Surface optical phonons in LiF(001) observed by inelastic helium scattering

Abstract
The vibrational spectrum of the LiF(001) surface along the direction is studied by Hebeam inelastic scattering with time-of-flight detection. The low-energy region of the spectrum shows the Rayleigh mode in good agreement with previous measurements. In the high-energy region both bulk and surface optical branches are detected. In particular, the Lucas mode S4 and the surface branch S2 are observed to have dispersions slightly different from those predicted by theoretical calculations.