Plasmonic Observation of High‐Density Nanoclustering in Low‐Temperature H₂O

There has been considerable scientific interest in comprehending the behavior and phase transitions of H₂O at the nanoscale in low temperatures. Herein, a highly sensitive and nondestructive surface plasmonic detection system operated at low temperatures to investigate the real-time nanoscale variation in H₂O density from a rapidly cooled thin ice layer formed at 77 K is employed. The nanoslit device exhibits a distinct plasmonic response at 180-250 K, correlated to an increase in the local density of H₂O at the nanometer scale. Along with theoretical analyses, it is revealed that high-density H₂O clusters form by vigorous aggregation of H₂O molecules within the interphase liquid region between polymorphic ice crystals. The utilization of ice-active materials, known to inhibit ice growth, suppresses the initiation of such high-density nanoclustering at 180 K. These results contribute to the comprehension of the interplay between polymorphic crystals and density-variant interphases in low-temperature H₂O systems.