  Cryogenic atom probe tomography (cryo-APT) is being developed to enable
nanoscale compositional analyses of frozen liquids. Yet, the availability of
readily available substrates that allow for the fixation of liquids while
providing sufficient strength to their interface, is still an issue. Here we
propose the use of 1-2 microns thick binary alloy film of gold-silver (AuAg)
sputtered onto flat silicon, with sufficient adhesion without an additional
layer. Through chemical dealloying, we successfully fabricate a nanoporous
substrate, with open-pore structure, which is mounted on a microarray of Si
posts by lift out in the focused-ion beam, allowing for cryogenic fixation of
liquids. We present cryo-APT results obtained after cryogenic sharpening,
vacuum cryo-transfer and analysis of pure water on top and inside the
nanoporous film. We demonstrate that this new substrate has the requisite
characteristics for facilitating cryo-APT of frozen liquids, with a relatively
lower volume of precious metals. This complete workflow represents an improved
approach for frozen liquid analysis, from preparation of the films to the
successful fixation of the liquid in the porous network, to cryo-atom probe
tomography.
