Direct Measurement of Mechanical Properties of Vitreous Ice by Cryo-FIB

Abstract

Low-density amorphous ice, also known as “vitreous” ice, is the most abundant phase of water in the universe, although it is not naturally found on this planet. The most common scientific/commercial application for vitreous ice is the preparation of specimens for cryo-electron microscopy (cryo-EM) in their native state by plunge-freezing or high-pressure freezing. Simulation/modeling of vitreous ice has produced controversial and sometimes contradictory results (add two or more references), so an experimental approach is warranted. Understanding the physics of vitreous ice is significant not only to model extraplanetary phenomena such as cryovolcanism but also to improve the performance of biological applications such as cryo-EM. During data collection by cryo-EM, the beam-induced motion significantly degrades image quality [1]. It has been theorized that this motion is largely caused by the relief of mechanical stress generated during the plunge freezing process [2]. As a first step towards understanding the mechanics of amorphous ice, including the mechanical behavior on cryo-EM grids, we developed a new approach to perform nanoindentation tests on vitreous and crystalline ice specimens.