Freestanding 2D metal oxides at the single-atomic-layer limit

Two-dimensional (2D) metal-oxides offer a versatile platform for exploring quantum phenomena and enable functionalities beyond those of their bulk counterparts1,2. Despite advances in synthesizing ultra-thin3-7 and freestanding oxides8-11, controlled fabrication at the single-atomic-layer limit has remained a formidable challenge. Here, we report the controlled fabrication of diverse freestanding 2D metal oxides (MO), including CrO, ErO and BiO, down to the single-atomic-layer limit via electron-beam induced dehalogenation of layered metal oxyhalides (MOX). Using monolayer CrO as a representative system, which features a single-atomic-layer square lattice, we obtain freestanding single-crystalline domains exceeding 104 nm2, with prospects for scalability. Density functional theory confirms both the thermodynamic and kinetic stability of freestanding CrO monolayer, predicting a Néel antiferromagnetic order below 116 K. Combined experimental and theoretical analysis reveals that ionization-driven halogen selective removal followed by lattice relaxation underpins the MOX-to-MO transformation, a mechanism likely generalizable across the MOX family. This approach further enables the fabrication of MOX-MO lateral heterostructures and twisted MO bilayers, opening new opportunities for designer 2D metal oxide monolayers, heterostructures, and moiré superlattices.