Substrate- to Laterally-Driven Self-Assembly Steered by Cu Nanoclusters: The Case of FePcs on an Ultrathin Alumina Film

Abstract

We show that, for the formation of a metallorganic monolayer, it is possible to artificially divert from substrate- to laterally-driven self-assembly mechanisms by properly tailoring the corrugation of the potential energy surface of the growth template. By exploiting the capability of an ultrathin alumina film to host metallic nanoparticle seeds, we tune the symmetry of a iron phthalocyanine (FePc) two-dimensional crystal, thus showing that it is possible to switch from trans to lateral dominating interactions in the controlled growth of an organic/inorganic heterostack. Finally, by selecting the size of the metallic clusters, we can also control the FePc-metal interaction strength.

Tetrapyrroles at near-ambient pressure: porphyrins and phthalocyanines beyond the pressure gap

“…These elements are of paramount importance, since they can be exploited for tailoring purposes in biomimetic systems (figure 9) [10,45]. At surfaces, the tuning role of axial ligands is played by the surface trans-effect [10], where hybridization of the LUMO with the substrate states takes place [46,47] while the surrounding metalorganic coordination environment (lateral interactions among tectons) governs the selfassembly [9,26,30,48,49], the charge delocalization [37], and the chemical/thermal stability [50]. In order to draw a characterizing picture of natural systems in the view of steering the surface synthetic counterpart, we can make further representing examples [4], referring to heme-based enzymes all containing a single Fe atom.…”

“…This is extremely interesting in view of potential applicative ideas in which charge generation by impinging light (light harvesting, exciton formation) and charge separation (photovoltaics) are strategic properties. Lateral interactions can yield intersystem crossing [50]; (e) best DFT structures for the FePc molecule adsorbed at the dot sites of the alumina film pre-seeded with 6-and 9-atom Cu clusters [50]; (f) cartoon of the FePc molecule adsorbed at the Ir(111) surface [105]; (g) STM images and structural models of the FePc monolayer self-assembled on a single graphene sheet grown on the Ir(111) termination [37]; (h) SFG CO uptake curves measured in situ at room temperature for the systems shown in (f) and (g), shown together with the best fit (dashed lines) and the ab initio predicted theoretical curve (red line) [37,105]. Adapted with permission from [37,50,105].…”

“…A first experimental spectroscopic evidence obtained in situ for the adsorption at room temperature and NAP conditions of a small ligand at the solid-gas interface is represented by the carbonylation, at equilibrium with the carbon monoxide gas phase, of iron phthalocyanines [37,50,105]. For FePcs adsorbed on the (111) termination of an iridium single crystal [105], the adsorption process occurs at CO pressures above the mbar yield.…”

“…The same internal C-O stretching energy is observed upon adsorption of a single CO ligand on the same FePc molecule supported on an ultra-thin oxide film ( figure 20(a)). The formation of the FePc metalorganic monolayer on the ultrathin alumina film grown on the Ni 3 Al(111) termination can be steered, since it is possible to artificially divert from substrate-to laterally-driven self-assembly mechanisms by properly tailoring the corrugation of the potential energy surface of the growth template [50]. By exploiting the capability of the Al 2 O 3 /Ni 3 Al(111) supercell dot sites to host metallic nanoparticle seeds, the symmetry of the FePc 2D crystal is tuned, thus showing that it is possible to switch from trans to lateral dominating interactions in the controlled growth of the organic/inorganic heterostack (figures 20(b), (d)).…”

“…Monocarbonylation of FePcs at NAP: (a) SFG spectra of the C-O internal stretching region collected at room temperature in situ for FePc monolayers self-assembled on (from top to bottom) the ultrathin alumina film grown on Ni 3 Al(111)[50], the Cuseeded alumina film[50], the bare Ir(111) termination[105], and a single graphene sheet on Ir(111) [37]; (b) STM image of the FePc/ Al 2 O 3 /Ni 3 Al(111) superstructure [50]; (c) DFT structure of the FePc at the dot sites of the alumina ultrathin film, showing that no binding occurs [50]; (d) STM image of the FePc/Cu 10 /Al 2 O 3 /Ni 3 Al(111) superstructure…”