UV radiation enhanced oxygen vacancy formation caused by the PLD plasma plume

Pulsed Laser Deposition is a commonly used non-equilibrium physical deposition technique for the growth of complex oxide thin films. A wide range of parameters is known to influence the properties of the used samples and thin films, especially the oxygen-vacancy concentration. One parameter has up to this point been neglected due to the challenges of separating its influence from the influence of the impinging species during growth: the UV-radiation of the plasma plume. We here present experiments enabled by a specially designed holder to allow a separation of these two influences. The influence of the UV-irradiation during pulsed laser deposition on the formation of oxygen-vacancies is investigated for the perovskite model material SrTiO3. The carrier concentration of UV-irradiated samples is nearly constant with depth and time. By contrast samples not exposed to the radiation of the plume show a depth dependence and a decrease in concentration over time. We reveal an increase in Ti-vacancy–oxygen-vacancy-complexes for UV irradiated samples, consistent with the different carrier concentrations. We find a UV enhanced oxygen-vacancy incorporation rate as responsible mechanism. We provide a complete picture of another influence parameter to be considered during pulsed laser depositions and unravel the mechanism behind persistent-photo-conductivity in SrTiO3

Enhanced Thermoelectric Power Factor of NaxCoO2 Thin Films by Structural Engineering

By controlling the crystallinity and average grain size of thermoelectric NaxCoO2 thin films, a doubling of the thermoelectric power factor is achieved in combination with a strong suppression of the thermal conductivity. These structurally engineered NaxCoO2 thin films outperform single crystalline and polycrystalline samples at room temperature and demonstrate the potential of thermoelectric oxide thin films

Effect of Growth Induced (Non)Stoichiometry on the Structure, Dielectric Response, and Thermal Conductivity of SrTiO₃ Thin Films

We report dramatic variations in cation stoichiometry in SrTiO₃ thin films grown via pulsed laser deposition and the implications of this nonstoichiometry for structural, dielectric, and thermal properties. The chemical composition of SrTiO₃ thin films was characterized via X-ray photoelectron spectroscopy and Rutherford backscattering spectrometry. These studies reveal that deviations in laser fluence and deposition geometry can result in deviations of cation stoichiometry as large as a few percent. Additionally, X-ray diffraction was used to probe structural evolution and revealed an asymmetric strain relaxation mechanism in which films possessing Sr-excess undergo relaxation before those possessing Sr-deficiency. Furthermore, the dielectric constant decreases and the loss tangent increases with increasing nonstoichiometry with intriguing differences between Sr-excess and -deficiency. Thermal conductivity is also found to be sensitive to nonstoichiometry, with Sr-excess and -deficiency resulting in 65% and 35% reduction in thermal conductivity, respectively. These trends are explained by the expected defect structures