Secondary ion emission dynamics of solid ammonia bombarded by heavy ions

Relevant phenomena occurring in the projectile-solid interaction and the subsequent emission of secondary ions from the sample surface will be theoretically treated in this work. The goal is to determine the velocity and energy distributions of the secondary ions emitted from a target of solid ammonia, through the description of secondary electron emission by the nuclear track and the establishment of secondary ion trajectories. Calculations were made with the computer code SEID. Theoretical distributions, valid for secondary ions that no longer interact with the solid, were compared with the experimental distributions obtained for ammonia ice bombarded by 252Cf fission fragments. It was observed that ionic species of mass ∼ 86 u, located within 10 Angstrom from the projectile impact point, are desorbed without being neutralized, unlike lighter ions (∼ 18 u) that leave the surface from more distant regions. Considering the ionization energy (I = 35 eV) of NH4, the experimental value of 6 km/s was reproduced. These comparisons also show that the model partially describes the behavior observed in the energy distribution of the emitted ions. As a result, new processes are proposed to be included in the model. (authors)