First-Principles Investigation of a Rippled Graphene Phase on Ir(001): The Close Link between Periodicity, Stability, and Binding

The formation of ordered one-dimensional
graphene ripples of nanometer
periodicity with exceptionally large buckling has recently been observed
on Ir(001). In this phase, chemisorbed lines of graphene, only a few
atoms wide, strongly bind to the substrate along Ir[010], while the
whole graphene film markedly buckles between these periodic lines,
forming regular ripples along Ir[100]. We have performed a dispersion-corrected
density functional theory study to investigate the microscopic mechanisms
responsible for the formation of this new phase. Based on the calculated
trends of the chemisorption and rippling energies, the occurrence
of a buckled chemisorbed phase with a specific nanoscale periodicity
is explained. We have also examined how the increased curvature of
graphene affects its electronic structure and chemisorption energy
on Ir, finding a new feature in the conduction density-of-states spectrum
close to the Fermi energy. The corresponding states are identified
as the ones largely responsible for the strong local chemisorption
of graphene.