Formation of one-dimensional molecular chains on a solid surface: Pyrazine/Si(001)

We have studied the chemisorption of pyrazine on Si(001)-2x1 at room temperature using scanning tunneling microscopy (STM), photoelectron diffraction (PED), and the density functional theory (DFT). In STM, protrusions ascribed to the pyrazine adsorbate were observed between the Si dimer rows and arrange themselves one-dimensionally (1D) along the dimer bond direction. Multiple scattering analysis of N 1s and C 1s PED patterns showed that a double-dimer bridging (DDB) configuration, in which pyrazine molecule forms bridging between the dimer rows with two Si-N bonds, is formed. DFT cluster calculations showed, however, that N-end-on configuration is more stable than the DDB configuration for a single molecule adsorption. The stability for the DDB configuration as a 1D chain is discussed on the basis of "polymerization" of the adsorbates through dangling bonds at the distal points of the 1D chain.