Holography ofGe(111)−c(2×8)by Surface Core-Level Photoemission

Energy-extended photoelectron holography has been applied for the first time to image surface structure using intrinsic surface core-level shifts. The $\mathrm{Ge}\mathrm{}\left(111\right)\mathrm{}-c(2\mathrm{}\times 8)$ $3d$ core level exhibits a surface component shifted by 0.8 eV relative to the bulk. Angle-resolved photoemission from this so-called $S2\mathrm{}$ component shows intensity oscillations as a function of photon energy. Inversion of the data collected at many emission angles yields a three-dimensional image of the nearby atoms, showing conclusively that the $S2\mathrm{}$ emission is due to adatoms bonded in $T_4$ sites.