A microscopic model is presented to describe the probability of charge transfer for the desorption of ions from surfaces. The model explicitly incorporates the electronic structure of the system by including orbitals for each atom that interact via a time dependent hopping integral. This prescription also takes into account the motion of the nuclei which may occur in conjunction with energetic ion bombardment. As a consequence, the model is three-dimensional in nature and incorporates the electronic structure of the system at the time of desorption of the atom. The initial motions studied are ones where the adsorbate atom desorbs perpendicularly to the surface with a given velocity, v. For this motion and velocities less than ∼ 106 cm/s we find that the ionization probability R+ is proportional to vn with n between 2 and 4. For higher velocities R+ can depend more exponentially on (-const./v). The effect of the various parameters in the model including the atomic orbital energies, the coupling strength and effective range, and the assumed motion of the desorbing atom are examined in detail. The relevance of this model to a fundamental understanding of SIMS experiments is also stressed.
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Surfaces and Interfaces
- Surfaces, Coatings and Films
- Materials Chemistry