Optical and dielectric results of Y0.225Sr0.775CoO3± thin films studied by spectroscopic ellipsometry technique

Abstract

Y0.225Sr0.775CoO3±δ thin films have been deposited on SrTiO3 (1 1 1), SrTiO3 (1 0 0), LaAlO3 (1 0 0) and MgO (1 1 1) single crystals substrates at 500 °C by pulsed laser deposition (PLD) method. The optical measurements of these films were studied by ellipsometric method in the spectral range from 310 to 1240 nm. The dependence of the optical constants, the refractive index (n), the extinction coefficient (k), the dielectric loss (ε‵) and the dielectric tangent loss (ε‵‵) of these films on the different single crystal substrates was also studied. The normal dispersion of refractive index of the films could be described using the Wemple–DiDomenico single oscillator method. The optical dispersion parameters Eo and Ed were determined according to the above oscillator method. Y0.225Sr0.775CoO3±δ thin films on different substrates have two direct and indirect allowed transitions corresponding to the energy gap Egd and Egind. The variation in either Egd or Egind with different substrates revealed that, orientation of the substrates affected the energy gap value. Other optical parameters such as the surface energy loss function and the volume energy loss function. were calculated optically. The effective mass of the film has also been calculated from both electrical and optical measurements.