Anisotropic van der Waals Epitaxy and Sliding of CsPbBr₃ Microplatelets on ReSe₂

The growth of highly crystalline semiconductor nanostructures with low defect concentration is essential for realizing their optoelectronic properties and for their efficient integration into functional nanodevices. Our group has shown that nanowires can grow on a single crystal or amorphous substrates using covalent epitaxy and graphoepitaxy to generate well-aligned and guided nanowires with controlled crystallographic orientation. However, covalent epitaxial relations often induce strain and stress in the nanocrystals, leading to dislocations and other defects, which affect the physical properties of semiconductor nanostructures. Substituting covalent substrates with 2D van der Waals (vdW) layered materials could relieve stress and strain issues, as weaker interactions are formed between the top layer of the vdW material and the formed nanostructure. Therefore, we suggest extending the guided growth approach by using vdW epitaxy on 2D materials. Here we present the vapor-solid growth of micro- and nano-platelets of well-ordered cubic CsPbBr₃ on 2D layered triclinic ReSe₂ substrate. X-ray photoelectron spectroscopy (XPS) and cathodoluminescence (CL) measurements revealed type I band alignment, with energy transfer from the CsPbBr₃ platelets to the ReSe₂ substrate. Such heterostructure could be integrated into an enhanced photodetector compared to ReSe₂ based photodetector. To further investigate the vdW epitaxial nature of the heterostructure, we characterized the heterostructure interface by applying lateral force and sliding the CsPbBr₃ platelets on the ReSe₂ using atomic force microscopy (AFM). Our results indicate that some sliding directions are preferable to others, which could be attributed to the in-plane anisotropy of the ReSe₂ surface. These results open a route for the ordered design of heterostructure devices with interesting energy transfer mechanisms and improved optical and electrical properties owing to the lower miss-match stresses induced by vdW vs. covalent epitaxy.