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Self-assembly of a zinc-porphyrin on HOPG studied by STM at the liquid-solid interface and stepwise growth of molecular wires

Ferreira, Q. ; Bragança, A. ; Alcácer, L. ; Morgado, J.

Self-assembly of a zinc-porphyrin on HOPG studied by STM at the liquid-solid interface and stepwise growth of molecular wires, Proc International Conf. on NANO-Structures SElf-Assembly - NANOSEA, S. Margherita di Pula, Italy, Vol. n.a, pp. n.a - n.a, June, 2012.

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Abstract
Controlling the ordering and the properties of single molecules and their aggregates is of
increasing importance, not only from a fundamental point of view but also when aiming at the
development of unimolecular electronics.
In this communication we report on the assembly of a zinc-porphyrin (ZnOEP) on HOPG
from a tetradecane droplet, using STM to image the various stages of the self-assembly
process, until a close packing arrangement is attained. At the early stages of ZnOEOP
assembly on HOPG we observe a polymorphic monolayer with the presence of a metastable
phase (α), which, over two hours, is converted into the thermodynamically stable one (β)
(Figure 1).
Once the fully packed ZnOEP monolayer is formed, we proceeded to the fabrication of
molecular wires anchored on such monolayer.
The process is based on the alternating combination of bipyridine (BP) and ZnOEP, being the
binding between units due to the formation of Zn-N bonds [1]. We used STM to follow the
growth at each step, confirming the high ordering of the molecular wires up to 25 units.
Preliminary measurements of their electrical properties will be presented and discussed.