Self-organized growth of tetrathiafulvalene–tetracyanoquinodimethane molecular wires using the coevaporation method under a static electric field

Wire-like crystals of tetrathiafulvalene-tetracyanoquinodimethane (TTF–TCNQ) charge-transfer complexes were grown under a static electric field by employing electric-field assisted evaporation. TTF–TCNQ molecular wires grew from the edges of two gold electrodes opposite to each other along the electric lines of force, and finally make a connection at their front end to form a single wire. Self-organization of the wire bridge is derived from a higher local electric field between the tips of the opposing molecular wires. Oriented molecular wires, which have diffuse branches, exhibit the effects of a local electric field. Preferential growth of TCNQ at the tip of the molecular wire during coevaporation of TTF and TCNQ is clearly revealed by microscopic Raman spectroscopy. Asymmetrical growth of coevaporated TTF–TCNQ wire under a static electric field is dominated by the drift motion of TCNQ−.