Nanoscale Analysis of Frozen Water by Atom Probe Tomography Using Graphene Encapsulation and Cryo-Workflows: A Parametric Study

TL;DR

This study demonstrates the use of atom probe tomography with graphene encapsulation and cryo-workflows to analyze hydrated water samples at the nanoscale, comparing different transfer and analysis parameters.

Contribution

It introduces a new cryogenic sample preparation protocol for APT of hydrated materials and provides a parametric analysis of transfer and analysis conditions.

Findings

Cryo-transfer improves sample integrity during analysis.

Different flight path and pulsing modes affect data quality.

Graphene encapsulation enables nanoscale analysis of water.

Abstract

There has been an increasing interest in atom probe tomography (APT) to characterise hydrated and biological materials. A major benefit of APT compared to microscopy techniques more commonly used in biology is its combination of outstanding 3D spatial resolution (~0.2 nm) and mass sensitivity. APT has already been successfully used to characterise biological materials, revealing key structural information at the atomic scale, however there are many challenges inherent to the analysis of hydrated materials. New preparation protocols, often involving sample preparation and transfer at cryogenic temperature, enable APT analysis of hydrated materials and have the potential to enable 3D atomic scale characterisation of biological materials in the near-native hydrated state. In this study, APT specimens of pure water at the tips of tungsten needles were prepared at room temperature by graphene encapsulation. A parametric study was conducted where samples were transferred at either room temperature or cryo-temperature and analysed by APT by varying parameters such as the flight path and pulsing mode. The differences between the acquisition scenarios are presented along with recommendations for future studies.