Abstract
We report the complex dielectric function ε = ε(1) + iε(2) of MoS(2)/WS(2) and WS(2)/MoS(2) heterostructures and their constituent monolayers MoS(2) and WS(2) for an energy range from 1.5 to 6.0 eV and temperatures from 39 to 300 K. Comparisons between the optical properties of the heterostructures and their monolayers were conducted. Critical-point (CP) energies of the heterostructures were traced back to their origins in the monolayers. Low-temperature measurements confirmed the existence of only three excitonic CPs from 1.5 to 2.5 eV due to the overlap of trion B(-) of the MoS(2) monolayer and exciton A(0) of the WS(2) monolayer. Due to the dielectric screening effect, most CPs exhibit red shifts in the heterostructures compared to their monolayer counterparts.