High Temperature Ellipsometry of the Conductive Oxide LaNiO3

Abstract

La Ni O 3 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 200–600μbars, 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 650to700°C for the substrate temperature and in the oxygen pressure range from 300to400μbars. 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, tanΨ and cosΔ. 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 240to400°C. Analysis of the ellipsometric parameters using a Drude-Lorentz dispersion relation indicates a modification in the free electron behavior at high temperatures.