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Expanding the world of 2D materials Two-dimensional (2D) materials have a wide variety of potential applications in the electronics industry. However, certain compositions of 2D materials are difficult to obtain owing to the challenges in exfoliating thin sheets from bulk crystals. Zavabeti et al. exploited liquid metals to synthesize 2D Ga2O3, HfO2, Gd2O3, and Al2O3. The 2D sheets appear as a surface layer in gallium-based liquid metals after the Hf, Gd, or Al is dissolved into the bulk alloy. The 2D oxide that appears on the surface is the oxide with the lowest energy, suggesting that it should be possible to make other 2D oxides by using the same process. Science, this issue p. 332 Several new 2D materials were synthesized as surface layers of gallium-based liquid metals. Two-dimensional (2D) oxides have a wide variety of applications in electronics and other technologies. However, many oxides are not easy to synthesize as 2D materials through conventional methods. We used nontoxic eutectic gallium-based alloys as a reaction solvent and co-alloyed desired metals into the melt. On the basis of thermodynamic considerations, we predicted the composition of the self-limiting interfacial oxide. We isolated the surface oxide as a 2D layer, either on substrates or in suspension. This enabled us to produce extremely thin subnanometer layers of HfO2, Al2O3, and Gd2O3. The liquid metal–based reaction route can be used to create 2D materials that were previously inaccessible with preexisting methods. The work introduces room-temperature liquid metals as a reaction environment for the synthesis of oxide nanomaterials with low dimensionality.