Liquid-solid surface phase transformation of fluorinated fullerene on monolayer tungsten diselenide

TL;DR

This study investigates the phase transformation of fluorinated fullerene on monolayer tungsten diselenide, revealing how intermolecular interactions and thermodynamics influence the transition from liquid to solid phases at 2D organic/TMD interfaces.

Contribution

It provides new insights into the growth behavior and phase transformation mechanisms of organic molecules on 2D TMD surfaces using experimental and theoretical approaches.

Findings

Liquid-solid phase transition observed with increasing coverage.

Intermolecular dipole-dipole interactions stabilize liquid phases.

Surface molecule density affects dipole moments and phase behavior.

Abstract

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.