Incongruent pulsed laser deposition strategy for thin film growth of Ca3Co4O9 thermoelectric compound

Abstract Pulsed laser deposition (PLD) is commonly used to grow thin film materials with complex stoichiometry and crystal structures, since it achieves a congruent transfer of the target cation elements to the substrate. Although the incongruent PLDs were previously observed via regulating the plasma/background interaction regimes, the incongruent PLDs were seldom investigated and applied practically for the thin film depositions. Herein, we demonstrate the incongruent pulsed laser deposition of Ca 3 Co 4 O 9 thermoelectric thin films, via regulating the target compositions and the oxygen background pressures to preferential scattering the plasma cation compositions. To compare the deposition properties via incongruent and congruent thin film growth, we systematically investigate the crystal structures, surface morphologies, elemental distributions and thermoelectric transportation behaviors for Ca 3 Co 4 O 9 thin films grown at various target compositions and background pressure ranges. A stoichiometric Ca 3 Co 4 O 9 thin film composition is achievable via designing an incongruent PLD strategy, in which case the Ca/Co ratios in the targets are enlarged actively while the PLDs are performed at a pressure range of 10 0  Pa to further preferential scatter of the lighter Ca compared to Co. Nevertheless, the incongruently grown thin films exhibit lower thermoelectric performances, compared to the one at a similar composition grown via the congruent PLD strategy. This result may associate to the localized composition inhomogeneity in the Ca 3 Co4O 9 grown incongruently, and their electronical resistivities are largely elevated by the resultant impurities that are hardly detectable by X-ray diffractions. The present work reveals the complexity in deposition mechanism and kinetics when performing incongruent PLDs, in particular, for growing multiple elemental thin film materials.