Clear knowledge of solid-molecule interfacial structures is essential to the understanding of interfacial phenomena and the influence by surface effects and intermolecular interactions. Molecules that can form hydrogen bonds are of particular interest. Here, the structures of (sub)nanometer-thick ethanol assemblies on highly orientated pyrolytic graphite (HOPG) are studied using reflection high-energy electron diffraction (RHEED). Depending on the thickness and the deposition temperature, two different structures can be identified: (1) an interfacial one forming after deposition at ~100 K and being commensurate with the graphite substrate near the interface (within a range of nominal 1.5 nm), and (2) a monoclinic structure appearing at ≥114 K if the molecular overlayer is ~2 nm or above. Moreover, formation of the monoclinic crystallites is a two-step process, converting from a two-dimensional layered structure to a three-dimensional crystalline network at ~144 K. These thickness-dependent structures and their temperature-dependent evolution signify a delicate interplay between the interfacial/interlayer van der Waals force and intermolecular hydrogen bonds. We will conclude the presentation with remarks on solid-overlayer interfacial behavior and structure-property relation.

Thickness-dependent ordering of ethanol nanofilms on graphite

ACS Fall 2021

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