THE SOFT-X-RAY PHOTOCHEMISTRY OF PHYSISORBED SIF4 .2. MECHANISMS AND KINETICS

We present an analysis of the extensive photolysis of an adsorbate res ulting from adsorbate core-level excitation. The system studied was Si F4 adsorbed on Ge(100) at 30 K. Photolysis fragments and molecular spe cies (identified with Si 2p soft x-ray photoemission spectroscopy) wer e measured as a function of monochromatic (140-eV) photon exposure and adsorbate coverage. The photolysis cross sections for 55-140-eV photo ns were determined and the neutral photon-stimulated desorption cross section for a selected SiF4 excitation is also presented. In the Si 2p absorption region, it was found that the photolysis cross section was one to three times the preedge value and comparable in magnitude to t hat of gas phase photoabsorption, while the total yield increased at m ost by a factor of 1.4. Both of these observations indicate that direc t core excitation of the adsorbate is a major path by which photolysis occurs as opposed to an indirect, substrate-driven one. (C) 1995 Amer ican Institute of Physics.