Optical properties of rough LaNiO3 thin films studied by spectroscopic ellipsometry and reflectometry

Optical characterization of sol-gel deposited lanthanum nickel oxide, LaNiO3 (LNO) film on Pt-coated Si substrate was performed by spectroscopic ellipsometry and reflectometry. The sum of five Lorentz oscillators was used for LNO dispersion parameterization in spectral range from 190 to 1000 nm. Two theoretical approaches: Raileigh-Rice theory (RRT) and effective medium approximation (EMA) were considered to account for the effect of LNO upper boundary roughness. Root mean square (rms) values of the heights of irregularities obtained by atomic force microscopy (AFM) and RRT were 2.09 and 5.62 nm, respectively. Effective layer thickness in EMA approach was found to be 4.62 nm. Higher values of roughness determined from optical methods with respect to the AFM may be assigned to the effect of convolution of AFM tip and boundary irregularities.