Metallene: Ångström‐Scale 2D Metals

Abstract

Abstract Atomically thin 2D metals, also termed metallenes, constitute a distinctive class of 2D materials in which metallic bonding is preserved at the ångström scale. Quantum confinement imparts ultrahigh carrier mobility, tunable plasmonic resonances, and exposed surfaces composed of low‐coordination active sites. Although “2D metals” have historically encompassed various metallic nanostructures, recent breakthroughs have enabled the isolation of structurally well‐defined metallenes with ambient stability and quantum‐confined properties not observed in their bulk counterparts. This review provides a comprehensive overview of metallene research, focusing on their synthetic chemistry, low‐dimensional metrics, and structure‐function relationships. This unified framework provides cross‐disciplinary insights for rational design in catalysis, plasmonics, electronics, and biomedical applications. Rigorous criteria are first established to distinguish true monolayer metals from quasi‐2D nanosheets, emphasizing bonding anisotropy, lattice continuity, and spectroscopic fingerprints. State‐of‐the‐art fabrication strategies are then benchmarked for scalability and technology readiness. Next, the engineering toolbox, including doping, hierarchical hetero‐structuring, and defect/phase/strain modulation, is surveyed, which tailors these intrinsic traits and translates them into record performances across diverse applications. Finally, outstanding challenges, including thermodynamic metastability, limited synthetic precision, unclear dynamic structure‐function relationships, and device integration, and delineate research directions aimed at accelerating the rational design and practical implementation of metallenes are outlined.