Electron dynamics image-potential states

So far, we have discussed the electron dynamics mainly for image-potential states. Owing to their relatively long lifetimes, they serve as a model system to study electron scattering processes at surfaces by time-resolved 2-PPE. Studies on other systems are relatively scarce because the overlap of adsorbate or surface states with bulk bands is usually relatively large and the lifetime is below the attainable time resolution. Figure 6.15 shows time-resolved data for the lowest unoccupied molecular orbital (LUMO) of C Fg on Cu(lll) [89[. The population dynamics is... 

First of all, the existence of the surface establishes a certain correlation between different electronic states, particularly between incident and reflected electrons. In addition there are electron density variations both within the surface and along the surface normal. Since the screening radius increases with decreasing electron density, it is obviously unrealistic to third of a spherical potential hole accompanying its electron in the immediate surface region, where the electron density drops very rapidly to zero. At the very lowest densities, in particular, the potential must somehow go over in continuous fashion into the classical image potential applying far away from the metal surface. Finally, from the dynamic nature of these interactions it follows that the problem must be dealt with self-consistently each electron contributes to the holes of all the other electrons in a manner dependent on the detailed features of its own potential hole. 

---