Crystalline-Amorphous Heterostructure: A Novel Configuration for Silver Nanoclusters

Heterostructured composite materials with multiple components have potential applications in diverse aspects, as they tend to exhibit superior physicochemical properties than the sum of their single counterparts. However, the fabrication of heterostructures composed of atomic-precise metal nanoclusters (NCs) is seldom reported owing to their inherent instability, leading to the decomposition of metal NCs during the formation of peripheral layers. Here, a spontaneously formed amorphous-crystalline heterostructured Ag₄₀@Ag₁₂ is discovered, wherein the amorphous Ag₄₀ NCs are enveloped by a single crystal of Ag₁₂ NCs. The formation of Ag₄₀@Ag₁₂ involves three stages, including initial crystallization of Ag₄₀ NCs, partial decomposition (self-sacrifice) of Ag₄₀ NCs enabling Ag₁₂ assembly, and epitaxial-growth crystallization of the Ag₁₂ NCs. The partially decomposed Ag₄₀ NCs provide starting materials for the formation and crystallization of Ag₁₂ NCs to encapsulate the Ag₄₀ seeds, while the residual Ag₄₀ loses its crystallinity in solution simultaneously. This work not only reports a novel class of heterostructured materials for the first time but also provides new insights into the macroscopic co-assembly of distinct silver clusters.