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 optimized 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 analyzing water ice layers which are several micrometers 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.
Highlights
Atom probe tomography (APT) provides 3D elemental mapping, typically with sub-nanometer resolution (De Geuser & Gault, 2020; Gault et al, 2021), and an elemental sensitivity down to the range of tens of parts per million (Haley et al, 2020)
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 optimized instruments for cryo-enabled electron microscopy
Deploying these capabilities of atom probe tomography (APT) to study wet chemical systems has been hindered by the lack of available specimen preparation strategies for frozen liquids. Efforts in this direction were reported (Stintz & Panitz, 1991, 1992; Pinkerton et al, 1999); no workflows have established the use of the APT technique for routine analyses of frozen liquids. This contrasts with transmission electron microscopy (TEM), which over the past decades has seen tremendous developments in standardized workflows allowing preparation and handling of specimens at cryogenic temperature (Livesey et al, 1991; Marko et al, 2007; Parmenter & Nizamudeen, 2021), as well as the analysis of liquids via graphene encapsulation (Park et al, 2015), recently achieving atomic resolution (Nakane et al, 2020)
Summary
Atom probe tomography (APT) provides 3D elemental mapping, typically with sub-nanometer resolution (De Geuser & Gault, 2020; Gault et al, 2021), and an elemental sensitivity down to the range of tens of parts per million (Haley et al, 2020) Deploying these capabilities of APT to study wet chemical systems has been hindered by the lack of available specimen preparation strategies for frozen liquids. Efforts in this direction were reported (Stintz & Panitz, 1991, 1992; Pinkerton et al, 1999); no workflows have established the use of the APT technique for routine analyses of frozen liquids.
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