Electron beams carve free-standing metal oxide layers one atom thick

Researchers report the controlled fabrication of free-standing two-dimensional metal oxides down to the single-atomic-layer limit, a goal that has long eluded synthesis efforts despite progress in making ultrathin oxides. Writing in Nature Materials, the team describes how electron-beam-induced dehalogenation of layered metal oxyhalides strips away halogen atoms and leaves behind stable monolayers of chromium oxide, erbium oxide and bismuth oxide.

When an electron beam removes the halogens selectively, the remaining metal oxide lattice relaxes into a free-standing sheet no thicker than a single atomic layer. Combined experimental and theoretical analysis indicates that ionization-driven halogen removal and lattice relaxation together underpin this conversion from oxyhalide to oxide, a mechanism the authors suggest may extend to other metal oxyhalides.

Using monolayer chromium oxide, or CrO, as a representative system, the researchers obtained free-standing single-crystalline domains exceeding 10,000 square nanometres and demonstrated controllable patterning at the micrometre scale. The monolayer features a single-atomic-layer square lattice, and density functional theory calculations confirm both its thermodynamic and kinetic stability.

The calculations also predict that monolayer CrO should order antiferromagnetically, showing Néel antiferromagnetic order below 230 kelvin. Because this figure is a theoretical prediction rather than a measured magnetic transition, direct experimental confirmation of the magnetic ordering temperature remains an open question for future work.

Beyond isolated monolayers, the method enables more complex architectures. The team fabricated coherent CrOCl–CrO lateral heterostructures, in which the parent oxyhalide and the converted oxide coexist side by side within the same crystal, as well as aligned and twisted bilayers of the metal oxide.

The fabricated bilayers exhibit pronounced excitonic responses with an unusually large exciton binding energy, according to the study. The authors say this opens opportunities for exploring emergent excitonic phenomena in low-dimensional oxides.

Two-dimensional metal oxides are considered a versatile platform for exploring quantum phenomena, and their properties can differ substantially from those of their bulk counterparts. Achieving controlled fabrication at the single-atomic-layer limit had remained a formidable challenge, which the new electron-beam subtraction approach now addresses in a controllable way.

The work expands the accessible material space of two-dimensional quantum systems by adding free-standing metal oxide monolayers, lateral heterostructures and moiré superlattices to the toolkit available to researchers. Because the conversion is performed directly on layered oxyhalide crystals, it offers a route to atomically thin oxides that are difficult to obtain by conventional growth methods.

The study, published on 29 October 2026, was carried out by researchers including Meng Gao, Deping Guo and Wu Zhou, with contributions from collaborators at several institutions.

Subject of Research: Electron-beam fabrication of free-standing single-atomic-layer two-dimensional metal oxides

Article Title: Free-standing two-dimensional metal oxides at the single-atomic-layer limit

Article References: Gao, M., Guo, D., Li, A., Wang, R., Jin, Z., Huang, C., Lu, Y., Pan, Y., Dai, J., Huang, P., Liu, K., Wang, C., Bao, L., Zhou, L., Qiao, J., Ji, W., Pennycook, S. J., Gao, H.-J., & Zhou, W. (2026). Free-standing two-dimensional metal oxides at the single-atomic-layer limit. Nature Materials. https://doi.org/10.1038/s41563-026-02793-2

Image Credits: AI Generated

DOI: 10.1038/s41563-026-02793-2

Keywords: two-dimensional materials, metal oxides, electron microscopy, oxyhalides, monolayers, excitons, moiré superlattices, antiferromagnetism, density functional theory, heterostructures, Free-standing, two-dimensional