Influence of cumulenic chains on the vibrational and electronic properties of sp/sp2 amorphous carbon

TL;DR

This study investigates how cumulene-like sp hybridized chains in amorphous carbon films affect their vibrational and electronic properties, revealing temperature-dependent stability and a self-doping mechanism that alters electrical conductivity.

Contribution

It provides the first evidence that pure carbon systems with sp hybridization influence bulk properties through cumulene chains, with detailed characterization of their stability and electronic effects.

Findings

Cumulene chains are stable below 250 K.

They cause a Fermi level pinning, affecting electrical transport.

Heating above 250 K leads to formation of graphitic nanodomains.

Abstract

We report the production and characterization of a form of amorphous carbon films with sp/sp2 hybridization (atomic fraction of sp hybridized species > 20%) where the predominant sp bonding appears to be (=C=C=)n cumulene. Vibrational and electronic properties have been studied by in situ Raman spectroscopy and electrical conductivity measurements. Cumulenic chains are substantially stable for temperatures lower than 250 K and they influence the electrical transport properties of the sp/sp2 carbon through a self-doping mechanism by pinning the Fermi level closer to one of the mobility gap edges. Upon heating above 250 K the cumulenic species decay to form graphitic nanodomains embedded in the sp2 amorphous matrix thus reducing the activation energy of the material. This is the first example of a pure carbon system where the sp hybridization influences bulk properties.