Damage buildup and the molecular effect in Si bombarded with PFn cluster ions

We study the molecular effect (ME) in damage accumulation in Si bombarded at room temperature with atomic P and F and cluster PFn (n = 2 and 4) ions with an energy of 2.1 keV/amu. Correct ion irradiation conditions for unambiguous studies of the ME are discussed. Rutherford backscattering/channeling spectrometry results show that the damage buildup behavior strongly depends on the cluster ion size, and the ME efficiency increases rapidly with increasing the number of atoms in cluster ions. Moreover, the ME efficiency decreases with increasing the defect generation rate, indicating that dynamic annealing processes, rather than nonlinear energy spikes, play a major role in the ME for these irradiation conditions.