Materials analysis using MeV-ions: fundamental challenges and in-situ applications

Abstract: The interaction of energetic ions with matter is highly relevant for a wide range of applications. Amongst them, material characterization employing ion beams is widely used due to its capability of high-resolution composition depth profiling. The non-destructive nature of these techniques makes them appealing, although there are still several aspects  which can be improved and thus deserve attention. For example, better understanding of energy deposition of ions in matter, can improve simultaneous depth profiling of light and heavy atomic species in a single target. Also, the synthesis of advanced material systems requires complex, multi-step protocols. This situation creates an increased demand for in-situ material characterization, keeping the benefits of ion beam analysis. The present thesis addresses the above mentioned open aspects which are of both fundamental and applied character.First, the energy loss of heavy ions in solid matter, at energies relevant for recoil spectrometry, is investigated. The contribution of inelastic and elastic collisions of heavy ions to the total energy loss as well as the validity of the single scattering assumption  are assessed. This analysis is performed by a combination of experiments using different ions and target materials and corresponding Monte Carlo simulations. A non-trivial dependence of elastic losses and trajectory length on probing depth is found. These observations are not accounted for in several common analysis packages and their implications for depth-profiling are discussed.Second, the potential of tracking material modification processes, such as annealing or reactive thin film deposition, in-situ by MeV ion beams is investigated. An experimental setup, SIGMA - Set-up for In-situ Growth, Materials modification and Analysis, was constructed. SIGMA holds equipment for thin film growth, low energy ion implantation, sputtering, annealing and controlled exposure to reactive gases, while several ion beam analytical techniques are available.Within this thesis, two studies associated with the rapidly growing field of sustainable energy were performed illustrating the capabilities of SIGMA. First,  the growth of photochromic yttrium oxyhydride thin films was monitored in-situ. This study established the complete synthesis path of this material class and furthermore showed that the initial oxidation rate affects the post oxidation rate and the persistence of the photochromic effect. In a second investigation, deuterium implantation in tungsten was combined with in-situ ion beam analysis and thermal desorption spectroscopy to track the deuterium release during annealing. The employed combination of techniques permits to correlate depth-resolved information from ex-situ analysis with data accessible at operating future fusion devices.