Molecular dynamics in thin films of 6BT liquid crystal

The continued miniaturization of devices is driving a surge of scientific curiosity toward ultrathin liquid crystal films and their unique properties. In this study, we demonstrate for the first time the successful formation of ultra-thin films of 4-hexyl-4′-isothiocyanatobiphenyl (6BT) liquid crystal by the organic molecular beam deposition (OMBD) method at room temperature. By combining ellipsometry and X-ray reflectometry, we precisely characterize film thickness with nanometer resolution. Fourier-transform infrared spectroscopy (FTIR) unveils a fascinating thickness-dependent molecular ordering: initial self-assembly of aromatic and alkyl segments at minimal thicknesses, followed by a pronounced alignment of isothiocyanate ( NCS) groups as films grow thicker. Complemented by broadband dielectric spectroscopy, our work reveals detailed vibrational and relaxation dynamics, shedding light on how bulk-like behaviours emerge in ultrathin geometries. This breakthrough offers new pathways for tuning liquid crystal functionalities in next-generation nanoscale devices. Graphical abstract • The organic molecular beam deposition method enables the formation of stable thin layers of liquid crystal at room temperature. • Vibrational dynamics show that at room temperature, aromatic and alkyl segments of 6BT organize first, while the influence of the NCS group increases with layer thickness. • Relaxation dynamics indicate bulk-like behaviour only in the SmE phase for ultrathin films. • A persistent high-frequency process across all temperatures is attributed to the paranematic effect due to strong surface anchoring.