Structure of pyrrole on Ge(100)

The adsorption structures of pyrrole on a Ge(100) surface at low coverage have been investigated using ab initio density-functional theory (DFT) calculations. The most stable configuration is that the adsorbed pyrrole molecule with H dissociated forms a bridge between two down-Ge atoms of neighboring dimer rows through N-Ge bonding and C-Ge interaction. The corresponding simulated images explain well the flower-like features with a dark side observed in the experiment. Also, C-H dissociative structures are found to contribute as a minority to the features. A similar configuration to the most stable one, but with a dissociated H out of the region of interest, can explain the flower-like feature without a dark side. Finally, a C- and Nend-on configuration may be a possible candidate for bright protrusions in the STM images.