Wrinkles of graphene on Ir(111): Macroscopic network ordering and internal multi-lobed structure

TL;DR

This study investigates the ordered network of wrinkles in epitaxial graphene on Ir(111), revealing a frustrated, multi-lobed structure influenced by substrate interactions and temperature, with implications for graphene applications.

Contribution

It introduces a detailed analysis of the macroscopic wrinkle network and internal multi-lobed structure in epitaxial graphene on Ir(111), combining microscopy and modeling.

Findings

The wrinkle network forms a quasi-hexagonal, Voronoi-like pattern.

Wrinkle junctions often join three wrinkles, indicating frustration.

Multi-lobed wrinkles are explained by van der Waals and bending energy interplay.

Abstract

The large-scale production of graphene monolayer greatly relies on epitaxial samples which often display stress-relaxation features in the form of wrinkles. Wrinkles of graphene on Ir(111) are found to exhibit a fairly well ordered interconnecting network which is characterized by low-energy electron microscopy (LEEM). The high degree of quasi-hexagonal network arrangement for the graphene aligned to the underlying substrate can be well described as a (non-Poissonian) Voronoi partition of a plane. The results obtained strongly suggest that the wrinkle network is frustrated at low temperatures, retaining the order inherited from elevated temperatures when the wrinkles interconnect in junctions which most often join three wrinkles. Such frustration favors the formation of multi-lobed wrinkles which are found in scanning tunneling microscopy (STM) measurements. The existence of multiple lobes is explained within a model accounting for the interplay of the van der Waals attraction between graphene and iridium and bending energy of the wrinkle. The presented study provides new insights into wrinkling of epitaxial graphene and can be exploited to further expedite its application.