Understanding Controls on Interfacial Wetting at Epitaxial Graphene: Experiment and Theory

TL;DR

This study combines experimental and theoretical approaches to understand how the interfacial water contact angle on epitaxial graphene varies with film thickness and surface structure, revealing the influence of the buffer layer and defects.

Contribution

It provides new insights into the atomic-scale factors controlling water interfacial behavior on epitaxial graphene, integrating high-resolution measurements with molecular dynamics simulations.

Findings

The water contact angle decreases with the presence of the buffer layer.

Epitaxial defects and substrate interactions influence interfacial water structure.

The buffer layer exhibits a contact angle of 73°, smaller than multilayer graphene's 93°.

Abstract

The interaction of interfacial water with graphitic carbon at the atomic scale is studied as a function of the hydrophobicity of epitaxial graphene. High resolution X-ray reflectivity shows that the graphene-water contact angle is controlled by the average graphene thickness, due to the fraction of the film surface expressed as the epitaxial buffer layer whose contact angle (contact angle \theta_c = 73{\deg}) is substantially smaller than that of multilayer graphene (\theta_c = 93{\deg}). Classical and ab initio molecular dynamics simulations show that the reduced contact angle of the buffer layer is due to both its epitaxy with the SiC substrate and the presence of interfacial defects. This insight clarifies the relationship between interfacial water structure and hydrophobicity, in general, and suggests new routes to control interface properties of epitaxial graphene.