Van der Waals imprinting of black-phosphorus-like binary alloyed monolayers with tunable band gaps and moiré superstructures

Fabrication of isostructural isovalent alloys is a powerful approach to discovering novel materials with emergent properties. This approach has been well established in traditional bulk materials, yet remains to be fully exploited in two-dimensional systems. Here we use black- phosphorus (BP)-like group-VA binary alloyed monolayers on BP-like group IV-VI substrates to demonstrate the enabling power of isomorphism and isovalency in fabricating two-dimensional alloyed monolayers with tunable properties. We achieve the formation of nearly freestanding BP-like Sb1-xBix (0 <= x <= 1) monolayers on the GeSe substrate, with a semiconductor-to-metal transition and tunable moire superstructures as x increases. In contrast, BP-like Pb,Bi i , monolayers can be stabilized only for low Pb concentrations, and the contrasting behaviors are attributable to preservation or breakdown of isovalency in the two cases. This study establishes a generic approach to growing alloyed monolayers via van der Waals imprinting, opening a new avenue for materials discoveries with desirable functionalities.