The adsorption and ordering of zinc phthalocyanine (ZnPc) and octachloro zinc phthalocyanine (ZnPcCl(8)) on an Ag(111) surface is studied in situ by scanning tunneling microscopy under ultrahigh vacuum. Two-dimensional self-assembled supramolecular domains are observed for these two molecules. We show how substituting chlorine atoms for half of the peripheral hydrogen atoms on ZnPc influences the self-assembly mechanisms. While intermolecular interactions are dominated by van der Waals forces in ZnPc molecular networks, ZnPcCl(8) molecular packing undergoes a sequential phase evolution driven by the creation of C-Cl...H-C hydrogen bonds between adjacent molecules. At the end of this evolution, the final molecular assembly involves all possible hydrogen bonds. Our study also reveals the influence of molecule-substrate interactions through the presence of fault lines generating a stripe structure in the molecular film.

[a] Supramolecular structures formed by the self-assembly of functional molecular building blocks are a promising class of materials for future technologies. [1][2][3] Hydrogen bonding is a key ingredient in their fabrication, as it provides high selectivity and directionality. Hydrogen bonding has recently been used to prepare both two-dimensional (2D) and linear nanostructures at surfaces by molecular beam epitaxy. [4][5][6][7][8] Herein, we show that molecular films can evolve with time into a close-packed arrangement induced by the activation of an original 2D hydrogen-bond network consisting of H···Cl bonds. Scanning tunneling microscopy (STM) experiments combined with density functional calculations were performed on chlorine-zincphthalocyanines (ZnPcCl 8 ; see Figure 1 for structure) adsorbed onto Ag(111). We demonstrate that the location of the chlorine atoms on the phenyl rings predetermines the final 2D molecular network.The adsorption of large, flat metal-phthalocyanine (MPc) molecules on both metallic and semiconductor surfaces is well documented. [9][10][11][12][13] For this class of molecules, self-assembly is governed by the subtle balance between molecule-molecule and molecule-surface interactions, which can be tuned by the modification of the surrounding atoms of the phthalocyanine. [14] A large variety of arrangements at surfaces, depending on the nature of the central atom and the surrounding atoms of the molecule, has been reported. Intermolecular interactions influence the way molecules organize themselves on top of a surface. They can either be electrostatic in nature, including both multipolar static and dynamical Van der Waals contributions, or arise from orbital overlapping, or both. ZnPcC 8 , which is obtained from the substitution of chlorine atoms for eight of the sixteen surrounding hydrogen atoms, was chosen because it is capable of organizing itself into compact molecular arrangements mainly governed by hydrogen bonds. Phthalocyanines are well-known electron acceptors and their interactions with a metallic surface result from partial charge transfer from the surface electronic states to the lowest unoccupied molecular orbital (LUMO) of p type.[15] Thus, depending on the strength of the overlapping, the symmetry of the host surface may, more or less, influence the way molecules adsorb and organize themselves on this surface. Because of its moderate reactivity and oxidation potential (that is, its electron-donor character), Ag metal seems a good choice as a substrate with little influence on the molecular arrangement, because of its low surface energy. Looking for minimal substrate-molecule interactions, Ag (111) Herein is presented a combined experimental and theoretical approach to the molecular packing of ZnPcCl 8 molecules deposited onto Ag(111) surfaces. STM was performed at room temperature, and theoretical calculations were based on density functional theory (DFT) within the framework of the projector-augmented wave (PAW) method.[16] The evolution of the three different 2D...

The growth of Cu on an Ag͑111͒ surface is studied using scanning tunneling microscopy at room temperature and for low Cu coverage ranging from 0.02 to 1.5 monolayers. Three-dimensional islands are found to grow at the Ag surface steps. During this Volmer-Weber growth, the erosion of steps and the formation of vacancy domains inside the terraces indicate that a large redistribution of Ag atoms takes place. Moreover, STM images from the top of islands reveal a ͑9 ϫ 9͒ reconstruction which is well known to occur in the reverse case, where one Ag monolayer is deposited on Cu͑111͒. These findings combined with molecular dynamics simulations allow us to conclude that the Cu islands are capped, from the very beginning of the growth, by one monolayer of Ag atoms diffusing from the eroded regions.