Enabling near-atomic–scale analysis of frozen water

Abstract

Transmission electron microscopy went through a revolution enabling routine cryo-imaging of biological and (bio)chemical systems, in liquid form. Yet, these approaches typically lack advanced analytical capabilities. Here, we used atom probe tomography to analyze frozen liquids in three dimensions with subnanometer resolution. We introduce a specimen preparation strategy using nanoporous gold. We report data on 2- to 3-μm-thick layers of ice formed from both high-purity deuterated water and a solution of 50 mM NaCl in high-purity deuterated water. The analysis of the gold-ice interface reveals a substantial increase in the solute concentrations across the interface. We explore a range of experimental parameters to show that atom probe analyses of bulk aqueous specimens come with their own challenges and discuss physical processes that produce the observed phenomena. Our study demonstrates the viability of using frozen water as a carrier for near-atomic–scale analysis of objects in solution by atom probe tomography.

Status and Direction of Atom Probe Analysis of Frozen Liquids

“…The formation of metastable molecular ions from a combination of water molecules was discussed from a theoretical perspective by Karahka & Kreuzer (2011) and is consistent with previous experimental reports (Tsong, 1985). For data from the LEAP, Figure 12a, the drop in the level of background from 60 pJ at 25 kHz and 40 pJ at 200 kHz can be ascribed primarily to lower electrostatic field leading to less evaporation at the DC field in between the thermal pulses, as discussed in detail in El-Zoka et al (2020).…”

“…For data from the LEAP, Figure 12a, the drop in the level of background from 60pJ@25kHz and 40pJ@200kHz can be ascribed primarily to lower electrostatic field leading to less evaporation at the DC field in between the thermal pulses, as discussed in detail in ref. (El-Zoka et al, 2020).…”

“…The bonding of a proton to H2O is an exothermic reaction, so highly localised heating associated to this process could potentially play on role on the detachment of charged surface species. open questions since little is known of the field evaporation behaviour of ice, despite the few reports from (Pinkerton et al, 1999;Stuve, 2012) on the very thin ice layers and the thicker layers (Schwarz et al, 2020;El-Zoka et al, 2020). The state-of-the-art is more advanced and efforts on atomistic simulations are ongoing that provide precious insights into the detailed mechanisms of field evaporation in metals (Ashton et al, 2020).…”

Atom Probe Tomography of a Cu-Doped TiNiSn Thermoelectric Material: Nanoscale Structure and Optimization of Analysis Conditions

“…The Xe-plasma beam typically enables production of samples more quickly than conventional Ga ion beam instruments. It also offers alternative in-situ preparation approaches currently being explored on a number of different systems (Halpin et al, 2019;El-Zoka et al, 2020;Famelton et al, 2021).…”

A Liquid Metal Encapsulation for Analyzing Porous Nanomaterials by Atom Probe Tomography

“…Then, a cryogenically-cooled stage is used during the focused ion beam (FIB) milling of needle-shaped specimen suitable for atom probe from the Fe-Field metal composite. Cryo-FIB has recently proven advantageous for avoiding ingress of Ga (Dantas De Morais et al, 2014) and modifications of the specimen's composition and structure during the preparation of APT specimens (Rivas et al, 2020;Lilensten & Gault, 2020;Chang et al, 2019) and for the preparation of specimens from low-melting point materials (Schreiber et al, 2018;El-Zoka et al, 2020). By using this approach, we successfully analyzed the microporous, reduced iron that exhibits a bimodal pore distribution, and show data both the Fe and the filling material.…”