The Role of Gold Adatoms and Stereochemistry in Self-Assembly of Methylthiolate on Au(111)

摘要

On the basis of high resolution STM images and DFT modeling, we have resolved low- and high-coverage structures of methylthiolate (CH_3S) self-assembled on the Au(111) surface. The key new finding is that the building block of all these structures has the same stoichiometry of two thiolate species joined by a gold adatom. The self-arrangement of the methylthiolate-adatom complexes on the surface depends critically on their stereochemical properties. Variations of the latter can produce local ordering of adatom complexes with either (3 × 4) or (3 × 4 3~(1/3)) periodicity. A possible structural connection between the (3 × 4 3~(1/3)) structure and commonly observed (3~(1/3) × 3~(1/3))R30° phase in methylthiolate self-assembled monolayers is developed by taking into account the reduction in the long-range order and stereochemical isomerization at high coverage. We also suggest how thp observed self-arrangements of methylthiolate may be related to the c(4 × 2) phase of its longer homologues.