| 1. |
- Samuelsson, Mattias, 1976-
(författare)
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High power impulse magnetron sputtering under industrial conditions
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, the recent development step of magnetron sputtering, termed high power impulse magnetron sputtering (HiPIMS) has been studied. Compared to conventional magnetron sputtering HiPIMS provides a higher plasma density which can ionise the sputtered material. The beneficial influence of the coating properties due to this ionisation has been extensively shown in academic publications. Here, industrial conditions, i.e. no substrate heating and high vacuum conditions have been used during the studies, of which one was performed in an industrial deposition system.For eight metallic targets, films were deposited with HiPIMS and conventional sputtering. The films were evaluated by Rutherford back scattering analysis, scanning electron microscopy, and profilometry. It was found that the density of the HiPIMS grown films exhibited a statistically significant higher density of approximately 5-15% in comparison to films deposited using DCMS under identical conditions. A global plasma model was employed to evaluate the degree of ionisation for some of the target materials, and process conditions used in the study. Conformity between density increase and degree of ionisation as assessed by the plasma model was confirmed.The influence of using HiPIMS during reactive sputtering of TiC was also studied. A metallic Ti target was sputtered in a gas mixture of Ar and C2H2. The coatings were evaluated by X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, 4 point probe resistivity measurements, and nanoindentation. The coatings were found to be nanocomposite TiC/a-C:H. For the HiPIMS process the transition zone between metallic and compound target states was found to be significantly expanded over a wide reactive gas flow range. The implications of choice of deposition method for coating composition, chemical structure, as well as electrical and mechanical properties were evaluated for DCMS and HiPIMS. The process behaviour was suggested to be due to the pulsed nature of the HiPIMS, the high plasma density, and ion content of the particles reaching the substrate.
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| 2. |
- Samuelsson, Mattias
(författare)
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Fundamental aspects of HiPIMS under industrial conditions
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fundamental aspects of the high power impulse magnetron sputtering (HiPIMS) process and its implication for film growth under industrial conditions have been studied. The emerging HiPIMS technique exhibits a higher plasma density and an enhanced degree of ionisation of sputtered material as compared to conventional direct current magnetron sputtering (DCMS). The increased ionisation permits control of the deposition flux and facilitates an intense ion bombardment of the growing films. The latter allows for growth of well adherent, smooth, and dense thin films. Moreover, the technique offers increased stability of reactive processes, control of film phase constitution as well as tailoring of e.g. optical and mechanical properties.In the present work, it was shown, for eight different metals (Al, Ti, Cr, Cu, Zr, Ag, Ta, and Pt), that films grown using HiPIMS exhibit a 5-15% higher density than films grown using DCMS under otherwise identical conditions. Through simulations of the fundamental ionisation processes in the plasma discharge, a correlation between high ionisation degree and film densification was established. The densification was suggested to be a consequence of increased ion irradiation of the growing films in the HiPIMS case. This knowledge was used to investigate the degree of ionisation in the deposition flux required for film modifications. Using a hybrid process, where DCMS and HiPIMS were combined on a single Cr cathode, independent control of the degree of ionisation from other experimental parameters was achieved. The results showed that the majority of the ion irradiation induced modifications of surface related film properties occurred when ~40% of the total average power was supplied by the HiPIMS generator. Under such conditions, the power normalised deposition rate was found to be ~80% of that of DCMS. This was attributed to a reduction in back-attracted ionised sputtered material, which is considered to be the main reason for the low deposition rate of HiPIMS. Thus, enhanced film properties were attainable largely without sacrificing deposition rate.Compound carbide and boride films were synthesised using both reactive processes and compound sources. Reactive deposition of TiC/a-C:H thin films using C2H2 as reactive gas, i.e. carbon source, was demonstrated. It was found that the high plasma density processes (i.e. HiPIMS) facilitated growth conditions for the film structure formation closer to thermodynamic equilibrium than did processes exhibiting lower plasma densities (i.e. DCMS). This was manifested in a high stoichiometry of the carbide phase, whilst excess a-C was removed by physical sputtering. Moreover, the feasibility of using HiPIMS for thin film growth from a compound source, obtaining the same composition in the films as the sputtering source, was demonstrated through synthesis of ZrB2 films.
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| 3. |
- Ek, Lena, 1961-
(författare)
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Cognitive Deficits Reflecting Diffuse and Focal Brain Lesions Caused by Slow Growing Brain Tumors - Low-grade Gliomas
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The overall purpose was to characterize the impact that low-grade glioma (LGG) – a type of slowly growing brain tumor – has on cognitive functions. Paper I was an in-depth analysis of cognitive dysfunction of patients with histological proven LGG. The pattern varied among patients, revealing three subgroups: 1) patients with severe cognitive dysfunction; 2) patients with mild cognitive dysfunction; 3) patients with selective dysfunction due to tumor localization. In the first two subgroups the patients had slowed information-processing speed. Patients with a favorable prognosis performed better than those with unfavorable prognosis. Nonworking patients showed more pronounced dysfunction than working patients. Paper II studied cognitive functions of patients who were in the early stage of the disease and had not yet received any major medical treatments. Patients’ performances ranked at the lower end of normal limits, which contrasted with those of the individually matched controls, whose performances ranked at the upper end. Patients had slower information-processing-speed and less effective executive functions. Patients with frontal tumors had various executive problems due to tumor localization. Paper III investigated cognitive impairment at the individual level in relation to neurological symptoms, radiological characteristics of the tumor, depression, and fatigue. Paper III included the same patients as Paper II. The results showed that the majority of the patients did not have more than selective impairment. One subgroup, consisting of younger patients with large left frontal tumors showed obvious cognitive impairment, including slowed information-processing speed. The thesis showed that diffuse brain injury was closely connected to LGG. A subgroup of patients in the early phase of the disease showed signs of mild diffuse brain injury. The majority of the patients who were in later stage of the disease displayed cognitive signs of diffuse brain injury.
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