Surface-energy-compensated fabrication of single-crystal alloy films with atomic-scale flatness

Single-crystal alloy thin films (SATFs), featuring highly ordered atomic lattices and superior composition-dependent properties, hold great potential for applications including crystal epitaxy, surface catalysis, and energy conversion. However, their scalable synthesis and practical applications have been hindered by the difficulty of achieving wafer-scale single crystallinity, atomic-scale surface flatness, as well as flexible and uniform control of alloy composition. Here, we developed a surface-energy-compensated technique for synthesizing a series of wafer-scale binary and ternary SATFs with sub-nanometer roughness (minimum roughness lower than 0.2 nm) and uniform, controllable elemental composition with a wide range (5 ~ 50 at%). Furthermore, using CuPtNi(111) ternary SATFs as epitaxial substrates, we achieve wafer-scale synthesis of wrinkle-free graphene single crystals exhibiting fine electronic quality, including a uniform sheet resistance of 552 Ω sq^-1 with 4.5% deviation, an ultrahigh carrier mobility up to over half a million cm² V^-1 s^-1 at 1.7 K, and well-developed quantum plateaus.