Development of a Time of Flight - Energy spectrometer for applications in Heavy Ion - Elastic Recoil Detection thin film analysis
Doctoral Thesis
2010
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University of Cape Town
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Two principal aims of this work were firstly, to build and characterise a Time of Fight –Energy spectrometer and demonstrate its usability in Heavy Ion – Elastic Recoil Detection thin film materials analysis, and secondly, to measure stopping powers of heavy ions in thin foil compound materials using the newly built spectrometer. Key to the performance of the assembled spectrometer was its timing resolution. Characterisation measurements using a 27.5 MeV Kr15+ incident beam showed that the best timing resolution could be obtained when measurements are performed without timing preamplifiers in the signal processing chain. The best example was that of a resolution of 190 ps for 18 MeV 40Ca ions. The resultant depth resolution was found to be 6.8 nm for 40Ca recoils ejected from the surface layers of a CaF2 film on a Si substrate. A mass calibration procedure was devised for identification of light impurities in known sample structures, and the mass resolution, also a direct result of time resolution, was found to range between 0.8 u and 1.7 u in the atomic mass range 12 u to 40 u, respectively. Spectrum analysis was implemented using the software code KONZERD, enabling elemental quantification and measurement of film thickness. The lowest detectable atomic concentrations measured were 0.46 at.% for carbon and 0.84 at.% for oxygen. The analytical depth was up to 0.6 μm. Measurements were also carried out to determine stopping powers of ZrO2 and Mylar foils for 12C, 16O, 19F, 24Mg, 27Al and 28Si ions in the 0.1 – 0.6 MeV/u energy range. Of these, 27Al and 24Mg stopping power data generated in this work are the first such measurements for ZrO2, and 24Mg and 19F for Mylar.
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Msimanga, M. 2010. Development of a Time of Flight - Energy spectrometer for applications in Heavy Ion - Elastic Recoil Detection thin film analysis. University of Cape Town.