Quantitative determination of adsorbate-adsorbate interactions

A new concept called configuration distribution analysis is introduced to e xtract quantitative information on adsorbate-adsorbate interactions from hi gh-resolution scanning tunneling microscopy data. From atom-resolved nitrog en island configurations on an Fe(100) surface we show that the propensity to form small, compact c(2 X 2) nitrogen islands is due to a nearest neighb or repulsion and next-nearest neighbor attraction. We demonstrate the impor tance of including many-body terms and elastic interactions to account for the detailed description of the island distribution.