Enabling Interface-Dependent Energy Transfer in PbI₂/SnS mixed-dimensional van der Waals Heterostructures Through Contact Geometry

Heterostructures composed of van der Waals (vdW) layered semiconductor materials have attracted attention due to their anisotropic optoelectronic properties. By leveraging the structural anisotropy of 2D lattice, a new heterostructure configuration in which the vdW layer edges faced with the surface of other layers could provide additional control of exciton/charge transfer at the heterojunction, unlike conventional vertically-stacked or laterally-connected vdW heterostructure geometries. In this sense, the ability to integrate multi-dimensional vdW layered structures with various stacking orientations is of critical importance.<br/>In this study, we report mixed-dimensional heterostructures based on the vdW multilayer semiconductor materials – 1D lead iodide (PbI₂) nanowires and 2D tin sulfide (SnS) flakes and demonstrate that the exciton energy transfer at the heterointerface is dependent on the contact geometry. By employing vapor-liquid-solid (VLS) growth using Pb catalysts, two different types of PbI₂ nanowires oriented in [001] and [010] directions were obtained, where their sidewall facets ({100} and {001} planes, respectively) form distinct contact interfaces with the {001} plane of SnS flakes after dry transfer. Structural characterizations in conjunction with optical analyses, including photo- and cathodoluminescence, revealed that the excitonic excitation in PbI₂ nanowire could be transferred to SnS through its sidewall edges at the heterointerface, which induces luminescence from SnS of which the bandgap is indirect. The vdW contact geometry-dependent energy transfer resulted in a substantial increase in excitonic emission of SnS domains from the heterointerfaces of PbI₂{100}/SnS{001} relative to those of PbI₂{001}/SnS{001}. Furthermore, we confirm that the transferred energy travels along the SnS domain edges efficiently via guided mode. Our results demonstrate a new toolbox for controlling the excitonic emission in vdW layered heterostructures for optoelectronic and nanophotonic applications.