New Research


2006/09/01

Tiles of Nanosize

Control of Two-Dimensional Nanostructures Based on Molecular Design

Assistant Professor Kazukuni Tahara, Professor Yoshito Tobe

A great deal of interest has been focused on the bottom-up nanotechnology which is based on the change of electronic state or structure of a single organic molecule or a small molecular assembly, in contrast to the top-down approach utilizing inorganic solid semiconductors, to construct an integrated circuit (IC). Although there remain hard problems to be solved for the achievement of the bottom-up approach, such as creation of molecules that function as a transistor and their integration to built a circuit, significant clues have been found through multidisciplinary, collaborative research works in the worldwide.
Above all, ‘two-dimensional (2D) self-assembly’ is believed to be a critical process to integrate organic molecules, because one can arrange molecules into a desired pattern on a solid surface by using this phenomena. We succeeded in making patterns as we wish on a graphite surface making use of triangle- or rhombus-shaped planar molecules constructed by conjugated pi-systems. In this system, interactions between the surface and the physisorped molecules and between the molecules play an important role for the determination of the observed 2D patterns. With these factors in mind, we designed the molecular shapes and size and adjusted the length of the alkyl chains attached on the periphery of the molecules like whiskers. On the basis of this approach, we succeeded in controlling the 2D nano-scale structures ranging from close-packed structures to network structures possessing voids of nanometer regime. The above figure displays, as an example, an STM (scanning tunneling microscope) image of a characteristic molecular ‘Kagomé’ structure, which was found for the first instance in a 2D system by us. It seems as if we are creating an artwork using rhombus-shaped ‘tiles of nanosize.’ Central to the mechanism forming such motifs is the interdigitation of alkyl chains between the neighboring molecules serving as ‘glue.’
We have been engaged in the research work to create functional organic materials including not only 2D self-assembly systems described above but also development of molecular sensors and molecular machines based on molecular recognition event and the synthesis of novel giant pi-electronic systems and their self-association.


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