Correlation between electrical and ellipsometric properties on high-quality epitaxial thin films of the conductive oxide LaNiO3 on STO (001)

Direct current (dc) electrical transport properties (resistivity and Hall) and spectroscopic ellipsometric measurements have been combined to study high-quality epitaxial thin films of LaNiO3 (LNO) on SrTiO3 (001) substrates. Stoichiometry of LaNiO3 films was changed by varying the oxygen partial pressure between 240 and 420 mu bar during the growth in a pulsed laser deposition setup. Structural and temperature-dependent transport properties conform to epitaxial LaNiO3. The ellipsometric data, measured in the 350-850 nm spectral range, are adjusted with a dispersion relation of Drude-Lorentz (DL) type. In addition to the Drude term, only one Lorentz oscillator was used in the modeling for consistency with existing density of states calculations. Increasing oxygen pressure does not induce significant variations of the electronic density, the Hall mobility, or the Drude plasma energy. Neither are the pseudo-cubic lattice parameter and the Lorentz oscillator resonance energy significantly modified. Resistivity from dc transport and optical resistivity from the DL dispersion relation are found to be in good agreement in the case of epitaxial LNO films, giving an elegant way to control the electrical properties of the LaNiO3 conductive oxide thin films in situ by the spectroscopic ellipsometry technique during growth.