| AVS 62nd International Symposium & Exhibition | |
| Surface Science | Wednesday Sessions |
| Session SS+AS-WeA |
| Session: | Surface Dynamics, Non-Adiabaticity, and Single Molecule Phenomena |
| Presenter: | Leszek Markowski, University of Wroclaw, Poland |
| Correspondent: | Click to Email |
It is well known that irradiation of the solid with electrons or photons can cause its decomposition. This process, or, more adequately processes, is very fast (typically finalized within a time shorter than 10-14 s) and is realized mainly by desorption of atoms or ions.Unfortunately, until now, existing models still do not give a proper value of the desorption yield and, simultaneously, a correct kinetic-energy distribution of emitted particles, as compared to the experimental observations.
In this talk a classical, quasi-quantum and quantum description of the positive ion desorption from ionic crystal surface, in which three potentials are involved, will be discussed and compared. It will be shown that the quantum description allows to explain some effects observed experimentally, such as a periodicity of small oscillations on the kinetic energy distribution (KED) curves (predicted by Wave-Packet Squeezing model) and emission through a temporarily existing potential barrier from the temporary bounded states located above the vacuum level. Moreover, analysis method of the ion KED oscillation and the fitting procedure which allows to determined a final effective desorption potential will be presented.
For two examples discussed, Li+ desorption from LiF and Na+ desorption from NaCl, desorption from two desorption sites can be distinguished – dominating ion desorption channel from adatom sites (more than 95%) and marginal one from the sites in the first surface layer. For the second desorption channel neighboring negative ions, due to surface relaxation lying in the first surface layer slightly above positive one, can act as a two-dimensional array of rosette-like apertures. In consequence, positive ions after passing through them may form diffraction pattern.
Finally, it appears that when desorption process is described using three potentials both the ions desorption efficiency and their kinetic-energy distribution are in agreement with the experimental results.