Complex dielectric function, Cole-Cole, and optical properties evaluation in BiMnO3 thin-films by Valence Electron Energy Loss Spectrometry (VEELS) analysis

Abstract

Valence Electron Energy Loss Spectrometry-Transmission Electron Microscopy (VEELS-TEM) analyses were found to provide important information on optical properties and the dielectric function of BiMnO3 thin films grown, via radio frequency (RF) magnetron sputter-deposition on SrTiO3 substrates. The research described in this article involved using Kramer's–Krӧnig analysis to determine bandgap, complex dielectric function, and static dielectric constant, ε* = 4.68 of the grown BiMnO3 thin films. The reflection coefficient Ґl of the BiMnO3 thin films was used to elucidate the reflection loss in the BiMnO3 thin films. The bandgap energy of the films was determined using a polynomial fit in the energy loss function (ELF) plot with an Eg = 1.63 eV. The scope of the Cole-Cole plot demonstrates the bandgap and the plasmon region in the BiMnO3 films, which is reported here for the first time. A key contribution of this article relates to describing formulations used for transforming the experimentally obtained dielectric constant components of the BiMnO3 films to produce Cole-Cole plots and applying Kramers-Krӧnig analysis to transform a single scattering energy loss function, to enable determination of the complex dielectric function ε′andε″ and structure of BiMnO3 films.