ADSORPTION AND STRUCTURE OF CF4 ON CU(110)

Halogenated methane molecules, such as CF4-xClx(x = 0,...,3), offer th e possibility to systematically vary the dipole moment and the symmetr y of an adsorbate and to study the influence on the adlayer structure and dynamics. in a first step, the adsorption and structure of unpolar CF4 on the Cu(110) surface have been studied using helium atom scatte ring. From specular He-reflection the isosteric heat of adsorption of the CF4 monolayer and the lateral interaction between CF4 molecules is determined to 159 +/- 6 and 40 +/- 5 meV per molecule, respectively. In the submonolayer range a high-order commensurate (HOC) (n x 18) pha se (n approximate to 26) is observed, which converts into a (2 x 18) s tructure for coverages above one monolayer. The diffraction data seem to indicate that the internal arrangement of the molecules is quasi-he xagonal at low coverage but quasi-square in the (2 x 18) phase.