A HELIUM ATOM SCATTERING STUDY OF THE GROWTH AND DYNAMICS OF CH4 AND C2H6 ON CU(001)

The growth, structure and dynamics of methane and ethane monolayers on Cu(001) have been studied using high resolution helium atom scatterin g. Specular intensity measurements of the growth behavior reveal an is land growth mode for methane and ethane, indicative of an attractive i nteratomic interaction. Diffraction measurements show that the methane monolayer forms a hexagonal structure, incommensurate in one directio n, with a lattice constant of 4.18 Angstrom, while ethane forms a stru cture with an interatomic distance of 5.10 Angstrom. The frustrated tr anslational vibrations perpendicular to the surface (S mode) of methan e and ethane have been measured with inelastic helium scattering and h ave 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 sire compared with recent measurements made for C2H4 and larger alkane s adsorbed on Cu(001). (C) 1997 American Institute of Physics.