Progress in molecular self-assembly at surfaces has enabled fabrication of increasingly complex molecular nanostructures.  This includes graphene-based nanoribbons (GNRs) synthesized via step-growth polymerization from chemically-engineered monomer precursors.  Using this technique we have developed a new 'N=13' monomer that allows growth of fully cyclized GNRs having a width almost twice the width seen for previous bottom-up-synthesized GNRs, thus enabling the GNR energy gap to be tuned ('N' measures the width of the GNR in terms of carbon atoms).  Combining these new N=13 monomers with previously reported N=7 precursors allows bottom-up fabrication of new GNR-based heterojunctions that exhibit a spatially varying width and energy gap.  Such heterojunctions enable a new form of molecular bandgap engineering, as demonstrated by our scanning tunneling spectroscopy measurements.  A current limitation of this technique, however, is that so far the structures can only be grown on metals.  We are using scanned probe microscopy to explore new bottom-up synthesis routes that, in principle, should not be limited to metallic substrates.

Synthesis at the single molecule Level: Polymerization, cyclization, and molecular heterojunctions

248th National Meeting (2014)

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