Status and direction of atom probe analysis of frozen liquids

TL;DR

This paper reviews recent advances in atom probe tomography (APT) for analyzing frozen liquids, highlighting new methods, challenges, and future prospects for cryogenic specimen analysis.

Contribution

It introduces recent approaches for APT analysis of frozen liquids, comparing their merits and discussing the physics and challenges involved.

Findings

APT can analyze water ice layers of several microns thick.

Different preparation methods enable analysis of frozen liquids.

Preliminary results reveal challenges in understanding field evaporation physics.

Abstract

Imaging of liquids and cryogenic biological materials by electron microscopy has been recently enabled by innovative approaches for specimen preparation and the fast development of optimised instruments for cryo-enabled electron microscopy (cryo-EM). Yet, Cryo-EM typically lacks advanced analytical capabilities, in particular for light elements. With the development of protocols for frozen wet specimen preparation, atom probe tomography (APT) could advantageously complement insights gained by cryo-EM. Here, we report on different approaches that have been recently proposed to enable the analysis of relatively large volumes of frozen liquids from either a flat substrate or the fractured surface of a wire. Both allowed for analysing water ice layers which are several microns thick consisting of pure water, pure heavy-water and aqueous solutions. We discuss the merits of both approaches, and prospects for further developments in this area. Preliminary results raise numerous questions, in part concerning the physics underpinning field evaporation. We discuss these aspects and lay out some of the challenges regarding the APT analysis of frozen liquids.