A first-principles study of electronic and optical responses of multi-layered PtSe2 sandwiched between WSe2 and mica

An ab initio approach was used to define the structural, electronic, and optical properties of PtSe2 and WSe2 as monolayer (ML) systems and four heterostructures based on 1 ML WSe2 on different thicknesses of PtSe2, on a mica substrate, as van der Waals (vdW) heterostructures. The MLs of WSe2 and PtSe2 exhibited a direct/indirect band gap of 1.68 eV/1.36 eV. In relation to the heterostructures, the increasing PtSe2 thickness from 1 to 4 MLs affects the interlayer spacing and band alignment, reducing the band gap; moreover, the PtSe2 thickness increasing brings to a gradual transition from indirect to direct bandgap. PDOS analysis shows that both Pt and W orbitals contributed to the valence band, Pt contribution is dominant in the conduction band, but the Se atoms possess the higher DOS before and after the Fermi level in all the interfaces. The MPSH results indicate an enhanced orbital delocalization, which exhibits the smallest HOMO–LUMO separation. The optical properties in the frequency (THz) range showed that the absorption response depends on the number of layers in the heterostructures, with the WSe2@3MLPtSe2 system demonstrating the highest in-plane absorption intensity. However, the real part (Re(ω)) of dielectric function showed the higher values for WSe2/3MLsPtSe2 with in-plane = 6.54 and out-of-plane = 1.59 than others; this interface indicated higher peak intensity along the in-plane direction in the frequency of 24 THz in the imaginary part (Im(ω)), while WSe2/1MLPtSe2 showed the lowest one. These findings demonstrate that WSe2/3MLsPtSe2 heterostructure exhibited as good candidate for THz optoelectronic applications.