Ultrastable glasses can be produced via vapor deposition, exhibiting superior thermodynamic and kinetic stability compared to their liquid-cooled counterparts. Although often considered equivalent to liquid-cooled glasses aged for ${10}^6$ of years, their structural evolution with increasing stability remains poorly understood. Here, using Cs-corrected scanning transmission electron microscopy, we directly observe the nanoscale spatial heterogeneity of vapor-deposited and liquid-cooled Zr-Cu-Al metallic glasses as a function of stability or energy. We find that the correlation length of spatial heterogeneity reaches a minimum in the most stable vapor-deposited metallic glasses with lowest energy, whereas larger heterogeneity is observed in the more stable liquid-cooled glasses. Complementary simulations reveal that this minimization of heterogeneity arises from the reduction of distorted icosahedral structures with medium-range ordering. Our study provides compelling evidence that vapor-deposited metallic glasses undergo a distinct evolution of spatial heterogeneity compared to their liquid-cooled counterparts as stability increases.

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• Glass transition
• Metallic glasses
• Electron microscopy
• Molecular dynamics