Surface-Resonance Fine Structure in Low-Energy Electron Diffraction

We demonstrate that the reflection of electrons from the image potential barrier outside the surface of a metal crystal induces a surface-resonance fine structure in the low-energy electron diffraction intensity profiles just below the energy of emergence of a new beam. The resonance levels are arranged in a Rydberg series with the constant $\frac{1}{16}$ Ry. The beam emergence from aluminum (001) near 18 eV is calculated and comparison with measured resonances is sought.