Quasi one-Dimensional Band Dispersion and Metallization In long Range Ordered Polymeric wires

TL;DR

This study investigates the electronic properties of ordered poly(para-phenylene) chains, revealing their quasi-one-dimensional band structure, metallic behavior, and the role of surface interactions through experimental and theoretical methods.

Contribution

It provides a comprehensive characterization of the band structure and metallic transition in polymeric wires using combined experimental and computational approaches.

Findings

Observation of Fermi level crossings in chains longer than ten phenyl rings.

Identification of a graphene-like quasi-1D valence band with a 1.15 eV gap.

Full theoretical description of the organic band structure, including dispersion and charge transfer.

Abstract

We study the electronic structure of an ordered array of poly(para-phenylene) chains produced by surface-catalyzed dehalogenative polymerization of 1,4-dibromobenzene on copper (110). The quantization of unoccupied molecular states is measured as a function of oligomer length by scanning tunneling spectroscopy, with Fermi level crossings observed for chains longer than ten phenyl rings. Angle-resolved photoelectron spectroscopy reveals a graphene-like quasi one-dimensional 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 organic band-structure, including the k dispersion, the gap size and electron charge transfer mechanisms which drive the system into metallic behaviour. Therefore the entire band structure of a carbon-based conducting wire has been fully determined. This may be taken as a fingerprint of {\pi}-conjugation of surface organic frameworks.