Quadrupole mass spectrometry and time-of-flight analysis of ions resulting from 532nm pulsed laser ablation of Ni, Al, and ZnO targets

Abstract

This work describes the design and validation of an instrument to measure the kinetic energies of ions ejected by the pulsed laser ablation (PLA) of a solid target. Mass spectra show that the PLA of Ni, Al, and ZnO targets, in vacuum, using the second harmonic of a Nd:YAG laser (532nm, pulse duration ∼10ns) generates abundant Xn+ ions (n⩽3 for Ni, ⩽2 for Al, ⩽3 and ⩽2 for Zn and O respectively from ZnO). Ions are selected by their mass∕charge (m∕z) ratio prior to the determination of their times of flight. PLA of Ni has been studied in most detail. The mean velocities of ablated Nin+ ions are shown to follow the trend v(Ni3+)>v(Ni2+)>v(Ni+). Data from Ni2+ and Ni3+ are fitted to shifted Maxwellian functions and agree well with a model which assumes both thermal and Coulombic contributions to ion velocities. The dependence of ion velocities on laser pulse energy (and fluence) is investigated, and the high energy data are shown to be consistent with an effective accelerating voltage of ∼90V within the plume. The distribution of velocities associated with Ni3+ indicates a population at cooler temperature than Ni2+.