PbI2 van der Waals Nanowires: Tunable Stacking Orientations and Optoelectronics

초록

Van der Waals (vdW)-layered direct bandgap semiconductor materials such as lead iodide (PbI2) possess anisotropic optoelectronic properties that are highly dependent on their layer stacking structures. Here, we report the control of PbI2 layer growth orientation, or stacking axis, via a vapor?liquid?solid (VLS) growth mechanism. The vdW PbI2 layers initially grow with transverse stacking relative to the [0001]-oriented growing axis, and the controlled introduction of PbBr2 induces twin boundary (TB) formation, which is responsible for the change in the stacking axis (i.e., kinking). By varying the duration of the PbBr2 introduction, two different types of kinking modes are confirmed: Type I kink in parallel with TB propagation accompanying two mirrored stacking c-axes and Type II kink, in which the layers are stacked parallel to the growing segment. Optoelectronic analyses using photoluminescence and cathodoluminescence reveal that the kinked structures exhibit asymmetric band-edge excitonic emission profiles, which are distinct from those of the single-segmented vdW nanowires. These results demonstrate a new methodology to modulate the structure-dependent optoelectronic/photonic properties of vdW layered materials, which cannot be achieved using conventional 2D design platforms.