Abstract
On-surface covalent self-assembly of organic molecules is a very promising bottom–up approach for producing atomically controlled nanostructures. Due to their highly tuneable properties, these structures may be used as building blocks in electronic carbon-based molecular devices. Following this idea, here we report on the electronic structure of an ordered array of poly(para-phenylene) nanowires produced by surface-catalysed dehalogenative reaction. By scanning tunnelling spectroscopy we follow the quantization of unoccupied molecular states as a function of oligomer length, with Fermi level crossing observed for long chains. Angle-resolved photoelectron spectroscopy reveals a quasi-1D valence band as well as a direct gap of 1.15 eV, as the conduction band is partially filled through adsorption on the surface. Tight-binding modelling and ab initio density functional theory calculations lead to a full description of the band structure, including the gap size and charge transfer mechanisms, highlighting a strong substrate–molecule interaction that drives the system into a metallic behaviour.
Highlights
On-surface covalent self-assembly of organic molecules is a very promising bottom–up approach for producing atomically controlled nanostructures
We recorded differential conductivity maps as a function of chain length, to build the k-resolved band structure associated with the conduction band of the infinite polymer
Assuming the PPP polymer as being a 3ptype AGNR with p 1⁄4 1 and w 1⁄4 2.4 Å (Supplementary Fig. 9, Supplementary Note 7), we expect a bandgap of 2.45 eV from density functional theory (DFT) calculations corrected at 4.1 eV including GW corrections[6]
Summary
On-surface covalent self-assembly of organic molecules is a very promising bottom–up approach for producing atomically controlled nanostructures Due to their highly tuneable properties, these structures may be used as building blocks in electronic carbon-based molecular devices. An emerging bottom–up approach for producing such carbon nanostructures, exploits covalent linking (polymerization) of precursor molecules on metal surfaces[9,10,11,12,13,14,15,16,17,18,19,20] In these materials, functional properties, including the geometry and the bandgap, can be tailored by means of a judicious choice of monomer and supporting surfaces[21,22,23,24]. The polymer is here fully commensurate with the surface and may be grown to long size with little or no strain arising from lattice mismatch (Supplementary Note 3)
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