Stoichiometric transfer of complex oxides by pulsed laser deposition

The interaction of a spatially uniform 248 nm excimer laser beam with targets of various oxides (YBa2Cu3O7 − δ, Y2BaCuO5, Y2O3 and SrTiO3) is investigated. We identify two different mechanisms for non-stoichiometric ablation. Evidence is found that in YBa2Cu3O7 − δ and Y2BaCuO5 the non-stoichiometric ablation at low fluences is due to a phase transformation of the target surface. This is a gradual process, only observable after prolonged irradiation of the target. For congruently melting SrTiO3 such a phase transformation is neither expected nor observed. We find, however, that at low fluences within 100 laser shots the target surface composition equilibrates to a stable, Ti-rich composition. In this case, the mechanism we propose is preferential ablation, which is accompanied by bulk diffusion to compensate the induced surface depletion.