Two-dimensional (2D) crystals are promising materials for developing future nano-enabled technologies^1,2,3,4,5,6. The cleavage of weak, interlayer van der Waals bonds in layered bulk crystals enables the production of high-quality 2D, atomically thin monolayers^7,8,9,10. Nonetheless, as earth-abundant compounds, metal oxides are rarely accessible as pure and fully stoichiometric monolayers owing to their ion-stabilized ‘lamellar’ bulk structure^11,12,13,14. Here, we report the discovery of a layered planar hexagonal phase of oxides from elements across the transition metals, post-transition metals, lanthanides and metalloids, derived from strictly controlled oxidation at the metal–gas interface. The highly crystalline monolayers, without the support of ionic dopants or vacancies, can easily be mechanically exfoliated by stamping them onto substrates. Monolayer and few-layered hexagonal TiO₂ are characterized as examples, showing p-type semiconducting properties with hole mobilities of up to 950 cm² V⁻¹ s⁻¹ at room temperature. The strategy can be readily extended to a variety of elements, possibly expanding the exploration of metal oxides in the 2D quantum regime.

二维 (2D) 晶体是用于开发未来纳米技术的有前途的材料^1,2,3,4,5,6。层状块状晶体中弱的层间范德华键的裂解能够生产高质量的二维原子薄单层^7,8,9,10。尽管如此，作为地球上丰富的化合物，金属氧化物由于其离子稳定的“层状”本体结构而很少作为纯的和完全化学计量的单层获得^11,12,13,14. 在这里，我们报告了从过渡金属、过渡后金属、镧系元素和准金属的元素中发现的层状平面六方相氧化物，这些氧化物源自金属-气体界面处严格控制的氧化。高度结晶的单层，没有离子掺杂剂或空位的支持，可以很容易地通过将它们压印到基板上进行机械剥离。以单层和少层六方 TiO ₂为例进行了表征，显示出 p型半导体特性，空穴迁移率高达 950 cm ²  V ^-1  s ^-1在室温下。该策略可以很容易地扩展到各种元素，可能会扩大对二维量子体系中金属氧化物的探索。