Free-standing two-dimensional metal oxides at the single-atomic-layer limit.

Controlled electron-beam-induced dehalogenation fabricates free-standing monolayer CrO with single-atomic-layer square lattice, yielding single-crystalline domains exceeding 10 4 nm 2.

• Why it matters: Achieving reliable fabrication of free-standing two-dimensional metal oxides at the single-atomic-layer limit has been difficult, limiting access to quantum and excitonic functionalities beyond bulk materials.
• What they did: The method uses electron-beam-induced dehalogenation of layered metal oxyhalides (MOX) to produce free-standing two-dimensional metal oxides such as CrO, ErO, and BiO, with monolayer CrO studied in detail.
• The result: For monolayer CrO, density functional theory predicts Néel antiferromagnetic order below 230 K, and experiments plus theory indicate halogen-selective removal and lattice relaxation drive the CrOCl-to-CrO transformation, enabling MOX–MO lateral heterostructures and oxide bilayers with unusually large exciton binding energy.

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