EMPIRICAL MODELING OF ION-BEAM-INDUCED HYDROGEN DEPLETION

The analysis of materials including or implanted with hydrogen by mean s of an ion beam often causes depletion of the hydrogen content. This phenomenon, commonly observed during ERD analyses, is particularly pro nounced with polymers or polymer-like materials. Direct measurement of the original hydrogen profile of the quantitative determination of hy drogen is therefore very difficult. However, measurements of the total quantity of hydrogen as a function of the total analysing fluence can be made and, in principle, can be extrapolated to zero fluence, i.e. to the original quantity of hydrogen. For that purpose, it is common p ractice to use multiple-term inverse exponential curves to fit the exp erimental data. This practice is however inadequate and the results ob tained are of questionable rigor and meaning. We have deduced a mathem atically more elegant and physically more plausible function for the f itting based on the generalized exponential integral function which ha s a minimum number of parameters and which seems to be applicable to a ll common hydrogen depletion curves. The small number of parameters in the equation and their coherence indicate a possible link with a phys ical process. The equation, although empirical, could therefore be use ful for the comparison of different depletion curves and it may even g ive some insights for the development of a quantitative, physical mode l.