Freestanding-Mimetic Growth of Ultralong A17 Bismuth Nanoribbons via Dielectric-Mediated Van der Waals Epitaxy.

Metastable A17-phase bismuth (A17 Bi) exhibits exceptional electronic properties, yet controlling its epitaxial growth remains challenging due to unresolved anisotropic faceting energetics. Here, we demonstrate a dielectric-mediated van der Waals epitaxy that enables freestanding-mimetic growth of ultralong A17 Bi nanoribbons with lengths exceeding 30 µm and aspect ratios larger than 150. Using the primary overlay alignment that minimizes lattice misfit between bismuthene and mica, the weak heteroepitaxial interaction facilitates the formation of multilayer, ultralong A17 Bi nanoribbons. The faceting energetics of three distinct edges, i.e., zigzag facet at longitudinal edges, armchair and diagonal facets at terminal edges, are studied, which helps to elucidate a Wulff construction framework governed by kinetic competition between edge-specific growth rates. This work provides critical insights into vapor-phase epitaxy of A17 Bi that yields solution synthesis like morphologies, bridging a key gap between epitaxial control and crystallographic design.