012
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Ingår i: Chemical Vapor Deposition. - : Wiley. - 0948-1907 .- 1521-3862. ; 18:1-3, s. 10-16
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Tidskriftsartikel (refereegranskat)abstract
- A new ternary solid solution, Cu3-xNix+yN, is prepared by gas-pulsed CVD at 260 degrees C. Gas pulses of the precursor mixtures Cu(hfac)2+NH3 and Ni(thd)2+NH3, separated by intermittent ammonia pulses, are employed for the deposition of Cu3N and Ni3N, respectively. A few monolayers of the nitrides are grown in each CVD pulse and then mixed by diffusion to produce the solid solution. The metal content of the solid solution can be varied continuously from 100% to about 20% Cu, which means that the electrical properties can be varied from 1.6eV (band gap of Cu3N) to metallic (Ni3N). This is of interest for various applications, e.g., solar energy, catalysis, and microelectronics.
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| 5. |
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| 6. |
- Lindahl, Erik, et al.
(författare)
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In situ study of nickel formation during decomposition of chemical vapor deposition Ni3N films
- 2010
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 28:5, s. 1203-1209
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Tidskriftsartikel (refereegranskat)abstract
- The thermal decomposition of Ni3N thin films, deposited by chemical vapor deposition on SrTiO3 (001) and Si (100) substrates, has been studied by in situ x-ray diffraction, as well as temperature-programed controlled gas emission in both inert and hydrogen atmospheres. The decomposition at inert atmosphere conditions starts at the film/substrate interface, which results in a high degree of ordering in the formed nickel film. In the H-2 atmosphere, the initial film ordering is less pronounced and the decomposition occurs from the film surface and downward. This means that by choosing the annealing atmosphere, inert or hydrogen, the formation of the Ni film can be localized to either the original nitride/substrate interface or to the surface of the nitride. The annealed films show a cube-on-cube growth with respect to the SrTiO3 (001) substrate. The film morphology after the annealing experiments resembles the one of the as-deposited films. The lowest resistivity value is measured for the films annealed in the H-2 atmosphere. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3478298]
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