Energy-extended photo-electron holography was used, for the first time, to image surface structures by exploiting intrinsic surface core-level shifts. The Ge(111)-c(2 x 8) 3d core level exhibited a surface component which was shifted by 0.8eV with respect to the bulk. Angle-resolved photo-emission from this so-called S2 component revealed intensity oscillations as a function of the photon energy. Inversion of the data which were collected at many emission angles yielded a 3-dimensional image of the nearby atoms. This showed conclusively that the S2 emission was due to adatoms which were bonded at T4 sites.

M.T.Sieger, J.M.Roesler, D.S.Lin, T.Miller, T.C.Chiang: Physical Review Letters, 1994, 73[23], 3117-20