Chiral adsorption structures of styrene on Ge(001): A first-principles study

We investigated the chiral adsorption structures of styrene on the Ge(001) surface by first-principles density functional calculations within the generalized gradient approximation. Our calculated energy profile for the reaction pathways shows that styrene adsorbs not only on top of a single dimer but also across the ends of two adjacent dimers in the same dimer row. In the latter adsorption configuration (termed the "end-bridge" configuration), we predict the existence of two different structures where two unsaturated Ge atoms within the two adjacent dimers are differently displaced up and down or down and up. Additional styrene adsorption on these two different end-bridge structures proceeds to formation of the cis- and trans-paired end-bridge (PEB) structures. The relative stability of the two different end-bridge structures provides an explanation for a recent scanning tunneling microscopy observation that the populations of the cis-PEB and trans-PEB structures are different from each other.