Van Hove anomaly in the phonon dispersion of monolayer Ar/Pt(111)

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Abstract
Inelastic He scattering has been used to study the surface-phonon dispersion and phonon linewidths of the Ar monolayer physisorbed on Pt(111). As in the previously studied Kr/Pt(111) system a strong vibrational coupling between the adlayer and the Pt substrate is found. In addition, a pronounced enhancement of the linewidth broadening in a narrow region in reciprocal space has been observed, presenting the first experimental evidence of adsorbate coupling to the longitudinal bulk band edge and the longitudinal surface resonance of the Pt substrate due to the Van Hove singularity of the projected phonon density of states.