 To ensure this very low primary current densities are used generally in the range of 10−10 – 10−9 A/cm² (primary ion dose is below 1012 - 1013 ions/cm2).This leads to extremely small sputtering rates of fraction of a monolayer per hour and hence small secondary ion current density.Additionally, these emitted secondary ions are of low kinetic energy and emitted up to 20 nm from the impact site with surface annealing occurring in femto-seconds.