Atomic Force Microscopy Studies of Hydrogen-Bonded Nanostructures on Surfaces
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Bottom-up strategies in molecular nanotechnology, including the self-assembly of small molecular building blocks into supramolecular aggregates based on noncovalent interactions, are regarded as a viable route to realize molecular devices, as well as to fabricate and template well-defined nanometer-scale structures and objects. Recent progress in nanostructuring has enabled several groups to control the arrangement of molecules and supramolecular aggregates on surfaces by exploiting designed intermolecular interactions and/or scanning probe microscopy (SPM) approaches at variable temperatures. This work, which is based on the profound knowledge in the fields of supramolecular chemistry and intermolecular (surface) forces, will ultimately lead to a general strategy to develop hierarchical functional nanostructures with molecular precision.
We have designed and investigated rosette nanostructures, which are based on multiple hydrogen bonding between the basic building blocks—melamine-substituted calixarenes and 5,5-diethylbarbiturate (DEB). These thermodynamically stable nanostructures can be ordered on solid substrates in highly regular, chiral 2-D assemblies, or immobilized as individual entities in self-assembled monolayers (SAM). In this article, we review our recent progress in the formation, and in particular in the real-space structural analysis, of nanometer-sized supramolecular rosette nanostructures and their aggregates in 2-D via atomic force microscopy (AFM).