Origin of the photoemission final-state effects in Bi2Sr2CaCu2O8 by   very-low-energy electron diffraction
  Very-low-energy electron diffraction with a support of full-potential band calculations is used to achieve the energy positions, K// dispersions, lifetimes and Fourier compositions of the photoemission final states in Bi2Sr2CaCu2O8 at low excitation energies. Highly structured final states explain the dramatic matrix element effects in photoemission. Intense c(2x2) diffraction reveals a significant extrinsic contribution to the shadow Fermi surface. The final-state diffraction effects can be utilized to tune the photoemission experiment on specific valence states or Fermi surface replicas. 
V. N. Strocov, R. Claessen, P. Blaha