Mono and dual doped monolayer graphene with aluminum, silicon, phosphorus and sulfur

Abstract

Herein, we investigated the mono and dual doped graphene (DDG) systems that can be constructed when 2 carbon atoms are replaced by two 3p dopants: Al, Si, P or S. Although the latter elements have an atomic radius much larger than that of carbon, for most of the systems studied the dopants prefer to interact between themselves instead with the carbon atoms. The exception to this rule was graphene doped with two P atoms which favored a para disposition of the dopants. While in some cases like, SiSi, SS and SiP doped graphene the traditional ortho disposition of the dopants is preferred; for other systems like AlS or AlP DDG graphene, only one of the dopants fits in the graphene plane, while the other adopts a bridged structure. The most extreme case is PS DDG, for which the S atom is covalently bonded to P and no direct S-C bonding is observed. Analysis of the formation energies indicated that the use of two dopants is a useful procedure to reduce the formation energies of doped graphenes. HSE calculations showed that addition second dopant to the monodoped graphene systems does not increase the size of the band gaps. On the contrary, in all cases studied the gaps determined for the doped graphenes containing two dopants were smaller than those calculated when just one dopant is present. Moreover, in some cases the addition of a second dopant restored the semimetallic character of graphene. Thus, care must be taken when it is postulated that a gap is opened by substitutional doping, since the presence and magnitude of the gaps completely depends on the concentration as well as the position of the dopants.