Investigating the dielectric functions of molecular beam epitaxy-grown PtSe₂ films via in-situ spectroscopic ellipsometry

PtSe₂ has the distinct advantage high-tunability in its band gap, mainly due to quantum confinement and strong interlayer coupling produced between individual PtSe₂ sheets. For this study, we have used a series of PtSe₂ films, grown either by directly selenizing ultrathin metal Pt films or by co-depositing Pt and Se on Al₂O₃ (0001) substrates using molecular beam epitaxy. In-situ spectroscopic ellipsometry were performed on all samples while they were grown inside the MBE chamber. Modeling the ellipsometry spectra, we determined the thickness and the dielectric function of a series of PtSe₂. To obtain reliable fits for the experimental spectra, the dielectric function of PtSe₂ was represented as a collection of six oscillators, each representing an electronic transition in the Brillouin zone. The first oscillator, representing the fundamental band gap of PtSe₂ was located around 1.22 eV, which is consistent with previous published results.