Nj. Sack et al., TRANSMISSION OF LOW-ENERGY (LESS-THAN-10EV) OXYGEN IONS THROUGH ULTRATHIN XENON FILMS, Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms, 90(1-4), 1994, pp. 451-455
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.