Age and Structure of a Model Vapor-Deposited Glass

TL;DR

This study uses computational modeling to compare vapor-deposited glasses with traditionally cooled glasses, finding structural equivalence at the same energy level and observing hot particle cascades during deposition.

Contribution

It demonstrates that vapor-deposited glasses can be structurally identical to ordinary glasses at the same energy, and explores the dynamics of hot particle cascades during vapor deposition.

Findings

Structures are statistically identical at the same inherent structure energy.

Hot particle cascades propagate into the film during deposition.

Vapor-deposited glasses are comparable to aged ordinary glasses.

Abstract

Glass films prepared by a process of physical vapor deposition have been shown to have thermodynamic and kinetic stability comparable to those of ordinary glasses aged for thousands of years. A central question in the study of vapor-deposited glasses, particularly in light of new knowledge regarding anisotropy in these materials, is whether the ultra-stable glassy films formed by vapor deposition are ever equivalent to those obtained by liquid cooling. We present a computational study of vapor deposition for a two-dimensional glass forming liquid using a methodology which closely mimics experiment. We find that for the model considered here, structures that arise in vapor-deposited materials are statistically identical to those observed in ordinary glasses, provided the two are compared at the same inherent structure energy. We also find that newly deposited hot molecules produce cascades of hot particles that propagate far into the film, possibly influencing the relaxation of the material.