Quantitative Determination of Adsorbate-Adsorbate Interactions

A new concept called configuration distribution analysis is introduced to extract quantitative information on adsorbate-adsorbate interactions from high-resolution scanning tunneling microscopy data. From atom-resolved nitrogen island configurations on an Fe(100) surface we show that the propensity to form small, compact $c(2\times 2)$ nitrogen islands is due to a nearest neighbor repulsion and next-nearest neighbor attraction. We demonstrate the importance of including many-body terms and elastic interactions to account for the detailed description of the island distribution.