LaNiO3 is a metallic perovskite with suitable electric properties to be used as an conductive electrode in an all oxide hetero-structure. The fabrication of a such material on a SrTiO3 (100) substrate by pulsed laser deposition has been studied in function of the oxygen partial pressure and substrate temperature. The variation of these two growth parameters results in changes in structure, morphology, optical and electrical properties of the thin films. An epitaxial growth has been obtained for an optimal set of parameters. High temperature in-situ spectroscopic ellipsometry (SE) was used to study the growth and the thermal variation of the optical properties in the temperature range of 300K to 1070K.
The characteristic feature of a conducting medium is the presence of free electric charges. The adjustement of the ellipsometric parameters has been realized with a Drude-Lorentz model. The Drude part corresponds to the oscillations of free electrons whereas the Lorentz part is due to the bound electrons. Both free and bound electrons contribute to the optical properties. The refractive index n and the extinction coefficient k are obtained from the adjusted optical model and they are consistent with the literature for measurements at the ambient temperature. The resistivities can be calculated from the Drude part of the parameters and they are in agreement with the measures by a 4 probes techniques on the films. During the growth, an evolution of the optical properties is observed and the film thickness is given until the skin depth is reached. More interesting is the thermal evolution of both n, k during the cooling. The main observation is a change in thermal variation of n and k at a temperature of about 524K. The analysis of the model parameters indicates a change in the electric properties essentially related to the free carriers. Implications to the use of LaNiO3 as a high temperature electrode will be discussed.