Coverage dependent structures of oligopyridine adlayers on (111) oriented Ag films.

The coverage dependent formation of ordered structures in vapor deposited 2,4'-bis(terpyridine)derivatives (2,4'-BTP) on (111) oriented Ag films was investigated by STM. Following a two-dimensional (2D) disordered gas phase at lowest coverages, a sequence of at least three ordered structures is observed with increasing coverage. These include a 'parallel chain structure' (PCS), a 'quasi-quadratic network' (QQN) structure, and a 'packed windmill structure' (PWS), with ideal coverages of 0.37, 0.4, and 0.44 molecules nm(-2). At intermediate coverages between 0.37 and 0.44 molecules nm(-2), these structures coexist in larger islands. The energetics of the different phases, whose structures are mainly determined by attractive C-H[dot dot dot]N bridges, are discussed in a picture including C-H[dot dot dot]N and C-H[dot dot dot]H-C interactions and lateral variations in the substrate-adsorbate interactions.