Stacking Orientation-Dependent Photoluminescence Pathways in Artificially Stacked Bilayer WS2 Nanosheets Grown by Chemical Vapor Deposition: Implications for Spintronics and Valleytronics

Having a direct optical band gap, monolayers of transition metal dichalcogenide (TMD) nanosheets have attracted great attention due to their exceptional optical properties and potential applications in spintronics and valleytronics. Recently, the stacking configuration of layered materials has been proved to offer an additional degree of freedom to control their physical properties. Unique physical properties, such as interlayer excitons and superconductivity, have been observed in homobilayers of TMDs by controlling their stacking orientation. Here, we use artificial stackings of chemical vapor deposition (CVD)-grown tungsten disulfide (WS2) to fabricate homobilayers with various stacking angles. The artificial stacks showed a 60 degrees periodic change of their photoluminescence (PL) spectra with the stacking angle. An additional low-energy PL peak was observed for the low-angle stacked bilayers, which was revealed by electro-optical measurements to originate in the indirect intralayer exciton relaxation. In addition, we found the high optical quality of our CVD-grown WS2 to be a key factor in observing the intrinsic exciton dynamics free from defect-induced localized excitons. Our work sheds light on the controlled modulation of the optical properties of TMD homobilayers by tuning the stacking of high-quality monolayers.