High resolution helium atom scattering from an epitaxially grown one monolayer film of KCN on KBr(001)

Abstract High resolution helium atom diffraction and single phonon inelastic scattering experiments were performed on a single monolayer KCN film epitaxially grown onto a KBr(001) substrate. Although the cleaved surface of single crystal KCN appears disordered, the one monolayer film was stabilized by the substrate. The measurements from this film in the 〈100〉 direction gave dispersion curves with a Rayleigh mode, a dispersionless mode near 12 meV, a possible crossing mode, and a suggestion of a weak interface mode near 2 meV. The Debye temperature of the film was found to be 127 K, which was very close to that found for the cleaved single crystal KCN. A kink in the Debye-Waller factor near 150–160 K may be associated with a surface phase transition.