Adsorption of pyrimidine molecules on Pd(110) observed by scanning tunneling microscopy

Adsorbed states of pyrimidine molecules on Pd(110) have been studied by a scanning tunneling microscope (STM). The pyrimidine molecules are preferentially adsorbed on terraces, not at steps. The isolated pyrimidine molecule shows a 0.6 nm × 0.6 nm rectangular shape with two parts of elongated protrusions. Two adsorption sites are observed: on-top site of the Pd[10] row and the midway between two [10] rows. Pyrimidine molecules show a strong tendency to form dimers even at a low coverage (0.01 ML), indicating that there is an attractive interaction between two adsorbed molecules.