Fabrication and characterization of ordered atomic-scale structures - a step towards future atomic-scale technology

The quest for a reliable method of fabricating ordered atomic-scale structures is a prequisite for future atomic-scale technology. The interest in such nanostructured materials consisting of building blocks of a small number of atoms or molecules arises from their promising new optic, catalytic, magnetic and electronic poperties, which are fundamentally different from those of their macroscopic bulk counterparts: small is different. Here, we present and review three examples concerning atomic and supramolecular self-assembly investigated by low-temperature scanning tunneling microscopy (STM). (i) First is the self-assembly of a two-dimensional array of individual Ce adatoms (the smallest possible building block) on a metal surface based on long-range interactions between adatoms mediated by surface state electrons. Ce is a magnetic atom, and such a hexagonal super-lattice of magnetic adatoms might be useful for the development of future atomic-scale magnetic devices. (ii) Next is the conservation of chirality in a hierarchical supramolecular self-assembly of pentagonal symmetry of the organic molecule rubrene on a reconstructed Au(111) surface. We show the spontaneous chiral resolution of the racemate into disjoint homochiral complex architectures and demonstrate the ability to monitor directly the evolution of chiral recognition processes on the molecular and the supramolecular level. (iii) Finally, using the highly localized current of electrons tunneling through a double barrier STM junction, we excite luminescence from a selected C-60 molecule in the surface layer of fullerene nanocrystals self-assembled on an ultrathin NaCl film on Au(111). In the observed fluorescence and phosphorescence spectra, pure electronic, as well as vibronically induced transitions of an individual C-60 molecule, are identified, leading to unambiguous chemical recognition on a single-molecule scale.