Structure determination of the Si3N4/Si(111)-(8 x 8) surface:: A combined study of Kikuchi electron holography, scanning tunneling microscopy, and ab initio calculations

A comprehensive atomic model for the reconstructed surface of Si3N4 thin layer grown on Si(lll) is presented. Kikuchi electron holography images clearly show the existence of adatoms on the Si3N4(0001)/Si(111)-(8 x 8) surface. Compared with the nb 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.