Electron stimulated desorption of cations from SiCl4 multilayers adsorbed on Si(1Â 1Â 1)

We have examined the low-energy (5-50 eV) electron-stimulated desorption (ESD) of SiCl4 multilayers adsorbed on Si(1 1 1) surfaces. A threshold energy of 17 eV was found for Cl+, the major ESD product. The formation of SiCl3+ also required 17 eV. This low-energy threshold was assigned to direct ionization of the 7t2 and 7a1 bonding orbitals and possible unimolecular decay of the resulting highly excited parent ion. Resonant structure between 22 and 32 eV was also observed in the Cl+ channel. This was associated with resonant transitions from the 6t2, 6a1 to the antibonding 8a1 or 9t2 levels followed by Auger decay. The resultant 2-hole, 1-electron final states Coulomb explode yielding primarily Cl+ desorption. A threshold near 25 eV was observed for all other ESD products (i.e. SiCl+, SiCl2+ and Si+). We correlate this threshold with direct ionization of the 6t2 and 6a1 levels which then decay to form several 2-hole states which also Coulomb explode.