Bruno Berini, W. Noun, Yves Dumont, E. Popova, Niels Keller

High temperature ellipsometry of the conductive oxide LaNiO₃

Journal of Applied Physics 101 (2007) 023529

LaNiO₃ thin films have been deposited on SrTiO₃ (100) by pulsed laser deposition. Substrate temperature and oxygen pressure have been investigated in the ranges of 640–840 °C and 200–600 μbars, respectively. The use of LaNiO₃ as an electrode requires good electrical, structural, and morphological properties. Optimized deposition parameters were determined to be in the range from 650 to 700 °C for the substrate temperature and in the oxygen pressure range from 300 to 400 μbars. Spectroscopic ellipsometry has been used to study in situ the growth of LaNiO₃ at high temperature and variation of the optical constants during the cooling from growth to ambient temperature. The metallic behavior of the LaNiO₃ is directly observed from the spectral variation of the ellipsometric parameters, tan Psi and cos Delta. For the initial stages of the film growth a determination of the thickness by ellipsometry is possible until the skin depth is reached. The optical constants, refractive index n and extinction coefficient k, have been calculated using a simple model of reflection for the light from a semi-infinite metal during the thermal variation. A linear decrease of the optical constants with a change in curve slope is observed in the temperature interval from 240 to 400 °C. Analysis of the ellipsometric parameters using a Drude-Lorentz dispersion relation indicates a modification in the free electron behavior at high temperatures.

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