Binding and ordering of large organic molecules on an anisotropic metal surface:: PVBA on Pd(110)

The adsorption and ordering characteristics of 4-trans-2-(pyrid-4-yl-vinyl) benzoic acid (PVBA) on a Pd(110) surface were investigated by variable temperature scanning tunneling microscopy, PVBA is a rigid organic molecule (m = 225 amu) designed for nonlinear optics, The molecules adsorb flat on the surface and bind diagonally to three neighbouring Pd-rows, which configuration is maintained at all submonolayer coverages, With the completion of the first monolayer a parquet pattern evolves, resulting from the fixed bonding geometry and space limitations. Monte Carlo simulations of the film growth confirm that the monolayer ordering is stochastic in nature, even if an extrinsic precursor mechanism is operative in the adsorption, The lateral interactions between adsorbed molecules and Pd steps or adatoms at the surface are weak. (C) 1999 Elsevier Science B.V. All rights reserved.