Tunneling effect in electron-stimulated desorption of Li+ from LiF/Si(1 0 0)

It is shown that the kinetic-energy distributions of 6Li+ and 7Li+ ions desorbed during electron irradiation from the system LiF/Si(1 0 0) exhibit fine structures. Their character suggests that they correspond to Li+ ions emitted according to the wave packet squeezing desorption model. This observation enables us to determine the final repulsion potential active in the Li+ desorption process. The oscillatory-structure onsets show that these potentials have the potential-energy barrier of a height of about 1.4 eV for the virgin LiF samples and of about 2.8 eV for LiF preirradiated with a dose of 50 μC/mm2. For preirradiated samples the oscillatory structures are less pronounced, but for such samples relatively strong and very narrow peaks located at 2.12 eV for 6Li+ and at 2.03 eV for 7Li+, respectively, can be detected. These peaks are interpreted as ions trapped in the temporary bound-states located above the vacuum level of the sample. Due to a relatively high transmission coefficient the ions can tunnel trough the temporary existing potential barrier. The lifetime of the potential barrier estimated from the peak energy width and the Heisenberg uncertainty principle is about 7 fs. Some other aspects of the dynamic lattice distortion are also discussed.