A helium atom scattering study of the growth and dynamics of CH4 and C2H6 on Cu(001)

Abstract

The growth, structure and dynamics of methane and ethane monolayers on Cu(001) have been studied using high resolution helium atom scattering. Specular intensity measurements of the growth behavior reveal an island growth mode for methane and ethane, indicative of an attractive interatomic interaction. Diffraction measurements show that the methane monolayer forms a hexagonal structure, incommensurate in one direction, with a lattice constant of 4.18 Å, while ethane forms a structure with an interatomic distance of 5.10 Å. The frustrated translational vibrations perpendicular to the surface (S mode) of methane and ethane have been measured with inelastic helium scattering and have frequencies of 6.5 meV and 6.8 meV, respectively. In addition, the desorption energies were determined to be 165 meV for methane and 260 meV for ethane, in both cases independent of coverage. These results are compared with recent measurements made for C2H4 and larger alkanes adsorbed on Cu(001).