THE SOFT-X-RAY PHOTOCHEMISTRY OF PHYSISORBED SIF4 .1. REACTIONS OF THE MOLECULAR-SPECIES THROUGH DESORPTION AND DISSOCIATION

We present evidence that demonstrates photolysis of SiF4 adsorbed on G e(100) at 30 K. Silicon 2p soft x-ray photoemission spectroscopy (PES) indicates that upon irradiation, the molecularly adsorbed SiF4 dissoc iates into SiFn species (where n = 0,1,2,3) and desorbs as molecular S iF4. Also, the Si 2p PES from undissociated molecules exhibits a numbe r of distinct kinetic-energy shifts. These are attributed to anisotrop ic adsorption in which different molecular sites have different appare nt Si 2p binding energies. A structure of the adsorbate layer is propo sed to account for the varying core hole screening. Examination of the gas phase during irradiation confirms molecular desorption and shows the system to have a significant neutral molecular desorption yield. C hanges in the valence-level photoemission structure and signal intensi ty are consistent with the observed fragmentation and desorption, both of which lead to disappearance of the molecularly adsorbed species. ( C) 1995 American Institute of Physics.