Correlating ultrastability with fragility and surface mobility in vapor deposited tetrahedral glasses

TL;DR

This study uses molecular dynamics simulations to explore how local tetrahedrality influences ultrastability, fragility, and surface mobility in vapor-deposited tetrahedral glasses like silicon and water.

Contribution

It demonstrates that increasing tetrahedrality enhances ultrastability, fragility, and surface mobility, revealing strong links between bulk and surface dynamics in these glasses.

Findings

Ultrastability correlates with increased fragility.

Surface mobility significantly increases with tetrahedrality.

Bulk and surface dynamics are strongly connected in ultrastable glasses.

Abstract

Several experiments on molecular and metallic glasses have shown that the ability of vapor deposition to produce ultrastable glasses is correlated with their structural and thermodynamic properties. Here we investigate the vapor deposition of a class of tetrahedral materials (including silicon and water) via molecular dynamics simulations of the generalized Stillinger-Weber potential. By changing a single parameter that controls the local tetrahedrality, we show that the emergence of ultrastable behavior is correlated with an increase in the fragility of the model. At the same time, while the mobility of the surface compared to the bulk shows only slight changes at low temperature, with increasing the tetrahedrality, it displays a significant enhancement towards the glass transition temperature. Our results point towards a strong connection between bulk dynamics, surface dynamics and glass-ultrastability ability in this class of materials.