The introduction of cryogenic stage and specimen preparation to high-resolution imaging techniques, such as electron microscopy (EM) and atom probe tomography (APT), allows exploring the biological samples in their near-native state and acquiring the structural and chemical information at nanoscale. Several coating approaches have been developed primarily for cryo-EM such as sputter coating and condensation based approach [Hayles et al., 2007]. As for APT, the approach requires the specimens to be needle-shaped with apex ~ 100 nm, while recently conductive coating in room temperature has been proved to be both feasible and valuable [Adineh et al., 2017, 2018].
In this study, we aim to apply and optimize the condensation method on submicron needle shape or curved geometries to produce a thin conductive layer in the cryogenic environment. Firstly, cryo-FIB (focused ion beam) is performed to mill the target frozen-hydrated specimen into a needle shape. The gas injection needle is then inserted, and gas (C9H16Pt) released will be condensed on the cryogenically cooled needle to form a conductive layer. The parameters and their interactions are studied including (1) The effects of needle-to-surface distance and condensation time on coating layer thickness; (2) morphology of the coating layer in the cryogenic condition, and morphology after reaching room temperature. Moreover, the mechanical properties of the coating layer with both electron beam and ion beam curing are also interesting subjects to investigate. From the preliminary experiment results, it has been found that with an extended condensation time, the coating layer thickness is proportional to the condensation time; While given a minimal condensation time, the needle-to-surface distance has been shown to be a significant factor with an inverse correlation with the coating layer thickness. The condensed metallic layer can potentially maintain its integrity with cryo-to-room temperature cycles, to facilitate cross-platform specimen transfer and data acquisition.