Formation of oriented molecular nanowires on mica surface.

Molecular "nanowire" structures composed of the charge transfer complex of a bis-tetrathiafulvalene substituted macrocycle and tetrafluorotetracyanoquinodimethane were constructed on mica substrates by employing the Langmuir-Blodgett technique. The nanowires transferred from a dilute aqueous potassium chloride subphase had typical dimensions of 2.5 nm x 50 nm x 1 microm. The nanowires are oriented to specific directions, corresponding to the directions of the potassium-ion array on the mica surface having sixfold symmetry. Such correlation between the nanowires and the substrate surface was also observed when a dilute aqueous rubidium chloride subphase was used. On the other hand, the correlation completely disappeared when the subphase contained divalent cations, indicating that the molecular nanowires orient by recognizing the monocation array on the mica surface. The nanowires formed by the vertical dipping method coexist with the monolayers. Only nanowire structures are, however, observed when we apply the horizontal lifting method. Based on the crystal structure of a related complex, a possible structure of the nanowires is presented. The conductivity of the nanowires was estimated to be of the order of 10(-3) S x cm(-1). The nanowires formed specific (regular) structures such as T-shape junctions, suggesting their use in construction of future molecular nanoscale devices.