TRANSMISSION OF LOW-ENERGY (LESS-THAN-10EV) OXYGEN IONS THROUGH ULTRATHIN XENON FILMS

In studies of desorption induced by electronic transitions (DIET) such as electron or photon stimulated desorption, it is important to know whether the desorbing species originate solely from the outermost surf ace layer, or also from layers beneath the surface. In order to gain b etter understanding of the charge transfer, elastic scattering, and ot her inelastic processes involved in this issue, we are currently perfo rming a series of experimental studies of the transmission of low ener gy ions (approximately 7 eV) through ultrathin films (submonolayer to multilayer) of condensed gases. Here we report on the first quantitati ve measurements of the yield, angle, and energy of oxygen ions after t ransmission through ultrathin films of xenon. In our novel approach, a focused 300 eV electron beam bombards a target at 25 K consisting of an oxidized tungsten (100) crystal with adsorbed overlayers of xenon. In the absence of the xenon, O+ ions desorb in a sharp beam normal to the surface, as measured in a velocity and angle resolving ESDIAD appa ratus (electron stimulated desorption ion angular distribution). When Xe layers are present, some oxygen ions penetrate several monolayers o f xenon without significant change in energy and angle while others se em to be scattered by large-angle elastic scattering or to be attenuat ed from the O+ beam. The work presented is the first experimental stud y of the depth of origin of desorbing ions in DIET processes.