Surface Freezing of Triacontane at SiOx/Air Interfaces:  Submonolayer Coverage

The topology and molecular ordering of submonolayer triacontane films at SiO x /air interfaces has been investigated near the bulk melting temperature. Island regions, about an extended monolayer thicker than the neighboring regions, are observed by surface force microscopy and these regions continue to exist above the bulk melting transition. X-ray reflectivity and grazing incidence angle diffraction confirm the surface freezing behavior of the alkanes. The melting temperature of the solid monolayer regions seems to coincide with the wetting transition temperature observed in samples with higher coverage. The diffraction data also reveal that the triacontane in the monolayer regions exhibits long-range order at temperatures above the bulk melting temperature, consistent with a rotator phase.