Vitrification from physical vapor deposition is known to be an efficient way for tuning the kinetic and thermodynamic stability of glasses and significantly improve their properties. There is a general consensus that preparing stable glasses requires the use of high substrate temperatures close to the glass transition one, Tg. Here, we challenge this empirical rule by showing the formation of Zr-based ultrastable metallic glasses (MGs) at room temperature, i.e., with a substrate temperature of only 0.43Tg. By carefully controlling the deposition rate, we can improve the stability of the obtained glasses to higher values. In contrast to conventional quenched glasses, the ultrastable MGs exhibit a large increase of Tg of ∼60 K, stronger resistance against crystallization, and more homogeneous structure with less order at longer distances. Our study circumvents the limitation of substrate temperature for developing ultrastable glasses, and provides deeper insight into glasses stability and their surface dynamics.

By decreasing the rate of physical vapor deposition, ZrCuAl metallic glass with improved stability and mechanical performances can be formed. With scanning transmission electron microscopy, we found that the glass deposited at higher rate exhibits a heterogeneous structure with compositional fluctuations at distances of a few nanometers, which gradually disappear on decreasing the deposition rate and eventually a homogeneous, featureless structure is developed approaching ultrastability. This microscopic structural evolution suggests the existence of two dynamical processes: the faster diffusion driven by the kinetic energy of the depositing atoms, which leads to nanoscale compositional fluctuations, and the slower collective rearrangements that equilibrate the deposited atoms and eliminate the compositional and structural heterogeneity.

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