Étude de la phase transitoire lors de la pulvérisation ionique des films minces de polymères
(2013)
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- (en) The goal of this Ph.D. work was to gain a deeper understanding of the modifications of the physico-chemical properties of the surface of insulating polymeric thin films in the transitory phase of sputtering, before a steady-state is reached. For this purpose, polymer films were first bombarded by keV Cs+ ions and then investigated using both secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS). At high impact energy (12.5 keV), it is shown that the SIMS signals of some elements with high electronic affinity exhibit an oscillatory behavior before attaining the equilibrium. Based on the comparison with data obtained from TRIDYN calculations, this oscillation could be related to the variations of both the sputter yield and the cesium surface concentration, which highly perturbs the ionization probability of these elements. During Cs+ sputtering of an insulating polymeric thin film a positive electric charge accumulates on the film surface. Via the study of the kinetic energy distributions of secondary ions, it could be shown that the accumulated charge density induced a high electric field in the film, permitting to reach the dielectric breakdown voltage, i.e. the minimum voltage that causes a portion of an insulator to become electrically conductive. After the breakdown, this conducting phase neutralizes the surface charge created upon sputtering. The XPS study of the film surface also showed that the bombarded film contained a conducting phase, consisting mainly of carbon islands and of metallic cesium clusters. The improved understanding of these phenomena constitutes a valuable assistance for interpretation of polymer depth-profiling experiments carried out using atomic primary ions.
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Wahoud, F. (2013). Étude de la phase transitoire lors de la pulvérisation ionique des films minces de polymères. https://hdl.handle.net/2078.5/161275