Combined helium-atom-scattering and molecular-dynamics study of aluminum surface-phonon anharmonicities and linewidths

The temperature dependence of the Rayleigh surface-phonon energies and widths have been measured with high-resolution helium-atom scattering for the {Γ}{}-X{} direction and the {Γ}{}-M{} directions on Al(100) and Al(111), respectively. Over a wide range of wave vectors the measured shifts and widths are in good agreement with a molecular-dynamics simulation based on a simple nearest-neighbor Morse potential. Contrary to previous reports of an enhanced shift in frequency with temperature on Cu(110), these results indicate that this measure of anharmonicity on close-packed aluminum surfaces is about 30% greater than that of the bulk.