Scalable Substrate Development for Aqueous Biological Samples for Atom Probe Tomography

TL;DR

This paper introduces two innovative, scalable substrate designs for preparing aqueous biological samples for atom probe tomography, simplifying specimen preparation and improving reliability.

Contribution

It presents two novel substrate designs that enable FIB-only preparation of biological specimens for APT, using nanoporous alpha brass for enhanced stability.

Findings

Successful demonstration of FIB-only specimen preparation using new substrates

APT datasets obtained from biological samples on the proposed substrates

Designs are low-cost, scalable, and compatible with existing APT workflows

Abstract

Reliable and consistent preparation of atom probe tomography (APT) specimens from aqueous and hydrated biological specimens remains a significant challenge. One particularly difficult process step is the use of a focused ion beam (FIB) instrument for preparing the required needle-shaped specimen, typically involving a "lift-out" procedure of a small sample of material. Here, two alternative substrate designs are introduced that enable using FIB only for sharpening, along with example APT datasets. The first design is a laser-cut FIB-style half-grid close to those used for transmission-electron microscopy, that can be used in a grid holder compatible with APT pucks. The second design is a larger, standalone self-supporting substrate called a "crown", with several specimen positions that self-aligns in APT pucks, prepared by electrical discharge machining (EDM). Both designs are made nanoporous, to provide strength to the liquid-substrate interface, using chemical and vacuum dealloying. We select alpha brass a simple, widely available, lower-cost alternative to previously proposed substrates. We present the resulting designs, APT data, and provide suggestions to help drive wider community adoption.