Raman Spectroscopy of Lattice-Matched Graphene on Strongly Interacting Metal Surfaces

Regardless of the
widely accepted opinion that there is no Raman
signal from single-layer graphene when it is strongly bonded to a
metal surface, we present Raman spectra of a graphene monolayer on
Ni(111) and Co(0001) substrates. The high binding energy of carbon
to these surfaces allows formation of lattice-matched (1 × 1)
structures where graphene is significantly stretched. This is reflected
in a record-breaking shift of the Raman G band by more than 100 cm–1 relative to the case of freestanding graphene. Using
electron diffraction and photoemission spectroscopy, we explore the
aforementioned systems together with polycrystalline graphene on Co
and analyze possible intercalation of oxygen at ambient conditions.
The results obtained are fully supported by Raman spectroscopy. Performing
a theoretical investigation of the phonon dispersions of freestanding
graphene and stretched graphene on the strongly interacting Co surface,
we explain the main features of the Raman spectra. Our results create
a reliable platform for application of Raman spectroscopy in diagnostics
of chemisorbed graphene and related materials.