  Hybrid van der Waals (vdW) heterostructures constructed by the integration of
organic molecules and two-dimensional (2D) transition metal dichalcogenide
(TMD) materials have useful tunable properties for flexible electronic devices.
Due to the chemically inert and atomically smooth nature of the TMD surface,
well-defined crystalline organic films form atomically sharp interfaces
facilitating optimal device performance. Here, the surface phase transformation
of the supramolecular packing structure of fluorinated fullerene (C60F48) on
single-layer (SL) tungsten diselenide (WSe2) is revealed by low-temperature
(LT) scanning tunnelling microscopy (STM), from thermally stable liquid to
solid phases as the coverage increases. Statistical analysis of the
intermolecular interaction potential reveals that the repulsive dipole-dipole
interaction induced by interfacial charge transfer and substrate-mediated
interactions play important roles in stabilizing the liquid C60F48 phases.
Theoretical calculations further suggest that the dipole moment per C60F48
molecule varies with the surface molecule density, and the liquid-solid
transformation could be understood from the perspective of the thermodynamic
free energy for open systems. This study offers new insights into the growth
behaviour at 2D organic/TMD hybrid heterointerfaces.
