A series of para-oligophenylene mono-and dicarboxylic acids (R-(C 6 H 4 ) n COOH, n=1-3, R=H,COOH) was studied. Adsorbed on Au(111)/mica modified by an underpotential deposited bilayer of Ag, the self-assembled monolayers (SAMs) were analysed by near edge X-ray absorption fine structure spectroscopy, X-ray photoelectron spectroscopy and scanning tunneling microscopy. In all cases SAMs are formed with molecules adopting an upright orientation and anchored to the substrate by a carboxylate. Except benzoic acid, all SAMs could be imaged at molecular resolution, which revealed highly crystalline layers with a dense molecular packing. The structures of the SAMs are described by a rectangular (5×√3) unit cell for the prevailing phase of the monocarboxylic acids and an oblique (√93×√133) unit cell for the dicarboxylic acids, thus, evidencing a pronounced influence of the second COOH moiety on the SAM structure. Density functional theory calculations suggest that hydrogen bonding between the SAM terminating COOH moieties accounts for the difference. Contrasting other classes of SAMs, the systems studied here are determined by intermolecular interactions whereas molecule-substrate interactions play a secondary role. Thus, eliminating problems arising from the mismatch between the molecular and substrate lattices, coordinatively bonded carboxylic acids on silver should provide considerable flexibility in the design of SAM structures.
Standing on their own two feet: Underpotential deposition of Cu on Au(111) yields a surface onto which 1,3‐benzenedicarboxylic acid (IPA) and 1,3,5‐benzenetricarboxylic acid (TMA) adsorb in a bipodal configuration. Both molecules form highly crystalline isostructural monolayers, thus demonstrating the potential of the IPA moiety as tecton for self‐assembled monolayers. A thin film of a Cu–TMA coordination polymer was grown on a patterned TMA monolayer.
High resolution atomic force microscopy
(AFM) is used to resolve the evolution of crystallites of a metal
organic framework (HKUST-1) grown on Au(111) using a liquid-phase
layer-by-layer methodology. The nucleation and faceting of individual
crystallites is followed by repeatedly imaging the same submicron
region after each cycle of growth and we find that the growing surface
is terminated by {111} facets leading to the formation of pyramidal
nanostructures for [100] oriented crystallites, and triangular [111]
islands with typical lateral dimensions of tens of nanometres. AFM
images reveal that crystallites can grow by 5–10 layers in
each cycle. The growth rate depends on crystallographic orientation
and the morphology of the gold substrate, and we demonstrate that
under these conditions the growth is nanocrystalline with a morphology
determined by the minimum energy surface.
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