Mechanism of MeV ion induced hydrogen depletion from organic layers

In many materials, the loss of hydrogen during elastic recoil detection (ERD) analysis and nuclear reaction analysis (NRA) with MeV ions is observed. This phenomenon, which is especially pronounced in organic materials, limits the accuracy of the quantitative measurements feasible with these techniques. The MeV ion induced depletion was investigated in an ion beam analysis study, using a wide range of projectiles and energies. From the results we conclude that the evolution of hydrogen from electropolymerized porphyrin layers is molecular, which leads to a model incorporating second order kinetics. With this model, the dependence of hydrogen content on the primary ion flux is described by only the initial amount of hydrogen, the probability of ion induced bond breaking and a characteristic distance within two liberated hydrogen atoms will combine to a hydrogen molecule. When incorporating the energy deposited by the primary ion within the ion track into the model, the observed quadratic dependence of ion induced damage on the stopping power is also explained.