Recondensation-induced target modification and compositional gradients in LiMn₂O₄ films

Xiaochun Huang, Natacha Ohannessian, Thomas Lippert, and Christof W. Schneider;

Abstract:

Achieving stoichiometric transfer from multi-elemental targets is a critical challenge in pulsed laser deposition (PLD) in particular if mass-ratios of target elements are large like in lithium-containing complex oxides. This study identifies the often overlooked recondensation effect as the origin of through-thickness compositional gradients in LiMn₂O₄ films deposited under elevated oxygen pressures. Using secondary ion mass spectrometry (SIMS) depth profiling, we show that films grown at low oxygen pressures (≤0.01 mbar) are chemically homogeneous, whereas higher pressures (≥0.05 mbar) lead to a continuous lithium depletion as deposition proceeds. A combination of plasma mass spectrometry and SIMS analysis of the target surface reveals that this compositional inhomogeneity at higher pressures stems from the accumulation of a lithium-deficient recondensed layer at the ablation crater and surrounding areas, which is subsequently ablated as the ablation spot moves. Element-resolved plume imaging reveals that at PLD-relevant high-pressure conditions, light elements (Li and O) rapidly escape into the background gas, while heavier Mn species remain confined near the target, promoting a preferential recondensation of Mn. These results highlight the recondensation-induced target modification as a critical, pressure-dependent parameter in PLD and provide key insights into the stoichiometric growth of complex multi-element oxide thin films.