{\Pi} Band Dispersion along Conjugated Organic Nanowires Synthesized on a Metal Oxide Semiconductor

TL;DR

This study demonstrates the synthesis of ordered poly(p-phenylene) nanowires on TiO2 surfaces, revealing a highly dispersive {c} band indicative of successful conjugated polymer formation, which could enable new molecule-semiconductor devices.

Contribution

It provides the first spectroscopic evidence of atomically precise carbon nanostructures synthesized on transition-metal oxide surfaces, expanding bottom-up nanostructure fabrication.

Findings

Successful synthesis of poly(p-phenylene) on TiO2(110) surface.

Identification of a highly dispersive {c} band via spectroscopy.

Establishment of a method for bottom-up production of molecule-semiconductor devices.

Abstract

Surface confined dehalogenation reactions are versatile bottom-up approaches for the synthesis of carbon-based nanostructures with predefined chemical properties. However, for devices generally requiring low conductivity substrates, potential applications are so far severely hampered by the necessity of a metallic surface to catalyze the reactions. In this work we report the synthesis of ordered arrays of poly(p-phenylene) chains on the surface of semiconducting TiO2(110) via a dehalogenative homocoupling of 4,4"-dibromoterphenyl precursors. The supramolecular phase is clearly distinguished from the polymeric one using low energy electron diffraction and scanning tunneling microscopy as the substrate temperature used for deposition is varied. X ray photoelectron spectroscopy of C 1s and Br 3d core levels traces the temperature of the onset of dehalogenation to around 475 K. Moreover, angle-resolved photoemission spectroscopy and tight-binding calculations identify a highly dispersive band characteristic of a substantial overlap between the precursor's {\pi} states along the polymer, considered as the fingerprint of a successful polymerization. Thus, these results establish the first spectroscopic evidence that atomically precise carbon based nanostructures can readily be synthesized on top of a transition-metal oxide surface, opening the prospect for the bottom-up production of novel molecule-semiconductor devices.