Electronic edge |

The cluster represents the region of a solid close to the
emitter. The solid is assumed to extend towards negative
values of *z*. The electronic edge is taken as the
value of *z* below which the photoelectron can suffer
inelastic losses. Therefore, the electron inelastic mean
free path will apply while the photoelectron is moving
inside the solid, that is, for *z* below the electronic edge.
Besides, the photoelectron suffers refraction when it crosses
the electronic edge, and this is accounted for by a transmission
factor and a change of angles of emission as described by a
step potential of height V_{0} (see inner potential).