Abstract
Morphotaxy, a process by which a 2D material is chemically modified while retaining its original physical dimensions, is an emerging strategy for synthesizing unconventional materials at the atomically thin limit. Morphotaxy is typically implemented by vapor-phase reactions on mechanically exfoliated or vapor-deposited 2D van der Waals (vdW) materials. Here we report a method for converting solution-processed films of 2D InSe into InI(2) and InBr(2) using dilute I(2) and Br(2) solutions, respectively. The converted materials retain the physical dimensions of the original 2D flakes, providing access to non-vdW indium halides in ultrathin form. Liquid-phase exfoliation directly enables this morphotaxial reaction by producing nanosheets with high surface areas and introducing residual polyvinylpyrrolidone that stabilizes the flake morphology and slows the reactivity of I(2) and Br(2). Overall, this work presents a versatile strategy for achieving atomically thin metal halides and offers mechanistic insights relevant to the morphotaxial halogenation of other solution-processed 2D materials.