The dispersion curves of the surface phonon of the clean TaC(1 0 0) have been experimentally determined over the entire Brillouin zone of the Λ-M symmetry axis. This includes the first experimental observation of the Lucas mode, one of the microscopic optical surface phonon studied by using high resolution electron energy loss spectroscopy. From both the selection rule of the scattering and the vibrational energy (frequency), each mode has been assigned. Those dispersion curves strongly suggest the enhancement of the force constant of the surface atoms.
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