Tunable Optical Properties of Cu/VSe2 from the Visible to Terahertz Spectral Range: A First-Principles Study

In this study, Density Functional Theory (DFT) and Density Functional TightBinding (DFTB) calculations were used to study two different interfaces of Cu/VSe2 as well as four nanodiodes of VSe2 bulk including/excluding the Cu layer. We calculated the electronic and optical properties of two systems of two Cu/VSe2 in which Cu atoms are positioned on the top and at the corner of the VSe2 monolayer lattice. The electronic band structure calculations revealed that the metallic properties of the VSe2 monolayer did not change with the interface of Cu atoms; however, the peak around the Fermi level (EF) in Cu/VSe2(Top) shifted downward to lower energies. The optical properties showed that in the visible range and the wavelengths related to the interband transition/intraband excitation of Cu atoms, the enhancement of Re(ω) values could be observed for both Cu/VSe2(Top) and Cu/VSe2(Corner) nanostructures, while in infrared/terahertz ranges, less/more negative values of Re(ω) were predicted. Through the effect of Cu atoms on the VSe2 monolayer, the intensity of the peaks in the Im(ω) part of the dielectric constant was increased from 0.2 THz for Cu@VSe2(Top) and 2.9 THz for Cu@VSe2(Corner) instead of the zero constant line in the pure system of VSe2. Refractive index (n) calculations indicated the higher indices at 5.4 and 4.6 for Cu/VSe2(Top) and Cu@VSe2(Corner), respectively, in comparison to the value of 2.9 for VSe2. Finally, DFTB calculations predicted higher current values from I(V) characteristic curves of Au/Cu/VSe2/Au and Ag/Cu/VSe2/Ag nanodiodes concerning two other devices without the presence of the Cu layer.