(A) real-time STM study of adsorption porcesses

Abstract

The adsorption structures of pyridine ($C_5H_5N$) on the Ge(100) surface at various coverages have been studied in detail by scanning tunneling spectroscopy (STM). Pyridine molecule adsorbs on the electron deficient buckled down-Ge atom of a Ge-Ge dimer. The other electron rich-Ge atom of the dimer maintains buckled-up state and then induces buckling of adjacent dimer row. Up to 0.25 ML, pyridine molecules adsorb on every other dimer and the substrate is reconstructed to the c(4×2) structure by asymmetric dimer rows. Above 0.25 ML, the c(4×2) structure is converted to p(2×2) by the adsorption of pyridine molecules on every dimer and imaged as brighter zigzag line. At 0.5 ML, all pyridine molecules adsorb on every dimer and substrate is reconstructed to the p(2×2) structure. However, some adsorbed pyridine molecules desorb due to the repulsive steric interaction between aromatic rings in the p(2×2) structure. Then, 0.25 ML adsorbed on every other dimer is most stable configuration.