Kinetic energy distributions of ions ejected during laser ablation of lead zirconate titanate and their correlation to deposition of ferroelectric thin films

Highly oriented lead zirconate titanate (PZT) has been deposited on MgO(100) by pulsed laser deposition, using Nd:YAG (532 nm, 4 ns) laser radiation, followed by subsequent annealing at 570°C. An estimated PbZr + Ti ratio of 0.86, obtained from an as-deposited calibration curve, showed the formation of a lead depleted PZT thin film. The full-width half-maximum (FWHM) of the PZT(001) peak decreased sharply as a function of increasing laser fluence indicated good crystallinity at 12 J/cm2 (FWHM 0.17°). The effect of extended laser irradiation on the durability of the target, the plume constituents and the stoichiometry of the PZT thin films was investigated by electron probe microanalysis and energy-dispersive mass spectrometry: The laser plasma contained excess quantities of Pb+ ions at low fluences (1.67 J/cm2) whilst congruent transfer was observed under high fluence (> 6 J/cm2) conditions. High laser fluence and the presence of oxygen serves to stabilise the PZT stoichiometry at temperatures (i.e. 570°C) which promote perovskite phase formation. Kinetic energy (KE) and mass spectrometric measurements were also used to characterise ionic species generated in the ablation plume. Pb+, Ti+, TiO+, Zr+, ZrO+ and O+ ions were detected and showed a trimodal KE distribution with the lowest energy peak constant between 10–40 eV. ZrO+ ions were also found to be particularly stable within the laser ablation plasma with respect to TiO+ species. At moderate laser fluences (< 10 J/cm2) mean kinetic energies of up to 180 eV of the ions were detected. The average KE increased linearly with laser fluence, with ion acceleration by electron-ion space charge interaction the most likely mechanism.