Fine structure in elastic-electron-yield spectra at transition-metal core energies

We present yield spectra of electrons elastically backscattered from surfaces of NiO, ${\mathrm{Cr}}_2$ ${\mathrm{O}}_3$, and Cu. The chromium- and nickel-oxide surfaces show fine structure above the $2p$ core excitation energies of the transition metals. The fine structure extends above the core threshold for at least 100 eV and is periodic in the free momentum of an excited $2p$ core electron at energies well above the bottom of the conduction band. We interpret the structure in terms of a model based on final-state interference of the excited electron. Accurate recovery of nearest-neighbor atomic distances may require consideration of multiple scattering.