Determining the thickness dependant dielectric functions of PtSe₂

PtSe₂ is a transition metal dichalcogenide which exhibits interesting optical and electrical properties. Interestingly, these properties vary as a function of thickness; In bulk form it manifests as a type II Dirac metal while at a few layers it behaves as a semiconductor. In this study we used molecular beam epitaxy to deposit PtSe₂ onto a sapphire substrate. While growing a PtSe₂ sample with a thickness of ~25nm, we obtained continuous in-situ spectroscopic ellipsometry spectra. These continuous spectra were analyzed by representing the dielectric function of PtSe₂ as a collection of oscillators, which represent the electronic transitions in the band structure. As thickness increases we find that the main absorption peak begins to redshift as well as increase in magnitude. Additionally, X-ray reflectivity was used to determine the thickness, density, and roughness of our PtSe₂ samples. These results were used as input parameters for spectroscopic ellipsometry analysis, where the films were represented as an effective medium with both PtSe₂ and void mixture.