Extracting the optical properties of PtSe2 thin films using Mueller Matrix Spectroscopic Ellipsometry

Previously, we used in situ spectroscopic ellipsometry to investigate the thickness-dependent dielectric functions of PtSe2, a transition metal dichalcogenide material that exhibits interesting optical and electrical properties. In that work, to obtain the dielectric functions from ellipsometry spectra we approximated the PtSe2 film as an isotropic layer, partly because the films were very thin (~25 nm) and due to the availability of limited in situ ellipsometric data. In this study, we use ex situ spectroscopic ellipsometry measurements to investigate several molecular-beam epitaxy-grown PtSe2 films, all of which were modelled assuming that they were anisotropic. After their growth, we performed X-ray diffraction, X-ray reflectivity and atomic force microscopy measurements to characterize the films. Subsequently, we used two ellipsometers to obtain Mueller Matrix based ellipsometric measurements on all of the PtSe2 film, covering a spectral range between 40 meV to 6 eV. By using Kramers-Kronig-consistent oscillators to represent the dielectric function, we fit the Muller matrix data to obtain the anisotropic dielectric function of PtSe2.