A model for chemical effects induced by MeV ion beams on hydrogenated species at the surface of solid materials

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Abstract
When resonant nuclear reactions are used for hydrogen analysis of solid materials, under beam impact a systematic variation of surface hydrogen content is observed as a function of the ion fluence, leading to a dynamic equilibrium value. This phenomenon has been investigated with 15N ions of energy close to 6.4 MeV and interpreted in the framework of chemical effects like adsorption, radiolysis and desorption. An analytical formulation is given which allows related coefficients to be extracted from the experimental data. Among the most predominant parameters are the vacuum quality (partial pressure of hydrogenated species), the chemical state of the pre-adsorbed species and the ion beam characteristics: electronic stopping and fluence.