Formation of highly ordered organic monolayers by dative bonding: pyridine on ge(100).

The adsorption of pyridine onto the Ge(100) surface has been studied using both real-time scanning tunneling microscopy (STM) and ab initio pseudopotential density functional calculations. The results show that pyridine molecules adsorb on the electron-deficient down-Ge atoms of the Ge=Ge dimers via Ge-N dative bonding, with the pyridine ring tilted to the surface. The electron-rich up-Ge atoms remaining after adsorption of pyridine induce an asymmetric dimer row, which is mainly reconstructed to the c(4 x 2) structure. At pyridine coverage of 0.25 ML, the adsorbed pyridine molecules form a perfectly ordered monolayer. The entire Ge substrate underlying this organic monolayer rearranges into the c(4 x 2) structure.