Growth and ordering of Ni(II) diphenylporphyrin monolayers on Ag(111) and Ag/Si(111) studied by STM and LEED

Abstract

The room temperature self-assembly and ordering of (5,15-diphenylporphyrinato)nickel(II) (NiDPP) on the Ag(111) and Ag/Si(111)-(√3 × √3)R30º surfaces have been investigated using scanning tunnelling microscopy and low-energy electron diffraction. The self-assembled structures and lattice parameters of the NiDPP monolayer are shown to be extremely dependent on the reactivity of the substrate, and probable molecular binding sites are proposed. The NiDPP overlayer on Ag(111) grows from the substrate step edges, which results in a single-domain structure. This close-packed structure has an oblique unit cell and consists of molecular rows. The molecules in adjacent rows are rotated by approximately 17° with respect to each other. In turn, the NiDPP molecules form three equivalent domains on the Ag/Si(111)-(√3 × √3)R30º surface, which follow the three-fold symmetry of the substrate. The molecules adopt one of three equivalent orientations on the surface, acting as nucleation sites for these domains, due to the stronger molecule-substrate interaction compared to the case of the Ag(111). The results are explained in terms of the substrate reactivity and the lattice mismatch between the substrate and the molecular overlayer.

Zinc(II) Tetraphenylporphyrin Adsorption on Au(111): An Interplay Between Molecular Self-Assembly and Surface Stress

“…Tetraphenylporphyrin adsorption at near monolayer coverage on noble metal (111) surfaces typically leads to a nearly square molecular lattice in which the porphyrin plane lies parallel to the surface, accompanied in some cases by molecular distortion. ,,,,− ,− On these surfaces, the TPP molecules form a compact self-assembled structure. As a result, the molecular coordination sites, as well as any possible rearrangement of the substrate surface atoms, must be investigated either by indirect experimental means or by energy minimization using ab initio theoretical methods. ,,− Results from such approaches suggest that free-base TPPs would adsorb preferentially centered on hollow sites, while MTPPs would prefer top sites, offering a stabilizing hybridization with the center metal d-levels. However, for these systems, owing to the molecular overlayer, the direct experimental relation between local order as described by theory and long-range order with respect to the surface structure cannot be obtained using scanning probe techniques.…”