Coverage-Dependent Structures of Cobalt−Phthalocyanine Molecules Adsorbed on Cu(001) Surface

Abstract

The morphologies, self-assembly structures, and stability of cobalt-phthalocyanines (CoPc) molecules adsorbed on Cu(001) with coverage ranging from 0.2 monolayer (ML) to 1.6 ML are investigated by ultrahigh-vacuum low-temperature scanning tunneling microscopy (UHV LT-STM) at liquid nitrogen temperature. Upon increasing the deposition of CoPc molecules various structures, such as isolated adsorption, quasi-hexagonal structure, square root(29) x square root(29) structure, are well characterized by the corresponding high-resolution STM images. The CoPc-CoPc intermolecular interaction and CoPc-substrate interfacial interaction dominate the structural evolutions. For the coverage higher than 1 ML, CoPc molecules preferentially locate on top of the molecules underneath and organize into square root(58) x square root(58) structure. As more and more CoPc molecules adsorb on the first layer, in some square root(58) x square root(58) regions molecular insertion leads to the formation of the square root(29) x square root(29) domain to effectively decrease the energy of the whole system.

Surface chemistry of porphyrins and phthalocyanines

“…(Compare the similar results for CuPc mentioned in this section above.) On Cu(1 1 1) [261,262], the Co center preferentially occupied bridge sites [240,262] (contrasting the findings for Cu (1 0 0) [260]) with two lobes of the ligand oriented along the closepacked [11̄0] direction and the other two lobes perpendicular to it. The latter interact more strongly with the substrate: they are bent towards the surface, resulting in the two-fold symmetry seen in STM images [240].…”

“…Only at full monolayer coverage, the molecules arranged in a (√29 Â √29)R21.81 superstructure with a square unit cell. In the second layer, CoPc was found to occupy positions exactly above the molecules in the first layer [260]. The four-fold molecular symmetry of CoPc (and FePc, CuPc) was maintained on Cu(1 0 0), while a symmetry perturbation was found on Cu(1 1 1) [239].…”

“…On Cu(1 0 0), CoPc was found to adsorb with the Co center on an on-top site, while the benzene rings were located above fourfold hollow sites [260]. The adsorbate structure was strongly coverage dependent on this surface: At low coverages, the molecules were isolated, while upon increasing the coverage to 0.83 ML, a quasi-hexagonal arrangement was observed, in which the Co centers still occupied on-top sites.…”

Structural study of monolayer cobalt phthalocyanine adsorbed on graphite

“…The interplay of single molecules on a substrate and their self-assembly properties were already investigated for various kinds of molecules and substrate materials [4][5][6][7][8][9][10][11][12][13] . Their small size makes them very suitable candidates to serve as building blocks of functional nanostructures.…”

Growth of Metal Phthalocyanine on Deactivated Semiconducting Surfaces Steered by Selective Orbital Coupling

“…Of them, metallic substrates provide more flexibility in tuning the MPc-substrate interaction through orbital hybridization and charge redistribution associated with the central transition-metal (TM) ion [16,20,21]. Nevertheless, this tunable hybridization has little influence on the orientation and ordering of MPc molecules at the hetero-interface, where close-packed flat-lying molecular structures are often observed in the first monolayer which then gradually relax into bulk configured molecular packing in multilayers [17,22,23,25]. Semiconducting substrates, on the other hand, provide a particular challenge to self-assemble organic molecules on top due to the existence of surface dangling bonds which localize molecules and prevent them from forming ordered structures.…”