In situ STM study of the adsorption of halogen derivatives of uracil on Au(111)

We present in this study scanning tunneling microscope images of 5-chloride uracil (5C1U) and 5-bromide uracil (SBrU) adsorbed on Au(111) in sulfuric acid solution under potential control. At a given potential, the molecular structure was studied and we have found that the change of the halogen substituents leads to dramatic changes in the molecular packing structure of the films. Both molecules form highly ordered films, but while SBrU assumes a lying, hydrogen bond stabilized, positioning, 5C1U assumes an upstanding positioning. (C) 2001 Elsevier Science B.V. All rights reserved.