Abstract
The BiFeO3 (BFO) thin film was deposited by pulsed-laser deposition on SrRuO3 (SRO)-buffered (111) SrTiO3 (STO) substrate. X-ray diffraction pattern reveals a well-grown epitaxial BFO thin film. Atomic force microscopy study indicates that the BFO film is rather dense with a smooth surface. The ellipsometric spectra of the STO substrate, the SRO buffer layer, and the BFO thin film were measured, respectively, in the photon energy range 1.55 to 5.40 eV. Following the dielectric functions of STO and SRO, the ones of BFO described by the Lorentz model are received by fitting the spectra data to a five-medium optical model consisting of a semi-infinite STO substrate/SRO layer/BFO film/surface roughness/air ambient structure. The thickness and the optical constants of the BFO film are obtained. Then a direct bandgap is calculated at 2.68 eV, which is believed to be influenced by near-bandgap transitions. Compared to BFO films on other substrates, the dependence of the bandgap for the BFO thin film on in-plane compressive strain from epitaxial structure is received. Moreover, the bandgap and the transition revealed by the Lorentz model also provide a ground for the assessment of the bandgap for BFO single crystals.
Highlights
BiFeO3 (BFO) has attracted extensive research activities as an excellent multiferroic material
The dielectric functions of SRO were extracted by minimizing the root mean square error (RMSE) value to fit the ellipsometric data of the SRO buffer layer to a three-medium optical model consisting of a semiinfinite STO substrate/SRO film/air ambient structure
In summary, the optical properties of the epitaxial (111) BFO thin film grown on SRO-buffered STO substrate by pulsed-laser deposition (PLD) were investigated
Summary
BiFeO3 (BFO) has attracted extensive research activities as an excellent multiferroic material It simultaneously exhibits ferroelectricity with Curie temperature (TC = 1,103 K) as well as antiferromagnetism with Neel temperature (TN = 643 K), and the properties make BFO potential for applications in electronics, data storage, and spintronics [1,2]. In the published literatures on optical studies, the BFO thin film is Spectroscopic ellipsometry (SE) is a widely used optical characterization method for materials and related systems at the nanoscale It is based on the measuring the change in the polarization state of a linearly polarized light reflected from a sample surface which consists of Ψ, the amplitude ratio of reflected p-polarized light to s-polarized light and Δ, the phase shift difference between the both [12]. Since SE allows various characterizations of the material, our group has studied some thin-film nanostructure using SE methods [15,16,17,18]
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