The conformations of organometallic polymers formed via the bottom-up assembly of monomer units on a metal surface are investigated, and the relationship between the adsorption geometry of the individual monomer units, the conformational structure of the chain, and the overall shape of the polymer is explored. Iodine-functionalized monomer units deposited onto a Au (111) substrate are found to form linear chain structures, where each monomer is linked to its neighbors via an Au adatom. Lateral manipulation of the linear chains using a scanning tunneling microscope allows the structure of the chain to be converted from a linear geometry to a curved one, and it is shown that a transformation of the overall shape of the chain is coupled to a conformational re-arrangement of the chain structure as well as a change in the adsorption geometry of the monomer units within the chain. The observed conformational structure of the curved chain is well ordered and distinct from that of the linear chains. The structures of both the linear and curved chains are investigated by a combination of scanning tunneling microscopy measurements and theoretical calculations.

Atomistic simulations were used to investigate the surface structure and stability of siliceous and sodium aluminosilicate (Na-A) forms of the zeolite LTA. First, the surface structures were optimized with static lattice minimization. These simulations predict that the single 4-ring termination of {100} and the double 4-ring of {111} are equally stable for siliceous LTA. The inclusion of aluminum ions into the framework stabilizes the {100} relative to the {111} surface. One consequence of this change in surface stability is that the predicted equilibrium morphology changes from spherical for purely siliceous to cubic. Slabs of LTA were then immersed in water and simulated using molecular dynamics. The siliceous LTA was found to have hydrophobic regions, whereas in the aluminosilicate the water density resides at distinct crystallographic sites. The zeolite surfaces were shown to impose significant water ordering near the surfaces. This, in turn, affects the water diffusivity. The diffusivity of water is correlated with water structure, which leads to clear anisotropy in the diffusion coefficient. The presence of water is also found to increase the surface stability of the {100} surfaces. Finally, we found that Na+ ions leach into the solution, migrating between surface adsorption sites and moving through the 6- and 8-rings, hence forming a diffuse sodium layer above the LTA surface, which also has important implications for atom transport near zeolite surfaces.

Templated assembly of organic molecules constitutes a promising approach for fabricating functional nanostructures at surfaces with molecular-scale control. Using the substrate template for steering the adsorbate growth enables creating a rich variety of molecular structures by tuning the subtle balance of intermolecular and molecule−surface interactions. On insulating surfaces, however, surface templating is largely absent due to the comparatively weak molecule−surface interactions compared to metallic substrates. Here, we demonstrate the activation of substrate templating in molecular self-assembly on a bulk insulator by controlled deprotonation of the adsorbed molecules upon annealing. Upon deposition of 4-iodobenzoic acid onto the natural cleavage plane of calcite held at room temperature, high molecular mobility is observed, indicating a small diffusion barrier. Molecular islands only nucleate at step edges. These islands show no commensurability with the underlying substrate, clearly indicating the absence of surface templating. Upon annealing the substrate, the molecules undergo a transition from the protonated to the deprotonated state. In the deprotonated state, the molecules adopt a well-defined adsorption position, resulting in a distinctly different, substrate-templated molecular structure that is stable at room temperature. Our work, thus, demonstrates the controlled activation of substrate templating by changing the molecule−surface interaction upon annealing.

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