| AVS 62nd International Symposium & Exhibition | |
| Spectroscopic Ellipsometry Focus Topic | Thursday Sessions |
| Session EL+EM+EN-ThM |
| Session: | Spectroscopic Ellipsometry: Novel Applications and Theoretical Approaches |
| Presenter: | Daniel Schmidt, National University of Singapore |
| Authors: | D. Schmidt, National University of Singapore L. You, Nanyang Technological University, Singapore X. Chi, National University of Singapore J. Wang, Nanyang Technological University, Singapore A. Rusydi, National University of Singapore |
| Correspondent: | Click to Email |
Single crystalline bismuth ferrite (BiFeO3) is a multiferroic perovskite structure and exhibits magnetic as well as strong ferroelectric behaviour at room-temperature. Since about a decade BiFeO3 is of strong research interest due to its potential applicability in ferroelectric memory devices and spintronics, for example [1].
While the lattice system of bulk BiFeO3 is rhombohedral, the crystal structure of thin films can be engineered by introducing epitaxial strain. Depending on the choice of single crystalline substrate materials the thin film BiFeO3 crystal structure and associated physical properties can be modified.
Here, we present the anisotropic optical properties of high-quality multiferroic BiFeO3 thin films determined with Mueller matrix ellipsometry at room-temperature within the spectral range of 0.6 and 6.5 eV. The full dielectric function tensors of tetragonal-like and rhombohedral-like BiFeO3 phases epitaxially grown on LaAlO3 and SrTiO3 single crystal substrates, respectively, are discussed. Significant birefringence and dichroism are observed as well as strain-induced differences in critical point energies between both phases.
The importance of careful optical analysis of anisotropic Mueller matrix data will be discussed, which allows for characterization of subtle sub-band gap crystal field transitions and reveals indications of an indirect band gap. Such transitions have been observed before by means of other techniques but not by ellipsometry. Additionally, the analysis of Mueller matrix data revealed that an unintentional substrate miscut can introduce an overall polarization tilt of the ferroelectric thin films. This tilt was confirmed by extensive in- and out-of-plane piezoelectric force microscopy studies.
An accurate determination of the dielectric function tensor is of high importance to verify or, if necessary, improve and correct ab-inito calculations, which are crucial for understanding the driving physical principles in such complex materials. A comparison of the experimental results with state-of-the art first-principle calculations will be presented.
[1] G. Catalan and J.F. Scott, Adv. Mater. 21, 2463 (2009).