Interfacial Coupling Controls Molecular Epitaxy of HMTP on Graphene/SiC

TL;DR

This study shows that interfacial coupling controls the molecular epitaxy of HMTP on graphene/SiC, and hydrogen intercalation can be used to engineer the interface for better organic film crystallinity.

Contribution

It demonstrates how interfacial coupling influences molecular growth and how hydrogen intercalation can restore epitaxial growth on graphene/SiC.

Findings

HMTP forms highly ordered epitaxial layers on single-layer graphene.

Growth on the buffer layer is initially amorphous and becomes polycrystalline.

Hydrogen intercalation decouples the buffer layer, restoring epitaxial growth.

Abstract

Epitaxial growth critically influences structural and electronic properties of organic semiconductors. Graphene serves as a prominent van der Waals template for molecular self-assembly; however, graphene on SiC is intrinsically heterogeneous, with decoupled monolayer graphene coexisting with residuals of a covalently bound buffer layer, which may affect molecular ordering. Here, we track the ordering of the molecular donor, 2,3,6,7,10,11-hexamethoxytriphenylene (HMTP), from the first layer to thin films, combining low-energy electron microscopy and diffraction with X-ray diffraction. HMTP forms highly ordered epitaxial layers on single-layer graphene, whereas growth on the buffer layer initiates as amorphous and evolves into polycrystalline films with weak orientation with respect to the substrate. Crucially, hydrogen intercalation decouples the buffer layer, converting it into quasi-freestanding monolayer graphene and restoring epitaxial growth. These findings demonstrate that interfacial coupling governs molecular epitaxy on graphene/SiC, and interface engineering via hydrogen intercalation provides a scalable route to control organic thin-film crystallinity on graphene.