  The phonon dispersion of graphene on Ir(111) has been determined by means of
angle-resolved inelastic electron scattering and density functional
calculations. Kohn anomalies of the highest optical-phonon branches are
observed at the $\Gamma$ and K point of the surface Brillouin zone. At K the
Kohn anomaly is weaker than observed from pristine graphene and graphite. This
observation is rationalized in terms of a decrease of the electron-phonon
coupling due to screening of graphene electron correlations by the metal
substrate.
