Depressions by stacking faults in nanorippled graphene on metals

• Main Authors: Förster, Georg Daniel, Artaud, Alexandre, Mazaleyrat, Estelle, Förster, Georg, Tonnoir, Charlène, Gilles, Bruno, David, Philippe, Guisset, Valérie, Magaud, Laurence, Calvo, Florent, Chapelier, Claude, Coraux, Johann
• Format: Journal Article
• Language: English
• Published: 11-02-2020
• Subjects: Physics - Materials Science
• DOI: 10.48550/arxiv.2002.04478

2D Materials, IOP Publishing, 2020, 7 (2), pp.025016 A broad variety of defects has been observed in two-dimensional materials.
Many of these defects can be created by top-down methods such as electron
irradiation or chemical etching, while a few of them are created along
bottom-up processes, in particular during the growth of the material, in which
case avoiding their formation can be challenging. This occurs e.g. with
dislocations, Stone-Wales defects, or atomic vacancies in graphene. Here we
address a defect that has been observed repeatedly since 2007 in epitaxial
graphene on metal surfaces like Ru(0001) and Re(0001), but whose nature has
remained elusive thus far. This defect has the appearance of a vacant hill in
the periodically nanorippled topography of graphene, which comes together with
a moir{\'e} pattern. Based on atomistic simulations and scanning tunneling
microscopy/spectroscopy measurements, we argue that such defects are
topological in nature and that their core is a stacking fault patch, either in
graphene, surrounded by loops of non-hexagonal carbon rings, or in the
underlying metal. We discuss the possible origin of these defects in relation
with recent reports of metastable polycyclic carbon molecules forming upon
graphene growth. Like other defects, the vacant hills may be considered as
deleterious in the perspective of producing high quality graphene. However,
provided they can be organized in graphene, they might allow novel optical,
spin, or electronic properties to be engineered.