Adsorption and Desorption Studies of CF3Cl on Si(111)(7x7) Surface

L.-C. Chou；C.-R. Wen；J. Chen

Chinese Journal of Physics

38卷5期（2000 / 10 / 01）

987 - 998

英文

We have investigated the interaction of CF3Cl with the Si(111)(7 × 7) surface at 30 K using ultraviolet photoelectron spectroscopy (UPS), x-ray photoelectron spectroscopy (XPS) and electron-stimulated desorption (ESD). Examination of the valence-level UPS spectra and the Si(2p), F(1s), C(1s) and Cl(2p) core-level XPS spectra, shows that CF3Cl is adsorbed molecularly on the Si(111)(7 × 7) surface. The peak at -6.14 eV in the UPS spectrum was assigned to the ionization of 5e orbital, the peak at -10.9 eV was attributed to the ionization of the 3e orbital, and the unresolved structure in the energy range -7.5 to -10.5 eV was ascribable to the ionization of the 5a1, 1a2, and 4e orbitals. The broadening of the line widths of the photoemission peaks emitted from CF3Cl/Si(111) is explained by Heisenberg's uncertainty principle. The work function change (∆ø) with increasing coverage of adsorbed molecules was obtained and interpreted as due to the orientation of the adsorbed molecule which has small permanent dipole moment and polarizability. The orbital energy shifts of the 5e and 3e orbitals of CF3Cl, as the molecule changes from the gas-phase state to an adsorbed state, are found to be -1.07 and -0.94 eV, respectively. The ESD mass spectrum for CF3Cl/Si(111)(7 × 7) of dose = 1.3 × 10^15 molecules/cm^2 in the range 10-71 amu at an incident electron energy of 250 eV was measured; it shows that F^+ , CF^+ and CF3^+ are the major desorbing ions, C^+ , CF2^+ , CCl^+ , CCl^++ and CFCl^+ are the minor desorbing ions. The desorption of these positive ions are assigned to various dissociation processes via ionizing the valence orbital.