Adsorption-conversion synthesis of ultrathin intermetallics and high-entropy alloys

Two-dimensional intermetallic compounds (IMCs) and high-entropy metallic alloys (HEMAs) have recently attracted much attention for their emergent physical phenomena. However, the synthesis of two-dimensional single crystals of IMCs and HEMAs represents a considerable challenge due to their intrinsic thermodynamic instability and kinetic uncontrollability. Here we report an adsorption-conversion strategy to synthesize diverse Fe-, Co-, Ni-, Cu- and Pd-based ultrathin single crystals of IMCs and HEMAs, including the compositions that were previously inaccessible. During growth, metal atoms liberated from decomposed surface adsorbates incorporate into the metallic matrix, whereas residue surface Cl atoms kinetically drive the formation of two-dimensional structures by enhancing the energy difference among various facets. The resulting materials exhibit a conductivity of up to 3 × 10⁷ S m^-1 and an ultralow temperature coefficient of resistance of 2 ppm K^-1. Our work establishes a broad family of ultrathin IMCs and HEMAs as a versatile material platform for exploring emergent physicochemical properties.