MicroCup: A Cryogenic Specimen Preparation Strategy for Atom Probe Tomography of Organic Molecular Liquids.

Atom probe tomography (APT) of organic molecular liquids is limited by poorly reproducible specimen geometry, reduced milling rates, and beam sensitivity during cryo-focused ion beam (FIB) preparation. Here, we introduce a MicroCup strategy that confines liquids in a FIB-prepared cavity prior to phase separation, enables reproducible specimen geometry, and minimizes beam exposure in the region of interest. Using the liquid crystals 4'-octyl-4-cyanobiphenyl (8CB) and 4'-octyloxy-4-cyanobiphenyl (8OCB) as model systems, we establish stable and reproducible field evaporation in three independent measurements for each material, enabling the detected intact ion molecular preservation above 70% in smectic-like phases with interpretable fragmentation behavior. Comparative analysis further shows that the oxygen atom in 8OCB promotes preferential cleavage pathways associated with bond polarization under high electric fields. By inducing partial crystallization within the MicroCup cavity, distinct regions could be resolved: 8CB shows broadly similar evaporation behavior across crystalline and amorphous regions, whereas 8OCB exhibits clearer regional contrast, with smectic-like regions dominated by intact molecular or large fragments and crystalline domains producing small alkyl fragments and ether-type species. These results provide spatially resolved evidence of a solid-liquid interface in a freeze-prepared organic liquid by APT and establish a reproducible workflow for probing local phase behavior in soft materials.