Engineering few-layer graphene by S-doping: from sustaining linear dispersion to flat bands

TL;DR

This study uses first-principles calculations to explore how sulfur doping alters the electronic properties of few-layer graphene, enabling tunable band structures from metallic to insulating and from linear to flat bands.

Contribution

It systematically investigates the effects of basal plane S-doping on multilayer graphene's electronic properties, revealing new ways to engineer its band structure for technological applications.

Findings

S-doping can sustain Dirac cones or open band gaps depending on doping type.

In multilayer graphene, S-doping modifies Dirac cones into hyperbolic bands and introduces flat bands.

S-doped FLG can be tuned from metallic to insulating states with various electronic behaviors.

Abstract

Motivated by the technological relevance of S-doped few-layer graphene (FLG) in battery applications and in the oxygen reduction reaction, we systematically explore the effect of basal plane S-doping on the electronic properties of mono-, bi-, and four-layer graphene, using first-principles calculations with van der Waals corrections. In the monolayer we find a variety of effects ranging from a sustained Dirac cone with localized impurity bands away from the Fermi level in thiophenic doping (2V1S) to a band gap opening of 0.4 eV and flat bands close to the Fermi-level in graphitic doping (1V1S) and an additional $n$-type doping together with spin-polarization, when three S-atoms are adsorbed in a four-site vacancy (4V3S). Incorporation in FLG leads to modification of the Dirac cone into a set of hyperbolic touching bands in 2V1S; reduction (bilayer) and closing of the band gap with additional hyperbolic touching bands in conjunction with the flat band at the Fermi level in 1V1S and 4V3S and a reduction of spin polarization in the latter. Overall, S-doping enables design of the band structure and tuning the electronic behavior of FLG from metallic to insulating and from linear dispersive to flat bands that makes S-doped FLG a promising material for versatile technological applications.