Sputtering by highly charged ions: Application of the XY–TOF technique to secondary ion ejection from LiF

The accelerator facilities of GANIL allow studying ion–surface collisions in a wide range of projectile velocities. On the one hand, high velocity heavy ions (MeV/u) where the electronic energy loss is dominant (electronic sputtering), and on the other hand, low velocity highly charged ions (keV/q) are available. In the latter case, nuclear stopping (elastic collision cascades) is more important. Possibly, further effects related to the high projectile charge and corresponding high potential energy can occur (potential sputtering). We use a combination of imaging techniques (XY) and time-of-flight (TOF) spectroscopy to measure the complete velocity vector of emitted secondary ions. We present results on energy and angular distributions of 7Li+ (atomic ions) sputtered from a LiF crystal by Ca17+ (9 MeV/u) and Xe21+ (17 keV/q = 350 keV) ions. The energy distributions differ strongly thus clearly showing that the material responds differently to energy deposition by purely electronic stopping (high velocity projectiles) and slow highly charged ions. We also compare the angular distributions of emitted Li+ ions and neutrals in the electronic stopping regime.