Phonon dispersion of graphite by inelastic x-ray scattering

We present the full in-plane phonon dispersion of graphite obtained from inelastic x-ray scattering, including the optical and acoustic branches, as well as the midfrequency range between the K and M points in the Brillouin zone, where the experimental data have been unavailable so far. The existence of a Kohn anomaly at the K point is further supported. We fit a fifth-nearest neighbor force-constant model to the experimental data, making improved force-constant calculations of the phonon dispersion in both graphite and carbon nanotubes available.