X-ray initiated molecular photochemistry of Cl-containing adsorbates on a Si(1 0 0) surface using synchrotron radiation

Abstract

X-ray initiated molecular photochemistry for SiCl 4 and CCl 4 adsorbed on Si(1 0 0) at ∼90 K following Cl 2p core-level excitation is investigated by photon stimulated ion desorption and ion kinetic energy distribution measurements. The Cl 2 p → 8 a 1 ∗ excitation of solid SiCl 4 induces the significant enhancement (∼900%) of the Cl + yield, while the Cl 2 p → 7 a 1 ∗ excitation of condensed CCl 4 leads to a moderate enhancement (∼500%) of the Cl + yield. The enhancement of Cl + yield at the specific core-excited states is strongly correlated to the ion escaped energy. Upon X-ray exposure for CCl 4 adsorbed on Si(1 0 0) (20-L exposure), the Cl + yields at 7 a 1 ∗ resonances decrease and new structures at higher photon energies are observed. Cl + yields at these new resonances are significantly enhanced compared to those at other resonances. These changes are the results of desorption and surface reaction of the CCl 4–Si surface complex due to X-ray irradiation. We have demonstrated that state-specific enhancement of ion desorption can be successfully applied to characterize the reaction dynamics of adsorbates adsorbed on surfaces by X-ray irradiation.