Ethanol on Graphite: Ordered Structures and Delicate Balance of Interfacial and Intermolecular Forces

Clear knowledge of solid-molecule interfacial structures is essential to the understanding of interfacial phenomena and the interplay of surface effects and intermolecular forces. Molecules that can form hydrogen bonds are of particular interest. Here, we report the structures and phase-transition behavior of (sub)nanometer thick ethanol assemblies deposited on highly orientated pyrolytic graphite. Depending on the film thickness and temperature, three ordered structures of ethanol are observed: first, an interfacial one formed after deposition at similar to 100 K that is nearcommensurate with the supporting graphene lattice, up to a nominal thickness of 1.5 nm; second, stacking of two-dimensional layered sheets at >= 114 K for the upper part of thicker films of similar to 2 nm and above; and third, a monoclinic bulk-like structure appearing at similar to 144 K before desorption. Importantly, the whole amorphous-tocrystalline transition undergoes a complex multistep process, with the extension of the interfacial structure reaching much further away from the substrate surface and then being replaced within a low-temperature range. Together with the lattice strain found in the interfacial assembly, these thickness- and temperature-dependent structures and transition behavior signify a delicate balance between all interfacial and intermolecular forces involved and molecular free energy.

Automated summary

A clear understanding of solid-molecule interfacial structures is crucial for comprehending interfacial phenomena and the interplay of surface effects and intermolecular forces. The study on the structures and phase-transition behavior of ethanol assemblies deposited on highly orientated pyrolytic graphite revealed a complex multistep process, reflecting a delicate balance between interfacial and intermolecular forces, and molecular free energy.