Revealing nanoscale molecular organization in Liquid Crystals via cryogenic Atom Probe Tomography

While liquid crystals (LCs) have been extensively studied, obtaining a comprehensive nanoscale picture of their molecular organization remains challenging, as conventional techniques face an intrinsic trade-off between spatial and chemical resolution. Here, cryogenic atom probe tomography (cryo-APT) is introduced as a new analytical approach for LC materials, using 4′-pentyl-4-cyanobiphenyl (5CB) and 4′-octyl-4-cyanobiphenyl (8CB) as representative model compounds. This was enabled by a tailored cryogenic focused ion beam (cryo-FIB) protocol optimized for small organic molecules. The method enables controlled field evaporation of both intact molecules and diagnostic fragments, achieving over 90% molecular retention while preserving four characteristic dissociation patterns. By spatially correlating these fragmentation profiles with the local electric field derived from the tip geometry, we reveal field-directed dissociation pathways of the n CB molecules. In parallel, the distribution of intact molecular ions enables nanoscale visualization of material structure. The observed structures correspond to frozen configurations that kinetically preserve molecular arrangements inherited from the parent LC state, rather than equilibrium LC phases. We resolve homogeneous mixing of 5CB and 8CB in the nematic phase and directly observe the sub-nanometer crystalline layering in a supercooled 8CB sample, with contrast to the surrounding amorphous matrix suggesting the presence of a solid-liquid interfacial configuration. This work establishes cryo-APT as a new powerful analytical platform for LC research and reveals its broad potential for application in soft matter systems, as it enables 3D atomic-scale compositional mapping of LC systems which conventional microscopy techniques struggle to analyze. • Frozen liquid molecular systems become accessible to atom probe analysis. • Cryogenic focused ion beam preparation enables morphology control of liquid samples. • Electric field effects on molecular dissociation are quantitatively resolved. • Nematic homogeneity and crystalline ordering are directly visualized.