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For past decades, enormous efforts have been devoted to explore the technical scheme to produce miniaturized structures with nanometer-scale precision using self-organizing features of organic molecules. The reason is not only that miniaturized organic components would be a strong candidate to overcome the various constraints imposed by silicon-based device technologies, but also it would open a door to the frontier of material science and engineering. To date, the accumulation of fundamental knowledge concerning the physical properties of organic molecules has enabled us to construct self-organized nano-meter scale structures adopting its self-assembling and mutual recognizing features in some limited cases. In order to proceed these techniques the detailed mechanism of self-organizing features should be elucidated much more in detail. For this purpose, it is meaningful to investigate the conformational correlations when two sole molecules with specific mutual recognition function gradually come close with each other on a surface. However, in many cases, organic molecules can move on the surface rather freely because of its weak attractive force between molecules and surfaces, and that it is not easy to obtain snap shot images of on going phenomena, such as spontaneous assembling and mutual recognizing.
Considering the situations, by means of SPM techniques, we are investigating the conformational correlation change of specially designed porphyrin-based molecules adsorbed along the terrace edge lines formed on the single crystalline surface, when their relative distance of molecules is gradually reduced. In this case, terrace edge lines work as a sticky guide rail to regulate the diffusion of molecules on the surface. Preliminary results indicate that their positional correlation strongly depends on the relative distances along the edge line and species of their chemical functional groups, which suggests that these techniques can be used as a test bed to investigate their mutual recognition and self orientation phenomena in the single molecule scale. Systematic investigation of these phenomena is expected to give us useful information to develop spontaneous nano-meter scale structuring using organic molecules.
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