Structure Determination of theSi3N4/Si(111)-(8×8)Surface: A Combined Study of Kikuchi Electron Holography, Scanning Tunneling Microscopy, andab initioCalculations

A comprehensive atomic model for the reconstructed surface of ${\mathrm{Si}}_3{\mathrm{N}}_4$ thin layer grown on Si(111) is presented. Kikuchi electron holography images clearly show the existence of adatoms on the ${\mathrm{Si}}_3{\mathrm{N}}_4\left(0001\right)/\mathrm{Si}\left(111\right)-(8\times 8)$ surface. Compared with the ab initio calculations, more than 30 symmetry-inequivalent atomic pairs in the outmost layers are successfully identified. Scanning tunneling microscopy (STM) images show diamond-shaped unit cells and nine adatoms in each cell. High-resolution STM images reveal extra features and are in good agreement with the partial charge density distribution obtained from total-energy calculations.