XeF excimer laser ablation of metallic targets probed by energy-selective time-of-flight mass spectrometry

The kinetic energy distributions (KEDs) of ions produced during XeF laser ablation of metallic targets (Al and Cu) have been investigated by energy selective time-of-flight mass spectrometry (ES-TOFMS). The observed Cu(+) and Al(+) emitted ions are characterised by a bimodal KED. The first peak is located at very low kinetic energy (similar to 1 eV) and can be related to a thermionic component; the second one is strongly dependent on laser fluence and is due to energetic ions emitted from the laser produced plasma. In laser ablation of copper we observe only the thermal component at a laser fluence Lower than similar to 2.5 J cm(-2), whereas for aluminium targets the high kinetic part is always present. This feature has been analysed in terms of the basic mechanisms involved in laser-vapour interaction and plume ionisation.