Up to the late 1980's the surface structure was mainly derived from inspection of low energy electron diffraction (LEED) patterns, which gave access to the structure of the surface unit cell and to the defect density. Differences in the substrate and film lattices resulted in the emergence of additional diffraction spots, in addition to the substrate related reflections . Furthermore, the defect density in the deposit films, including also steps and island formation, was derived from spot splitting and the width of the additional diffraction spots . Similar information was obtained also from Xray scattering . A more local picture, up to the quantitative determination of specific atomic structures, was possible with the advent and introduction of scanning tunneling microscopy. High resolution imaging, up to atomic resolution and even with chemical contrast between different metals , allowed the identification and quantification of characteristic structural elements such as misfit dislocations , and even to quantify the two-dimensional distribution of surface atoms in bimetallic surface layers . Information on the nature and abundance of different adsorption sites was also obtained by spectroscopic titration of different adsorption sites using suitable adsorbates such as CO .