Energy distribution of ions produced by excimer-laser ablation of solid and molten targets

The kinetic energy distribution of ions ejected from targets ablated by high-fluence excimer-laser pulses has been determined by analyzing the time-of-flight (TOF) delayed current of ions overcoming an adjustable electrostatic potential barrier before the detector. Targets of solid and liquid Si acid Ge and of solid Cu have been used. The laser energy fluence was varied in the range typical of pulsed laser deposition (PLD) of thin films, namely between 1 and 8 J/cm(2). The measurements reveal components with different charge-to-mass ratio and distinct components with the same charge/mass ratio, The most probable kinetic energy has values of several tens of eV for singly charged ions, and is larger by a factor exceeding 2 for doubly charged ions. The role of target material and state, solid or liquid, laser photon energy and fluence has been investigated and is discussed in comparison to the findings of previous investigations. An estimate of the electrostatic plasma potential in PLA, based on electron loss rate arguments, is presented to account for the high ion energies observed.