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 Ga ₂ O ₃ , HfO ₂ , Gd ₂ O ₃ , and Al ₂ O ₃ . 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

The exfoliation of two dimensional (2D) oxides, established on the surface of specific liquid metals, has recently been introduced. One such liquid metal is molten tin, which forms a variety of surface 2D oxides. However, the development behaviour of these surface tin oxides is still unknown. Here the evolution of stoichiometry and thickness from single-layer SnO to highly oxidised multi-layer SnO₂ in ambient oxygen is explored.

Metal oxychalcogenides are emerging as a new motif of group VI-A semiconductors with unique electronic properties. Among this family, two dimensional (2D) oxysulfide materials have been increasingly involved in the development of next-gen electronic and optoelectronic devices. However, current synthesis routes for 2D metal oxysulfides are still limited to vapor phase deposition techniques, hindering access to ultra-thin, well-defined, and highly crystalline structures. Herein, we report a new synthesis approach for atomically thin and large-area indium oxysulfide nanosheets (2D In₂O_3−xS_x, x is from 0 to 0.41). The process consists of printing indium oxide skins out of molten indium metal and a subsequent sulfur insertion conducted in a trisulfur radical anion solution. Back-gated field-effect transistors (FETs) based on 2D In₂O_3−xS_x reveal a notably high electron mobility of ∼20.4 cm² V⁻¹ s⁻¹, corresponding to approximately 270% mobility enhancement over as-synthesized indium oxide. In addition, 2D In₂O_3−xS_x based photodetectors exhibit an excellent performance in ultraviolet (UV) region, with a photoresponsivity of ∼3.4 × 10³ A W⁻¹ greatly surpassing that of many commercial materials. More importantly, the same reaction parameters can be employed to obtain 2D bismuth oxysulfide and 2D tin oxysulfide, offering a furnace-free approach for 2D oxysulfide semiconductor fabrication.