Surface gateways modulating dynamics in metallic glasses

This study demonstrates that the surface of metallic glasses (MGs) significantly influences bulk dynamics, challenging the conventional view of surface effects being limited to a few atomic layers. By applying a surface confinement approach (depositing a thin crystalline platinum layer on a La-based MG), we show that all three characteristic relaxation processes (α, β, and β′) can be modulated. Specifically, the confinement decouples the relaxation modes: it enhances the fast β′-relaxation while suppressing both the slow β- and primary α-relaxations, and markedly delays crystallization. Microstructural analysis reveals that surface confinement stabilizes free volume (FV) and is inferred to restrict out-of-plane atomic motion. These findings illustrate that the surface acts like a gate, regulating FV to influence overall relaxation dynamics. This work challenges the conventional understanding of surfaces in MGs and establishes a foundation for tuning bulk properties through surface engineering, offering new pathways for designing MGs with tailored stability and performance.